Glaucoma is the second leading cause of blindness worldwide after cataract. Retinal nerve fiber layer thickness (RNFLT), phase retardation, and birefringence measured by Polarization Sensitive Optical Coherence Tomography (PS-OCT) have been used for glaucoma diagnosis. We first investigated two different image registration algorithms, a mutual information (MI) based algorithm and a log-polar transform cross-correlation (LPCC) based algorithm, on both human and non-human primate models. We evaluated the effects of image registration on longitudinal analysis of RNFLT in non-human primates using PS-OCT. Then, we investigated thickness, phase retardation, birefringence, and reflectance of the retinal nerve fiber layer as measured by PS-OCT in normal and glaucomatous non-human primates in a longitudinal study. We defined a new Reflectance Index (RI) and demonstrated that it might be an earlier indicator of glaucoma onset than RNFLT, phase retardation, or birefringence. Finally, we validated this finding on cross-sectional clinical study on human eyes measured by PS-OCT and RTVue OCT. For the data measured by PS-OCT, we showed that for distinguishing between glaucomatous and healthy eyes, as well as for distinguishing between glaucoma suspect and healthy eyes, our new normalized RNFL reflectance index (NRRI) performs significantly better than phase retardation and birefringence. The performances of NRRI and RNFL thickness in both conditions were statistically indistinguishable in this study, which is likely due to the limited sample size. For the data measured by RTVue OCT, the performances of NRRI and RNFL thickness were statistically indistinguishable for distinguishing between glaucomatous and healthy eyes. NRRI performs significantly better than RNFL thickness for distinguishing between glaucoma suspect and healthy eyes. NRRI also performs significantly better than temporal, superior, nasal, inferior and temporal (TSNIT) average and nerve fiber indicator (NFI) from GDx VCC for distinguishing between glaucoma suspect and healthy eyes. NRRI is a promising parameter for distinguishing glaucoma suspect and healthy eyes and may indicate disease in the pre-perimetric stage. / text

Yes / To introduce and evaluate the performance in detecting glaucomatous abnormalities of a novel method for extracting en face slab images (SMAS), which considers varying individual anatomy and configuration of retinal nerve fiber bundles. Dense central retinal spectral domain optical coherence tomography scans were acquired in 16 participants with glaucoma and 19 age-similar controls. Slab images were generated by averaging reflectivity over different depths below the inner limiting membrane according to several methods. SMAS considered multiple 16 µm thick slabs from 8 to 116 µm below the inner limiting membrane, whereas 5 alternative methods considered single summary slabs of various thicknesses and depths. Superpixels in eyes with glaucoma were considered abnormal if below the first percentile of distributions fitted to control data for each method. The ability to detect glaucoma defects was measured by the proportion of abnormal superpixels. Proportion of superpixels below the fitted first percentile in controls was used as a surrogate false-positive rate. The effects of slab methods on performance measures were evaluated with linear mixed models. The ability to detect glaucoma defects varied between slab methods, χ2(5) = 120.9, P

Yes / To assess how objectively-detected defects of retinal nerve fibre bundle (RNFB) reflectance in en face OCT images relate to circumpapillary retinal nerve fibre layer thickness (cpRNFLT) and visual field defects. Cross-sectional study. 16 participants with early-glaucoma and 29 age-similar healthy controls, among which 22 had usable en face images to establish normative levels of RNFB reflectance. All participants underwent cpRNFLT scans, visual field examination and wide-field OCT. En face reflectivity was assessed objectively using the Summary of Multiple Anatomically-Adjusted Slabs (SMAS) method. En face defects were deemed concordant with cpRNFLT when they had at least one cpRNFLT point with p

Glaucoma is an ophthalmic pathology that is the second leading cause of blindness. The laboratory design of a Polarization Sensitive Spectral Domain Optical Coherence Tomographic System aims to detect early glaucoma symptoms and prevent vision loss that occurs due to late or no glaucoma diagnosis. In order to perform human clinical trials at partner hospitals across the country, a miniaturized and portable version of the laboratory system was developed. The system facilitates easy transportation and clinical testing of the otherwise voluminous laboratory system across different eye centers. Significant consideration was given for performance optimization, cost reduction, design improvements and providing a friendly user-patient interface. / text

