Optical coherence tomography longitudinal evaluation of retinal nerve fiber layer thickness in glaucoma

The relationship between retinal ganglion cell function and retinal nerve fiber thickness in early glaucoma

PURPOSE

To compare relative reduction of retinal ganglion cell (RGC) function and retinal nerve fiber layer (RNFL) thickness in early glaucoma by means of steady-state pattern electroretinogram (PERG) and optical coherence tomography (OCT), respectively.

METHODS

Eighty-four persons with suspected glaucoma due to disc abnormalities (GS: mean age 56.6 +/- 13.8 years, standard automated perimetry [SAP] mean deviation [MD] -0.58 +/- 1.34 dB) and 34 patients with early manifest glaucoma (EMG, mean age 65.9 +/- 10.7 years, SAP MD -2.7 +/- 4.5 dB) were tested with PERG and OCT. Both GS and EMG patients had small refractive errors, corrected visual acuity > or =20/25, and no systemic or retinal disease other than glaucoma.

RESULTS

MDs from age-predicted normal values were larger for PERG amplitude (GS: -1.113 dB; EMG: -2.352 dB) compared with the PERG-matched RNFL thickness (GS: -0.217 dB; EMG: -0.725 dB). Deviations exceeding the lower 95% tolerance intervals of the normal population were more frequent for PERG amplitude (GS: 26%; EMG: 56%) than PERG-matched RNFL thickness (GS: 6%; EMG: 29%).

CONCLUSIONS

In early glaucoma, reduction in RGC electrical activity exceeds the proportion expected from lost RGC axons, suggesting that a population of viable RGCs in the central retina is dysfunctional. By combining PERG and OCT it is, in principle, possible to obtain unique information on reduced responsiveness of viable RGCs.

Baseline optical coherence tomography predicts the development of glaucomatous change in glaucoma suspects

PURPOSE

To assess whether baseline retinal nerve fiber layer (RNFL) measurements obtained with optical coherence tomography (OCT2; Carl Zeiss Meditec, Dublin, California, USA) are predictive of the development of glaucomatous change.

DESIGN

Cohort study.

METHODS

Participants were recruited from the University of California, San Diego (UCSD) longitudinal Diagnostic Innovations in Glaucoma Study (DIGS). One eye was studied from each of 114 glaucoma suspects with normal standard automated perimetry (SAP) and OCT RNFL imaging at baseline. The cohort was divided into two groups based on the development of glaucomatous change (repeatable abnormal visual fields and/or a change in the stereophotographic appearance of the optic disk). Cox proportional hazards models were used to determine the predictive ability of OCT RNFL thickness measurements.

RESULTS

Over a 4.2-year average follow-up period, 23 eyes (20%) developed glaucomatous changes and 91 (80%) did not. At baseline, thinner RNFL measurements, higher SAP pattern standard deviation (PSD), "glaucoma" stereophotograph assessment, and thinner central corneal thickness (CCT) were associated with the study endpoints in univariate analysis. After adjusting for age, intraocular pressure (IOP), CCT, and PSD in multivariate models, a 10 mum thinner average, superior and inferior RNFL at baseline was predictive of glaucomatous change [hazard ratio (95% CI); 1.51 (1.11 to 2.12), 1.57 (1.17 to 2.18), and 1.49, (1.19 to 1.91), respectively]. Results were consistent when stereophotographic assessment was included in multivariate analysis.

CONCLUSIONS

Thinner OCT RNFL measurements at baseline were associated with development of glaucomatous change in glaucoma suspect eyes. RNFL thinning was an independent predictor of the glaucomatous change, even when adjusting for stereophotograph assessment, age, IOP, CCT, and PSD.

Scanning laser polarimetry with variable corneal compensation and optical coherence tomography in tilted disk

PURPOSE

To determine whether scanning laser polarimetry with variable corneal compensation (GDx-VCC) or optical coherence tomography (OCT) is helpful for the analysis of the retinal nerve fiber layer (RNFL) thickness in glaucoma subjects with tilted disk.

DESIGN

Retrospective case-control study.

