Quantification of nerve fiber layer thickness in normal and glaucomatous eyes using optical coherence tomography

Peripapillary retinal nerve fibre layer thickness measurement with SD-OCT in normal and glaucomatous eyes: distribution and correlation with age

AIM

To determine peripapillary retinal fiber layer thickness (RNFL) measured with spectral domain optical coherence tomography (SD-OCT) in normal and glaucomatous eyes in a large sample of exclusively white population and compare results with other similarly constructed studies.

METHODS

Average, maximum, minimum and per quadrant RNFL thickness were measured in normal and glaucomatous Greek patients with a scanning laser ophthalmoscope (SLO)/SD-OCT device. The effect of age in normal RNFL thickness was also determined.

RESULTS

A total of 278 normal (278 patients) and 67 glaucomatous (67 patients) eyes were included in the study. Average RNFL thickness was 114.8±13.3µm in normal and 92.1±18.5µm in glaucomatous eyes (P<0.001). In normal discs, superior quadrant was the thickest, followed by the inferior, nasal and temporal. Decline of normal RNFL thickness with age was statistically significant for average RNFL thickness (1.92µm per decade of life) and for the superior and inferior quadrants of the disc.

CONCLUSION

SD-OCT peripapillary RNFL measurements can be used to distinguish between normal and glaucomatous eyes and establish normative databases, since normal disc measurements differ between different ethnic groups and between different SD-OCT devices.

Path-length-multiplexed scattering-angle-diverse optical coherence tomography for retinal imaging

A low-resolution path-length-multiplexed scattering angle diverse optical coherence tomography (PM-SAD-OCT) is constructed to investigate the scattering properties of the retinal nerve fiber layer (RNFL). Low-resolution PM-SAD-OCT retinal images acquired from a healthy human subject show the variation of RNFL scattering properties at retinal locations around the optic nerve head. The results are consistent with known retinal ganglion cell neural anatomy and principles of light scattering. Application of PM-SAD-OCT may provide potentially valuable diagnostic information for clinical retinal imaging.

Imaging of the optic nerve and retinal nerve fiber layer: an essential part of glaucoma diagnosis and monitoring

Because glaucomatous damage is irreversible early detection of structural changes in the optic nerve head and retinal nerve fiber layer is imperative for timely diagnosis of glaucoma and monitoring of its progression. Significant improvements in ocular imaging have been made in recent years. Imaging techniques such as optical coherence tomography, scanning laser polarimetry and confocal scanning laser ophthalmoscopy rely on different properties of light to provide objective structural assessment of the optic nerve head, retinal nerve fiber layer and macula. In this review, we discuss the capabilities of these imaging modalities pertinent for diagnosis of glaucoma and detection of progressive glaucomatous damage and provide a review of the current knowledge on the clinical performance of these technologies.

Microcystic macular edema: retrograde maculopathy caused by optic neuropathy

PURPOSE

To investigate retrograde axonal degeneration for its potential to cause microcystic macular edema (MME), a maculopathy that has been previously described in patients with demyelinating disease. To identify risk factors for MME and to expand the anatomic knowledge on MME.

DESIGN

Retrospective case series.

PARTICIPANTS

We included 117 consecutive patients and 180 eyes with confirmed optic neuropathy of variable etiology. Patients with glaucoma were excluded.

METHODS

We determined age, sex, visual acuity, etiology of optic neuropathy, and the temporal and spatial characteristics of MME. Eyes with MME were compared with eyes with optic neuropathy alone and to healthy fellow eyes. With retinal layer segmentation we quantitatively measured the intraretinal anatomy.

MAIN OUTCOME MEASURES

Demographic data, distribution of MME in the retina, and thickness of retinal layers were analyzed.

RESULTS

We found MME in 16 eyes (8.8%) from 9 patients, none of whom had multiple sclerosis or neuromyelitis optica. The MME was restricted to the inner nuclear layer (INL) and had a characteristic perifoveal circular distribution. Compared with healthy controls, MME was associated with significant thinning of the ganglion cell layer and nerve fiber layer, as well as a thickening of the INL and the deeper retinal layers. Youth is a significant risk factor for MME.

CONCLUSIONS

Microcystic macular edema is not specific for demyelinating disease. It is a sign of optic neuropathy irrespective of its etiology. The distinctive intraretinal anatomy suggests that MME is caused by retrograde degeneration of the inner retinal layers, resulting in impaired fluid resorption in the macula.

The relationship between the optical density of cataract and its influence on retinal nerve fibre layer thickness measured with spectral domain optical coherence tomography

PURPOSE

The purpose of this study was to model the influence of cataract on Spectral Domain Optical Coherence Tomography (SDOCT) image quality and Retinal Nerve Fibre Layer (RNFL) thickness measurements.

METHODS

SDOCT images, made with two different devices (3DOCT-1000, Topcon and Cirrus HD-OCT), before and after cataract surgery were compared and judged against measurements from normal subjects using artificial filters simulating the effects of cataract. Optical density of the images was calculated based on a mathematical model described previously.

RESULTS

In total, forty-eight eyes were included for pre- and postoperative cataract extraction measurements. OCT image quality significantly (p < 0.001) improved postoperative and postoperative RNFL thickness was significantly (p < 0.001) thicker in both groups of patients. The measurements using artificial filters showed a rather precise linear relation between change in filter induced optical density and change in RNFL thickness (R = 0.941, p < 0.001 for 3DOCT-1000 and R = 0.785, p < 0.001 for Cirrus HD-OCT). For the patient groups, the relation was less marked, 3DOCT-1000 Rs = 0.697, p < 0.03 and Cirrus HD-OCT Rs = 0.444, p < 0.03. The predictive potential based on the found linear relationship between OCT-effective optical density of cataract and the cataract-induced underestimation was however limited, and mean difference ± SD between predicted and measured RNFL thickness were 1.68 ± 7.55 (3DOCT-1000) and 3.71 ± 2.97 (Cirrus HD-OCT) micron.

CONCLUSIONS

A linear relationship exists between OCT-effective optical density of cataract and underestimation of RNFL thickness measured with OCT. This finding holds promise to correct for cataract-induced changes in RNFL measurements, but will differ for each type of OCT device.

Localized retinal nerve fiber layer defects detected by optical coherence tomography: the Beijing eye study

Objective

To assess the prevalence of localized retinal nerve fiber layer defects (LRNFLD) and associated factors in adult Chinese.

Methods

The population-based Beijing Eye Study 2011 included 3468 individuals (mean age: 64.6±9.8 years (range: 50–93 years)). The study participants underwent a detailed ophthalmological examination including spectral-domain optical coherence tomography (Spectralis^R-OCT) assisted measurement of the RNFL. A LRNFLD was defined as a sector in which the RNFL contour line dipped into the red zone for a length of <180°.

Results

Readable OCT images were available for 3242 (93.5%) subjects. LRNFLDs were detected in 640 eyes (9.9±0.4%) of 479 subjects (14.8±0.6%). In the age groups of 50–59 years, 60–69 years, 70–79 years, and 80+ years, the prevalence of LRNFLD per person increased from 9.9±0.9%, 11.6±1.0% and 20.6±1.4% to 33.0±3.2%, respectively. In multivariate analysis, prevalence of LRNFLDs was significantly associated with older age (P = 0.001; Odds Ratio (OR): 1.03; 95% Confidence Interval (CI): 1.01,1.05), myopic refractive error (P<0.001;OR:0.79;95%CI:0.74,0.85), larger beta zone of parapapillary atrophy (P<0.001; OR:1.34;95%CI:1.20,1.50), presence of glaucomatous optic neuropathy (P<0.001;OR:7.02;95%CI:3.87,12.7), presence of non-glaucomatous optic nerve damage (P = 0.001;OR:43.3;95%CI:8.24,227.1), and presence of diabetic retinopathy (P = 0.003;OR:2.79;95%CI:1.43,5.44).

Conclusions

OCT-defined LRNFLDs were present in a prevalence of 14.8±0.6% in a population-based study sample of subjects aged 50+ years. Prevalence of LRNFLDs increased with higher age, myopic refractive error, and larger parapapillary beta zone. Major ocular diseases associated with LRNFLs were glaucoma, non-glaucomatous optic nerve damage and diabetic retinopathy. These data may be helpful for a semiautomatic assessment of the RNFL.

