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

Short-wavelength automated perimetry results are correlated with optical coherence tomography retinal nerve fiber layer thickness measurements in glaucomatous eyes

PURPOSE

To determine the relationship between retinal nerve fiber layer (RNFL) thickness measured using optical coherence tomography (OCT) and short wavelength-sensitive visual function measured using short-wavelength automated perimetry (SWAP).

DESIGN

Retrospective observational case series.

METHODS

Subjects were recruited from the longitudinal University of California, San Diego, Diagnostic Innovations in Glaucoma Study and included 29 glaucoma patients with OCT imaging and reliable SWAP visual field (VF) testing within a 6-month window.

MAIN OUTCOME MEASURES

Correlations between deviation from normal (thinner than 97.5% of normal) RNFL measurements taken at 30 degrees sectors (12 sectors described as clock hours) and SWAP average pattern deviation within 21 VF zones were determined. The number of OCT-measured RNFL sectors outside of normal limits and the number of VF zones outside of normal limits also were compared.

RESULTS

The OCT nerve fiber layer thickness was outside of the normal limits in at least 1 sector in 26 (89.6%) patients. Twenty-eight (96.5%) patients had at least 1 SWAP VF zone outside of normal limits. Optical coherence tomography sectors 6-o'clock, 7-o'clock, and 8-o'clock (inferior and inferotemporal) and SWAP VF zones 13, 14, and 16 (superior hemifield central and arcuate areas) were the most frequently damaged. In general, the strongest R2 associations were between inferior and inferior temporal RNFL sectors (e.g., 6-o'clock, 7-o'clock) and superior nasal/arcuate VF zones (e.g., zones 13, 14, 15) and between superior and superior temporal RNFL sectors (e.g., 12-o'clock, 11-o'clock) and inferior central and arcuate VF zones (e.g., zones 5, 6, 7) (R2 range = 24.3%-37.3%, all Ps < or = 0.005). Most nonsignificant associations were found between superior RNFL sectors and superior VF zones.

CONCLUSION

Retinal nerve fiber layer thickness measured with OCT is topographically correlated with glaucomatous VF defects measured with SWAP.

An objective method to define outlier optical coherence tomograms and repeatability of retinal nerve fibre layer measurements

PURPOSE

To compare the variation in thickness and reflectivity of the retinal nerve fibre layer (RNFL), circumferentially and on repeated testing.

METHODS

In 24 normal eyes and 38 eyes with different optic neuropathies or retinopathies, third-party optical coherence tomography (OCT) software defined the RNFL border based on the reflectivity pattern across the retina and also provided measurements of the mean reflectivity and total retinal thickness in addition to RNFL thickness. A new Gaussian filtering method was implemented so that the weight of the applied filter was varied for each of five individually repeated scans until an optimum weight filter was determined.

RESULTS

The scans requiring the highest weight filter could be identified as 'outlier' scans that contained measurement or alignment artifacts. There was no difference in the weights of filtering needed for normal and abnormal eyes. The RNFL thickness and reflectivity, and retinal thickness were highly correlated with one another in normal and abnormal eyes.

CONCLUSIONS

A new Gaussian filtering routine was devised that not only defined the most reproducible substructure of the RNFL for a given patient's eye, but also provided a new method of quantifying measurement variability and identification of scans with measurement or alignment artifacts.

Optical coherence tomography and confocal scanning laser tomography for assessment of macular edema

PURPOSE

To compare optical coherence tomography (OCT) and confocal scanning laser tomography (cSLT) for quantitative retinal thickness mapping of the macula and their ability to detect macular edema.

DESIGN

Prospective, comparative, clinical observational study.

METHODS

The study population of 138 eyes (97 patients) was divided into a study group consisting of 45 (32.6%) eyes with macular edema and a control group consisting of 93 (67.4%) eyes without macular edema. All patients underwent OCT and cSLT of the macula. Retinal thickness measurements obtained by OCT were compared with signal width and edema index, determined by cSLT.

RESULTS

The OCT measurements and cSLT edema index were significantly (P <.001) correlated with each other. Correlation coefficients decreased (P <.001) with increasing diameter of the measurement circle. In the macular edema group, correlation coefficients were significantly (P <.001) higher than in the control group. To separate the study and control groups, receiver operator characteristic curves covered a larger area for OCT measurements than for cSLT measurements. Retinal thickness measurements and edema index correlate with visual acuity (correlation coefficient r = -.653 for OCT, r = -.608 for cSLT; P <.001).

CONCLUSIONS

Macular edema can be quantitatively mapped by OCT and cSLT. The retinal thickness and edema index measurements correlate with visual acuity. The fast and standard examination modes of OCT give similar measurements. Both OCT and cSLT can differentiate between eyes with and without macular edema, with OCT showing a higher predictive value.

STRATUS optical coherence tomography in unilateral colobomatous excavation of the optic disc and secondary retinoschisis

PURPOSE

To report the STRATUS optical coherence tomography (STRATUSOCT) findings in a patient with unilateral coloboma-like excavation of the optic disc without pit but secondary retinoschisis, as well as to discuss the possible involved pathophysiologic mechanisms.

METHODS

Observational case report. STRATUSOCT findings in a 66-year-old woman with a coloboma-like excavation of the optic disc without pit but secondary retinoschisis encompassing the macular region, along with evidence of a mild epiretinal membrane superonasal to the disc were evaluated.

RESULTS

STRATUSOCT showed signs of a connection between the perineural space and the inner retinal layers on the temporal optic disc border, as well as schisis-like changes extending from the disc to the macula, with cystoid degeneration and two lamellar holes in their nasal portion.

CONCLUSION

The use of third generation OCT afforded an enhanced visualization of retinal structures, revealing signs of fluid at several distinct levels, as well as deep and superficial inner breaks apart from the schisis cavity. We are unaware of such previous reports, and could find no reference to them in a computerized search using MEDLINE. In addition, our study supports a common pathomechanism for the development of macular complications in optic pits and colobomas.

The nerve fibre layer symmetry test: computerized evaluation of human retinal nerve fibre layer thickness as measured by optical coherence tomography

PURPOSE

To present and test a new interpretative concept, the nerve fibre layer symmetry test (NST), for computerized evaluation of retinal nerve fibre layer thickness (RNFLT) as measured by optical coherence tomography (OCT) in glaucoma.

METHODS

The NST concept was constructed and tested in a pilot study. A total of 32 healthy and 40 age-matched glaucomatous eyes were included and examined by OCT, computerized perimetry, RNFL/disc photography, tonometry and a general ophthalmologic examination.

RESULTS

The observed NST sensitivity and specificity were high, at 38/40 eyes (95%) and 32/32 eyes (100%), respectively, and 40/40 eyes (100%), and 31/32 eyes (97%), respectively, when correcting the OCT RNFLT measurement for the influence of variability in image signal/quality. The NST sensitivity was 8-10% higher than the single most sensitive traditional OCT RNFLT parameter; this difference was not statistically significant in this small sample.

CONCLUSION

The NST showed high specificity and sensitivity for detection of RNFLT attenuation indicating early to severe glaucoma. Although promising, the NST needs to be further developed and validated in larger study samples and in patients with various stages of glaucomatous damage.

Optical coherence tomography analysis of axonal loss in band atrophy of the optic nerve

AIMS

To measure axonal loss in patients with band atrophy of the optic nerve caused by optic chiasm compression using optical coherence tomography and to evaluate its ability in identifying this pattern of retinal nerve fibre layer (RNFL) loss.

METHODS

Twenty eyes from 16 consecutive patients with band atrophy of the optic nerve and permanent temporal hemianopia due to chiasmal compression, and 20 eyes from an age and sex matched control group of 16 healthy individuals, were studied prospectively. All patients were submitted to an ophthalmic examination including perimetry and evaluation of the RNFL using optical coherence tomography. Mean RNFL thickness around the optic disc was compared between the two groups.