METHODS

We included 21 glaucomatous eyes with tilted disk and 35 glaucomatous eyes without tilted disk. Peripapillary RNFL thickness measurement by GDx-VCC and OCT, and also visual field testing with a Humphrey Field Analyzer program 30-2 (HFA) were performed in all subjects.

RESULTS

In the group without tilted disk, the RNFL thickness values obtained with GDx-VCC and OCT analysis had a good correlation with mean deviation (MD), and clearly showed stage-dependent reduction. Conversely, in the group with tilted disk, a discrepancy in the RNFL measurement between GDx-VCC and OCT was observed. The correlation of RNFL measurement to the visual field was further examined at each hemifield (superior and inferior). In the group without tilted disk, the measurements of both instruments at each hemifield were in good correlation with the mean pattern deviation values. However, in the group with tilted disk, the GDx-VCC derived values did not correlate with the visual field defect in both hemifields, whereas OCT was in good association with both mean pattern deviation values. Infrared images acquired with a wavelength of nearly 780 nm revealed a high reflex from the sclera in the tilted disk.

CONCLUSIONS

Our study has suggested that RNFL analysis by OCT is more suitable for the glaucoma assessment in the tilted disk compared with GDx-VCC.

Retinal nerve fiber layer thickness in amblyopic eyes

PURPOSE

To compare the peripapillary retinal nerve fiber layer (RNFL) thickness of sound and amblyopic eyes.

DESIGN

Prospective observational case series.

METHODS

SETTING

Institutional.

STUDY POPULATION

Patients with unilateral strabismic, anisometropic, or combined amblyopia.

OBSERVATION

Fast RNFL analysis with ocular coherence tomography (OCT) of sound and amblyopic eyes.

MEASURE

Mean RNFL thickness.

RESULTS

For the 17 patients (mean age 10.7 years) in whom both eyes were imaged, the mean thickness of the sound eye was 109.2 microm (median 112.7) and of the amblyopic eye was 104.2 microm (median 105.0), and the average difference (sound eye less amblyopic eye) was 5.0 microm (median 3.0) (95% confidence interval -2.3, 12.2, P = .17). The sound eye was 10 microm or more thicker than the amblyopic eye in four patients; the amblyopic eye was 10 microm or more thicker than the sound eye in one patient; and the difference was within 10 microm in 12 patients. Test-retest data were obtained for 23 pairs of sound eyes and 21 pairs of amblyopic eyes, with 75% of the test-retest pairs within 7%.

CONCLUSIONS

We found a small, but not clinically significant, difference in nerve fiber layer (NFL) thickness between amblyopic and sound eyes. Reliability was excellent, with most eyes testing within 7% of the first test.

Peripapillary fundus perimetry in eyes with glaucoma

AIMS

To evaluate, with fundus perimetry, the peripapillary differential light threshold (DLT) in eyes with glaucoma and ocular hypertension (OHT), and compare it with peripapillary retinal nerve fibre layer (RNFL) thickness.

METHODS

35 glaucomatous, 29 OHT and 24 control eyes were included. Peripapillary DLT at 1 degrees from the optic nerve head was quantified with fundus perimetry; peripapillary RNFL thickness was measured over the same area by optical coherence tomography.

RESULTS

Mean (SD) peripapillary DLT was 19.2 (1.7), 17.6 (4.2) and 10.1 (6.9) dB in control, OHT and glaucomatous eyes, respectively (p<0.001). Mean (SD) RNFL thickness was 98.4 (35.3), 83.9 (35.1) and 55.8 (28.2) microm, respectively (p<0.001). Mean peripapillary DLT showed higher sensitivity and specificity in differentiating the three groups compared with RNFL thickness.

CONCLUSION

Progressive, significant reduction of peripapillary DLT was documented in OHT and glaucomatous eyes compared with controls (p<0.001). DLT reduction parallels RNFL reduction.

