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.

Detecting visual function abnormalities using the Swedish interactive threshold algorithm and matrix perimetry in eyes with glaucomatous appearance of the optic disc.

OBJECTIVE: To compare the ability of 24-2 frequency-doubling perimetry (FDP-Matrix) with standard automated perimetry with the Swedish interactive threshold algorithm (SAP-SITA) in detection of visual function abnormalities in patients with glaucomatous-appearing optic discs (GAOD). METHODS: This observational case-control study included 80 patients with GAOD and 54 control subjects diagnosed by masked assessment of optic disc stereoscopic photographs. Abnormal visual function at SAP-SITA and FDP-Matrix testing required consistent abnormalities in 2 visual field examinations, determined using the glaucoma hemifield test outside 99% normal limits, pattern standard deviation outside 95% normal limits, or 3 contiguous points in the pattern deviation probability plot outside 95% normal limits (at least 1 P<1%) within the same hemifield. RESULTS: The FDP-Matrix and SAP-SITA detected abnormal visual function in 51% and 44%, respectively, of GAOD eyes (P = .26), and both perimetry techniques identified 11% of healthy eyes as abnormal. Agreement between FDP-Matrix and SAP-SITA was moderate (kappa = 0.49), as only 35% of GAOD eyes and 2% of healthy eyes had both visual field test results flagged as abnormal. CONCLUSIONS: The FDP-Matrix detected abnormal visual function in more eyes with GAOD than did SAP-SITA, although this difference was not significant. Each visual field test tended to identify different subsets of eyes with GAOD as abnormal. Combination of these perimetry techniques may improve the detection of visual function abnormalities in patients with glaucoma.

Selective perimetry in glaucoma diagnosis.

PURPOSE OF REVIEW: Selective perimetry evaluates visual function by using visual stimuli that attempt to target specific subpopulations of retinal ganglion cells, which is designed to improve sensitivity to detect glaucomatous functional loss. This paper reviews recent studies that have assessed the characteristics of new strategies/programs of selective perimetry. RECENT FINDINGS: Selective perimetry is usually compared against an existing standard technique--standard automated perimetry. Recent studies did not consider standard automated perimetry results as part of inclusion/exclusion criteria, avoiding selection bias and permitting fair comparisons between perimetry techniques. Furthermore, the Swedish Interactive Threshold Algorithm is replacing Full-Threshold as the standard automated perimetry gold-standard strategy, and comparisons of the diagnostic performance of function-specific perimetry may be influenced by which standard automated perimetry technique is used as the reference. These factors may impact our perception about the role of selective perimetry in glaucoma management. SUMMARY: The lack of a perfect gold-standard diagnostic test for glaucoma limits the interpretation of results from cross-sectional studies evaluating visual field tests. Nevertheless, evidence suggests that visual dysfunction in eyes with early glaucoma varies significantly between individuals and no single technique is superior to the others in all patients. A multimodal functional assessment may be more effective in detecting/quantifying visual impairment associated with early glaucoma.

Effect of glaucomatous damage on repeatability of confocal scanning laser ophthalmoscope, scanning laser polarimetry, and optical coherence tomography.

