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

Patterns of retinal nerve fiber layer loss in multiple sclerosis patients with or without optic neuritis and glaucoma patients

OBJECTIVE

Optical coherence tomography (OCT) has gained increasing attention in multiple sclerosis (MS) research and has been suggested as outcome measure for neuroprotective therapies. However, to date it is not clear whether patterns of retinal nerve fiber layer thickness (RNFLT) loss are different in MS compared to other diseases such as glaucoma and data on RNFLT loss in MS patients with or without optic neuritis (ON/NON) have remained inconsistent or even contradictory.

METHODS

In this large cross-sectional study we analyzed the patterns of axonal loss of retinal ganglion cells in MS eyes (n=262) with and without history of ON (MS/ON: 73 eyes; MS/NON: 189 eyes) and patients eyes with glaucomatous optic disc atrophy (GA: n=22; 39 eyes) in comparison to healthy control eyes (HC: n=406 eyes).

RESULTS

We found that significant average and quadrant RNFLT loss is detectable by OCT in both MS and GA patients compared to healthy controls (p<0.01). The age- and gender adjusted average and quadrant RNFLT did not differ significantly between MS and GA patients (p>0.05). Average (p<0.0001) and quadrant (p<0.05) RNFL thinning is significantly more severe in MS/ON versus MS/NON eyes, and the extent of RNFL thinning varies across quadrants in MS/ON eyes with the highest degree of RNFLT loss in the temporal quadrant (p<0.001).

CONCLUSION

RNFLT reduction across all four quadrants in MS patients as a whole as well as in MS/NON eyes argues for a diffuse neurodegenerative process. Superimposed inflammatory attacks to the optic nerve may cause additional axonal damage with a temporal preponderance. Future studies are necessary to further evaluate the capacity of OCT to depict disease specific damage patterns.

Axonal loss occurs early in dominant optic atrophy

PURPOSE

This study set out to investigate retinal nerve fibre layer (RNFL) thickness and best corrected visual acuity (BCVA) in relation to age in healthy subjects and patients with OPA1 autosomal dominant optic atrophy (DOA).

METHODS

We carried out a cross-sectional investigation of RNFL thickness and ganglion cell layer density in 30 healthy subjects and 10 patients with OPA1 DOA using optical coherence tomography (OCT). We then performed a regression analysis of RNFL thickness and BCVA versus age.

RESULTS

Both healthy subjects and DOA patients demonstrated a gradual reduction in RNFL thickness with age; the relationship was best described statistically by a model that assumed a constant offset between the two groups. Best corrected VA decreased significantly with age in DOA patients, in whom BCVA was correlated with peripapillary RNFL thickness in the inferior and superior peripapillary quadrants and with total macular thickness at eccentricities of 500-3000 microm. The observations were best described by a constant offset of 41.9 microm separating the two groups and an annual decrease in RNFL thickness of 0.48 microm (p < 0.0001). In patients with DOA, increasing age was associated with decreasing BCVA (p = 0.046).

CONCLUSIONS

This cross-sectional study found evidence of comparable age-related decreases in RNFL thickness in healthy subjects and in DOA patients, where the deficit in DOA patients is best described using a model that assumes the deficit between the groups does not vary with age. The gradual reduction of BCVA with age may be a consequence of a relative deficit in RNFL thickness that is established before the second decade of life.

Comparison of spectral/Fourier domain optical coherence tomography instruments for assessment of normal macular thickness

PURPOSE

The purpose of this study was to report normal macular thickness measurements and assess reproducibility of retinal thickness measurements acquired by a time-domain optical coherence tomography (OCT) (Stratus, Carl Zeiss Meditec, Inc., Dublin, CA) and three commercially available spectral/Fourier domain OCT instruments (Cirrus HD-OCT, Carl Zeiss Meditec, Inc.; RTVue-100, Optovue, Inc., Fremont, CA; 3D OCT-1000, Topcon, Inc., Paramus, NJ).

METHODS

Forty randomly selected eyes of 40 normal, healthy volunteers were imaged. Subjects were scanned twice during 1 visit and a subset of 25 was scanned again within 8 weeks. Retinal thickness measurements were automatically generated by OCT software and recorded after manual correction. Regression and Bland-Altman plots were used to compare agreement between instruments. Reproducibility was analyzed by using intraclass correlation coefficients, and incidence of artifacts was determined.

RESULTS

Macular thickness measurements were found to have high reproducibility across all instruments with intraclass correlation coefficients values ranging 84.8% to 94.9% for Stratus OCT, 92.6% to 97.3% for Cirrus Cube, 76.4% to 93.7% for RTVue MM5, 61.1% to 96.8% for MM6, 93.1% to 97.9% for 3D OCT-1000 radial, and 31.5% to 97.5% for 3D macular scans. Incidence of artifacts was higher in spectral/Fourier domain instruments, ranging from 28.75% to 53.16%, compared with 17.46% in Stratus OCT. No significant age or sex trends were found in the measurements.

CONCLUSION

Commercial spectral/Fourier domain OCT instruments provide higher speed and axial resolution than the Stratus OCT, although they vary greatly in scanning protocols and are currently limited in their analysis functions. Further development of segmentation algorithms and quantitative features are needed to assist clinicians in objective use of these newer instruments to manage diseases.

Screening for glaucoma in high-risk populations using optical coherence tomography

OBJECTIVE

To estimate the diagnostic accuracy of Stratus optical coherence tomography (OCT) for glaucoma screening in high-risk populations.

DESIGN

Cross-sectional evaluation of a diagnostic test for screening.

PARTICIPANTS

Three hundred thirty-three community-based volunteer participants with risk factors for glaucoma.

METHODS

The optic nerve and peripapillary retinal nerve fiber layer (RNFL) of participants' eyes were scanned using the Stratus OCT. Based on an ophthalmologic examination and frequency doubling perimetry, eyes were classified into 4 categories: normal, possible glaucoma, probable glaucoma, and definitive glaucoma.

MAIN OUTCOME MEASURES

The sensitivities, specificities, positive and negative likelihood ratios of the RNFL, optic disc parameters, and their combinations were calculated.

RESULTS

The right eyes were retained for analyses. After excluding eyes with missing data or with poor quality scans, the data of 210 right eyes were analyzed. Six eyes had definitive glaucoma. Combining the best performing optic nerve head parameters (cup diameter or cup/disc vertical ratio or cup/disc area ratio) and RNFL parameters (superior average or inferior average or overall average) using AND-logic resulted in a sensitivity of 67% (95% confidence interval [CI], 24%-94%), specificity of 96% (95% CI, 92%-98%), a positive likelihood ratio of 17.08 (95% CI, 7.06-41.4), and a negative likelihood ratio of 0.35 (95% CI, 0.11-1.08).

CONCLUSIONS

When adequate quality scans may be obtained, the Stratus has moderate sensitivity and high specificity for definitive glaucoma. Specificity is increased when parameters from both the optic nerve head and RNFL scans are combined.

Generalized Jones matrix optical coherence tomography: performance and local birefringence imaging

Phase retardation imaging including local birefringence imaging of biological tissues is described by generalized Jones-matrix optical coherence tomography. The polarization properties of a local tissue can be obtained from two Jones matrices that are measured by backscattered lights from the front and back boundaries of the local tissue. The error in the phase retardation measurement due to background noise is analyzed theoretically, numerically, and experimentally. The minimum detectable phase retardation is estimated from numerical simulations. The theoretical analysis suggests that the measurements with two orthogonal input polarization states have the lowest retardation error. Local birefringence imaging is applied to the human anterior eye chamber and skin in vivo.