Retinal nerve fiber layer thickness. The Beijing Eye Study 2011

PURPOSE

To measure retinal nerve fiber layer (RNFL) thickness in a population-based setting.

METHODS

In the population-based Beijing Eye Study 2011 with 3468 individuals, RNFL thickness was measured in a subgroup of 1654 (47.7%) study participants by spectral domain optical coherence tomography (iVue SD-OCT).

RESULTS

Mean RNFL thickness was significantly (P<0.001) higher in the inferior sector (131.4±20.6 µm) than the superior sector (126.1±19.1 µm), where it was higher than in the temporal sector (79.8±12.2 µm;P<0.001), where it was higher than in the nasal sector (75.1±12.6 µm;P<0.001). In multivariate analysis, mean global RNFL thickness (103.2±12.6 µm) increased significantly with younger age (standardized correlation coefficient beta:-0.30;P<0.001), larger neuroretinal rim area (beta:0.26;P<0.001), shorter axial length (beta:-0.21;P<0.001), thicker subfoveal choroidal thickness (beta:0.15;P<0.001), larger optic disc area (beta:0.10;P<0.001), less refractive lens power (beta:0.10;P<0.001), flatter anterior cornea (beta:0.07;P = 0.01) and female gender (beta:0.05;P = 0.03). In this population with an age of 50+ years, the age-related decline in RNFL thickness was 0.5 µm per year of life or 0.36% of an original RNFL thickness of 137 µm at baseline of the study at 50 years of age. Mean global RNFL thickness decreased by 2.4 µm for each mm enlargement of axial length.

CONCLUSIONS

The RNFL profile shows a double hump configuration with the thickest part in the inferior sector, followed by the superior sector, temporal sector and nasal sector. Factors influencing global RNFL thickness were younger age, larger neuroretinal rim, shorter axial length, thicker subfoveal choroid, larger optic disc, less refractive lens power, flatter anterior cornea and female gender. Beyond an age of 50+ years, RNFL decreased by about 0.3% per year of life at an age of 50+ years and by 2.4 µm per mm of axial elongation. These findings may be of interest for the knowledge of the normal anatomy of the eye and may be of help to diagnose diseases affecting the RNFL.

Clinicopathologic correlation of disc and peripapillary region using SD-OCT

PURPOSE

To describe a technique for evaluating peripapillary and optic nerve head (ONH) anatomy using spectral domain optical coherence tomography (SD-OCT) raster scanning in humans and compare quantifiable parameters between diagnosis categories.

METHODS

Ninety-five eyes of 51 consecutive patients were evaluated in this retrospective cross-sectional pilot study. Cirrus 5-line raster SD-OCTs with a resolution of 5 to 15 μm obtained through the ONH were included. A single observer manually measured neural canal opening (NCO), prelaminar canal depth (PLCD), peripapillary choroidal thickness (PPCT), and canal nerve fiber layer (CNFL) in normals, ocular hypertension, primary open-angle glaucoma (POAG), low-pressure glaucoma (LPG), secondary glaucoma, and early atrophic age-related macular degeneration. Clinical information, including central corneal thickness (CCT), was obtained via medical record review. Mean anatomical values within diagnosis categories were compared using one-way analysis of variance and multivariate analysis. Bivariate analysis was used to investigate relationships between continuous variables, and significant (p < 0.05) relationships were incorporated into the final statistical model.

RESULTS

Horizontal NCO was significantly greater in eyes with LPG than that in normals (p = 0.021). The PPCT was thinner in age-related macular degeneration (p = 0.001) and glaucoma (p = 0.004) compared with that in controls (normals). Mean CNFL was thinner in POAG (p < 0.001) and LPG (p = 0.053) compared with that in normals. Vertical NCO was inversely correlated to CCT (p = 0.013). Multivariate analysis indicated a positive correlation between PLCD and PPCT (p = 0.008) and an inverse correlation between CNFL and PLCD (p < 0.001). Controlling for PPCT, PLCD and CCT were inversely correlated (p < 0.001).

CONCLUSIONS

The SD-OCT raster scanning may be used to quantify ONH anatomy in humans. The NCO differences between POAG and LPG may indicate a distinct structural vulnerability in LPG. In addition, CNFL, PPCT, and PLCD may be important parameters to consider in glaucoma. The PLCD correlates with PPCT and should be considered in new models of glaucoma pathogenesis.

Reproducibility of a long-range swept-source optical coherence tomography ocular biometry system and comparison with clinical biometers

OBJECTIVE

To demonstrate a novel swept source optical coherence tomography (SS-OCT) imaging device using a vertical cavity surface-emitting laser (VCSEL) capable of imaging the full eye length and to introduce a method using this device for noncontact ocular biometry. To compare the measurements of intraocular distances using this SS-OCT instrument with commercially available optical and ultrasound biometers. To evaluate the intersession reproducibility of measurements of intraocular distances using SS-OCT.

DESIGN

Evaluation of technology.

PARTICIPANTS

Twenty eyes of 10 healthy subjects imaged at the New England Eye Center at Tufts Medical Center and Massachusetts Institute of Technology between May and September 2012.

METHODS

Averaged central depth profiles were extracted from volumetric SS-OCT datasets. The intraocular distances, such as central corneal thickness (CCT), aqueous depth (AD), anterior chamber depth (ACD), crystalline lens thickness (LT), vitreous depth (VD), and axial length (AL), were measured and compared with a partial coherence interferometry device (IOLMaster; Carl Zeiss Meditec, Inc., Dublin, CA) and an immersion ultrasound (IUS) A-scan biometer (Axis-II PR; Quantel Medical, Inc., Cournon d'Auvergne Cedex, France).

MAIN OUTCOME MEASURES

Reproducibility of the measurements of intraocular distances, correlation coefficients, and intraclass correlation coefficients.

RESULTS

The standard deviations of the repeated measurements of intraocular distances using SS-OCT were 6 μm (CCT), 16 μm (ACD), 14 μm (AD), 13 μm (LT), 14 μm (VD), and 16 μm (AL). Strong correlations among all 3 biometric instruments were found for AL (r > 0.98). The AL measurement using SS-OCT correlates better with the IOLMaster (r=0.998) than with IUS (r=0.984). The SS-OCT and IOLMaster measured higher AL values than ultrasound (175 and 139 μm, respectively). No statistically significant difference in ACD between the optical (SS-OCT or IOLMaster) and ultrasound methods was detected. High intersession reproducibility of SS-OCT measurements of all intraocular distances was observed with intraclass correlation coefficients >0.99.

CONCLUSIONS

The SS-OCT using VCSEL technology enables full eye length imaging and high-precision, noncontact ocular biometry. The measurements with the prototype SS-OCT instrument correlate well with commercial biometers. The SS-OCT biometry has the potential to provide clinically useful comprehensive biometric parameters for pre- and postoperative eye evaluation.

Individual A-scan signal normalization between two spectral domain optical coherence tomography devices

PURPOSE

We developed a method to normalize optical coherence tomography (OCT) signal profiles from two spectral-domain (SD) OCT devices so that the comparability between devices increases.

METHODS

We scanned 21 eyes from 14 healthy and 7 glaucoma subjects with two SD-OCT devices on the same day, with equivalent cube scan patterns centered on the fovea (Cirrus HD-OCT and RTVue). Foveola positions were selected manually and used as the center for registration of the corresponding images. A-scan signals were sampled 1.8 mm from the foveola in the temporal, superior, nasal, and inferior quadrants. After oversampling and rescaling RTVue data along the Z-axis to match the corresponding Cirrus data format, speckle noise reduction and amplitude normalization were applied. For comparison between normalized A-scan profiles, mean absolute difference in amplitude in percentage was measured at each sampling point. As a reference, the mean absolute difference between two Cirrus scans on the same eye also was measured.

RESULTS

The mean residual of the A-scan profile amplitude was reduced significantly after signal normalization (12.7% vs. 6.2%, P < 0.0001, paired t-test). All four quadrants also showed statistically significant reduction (all P < 0.0001). Mean absolute difference after normalization was smaller than the one between two Cirrus scans. No performance difference was detected between health and glaucomatous eyes.