Retinal assessment using optical coherence tomography

Over the 15 years since the original description, optical coherence tomography (OCT) has become one of the key diagnostic technologies in the ophthalmic subspecialty areas of retinal diseases and glaucoma. The reason for the widespread adoption of this technology originates from at least two properties of the OCT results: on the one hand, the results are accessible to the non-specialist where microscopic retinal abnormalities are grossly and easily noticeable; on the other hand, results are reproducible and exceedingly quantitative in the hands of the specialist. However, as in any other imaging technique in ophthalmology, some artifacts are expected to occur. Understanding of the basic principles of image acquisition and data processing as well as recognition of OCT limitations are crucial issues to using this equipment with cleverness. Herein, we took a brief look in the past of OCT and have explained the key basic physical principles of this imaging technology. In addition, each of the several steps encompassing a third generation OCT evaluation of retinal tissues has been addressed in details. A comprehensive explanation about next generation OCT systems has also been provided and, to conclude, we have commented on the future directions of this exceptional technique.

Retinal Nerve Fiber Layer Thickness in Normal Children Measured with Optical Coherence Tomography

PURPOSE

To measure the peripapillary retinal nerve fiber layer (RNFL) thickness in normal children.

DESIGN

Observational cross-sectional study.

PARTICIPANTS

Ninety-two eyes of 92 normal children ages 4 to 17 years presenting to the Ophthalmology Clinic at the Harkness Eye Institute, Department of Ophthalmology, Columbia University.

METHODS

Retinal nerve fiber layer thickness was measured with optical coherence tomography (OCT). Patient cooperation and signal strength of the OCT scans were assessed. Optic disc photographs were evaluated by a glaucoma specialist in a masked fashion. Eyes with abnormal optic discs were excluded. One eye of each subject was randomly selected for statistical analysis. The effect of several factors on RNFL thickness was investigated statistically.

MAIN OUTCOME MEASURES

Retinal nerve fiber layer thickness.

RESULTS

Ninety-one percent of the study subjects were Hispanic; 8%, African American; and 1%, Caucasian. Optical coherence tomography measurements were obtained in 117 of 121 (96.7%) subjects, and disc photographs were available for 92 of them. Mean age (+/-standard deviation [SD]) was 9.7+/-2.7 years. Mean global RNFL thickness (+/-SD) was 107.0+/-11.1 microm (range, 78.1-134.6). The RNFL was thickest inferiorly (136.9+/-16.9 microm) and superiorly (135.4+/-19.3 microm), thinner nasally (83.0+/-18.0 microm), and thinnest temporally (72.5+/-13.4 microm). In univariate regression analysis, age (P = 0.013) and refraction (P<0.001) had a significant effect on RNFL thickness; age had a significant effect on refraction (P<0.001). When controlling for refraction, age no longer had a significant effect.

CONCLUSIONS

Optical coherence tomography can be used to measure RNFL thickness in children. Refraction had an effect on RNFL thickness. In normal children, variation in RNFL thickness is large. The normative data provided by this study may assist in identifying changes in RNFL thickness in children.

Glaucoma screening: current trends, economic issues, technology, and challenges

PURPOSE OF REVIEW

Glaucoma is one of the leading causes of irreversible blindness worldwide. Early glaucoma detection and treatment are currently the only known methods for preventing blindness and low vision resulting from this frequently asymptomatic disease.

RECENT FINDINGS

New technologies for detecting early glaucomatous damage are important in diagnosing optic nerve disease, not only in community screening settings but also in clinics. Imaging of the optic nerve head and macula and retinal nerve fiber layer analysis can provide quick, automated, and quantitative measurements in agreement with clinical estimates of optic disc structure and visual function. In the area of perimetry, frequency-doubling technology is a promising and feasible mass-screening method with reasonable sensitivity for detecting visual field loss. Central corneal thickness has emerged as a new risk factor for the development and progression of glaucoma, thereby complicating the role of tonometry and measurement of intraocular pressure as screening parameters for glaucoma. Along with technological advances, strides are also being made with public policy and legislative efforts to bring glaucoma onto the national and global health care agenda. These initiatives incorporate vision-screening goals into national disease prevention programs emphasizing the need for early glaucoma detection and treatment.