Optical Coherence Tomography (OCT) is a non-invasive three-dimensional imaging technique. OCT synthesizes a cross-sectional image from a series of lateral adjacent depth scans, and with a two-dimensional scanning scheme, three-dimensional intensity image of sample can be constructed. Due to its non-invasive capability, OCT has been widely applied in ophthalmology, cardiology and dermatology; and in addition to three-dimensional intensity image construction, various functional OCT imaging techniques have been developed for clinical application. My research is focused on developing functional OCT systems for application in ophthalmology, including polarization-sensitive optical coherence tomography (PS-OCT) for retinal nerve fiber layer (RNFL) birefringence measurement and dual-wavelength photothermal optical coherence tomography (DWP-OCT) for microvasculature blood oxygen saturation (SO2) measurement. In the study, a single-mode-fiber based polarization-sensitive swept-source OCT (PS-SS-OCT) with polarization modulator, polarization-sensitive bulk-optics balanced detection module is constructed and polarization processing methods based on Stokes vectors are applied to determine birefringence. PS-OCT is able to provide human subject's RNFL thickness, phase retardation, and birefringence information. Degradation in the degree of polarization (DOP) along depth is investigated and its difference between four quadrants of RNFL (superior, temporal, inferior and nasal) indicates the structural property difference. DWP-OCT is a novel functional OCT system consisting of a phase-sensitive optical coherence tomography system (PhS-OCT) and two photothermal excitation lasers. PhS-OCT is based on a swept-source laser operating in the 1060 nm wavelength range; the two photothermal excitation lasers with wavelength 770 nm and 800 nm are intensity modulated at different frequencies. PhS-OCT probe beam and two photothermal excitation beams are combined and incident on the sample, optical pathlength (op) change on the sample introduced by two photothermal excitation beams are measured and used for blood SO2 estimation. A polarization microscope is proposed for future study. The polarization microscope is an imaging technique providing molecular structure and orientation based on probe light's polarization state information. The polarization microscope uses a wavelength tunable light source, and can achieve any incident polarization state by a retarder-rotator combination. Specimen's birefringence can be determined based on the changing of detected light amplitude. / text

An Enhanced Polarization-Sensitive Swept Source Optical Coherence Tomography (EPS-SS-OCT) instrument for high sensitivity cross-sectional imaging of Retinal Nerve Fiber Layer (RNFL) has been designed, constructed, and verified. The instrument is capable of measuring the thickness and birefringence of the RNFL. Birefringence change of the RNFL could serve as an early indicator of glaucoma. The associated image processing methods for completely automated, time efficient algorithm to segment the RNFL in images of the human retina recorded by the EPS-SS-OCT. Detected RNFL boundaries are used to compute peripapillary thickness maps. Numerical algorithms to compute the birefringence of the detected RNFL layer are presented along with the associated phase retardation and birefringence peripapillary maps. Glaucoma affects the vitality of retinal ganglion cell axons in the retinal nerve fiber layer (RNFL) and may be clinically detected through a change in RNFL birefringence. Comprehensive peripapillary maps of healthy and glaucoma suspect human RNFL birefringence were constructed using EPS-SS-OCT. Presence of macrophages is a hallmark of several retinal diseases such as drusen and age related macular degeneration. Application of photothermal Optical Coherence Tomography (OCT) to detect macrophages in ex vivo arteries which have engulfed nanoclusters of gold coated iron oxide (nanorose) is reported. Nanorose engulfed by macrophages in arteries absorb incident laser (800nm) energy and cause optical pathlength (OP) variation which is measured using photothermal OCT. OP variation in polydimethyl siloxane tissue phantoms containing varying concentrations of nanorose match values predicted from nanoparticle and material properties. Measurement of OP variation in arteries in response to laser excitation provides an estimate of nanorose concentration in arteries 2.5x109 particles/ml. OP variation in nanoparticle containing artery sections and tissue phantoms taking up nanorose has a different magnitude and profile from that observed in control aorta and phantoms without macrophages and is consistent with macrophage presence as identified with RAM-11 histology staining. Our results suggest that tissue regions with macrophages taking up nanorose can be detected using photothermal OCT. / text

