Sensitive, noninvasive and objective detection of glaucomatous damage based on the assessment of ganglion cell atrophy with the scanning retinal thickness analyzer

Introduction: We have developed a method, the scanning Retinal Thickness Analyzer (RTA), to scan rapidly the posterior pole and generate a detailed map of the retinal thickness. The scanning RTA was applied in a pilot group of glaucoma patients to assess whether the method can be advantageous in the detection and diagnosis of glaucomatous damage. Methods: A scanning laser slit is projected on the retina, the image of the intersection with the two retinal boundaries is digitally recorded and an operator-free algorithm analyzes the images to generate a map of the retinal thickness. A commercial prototype (Talia - OcuMetrics) was used to scan 15 eyes of 10 glaucoma patients with clear media. The differences between the central posterior pole retinal thickness maps obtained in the glaucoma patients and the composite map of healthy subjects were calculated. The 90 percentile thickness losses in each of four quadrants of the central 20° concentric to the fovea were compared to the mean dB loss in the corresponding visual field region. Results: For mean visual field losses of >15dB, 5 to 15 dB and <5dB, the tissue losses were 85μm (max=130μm), 79μm and 51μm, respectively (the standard deviation for healthy subjects was ±22μm). The topography of the losses will be presented. Conclusion: The large loss of neuronal retina at the posterior pole is mainly due to atrophy of ganglion cells which are abundant in this region and partly to losses in nerve fibers. The scanning RTA promises to be a sensitive and objective tool for the early diagnosis of glaucomatous ganglion cells loss and for the assessment of treatment because a) a loss in retinal thickness as small as 44μm is beyond normal values with a 97.5% confidence, and b) severe glaucomatous damage is accompanied by a loss of up to 130μm.