PURPOSE: To determine and compare the effect of the severity of glaucomatous damage on the repeatability of retinal nerve fiber layer (RNFL) thickness with GDx-VCC (variable corneal compensation) and StratusOCT (optical coherence tomography; both produced by Carl Zeiss Meditec, Inc., Dublin, CA), and optic nerve head (ONH) topography with HRT-II (retinal tomograph; Heidelberg Engineering GmbH, Heidelberg, Germany) and StratusOCT. METHODS: With each of these techniques, two measurements were obtained from 41 eyes of 41 control subjects and 98 glaucomatous eyes (37 patients with early, 29 with moderate, and 32 with severe field loss). To evaluate test-retest variability at each stage, limits of agreement (Bland-Altman plots) and repeatability coefficients (RCs) were obtained from pairs of measurements. Comparisons of within-subject variances were used to compare repeatability of GDx-VCC versus StratusOCT for global RNFL and HRT-II versus StratusOCT for global ONH topography. Effects from age, visual acuity, and lens status were also included in the analysis as covariates. RESULTS: Test-retest variability of RNFL using GDx-VCC and StratusOCT were consistent through all stages of disease severity. Repeatability results of GDx-VCC were better than those of StratusOCT, except in severe cases. Test-retest variability of ONH topography using HRT-II and StratusOCT increased with increasing disease severity for rim area, cup area, and cup-to-disc (C/D) area ratio. In contrast, vertical C/D ratio from HRT-II, and horizontal C/D ratio from StratusOCT showed stable test-retest variability through all stages. Regardless of disease severity, repeatability results of HRT-II were better than those of StratusOCT. CONCLUSIONS: GDx-VCC and HRT-II showed better repeatability than StratusOCT. Although test-retest variability increased with disease severity for rim area, the variability for vertical C/D ratio (HRTII) and global RNFL (GDx-VCC) was stable across disease severity. These parameters, rather than rim area, may be more useful in detection of progression in patients with glaucoma who have more advanced field loss.

Correlations between retinal nerve fiber layer and visual field in eyes with nonarteritic anterior ischemic optic neuropathy.

PURPOSE: To evaluate correlations between retinal nerve fiber layer (RNFL) thickness with visual field (VF) sensitivities in eyes with nonartertic anterior ischemic optic neuropathy (NAION). DESIGN: Case-control study in an academic, institutional setting. METHODS: One eye from 21 patients with NAION and 32 healthy participants were included in this prospective study. Humphrey visual field (HVF) sensitivities were obtained from standard achromatic HVF test (24-2 SITA). RNFL was measured with scanning laser polarimetry (SLP, GDx-VCC) and optical coherence tomography (OCT, StratusOCT). Correlations were evaluated between RNFL and sensitivities from global, hemifields, and regional locations of the VF pertinent to the RNFL distribution. A total of 15 NAION eyes had inferior altitudinal HVF defects, and their global and regional RNFL was compared with that of control eyes. The main outcome measure was correlation between HVF sensitivities and RNFL. RESULTS: Correlations of global, hemifield, and sectorial HVF sensitivities with RNFL were greater when RNFL was measured with OCT than with SLP, except for nasal and inferonasal sectors. RNFL thickness was far lower in the hemiretinas corresponding to the relative unaffected hemifield in eyes with altitudinal VF defect compared with controls. CONCLUSIONS: In patients with NAION, RNFL measured by OCT provided better correlation to HVF changes than SLP did. Both instruments showed decreased RNFL in NAION eyes with altitudinal VF defects compared with control eyes, demonstrating loss of RNFL even in sectors of the optic disk that corresponded to relatively unaffected hemifield, suggesting greater damage beyond the extent estimated by VF methods.

Comparison of the Moorfields classification using confocal scanning laser ophthalmoscopy and subjective optic disc classification in detecting glaucoma in blacks and whites.

OBJECTIVE: To compare the diagnostic accuracy of the Moorfields regression classification (MRC) and subjective optic disc evaluation in discriminating early to moderate glaucomatous from nonglaucomatous eyes. DESIGN: Cross-sectional observational study. PARTICIPANTS: Two hundred thirty-three patients with glaucoma and 216 normal subjects were included in the analysis. Racial groups were defined by self-description. METHODS: All subjects underwent confocal scanning laser ophthalmoscopy, stereophotography, and standard perimetry. Glaucoma was defined by visual field defect alone and confirmed with a second visual field test. Stereo photographs were graded as either normal or glaucomatous appearing in a masked fashion by 2 independent graders and adjudicated by a third grader in cases of disagreement. Mean disc area was compared between patients correctly and incorrectly diagnosed with either technique. MAIN OUTCOME MEASURES: Sensitivity and specificity of MRC and subjective evaluation of stereophotographs in the detection of glaucomatous visual field loss. RESULTS: With the MRC, the sensitivity and specificity were higher using the 95% cutoff than using the 99.9% cutoff. Classification based on subjective photo assessment had a greater agreement with the diagnosis of glaucoma than the MRC for blacks (MRC, sensitivity = 62.5%, specificity = 93.2%; Photo, sensitivity = 76.5%, specificity = 91.5%) and whites (MRC, sensitivity = 67.0%, specificity = 92.2%; photo, sensitivity = 78.4%, specificity = 91.9%). Disc area was significantly larger in patients incorrectly diagnosed with the MRC (P = 0.0289). CONCLUSIONS: Subjective optic disc grading by glaucoma specialists outperformed the MRC with the HRT II in both black and white subjects. Both subjective and objective diagnostic methods were associated with similar sensitivity and specificity between racial groups. The MRC was more likely to provide an incorrect diagnosis in subjects with larger optic discs.