CONCLUSIONS

The reported signal normalization method successfully reduced the A-scan profile differences between two SD-OCT devices. This signal normalization processing may improve the direct comparability of OCT image analysis and measurement on various devices.

Evaluation of cystoid macular edema using optical coherence tomography and fundus autofluorescence after uncomplicated phacoemulsification surgery

Aim. To investigate the utility of fundus autofluorescence (FAF) and optical coherence tomography (OCT) in the evaluation of cystoid macular edema (CME) following cataract surgery. Materials and Methods. Forty eyes of 29 patients undergone phacoemulsification, with posterior chamber intraocular lens implantation surgery. Central macular thickness (CMT) of the patients was evaluated using OCT and FAF preoperatively and postoperative 1st, 30th, 60th, 90th, and 180th days. Results. CME was detected in three eyes (7.5%) of two patients using OCT. Hyperautofluorescence (HAF) was detected in two of these three eyes and resolved with treatment. In the remaining 37 eyes without CME, there was a significant increase in visual acuity when compared to preoperative values (P = 0.008) Mean macular thicknesses (MMT) of the eyes without CME were 174 ± 20 μm preoperatively and 179 ± 22 μm at day 1, 178 ± 19 μm at 1st month, and 168 ± 10 μm at 6th month postoperatively. In the eyes with CME, the MMTs, measured with OCT were 189 ± 23 μm preoperatively and 432 ± 361 on day 1, 343 ± 123 μm at 1st month, 345 ± 196 at 2nd month, and 200 ± 36 μm at 6th month postoperatively. Conclusion. We found a moderate increase in CMT in the first 3 months postoperatively, in the eyes without CME which did not cause visual disturbances. FAF is a noninvasive, rapid method for the evaluation and follow-up of CME following cataract surgery.

Glaucoma versus red disease: imaging and glaucoma diagnosis

PURPOSE OF REVIEW

The use of ophthalmic imaging for documentation and diagnosis of ocular disease is rising dramatically. Optical coherence tomography (OCT), confocal scanning laser tomography (CSLT), scanning laser polarimetry (SLP) and photographic imaging of the optic nerve head (ONH) are currently used to document baseline characteristics of the ONH and for diagnosing glaucoma and glaucoma progression secondary to loss of retinal nerve fiber layer (RNFL). Imaging modalities typically provide information on ONH and RNFL characteristics which are outside of the normal (relative to normative databases) in red lettering or boxes, whereas ONH and RNFL characteristics within the normal range are presented in green.

RECENT FINDINGS

As imaging modalities have become more sophisticated and are validated in research studies, clinicians have come to rely upon data from these imaging devices to aid in differentiating between normal and glaucomatous states of the ONH and RNFL - typically by examining if the data are green or red suggesting normal or abnormal. However, normative databases can sometimes be flawed relative to atypical ONH or RNFL morphologies and imaging can provide artifacts which do not represent true ocular disease but secondary to limitations of imaging technology.

SUMMARY

Ophthalmic imaging is an important adjunct to clinical diagnosis but the results from imaging devices need to be assessed critically relative to artifacts of imaging and the limitations of the technology and its normative databases.

Correlation between lateral geniculate nucleus atrophy and damage to the optic disc in glaucoma

PURPOSE

To investigate the relationship between morphological changes in the lateral geniculate nucleus (LGN), as measured by magnetic resonance imaging (MRI), and damage to the optic disc in primary open-angle glaucoma (POAG) patients.

METHODS

A total of 23 patients with POAG and 23 age- and gender-matched non-glaucomatous subjects were enrolled. Every patient had structural damage to the optic disc. Cup-to-disc ratio (CDR) and retinal nerve fiber layer thickness (RNFLT) were measured, and 3.0-Tesla MRI examinations performed. Bilateral LGNs were identified and manually extracted, and their maximum heights and volumes compared with the clinical damage to the optic disc.

RESULTS

In POAG patients, morphological changes in LGNs and RNFLT were consistently varied (P<0.05), while a negative correlation between LGN measurements and CDR was observed (P<0.05). LGN height was more significantly correlated with damage to the optic disc than was LGN volume. In contrast, no significant correlation was found between morphological changes in LGNs and age or optic disc parameters in the non-glaucomatous controls (P>0.05).

CONCLUSION

LGN atrophy in POAG patients was altered in a manner consistent with damage to the optic disc. Morphological changes in LGNs as measured by MRI and especially LGN maximum height may be useful ways to detect optic nerve neuropathy in glaucoma.

Evaluation of peripapillary retinal nerve fiber layer, macula and ganglion cell thickness in amblyopia using spectral optical coherence tomography

AIM

To investigate peripapillary retinal nerve fiber layer (RNFL), macula and ganglion cell layer thicknesses (GCC) in amblyopic eyes with spectral domain optical coherence tomography (SD-OCT).

METHODS

Thirty six patients with a history of unilateral amblyopia and thirty two children who had emmetropia without amblyopia were included in this study. In this institutional study, 36 eyes of 36 patients with amblyopia (AE), 36 fellow eyes without amblyopia (FE), and 32 eyes of 32 normal subjects (NE) were included. RNFL, GCC and macular thickness measurements were performed with RS-3000 OCT Retina Scan (Nidek Inc CA. USA).

RESULTS

The mean global thicknesses of the RNFL were 113.22±21.47, 111.57±18.25, 109.96±11.31µm in the AE, FE, and NE, respectively. There was no statistically significant difference for mean global RNFL thickness among the eyes (P=0.13). The mean thicknesses of the macula were 258.25±18.31, 258.75±19.54, 248.62±10.57µm in the AE, FE and NE, respectively. There was no statistically significant difference for thickness of macula among the eyes (P=0.06). The GCC was investigated into two parts: superior and inferior. The mean thicknesses of superior GCC were 102.57±13.32, 103.32±10.64, 100.52±5.88µm in the AE, FE, and NE, respectively. The mean thicknesses of inferior GCC were 103.82±12.60, 107.82±12.33, 105.86±10.79µm in the AE, FE and NE, respectively. There was no statistically significant difference for thickness of superior and inferior GCC between the eyes (P=0.63, P=0.46).

CONCLUSION

The macular thicknesses of AE and FE were greater than the NE, although it was not statistically significant. Amblyopia does not seem to have a profound effect on the RNFL, macula and GCC.

High dynamic range imaging concept-based signal enhancement method reduced the optical coherence tomography measurement variability

PURPOSE

To develop and test a novel signal enhancement method for optical coherence tomography (OCT) images based on the high dynamic range (HDR) imaging concept.

METHODS

Three virtual channels, which represent low, medium, and high signal components, were produced for each OCT signal dataset. The dynamic range of each signal component was normalized to the full gray scale range. Finally, the three components were recombined into one image using various weights. Fourteen eyes of 14 healthy volunteers were scanned multiple times using time-domain (TD)-OCT before and while preventing blinking in order to produce a wide variety of signal strength (SS) images on the same eye scanned on the same day. For each eye, a pair of scans with the highest and lowest SS with successful retinal nerve fiber layer (RNFL) segmentation was selected to test the signal enhancement effect. In addition, spectral-domain (SD)-OCT images with poor signal qualities were also processed.

RESULTS

Mean SS of good and poor quality scans were 9.0 ± 1.1 and 4.4 ± 0.9, respectively. TD-OCT RNFL thickness showed significant differences between good and poor quality scans on the same eye (mean difference 11.9 ± 6.0 μm, P < 0.0001, paired t-test), while there was no significant difference after signal enhancement (1.7 ± 6.2 μm, P = 0.33). However, HDR had weaker RNFL compensation effect on images with SS less than or equal to 4, while it maintained good compensation effect on images with SS greater than 4. Successful signal enhancement was also confirmed subjectively on SD-OCT images.

CONCLUSION

The HDR imaging successfully restored OCT signal and image quality and reduced RNFL thickness differences due to variable signal level to the level within the expected measurement variability. This technique can be applied to both TD- and SD-OCT images.