SUMMARY

Glaucoma awareness needs to be increased through better education, and compliance with follow-up care needs to be improved to decrease the economic and social costs from glaucoma. In addition, screening models need to be developed that will be effective in developing countries where the risk of blindness from glaucoma is highest.

Optic disc imaging in perimetrically normal eyes of glaucoma patients with unilateral field loss

PURPOSE

To compare the ability of optic disc and retinal nerve fiber layer (RNFL) imaging to discriminate perimetrically unaffected eyes of glaucoma patients from normal eyes.

METHODS

Forty-six primary open-angle glaucoma patients with glaucomatous visual field loss with achromatic perimetry in one eye and a normal visual field in the fellow eye and 46 normal controls were selected. Receiver operator characteristic (ROC) curves and sensitivities at fixed specificities were used to compare the performance of StratusOCT (Fast RNFL algorithm), GDx-VCC, HRT II, and clinical evaluation of optic disc photographs to distinguish perimetrically unaffected eyes of glaucoma patients from normal eyes.

RESULTS

The parameters with the largest area under the ROC curves (AUC) were as follows: inferior average RNFL thickness (0.92 +/- 0.03) for StratusOCT; linear cup-to-disc ratio (0.82 +/- 0.05) for HRT II; and nerve fiber layer index (0.69 +/- 0.06) for GDx-VCC. Clinical evaluation of stereoscopic disc photographs resulted in AUCs ranging between 0.80 and 0.85. The P values for pairwise comparisons of the AUCs of OCT's best parameter with those of HRT, GDx, and disc photographs were .06, < .001, and .17, respectively. The sensitivities at 95% specificity for the best parameters from StratusOCT (inferior average), HRT II (cup volume), GDx-VCC (temporal-superior-nasal-inferior-temporal average), and clinical evaluation of disc photographs were 61%, 39%, 37%, and 28%, respectively. OCT identified more perimetrically normal glaucomatous eyes as having abnormalities, compared to normals, than did HRT (P = .001), GDx (P = .001), or clinical evaluation of disc photographs (P < .001).

CONCLUSION

Optical coherence tomography (StratusOCT) may detect evidence of glaucomatous damage earlier than other imaging techniques and clinical evaluation of optic disc photographs in perimetrically unaffected eyes of primary open-angle glaucoma patients.

Optical coherence tomography machine learning classifiers for glaucoma detection: a preliminary study

PURPOSE

Machine-learning classifiers are trained computerized systems with the ability to detect the relationship between multiple input parameters and a diagnosis. The present study investigated whether the use of machine-learning classifiers improves optical coherence tomography (OCT) glaucoma detection.

METHODS

Forty-seven patients with glaucoma (47 eyes) and 42 healthy subjects (42 eyes) were included in this cross-sectional study. Of the glaucoma patients, 27 had early disease (visual field mean deviation [MD] > or = -6 dB) and 20 had advanced glaucoma (MD < -6 dB). Machine-learning classifiers were trained to discriminate between glaucomatous and healthy eyes using parameters derived from OCT output. The classifiers were trained with all 38 parameters as well as with only 8 parameters that correlated best with the visual field MD. Five classifiers were tested: linear discriminant analysis, support vector machine, recursive partitioning and regression tree, generalized linear model, and generalized additive model. For the last two classifiers, a backward feature selection was used to find the minimal number of parameters that resulted in the best and most simple prediction. The cross-validated receiver operating characteristic (ROC) curve and accuracies were calculated.

RESULTS

The largest area under the ROC curve (AROC) for glaucoma detection was achieved with the support vector machine using eight parameters (0.981). The sensitivity at 80% and 95% specificity was 97.9% and 92.5%, respectively. This classifier also performed best when judged by cross-validated accuracy (0.966). The best classification between early glaucoma and advanced glaucoma was obtained with the generalized additive model using only three parameters (AROC = 0.854).

CONCLUSIONS

Automated machine classifiers of OCT data might be useful for enhancing the utility of this technology for detecting glaucomatous abnormality.