RESULTS

The mean (SD) peripapillary RNFL thickness of eyes with band atrophy was 101.00 (9.89) microm, 62.21 (12.71) microm, 104.89 (12.60) microm, and 50.13 (16.88) microm in the superior, temporal, inferior, and nasal regions, respectively. The total RNFL mean was 79.94 (7.17) microm. In the control group, the corresponding values were 140.10 (16.06) microm, 86.50 (12.17) microm, 144.60 (15.70) microm, and 97.94 (16.02) microm. The total RNFL mean was 117.72 (9.53) microm. The measurements were significantly different between the two groups. Measurements in each of twelve 30 degrees divisions provided by the equipment also showed significantly different values between eyes with band atrophy and normal controls.

CONCLUSIONS

Optical coherence tomography was able to identify axonal loss in all four quadrants as well as in each of the twelve 30 degrees segments of the disc. Thus, it seems to be a promising instrument in the diagnosis and follow up of neuro-ophthalmic conditions responsible for RNFL loss, even if predominantly in the nasal and temporal areas of the optic disc.

Retinal thickness at the posterior pole in glaucoma and ocular hypertension

PURPOSE

Ganglion cells with nerve fibre layer contribute a substantial fraction to the retinal thickness (RT). In contrast to the analysis of papillary and peripapillary area, which have shown large variability in normal eyes, the variation of retinal cell density in the perifoveal region is reported to be less than 10%. By measuring RT at the posterior pole we wanted to detect retinal changes due to glaucoma and determine their correspondence with visual field (VF) changes.

METHODS

The Retinal Thickness Analyzer (RTA) was used to obtain RT maps in 21 normal eyes, 20 eyes with ocular hypertension and 22 eyes with glaucoma. A green laser slit (540 nm) of the RTA was focused on the retina at an angle and its intersection with the retina was imaged. The distance between the reflections from the vitreo-retinal and retina-retinal pigment interface is directly proportional to the RT. Five locations covering the central 20 degrees were scanned, generating 10 optical cross sections that were transformed into colour-coded RTA maps. Numerical data were presented for the perifoveal and posterior pole region.

RESULTS

In glaucomatous eyes significant localised thinning of the retina was present, identified as the increased number of clusters including at least four points that are 2 standard deviations below normal. The minimum retinal thickness was decreased in glaucoma eyes and the perifoveal temporal modulation and perifoveal temporal/nasal asymmetry--indicators of greater RT loss in the temporal and the nasal quadrant, respectively--were higher in eyes with glaucoma, but with overlapping global indices between the groups. In 16 of 22 eyes with glaucoma there was good agreement of RT changes with VF defects. In two eyes with typical glaucomatous damage at the optic disc but without VF defects localised changes of RT were detected.

CONCLUSIONS

The RTA enables objective noninvasive evaluation of the posterior pole and could become helpful in diagnosis of glaucoma before the onset of functional damage. However, at present its clinical usefulness is limited by overlapping values of retinal thickness between normal and glaucomatous populations.

Imaging in glaucoma

Structural assessment using the imaging technologies discussed herein provides reproducible quantitative measurements of posterior segment ocular structures. These measurements have been found to provide useful data for glaucoma detection in various regions of the posterior segment. Further studies are needed to evaluate the utility of these technologies for pre-perimetric glaucoma detection and for monitoring glaucoma progression over an extended period.

Reproducibility of nerve fiber thickness, macular thickness, and optic nerve head measurements using StratusOCT

PURPOSE

The measurement reproducibility of the third generation of commercial optical coherence tomography, OCT-3 (StratusOCT, software ver. A2, Carl Zeiss Meditec Inc., Dublin, CA) was investigated. The nerve fiber layer (NFL) thickness, macula thickness map, and optic nerve head (ONH) parameters in normal eyes were studied.

METHODS

Ten normal subjects were imaged six times (three before and three after dilation) per day, and the series was repeated on three different days. The order of the scans before pupil dilation was randomized in each of the 3 days of scanning. After pupil dilation, the scans were also randomized in each of the 3 days of scanning. Each series was performed separately for standard-density (128 A-scans per macular and ONH image and 256 A-scans per NFL image) and high-density (512 A-scans per image for all three scan types) scanning.

RESULTS

The mean macular thickness was 235 +/- 9.8 micro m. A-scan density (or image acquisition speed) had a statistically significant effect (P < 0.05) on the reproducibility of the mean macular thickness, macular volume, and a few sectors of the macular map. No significant dilation effect was found for any of the macular parameters. The best intraclass correlation coefficient (ICC; 94%) for macular scans was found for dilated high-density scanning, with an intervisit SD of 2.4 micro m and an intravisit SD of 2.2 micro m. The mean NFL thickness for standard scanning was 98 +/- 9 micro m. NFL reproducibility showed mixed results and had interactions between scan density and dilation for some parameters. For most of the NFL parameters, reproducibility was better with dilated standard-density scanning. The mean NFL thickness ICC for dilated standard scanning was 79%, with an intervisit SD of 2.5 micro m and an intravisit SD of 1.6 micro m. For the ONH analysis, the reproducibility was better for dilated standard-density scanning for almost all the parameters, except for disc area, horizontal integrated rim volume, and vertical integrated rim area, which were better before dilation. The best reproducibility was found for cup-to-disc ratio (ICC = 97%, with intervisit SD of 0.04 micro m and intravisit SD of 0.02 micro m).

CONCLUSIONS

StratusOCT demonstrated reproducible measurements of NFL thickness, macular thickness, and optic nerve head parameters. The best reproducibility was found for dilated standard scanning for NFL and ONH parameters and for dilated high-density scanning for macular parameters.

Optical coherence tomography for ultrahigh resolution in vivo imaging

Optical coherence tomography (OCT) is an emerging biomedical optical imaging technique that performs high-resolution, cross-sectional tomographic imaging of microstructure in biological systems. OCT can achieve image resolutions of 1-15 microm, one to two orders of magnitude finer than standard ultrasound. The image penetration depth of OCT is determined by the optical scattering and is up to 2-3 mm in tissue. OCT functions as a type of 'optical biopsy' to provide cross-sectional images of tissue structure on the micron scale. It is a promising imaging technology because it can provide images of tissue in situ and in real time, without the need for excision and processing of specimens.

Macular and retinal nerve fiber layer thickness measurement reproducibility using optical coherence tomography (OCT-3)

PURPOSE

To assess the reproducibility of retinal nerve fiber layer thickness and macular thickness measurements using OCT-3.

METHODS

Randomly chosen eyes of healthy individuals were scanned following pupillary dilation by two trained operators (RGO, RV) using OCT-3 (software version A1.1, Carl Zeiss Meditec, Inc., Dublin, CA), three times on separate days within a one-month period. Fast and regular macula (128 A-scans), and fast and regular RNFL (256 A-scans) scanning protocols were performed. Intra- and interoperator measurement reproducibility was evaluated.

RESULTS

Ten eyes of 10 subjects (6 females, 4 males) were enrolled. Mean age was 32 +/- 11.2 years (range, 21 to 52 years). Intraoperator reproducibility was high for both macular and RNFL thickness measurements. Mean coefficients of variation (CV) for mean total RNFL thickness measurements ranged from 6.9 +/- 6.4% to 8.0 +/- 3.5% for operators 1 and 2 in fast and regular RNFL protocols. Mean CV for mean macular thickness measurements ranged from 4.7 +/- 2.6% to 6.4 +/- 5.5% for operator 1 and 2 in fast and regular macula protocols. There was no difference in mean total RNFL and mean foveal thickness measurements performed on different days (P > 0.05 for all measurements in all protocols, for operators 1 and 2, ANOVA). Interoperator reproducibility was high for both macular and RNFL thickness measurements (P > 0.05 for all measurements in all protocols, paired t test).