Abstract This study was carried out to investigate in vivo the changes of the human lens autofluorescence (AF) with aging and cataractogenesis. Measurements were performed in the blue-green AF range (495 nm/520 nm) using a fluorometer designed, built and now clinically tested in our department. 43 random eyes of 43 healthy volunteers aged 6-86 years, five of each decade, were studied for effects of aging and 84 eyes of 84 patients with cortical, nuclear, posterior subcapsular or mixed lens opacities were studied for differences of various cataract types. The results were compared with the back light scatter values obtained by the commercially available Interzeag Lens Opacity Meter 701. Also AF and back light scatter of the lens were measured from 122 smoking males aged 57 to 76 years who participated in a cancer prevention study. The results were compared with the widely used subjective lens opacities classification system, LOCS III. In addition data was collected from 30 randomly chosen eyes of as many subjects with varying degrees of yellow-brown lens coloration in an otherwise healthy eye. We studied the influence of lens yellowing expressed by means of lens AF on visibility of retinal nerve fiber layer in black-and-white images. Lens AF profile consists of anterior and posterior peaks and a central plateau. The height of the anterior peak was used as a measure of the maximum AF value. The square root of the ratio between the posterior and the anterior AF peaks was used for estimating the lens transmission. Our technique was highly reproducible. The coefficient of variation was 3.9% for maximum AF and 2.9% for the lens transmission index. Both the maximum AF and light scatter were exponentially increased with age (r = 0.95 and 0.94, respectively; p < 0.0001). According to the regression line of AF begins to increase in early childhood. It appears by extrapolation to be absent at birth. In contrast light scatter in the lens was present even in young children. The lens transmission for blue-green light, determined from the lens AF curve, was almost unchanging with age up to 60 years. Thereafter it decreased rapidly and the interindividual variation increased.In cataractous lenses the mean AF and scatter values differed statistically significantly from those of age matched healthy controls. The highest AF values were measured in nuclear cataracts where AF was also related to visual acuity and an increasing yellow-brown colour of the nucleus. About half of the total variation of the transmission index values could be accounted for by changes in nuclear colour as assessed by the LOCS III grading system. The transmission index provided a more precise prediction about nuclear colour and opalescence than age or light scatter did. In cortical cataracts the AF curve was low and flattened and the maximum AF value was significantly lower than in the age matched control eyes. The highest light scatter values were measured from cortical cataracts, but the correlation between LOCS III cortical grades and light scatter values was rather weak. Posterior subcapsular cataracts cannot be quantified either with AF or with light scatter measurements. Lens yellowing, expressed as lens AF, had an actual effect on retinal nerve fiber layer visibility. AF measurements provided a better prediction about the visibility score than age or visual acuity did. The results of the present study indicate that the lens autofluorescence measurement may be a useful additional tool together with a subjective grading system in the follow-up of optical changes occurring in the nuclear region of the lens.

No / Purpose: To develop a perimetric test strategy, Structure Estimation of Minimum Uncertainty (SEMU), that uses structural information to drive stimulus choices. Methods: Structure Estimation of Minimum Uncertainty uses retinal nerve fiber layer (RNFL) thickness data as measured by optical coherence tomography to predict perimetric sensitivity. This prediction is used to set suprathreshold levels that then alter a prior probability distribution of the final test output. Using computer simulation, we studied SEMU’s performance under three different patient error response conditions: No Error, Typical False Positive errors, and Extremely Unreliable patients. In experiment 1, SEMU was compared with an existing suprathreshold cum thresholding combination test procedure, Estimation of Minimum Uncertainty (EMU), on single visual field locations. We used these results to finalize SEMU parameters. In experiment 2, SEMU was compared with full threshold (FT) on 163 glaucomatous visual fields. Results: On individual locations, SEMU has similar accuracy to EMU, but is, on average, one presentation faster than EMU. For the typical false-positive error condition, SEMU has significantly lower error compared with FT (SEMU average 0.33 dB lower; p < 0.001) and the 90% measured sensitivity range for SEMU is also smaller than that for FT. For unreliable patients, however, FT has lower mean and SD of error. Structure Estimation of Minimum Uncertainty makes significantly fewer presentations than FT (1.08 presentation on average fewer in a typical false-positive condition; p < 0.001). Assuming that a location in the field is marked abnormal if it falls below the 5th percentile of normal, SEMU has a false-positive rate of less than 10% for all error conditions compared with FT’s rate of 20% or more. Conclusions: On average, simulations show that using RNFL information to guide stimulus placement in a perimetric test procedure maintains accuracy, improves precision, and decreases test duration for patients with less than 15% false-positive rates.