Discrimination between glaucomatous and nonglaucomatous eyes using quantitative imaging devices and subjective optic nerve head assessment.

PURPOSE: To compare the diagnostic ability of the confocal scanning laser ophthalmoscope (HRT-II; Heidelberg Engineering, Heidelberg, Germany), scanning laser polarimeter (GDx-VCC; Carl Zeiss Meditec, Inc., Dublin, CA), and optical coherence tomographer (StratusOCT, Carl Zeiss Meditec, Inc.) with subjective assessment of optic nerve head (ONH) stereophotographs in discriminating glaucomatous from nonglaucomatous eyes. METHODS: Data from 79 glaucomatous and 149 normal eyes of 228 subjects were included in the analysis. Three independent graders evaluated ONH stereophotographs. Receiver operating characteristic curves were constructed for each technique and sensitivity was estimated at 80% of specificity. Comparisons of areas under these curves (aROC) and agreement (kappa) were determined between stereophoto grading and best parameter from each technique. RESULTS: Stereophotograph grading had the largest aROC and sensitivity (0.903, 77.22%) in comparison with the best parameter from each technique: HRT-II global cup-to-disc area ratio (0.861, 75.95%); GDx-VCC Nerve Fiber Indicator (NFI; 0.836, 68.35%); and StratusOCT retinal nerve fiber layer (RNFL) thickness (0.844, 69.62%), ONH vertical integrated rim area (VIRA; 0.854, 73.42%), and macular thickness (0.815, 67.09%). The kappa between photograph grading and imaging parameters was 0.71 for StratusOCT-VIRA, 0.57 for HRT-II cup-to-disc area ratio, 0.51 for GDX-VCC NFI, 0.33 for StratusOCT RNFL, and 0.28 for StratusOCT macular thickness. CONCLUSIONS: Similar diagnostic ability was found for all imaging techniques, but none demonstrated superiority to subjective assessment of the ONH. Agreement between disease classification with subjective assessment of ONH and imaging techniques was greater for techniques that evaluate ONH topography than with techniques that evaluate RNFL parameters. A combination of subjective ONH evaluation with RNFL parameters provides additive information, may have clinical impact, and deserves to be considered in the design of future studies comparing objective techniques with subjective evaluation by general eye care providers.

Differences in optic disc topography between black and white normal subjects.

PURPOSE: To determine if differences in optic disc topography exist between blacks and whites independent of racial differences in the area of the scleral canal. DESIGN: Cross-sectional observational study. PARTICIPANTS: A cohort of 146 eyes from black subjects and 97 eyes from white subjects without detectable ocular disease. METHODS: Reliable bilateral images were obtained using a retinal topographer. Mean values for all topographic parameters were compared both unadjusted and adjusted for differences in optic disc area and/or reference plane height. Comparisons of group differences for parameters and linear discriminant functions were adjusted for interocular dependence and multiple comparisons. RESULTS: Blacks had a significantly greater optic disc area (mean disc area in right eye: black subjects, 2.14 mm(2); white subjects, 1.96 mm(2) [P = 0.02]; mean disc area in left eye: black subjects, 2.18 mm(2); white subjects, 2.02 mm(2) [P = 0.04]). Most racial differences in optic disc parameters were not significant after adjustment for differences in optic disc area and reference plane height. However, eyes of black subjects demonstrated a deeper maximum cup depth than those of whites (P = 0.004), independent of differences in disc area and reference plane height. The values of linear discriminant functions did not differ significantly between racial groups, and the Moorfield classification correctly identified a similar proportion of subjects as normal in each racial group. CONCLUSIONS: Most of the normal variation in optic disc topography between blacks and whites seen with a retinal topographer is due to either differences in disc area or differences in reference plane height. However, small residual differences remain in cup depth independent of these parameters. These racial differences in optic disc structure should be considered in the statistical judgment of disease status based on these parameters. The Moorfield classification, which takes disc area into account, performed with similar specificity in each racial group.

