Psychophysical investigation of ganglion cell loss in early glaucoma

Purpose: To evaluate ganglion cell loss in early glaucoma using a variety of psychophysical tests and to identify optimal perimetric technique(s) for detection of early glaucomatous visual function loss. Methods: Five perimetric tests. short wavelength automated perimetry (SWAP), temporal modulation perimetry (TMP), frequency doubling technology perimetry (FDT). detection acuity perimetry (DAP), and resolution acuity perimetry (RAP) were compared in their ability to discriminate between normal individuals and patients with early glaucoma or glaucoma Suspects. Comparisons were also made by their ability to produce repeatable defects. The tests examined different visual functions that are likely to be mediated by different retinal ganglion cell subpopulations.. thereby permitting examination of hypotheses of ganglion cell death in early glaucoma. Results: All visual field tests demonstrated high performance in separating glaucoma patients from normal individuals. SWAP, TMP. FDT, and DAP provided the greatest discrimination between normal individuals and high- and low-risk glaucoma Suspects. However, SWAP, TMP. and FDT obtained better consistency across the various analysis approaches (global indices and pointwise) than DAP and RAP Of all the test types, FDT exhibited the highest proportion of repeatable abnormal test locations, with poor confirmation rates achieved by DAP and RAP. Conclusion: The performance of SWAP FDT, and TMP suggests that these test types may all be suitable for detection of early loss of visual function in glaucoma. Ganglion cell subpopulations with lower levels of redundancy and/or those with larger cell sizes offer the most parsimonious explanation for earliest ganglion cell losses occurring in glaucoma.