Foveal threshold elevations associated with age-related drusen

Age-related macular degeneration (AMD) is the leading cause of severe vision loss in the U.S. population over the age of 60. Drusen are the hallmark of AMD. At present, there is no reliable indicator of which patients with drusen are at risk of developing vision loss from AMD. Earlier studies indicate that foveal threshold are elevated in patients with drusen. Dark-adapted thresholds were measured at fixation and at 30 deg in the temporal visual field in 49 normal subjects under the age of 50 years and in 40 elderly patients with good visual acuity and no pathology other than clinically significant drusen in the eye studied. The mean foveal threshold for the drusen patients was 0.77 log unit greater than the mean foveal threshold for the younger normal subjects. The variance on the foveal threshold distribution for the drusen patients was significantly greater than the variance on the foveal threshold distribution for the younger normal subjects. At 30 deg temporal field there was no significant difference between the means or variances of threshold distributions for the drusen patients and for the younger normal subjects. There is no significant correlation between log foveal absolute thresholds and log visual acuity. There is only a weak rank-order correlation between log foveal threshold rank and rank of drusen severity (r' = 0.35). There was a nonsignificant trend for foveal thresholds to be higher in patients who had exudative maculopathy in the fellow eye. These patients are at higher risk of developing vision loss than are patients who have drusen only in both eyes. The results suggest that there may be a subgroup of patients with only drusen who have abnormally high foveal thresholds, possibly due to early macular pathology not evident on clinical examination.