Faculty Bibliography

AIMS: The purpose of this study was to compare the day-to-day reproducibility of optical coherence tomography (OCT; StratusOCT, Carl Zeiss Meditec, Dublin, CA) measurements of retinal nerve-fibre layer (RNFL) measurements at time points 1 year apart. METHODS: One eye in each of 11 healthy subjects was examined using the StratusOCT fast RNFL scan protocol. Three fast RNFL scans with signal strength > or =7 were obtained on each of 3 days within a month. This protocol was repeated after 12 months. A linear mixed effects model fitted to the nested data was used to compute the variance components. RESULTS: The square root of the variance component that was attributed to the differences between subjects was 7.17 microm in 2005 and 7.28 microm in 2006. The square roots of the variance component due to differences between days within a single subject were 1.95 microm and 1.50 microm, respectively, and for within day within a single subject were 2.51 microm and 2.55 microm, respectively. There were no statistically significant differences for any variance component between the two testing occasions. CONCLUSIONS: Measurement error variance remains similar from year to year. Day and scan variance component values obtained in a cohort study may be safely applied for prediction of long-term reproducibility.

AIMS: To assess performance of classifiers trained on Heidelberg Retina Tomograph 3 (HRT3) parameters for discriminating between healthy and glaucomatous eyes. METHODS: Classifiers were trained using HRT3 parameters from 60 healthy subjects and 140 glaucomatous subjects. The classifiers were trained on all 95 variables and smaller sets created with backward elimination. Seven types of classifiers, including Support Vector Machines with radial basis (SVM-radial), and Recursive Partitioning and Regression Trees (RPART), were trained on the parameters. The area under the ROC curve (AUC) was calculated for classifiers, individual parameters and HRT3 glaucoma probability scores (GPS). Classifier AUCs and leave-one-out accuracy were compared with the highest individual parameter and GPS AUCs and accuracies. RESULTS: The highest AUC and accuracy for an individual parameter were 0.848 and 0.79, for vertical cup/disc ratio (vC/D). For GPS, global GPS performed best with AUC 0.829 and accuracy 0.78. SVM-radial with all parameters showed significant improvement over global GPS and vC/D with AUC 0.916 and accuracy 0.85. RPART with all parameters provided significant improvement over global GPS with AUC 0.899 and significant improvement over global GPS and vC/D with accuracy 0.875. CONCLUSIONS: Machine learning classifiers of HRT3 data provide significant enhancement over current methods for detection of glaucoma.

PURPOSE: To demonstrate ultrahigh-speed optical coherence tomography (OCT) imaging of the retina and optic nerve head at 249,000 axial scans per second and a wavelength of 1060 nm. To investigate methods for visualization of the retina, choroid, and optic nerve using high-density sampling enabled by improved imaging speed. METHODS: A swept-source OCT retinal imaging system operating at a speed of 249,000 axial scans per second was developed. Imaging of the retina, choroid, and optic nerve were performed. Display methods such as speckle reduction, slicing along arbitrary planes, en face visualization of reflectance from specific retinal layers, and image compounding were investigated. RESULTS: High-definition and three-dimensional (3D) imaging of the normal retina and optic nerve head were performed. Increased light penetration at 1060 nm enabled improved visualization of the choroid, lamina cribrosa, and sclera. OCT fundus images and 3D visualizations were generated with higher pixel density and less motion artifacts than standard spectral/Fourier domain OCT. En face images enabled visualization of the porous structure of the lamina cribrosa, nerve fiber layer, choroid, photoreceptors, RPE, and capillaries of the inner retina. CONCLUSIONS: Ultrahigh-speed OCT imaging of the retina and optic nerve head at 249,000 axial scans per second is possible. The improvement of approximately 5 to 10x in imaging speed over commercial spectral/Fourier domain OCT technology enables higher density raster scan protocols and improved performance of en face visualization methods. The combination of the longer wavelength and ultrahigh imaging speed enables excellent visualization of the choroid, sclera, and lamina cribrosa.

MRI has long been applied to clinical medical and neurological cases for the structural assessment of tissues as well as their physiological and functional needs and processes. These uses are at a variety of developmental stages in ophthalmology, from common use of clinical structural assessment for neuro-ophthalmology and evaluation of space-occupying lesions to the beginning stages of experimentally measuring functional activation of specific layers within the retina and measurement of physiological oxygen responses. New MRI methodologies, such as the use of orbital coils and Gd-DTPA image enhancement, have been researched, developed, and validated in the eye, opening new possibilities for this technology to enter the clinic. This review aims to summarize the clinical ophthalmological uses of MRI, focusing on the current use of the technology and future applications.

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.

PURPOSE: To determine the relationship between central corneal thickness (CCT) and retinal nerve fiber layer (RNFL) thickness obtained by scanning laser polarimetry (GDx-VCC; Carl Zeiss Meditec, Dublin, California, USA), confocal scanning laser ophthalmoscopy (HRT II; Heidelberg Engineering, Heidelberg, Germany), and optical coherence tomography (Stratus OCT; Carl Zeiss Meditec). DESIGN: Multicenter clinical trial, retrospective cross-sectional study. METHODS: One hundred and nine healthy subjects from the Advanced Imaging in Glaucoma Study were enrolled in this study. All subjects had a standard clinical examination, including visual field (VF) and good-quality scans from all three imaging devices. CCT was measured using an ultrasonic pachymeter. A linear mixed-effects model was used to assess the relationship between RNFL thickness and CCT, accounting for clustering of eyes within subjects, testing site, ethnicity, family history of glaucoma, axial length intraocular pressure, and VF global indices. RESULTS: For OCT and GDx, there was a slight nonstatistically significant positive relationship between CCT and RNFL thickness. For HRT, there was a slight nonstatistically significant negative relationship between CCT and RNFL thickness. Relationships for each device were found to differ between sites. CONCLUSIONS: CCT was not statistically significantly related to RNFL thickness in healthy eyes.