Pulsar perimetry in the diagnosis of early glaucoma

PURPOSE

To assess the ability of Pulsar perimetry (Pulsar) in detecting early glaucomatous visual field (VF) damage in comparison with Frequency Doubling Technology (FDT), Scanning Laser Polarimetry (SLP, GDx VCC), and Heidelberg Retina Tomography (HRT).

DESIGN

Prospective observational cross-sectional case study.

METHODS

This multicenter study included: 87 ocular hypertensives (OHT); 67 glaucomatous optic neuropathy (GON) patients; 75 primary open-angle glaucoma (POAG) patients; and 90 normals. All patients underwent standard automated perimetry (SAP) HFA 30-2, Pulsar T30W, FDT N-30, HRT II, and GDx VCC. Area under Receiver Operating Characteristic Curves (AROCs) for discriminating between healthy and glaucomatous eyes and agreement among instruments were determined.

RESULTS

The best parameters for Pulsar, FDT, HRT, and GDx were, respectively: loss variance square root; no. of areas with P< 5%; Cup-Shape-Measure; and Nerve Fiber Indicator (NFI). In detecting POAG eyes, Pulsar (AROC, 0.90) appeared comparable with FDT (0.89) and significantly better than HRT (0.82) and GDx (0.79). For GON, Pulsar ability (0.74) was higher than GDx (0.69) and lower than FDT (0.80) and HRT (0.83). The agreement among instruments ranged from 0.12 to 0.56. Pulsar test duration was significantly shorter than SAP and FDT (P< .001).

CONCLUSIONS

Pulsar T30W test is a rapid and easy perimetric method, showing higher sensitivity than SAP in detecting early glaucomatous VF loss. Its diagnostic ability is good for detecting early perimetric POAG eyes and fair for GON eyes. Pulsar performance was comparable with FDT, HRT, and GDx, even if the agreement between instruments was poor to fair.

Relationship between pattern electroretinogram, standard automated perimetry, and optic nerve structural assessments

PURPOSE

To examine the relationship between retinal ganglion cell function measured using pattern electroretinogram optimized for glaucoma screening (PERGLA), retinal nerve fiber layer (RNFL) thickness, and optic nerve head topography.

METHODS

Twenty-nine normal, 28 glaucoma, and 37 glaucoma suspect volunteers were enrolled. All participants were age similar. One randomly selected eye underwent complete eye examination, standard automated perimetry (SAP), scanning laser polarimetry with enhanced corneal compensation (GDxECC), optical coherence tomography, Heidelberg retina tomograph (HRT), and PERGLA measurements. PERGLA amplitude (microV) was converted to dB for comparison with SAP mean deviation (MD) and pattern SD. The correlation between PERGLA amplitude in dB and the average of sensitivity values for 16 central test locations of SAP were calculated. Analysis of variance, Pearson and Spearman rank correlations, coefficient of variation, and intraclass correlation coefficients were calculated.

RESULTS

PERGLA amplitude in glaucomatous eyes was significantly lower than normal eyes (0.47+/-0.20 vs. 0.70+/-0.28 microV, P<0.001) but not glaucoma suspects (0.54+/-0.21 microV, P=0.84). PERGLA amplitude was inversely correlated with age (r=-0.31, P=0.002). PERGLA amplitude (in dB) was associated with the sensitivity values of the SAP central 16 test locations (r=0.40, P<0001) across the entire cohort, GDxECC superior RNFL thickness (r=0.38, P<0.001), and HRT Moorfields regression analysis classification (rho=-0.34, P=0.001). The coefficient of variation and intraclass correlation coefficients were 14.5% and 0.89 for PERGLA amplitude, 2.4% and 0.98 for optical coherence tomography average RNFL, 2.2% and 0.97 for GDxECC temporal superior nasal inferior temporal average, and 6.3% and 0.94 for HRT rim area.

CONCLUSIONS

Retinal ganglion cell function measured using PERGLA is reduced in glaucoma and demonstrates modest correlations with central SAP sensitivity values and structural measures of optic nerve topography and RNFL thickness.

Detection of glaucoma progression with stratus OCT retinal nerve fiber layer, optic nerve head, and macular thickness measurements

PURPOSE

To evaluate and compare the ability of optical coherence tomography (OCT) retinal nerve fiber layer (RNFL), optic nerve head, and macular thickness parameters to detect progressive structural damage in glaucoma.

METHODS

This observational cohort study included 253 eyes of 253 patients. Images were obtained annually with the Stratus OCT (Carl Zeiss Meditec, Inc., Dublin, CA) along with optic disc stereophotographs and standard automated perimetry (SAP) visual fields. The median follow-up time was 4.01 years. Progression was determined by the Guided Progression Analysis software for SAP (Carl Zeiss Meditec, Inc.) and by masked assessment of optic disc stereophotographs performed by expert graders. Random coefficient models and receiver operating characteristic (ROC) curves were used to evaluate the relationship between change in Stratus OCT parameters over time and progression as determined by SAP and/or stereophotographs.

RESULTS

From the 253 eyes, 31 (13%) showed progression over time by stereophotographs and/or SAP. Mean rates of change in average RNFL thickness were significantly higher for progressors compared with nonprogressors (-0.72 mum/y vs. 0.14 mum/y; P = 0.004), with sensitivity of 77% for specificity of 80%. RNFL parameters performed significantly better than ONH and macular thickness measurements in discriminating progressors from nonprogressors. The parameters with the largest ROC curve areas for each scanning area were inferior RNFL thickness (0.84), cup area (0.66), and inferior inner macula thickness (0.64).

CONCLUSIONS

Stratus OCT RNFL parameters discriminated between eyes progressing by visual fields or optic disc photographs and eyes that remained stable by these methods and performed significantly better than ONH and macular thickness parameters in detecting change over time.

Comparison of shape-based analysis of retinal nerve fiber layer data obtained From OCT and GDx-VCC

PURPOSE

To directly compare in 1 population: (1) the performance of Optical Coherence Tomograph (OCT) and GDx-Variable Corneal Compensator (VCC) when using Wavelet-Fourier Analysis (WFA) and Fast-Fourier Analysis (FFA), (2) the performance of these shape-based and standard metrics, and (3) the shape of the retinal nerve fiber layer (RNFL) temporal, superior, nasal, inferior, temporal (TSNIT) curves obtained by the 2 different devices.

METHODS

RNFL estimates were obtained from 136 eyes of 136 individuals (73 healthy and 63 mild glaucoma). WFA and FFA with and without asymmetry measures were performed on the TSNIT RNFL estimates to identify glaucoma from healthy eyes. Performance of WFA, FFA, and the standard metrics of OCT (Inferior Average) and GDX-VCC (Nerve Fiber Indicator) was evaluated by calculating receiver operating characteristic area. Measurements were obtained at a custom radius (33 to 41 pixels) for GDx-VCC to match the OCT radius (1.73 mm).

RESULTS

WFA and FFA shape analysis significantly improved performance of both OCT (0.937) and GDx-VCC (0.913) compared with Inferior Average and Nerve Fiber Indicator (0.852 and 0.833, respectively). With either shape-based or standard metrics, OCT performance was slightly, but not significantly, better than GDx-VCC performance. Comparison of RNFL curves revealed that the GDx-VCC curves were more jagged and the peaks shifted more nasally when compared with the OCT RNFL curves.

CONCLUSIONS

Performance of both OCT and GDx-VCC devices are improved by shape-based analysis methods. Classification performance was greater when using WFA for the OCT, and greater with FFA for the GDx-VCC. Significant differences between the machines exist in the measured TSNIT thicknesses, possibly because of GDx-VCC's measurements being affected by polarization magnitude varying with angle.

