Faculty Bibliography

PURPOSE: This study explored the efficacy of optical coherence tomography (OCT) as a high-resolution, noncontact method for imaging the palisades of Vogt by correlating OCT and confocal microscopy images. METHODS: Human limbal rims were acquired and imaged with OCT and confocal microscopy. The area of the epithelial basement membrane in each of these sets was digitally reconstructed, and the models were compared. RESULTS: OCT identified the palisades within the limbus and exhibited excellent structural correlation with immunostained tissue imaged by confocal microscopy. CONCLUSIONS: OCT successfully identified the limbal palisades of Vogt that constitute the corneal epithelial stem cell niche. These findings offer the exciting potential to characterize the architecture of the palisades in vivo, to harvest stem cells for transplantation more accurately, to track palisade structure for better diagnosis, follow-up and staging of treatment, and to assess and intervene in the progression of stem cell depletion by monitoring changes in the structure of the palisades.

PURPOSE: To isolate and characterize stem cells from human trabecular meshwork (TM) and to investigate the potential of these stem cells to differentiate into TM cells. METHODS: Human trabecular meshwork stem cells (TMSCs) were isolated as side population cells by fluorescence-activated cell sorting or isolated by clonal cultures. Passaged TMSCs were compared with primary TM cells by immunostaining and quantitative RT-PCR. TMSC purity was assessed by flow cytometry and TMSC multipotency was examined by induction of neural cells, adipocytes, keratocytes, or TM cells. Differential gene expression was detected by quantitative RT-PCR, immunostaining, and immunoblotting. TM cell function was evaluated by phagocytic assay using inactivated Staphylococcus aureus bioparticles. RESULTS: Side population and clonal isolated cells expressed stem cell markers ABCG2, Notch1, OCT-3/4, AnkG, and MUC1 but not TM markers AQP1, MGP, CHI3L1, or TIMP3. Passaged TMSCs are a homogeneous population with >95% cells positive to CD73, CD90, CD166, or Bmi1. TMSCs exhibited multipotent ability of differentiation into a variety of cell types with expression of neural markers neurofilament, beta-tubulin III, GFAP; or keratocyte-specific markers keratan sulfate and keratocan; or adipocyte markers ap2 and leptin. TMSC readily differentiated into TM cells with phagocytic function and expression of TM markers AQP1, CHI3L1, and TIMP3. CONCLUSIONS: TMSCs, isolated as side population or as clones, express specific stem cell markers, are homogeneous and multipotent, with the ability to differentiate into phagocytic TM cells. These cells offer a potential for development of a novel stem cell-based therapy for glaucoma.

PURPOSE: Commercial optical coherence tomography (OCT) systems use global signal quality indices to quantify scan quality. Signal quality can vary throughout a scan, contributing to local retinal nerve fibre layer segmentation errors (SegE). The purpose of this study was to develop an automated method, using local scan quality, to predict SegE. METHODS: Good-quality (global signal strength (SS) >/= 6; manufacturer specification) peripapillary circular OCT scans (fast retinal nerve fibre layer scan protocol; Stratus OCT; Carl Zeiss Meditec, Dublin, California, USA) were obtained from 6 healthy, 19 glaucoma-suspect and 43 glaucoma subjects. Scans were grouped based on SegE. Quality index (QI) values were computed for each A-scan using software of our own design. Logistic mixed-effects regression modelling was applied to evaluate SS, global mean and SD of QI, and the probability of SegE. RESULTS: The difference between local mean QI in SegE regions and No-SegE regions was -5.06 (95% CI -6.38 to 3.734) (p<0.001). Using global mean QI, QI SD and their interaction term resulted in the model of best fit (Akaike information criterion=191.8) for predicting SegE. Global mean QI >/= 20 or SS >/= 8 shows little chance for SegE. Once mean QI<20 or SS<8, the probability of SegE increases as QI SD increases. CONCLUSIONS: When combined with a signal quality parameter, the variation of signal quality between A-scans provides significant information about the quality of an OCT scan and can be used as a predictor of segmentation error.

Optical coherence tomography captures a major role in clinical assessment in eye care. Innovative hardware and software improvements in the technology would further enhance its usefulness. In this review, we present several promising initiatives currently in development or early phase of assessment that we expect to have a future impact on optical coherence tomography.

The broadening frontier of technology used in ocular imaging is continuously affecting the landscape of clinical eye care. With each wave of enhanced imaging modalities, the field faces the difficulties of optimally incorporating these devices into the clinic. Ocular imaging devices have been widely incorporated into clinical management after their diagnostic capabilities have been documented in a wide range of ocular disease. In this review, we are presenting the main commercially available devices for imaging of the posterior segment of the eye.