Glaucoma is the second leading cause of blindness in the world. The disease is characterized by irreversible damage to retinal ganglion cells. Once glaucoma is detected, further vision loss can be prevented by pharmacological or surgical treatment. However, current diagnostic methods lack the necessary sensitivity and up to 40% of vision maybe irreversibly lost before detection occurs. A Swept Source Polarization-Sensitive Optical Coherence Tomography (SS-PSOCT) instrument for high sensitivity cross-sectional imaging of optical anisotropy in turbid media has been designed, constructed, and verified. A multiple-state nonlinear fitting algorithm was used to measure birefringence of the retinal nerve fiber layer with less than 1%± average uncertainty. To perform eye imaging efficiently a slit-lamp based interface for the SS-PSOCT instrument with a Line Scanning Laser Ophthalmoscope (LSLO) was used. This interface allowed for repeatable, stable, and registered measurements of the retina. A fixation target was used to stabilize the volunteer’s eye and image desired areas of the retina. The LSLO allowed for an optimization of the location of OCT scans on the retina and provided a fundus blood vessel signature for registration between different imaging sessions. The SS-PSOCT system was used to measure depth-resolved thickness, birefringence, phase retardation and optic axis orientation of the retinal nerve fiber layer in normal volunteers. The peripapillary area around the optic nerve head (ONH) is most sensitive to glaucoma changes and hence data was acquired as concentric ring scans about the ONH with increasing diameters from 2mm to 5mm. Imaging of normal patients showed that higher values of phase retardation occurred superior and inferior to the optic nerve head especially next to blood vessels and thicker parts of the retinal nerve fiber layer. / text

PURPOSE. Confocal laser scanning ophthalmoscopy (HRT; Heidelberg retinal tomograph II) and scanning laser polarimetry (GDx-variable corneal compensator [VCC]) were used to investigate whether early indicators of retinal nerve fiber layer (RNFL) thickness loss could be observed in patients infected with the human immunodeficiency virus (HIV) that had no associated retinopathy or optic neuropathy and were concomitantly receiving antiretroviral medications. METHODS. HRT and GDx-VCC parameters obtained from a group of 13 HIV-positive subjects (n = 26 eyes) on antiretroviral therapy examined with HRT, with a subgroup of six subjects (n = 12 eyes) examined with both HRT and GDx-VCC, were compared with those of a matched HIV-negative control cohort (13 subjects, n = 26 eyes) examined with HRT, with a subgroup of five subjects (n = 10 eyes) examined with both HRT and GDx-VCC. We employed generalized estimating equations for statistical analysis. RESULTS. Reduced mean values for the HRT height variation contour (p < 0.045) and HRT mean RNFL thickness (p < 0.023) were observed in HIV-positive subjects controlling for age, sex, and race. A significantly reduced mean value corresponding to the GDx-VCC superior maximum (p < 0.014) and inferior maximum (p < 0.016) were also observed for the HIV-positive cohort analyzed controlling for age, sex, and race. CONCLUSION. HRT and GDx-VCC indicators of RNFL thickness appear to be significantly reduced in HIV-positive subjects without retinopathy or optic nerve disease using antiretroviral medication, suggesting RNFL loss occurs in this population of HIV-positive patients. The lack of correlation between CD4 counts, viral load, number of antiretroviral medications used, or years from diagnosis of HIV and RNFL thinning, suggests that possibly other factors associated with HIV infection may contribute to the apparent RNFL thickness loss.