Macular thickness measurements in normal eyes with time-domain and Fourier-domain optical coherence tomography

PURPOSE

To compare macular thickness measurements using time-domain optical coherence tomography (OCT) and Fourier-domain OCT.

METHODS

Thirty-two eyes from 32 normal patients underwent complete ophthalmic evaluation. Macular scanning using the StratusOCT and the RTVue-100 OCT were performed for a total of three times each on the same visit. The average retinal thicknesses of the nine macular sectors as defined by the Early Treatment Diabetic Retinopathy Study, along with the foveal center point and macular volume, were recorded. The SD, the coefficient of variation, and the intraclass correlation coefficient were calculated for each parameter studied. Comparisons were made between the two OCTs in terms of retinal thicknesses measurements, their reproducibility, and macular regional differences. Correlations between retinal thickness and demographic variables (age and gender) were also investigated. Due to known differences in segmentation algorithms of the two OCTs, software calipers were used to measure the distance from the internal limiting membrane to the photoreceptor inner segment-outer segment junction at the foveal center point on all RTVue scans to allow a more fair comparison.

RESULTS

The RTVue yielded greater retinal thickness measurements in nearly all macular subfields compared with the StratusOCT. Even after accounting for differences in segmentation algorithms, significant disparities were still evident with the RTVue measurements less than those of the StratusOCT at the foveal center. On both machines, the macula was thinnest at the fovea and thickest within the 3 mm ring. There were some consistent regional variations in macular thickness evident on both OCTs. Compared with the StratusOCT, the RTVue generally had lower coefficients of variation and higher intraclass coefficients, suggesting better reproducibility. Age and gender also appeared to be important determinants in some macular thickness parameters.

CONCLUSION

Compared with StratusOCT, the RTVue fourier-domain OCT yields greater retinal thickness measurements with greater reproducibility, presumably due to different segmentation algorithms, increased sampling density, and greater resolution. However, regional differences across the macula can be consistently observed with both devices.

Scanning laser polarimetry and optical coherence tomography for detection of retinal nerve fiber layer defects

PURPOSE

To compare the ability of scanning laser polarimetry with variable corneal compensation (GDx-VCC) and Stratus optical coherence tomography (OCT) to detect photographic retinal nerve fiber layer (RNFL) defects.

METHODS

This retrospective cross-sectional study included 45 eyes of 45 consecutive glaucoma patients with RNFL defects in red-free fundus photographs. The superior and inferior temporal quadrants in each eye were included for data analysis separately. The location and presence of RNFL defects seen in red-free fundus photographs were compared with those seen in GDx-VCC deviation maps and OCT RNFL analysis maps for each quadrant.

RESULTS

Of the 90 quadrants (45 eyes), 31 (34%) had no apparent RNFL defects, 29 (32%) had focal RNFL defects, and 30 (33%) had diffuse RNFL defects in red-free fundus photographs. The highest agreement between GDx-VCC and red-free photography was 73% when we defined GDx-VCC RNFL defects as a cluster of three or more color-coded squares (p<5%) along the traveling line of the retinal nerve fiber in the GDx-VCC deviation map (kappa value, 0.388; 95% confidence interval (CI), 0.195 to 0.582). The highest agreement between OCT and red-free photography was 85% (kappa value, 0.666; 95% CI, 0.506 to 0.825) when a value of 5% outside the normal limit for the OCT analysis map was used as a cut-off value for OCT RNFL defects.

CONCLUSIONS

According to the kappa values, the agreement between GDx-VCC deviation maps and red-free photography was poor, whereas the agreement between OCT analysis maps and red-free photography was good.

Structural and functional relationships in glaucoma using standard automated perimetry and the Humphrey Matrix

Purpose

To evaluate and compare correlations between structural and functional loss in glaucoma as assessed by optical coherence tomography (OCT), scanning laser polarimetry (GDx VCC, as this was the model used in this study), standard automated perimetry (SAP), and the Humphrey Matrix (Matrix).

Methods

Ninety glaucomatous eyes identified with SAP and 112 eyes diagnosed using Matrix were independently classified into six subgroups, either S1/M1 (MD>-6dB), S2/M2 (-12<MD<-6dB) or S3/M3 (MD<-12dB), according to the mean deviation (MD) of each test. Average and sectoral retinal nerve fiber layer (RNFL) thickness and percentage of abnormal classifications using the internal normative databases of OCT and GDx VCC were compared among the six subgroups.

Results

In the SAP subgroups, RNFL thickness values obtained by OCT in the nasal and temporal quadrants and the inferior averages of GDx VCC did not differ between the S1 and S2 subgroups (p=0.137, 0.738 and 0.149, respectively). In the Matrix subgroups, no measurement parameters differed between the M1 and M2 groups except for the overall mean and average inferior RNFL thickness given by OCT and the NFI values of GDx VCC (p=0.013, 0.016 and 0.029, respectively). When abnormal classifications were compared, all measurement parameters, without exception, were significantly different in both the SAP and the Matrix subgroups.

Conclusions

SAP subgroups showed a good correlation of structural and functional defects when assessed using OCT and GDx VCC. These correlations were weaker in the Matrix subgroups, especially in the early stages of glaucoma.

Discriminating ability of optical coherence tomography data in staging glaucomatous damage

OBJECTIVE

To evaluate the ability of retinal nerve fibre layer (RNFL) thickness and optic nerve head (ONH) measurements, as determined by optical coherence tomography (OCT), to discriminate between normal eyesight and glaucoma and also among the different stages of glaucoma.

DESIGN

Observational cross-sectional study.

PARTICIPANTS

Eighty-one controls and 213 glaucoma patients were enrolled in the study.

METHODS

The discriminating powers of OCT parameters for the detection of glaucoma and subgroups were compared by the area under the receiver operating characteristic (AUROC) curves.

RESULTS

The best RNFL thickness parameters for discriminating between early glaucoma and control eyes were inferior (0.74 [SE 0.04] microm), average (0.74 [SD 0.03] microm), and superior (0.68 [SD 0.03] microm). Among the ONH parameters, the best AUROC curve values were cup area (0.83 [SD 0.33]), cup/disc (C/D) area ratio (0.82 [SD 0.03]), and vertical integrated rim area (VIRA) (0.82 [SD 0.03]). The best AUROC values belonged to the RNFL thickness and were inferior (0.80 [SD 0.03]), superior (0.79 [SD 0.03]), and 6 o'clock (0.78 [SD 0.03]). The highest AUROC values were horizontal integrated rim width (HIRW) (0.74 [SD 0.04]), VIRA (0.64 [SD 0.04]), and rim area (0.63 [SD 0.04]) among the ONH parameters for early versus moderate glaucoma. The best AUROC values were inferior (0.81 [SD 0.03]), 6 o'clock (0.79 [SD 0.03]), and superior (0.78 [SD 0.04]) among the RNFL, and the best AUROC values were cup area (0.81 [SD 0.03]), VIRA (0.81 [SD 0.03]), and C/D area ratio (0.80 [SD 0.03]) among the ONH parameters, for moderate versus advanced glaucoma.

CONCLUSIONS

RNFL and ONH OCT parameters might provide information for determining glaucomatous damage.

Retinal nerve fiber layer thickness measurement comparability between time domain optical coherence tomography (OCT) and spectral domain OCT

PURPOSE

Time domain optical coherence tomography (TD-OCT) has been used commonly in clinical practice, producing a large inventory of circular scan data for retinal nerve fiber layer (RNFL) assessment. Spectral domain (SD)-OCT produces three-dimensional (3-D) data volumes. The purpose of this study was to create a robust technique that makes TD-OCT circular scan RNFL thickness measurements comparable with those from 3-D SD-OCT volumes.

