William Fischer

Race- and sex-related differences in retinal thickness and foveal pit morphology.

PURPOSE To examine sex- and race-associated differences in macular thickness and foveal pit morphology by using spectral-domain optical coherence tomography (SD-OCT). METHODS One hundred eighty eyes of 90 healthy patients (43 women, 47 men) underwent retinal imaging with spectral-domain OCT. The lateral scale of each macular volume scan was corrected for individual differences in axial length by ocular biometry. From these corrected volumes, Early Treatment Diabetic Retinopathy Study (ETDRS) grids of retinal thickness were generated and compared between the groups. Foveal morphology was measured with previously described algorithms. RESULTS Compared with the Caucasians, the Africans and African Americans had reduced central subfield thickness. Central subfield thickness was also reduced in the women compared with the men, although the women also showed significant thinning in parafoveal regions. There was no difference between the sexes in foveal pit morphology; however, the Africans/African Americans had significantly deeper and broader foveal pits than the Caucasians. CONCLUSIONS Previous studies have reported race- and sex-associated differences in macular thickness, and the inference has been that these differences represent similar anatomic features. However, the data on pit morphology collected in the present study reveal an important and significant variation. Between the sexes, the differences are due to global variability in retinal thickness, whereas the variation in thickness observed between the races appears to be driven by differences in foveal pit morphology. These differences have important implications for the use of SD-OCT in detecting and diagnosing retinal disease.

In vivo imaging of retinal pigment epithelium cells in age related macular degeneration.

Morgan and colleagues demonstrated that the RPE cell mosaic can be resolved in the living human eye non-invasively by imaging the short-wavelength autofluorescence using an adaptive optics (AO) ophthalmoscope. This method, based on the assumption that all subjects have the same longitudinal chromatic aberration (LCA) correction, has proved difficult to use in diseased eyes, and in particular those affected by age-related macular degeneration (AMD). In this work, we improve Morgans method by accounting for chromatic aberration variations by optimizing the confocal aperture axial and transverse placement through an automated iterative maximization of image intensity. The increase in image intensity after algorithmic aperture placement varied depending upon patient and aperture position prior to optimization but increases as large as a factor of 10 were observed. When using a confocal aperture of 3.4 Airy disks in diameter, images were obtained using retinal radiant exposures of less than 2.44 J/cm(2), which is ~22 times below the current ANSI maximum permissible exposure. RPE cell morphologies that were strikingly similar to those seen in postmortem histological studies were observed in AMD eyes, even in areas where the pattern of fluorescence appeared normal in commercial fundus autofluorescence (FAF) images. This new method can be used to study RPE morphology in AMD and other diseases, providing a powerful tool for understanding disease pathogenesis and progression, and offering a new means to assess the efficacy of treatments designed to restore RPE health.

Imaging individual neurons in the retinal ganglion cell layer of the living eye

Significance Retinal ganglion cells are the primary output neurons of the retina that process visual information and transmit it to the brain. We developed a method to reveal these cells in the living eye that does not require the fluorescent labels or high light levels that characterize more invasive methods. The death of these cells causes vision loss in glaucoma, the second leading cause of blindness worldwide. The ability to image these cells in the living eye could accelerate our understanding of their role in normal vision and provide a diagnostic tool for evaluating new therapies for retinal disease. Although imaging of the living retina with adaptive optics scanning light ophthalmoscopy (AOSLO) provides microscopic access to individual cells, such as photoreceptors, retinal pigment epithelial cells, and blood cells in the retinal vasculature, other important cell classes, such as retinal ganglion cells, have proven much more challenging to image. The near transparency of inner retinal cells is advantageous for vision, as light must pass through them to reach the photoreceptors, but it has prevented them from being directly imaged in vivo. Here we show that the individual somas of neurons within the retinal ganglion cell (RGC) layer can be imaged with a modification of confocal AOSLO, in both monkeys and humans. Human images of RGC layer neurons did not match the quality of monkey images for several reasons, including safety concerns that limited the light levels permissible for human imaging. We also show that the same technique applied to the photoreceptor layer can resolve ambiguity about cone survival in age-related macular degeneration. The capability to noninvasively image RGC layer neurons in the living eye may one day allow for a better understanding of diseases, such as glaucoma, and accelerate the development of therapeutic strategies that aim to protect these cells. This method may also prove useful for imaging other structures, such as neurons in the brain.

Photographic Reading Center of the Idiopathic Intracranial Hypertension Treatment Trial (IIHTT): Methods and Baseline Results.