Comparison of functional and morphological diagnostics in glaucoma patients and healthy subjects

PURPOSE

To evaluate the diagnostic value of microperimetry (MP), blue-on-yellow perimetry (B/YP), confocal scanning laser ophthalmoscopy (Heidelberg Retina Tomograph, HRT, III) and optical coherence tomography (OCT) in discriminating eyes with early glaucoma from healthy subjects.

MATERIAL AND METHODS

Prospective examination of 22 eyes of subjects with early primary open-angle glaucoma and 24 eyes of healthy control subjects. After a complete ophthalmological examination, B/YP, MP, OCT and HRT III were determined. Morphological and functional parameters were analysed.

RESULTS

Mean sensitivity threshold values obtained with B/YP and MP did not show significant differences between glaucoma patients and the control group (p = 0.321 and p = 0.281). Retinal nerve fibre layer (RNFL) thickness was significantly decreased in patients with glaucoma with both HRT III and OCT (p = 0.018 and p < 0.001).

CONCLUSIONS

While B/YP and MP had no ability to discriminate between subjects with early glaucoma and healthy subjects, RNFL thickness measured with HRT III and OCT showed a significant difference. In early primary open-angle glaucoma, morphological changes like RNFL thickness seem to occur prior to functional defects in the visual field.

Short duration transient visual evoked potentials in glaucomatous eyes

PURPOSE

To investigate the correlation between structural and functional damage in patients with asymmetric glaucoma using a newly developed short duration transient visual evoked potential (SD-tVEP) device.

METHODS

Twenty-five patients with visual acuity ≥20/30 and asymmetric visual field (VF) loss [inter-eye difference in mean deviation index (MD) of at least 3 dB] were enrolled. Patients underwent optical coherence tomography (OCT) for macular thickness measurement, scanning laser polarimetry with variable corneal compensation for retinal nerve fiber layer measurement, and SD-tVEP (10% and 85% Michelson contrast, acquisition time of 20 s) in both eyes within 2 months. We correlated VF MD and structural test results with SD-tVEP P100 latency and Delta Amplitude (N75-P100).

RESULTS

Using 10% contrast, there was a significant difference in SD-tVEP latency and amplitude between eyes with better and worse VF MD (P<0.001). MD correlated significantly with both SD-tVEP parameters (r>0.33, P≤0.01). When using 85% contrast, SD-tVEP amplitude differed between eyes (P=0.01) and MD values correlated significantly with amplitude results (r=0.32, P=0.01), but not with latency (P=0.46). In eyes with more advanced VF loss, there was a positive and significant correlation between SD-tVEP amplitude (85% contrast) and macular thickness on OCT (r=0.47, P=0.01), but not with retinal nerve fiber layer measured with polarimetry (P=0.26).

CONCLUSIONS

In cases of asymmetric glaucoma, SD-tVEP results correlate significantly with the level of VF damage as measured by MD. In the eyes with more advanced VF loss, reduced SD-tVEP amplitude was associated with decreased macular thickness on OCT. These findings suggest that SD-tVEP may be a fast and objective method to assess or screen for functional damage in glaucomatous eyes.

Effect of axonal micro-tubules on the morphology of retinal nerve fibers studied by second-harmonic generation

Many studies suggest that the degradation of microtubules in the retinal ganglion cells may be an early event in the progression of glaucoma. Because reflectance and birefringence of the retinal nerve fibers arise primarily from microtubules, the optical properties have been intensively studied for early detection of the disease. We previously reported a novel nonlinear optical signal from axonal microtubules for visualizing the retinal nerve fibers, namely second-harmonic generation (SHG). We demonstrate the use of axonal SHG to investigate the effect of microtubules on the morphology of the retinal nerve fiber bundles. Time-lapse SHG imaging of ex vivo rat retinal flat mounts was performed during pharmacological treatment of nocodazole, and the intensity of axonal SHG and the changes in nerve fiber bundle morphology were monitored. We found that the microtubule disruption does not lead to immediate modification in the morphology of the nerve fibers. Our results indicate that microtubular SHG may provide a useful means for sensitive detection of axonal injuries. Since the intrinsic radiation depends on the regular architecture of the cytoskeleton element as maintained by active cellular regulations, the intensity of signal reflects the health of the retinal ganglion cell axons.

Retinal nerve fiber layer and optic disc measurements by spectral domain OCT: normative values and associations in young adults

PURPOSE

To determine normative values and associations of retinal nerve fiber layer (RNFL) and optic disc parameters in normal eyes measured by spectral domain optical coherence tomography (OCT).

METHODS

In a population-based setting, 1521 young adults were examined as part of the Sydney Adolescent Vascular and Eye Study (SAVES). Their mean age was 17.3±0.6 years. RNFL and optic disc parameter measurements were made using Cirrus HD-OCT 4000.

RESULTS

The average RNFL was found to be 99.4±9.6 μm. RNFL thickness was least for the temporal quadrant (69.9±11.2 μm), followed by the nasal (74.3±12.8 μm), superior (124.7±15.7 μm) and inferior (128.8±17.1 μm) quadrants. The mean disc area in this population was 1.98±0.38 mm(2) with a mean rim area of 1.50±0.30 mm(2) and a mean cup/disc ratio of 0.44±0.18. Multivariate-adjusted RNFL thickness was marginally greater in East Asian than in white participants (100.1 μm vs 99.5 μm; P=0.0005). The RNFL was thinner with greater axial length (P<0.0001), less positive spherical equivalent refractions (P<0.0001), smaller disc area and rim area (P<0.0001).

CONCLUSION

This study documents normative values for the RNFL and optic disc measured using Cirrus HD-OCT in young adults. The values and associations reported in this study can inform clinicians on the normal variation in RNFL and optic disc parameters.

A formula to predict spectral domain optical coherence tomography (OCT) retinal nerve fiber layer measurements based on time domain OCT measurements

PURPOSE

To establish and validate a formula to predict spectral domain (SD)-optical coherence tomography (OCT) retinal nerve fiber layer (RNFL) thickness from time domain (TD)-OCT RNFL measurements and other factors.

METHODS

SD-OCT and TD-OCT scans were obtained on the same day from healthy participants and patients with glaucoma. Univariate and multivariate linear regression relationships were analyzed to convert average Stratus TD-OCT measurements to average Cirrus SD-OCT measurements. Additional baseline characteristics included age, sex, intraocular pressure, central corneal thickness, spherical equivalent, anterior chamber depth, optic disc area, visual field (VF) mean deviation, and pattern standard deviation. The formula was generated using a training set of 220 patients and then evaluated on a validation dataset of 105 patients.

RESULTS

The training set included 71 healthy participants and 149 patients with glaucoma. The validation set included 27 healthy participants and 78 patients with glaucoma. Univariate analysis determined that TD-OCT RNFL thickness, age, optic disc area, VF mean deviation, and pattern standard deviation were significantly associated with SD-OCT RNFL thickness. Multivariate regression analysis using available variables yielded the following equation: SD-OCT RNFL = 0.746 × TD-OCT RNFL + 17.104 (determination coefficient [R(2)] = 0.879). In the validation sample, the multiple regression model explained 85.6% of the variance in the SD-OCT RNFL thickness.

CONCLUSIONS

The proposed formula based on TD-OCT RNFL thickness may be useful in predicting SD-OCT RNFL thickness. Other factors associated with SD-OCT RNFL thickness, such as age, disc area, and mean deviation, did not contribute to the accuracy of the final equation.

Agreement between retinal nerve fiber layer measures from Spectralis and Cirrus spectral domain OCT

PURPOSE

An assessment of the retinal nerve fiber layer (RNFL) provides important information on the health of the optic nerve. There are several non-invasive technologies, including spectral domain optical coherence tomography (SD OCT), that can be used for in vivo imaging and quantification of the RNFL, but often there is disagreement in RNFL thickness between clinical instruments. The purpose of this study was to investigate the influence of scan centration, ocular magnification, and segmentation on the degree of agreement of RNFL thickness measures by two SD OCT instruments.

METHODS

RNFL scans were acquired from 45 normal eyes using two commercially available SD OCT systems. Agreement between RNFL thickness measures was determined using each instrument's algorithm for segmentation and a custom algorithm for segmentation. The custom algorithm included ocular biometry measures to compute the transverse scaling for each eye. Major retinal vessels were identified and removed from RNFL measures in 1:1 scaled images. Transverse scaling was also used to compute the RNFL area for each scan.