CONCLUSION

OCT-3 RNFL and macular thickness measurements are reproducible in normal eyes. These results should be validated in ocular hypertensive and glaucomatous eyes.

L’imagerie automatisée du nerf optique et des fibres nerveuses est essentielle en pratique

Chronic open-angle glaucoma is a progressive optical neuropathy. Automated imaging of the optic disc and optic nerve fibers provides reliable analysis of the optic nerve as well as long-term follow-up of neuropathy patients. HRT, GDX-VCC, and OCT, which analyze the optic disc and optical fibers, provide indisputable assistance in improving screening techniques and the follow-up of progressive glaucoma.

Primary open-angle glaucoma

Primary open-angle glaucoma is a progressive optic neuropathy and, perhaps, the most common form of glaucoma. Because the disease is treatable, and because the visual impairment caused by glaucoma is irreversible, early detection is essential. Early diagnosis depends on examination of the optic disc, retinal nerve fibre layer, and visual field. New imaging and psychophysical tests can improve both detection and monitoring of the progression of the disease. Recently completed long-term clinical trials provide convincing evidence that lowering intraocular pressure prevents progression at both the early and late stages of the disease. The degree of protection is related to the degree to which intraocular pressure is lowered. Improvements in therapy consist of more effective and better-tolerated drugs to lower intraocular pressure, and more effective surgical procedures. New treatments to directly treat and protect the retinal ganglion cells that are damaged in glaucoma are also in development.

Optical coherence tomography in the diagnosis of juvenile X-linked retinoschisis

PURPOSE

To describe the value of optical coherence tomography (OCT) as a diagnostic tool in the diagnosis of X-linked retinoschisis.

METHODS

We report three boys aged between 8 and 17 years, diagnosed with X-linked retinoschisis. During investigations they were examined with OCT (Zeiss Humphrey OCT 1, upgraded version). Single scans of the central posterior pole and the region around the vascular arcades were obtained. Two of the boys underwent full-field ERG according to ISCEV standards. Genetic analysis was performed in all three boys, with sequencing of the XLRS gene.

RESULTS

The OCT results revealed a pattern with a cleavage of the retina in two distinct planes, one deep (outer retina) and one superficial. This was very obvious in one patient and a similar but not as pronounced pattern was seen in the other two cases. The two layers were superficially connected with thin-walled, vertical palisades, separated by low reflective, cystoid spaces, confluent and most prominent in the foveal region.

CONCLUSION

Full-field ERG and/or DNA analysis are well known methods used for diagnosis of X-linked juvenile retinoschisis. In this paper, we suggest that OCT can also be a helpful diagnostic tool.

Ultrahigh-resolution full-field optical coherence tomography

We have developed a white-light interference microscope for ultrahigh-resolution full-field optical coherence tomography of biological media. The experimental setup is based on a Linnik-type interferometer illuminated by a tungsten halogen lamp. En face tomographic images are calculated by a combination of interferometric images recorded by a high-speed CCD camera. Spatial resolution of 1.8 microm x 0.9 microm (transverse x axial) is achieved owing to the extremely short coherence length of the source, the compensation of dispersion mismatch in the interferometer arms, and the use of relatively high-numerical-aperture microscope objectives. A shot-noise-limited detection sensitivity of 90 dB is obtained in an acquisition time per image of 4 s. Subcellular-level images of plant, animal, and human tissues are presented.

Quantitative assessment of structural damage in eyes with localized visual field abnormalities

PURPOSE

To evaluate the pattern of structural damage in the macula and peripapillary retinal nerve fiber layer (RNFL) using optical coherence tomography (OCT) and scanning laser polarimetry (SLP-VCC) in glaucomatous eyes with localized visual field defects.

DESIGN

Prospective, cross-sectional analysis.

METHODS

Complete examination, automated achromatic perimetry (AAP), Stratus OCT imaging (512 A-scans) of the peripapillary retina and macula, and SLP-VCC imaging of the peripapillary RNFL were performed. Thickness values in the retinal segments associated with the visual field defect (glaucomatous segments) were compared with corresponding segments across the horizontal raphe (nonglaucomatous segments) and age-matched normal controls.

RESULTS

Forty eyes of 40 patients (20 normal, 20 glaucomatous) were enrolled (mean age, 71 +/- 10 years; range, 50 to 89). Mean RNFL thickness using SLP-VCC and OCT in the nonglaucomatous segments of glaucomatous eyes (54.0 +/- 9.7 microm, 64.7 +/- 19.0 microm) were significantly (P =.009, <0.0001) reduced compared with the thickness measurements in the corresponding segments of age-matched normal subjects (62.5 +/- 9.2 microm, 105.6 +/- 19.0 microm) respectively. No significant (P =.4) differences in the macular thickness measurements were observed between nonglaucomatous (239.0 +/- 19.4 microm) and normal segments (243.5 +/- 15.0 microm). Compared with age-matched controls, RNFL thickness in the nonglaucomatous segment was abnormal in 15 of 20 patients (75%) with SLP-VCC and in 18 of 20 patients (90%) with OCT. Macular thickness in the nonglaucomatous segment was abnormal in 11 of 20 patients (55%).

CONCLUSIONS

Diffuse RNFL and retinal ganglion cell loss is present in eyes with localized visual field abnormalities. Detection of localized changes in macular thickness is limited by measurement overlap among normal and glaucomatous eyes.

Retinal Nerve Fiber Loss in High- and Normal-Tension Glaucoma by Optical Coherence Tomography

PURPOSE

To compare the pattern of retinal nerve fiber layer (RNFL) damages in high-tension and normal-tension primary chronic open-angle glaucoma using optical coherence tomography (OCT).

METHODS

Age- and refractive error-matched patients with normal-tension glaucoma (NTG) (n = 38) and high-tension glaucoma (HTG) (n = 48) and normal subjects (n = 48) were recruited. All subjects underwent complete eye examinations and OCT RNFL assessments.

RESULTS

No statistically significant difference was found between eyes with HTG and NTG for any OCT RNFL thickness parameters (p > 0.05). Inferotemporal thickness values were significantly lower than the superotemporal thickness values in both glaucoma groups (p < 0.001), but no difference was observed in the normal group. Compared with the results from normal subjects, several OCT parameters, including average, superior, inferior, inferotemporal, and superotemporal values, were significantly lower in patients with HTG and NTG (p < 0.01).

CONCLUSIONS

A mixture of diffuse RNFL damage (superotemporal and inferotemporal regions) and local damage in inferotemporal region was observed in patients with HTG and NTG, suggesting that HTG and NTG may undergo same pathological process.

Identifying early glaucoma with optical coherence tomography

PURPOSE

To evaluate performance of optical coherence tomography (OCT) for detection of early glaucoma.

DESIGN

Observational case-control study.

METHODS

SETTING

University-based tertiary care center.

STUDY POPULATION

One eye from 50 normals, 42 glaucoma suspects, and 59 early glaucoma patients meeting the following criteria: visual field (VF) mean deviation > or =-6.00 dB, age > or =40 years, spherical refractive error < or =5 diopters, astigmatism < or =3 diopters, and visual acuity > or =20/30.

OBSERVATION PROCEDURE

Early glaucoma by VF (EGVF) was described as repeatable abnormal achromatic VFs based on predefined criteria. Glaucoma suspects (GS) were defined as presence of glaucomatous disk appearance with normal achromatic VFs.

OUTCOME MEASURES

Average nerve fiber layer thickness (NFLT) and NFLT in each of four quadrants and 12 clock-hour sectors. Receiver operating characteristic curves and sensitivity and specificity were used to assess the performance of OCT.