PURPOSE To describe the methods used by the Photographic Reading Center (PRC) of the Idiopathic Intracranial Hypertension Treatment Trial (IIHTT) and to report baseline assessments of papilledema severity in participants. METHODS Stereoscopic digital images centered on the optic disc and the macula were collected using certified personnel and photographic equipment. Certification of the camera system included standardization and calibration using a model eye. Lay readers assessed disc photos of all eyes using the Frisén grade and performed quantitative measurements of papilledema. Frisén grades by PRC were compared with site investigator clinical grades. Spearman rank correlations were used to quantify associations among disc features and selected clinical variables. RESULTS Frisén grades according to the PRC and site investigators grades, matched exactly in 48% of the study eyes and 42% of the fellow eyes and within one grade in 94% of the study eyes and 92% of the fellow eyes. Frisén grade was strongly correlated (r > 0.65, P < 0.0001) with quantitative measures of disc area. Cerebrospinal fluid pressure was weakly associated with Frisén grade and disc area determinations (r ≤ 0.31). Neither Frisén grade nor any fundus feature was associated with perimetric mean deviation. CONCLUSIONS In a prospective clinical trial, lay readers agreed reasonably well with physicians in assessing Frisén grade. Standardization of camera systems enhanced consistency of photographic quality across study sites. Images were affected more by sensors with poor dynamic range than by poor resolution. Frisén grade is highly correlated with quantitative assessment of disc area. (ClinicalTrials.gov number, NCT01003639.).

Long-Term Reduction in Infrared Autofluorescence Caused by Infrared Light Below the Maximum Permissible Exposure

PURPOSE Many retinal imaging instruments use infrared wavelengths to reduce the risk of light damage. However, we have discovered that exposure to infrared illumination causes a long-lasting reduction in infrared autofluorescence (IRAF). We have characterized the dependence of this effect on radiant exposure and investigated its origin. METHODS A scanning laser ophthalmoscope was used to obtain IRAF images from two macaques before and after exposure to 790-nm light (15-450 J/cm(2)). Exposures were performed with either raster-scanning or uniform illumination. Infrared autofluorescence images also were obtained in two humans exposed to 790-nm light in a separate study. Humans were assessed with direct ophthalmoscopy, Goldmann visual fields, multifocal ERG, and photopic microperimetry to determine whether these measures revealed any effects in the exposed locations. RESULTS A significant decrease in IRAF after exposure to infrared light was seen in both monkeys and humans. In monkeys, the magnitude of this reduction increased with retinal radiant exposure. Partial recovery was seen at 1 month, with full recovery within 21 months. Consistent with a photochemical origin, IRAF decreases caused by either raster-scanning or uniform illumination were not significantly different. We were unable to detect any effect of the light exposure with any measure other than IRAF imaging. We cannot exclude the possibility that changes could be detected with more sensitive tests or longer follow-up. CONCLUSIONS This long-lasting effect of infrared illumination in both humans and monkeys occurs at exposure levels four to five times below current safety limits. The photochemical basis for this phenomenon remains unknown.

Safety assessment in macaques of light exposures for functional two-photon ophthalmoscopy in humans

Two-photon ophthalmoscopy has potential for in vivo assessment of function of normal and diseased retina. However, light safety of the sub-100 fs laser typically used is a major concern and safety standards are not well established. To test the feasibility of safe in vivo two-photon excitation fluorescence (TPEF) imaging of photoreceptors in humans, we examined the effects of ultrashort pulsed light and the required light levels with a variety of clinical and high resolution imaging methods in macaques. The only measure that revealed a significant effect due to exposure to pulsed light within existing safety standards was infrared autofluorescence (IRAF) intensity. No other structural or functional alterations were detected by other imaging techniques for any of the exposures. Photoreceptors and retinal pigment epithelium appeared normal in adaptive optics images. No effect of repeated exposures on TPEF time course was detected, suggesting that visual cycle function was maintained. If IRAF reduction is hazardous, it is the only hurdle to applying two-photon retinal imaging in humans. To date, no harmful effects of IRAF reduction have been detected.

AMYLOID AS A BIOMARKER OF ALZHEIMER'S DISEASE IN POST-MORTEM RETINAS IN HUMAN AND DOG MODELS OF ALZHEIMER'S DISEASE

O3-12-05 AMYLOID AS A BIOMARKER OFALZHEIMER’S DISEASE IN POST-MORTEM RETINAS IN HUMAN AND DOG MODELS OFALZHEIMER’S DISEASE Melanie C. W. Campbell, Marsha L. Kisilak, David DeVries, Chris Cookson, Michael Hamel, Theodore Chow, Jennifer J. Hunter, Melissa Brooks, Jennifer Strazzeri, William Fischer, Lewis DiVincenti, Joseph A. Araujo, Ian Mackenzie, Chongzhao Ran, Laura Emptage, University of Waterloo, Waterloo, ON, Canada; University of Rochester, Rochester, NY, USA; 3 Vivocore Inc, Toronto, ON, Canada; 4 Intervivo Solutions, Toronto, ON, Canada; 5 University of British Columbia, Vancouver, BC, Canada; Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA. Contact e-mail: mcampbel@uwaterloo. ca