RESULTS

Instrument-derived global RNFL thickness measured from the two instruments correlated well (R(2) = 0.70, p < 0.01) but with significant differences between instruments (mean of 6.7 μm; 95% limits of agreement of 16.0 μm to -2.5 μm, intraclass correlation coefficient = 0.62). For recentered scans with custom RNFL segmentation, the mean difference was reduced to 0.1 μm (95% limits of agreement 6.1 to -5.8 μm, intraclass correlation coefficient = 0.92). Global RNFL thickness was related to axial length (R = 0.24, p < 0.01), whereas global RNFL area measures were not (R(2) = 0.004, p = 0.66). Major retinal vasculature accounted for 11.3 ± 1.6% (Cirrus) or 11.8 ± 1.4% (Spectralis) of the RNFL thickness/area measures.

CONCLUSIONS

Sources of disagreement in RNFL measures between SD-OCT instruments can be attributed to the location of the scan path and differences in their retinal layer segmentation algorithms. In normal eyes, the major retinal vasculature accounts for a significant percentage of the RNFL and is similar between instruments. With incorporation of an individual's ocular biometry, RNFL area measures are independent of axial length, with either instrument.

Wavelength-dependent change of retinal nerve fiber layer reflectance in glaucomatous retinas

PURPOSE

Retinal nerve fiber layer (RNFL) reflectance is often used in optical methods for RNFL assessment in clinical diagnosis of glaucoma, yet little is known about the reflectance property of the RNFL under the development of glaucoma. This study measured the changes in RNFL reflectance spectra that occurred in retinal nerve fiber bundles with different degrees of glaucomatous damage.

METHODS

A rat model of glaucoma with laser photocoagulation of trabecular meshwork was used. Reflectance of the RNFL in an isolated retina was measured at wavelengths of 400-830 nm. Cytostructural distribution of the bundles measured optically was evaluated by confocal imaging of immunohistochemistry staining of cytoskeletal components, F-actin, microtubules, and neurofilaments. RNFL reflectance spectra were studied in bundles with normal-looking appearance, early F-actin distortion, and apparent damage of all cytoskeletal components. Changes of RNFL reflectance spectra were studied at different radii (0.22, 0.33, and 0.44 mm) from the optic nerve head (ONH).

RESULTS

Bundles in 30 control retinas and 41 glaucomatous retinas were examined. In normal retinas, reflectance spectra were similar along the same bundles. In glaucomatous retinas, reflectance spectra changed along bundles with the spectra becoming flatter as bundle areas approached the ONH.

CONCLUSIONS

Elevation of intraocular pressure (IOP) causes nonuniform changes in RNFL reflectance across wavelengths. Changes of reflectance spectra occur early in bundles near the ONH and prior to apparent cytoskeletal distortion. Using the ratio of RNFL reflectance measured at different wavelengths can provide early and sensitive detection of glaucomatous damage.

Influence of anterior segment power on the scan path and RNFL thickness using SD-OCT

PURPOSE

Retinal nerve fiber layer (RNFL) thickness measures with spectral domain-optical coherence tomography (SD-OCT) provide important information on the health of the optic nerve. As with most retinal imaging technologies, ocular magnification characteristics of the eye must be considered for accurate analysis. While effects of axial length have been reported, the effects of anterior segment optical power on RNFL thickness measures have not been described fully to our knowledge. The purpose of our study was to determine the influence of the optical power change at the anterior corneal surface, using contact lenses, on the location of the scan path and measurements of RNFL thickness in normal healthy eyes.

METHODS

We recruited 15 normal subjects with less than 6 diopters (D) of ametropia and no ocular pathology. One eye of each subject was selected randomly for scanning. Baseline SD-OCT scans included raster cubes centered on the optic nerve and macula, and a standard 12-degree diameter RNFL scan. Standard 12-degree RNFL scans were repeated with 10 separate contact lenses, (Proclear daily, Omafilcon A/60%) ranging from +8 to -12 D in 2-D steps. The extent of the retinal scan, and RNFL thickness and area measures were quantified using custom MATLAB programs that included ocular biometry measures (IOL Master).

RESULTS

RNFL thickness decreased (0.52 μm/D, r = -0.33, P < 0.01) and the retinal region scanned increased (0.52%/D, r = 0.97, P < 0.01) with increase in contact lens power (-12 to +8). The normalized/percentage rates of change of RNFL thickness (-0.11/mm, r = -0.67, P < 0.01) and image size (0.11/mm, r = 0.96, P < 0.01) were related to axial length. Changes in the retinal region scanned were in agreement with transverse scaling, computed with a three surface schematic eye (R(2) = 0.97, P < 0.01). RNFL area measures, that incorporated the computed transverse scaling, were not related significantly to contact lens power (863 μm(2)/D, r = 0.06, P = 0.47).

CONCLUSIONS

Measurements of RNFL thickness by SD-OCT are dependent on the optics of the eye, including anterior segment power and axial length. The relationships between RNFL thickness measures and optical power are a direct reflection of scan path location with respect to the optic nerve head rim, caused by relative magnification. An incorporation of transverse scaling to RNFL area measures, based on individualized ocular biometry, eliminated the magnification effect.

Does optic nerve head size variation affect circumpapillary retinal nerve fiber layer thickness measurement by optical coherence tomography?

PURPOSE

To determine the relationship between retinal nerve fiber layer (RNFL) thickness, optic disc size, and image magnification.

METHODS

The cohort consisted of 196 normal eyes of 101 participants in the Advanced Imaging for Glaucoma Study (AIGS), a multicenter, prospective, longitudinal study to develop advanced imaging technologies for glaucoma diagnosis. Scanning laser tomography was used to measure disc size. Optical coherence tomography (OCT) was used to perform circumpapillary RNFL thickness measurements using the standard fixed 3.46-mm nominal scan diameter. A theoretical model of magnification effects was developed to relate RNFL thickness (overall average) with axial length and magnification.

RESULTS

Multivariate regression showed no significant correlation between RNFL thickness and optic disc area (95% confidence interval [CI] = -0.9 to 4.1 μm/mm², P = 0.21). Linear regression showed that RNFL thickness depended significantly on axial length (slope = -3.1 μm/mm, 95% CI = -4.9 to -1.3, P = 0.001) and age (slope = -0.3 μm/y, 95% CI = -0.5 to -0.2, P = 0.0002). The slope values agreed closely with the values predicted by the magnification model.

CONCLUSIONS

There is no significant association between RNFL thickness and optic disc area. Previous publications that showed such an association may have been biased by the effect of axial length on fundus image magnification and, therefore, both measured RNFL thickness and apparent disc area. The true diameter of the circumpapillary OCT scan is larger for a longer eye (more myopic eye), leading to a thinner RNFL measurement. Adjustment of measured RNFL thickness by axial length, in addition to age, may lead to a tighter normative range and improve the detection of RNFL thinning due to glaucoma.

Phase-sensitive optical coherence tomography characterization of pulse-induced trabecular meshwork displacement in ex vivo nonhuman primate eyes

Glaucoma is a blinding disease for which intraocular pressure (IOP) is the only treatable risk factor. The mean IOP is regulated through the aqueous outflow system, which contains the trabecular meshwork (TM). Considerable evidence indicates that trabecular tissue movement regulates the aqueous outflow and becomes abnormal during glaucoma; however, such motion has thus far escaped detection. The purpose of this study is to describe anovel use of a phase-sensitive optical coherence tomography (PhS-OCT) method to assess pulse-dependent TM movement. For this study, we used enucleated monkey eyes, each mounted in an anterior segment holder. A perfusion system was used to control the mean IOP as well as to provide IOP sinusoidal transients (amplitude 3 mmHg, frequency 1 pulse/second) in all experiments. Measurements were carried out at seven graded mean IOPs (5, 8, 10, 20, 30, 40, and 50 mm Hg). We demonstrate that PhS-OCT is sensitive enough to image/visualize TM movement synchronous with the pulse-induced IOP transients, providing quantitative measurements of dynamic parameters such as velocity, displacement, and strain rate that are important for assessing the biomechanical compliance of the TM. We find that the largest TM displacement is in the area closest to Schlemm's canal (SC) endothelium. While maintaining constant ocular pulse amplitude, an increase of mean IOP results in a decrease of TM displacement and mean size of the SC. These results demonstrate that the PhS-OCT is a useful imaging technique capable of assessing functional properties necessary to maintain IOP in a healthy range, offering a new diagnostic alternative for glaucoma.

