Take Caution of Normal Visual Acuity in Posterior Cortical Atrophy!

Abstract

Higher-order visual symptoms of patients with posterior cortical atrophy (PCA) are not well recognized in routine ophthalmological examination. More specifically, vision as assessed by the Snellen or Monoyer chart may not be sensitive enough. We hypothesized increased visual difficulties related to 1) visual crowding and to 2) short distances/larger stimuli. We therefore aimed at comparing 1) far visual acuity measures using the Monoyer (each line is presented separately) and the ETDRS charts (all lines are presented at the same time), as well as 2) far and closer visual acuity using the ETDRS chart (at 4 and at 2 meters). These tests were performed in a group of patients with PCA (PCA-AD) and a group of typical amnesic form (T-AD as a control group) of Alzheimer disease (AD) without any ophthalmologic pathology. While the Monoyer chart did not allow to distinguish between the two groups, the PCA-AD group specifically displayed a decrease of visual acuity when the ETDRS chart, rather than the Monoyer chart, was tested at 4 meters (effect of visual crowding), and another decrease when the ETDRS chart was tested at 2 meters, rather than at 4 meters (effect of stimulus size/distance). This uncommon decrease of visual acuity with closer distance correlated with a score of higher-order visual symptoms (Q-ACP). The present study incites ophthalmologists to pay attention to the possible discrepancy between different conditions of visual acuity assessment and preconizes to combine these conditions for a better evaluation.