RESULTS

Average NFLT was 128.4 +/- 15.4, 102.0 +/- 25.4, and 86.5 +/- 31.5 microm in normal, GS, and EGVF eyes, respectively. Normal eyes were different from both glaucoma groups (P <.001); NFLT in the superior quadrant and at the 11 o'clock position had the highest area under the receiver operating characteristic curve (.840 and.933) in the GS and EGVF groups (P =.03). The sensitivity of the OCT for detection of glaucoma was 71% and 85% for the GS and EGVF groups with specificity fixed at 90%.

CONCLUSION

The OCT discriminates well between eyes with early perimetric glaucoma and normal eyes. However, its performance is less adequate in eyes with suspicious disk and normal VFs.

In vivo birefringence and thickness measurements of the human retinal nerve fiber layer using polarization-sensitive optical coherence tomography

Glaucoma causes damage of the nerve fiber layer, which may cause loss of retinal birefringence. Therefore, PS-OCT is a potentially useful technique for the early detection of glaucoma. We built a fiber-based PS-OCT setup that produces real-time images of the human retina in vivo, coregistered with retinal video images of the location of PS-OCT scans. Preliminary measurements of a healthy volunteer show that the double-pass phase retardation per unit of depth of the RNFL is not constant and varies with location, with values between 0.18 and 0.37 deg/microm. A trend in the preliminary measurements shows that the nerve fiber layer located inferior and superior to the optic nerve head is more birefringent than the thinner layer of nerve fiber tissue in the temporal and nasal regions.

Ultrahigh-resolution optical coherence tomography

In the past two decades, optical coherence tomography (OCT) has been established as an adjunct diagnostic technique for noninvasive, high-resolution, cross-sectional imaging in a variety of medical fields. The rapid development of ultrabroad bandwidth light sources has recently enabled a significant improvement in OCT imaging resolution, demonstrating the potential of OCT to accomplish its original goal of performing noninvasive optical biopsies, i.e., the in vivo visualization of microstructural morphology in situ, which had previously only been possible with histopathology. In addition, these novel light sources might also enable the use of spectroscopic OCT, an extension of ultrahigh-resolution OCT, for enhancing image contrast as well as detecting spatially resolved functional, biochemical tissue information. State-of-the-art-light sources that now permit ultrahigh-resolution OCT covering the whole wavelength region from 500 to 1600 nm are reviewed and fundamental limitations of OCT image resolution are discussed. Ex vivo ultrahigh-resolution OCT tomograms are compared with histological results; first clinical in vivo ultrahigh-resolution OCT and preliminary spectroscopic OCT results are presented and their impact for future clinical and research applications is discussed.

Correlation between morphological and functional retinal impairment in patients affected by ocular hypertension, glaucoma, demyelinating optic neuritis and Alzheimer's disease

In this article the correlations between the morphological evaluation of the nerve fiber layer (NFL) thickness (by OCT) and retinal functional assessment (by Pattern ERG recordings) performed in patients affected by ocular hypertension (OHT), glaucoma (OAG), demyelinating optic neuritis (MSON), and Alzheimer's disease (AD) are reported. In OHT eyes with ocular hypertension we observed that the inter-individual variation in NFL thickness is correlated with the variability of the PERG responses (the thinner the layer, the worse the visual function). In our OAG, MSON and AD eyes we observed a significant reduction in NFL thickness when compared with controls. In OHT, OAG, MSON and AD eyes abnormal PERG responses with delayed implicit times and reduced amplitudes were found. The impairment in the PERG parameters was significantly correlated to the reduction in NFL thickness. Our results suggest that in patients affected by ocular hypertension, glaucoma, demyelinating optic neuritis, and Alzheimer's Disease there is a reduction of NFL thickness evaluated "in vivo" by OCT, and this morphological involvement is correlated with electrophysiological responses assumed to be originating from the innermost retinal layers.

Retinal nerve fiber layer thickness measured with optical coherence tomography is related to visual function in glaucomatous eyes

PURPOSE

To determine the relationship between areas of glaucomatous retinal nerve fiber layer thinning identified by optical coherence tomography and areas of decreased visual field sensitivity identified by standard automated perimetry in glaucomatous eyes.

DESIGN

Retrospective observational case series.

PARTICIPANTS

Forty-three patients with glaucomatous optic neuropathy identified by optic disc stereo photographs and standard automated perimetry mean deviations >-8 dB were included.

METHODS

Participants were imaged with optical coherence tomography within 6 months of reliable standard automated perimetry testing.

MAIN OUTCOME MEASURES

The location and number of optical coherence tomography clock hour retinal nerve fiber layer thickness measures outside normal limits were compared with the location and number of standard automated perimetry visual field zones outside normal limits. Further, the relationship between the deviation from normal optical coherence tomography-measured retinal nerve fiber layer thickness at each clock hour and the average pattern deviation in each visual field zone was examined by using linear regression (R(2)).

RESULTS

The retinal nerve fiber layer areas most frequently outside normal limits were the inferior and inferior temporal regions. The least sensitive visual field zones were in the superior hemifield. Linear regression results (R(2)) showed that deviation from the normal retinal nerve fiber layer thickness at optical coherence tomography clock hour positions 6 o'clock, 7 o'clock, and 8 o'clock (inferior and inferior temporal) was best correlated with standard automated perimetry pattern deviation in visual field zones corresponding to the superior arcuate and nasal step regions (R(2) range, 0.34-0.57). These associations were much stronger than those between clock hour position 6 o'clock and the visual field zone corresponding to the inferior nasal step region (R(2) = 0.01).

CONCLUSIONS

Localized retinal nerve fiber layer thinning, measured by optical coherence tomography, is topographically related to decreased localized standard automated perimetry sensitivity in glaucoma patients.

Diattenuation and polarization preservation of retinal nerve fiber layer reflectance

The diattenuation spectrum of the retinal nerve fiber layer (RNFL) reflectance has been predicted to depend strongly on the relative refractive index (m) of light-scattering cylinders. To constrain the values of m, diattenuation of the RNFL reflectance of isolated rat retina was measured with a multispectral imaging micropolarimeter. The RNFL reflection has very weak intrinsic diattenuation at all wavelengths (400-830 nm), which rejects all values of m > or = 1.03. Degree of polarization (DOP) for reflection from the RNFL was also measured. DOP was close to unity at all wavelengths, which indicates that the RNFL is a polarization-preserving reflector.

Theoretical model of the polarization properties of the retinal nerve fiber layer in reflection

In several optical technologies for glaucoma diagnosis, polarized light is used to assess the retinal nerve fiber layer (RNFL) of the eye. For better understanding of the polarization properties of the RNFL, it was modeled as a thick birefringent slab containing parallel light-scattering cylinders, and the Mueller matrix for reflectance was derived. The model predicts that (1) the RNFL reflectance has weak intrinsic diattenuation; (2) the diattenuation spectrum depends strongly on the relative refractive indices of the cylinders; (3) both scattering and birefringence contribute to retardation; and (4) the RNFL reflectance generally preserves polarization, but depolarization may be detectable for thick RNFL at short wavelengths.

Evaluating pulsatile ocular blood flow analysis in normal and treated glaucomatous eyes

PURPOSE

To evaluate pulsatile ocular blood flow (POBF) analysis in normal subjects and glaucoma patients by comparison of POBF measurements with functional (as determined by visual field [VF]) and structural (as determined by optical coherence tomography [OCT]) measures.

DESIGN

Prospective, cross-sectional study.

METHODS

Forty-one eyes of 24 consecutive glaucoma patients and 20 eyes of 10 healthy subjects were studied; POBF analysis was performed on all subjects at the same visit as VF testing and OCT retinal nerve fiber layer (NFL) thickness measurement. The mean results of normal and glaucomatous eyes were compared for each method. Correlation between measurements obtained with each modality and the discriminating power using receiver operator characteristic curves was tested.