METHODS

Eleven eyes of 11 healthy subjects and 7 eyes of 7 subjects with glaucoma were enrolled. Each eye was scanned with one centered and eight displaced TD-OCT scanning circles. One 3-D SD-OCT cube scan was obtained at the same visit. The matching location of the TD-OCT scanning circle was automatically detected within the corresponding 3-D SD-OCT scan. Algorithm performance was assessed by estimating the difference between the detected scanning circle location on 3-D SD-OCT volume and the TD-OCT circle location. Global and sectoral RNFL thickness measurement errors between the two devices were also compared.

RESULTS

The difference (95% confidence interval) in scanning circle center locations between TD- and SD-OCT was 2.3 (1.5-3.2) pixels (69.0 [45.0-96.0] microm on the retina) for healthy eyes and 3.1 (2.0-4.1) pixels (93.0 [60.0-123.0] microm on the retina) for glaucomatous eyes. The absolute RNFL thickness measurement difference was significantly smaller with the matched scanning circle.

CONCLUSIONS

Scan location matching may bridge the gap in RNFL thickness measurements between TD-OCT circular scan data and 3-D SD-OCT scan data, providing follow-up comparability across the two generations of OCTs.

Effect of signal strength and improper alignment on the variability of stratus optical coherence tomography retinal nerve fiber layer thickness measurements

PURPOSE

To evaluate the effect of signal strength and improper scan alignment on retinal nerve fiber layer (RNFL) thickness measurement variability.

DESIGN

Retrospective, longitudinal clinical study.

METHODS

All eyes of healthy subjects with at least 2 fast RNFL scan sessions were selected from the Diagnostic Innovations in Glaucoma Study. The chronological first scan was considered to be the baseline. Absolute differences in signal strength and RNFL thickness measurements between baseline and subsequent scans were calculated. Regression analysis was conducted to assess whether signal strength and scan shifts along the horizontal (nasal-temporal) but not the vertical (superior-inferior) axis affect average RNFL thickness measurements.

RESULTS

Ninety-four eyes of 94 subjects were included. All eyes were tested twice or more on the same visit, whereas 30 eyes were followed up longitudinally for 32.4 +/- 13.3 months (1 scan per annual follow-up). For quadrants, absolute differences from baseline were greater than for average RNFL thickness and were significantly larger for scans acquired on separate visits. Average RNFL thickness increased only when the difference between the nasal and temporal quadrants increased (R2 = 0.16; P < .0001), suggesting it may be affected by horizontal but not vertical scan shifts. Differences in signal strength were associated with differences in average RNFL thickness (R2 = 0.19; P < .0001).

CONCLUSIONS

Even under optimal testing conditions, scan quality can adversely effect the ability to detect change over time. Therefore, caution is warranted when detecting glaucomatous progression using scan series of different quality. Careful overall assessment of quadrants and average RNFL thickness measurements is suggested to help identify scan misalignment.

Evaluating the Optic Disc and Retinal Nerve Fiber Layer in Glaucoma II: Optical Image Analysis

Glaucoma is a widespread, blindness-causing disease that is characterized in part by specific and sometimes subtle changes in optic disc and retinal nerve fiber layer topography. Several recently developed computer-based optical imaging techniques allow objective evaluation of the optic disc and retinal nerve fiber layer. These techniques use different optical properties and different properties of the retina to provide micron scale measurements of many aspects of optic disc and retinal nerve fiber layer structure. This article describes and evaluates 3 of these techniques: confocal scanning laser ophthalmoscopy, scanning laser polarimetry, and optical coherence tomography.

Concordance of retinal nerve fiber layer defects between fellow eyes of glaucoma patients measured by optical coherence tomography

PURPOSE

To determine the pattern of agreement of retinal nerve fiber layer (RNFL) defects between fellow eyes of glaucoma patients measured with optical coherence tomography (OCT).

DESIGN

Observational, cross-sectional study.

METHODS

Seventy-seven glaucoma patients (154 eyes) underwent OCT (Stratus) imaging with the fast RNFL thickness protocol in both eyes. RNFL thickness at each location (12 clock-hour sectors and 4 quadrants) was measured. Main outcome measures were correlations between fellow eyes for RNFL thickness and categorical classifications of RNFL thickness. Nonfellow pairs of eyes, matched randomly, were used as controls.

RESULTS

Fellow eyes showed significant correlations of RNFL thickness in all sectors and quadrants. Categorical ranking also showed significant agreement between fellow eyes in sectors 1 (P < .01) and 7 (P < .03), and in the superior quadrant (P < .01), inferior quadrant (P < .04), and total RNFL thickness (P < .04). None of the paired eyes in the control analysis showed significant correlations.

CONCLUSIONS

The measurement of RNFL thickness and its categorical classification with OCT identified symmetry between fellow eyes of glaucoma patients. Categorical agreement on defective locations was found mostly for the inferior and superior locations, which corresponds with the typical pattern of early glaucomatous damage. Glaucomatous RNFL damage in 1 eye is correlated with damage at corresponding locations of the fellow eye.

Optical coherence tomography of the retina and optic nerve - a review

Optical coherence tomography (OCT) is a rapid non-contact method that allows in vivo imaging of the retina, optic nerve head and retinal nerve fibre layer (RNFL). Since its introduction in Ophthalmology approximately a decade ago, the use of this technology has disseminated into the clinical practice. OCT has proven to be a useful ancillary tool for assessing retinal diseases because of its capability to provide cross-sectional images of the retina, and also to perform quantitative analysis of retinal morphology. In glaucoma, the OCT represents one of the methods capable of documenting and analysing optic disc and RNFL morphology in attempt to diagnose and monitor glaucomatous optic neuropathy. Recently, the spectral domain OCT became available, a new technique that allowed major improvements particularly regarding image acquisition speed and image resolution. Future studies will address how these major technological advances will impact the use of the OCT in research and clinical practice.

Evaluation of patient suitability for a retinal prosthesis using structural and functional tests of inner retinal integrity

The purpose of this study was to assess inner retinal structure and function in patients with retinitis pigmentosa (RP) using optical coherence tomography (OCT) imaging of the retina, and electrical stimulation of the retina with a contact lens electrode. OCT images of 17 RP patients were acquired at the macula and at four quadrants of the peripheral retina in both eyes. Analysis was made of the residual inner retinal thickness and nerve fibre layer thickness in RP patients, and this was compared to normal controls. Eight of these patients further underwent contact lens electrical stimulation of one eye and thresholds for phosphene perception were obtained. OCT imaging showed a significant amount of inner retinal preservation in the peripheral retina and the macula of RP patients despite severe visual acuity and visual field loss. Phosphene thresholds were obtained across the range of pulse durations tested but were much higher than those obtained in normal controls. Phosphene thresholds in RP patients moderately correlated with inner retinal thicknesses as measured by OCT. Preservation of inner retinal structure in patients with RP and the responsiveness of these eyes to electrical stimulation suggest adequate inner retinal preservation for a retinal prosthesis to be successful.

Retinal nerve fibre layer thickness measurement reproducibility improved with spectral domain optical coherence tomography

BACKGROUND/AIMS

To investigate retinal nerve fibre layer (RNFL) thickness measurement reproducibility using conventional time-domain optical coherence tomography (TD-OCT) and spectral-domain OCT (SD-OCT), and to evaluate two methods defining the optic nerve head (ONH) centring: Centred Each Time (CET) vs Centred Once (CO), in terms of RNFL thickness measurement variability on SD-OCT.

