Orientation Discrimination with Macular Changes Associated with Early AMD

Abstract

Age-related macular degeneration (AMD) is a condition that progressively reduces central vision in elderly individuals, resulting in a reduced capacity to perform many daily activities and a diminished quality of life. Recent studies identified clinical treatments that can slow or reverse the progression of exudative (wet) AMD and ongoing research is evaluating earlier interventions. Because early diagnosis is critical for an optimal outcome, the goal of this study is to assess psychophysical orientation discrimination for randomly positioned short line segments as a potential indicator of subtle macular changes in eyes with early AMD. Orientation discrimination was measured in a sample of 74 eyes of patients aged 47 to 82 years old, none of which had intermediate or advanced AMD. Amsler-grid testing was performed as well. A masked examiner graded each eye as level 0, 1, 2, or 3 on a streamlined version of the Age-Related Eye Disease Study (AREDS) scale for AMD, based on the presence and extent of macular drusen or retinal pigment epithelium (RPE) changes. Visual acuity in the 74 eyes ranged from 20/15 to 20/40, with no significant differences among the grading levels. Humphrey 10-2 and Nidek MP-1 micro-perimetry were used to assess retinal sensitivity at test locations 1 degrees from the locus of fixation. Average orientation-discrimination thresholds increased systematically from 7.4 degrees to 11.3 degrees according to the level of macular changes. In contrast, only 3 of 74 eyes exhibited abnormalities on the Amsler grid and central-field perimetric defects occurred with approximately equal probability at all grading levels. In contrast to Amsler grid and central-visual-field testing, psychophysical orientation discrimination has the capability to distinguish between eyes with and without subtle age-related macular changes.