RESULTS

The mean POBF (standard deviation [SD]) in the normal group was 1,010.4 (292.8) microl/min and 989.3 (305.5) microl/min in the glaucoma group (P =.90). Significant differences between groups were found for VF mean deviation and pattern standard deviation (P =.02, P =.004, respectively) and OCT mean NFL thickness (P <.0001). No correlation was found between POBF parameters and intraocular pressure, VF, or OCT variables except for intraocular pressure in glaucoma group (r = -.43, P =.003). The area under the receiver operator characteristic curves was higher for VF indexes and OCT mean NFL thickness than POBF parameters for distinguishing between normal and glaucomatous eyes.

CONCLUSIONS

The wide range of normal values and the low discriminating power of POBF between normal and glaucomatous eyes limits the clinical use of the device for glaucoma patients.

Optical coherence tomography assessment of retinal nerve fiber layer thickness changes after glaucoma surgery

PURPOSE

To assess changes in retinal nerve fiber layer (NFL) thickness in glaucoma patients after filtration surgery by using optical coherence tomography (OCT).

DESIGN

Retrospective observational case series.

PARTICIPANTS

Thirty-eight eyes of 31 glaucoma patients who underwent trabeculectomy or a combined procedure of cataract extraction and trabeculectomy were evaluated retrospectively.

METHODS

Eyes were imaged with OCT before surgery (1 week to 6 months before surgery; mean +/- standard deviation [SD], 71.3 +/- 61.2 days) and after surgery (6-12 months after surgery; 247.2 +/- 63.5 days) to measure peripapillary NFL thickness.

MAIN OUTCOME MEASURES

Changes in mean and segmental NFL thickness with respect to age, postoperative change in intraocular pressure (IOP), preoperative visual field test global indices, and change in visual field global indices.

RESULTS

A significant increase in the overall mean NFL thickness was present after surgery (P < 0.0001). Segmental analysis found a significant increase in NFL thickness in the nasal, superior, and temporal quadrants. IOP decreased after surgery from 22.0 +/- 6.4 mmHg to 11.4 +/- 4.7 mmHg (mean +/- SD). Twenty-eight (73.7%) of 38 eyes had an IOP reduction >30%. The mean NFL thickness increase (0.5- microm/mmHg decrease of IOP) was significantly correlated with the IOP reduction (r = -0.41; P = 0.03). No correlation was found between NFL thickness changes and age, preoperative visual field global indices, or change in visual field global indices.

CONCLUSIONS

A significant increase of the mean NFL thickness, which was related to IOP reduction, was detected after glaucoma filtration surgery.

Retinal thickness decreases with age: an OCT study

BACKGROUND/AIM

In three dimensional optic disc tomography a reference plane is required to calculate optic disc rim or cup values. The position of the reference plane often depends on the retinal thickness at the temporal disc margin. Originally it was assumed that the retinal thickness at the temporal disc margin is independent of age. The aim of the study was to check this hypothesis using optical coherence tomography, and additionally to determine the reproducibility of OCT measurements in this area.

METHODS

100 eyes of 100 healthy volunteers were included in this study. Three OCT scans were performed on each eye. The scans were aligned vertically and placed at the temporal edge of the optic disc. For each eye, the thickness of the whole retina as well as the thickness of the retinal nerve fibre layer were calculated together with their coefficients of variation. Thereafter retinal thickness and nerve fibre layer thickness were correlated with age.

RESULTS

The mean retinal thickness was 249 (SD 22) micro m. The mean nerve fibre layer thickness was 109 (22) micro m. The mean coefficients of variation were 3.5% (total retinal thickness) and 8.0% (nerve fibre layer thickness). Both the total retinal thickness and the nerve fibre layer thickness were significantly correlated with age (total retina: y = 269.5 - 0.53 x x; R(2) = 0.133; p = 0.0002, nerve fibre layer: y = 126.8 - 0.44 x x; R(2) = 0.094; p<0.0019.

CONCLUSIONS

Using OCT scans the total retinal thickness can be calculated with high reproducibility (coefficient of variation = 3.5%). The reproducibility of nerve fibre layer thickness measurements is clearly lower (coefficient of variation = 8.0%). Both the total retinal thickness and the nerve fibre layer thickness significantly decrease with age. This influence of the age related decrease in RNFL/retinal thickness on the reference plane, however, is negligible.

Detection of glaucomatous visual field changes using the Moorfields regression analysis of the Heidelberg retina tomograph

PURPOSE

To evaluate the sensitivity and specificity of optic disk examinations performed using the Moorfields regression analysis (MRA) of the Heidelberg Retina Tomograph (HRT) in differentiating normal from glaucomatous eyes.

DESIGN

Retrospective cross-sectional study.

METHODS

Five hundred and nineteen patients were included in the study for a total of 193 normal eyes, 213 with suspected glaucoma (primary open-angle glaucoma [POAG]), and 113 with POAG. The intervention consisted of optic disk imaging by means of HRT I. A mean of three repeated images was analyzed using version 2.01 software. The optic disk was classified as "normal/outside normal limits" on the basis of the MRA. The visual field was examined using the DS 24 II program (Humphrey perimeter), with a glaucomatous visual field being defined on the basis of an abnormal Glaucoma Hemifield Test and a statistically significant corrected pattern standard deviation greater than 2 dB. The results obtained with MRA were compared with those obtained using the multivariate discriminant analysis (MDA) provided in the HRT I. The main outcome measures were sensitivity, specificity, and positive and negative predictive values of HRT examination.

RESULTS

The sensitivity and specificity of the HRT-MRA examination were, respectively, 74% and 94% (83% and 75% with MDA) when the patients with suspected POAG were excluded from the analysis; the figures were 74% and 85%, and 41% and 94% (83% and 64%, and 60% and 75% with MDA) when the same patients were included as being normal or having POAG.

CONCLUSIONS

In a broad clinical setting including normal subjects, patients with suspected POAG, and POAG patients, the HRT-MRA showed a high degree of diagnostic accuracy. The MRA was less sensitive but more specific than MDA. Greater diagnostic ability may be added by HRT-MRA examinations than by HRT-MDA to standard POAG diagnostic studies.

Evaluation of retinal nerve fiber layer thickness in the area of apparently normal hemifield in glaucomatous eyes with optical coherence tomography

PURPOSE

The authors investigated the correlation between visual field defects detected by automated perimetry and the thickness of the retinal nerve fiber layer measured with optical coherence tomography, and examined whether there is a decrease in retinal nerve fiber layer thickness in the apparently normal hemifield of glaucomatous eyes.

PATIENTS AND METHODS

Forty-one patients with glaucoma and 41 normal control subjects were included in this study. Statistical correlations between the sum of the total deviation of 37 stimuli of each hemifield and the ratio of decrease in retinal nerve fiber layer thickness were evaluated. The statistical difference between the retinal nerve fiber layer thickness of the apparently normal hemifield in glaucomatous eyes and that of the corresponding hemifield in normal subjects was also evaluated.

RESULTS

There was a statistically significant correlation in the sum of the total deviation and retinal nerve fiber layer thickness decrease ratio (superior hemifield, P = 0.001; inferior hemifield, P = 0.003). There was no significant decrease in retinal nerve fiber layer thickness in the area that corresponded to the normal visual field in the hemifield defect with respect to the horizontal meridian in glaucomatous eyes (superior side, P = 0.148; inferior side, P = 0.341).

CONCLUSIONS

Optical coherence tomography was capable of demonstrating and measuring retinal nerve fiber layer abnormalities. No changes in the retinal nerve fiber layer thickness of the apparently normal hemifield were observed in glaucomatous eyes.