METHODS

Twenty-seven eyes (14 healthy subjects) had three circumpapillary scans with TD-OCT and three raster scans (three-dimensional or 3D image data) around ONH with SD-OCT. SD-OCT images were analysed in two ways: (1) CET: ONH centre was defined on each image separately and (2) CO: ONH centre was defined on one image and exported to other images after scan registration. After defining the ONH centre, a 3.4 mm diameter virtual circular OCT was resampled on SD-OCT images to mimic the conventional circumpapillary RNFL thickness measurements taken with TD-OCT.

RESULTS

CET and CO showed statistically significantly better reproducibility than TD-OCT except for 11:00 with CET. CET and CO methods showed similar reproducibility.

CONCLUSIONS

SD-OCT 3D cube data generally showed better RNFL measurement reproducibility than TD-OCT. The choice of ONH centring methods did not affect RNFL measurement reproducibility.

The effect of acute intraocular pressure elevation on peripapillary retinal thickness, retinal nerve fiber layer thickness, and retardance

PURPOSE

To determine whether acutely elevated intraocular pressure (IOP) alters peripapillary retinal thickness, retinal nerve fiber layer thickness (RNFLT), or retardance.

METHODS

Nine adult nonhuman primates were studied while under isoflurane anesthesia. Retinal and RNFLTs were measured by spectral domain optical coherence tomography 30 minutes after IOP was set to 10 mm Hg and 60 minutes after IOP was set to 45 mm Hg. RNFL retardance was measured by scanning laser polarimetry in 10-minute intervals for 30 minutes while IOP was 10 mm Hg, then for 60 minutes while IOP was 45 mm Hg, then for another 30 minutes after IOP was returned to 10 mm Hg.

RESULTS

RNFLT measured 1120 microm from the ONH center decreased from 118.1 +/- 9.3 microm at an IOP of 10 mm Hg to 116.5 +/- 8.4 microm at 45 mm Hg, or by 1.4% +/- 1.8% (P < 0.0001). There was a significant interaction between IOP and eccentricity (P = 0.0006). Within 800 microm of the ONH center, the RNFL was 4.9% +/- 3.4% thinner 60 minutes after IOP elevation to 45 mm Hg (P < 0.001), but unchanged for larger eccentricities. The same pattern was observed for retinal thickness, with 1.1% +/- 0.8% thinning overall at 45 mm Hg (P < 0.0001), and a significant effect of eccentricity (P < 0.0001) whereby the retina was 4.8% +/- 1.2% thinner (P < 0.001) within 800 microm, but unchanged beyond that. Retardance increased by a maximum of 2.2% +/- 1.1% 60 minutes after IOP was increased to 45 mm Hg (P = 0.0031).

CONCLUSIONS

The effects of acute IOP elevation on retinal thickness, RNFL thickness and retardance were minor, limited to the immediate ONH surround and unlikely to have meaningful clinical impact.

Comparison of retinal nerve fiber layer measurements using time domain and spectral domain optical coherent tomography

PURPOSE

To determine the agreement between peripapillary retinal nerve fiber layer (RNFL) thickness measurements from Stratus time domain optical coherence tomography (OCT) and Cirrus spectral domain OCT (Carl Zeiss Meditec, Dublin, CA) in normal subjects and subjects with glaucoma.

DESIGN

Evaluation of diagnostic test or technology.

PARTICIPANTS

A total of 130 eyes from 130 normal subjects and subjects with glaucoma were analyzed. The subjects were divided into groups by visual field criteria: normal (n = 29), glaucoma suspect (n = 12), mild glaucoma (n = 41), moderate glaucoma (n = 18), and severe glaucoma (n = 30).

METHODS

Peripapillary RNFL thickness was measured with Stratus Fast RNFL and Cirrus 200 x 200 Optic Disc Scan on the same day in 1 eye of each subject to determine agreement. Two operators used the same instruments for all scans.

MAIN OUTCOME MEASURES

Student paired t testing, Pearson's correlation coefficient, and Bland-Altman analysis of RNFL thickness measurements.

RESULTS

The average age of the glaucoma group was significantly more than that of the normal group: 68.3+/-12.3 years versus 55.7+/-12.1 years, respectively. For Stratus OCT, the average RNFL thickness (mean +/- standard deviation) was 99.4+/-13.2 microm, 94.5+/-15.0 microm, 79.0+/-14.5 microm, 62.7+/-10.2 microm, and 51.0+/-8.9 microm for the normal, suspect, mild, moderate, and severe groups, respectively. For Cirrus OCT, the corresponding measurements were 92.0+/-10.8 microm, 88.1+/-13.5 microm, 73.3+/-11.8 microm, 60.9+/-8.3 microm, and 55.3+/-6.6 microm. All Stratus-Cirrus differences were statistically significant by paired t testing (P<0.001) except for the moderate group (P = 0.11). For average RNFL, there was also a highly significant linear relationship between Stratus minus Cirrus difference and RNFL thickness (P<0.001). Bland-Altman plots showed that the systematic difference of Stratus measurements are smaller than Cirrus at thinner RNFL values but larger at thicker RNFL values.

CONCLUSIONS

RNFL thickness measurements between Stratus OCT and Cirrus OCT cannot be directly compared. Clinicians should be aware that measurements are generally higher with Stratus than with Cirrus except when the RNFL is very thin, as in severe glaucoma. This difference must be taken into account if comparing Stratus measurements with Cirrus measurements.

Effects of age on optical coherence tomography measurements of healthy retinal nerve fiber layer, macula, and optic nerve head

PURPOSE

To determine the effects of age on global and sectoral peripapillary retinal nerve fiber layer (RNFL), macular thicknesses, and optic nerve head (ONH) parameters in healthy subjects using optical coherence tomography (OCT).

DESIGN

Retrospective, cross-sectional observational study.

PARTICIPANTS

A total of 226 eyes from 124 healthy subjects were included.

METHODS

Healthy subjects were scanned using the Fast RNFL, Fast Macula, and Fast ONH scan patterns on a Stratus OCT (Carl Zeiss Meditec, Dublin, CA). All global and sectoral RNFL and macular parameters and global ONH parameters were modeled in terms of age using linear mixed effects models. Normalized slopes were also calculated by dividing the slopes by the mean value of the OCT parameter for interparameter comparison.

MAIN OUTCOME MEASURES

Slope of each OCT parameter across age.

RESULTS

All global and sectoral RNFL thickness parameters statistically significantly decreased with increasing age, except for the temporal quadrant and clock hours 8 to 10, which were not statistically different from a slope of zero. Highest absolute slopes were in the inferior and superior quadrant RNFL and clock hour 1 (superior nasal). Normalized slopes showed a similar rate in all sectors except for the temporal clock hours (8-10). All macular thickness parameters statistically significantly decreased with increasing age, except for the central fovea sector, which had a slight positive slope that was not statistically significant. The nasal outer sector had the greatest absolute slope. Normalized macular slope in the outer ring was similar to the normalized slopes in the RNFL. Normalized inner ring had shallower slope than the outer ring with a similar rate in all quadrants. Disc area remained nearly constant across the ages, but cup area increased and rim area decreased with age, both of which were statistically significant.

CONCLUSIONS

Global and regional changes caused by the effects of age on RNFL, macula, and ONH OCT measurements should be considered when assessing eyes over time.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Differences in retinal nerve fiber layer atrophy between multiple sclerosis subtypes

OBJECTIVES

To determine whether retinal nerve fiber layer (RNFL) atrophy in the afferent visual pathway may complement existing tools used to describe and characterize differences across MS subtypes.