Comparison of retinal nerve fiber layer thickness measurement bias and imprecision across three spectral-domain optical coherence tomography devices

PURPOSE

We compared retinal nerve fiber layer (RNFL) bias and imprecision among three spectral-domain optical coherence tomographs (SD-OCT).

METHODS

A total of 152 eyes of 83 subjects (96 healthy and 56 glaucomatous eyes) underwent peripapillary RNFL imaging using at least 2 of the following 3 SD-OCT devices on the same day: Cirrus HD-OCT (optic nerve head [ONH]) cube 200 × 200 protocol), RTVue-100 (ONH protocol [12 radial lines and 13 concentric circles]), and 3D OCT-1000 (3D Scan 256 × 256 protocol). Calibration equations, bias and imprecision of RNFL measurements were calculated using structural equation models.

RESULTS

The calibration equations for healthy and glaucoma RNFL thickness measurements among the 3 devices were: Cirrus = 2.136 + 0.831*RTVue; Cirrus = -15.521 + 1.056*3D OCT-1000; RTVue = -21.257 + 1.271*3D OCT-1000. Using Cirrus bias as an arbitrary reference, RTVue bias was 1.20 (95% CI 1.09-1.32, P < 0.05) times larger and 3D OCT-1000 was 0.95 (0.87-1.03, P > 0.05) times smaller. Relative to 3D OCT-1000, the RTVue bias was 1.27 (1.13-1.42, P < 0.05). RTVue imprecision (healthy eyes 7.83, 95% CI 6.43-9.58; glaucoma cases 5.71, 4.19-7.64) was statistically significantly higher than both Cirrus (healthy eyes 3.23, 2.11-4.31; glaucoma cases 3.53, 0.69-5.24) and 3D OCT-1000 (healthy eyes 4.07, 3.11-5.35; glaucoma cases 5.33, 3.77-7.67) in healthy eyes. The imprecision also was significantly higher for RTVue measurements in healthy compared to glaucomatous eyes. None of the other comparisons was statistically significant.

CONCLUSIONS

RTVue-100 showed higher imprecision (or higher measurement variability) than Cirrus HD-OCT and 3D OCT-1000 RNFL measurements. Three-dimensional cube scanning with post-hoc data sampling may be a factor reducing imprecision.

Sensitivity and specificity of machine learning classifiers and spectral domain OCT for the diagnosis of glaucoma

Purpose. To investigate the sensitivity and specificity of machine learning classifiers (MLC) and spectral domain optical coherence tomography (SD-OCT) for the diagnosis of glaucoma. Methods. Sixty-two patients with early to moderate glaucomatous visual field damage and 48 healthy individuals were included. All subjects underwent a complete ophthalmologic examination, achromatic standard automated perimetry, and RNFL imaging with SD-OCT (Cirrus HD-OCT; Carl Zeiss Meditec, Inc., Dublin, California, USA). Receiver operating characteristic (ROC) curves were obtained for all SD-OCT parameters. Subsequently, the following MLCs were tested: Classification Tree (CTREE), Random Forest (RAN), Bagging (BAG), AdaBoost M1 (ADA), Ensemble Selection (ENS), Multilayer Perceptron (MLP), Radial Basis Function (RBF), Naive-Bayes (NB), and Support Vector Machine (SVM). Areas under the ROC curves (aROCs) obtained for each parameter and each MLC were compared. Results. The mean age was 57.0±9.2 years for healthy individuals and 59.9±9.0 years for glaucoma patients (p=0.103). Mean deviation values were -4.1±2.4 dB for glaucoma patients and -1.5±1.6 dB for healthy individuals (p<0.001). The SD-OCT parameters with the greater aROCs were inferior quadrant (0.813), average thickness (0.807), 7 o'clock position (0.765), and 6 o'clock position (0.754). The aROCs from classifiers varied from 0.785 (ADA) to 0.818 (BAG). The aROC obtained with BAG was not significantly different from the aROC obtained with the best single SD-OCT parameter (p=0.93). Conclusions. The SD-OCT showed good diagnostic accuracy in a group of patients with early glaucoma. In this series, MLCs did not improve the sensitivity and specificity of SD-OCT for the diagnosis of glaucoma.

Agreement between spectral domain optical coherence tomography and retinal nerve fiber layer photography in chinese

PURPOSE

To compare spectral domain optical coherence tomography (OCT) and fundus photography to identify localized retinal nerve fiber layer defects (RNFLD) in Chinese patients with early-to-medium advanced glaucoma.

METHODS

Thirty-nine patients (48 eyes) with localized RNFLDs by fundus photography and 48 age-matched control individuals were included into the study. The individuals underwent spectral domain OCT of the retinal nerve layer. In OCT, a localized RNFLD was defined as a dipping of the retinal nerve fiber layer thickness curve into the red-colored band of the graph, measured at a peripapillary circle with a diameter of 3.46 mm.

RESULTS

In the 48 eyes of the study group, 63 localized RNFLDs were seen on the fundus photographs. On the OCTs, 58 of these 63 localized RNFLDs were detected, whereas 5 defects were not detected. Two localized RNFLDs seen on the OCTs were not found on the corresponding fundus photographs. The resulting sensitivity and specificity of OCT for detecting localized RNFLDs were 92% and 96%, respectively. The overall agreement rate between both methods was 94% (90/96), and the κ value was 0.90 (P<0.001). The results of both techniques correlated with each other for the determination of the location (Pearson correlation coefficient (r)=0.99; P<0.001) and the width of the localized RNFLDs (201 ± 123 degrees vs. 207 ± 115 degrees; r=0.93; P<0.001).

CONCLUSIONS

Spectral domain OCT as compared with examiner-performed assessment of conventional fundus photographs is capable of detecting and measuring localized retinal nerve fiber layer defects with a relatively high diagnostic precision.

Age and retinal nerve fiber layer thickness measured by spectral domain optical coherence tomography

Purpose

To evaluate the association between age and peripapillary retinal nerve fiber layer (RNFL) thickness measured by Cirrus high-definition (HD) spectral domain optical coherence tomography (OCT) in healthy Korean subjects.

Methods

A total of 302 eyes from 155 healthy Korean subjects (age range, 20 to 79 years) underwent RNFL thickness measurements using the Cirrus HD-OCT. Average, quadrant, and clock-hour RNFL thickness parameters were analyzed in terms of age using linear mixed effect models.

Results

Average RNFL demonstrated a slope of -2.1 µm per decade of age (p < 0.001). In quadrant analysis, superior (-3.4 µm/decade, p < 0.001) and inferior (-2.9 µm/decade, p < 0.001) quadrants showed steeper slopes, whereas temporal (-1.1 µm/decade, p < 0.001) and nasal (-1.0 µm/decade, p < 0.001) quadrants revealed shallower slopes. Among the 12 clock-hour sectors, clock hours 6 (-4.5 µm/decade, p < 0.001) and 1 (-4.1 µm/decade, p < 0.001) showed the greatest tendency to decline with age; RNFLs of the 3 (-0.2 µm/decade, p = 0.391) and 4 (-0.6 µm/decade, p = 0.052) o'clock hour sectors did not show significant decay.

Conclusions

RNFL thickness was associated with age, especially in superior and inferior areas. The topographic distribution of correlation between age and RNFL thickness was not uniform.

Relationship among visual field, blood flow, and neural structure measurements in glaucoma

PURPOSE

To determine the relationship among visual field, neural structural, and blood flow measurements in glaucoma.

METHODS

Case-control study. Forty-seven eyes of 42 patients with perimetric glaucoma were age-matched with 27 normal eyes of 27 patients. All patients underwent Doppler Fourier-domain optical coherence tomography to measure retinal blood flow and standard glaucoma evaluation with visual field testing and quantitative structural imaging. Linear regression analysis was performed to analyze the relationship among visual field, blood flow, and structure, after all variables were converted to logarithmic decibel scale.