Retinal nerve fiber loss pattern in high-tension glaucoma by optical coherence tomography

PURPOSE

To identify the pattern of retinal nerve fiber layer thinning in high-tension primary chronic open-angle glaucoma (HT-PCOAG) using optical coherence tomography.

METHODS

Retinal nerve fiber layer thickness was assessed with optical coherence tomography in 68 healthy controls and 68 age- and refractive error-matched patients with HT-PCOAG were recruited. Patients were divided into 3 subgroups according to their visual field mean deviation: early (> -3 dB), moderate (-3 to -7 dB), and moderately advanced (-7 to -15 dB).

RESULTS

Retinal nerve fiber layer thickness values in inferotemporal and superotemporal regions were significantly lower in all groups of glaucomatous eyes than in healthy eyes (P<0.001). Inferotemporal thickness values were significantly lower than the superotemporal thickness values (P<0.001) in the early glaucomatous stage, but not significantly so in moderate and moderately advanced stages.

CONCLUSIONS

Besides a diffuse retinal nerve fiber layer defect, a localized defect may present in the inferotemporal region in early-stage HT-PCOAG. These results also suggest that optical coherence tomography shows promise in providing quantitative data about the location and extent of retinal nerve fiber layer injury in glaucoma, and the findings are consistent with previous knowledge.

Analysis of macular volume in normal and glaucomatous eyes using optical coherence tomography

PURPOSE

To evaluate macular volume in normal and glaucomatous eyes using optical coherence tomography (OCT).

DESIGN

Case control study.

METHOD

The authors assessed 272 eyes of 164 subjects as part of an institutional study at New England Eye Center in Boston, Massachusetts; 202 eyes were in the study group and 70 eyes in the control group. Eyes were categorized as normal (70 eyes of 43 subjects), glaucoma suspect (70 eyes of 44 subjects), early glaucoma (70 eyes of 47 subjects), or advanced glaucoma (62 eyes of 43 subjects). Subjects underwent analysis with the commercially available OCT1 unit. Optical coherence tomography macular neurosensory retinal thickness maps were used to calculate macular volume for comparison to Humphrey visual field testing, intraocular pressure measurement, and stereo biomicroscopy of the optic nerve head and nerve fiber layer.

RESULTS

Using repeated measures regression, macular volume in normal (2.37 +/- 0.11 mm(3)) glaucoma suspect (2.33 +/- 0.16 mm(3)), and early glaucoma eyes (2.27 +/- 0.13 mm(3)) was significantly greater than in eyes with advanced glaucoma (2.12 +/- 0.23 mm(3), P =.0001, P =.0001, and P =.0008, respectively). Macular volume in normal eyes was significantly greater than in early glaucoma eyes (P =.01).

CONCLUSIONS

Optical coherence tomography retinal macular volume correlates with known structural defects of glaucoma, providing a potential objective and quantitative parameter for evaluation. Our data show a significant difference in macular volume between normal, glaucoma suspect, and early glaucoma eyes, compared with advanced glaucomatous eyes as well as between normal and early glaucomatous eyes. This correlates with a trend of decreasing macular volume in eyes with more advanced disease.

Correlation among retinal thickness, optic disc, and visual field in glaucoma patients and suspects: a pilot study

OBJECTIVE

To correlate losses of retinal thickness in the perifoveal area in glaucoma as measured by the Retinal Thickness Analyzer (Talia Technology Ltd, Israel) with optic nerve and visual field changes in glaucoma patients and suspects.

METHODS

Observational case series of 55 consecutive patients from the Glaucoma Service who either presented with a diagnosis of glaucoma or were referred for evaluation of suspected glaucoma. The Retinal Thickness Analyzer (Talia Technology, Ltd.) was used to obtain retinal thickness maps. Retinal thickness analysis, visual field testing, and stereophotography of the optic nerve head were performed, and a glaucoma specialist who was masked to patient status and identity data randomly graded the level of severity of each parameter. Spearman rank correlations were used to assess the relationships among the three numerical measures.

RESULTS

Retinal thickness losses correlated more strongly with severity of optic nerve head cupping (r = 0.75), whereas both of these measures correlated less strongly with the severity of visual field loss (r = 0.54).

CONCLUSIONS

Retinal thickness measurements at the posterior pole provide another measure of neural loss in glaucoma, and may help in the clinical assessment of optic nerve cupping. However, there are limitations of the technology that must be considered.

Scanning laser polarimetry with variable corneal compensation and optical coherence tomography in normal and glaucomatous eyes

PURPOSE

To evaluate the relationship between visual function and retinal nerve fiber layer (RNFL) measurements obtained with scanning laser polarimetry with variable corneal compensation (SLP-VCC) and optical coherence tomography (OCT).

DESIGN

Cross-sectional analysis of normal and glaucomatous eyes in a tertiary care academic referral practice.

METHODS

A commercial GDx nerve fiber analyzer was modified to enable the measurement of corneal polarization axis and magnitude so that compensation for corneal birefringence was eye specific. Complete examination, SLP with fixed corneal compensation (FCC) and variable corneal compensation (VCC), optical coherence tomography (OCT) imaging of the peripapillary RNFL, and automated achromatic perimetry were performed in all subjects. Exclusion criteria were visual acuity less than 20/40, diseases other than glaucoma, and unreliable perimetry.

RESULTS

Fifty-nine patients (59 eyes; 29 normal, 30 glaucomatous) were enrolled (mean age, 56.7 +/- 20.3 years, range, 20-91). All eyes with glaucoma had associated visual field loss (average mean defect, -8.4 +/- 5.8 dB). Using SLP-FCC, nine of 12 retardation parameters (75%) were significantly less in glaucomatous eyes. Using SLP-VCC, 11of 12 retardation parameters (92%) were significantly less in glaucomatous eyes. Multiple regression models constructed for each retardation parameter with visual field demonstrated that the following VCC parameters were statistically significant whereas FCC parameters were not: ellipse average (FCC, P =.28, VCC, P =.001), superior average (FCC, P =.38, VCC, P <.001), inferior average (FCC, P =.10, VCC, P =.008), average thickness (FCC, P =.30, VCC, P =.031), and superior integral (FCC, P =.43, VCC, P =.001). Similar results were obtained for multiple regression models constructed with OCT-derived RNFL thickness: ellipse average (FCC, P =.99, VCC, P =.002), superior average (FCC, P =.90, VCC, P <.001), inferior average (FCC, P =.61, VCC, P =.007), and superior integral (FCC, P =.92, VCC, P <.001).

CONCLUSIONS

Compared with fixed compensation, mean-based SLP parameters generated with SLP-VCC have greater correlation with visual function and RNFL thickness assessments obtained with OCT.

Evaluation of the glaucomatous damage on retinal nerve fiber layer thickness measured by optical coherence tomography

PURPOSE

To evaluate the relationship between visual field and retinal nerve fiber layer (RNFL) thickness measured by optical coherent tomography (OCT) and to assess the diagnostic ability of OCT to distinguish between early glaucomatous or glaucoma-suspect eyes from normal eyes.

DESIGN

Retrospective, non-randomized, cross-sectional study.

METHODS

A total of 160 eyes of 120 normal Japanese adults, 23 eyes of 16 patients with ocular hypertension, 38 eyes of 35 glaucoma-suspect patients, and 237 glaucomatous eyes of 140 glaucoma patients were enrolled in the study. The glaucoma group included 89 early glaucomatous eyes. Thickness of the RNFL around the optic disk was determined with three 3.4-mm diameter circle OCT scans. Average and segmental RNFL thickness values were compared among all groups. The correlation between mean deviation and RNFL thickness in glaucomatous eyes was also analyzed. Receiver operating characteristic (ROC) curve area was calculated to discriminate normal eyes from early glaucomatous or glaucoma-suspect eyes.