METHODS

Optical coherence tomography-measured RNFL values were compared over two years in 35 patients (70 eyes) with optic neuritis (ON) as a clinically isolated syndrome (CIS); 39 patients (78 eyes) with relapsing remitting MS (RRMS); and 7 patients (14 eyes) with secondary progressive MS (SPMS).

RESULTS

RNFL comparisons involving eyes without ON yielded greater differences between MS subtypes than ON-affected eyes. Overall RNFL values in non-affected eyes were reduced in SPMS patients (83.4 microm), relative to CIS (101.2 microm) (p=0.0009), and RRMS patients (103.7 microm) (p=0.001); and temporal RNFL atrophy was greater in RRMS (64.4 microm) eyes as compared to CIS eyes (73.2 microm) (p=0.02). In ON-affected eyes, RNFL atrophy was greater in SPMS patients (39.5 microm) than CIS patients (58.1 microm) (p=0.03), and in RRMS patients (48.2 microm) relative to CIS patients (p=0.05). RNFL values did not change significantly for any MS subtype during the two-year duration of the study.

INTERPRETATION

RNFL thickness may represent a structural marker, which can help distinguish MS subtypes, because the extent of atrophy is commensurate with disease progression. RNFL comparisons between non-affected eyes revealed greater differences between CIS, RRMS, and SPMS patients relative to ON-affected eyes, because the impact of prior ON may supplant the effects of disease subtype.

Diagnostic tools for glaucoma detection and management

Early diagnosis of glaucoma is critical to prevent permanent structural damage and irreversible vision loss. Detection of glaucoma typically relies on examination of structural damage to the optic nerve combined with measurements of visual function. To aid the clinician in evaluation of visual function and structure, computer-based devices such as confocal scanning laser ophthalmoscopy, scanning laser polarimetry, and optical coherence tomography provide quantitative assessments of structural damage, and visual function testing includes standard automated perimetry as well as selective techniques, including short-wavelength automated perimetry and frequency-doubling technology perimetry are available. This article will review current literature on diagnostic modalities available for glaucoma with emphasis on the best evidence available in the literature to support their use in clinical practice.

Optical coherence tomography: a window into the mechanisms of multiple sclerosis

The pathophysiology of multiple sclerosis (MS) is characterized by demyelination, which culminates in a reduction in axonal transmission. Axonal and neuronal degeneration seem to be concomitant features of MS and are probably the pathological processes responsible for permanent disability in this disease. The retina is unique within the CNS in that it contains axons and glia but no myelin, and it is, therefore, an ideal structure within which to visualize the processes of neurodegeneration, neuroprotection, and potentially even neurorestoration. In particular, the retina enables us to investigate a specific compartment of the CNS that is targeted by the disease process. Optical coherence tomography (OCT) can provide high-resolution reconstructions of retinal anatomy in a rapid and reproducible fashion and, we believe, is ideal for precisely modeling the disease process in MS. In this Review, we provide a broad overview of the physics of OCT, the unique properties of this method with respect to imaging retinal architecture, and the applications that are being developed for OCT to understand mechanisms of tissue injury within the brain.

Retinal blood flow detection in diabetic patients by Doppler Fourier domain optical coherence tomography

We present human retinal blood flow investigation for diabetic patients using Doppler Fourier domain optical coherence tomography (FDOCT). The scanning pattern consisted of two concentric circles around the optic nerve head. The blood flow in one patient with diabetes and no retinpathy and another patient with treated proliferative diabetic retinopathy were measured. The patient without retinopathy showed a total blood flow value at the lower level of the normal range. The flow distribution between superior and inferior retina was balanced. The patient with diabetic retinopathy had a flow value lower than the normal people. Our study shows that Doppler FD-OCT can be used to evaluate the total retinal blood flow in patients with retinal diseases.

Spectral domain-optical coherence tomography to detect localized retinal nerve fiber layer defects in glaucomatous eyes

This study examines the ability of RTVue, Cirrus and Spectralis OCT Spectral domain-optical coherence tomographs (SD-OCT) to detect localized retinal nerve fiber layer defects in glaucomatous eyes. In this observational case series, four glaucoma patients (8 eyes) were selected from the University of California, San Diego Shiley Eye Center and the Diagnostic Innovations in Glaucoma Study (DIGS) based on the presence of documented localized RNFL defects in at least one eye confirmed by masked stereophotograph assessment. One RTVue 3D Disc scan, one RTVue NHM4 scan, one Cirrus Optic Disk Cube 200x200 scan and one Spectralis scan centered on the optic disc (15x15 scan angle, 768 A-scans x 73 B-scans) were obtained on all undilated eyes within a single session. Results were compared with those obtained from stereophotographs. In 6 eyes the presence of localized RNFL defects was detected by stereophotography. In general, by qualitatively evaluating the retinal thickness maps generated, all SD-OCT instruments examined were able to confirm the presence of localized glaucomatous structural damage seen on stereophotographs. This study confirms SD-OCT is a promising technology for glaucoma detection as it may assist clinicians identify the presence of localized glaucomatous structural damage.

Comparison of OCT and HRT findings among normal, normal tension glaucoma, and high tension glaucoma

PURPOSE

To evaluate the relationship between optic disc and retinal nerve fiber layer (RNFL) measurements obtained with the optical coherence tomography (OCT) and the Heidelberg retina topography (HRT) in normal, normal tension glaucoma (NTG), and high tension glaucoma (HTG).

METHODS

Normal, NTG and HTG subjects who met inclusion and exclusion criteria were evaluated retrospectively. One hundred seventy eyes of 170 patients (30 normal, 40 NTG, and 100 HTG) were enrolled. Complete ophthalmologic examination, HRT, OCT, and automated perimetry were evaluated.

RESULTS

Disc area, cup area and cup/disc area ratio measured with HRT were significantly different between NTG and HTG (all p < 0.05). Mean RNFL thickness measured by OCT with ascanning diameter of 3.4 mm was larger in NTG than HTG (84.97+/-24.20 micrometer vs. 73.53+/-27.17 micrometer, p = 0.037). Four quadrant RNFL thickness measurements were not significantly different between NTG and HTG (all p > 0.05). Mean deviation and corrected pattern standard deviation measured by automated perimetry was significantly correlated with mean and inferior RNFL thickness in both NTG and HTG (Pearson's r, p < 0.05). Mean RNFL thickness/disc area ratio was significantly larger in HTG than NTG (35.21+/-18.92 vs. 31.30+/-10.91, p = 0.004).

CONCLUSIONS

These findings suggest that optic disc and RNFL damage pattern in NTG may be different from those of HTG.

Blood vessel contributions to retinal nerve fiber layer thickness profiles measured with optical coherence tomography

PURPOSE

To understand better the influence of retinal blood vessels (BVs) on the interindividual variation in the retinal nerve fiber layer (RNFL) thickness measured with optical coherence tomography (OCT).

SUBJECTS AND METHODS

RNFL thickness profiles were measured by OCT in 16 control individuals and 16 patients. The patients had advanced glaucoma defined by abnormal disc appearance, abnormal visual fields, and a mean visual field deviation worse than -10 dB.

RESULTS

In general, the OCT RNFL thickness profiles showed 4 local maxima, with the peak amplitudes in the superior and inferior regions occurring in the temporal (peripapillary) disc region. There was considerable variability among individuals in the location of these maxima. However, the 4 maxima typically fell on, or near, a major BV with the temporal and inferior peaks nearly always associated with the main temporal branches of the superior and inferior veins and arteries. In the patients' hemifields with severe loss (mean visual field deviation worse than -20 dB), the signals associated with the major BVs were in the order of 100 to 150 microm.

