ABSTRACT
INTRODUCTION: The effect of the unequal visual inputs in uniocular cataracts is addressed through the hypothesis that a marked inequality of the visual inputs will have an interference effect that will degrade the binocular vision relative to that of the better eye. We tested this hypothesis of reverse interference effect by both clinical and functional Magnetic Resonance Imaging assessments in an acute unilateral cataract patient. The patient was 63 year old woman who rapidly developed a dense sub-capsular cataract following steroid radio-chemotherapy treatment for breast cancer. METHODS: Clinical: Ophthalmologic evaluation and distance visual acuity (both uniocular and binocular), contrast sensitivity, binocular function, ocular motility and cover test to evaluate the presence of strabismus, and a slit lamp assessment of cataract density were performed. Neuroimaging: Functional MRI was run in a 1.5T Philips Intera Master with a SENSE neurovascular coil of 8 channels. The experimental design included three conditions: a) Binocular: both eyes viewing; b) OS-mono: left eye viewing, right eye occluded by a black cover; c) OD-mono: right eye viewing, left eye occluded by a black cover. RESULTS: Clinical: The logMAR visual acuity was 0.9 OD, hand movement at one meter OS, and 0.7 for binocular viewing, that is, the binocular acuity was worse than the better eye acuity alone. As hypothesized, adding a diffuser lens and a penlight glare on the cataract eye increased the interference signal from that eye, and thus further reduced the binocular acuity to 0.4. Binocular contrast sensitivity also was worse than the OD alone. Neuroimaging: The fMRI results were consistent with the clinical findings. The number of activated voxels in the visual cortex under binocular viewing was reduced by about 40 percent relative to that for the fellow eye alone. CONCLUSION: Clinical and fMRI data were well-correlated and consistent with the prediction for the marked binocular asymmetry. The results imply that the mechanisms operating under a severe binocular vision asymmetry caused by unilateral diffusion (blur without contour perception, or light perception only) exhibit an interference effect under binocular viewing that is not seen in the case of weaker asymmetry such as in functional amblyopia, or from the extreme case of total elimination of visual input from one eye, such as in occlusion or monocular blindness.