RESULTS

A significant relationship existed between the mean deviation and RNFL thickness in all parameters excluding the 3-o'clock area. The average RNFL thickness had the strongest correlation in all parameters (r = -0.729, P <.001). Retinal nerve fiber layer thickness at the 7-o'clock inferotemporal segment had the widest areas under the ROC curves in all parameters for early glaucomatous eyes (0.873).

CONCLUSIONS

Measurement of RNFL thickness by OCT is useful in detecting early RNFL damage. Furthermore, OCT measurements of RNFL thickness may provide clinically relevant information in monitoring glaucomatous changes.

The construction of a model eye for investigation of laser-tissue interactions in scanning laser ophthalmoscopy

PURPOSE

To develop a model eye to study laser-tissue interactions during retinal imaging with scanning ophthalmoscopy.

METHODS

A model eye was designed to match the optical properties of the human eye based on the Bennett and Rabbetts schematic eye.

RESULTS

Alterations in axial length resulted in changes in refractive error similar to those in the human eye (3.70 D for 1 mm in axial length). Perfusion-fixed retinal tissue could be successfully imaged using the Heidelberg Retina Tomograph and Optical Coherence Tomograph to provide images that are similar in quality to those obtained.

CONCLUSIONS

The model eye should be a valuable tool for investigating laser-tissue interactions during scanning laser ophthalmoscopy and the derivation of digital retinal and tomographic images. This model should also enable a determination of the accuracy with which digital imaging techniques, such as the optical coherence tomograph and Heidelberg Retina Tomograph, measure retinal structure.

Axonal loss after traumatic optic neuropathy documented by optical coherence tomography

PURPOSE

To report longitudinal retinal nerve fiber layer (RNFL) thickness measurements using optical coherence tomography (OCT) in a patient with traumatic optic neuropathy.

DESIGN

Observational case report.

METHODS

A 14-year-old boy with severe optic nerve trauma had repeated OCT scans of the peripapillary retinal nerve fiber layer at 3 days, 20 days, 40 days, and 70 days after injury.

RESULTS

There was gradual loss of nerve fibers as shown by the OCT color-coded map, RNFL thickness profile, and RNFL thickness measurements around the optic disk. At 70 days of follow-up, severe thinning of the RNFL was observable.

CONCLUSIONS

These findings suggest that OCT is able to assess and monitor axonal loss after traumatic optic neuropathy.

Retinal nerve fiber layer measurement by optical coherence tomography in glaucoma suspects with short-wavelength perimetry abnormalities

PURPOSE

To compare retinal nerve fiber layer (RNFL) measurements in normal and glaucoma subjects with short-wavelength automatic perimetry (SWAP) abnormalities and in chronic primary open-angle glaucoma (CPOAG) patients using optical coherence tomography (OCT).

METHODS

Forty-eight eyes of normal subjects, 34 eyes of glaucoma suspects with SWAP abnormalities, and 38 eyes of early CPOAG subjects were recruited. All normal and glaucoma suspects had normal conventional automated perimetry visual field results. All participants underwent full clinical ophthalmologic evaluation followed by OCT RNFL measurements.

RESULTS

Compared with normal controls, OCT RNFL thickness was significantly lower in glaucoma suspects with abnormal SWAP (inferotemporal and superotemporal thickness values) and CPOAG patients (average, superior, inferior, inferotemporal, and superotemporal thickness values) (P < 0.01). Some parameters were found to be significantly lower in CPOAG patients than the glaucoma suspects with abnormal SWAP (average, inferior, inferotemporal, and superotemporal thickness values) (P < 0.01).

CONCLUSIONS

OCT RNFL measurements appear to correlate well with SWAP abnormalities in glaucoma, and may detect glaucomatous damage earlier than standard conventional automated perimetry. This study suggests that OCT may recognize the earliest evidence of structure alterations in CPOAG.

Cartilage thickness measurements from optical coherence tomography

We describe a new semiautomatic image processing method for detecting the cartilage boundaries in optical coherence tomography (OCT). In particular, we focus on rabbit cartilage since this is an important animal model for testing both chondroprotective agents and cartilage repair techniques. The novel boundary-detection system presented here consists of (1) an adaptive filtering technique for image enhancement and speckle reduction, (2) edge detection, and (3) edge linking by graph searching. The procedure requires several steps and can be automated. The quantitative measurements of cartilage thickness on OCT images correlated well with measurements from histology.

The macular thickness and volume in glaucoma: an analysis in normal and glaucomatous eyes using OCT

PURPOSE

To evaluate macular volume in normal and glaucomatous eyes using Optical Coherence Tomography (OCT).

METHODS

Fifty eyes of 30 patients (age: 49-68); 20 eyes normal, 15 eyes with early glaucoma and 15 eyes with advanced glaucoma have been studied with the commercially available OCT unit (OCT 2000) (Humphrey Zeiss, Dublin, CA, USA). All eyes were examined at a scan length of 3.44 mm vertically across the fovea. OCT macular retinal thickness maps were used to calculate macular volume.

RESULTS

We observed significant differences between groups. Normals (7.35 +/- 0.455 mm3) and early glaucoma (7.09 +/- 0.475 mm3), each had significantly greater volume than subjects with advanced glaucoma (6.678 +/- 0.455 mm3).

CONCLUSIONS

Volumetric analysis of macular thickness with OCT tomograms may be a useful method of documenting and monitoring patients with early glaucoma and advanced glaucoma. In our analysis, and according to the observations of other authors, OCT macular volumes correlates significantly with glaucoma status.

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

OBJECTIVE

To evaluate the reliability of nerve fiber layer (NFL) thickness measurements by optical coherence tomography (OCT) in normal and glaucomatous eyes.

DESIGN

Prospective, comparative, observational case series and instrument validation study.

PARTICIPANTS

Twenty-four glaucomatous patients were compared with 24 gender- and age-matched normal subjects.

METHODS

Each individual underwent OCT measurements of NFL thickness. Five repetitions of a series of scans on five separate occasions within a 0.5-month period were performed. Each eye was scanned at three different nerve head programs (1.5 radius [R], R = 1.73 mm, 2.0 R). For each option (1.5 R, R = 1.73 mm, and 2.0R) and region (superior, inferior, temporal, nasal, and overall mean), variance components and intraclass correlation coefficients were determined using repeated measures regression. In these models, NFL thickness, as measured by OCT, was assumed to have three variance components: intersubject, intervisit (within-subject between-dates), and intravisit (within-subject within-date). The intraclass correlation coefficient (intersubject variance/total variance) was used as a measure of reliability.

MAIN OUTCOME MEASURES

Measurements of NFL thickness using OCT were performed.

RESULTS

Reliability values, as measured by intraclass correlation coefficients, resulted as follows: 1.5 R, 0.54/0.52 (normal/glaucoma); R = 1.73 mm, 0.50/0.50; 2.0 R, 0.49/0.50.

CONCLUSIONS

Our results indicate that the recent commercially available OCT provides reliable NFL thickness measurements in both healthy and glaucomatous eyes with each circle radius tested. The greatest amount of variability can be attributed to intersubject differences.

Quantitative analysis of axonal loss in band atrophy of the optic nerve using scanning laser polarimetry

AIMS

To measure axonal loss in patients with band atrophy from optic chiasm compression using scanning laser polarimetry (GDx, Laser Diagnostic Technologies, Inc, San Diego, CA, USA) and to evaluate the ability of this instrument to identify this pattern of retinal nerve fibre layer (RNFL) loss.