RESULTS

Retinal blood flow was reduced in glaucoma eyes compared to normal eyes (P < 0.001). Visual field loss was correlated with both reduced retinal blood flow and structural loss of rim area and retinal nerve fiber layer (RNFL). There was no correlation or paradoxical correlation between blood flow and structure. Multivariate regression analysis revealed that reduced blood flow and structural loss are independent predictors of visual field loss. Each dB decrease in blood flow was associated with at least 1.62 dB loss in mean deviation (P ≤ 0.001), whereas each dB decrease in rim area and RNFL was associated with 1.15 dB and 2.56 dB loss in mean deviation, respectively (P ≤ 0.03).

CONCLUSIONS

There is a close link between reduced retinal blood flow and visual field loss in glaucoma that is largely independent of structural loss. Further studies are needed to elucidate the causes of the vascular dysfunction and potential avenues for therapeutic intervention. Blood flow measurement may be useful as an independent assessment of glaucoma severity.

The Nature of Macular Damage in Glaucoma as Revealed by Averaging Optical Coherence Tomography Data

PURPOSE

To better understand the nature of glaucomatous damage, especially to the macula, the inner retinal thickness maps obtained with frequency domain optical coherence tomography (fdOCT) were averaged.

METHODS

Frequency domain optical coherence tomography macular and optic disc cube scans were obtained from 54 healthy eyes and 156 eyes with glaucomatous optic neuropathy. A manually corrected algorithm was used for layer segmentation. Patients' eyes were grouped both by mean deviation (MD) and hemifield classification using standard categories and 24-2 (6° grid) visual fields (VFs). To obtain average difference maps, the thickness of retinal nerve fiber (RNF) and retinal ganglion cell plus inner plexiform (RGC+) layers were averaged and subtracted from the average control values.

RESULTS

On the average difference maps, RGC+ and RNF layer thinning was seen in the patient groups with VFs classified as normal. The pattern of the thinning was the same, but the degree of thinning increased with decreased MD and with classification category (from normal to arcuate). This RGC+ thinning was largely within the central four points of the 24-2 (6° grid) field, after correcting for RGC displacement.

CONCLUSION

1. VF categories represent different degrees of the same pattern of RGC+ and RNFL layer thinning. 2. RGC+ damage occurs in the central macula even in patients with VFs classified as normal. 3. The 6° grid (24-2) pattern is not optimally designed to detect macular damage. 4. A schematic model of RGC projections is proposed to explain the pattern of macular loss, including the greater vulnerability of the inferior retinal region.

TRANSLATIONAL RELEVANCE

The 24-2 is not an optimal test pattern for detecting or following glaucomatous damage. Further, we suggest clinical fdOCT reports include RGC+ and RNFL probability plots combined with VF information.

Correlating RNFL thickness by OCT with perimetric sensitivity in glaucoma patients

PURPOSE

To determine whether a structure-function model developed for normal age-related losses of retinal ganglion cells also models the retinal ganglion cell losses in glaucomatous optic neuropathy.

METHODS

The model to relate age-related loss of retinal nerve fiber layer thickness and reduced sensitivity for standard automated perimetry was evaluated with data from 30 glaucoma patients and 40 normal individuals. Perimetry thresholds were translated into separate retinal ganglion cell body estimates for test locations in the superior and inferior visual fields. The retinal nerve fiber layer thickness from optical coherence tomography was also divided into regions representing the superior and inferior hemifields to obtain estimates of the axons in each hemifield. The 2 estimates of retinal ganglion cell populations were compared for corresponding regions.

RESULTS

Agreement between neural estimates was good for normal individuals and patients with early glaucomatous damage. Results for individuals with advanced glaucoma showed disparities between neural estimates that were proportional to the stage of disease. A correction factor for the stage of disease was introduced for the derivation of ganglion cell populations from the nerve fiber layer measurements, which produced agreement between the optical coherence tomography and perimetric estimates for all patients.

CONCLUSIONS

The modified structure-function model provided well-correlated relationships between the subjective measures of visual sensitivity and the objective measures of retinal nerve fiber layer thickness when parameters for the patient's age and the severity of the disease were included. The results suggest constitutive relationships between structure and function for the full spectrum of normal-to-advanced glaucomatous neuropathy.

Fourier Domain Oct Measurement of Macular, Macular Ganglion Cell Complex, and Peripapillary RNFL Thickness in Glaucomatous Chinese Eyes

Purpose.

To evaluate and compare the glaucoma discrimination ability of macula, macular ganglion cell complex (mGCC), and peripapillary nerve fiber layer (ppNFL) thickness in Chinese patients using Fourier-domain optical coherence tomography (FD-OCT).

Methods

A total of 64 normal subjects (N), 47 glaucoma suspects (GS), and 48 glaucoma patients (G) were enrolled in the study. The thickness of mGCC, ppNFL, and total macula were measured using RTVue-100 FD-OCT (software version: 4.0.7.5; Optovue). The GCC and ONH protocols were used for obtaining images in all subjects. For each binocular subject, one eye was chosen randomly for analysis.

Results.

The average thicknesses of macular, mGCC, and ppNFL in normal eyes were significantly different from those in GS or G eyes (p<0.001). The mGCC thickness correlated well with ppNFL thickness (correlation coefficients for N, GS, and G eyes are 0.397 [p=0.001], 0.822 [p<0.0001], and 0.865 [p<0.0001]). Areas under receiver operating characteristic curve of macular, mGCC, and ppNFL thickness are 0.940 (p<0.0001), 0.998 (p<0.0001), and 0.977 (p<0.0001), discriminating G from N eyes. There was no significant difference comparing the discriminating powers of NFL, GCC, and macular thickness.

Conclusions.

The mGCC measurements provide another measurement of neural loss in glaucoma, and may serve as a promising parameter for ppNFL thickness in the clinical assessment of glaucoma. For glaucomatous eyes, mGCC and ppNFL thicknesses performed better discriminating abilities compared with macular thickness.

Structure-function relationships using the Cirrus spectral domain optical coherence tomograph and standard automated perimetry

PURPOSE

To evaluate the relationship between glaucomatous structural damage assessed by the Cirrus Spectral Domain OCT (SDOCT) and functional loss as measured by standard automated perimetry (SAP).

METHODS

Four hundred twenty-two eyes (78 healthy, 210 suspects, 134 glaucomatous) of 250 patients were recruited from the longitudinal Diagnostic Innovations in Glaucoma Study and from the African Descent and Glaucoma Evaluation Study. All eyes underwent testing with the Cirrus SDOCT and SAP within a 6-month period. The relationship between parapapillary retinal nerve fiber layer thickness (RNFL) sectors and corresponding topographic SAP locations was evaluated using locally weighted scatterplot smoothing and regression analysis. SAP sensitivity values were evaluated using both linear as well as logarithmic scales. We also tested the fit of a model (Hood) for structure-function relationship in glaucoma.

RESULTS

Structure was significantly related to function for all but the nasal thickness sector. The relationship was strongest for superotemporal RNFL thickness and inferonasal sensitivity (R(2)=0.314, P<0.001). The Hood model fitted the data relatively well with 88% of the eyes inside the 95% confidence interval predicted by the model.

CONCLUSIONS

RNFL thinning measured by the Cirrus SDOCT was associated with correspondent visual field loss in glaucoma.

Evaluation of the nerve fiber layer and macula in the eyes of healthy children using spectral-domain optical coherence tomography

PURPOSE

To determine the normative values of the peripapillary retinal nerve fiber layer (RNFL), macular thickness, and macular volume in healthy children using spectral-domain optical coherence tomography (SD-OCT) and analyze the correlation of such values with age, refraction error, and biometric measurements.

DESIGN

Observational case series.

METHODS

This institutional study involved 107 eyes from 107 healthy pediatric patients (54 female, 53 male) with ages between 6 and 16 years. After the biometric measurements and refractive error values (in spherical equivalent) of the cases were obtained, the peripapillary RNFL, macular thickness, and macular volume values were calculated using the Spectralis OCT device.