CONCLUSIONS

The variation in the local peaks of the RNFL profiles of controls correlates well with the location of the main temporal branches of the superior and inferior veins and arteries. This correspondence is, in part, due to a direct BV contribution to the shape of the OCT RNFL and, in part, due to the fact that BVs develop along the densest regions of axons. Although the overall BV contribution was estimated to be relatively modest, roughly 13% of the total peripapillary RNFL thickness in controls, their contribution represents a substantial portion locally and increases in importance with disease progression.

Scan tracking coordinates for improved centering of Stratus OCT scan pattern

OBJECTIVE

To describe and evaluate a technique to optimize scan centering during the Stratus optical coherence tomography (OCT) image acquisition process using currently available scan tracking coordinates.

DESIGN

Observational clinical study.

PARTICIPANTS

Twelve eyes of six normal subjects were examined using the Fast retinal nerve fiber layer (RNFL) thickness and the Fast Optic Disc acquisition protocols.

METHODS

At visit 1, 3 consecutive measurements (trials) were taken by 2 different operators with the scan subjectively centered on the optic disc for the Fast RNFL thickness protocol and Fast Optic Disc protocol. At visit 2, 3 consecutive measurements were taken by positioning the scan using scan tracking coordinates. The scan coordinates were recorded twice by each operator and the limits of agreement and Bland-Altman plots were used to estimate agreement. The within subjects standard deviation (Sw) and the coefficient of variation (CV) were calculated for RNFL and optic disc parameters for each operator separately and differences by scan positioning method were evaluated using a 3-way (trial x operator x visit) analysis of variance for repeated measures.

RESULTS

The Sw and CV for the RNFL thickness parameters were generally higher when the scan was subjectively centered on the disc compared to when using the newly described coordinate system (eg, for operator 2, temporal sector Sw was 1.60+/-0.78 and 4.09+/-0.99 and CV was 2.2% and 5.7% with and without coordinate use, respectively). For the Fast RNFL protocol, the use of scan tracking coordinates resulted in significantly less variability than subjective placement of the scan circle using the landmark feature (currently recommended technique) in the temporal sectors only. No significant difference was found for any of the optic disc parameters. Bland-Altman plots showed good agreement within each operator for calculating scan coordinates suggesting this technique is reproducible.

CONCLUSIONS

Reproducibility of RNFL thickness measurements generally improves with the use of scan tracking coordinates, particularly in the temporal sector. However, small changes in the position of the scan do not significantly affect the reproducibility of optic disc parameters.

Relationship Between Visual Field Sensitivity and Retinal Nerve Fiber Layer Thickness Measured by Scanning Laser Polarimetry and Optical Coherence Tomography in Normal, Ocular Hypertensive and Glaucomatous Eyes

Purpose

To evaluate the correlation between automated achromatic perimetry (AAP) and the output of two retinal nerve fiber layer (RNFL) analysers: scanning laser polarimetry (GDx-VCC) and optical coherence tomography (OCT).

Methods

Quantitative RNFL measurements with GDx-VCC and Stratus-OCT were obtained in one eye from 52 healthy subjects, 38 ocular hypertensive (OHT) patients and 94 glaucomatous patients. All patients underwent a complete examination, including AAP using the Swedish interactive threshold algorithm (SITA). The relationship between RNFL measurements and SITA visual field global indices were assessed by means of the following methods: analysis of variance, bivariate Pearson's correlation coefficient, multivariate linear regression techniques and nonlinear regression models, and the coefficient of determination (r²) was calculated.

Results

RNFL thickness values were significantly lower in glaucomatous eyes than in healthy and ocular hypertensive eyes for both nerve fiber analysers (P≤0.001), except for the inferior 120° average thickness in GDx-VCC. Linear regression models constructed for GDx-VCC measurements and OCT-derived RNFL thickness with SITA visual field global indices demonstrated that, for the mean deviation, the only predictor in the model was the nerve fiber indicator for GDx-VCC (r²=0.255), and for the pattern standard deviation, the predictors in the model were the nerve fiber indicator for GDx-VCC (r²=0.246) and the maximum thickness in the superior quadrant for Stratus-OCT (r²=0.196). The best curvilinear fit was obtained with the cubic model.

Conclusions

Quantitative measurements of RNFL thickness using either GDx-VCC or OCT correlate moderately with visual field global indices in moderate glaucoma patients. We did not find a correlation between visual field global indices and RNFL thickness in early glaucoma patients. Further study is needed to develop new analytical methods that will increase RNFL analyser's sensitivity in early glaucoma patients.

Normative database of retinal nerve fiber layer and macular retinal thickness in a Thai population

PURPOSE

To investigate the distribution of retinal nerve fiber layer (RNFL) and macular retinal thickness measured by optical coherence tomography (OCT) in a Thai population.

METHODS

We studied one eye each of 250 healthy subjects [age > or = 18 years; spherical refractive error within +/-6 diopters (D); astigmatism < or =3 D; no ocular pathology]. A complete eye examination, standard automated perimetry, and fast RNFL and macular thickness measurement by OCT were performed, and a disc photograph was taken. The distributions of both thicknesses, including their relationship with demographic data, were analyzed.

RESULTS

The mean +/- SD age of the study population was 44.7 +/- 12.2 years. The mean +/- SD RNFL thickness was 109.3 +/- 10.5 m, which was 10% thicker than that in the OCT normative database. RNFL decreased 2.3 m per decade (P < 0.001). Sex and spherical equivalent were not associated with RNFL thinning. The mean +/- SD central foveal thickness was 183.2 +/- 1.3 m. The macular thickness in the outer area was significantly thinner than that in the inner area (P < 0.001). The temporal regions were the thinnest among the four quadrants (P < 0.001). Thinning of all macular areas, except the center, was found to be associated with advancing age (P < 0.05).

CONCLUSIONS

RNFL thickness in the measured Thai population was about 10% thicker than that in the original normative database. Macular thickness and RNFL thickness in the superior and inferior quadrants decreased with advancing age.

Effect of improper scan alignment on retinal nerve fiber layer thickness measurements using Stratus optical coherence tomograph

OBJECTIVE

Misalignment of the Stratus optical coherence tomograph scan circle placed by the operator around the optic nerve head (ONH) during each retinal nerve fiber layer (RNFL) examination can affect the instrument reproducibility and its theoretical ability to detect true structural changes in the RNFL thickness over time. We evaluated the effect of scan circle placement on RNFL measurements.

DESIGN

Observational clinical study.

METHODS

Sixteen eyes of 8 normal participants were examined using the Stratus optical coherence tomograph Fast RNFL thickness acquisition protocol (software version 4.0.7; Carl Zeiss Meditec, Dublin, CA). Four consecutive images were taken by the same operator with the circular scan centered on the optic nerve head. Four images each with the scan displaced superiorly, inferiorly, temporally, and nasally were also acquired. Differences in average and sectoral RNFL thicknesses were determined. For the centered scans, the coefficients of variation (CV) and the intraclass correlation coefficient for the average RNFL thickness measured were calculated.

RESULTS

When the average RNFL thickness of the centered scans was compared with the average RNFL thickness of the displaced scans individually using analysis of variance with post-hoc analysis, no difference was found between the average RNFL thickness of the nasally (105.2 microm), superiorly (106.2 microm), or inferiorly (104.1 microm) displaced scans and the centered scans (106.4 microm). However, a significant difference (analysis of variance with Dunnett's test: F=8.82, P<0.0001) was found between temporally displaced scans (115.8 microm) and centered scans. Significant differences in sectoral RNFL thickness measurements were found between centered and each displaced scan. The coefficient of variation for average RNFL thickness was 1.75% and intraclass correlation coefficient was 0.95.