Subjective and objective optic nerve assessment in African Americans and whites.

OBJECTIVE: To compare the ability of quantitative optic disc topography and subjective optic disc evaluation to discriminate early glaucomatous from normal eyes in African Americans and whites. METHODS: Monocular data from eyes of 88 African-American patients and 63 eyes of white patients with glaucoma were included in the analysis. Sixty-three eyes of African American normal subjects and 42 eyes of white normal subjects were used as a control group. Racial groups were defined by self-description. All subjects underwent topographic imaging, stereophotography, and standard perimetry. Glaucoma was defined by visual field defect alone. Stereophotos were graded in a masked fashion by three independent graders. The areas under the receiver operator curve (aROCs) were calculated for the overall stereophoto grade, each confocal scanning laser ophthalmoscope (CSLO) parameter, and previously described discriminant functions. After adjustment for disc area and age, the aROC associated with each parameter, discriminant function, and subjective stereophoto grade were compared between African Americans and whites. RESULTS: The aROC for masked stereophotographic disc evaluation and the best discriminatory CSLO parameter (cup-to-disc ratio, CDR) was similar in whites (0.869 stereophotographic, 0.858 CSLO CDR) and African Americans (0.865 stereophotographic, 0.850 CSLO CDR). No significant differences were found between the aROC with subjective stereophotographic assessment and the most discriminatory optic disc parameter in either racial group. CONCLUSIONS: Previously described racial differences in optic disc structure have little impact on the relative ability of subjective or objective methods to discriminate between glaucomatous and nonglaucomatous optic discs; however, differences in normative values necessitate race-specific cutoffs, to optimize disease detection strategies.

Racial differences in the association between optic disc topography and early glaucoma.

PURPOSE: To determine the structural characteristics of the optic disc that are associated with early glaucoma in African Americans and whites and whether these characteristics differ between the races. METHODS: Parameters of optic disc topography from 260 African American eyes and 193 white eyes were included in the analysis. One hundred forty-four eyes of African Americans and 109 eyes of normal white subjects were used as a control group. Logistic regression was used to calculate the association between early glaucoma, defined by the visual field, and cup, rim, and disc margin confocal scanning laser ophthalmoscopic (CSLO) parameters, using odds ratios at binary cut points. The cup, rim, and disc margin parameters identified as being independently associated with glaucoma in these reduced models were then included in a single multivariate model. Optic disc area was included in the analysis at each level of the model. This approach was used for the total study group and then separately for the African American and white groups. RESULTS: When accounting for difference in optic disc area, rim area had the highest independent association with early glaucoma in both groups, but this association was lower in African Americans (odds ratio [95% confidence interval]: 1.63 [1.12-2.36]) than in whites (odds ratio: 4.74 [2.18-10.28]). Additional independently associated parameters included cup shape, maximum elevation along the contour line, and the temporal-to-inferior contour line modulation ratio in whites and cup shape and the temporal-to-superior contour line modulation ratio in African Americans. CONCLUSIONS: Structural characteristics of the optic disc that are best associated with early glaucoma included cup shape and rim area in both groups, but with a less pronounced association in African Americans. In addition, several other race-specific parameters that were independently associated with early glaucoma differed significantly between African Americans and whites. These race-specific differences were independent from the effect of optic disc area.