RESULTS

Among the study group, with an average age of 10.46 ± 2.94 years, the average axial length (AL) was 23.33 ± 0.89 mm; the average spherical equivalent (SE) value was -0.27 ± 0.99 diopter. The average peripapillary RNFL thickness was 106.45 ± 9.41 μm; the average macular thickness was 326.44 ± 14.17 μm; and the average macular volume was 0.257 ± 0.011 mm(3). The aforementioned OCT measurements were not significantly correlated with age, SE, or AL values (P > .05 for all).

CONCLUSIONS

This study reports SD-OCT findings among healthy pediatric cases. SD-OCT can be reliably used for pediatric patients because of its short exposure time and high degree of image resolution.

Reproducibility of retinal nerve fiber layer thickness measurements using spectral domain optical coherence tomography

PURPOSE

To evaluate the reproducibility of the peripapillary retinal nerve fiber layer (RNFL) thickness measurements obtained by Spectralis spectral domain optical coherence tomography (OCT) (Heidelberg Engineering, Heidelberg, Germany) in normal and glaucoma participants.

METHODS

Participants were recruited from a university-based clinic. Peripapillary RNFL thickness measurements were repeated 3 times during the same visit using the follow-up function. One eye of each participant was randomly selected for statistical analysis. Reproducibility was evaluated using within-subject standard deviation (Sw), coefficient of variation (CV), and intraclass correlation coefficient (ICC). Spearman rank correlation coefficient analyses were used to assess the correlation of the standard deviation of the 3 measurements for each participant with the RNFL thickness value.

RESULTS

Forty-five normal participants and 33 glaucoma patients were included in the study. The CVs ranged from 1.45% [overall global (G)] to 2.59% [temporal quadrant (T)] in normal eyes and from 1.74% (G) to 3.22% (T) in the glaucomatous eyes. ICCs ranged from 0.977 (T) to 0.990 (G and inferior-nasal sector) in normal eyes and from 0.983 (T) to 0.997 (inferior quadrant) in glaucomatous eyes. Sw were from 1.34 μm (G) to 2.39 μm (superior-temporal and inferior-temporal sectors) in normal eyes and from 1.14 μm (G) to 2.25 μm (superior-nasal sector) in the glaucomatous eyes. There were no significant correlations between RNFL thickness values and the measurement variability for each participant.

CONCLUSIONS

Spectralis OCT shows excellent reproducibility for measuring the peripapillary RNFL thickness values in both healthy and glaucoma participants.

Retinal ganglion cell layer thickness and local visual field sensitivity in glaucoma

OBJECTIVE

To compare loss in sensitivity measured using standard automated perimetry (SAP) with local retinal ganglion cell layer (RGC) thickness measured using frequency-domain optical coherence tomography in the macula of patients with glaucoma.

METHODS

To compare corresponding locations of RGC thickness with total deviation (TD) of 10-2 SAP for 14 patients with glaucoma and 19 controls, an experienced operator hand-corrected automatic segmentation of the combined RGC and inner plexiform layer (RGC+IPL) of 128 horizontal B-scans. To account for displacement of the RGC bodies around the fovea, the location of the SAP test points was adjusted to correspond to the location of the RGC bodies rather than to the photoreceptors, based on published histological findings. For analysis, RGC+IPL thickness vs SAP (TD) data were grouped into 5 eccentricities, from 3.4° to 9.7° radius on the retina with respect to the fovea.

RESULTS

The RGC+IPL thickness correlated well with SAP loss within approximately 7.2° of the fovea (Spearman ρ = 0.71-0.74). Agreement was worse (0.53-0.65) beyond 7.2°, where the normal RGC layer is relatively thin. A linear model relating RGC+IPL thickness to linear SAP loss provided a reasonable fit for eccentricities within 7.2°.

CONCLUSION

In the central 7.2°, local RGC+IPL thickness correlated well with local sensitivity loss in glaucoma when the data were adjusted for RGC displacement.

Optical Coherence Tomography in Glaucoma

The optic disk and the RNFL are the principal sites of apparent glaucomatous damage which precedes glaucomatous visual field alterations. RNFL defects are known to precede detection of visual field defects by approximately 6 years. Accurate early detection and monitoring of ONH and RNFL defects has become the prime focus of effective management of glaucoma. Optical coherence tomography employs low-coherence interferometry to obtain cross-sectional images of the ocular tissues.

This review attempts to critically analyse the applications of both, anterior and posterior segment OCT in glaucoma management.

Retinal nerve fibre layer and visual function loss in glaucoma: the tipping point

AIMS

To determine the retinal nerve fibre layer (RNFL) thickness at which visual field (VF) damage becomes detectable and associated with structural loss.

METHODS

In a prospective cross-sectional study, 72 healthy and 40 glaucoma subjects (one eye per subject) recruited from an academic institution had VF examinations and spectral domain optical coherence tomography (SD-OCT) optic disc cube scans (Humphrey field analyser and Cirrus HD-OCT, respectively). Comparison of global mean and sectoral RNFL thicknesses with VF threshold values showed a plateau of threshold values at high RNFL thicknesses and a sharp decrease at lower RNFL thicknesses. A 'broken stick' statistical model was fitted to global and sectoral data to estimate the RNFL thickness 'tipping point' where the VF threshold values become associated with the structural measurements. The slope for the association between structure and function was computed for data above and below the tipping point.

RESULTS

The mean RNFL thickness threshold for VF loss was 75.3 μm (95% CI: 68.9 to 81.8), reflecting a 17.3% RNFL thickness loss from age-matched normative value. Above the tipping point, the slope for RNFL thickness and threshold value was 0.03 dB/μm (CI: -0.02 to 0.08) and below the tipping point, it was 0.28 dB/μm (CI: 0.18 to 0.38); the difference between the slopes was statistically significant (p<0.001). A similar pattern was observed for quadrant and clock-hour analysis.

CONCLUSIONS

Substantial structural loss (∼17%) appears to be necessary for functional loss to be detectable using the current testing methods.

Progression detection capability of macular thickness in advanced glaucomatous eyes

PURPOSE

To evaluate the progression rate of macular and circumpapillary retinal nerve fiber layer (RNFL) thickness in advanced glaucomatous eyes using spectral domain optical coherence tomography (Cirrus HD-OCT, Carl Zeiss Meditec, Dublin, CA).

DESIGN

Longitudinal, observational study.

PARTICIPANTS

A total of 98 eyes of 98 patients with advanced glaucoma (visual field [VF] mean deviation [MD] <-10 dB) with a mean follow-up time of 2.2 years.

METHODS

Three glaucoma experts independently reviewed optic disc and RNFL photographs and classified patients into 3 groups: progressed, stable, and undetermined (criterion 1). Patients in the undetermined group could not be evaluated because of advanced optic disc cupping. The eyes were also classified into 2 groups, progressed and stable, by serial VF data (criterion 2).

MAIN OUTCOME MEASURES

Progression rates as determined by linear regression analysis against patient age using serial macular and RNFL thickness parameters were compared among different groups.

RESULTS

By criterion 1, 25 eyes (25.5%) were classified as stable, 13 eyes (13.3%) were classified as progressed, and 60 eyes (61.2%) were classified as undetermined. By criterion 2, 86 eyes (87.8%) were classified as stable, and 12 eyes (12.2%) were classified as progressed. By criterion 1, the mean progression rate of average macular thickness was significantly higher in the progressed group than in the stable and undetermined groups (-4.74±4.40, -0.53±1.44, and -2.72±4.75 μm/year, respectively; P = 0.01). The undetermined group showed a higher progression rate than the stable group (P = 0.045). However, the progression rate of average RNFL thickness did not differ significantly among the 3 groups (-1.19±2.62, -0.33±1.29, and -1.21±2.75 μm/year, respectively; P = 0.34). By criterion 2, the mean progression rate of average RNFL thickness did not differ significantly between the stable and progressed groups (-0.90±2.42 and -2.08±2.85 μm/year; P = 0.459). However, the progression rate as revealed by average macular thickness was significantly different between the 2 groups (-2.22±4.33 and -5.12±2.40 μm/year, respectively; P = 0.039).

CONCLUSIONS

Exploration of changes over time in macular thickness may improve detection of progression in patients with advanced glaucoma.