Asymmetrical Vertical Phorias in Normal Subjects: The Influence of Unbalanced Illumination

Purpose: One goal of this investigation was to determine whether asymmetrical vertical hetereophorias, which are qualitatively similar to a dissociated vertical deviation (DVD), occur commonly in normal people. A second goal was to establish whether the magnitude or direction of vertical phoria depends on the illumination of the occluded eye, as would be expected if vertical eye position were influenced by a dorsal light reflex. Methods: Vertical phorias were estimated in 30 normal subjects using a Maddox rod in conjunction with a dark and an illuminated occluder. Results: On average, subjects exhibited a hypophoria of less than 1 min arc with both the dark and the illuminated occluder. Asymmetrical vertical phorias that were consistent with previously published criteria for a minute DVD were found in eight subjects when a dark occluder was used and in four subjects when an illuminated occluder was used. The proportions of subjects whose vertical phorias were consistent with a DVD did not differ significantly under the two conditions of occlusion. Conclusions: Asymmetrical vertical phorias that mimic a minute DVD do not occur commonly in normal people. Our finding that vertical phorias do not change systematically when an illuminated instead of a dark occluder is used suggests that normal subjects exhibit little or no vestige of the dorsal light reflex.