PURPOSE: To investigate the effects of central corneal thickness (CCT)-associated variants on primary open-angle glaucoma (POAG) risk using single nucleotide polymorphisms (SNP) data from the Glaucoma Genes and Environment (GLAUGEN) and National Eye Institute (NEI) Glaucoma Human Genetics Collaboration (NEIGHBOR) consortia. METHODS: A replication analysis of previously reported CCT SNPs was performed in a CCT dataset (n = 1117) and these SNPs were then tested for association with POAG using a larger POAG dataset (n = 6470). Then a CCT genome-wide association study (GWAS) was performed. Top SNPs from this analysis were selected and tested for association with POAG. cDNA libraries from fetal and adult brain and ocular tissue samples were generated and used for candidate gene expression analysis. RESULTS: Association with one of 20 previously published CCT SNPs was replicated: rs12447690, near the ZNF469 gene (P = 0.001; beta = -5.08 mum/allele). None of these SNPs were significantly associated with POAG. In the CCT GWAS, no SNPs reached genome-wide significance. After testing 50 candidate SNPs for association with POAG, one SNP was identified, rs7481514 within the neurotrimin (NTM) gene, that was significantly associated with POAG in a low-tension subset (P = 0.00099; Odds Ratio [OR] = 1.28). Additionally, SNPs in the CNTNAP4 gene showed suggestive association with POAG (top SNP = rs1428758; P = 0.018; OR = 0.84). NTM and CNTNAP4 were shown to be expressed in ocular tissues. CONCLUSIONS: The results suggest previously reported CCT loci are not significantly associated with POAG susceptibility. By performing a quantitative analysis of CCT and a subsequent analysis of POAG, SNPs in two cell adhesion molecules, NTM and CNTNAP4, were identified and may increase POAG susceptibility in a subset of cases.

PURPOSE: We sought to visualize the aqueous outflow system in 3 dimensions (3D) in living human eyes, and to investigate the use of commercially available spectral-domain optical coherence tomographic (SD-OCT) systems for this purpose. DESIGN: Prospective, observational study. PARTICIPANTS: One randomly determined eye in each of 6 normal healthy subjects was included. TESTING: We performed 3D SD-OCT imaging of the aqueous humor outflow structures with 2 devices: The Cirrus HD-OCT and the Bioptigen SDOIS. MAIN OUTCOME MEASURES: We created 3D virtual castings of Schlemm's canal (SC) and more distal outflow structures from scan data from each device. RESULTS: Virtual casting of the SC provided visualization of more aqueous vessels branching from SC than could be located by interrogating the 2-dimensional (2D) image stack. Similarly, virtual casting of distal structures allowed visualization of large and small aqueous outflow channel networks that could not be appreciated with conventional 2D visualization. CONCLUSIONS: The outflow pathways from SC to the superficial vasculature can be identified and tracked in living human eyes using commercially available SD-OCT.

PURPOSE: To describe morphometric details of the human aqueous humor (AH) outflow microvasculature visualized with 360-degree virtual castings during active AH outflow in cadaver eyes and to compare these structures with corrosion casting studies. METHODS: The conventional AH outflow pathways of donor eyes (n = 7) and eyes in vivo (n = 3) were imaged with spectral-domain optical coherence tomography (SD-OCT) and wide-bandwidth superluminescent diode array during active AH outflow. Digital image contrast was adjusted to isolate AH microvasculature, and images were viewed in a 3D viewer. Additional eyes (n = 3) were perfused with mock AH containing fluorescent tracer microspheres to compare microvasculature patterns. RESULTS: Observations revealed components of the conventional outflow pathway from Schlemm's canal (SC) to the superficial intrascleral venous plexus (ISVP). The superficial ISVP in both our study and corrosion casts were composed of interconnected venules (10-50 mum) forming a hexagonal meshwork. Larger radial arcades (50-100 mum) drained the region nearest SC and converged with larger tortuous vessels (>100 mum). A 360-degree virtual casting closely approximated corrosion casting studies. Tracer studies corroborated our findings. Tracer decorated several larger vessels (50-100 mum) extending posteriorly from the limbus in both raw and contrast-enhanced fluorescence images. Smaller tracer-labeled vessels (30-40 mum) were seen branching between larger vessels and exhibited a similar hexagonal network pattern. CONCLUSIONS: SD-OCT is capable of detailed morphometric analysis of the conventional outflow pathway in vivo or ex vivo with details comparable to corrosion casting techniques.

BACKGROUND AND OBJECTIVE: To evaluate the ability of structural assessment to predict glaucomatous visual field progression. PATIENTS AND METHODS: A total of 119 healthy eyes with suspected glaucoma and glaucomatous eyes with 5 or more optic nerve stereophotographs, optical coherence tomography (OCT), and confocal scanning laser ophthalmoscopy (CSLO) all acquired within 6 months of each other were enrolled. Odds ratios to predict progression were determined by generalized estimating equation models. RESULTS: Median follow-up was 4.0 years (range: 1.5 to 5.7 years). Fifteen eyes progressed by glaucoma progression analysis, 20 by visual field index, and 10 by both. Baseline parameters from stereophotographs (vertical cup-to-disc ratio and Disc Damage Likelihood Scale), OCT (global, superior quadrant, and inferior quadrant retinal nerve fiber layer thickness), and CSLO (cup shape measure and mean cup depth) were significant predictors of progression. Comparing the single best parameter from all models, only the OCT superior quadrant RNFL predicted progression. CONCLUSION: Baseline stereophotographs, OCT, and CSLO measurements may be clinically useful to predict glaucomatous visual field progression.

How will the ophthalmologist of the future practice? What will be the effect of government policy? How will this impact the mix of health care providers responsible for the delivery of eye care to patients? What part will health record technology play in clinical practice? These topics were discussed at the Knapp Symposium of the 2011 Annual Meeting of the American Ophthalmological Society. The health care system within which ophthalmology will be practiced will be radically different, ruled by changes in collaboration, communication, and practice guidelines. Given the coming uncertainty of our professional lives, it is vital that we anticipate, contemplate, and plan for our futures.