METHODS

19 eyes from 17 consecutive patients with band atrophy of the optic nerve and permanent temporal hemianopia due to chiasmal compression, and 19 eyes from an age and sex matched control group of 17 healthy individuals were prospectively studied. All patients were submitted to an ophthalmic examination including Goldmann perimetry and evaluation of the RNFL using scanning laser polarimetry. Mean RNFL thickness around the optic disc were compared between the two groups. The diagnostic performance of the deviation from normal analysis provided by the GDx software was also assessed.

RESULTS

The peripapillary RNFL thickness (mean (SD)) of eyes with band atrophy was 47.9 (7.63) micro m, 37.1 (8.48) micro m, 57.0 (9.31) micro m, and 37.2 (8.86) micro m in the superior, temporal, inferior, and nasal regions, respectively. The total average was 43.7 (12.0) micro m. In the control group, the corresponding values were 71.1 (12.2) micro m, 40.4 (10.9) micro m, 85.4 (14.0) micro m, and 49.8 (10.1) micro m. The total average measured 67.9 (11.2) micro m. The measurements from eyes with optic atrophy were significantly different from those in the control group in all regions but the temporal. The deviation from normal analysis provided by the GDx software failed to identify the majority of abnormalities in the temporal and nasal regions of patients with band atrophy.

CONCLUSIONS

Scanning laser polarimetry was able to identify axonal loss in the superior, inferior, and nasal regions, but failed to detect it in the temporal region of the optic disc, despite the fact that this area was clearly altered in eyes with band atrophy. This examination also showed poor sensitivity to detect axonal loss in the nasal region when GDx software analysis was used. The results of this study emphasise that RNFL evaluation using scanning laser polarimetry should be interpreted with caution in the study of eye diseases that lead to axonal loss predominantly in the nasal and temporal areas of the optic disc.

Optical coherence tomography measurement of macular and nerve fiber layer thickness in normal and glaucomatous human eyes

PURPOSE

To evaluate the hypothesis that macular thickness correlates with the diagnosis of glaucoma.

DESIGN

Cross-sectional study.

PARTICIPANTS

We studied 367 subjects (534 eyes), including 166 eyes of 109 normal subjects, 83 eyes of 58 glaucoma suspects, 196 eyes of 132 early glaucoma patients, and 89 eyes of 68 advanced glaucoma patients.

METHODS

We used optical coherence tomography (OCT) to measure macular and nerve fiber layer (NFL) thickness and to analyze their correlation with each other and with glaucoma status. We used both the commercial and prototype OCT units and evaluated correspondence between measurements performed on the same eyes on the same days.

MAIN OUTCOME MEASURE

Macular and NFL thickness as measured by OCT.

RESULTS

All NFL parameters both in prototype and commercial OCT units were statistically significantly different comparing normal subjects and either early or advanced glaucoma (P < 0.001). Inner ring, outer ring, and mean macular thickness both in prototype and commercial OCT devices were found to be significantly different between normal subjects and advanced glaucomatous eyes (P < 0.001). The outer ring was the only macular parameter that could significantly differentiate between normal and early glaucoma with either the prototype or commercial OCT unit (P = 0.003, P = 0.008, respectively). The area under the receiver operator characteristic (AROC) curves comparing mean NFL thickness between normal and advanced glaucomatous eyes was 1.00 for both the prototype and commercial OCT devices for eyes scanned on both machines on the same day. The AROC comparing mean macular thickness in normal and advanced glaucomatous eyes scanned on both machines on the same day was 0.88 for the prototype OCT device and 0.80 for the commercial OCT.

CONCLUSIONS

Both macular and NFL thickness as measured by OCT showed statistically significant correlations with glaucoma, although NFL thickness showed a stronger association than macular thickness. There was good correspondence between findings using both the prototype and commercial OCT units. Macular and NFL thickness measurements made with OCT may have usefulness in the clinical assessment of glaucoma.

Retinal nerve fiber layer measurement of the Hong Kong chinese population by optical coherence tomography

PURPOSE

To obtain retinal nerve fiber layer (RNFL) measurements by optical coherence tomography in a local, normal Hong Kong Chinese population and to identify the correlation of the measurement with age cross-sectionally.

METHODS

A total of 129 normal Hong Kong Chinese volunteers of different age groups were recruited for this study. The RNFL was measured by optical coherence tomography (OCT; OCT 2000; Humphrey Instruments, San Leandro, CA).

RESULTS

Mean +/- SD peripapillary RNFL measurements at the superior, inferior, temporal, and nasal regions were 145 +/- 24, 154 +/- 26, 98 +/- 32, and 87 +/- 16 microm, respectively. There was a highly significant negative correlation in average RNFL measurement with increasing age (3.3 microm per decade, < 0.001). A significant negative correlation with increasing age was also identified in the RNFL measurements in all the regions ( < 0.05) and decreased at similar extent.

CONCLUSION

The RNFL thickness of the Hong Kong Chinese population, as measured by OCT, appeared to decrease over time. The OCT normative values used for determining RNFL measures "outside of normal" should be developed on an age-specific, or at least age-adjusted, basis.

Transscleral optical coherence tomography--an experimental study in ex-vivo human eyes

BACKGROUND AND OBJECTIVE

To evaluate the potentials of a 1310-nm optical coherence tomography (OCT) system to penetrate the highly backscattering sclera in enucleated human eyes and provide visualization of intraocular structures by transscleral imaging.

STUDY DESIGN/MATERIALS AND METHODS

OCT-images were generated by an experimental prototype (Medical Laser Center, Lübeck, Germany) using a superluminescence diode with a wavelength of 1310 nm. OCT-images were taken from two enucleated human eyes using 100-200 axial scans with 60 Hz line scan frequency and compared to subsequent histologic sections.

RESULTS

Transscleral OCT allowed penetration of the sclera and the anterior chamber angle could be completely identified. Some change within the anterior eye segment could be demonstrated with high accuracy. Additionally, limited demonstration of the ciliary body region was achieved. Due to limited signal intensity no detailed imaging of the pars plana and pars plicata region was possible. However, more posterior measurements allowed transscleral visualization of a retinal detachment.

CONCLUSIONS

OCT using lightsources with a wavelength longer than that used in conventional OCT provides a promising imaging technique at high resolution allowing transscleral imaging of the anterior eye segment.

Development of a novel reference plane for the Heidelberg retina tomograph with optical coherence tomography measurements

PURPOSE

To develop an ideal reference plane for the Heidelberg Retina Tomograph (HRT) with the assistance of optical coherence tomography (OCT) measurements of the mean retinal nerve fiber layer (RNFL) thickness.

PATIENTS AND METHODS

The mean RNFL thickness was measured with OCT in eyes with early glaucoma (n = 50) and age-matched normal eyes (n = 40) at a circle as close as possible to the disc margin without touching it. Glaucomatous eyes were enrolled from chronic open-angle glaucoma patients with reproducible glaucomatous visual field defects with standard automated perimetry. One eye of each patient was randomly selected. A new reference plane was defined as located posteriorly from the mean height of the contour line by the amount of mean RNFL thickness measured with the OCT. Receiver-operating characteristic (ROC) curves were generated to compare the ability of parameters obtained with the conventional and the new reference plane to differentiate glaucomatous eyes from normal eyes. The same analysis was performed for early glaucomatous eyes with myopic refractive errors (n = 25).

RESULTS

The areas under the ROC curves (AUCs) were greater for rim area, rim area/disc area, and rim volume with the new reference plane compared with those with the conventional reference plane, but they were not significantly different. When the same analysis was performed for myopic glaucomatous eyes, the AUCs for rim area, rim area/disc area, and rim volume with the new reference plane were greater than those with the conventional reference plane ( = 0.002, 0.010, and 0.034, respectively).

CONCLUSION

A novel reference plane for the HRT defined by OCT measurements may improve the ability of the HRT to detect early glaucoma, especially in eyes with tilted discs.