CONCLUSIONS

In normal eyes, average RNFL thickness measurements are robust and similar with significant superior, inferior, and nasal scan displacement, but average RNFL thickness is greater when scans are displaced temporally. Parapapillary scan misalignment produces significant changes in RNFL assessment characterized by an increase in measured RNFL thickness in the quadrant in which the scan is closer to the disc, and a significant decrease in RNFL thickness in the quadrant in which the scan is displaced further from the optic disc.

Retinal nerve fiber layer and future risk of multiple sclerosis

BACKGROUND

Optical coherence tomography (OCT)--measured retinal nerve fiber layer (RNFL) values may represent a surrogate biomarker for axonal integrity in multiple sclerosis (MS). The purpose of this study was to determine whether RNFL measurements obtained within two years of an optic neuritis (ON) event distinguish patients at increased risk of developing clinically-definite MS (CDMS).

METHODS

Fifty consecutively sampled patients who experienced a single ON event were followed prospectively for a mean period of 34 months with OCT testing. Values of RNFL in clinically-affected and non-affected eyes were compared between patients who developed CDMS and those that did not develop MS after ON.

FINDINGS

Twenty-one patients (42%) developed CDMS during the course of the study, with a mean conversion time of 27 months. Mean RNFL values were thinner in the clinically-affected eyes of non-MS patients than CDMS eyes after one year (p = 0.0462) due to more severe ON events in the former. By year two, CDMS patients manifested more recurrent ON events and RNFL thinning than non-MS patients. Temporal RNFL values were thinner in the non-affected eyes of CDMS patients with a trend towards significance (p = 0.1302).

INTERPRETATION

Our results indicate that RNFL thickness does not reliably distinguish patients at higher risk of converting to CDMS after ON. The severity of ON has a greater effect on RNFL thickness than risk of CDMS at one year. The CDMS patients demonstrate progressive RNFL thinning likely due to recurrent sub-clinical ON events, which may help differentiate them from non-MS patients over time.

Thickness of receptor and post-receptor retinal layers in patients with retinitis pigmentosa measured with frequency-domain optical coherence tomography

PURPOSE

To better understand the effects of retinitis pigmentosa (RP) on post-receptor anatomy, the thicknesses of the receptor, inner nuclear, retinal ganglion cell (RGC), and retinal nerve fiber layers (RNFL) were measured with frequency-domain optical coherence tomography (fdOCT).

METHODS

FdOCT scans were obtained from the horizontal midline in 30 patients with RP and 23 control subjects of comparable age. Raw images were exported and the thicknesses of photoreceptor/RPE, inner nuclear, RGC plus inner plexiform, and nerve fiber layers were measured with a manual segmentation procedure aided by a computer program. The RNFL thickness was also measured in 20 controls and 25 patients using circular peripapillary fdOCT scans.

RESULTS

Results from controls were consistent with known anatomy. In patients with RP, the pattern of photoreceptor loss with eccentricity was consistent with the field constriction characteristic of RP. INL and RGC layer measures were comparable to normal subjects, although some patients showed slightly thicker RGC layers. However, RNFL layer thickness was significantly greater than normal; a majority of patients showed a thicker RFNL on both horizontal midline scans and peripapillary scans.

CONCLUSIONS

To make optimal use of OCT RNFL thickness as a measure of the integrity of RGCs in patients with RP, a better understanding of the causes of the thickening seen in the majority of the patients is needed. As the RGC layer thickness can be measured with fdOCT, RGC layer thickness may turn out to be a more direct and valid indicator of the presence of RGCs in patients with RP.

Retinal blood flow measurement by circumpapillary Fourier domain Doppler optical coherence tomography

We present in vivo human total retinal blood flow measurements using Doppler Fourier domain optical coherence tomography (OCT). The scan pattern consisted of two concentric circles around the optic nerve head, transecting all retinal branch arteries and veins. The relative positions of each blood vessel in the two OCT conic cross sections were measured and used to determine the angle between the OCT beam and the vessel. The measured angle and the Doppler shift profile were used to compute blood flow in the blood vessel. The flows in the branch veins was summed to give the total retinal blood flow at one time point. Each measurement of total retinal blood flow was completed within 2 s and averaged. The total retinal venous flow was measured in one eye each of two volunteers. The results were 52.90+/-2.75 and 45.23+/-3.18 microlmin, respectively. Volumetric flow rate positively correlated with vessel diameter. This new technique may be useful in the diagnosis and treatment of optic nerve and retinal diseases that are associated with poor blood flow, such as glaucoma and diabetic retinopathy.

Correlation between retinal nerve fibre layer thickness and retinal sensitivity

PURPOSE

To evaluate the relationship between retinal nerve fibre layer (RNFL) thickness measured by optical coherence tomography (OCT) and light threshold values obtained with the Micro Perimeter 1 (MP1).

METHODS

Forty-nine normal subjects and 37 glaucoma patients were included. Thickness of the RNFL around the optic disc was measured with Stratus OCT scans, and static threshold perimetry was performed with the MP1 at the same visit. Total average and mean 12-clock-hour RNFL thickness were measured with Stratus OCT. An automated 4-2-1 staircase strategy with Goldmann III stimuli was used for MP1. The correspondence between Stratus OCT and MP1 RNFL measurements in each clock-hour was best fit by a second-order polynomial.

RESULTS

Average RNFL thickness in the normal group was significantly higher than that in the glaucoma group in each clock hour. Comparing the normal and glaucomatous groups, retinal sensitivity differed significantly at 6, 7, 8 and 11 o'clock. In these regions, structure-function relationships were generally stronger than in other regions.

CONCLUSIONS

Structure-function associations may be strong when loss of nerve fibres is severe. However, significant reduction in retinal sensitivity does not emerge until the atrophy of nerve fibres is severe.

Projection OCT fundus imaging for visualising outer retinal pathology in non-exudative age-related macular degeneration

AIMS

To demonstrate ultrahigh-resolution, three-dimensional optical coherence tomography (3D-OCT) and projection OCT fundus imaging for enhanced visualisation of outer retinal pathology in non-exudative age-related macular degeneration (AMD).

METHODS

A high-speed, 3.5 mum resolution OCT prototype instrument was developed for the ophthalmic clinic. Eighty-three patients with non-exudative AMD were imaged. Projection OCT fundus images were generated from 3D-OCT data by selectively summing different retinal depth levels. Results were compared with standard ophthalmic examination, including fundus photography and fluorescein angiography, when indicated.

RESULTS

Projection OCT fundus imaging enhanced the visualisation of outer retinal pathology in non-exudative AMD. Different types of drusen exhibited distinct features in projection OCT images. Photoreceptor disruption was indicated by loss of the photoreceptor inner/outer segment (IS/OS) boundary and external limiting membrane (ELM). RPE atrophy can be assessed using choroid-level projection OCT images.

CONCLUSIONS

Projection OCT fundus imaging facilities rapid interpretation of large 3D-OCT data sets. Projection OCT enhances contrast and visualises outer retinal pathology not visible with standard fundus imaging or OCT fundus imaging. Projection OCT fundus images enable registration with standard ophthalmic diagnostics and cross-sectional OCT images. Outer retinal alterations can be assessed and drusen morphology, photoreceptor impairment and pigmentary abnormalities identified.