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J. M. Gallardo, K. Holopigian, S. Hornik, V. Greenstein; Occluder Density and Visual Field Sensitivity in Control Subjects and Patients With Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2892.
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Standard visual testing procedures require occlusion of the untested eye. Typically, opaque occluders are used in clinical settings. However, there is conflicting information in the literature as to the effects of occluder density on visual function of control subjects. Fuhr, et al  compared performance with a translucent occluder to a standard black occluder and reported that subjects experienced less "blankout" and had small but significant (0.7 db) increases in Humphrey visual field (HVF) sensitivity with the translucent occluder. However, Sreenivasan, et al  found that opaque occluders could prevent visual field lens artifacts created by frosted cylindrical lenses. We examined the effects of occluder density on HVF performance in control subjects and patients with retinitis pigmentosa (RP).
Seven control subjects (mean age 46.6 + 17.3) with normal visual acuity and normal HVF sensitivity and seven patients with RP (mean age 43.7 + 7.7) with visual acuity of 20/160 or better and decreased HVF sensitivity participated in this study. Visual sensitivity at the fovea and at eight locations with a radius of 5 degrees around the fovea was measured with the HVF using a modified threshold program. For all subjects the right eye was tested; the left eye was occluded but remained open. Two occluders were used: a standard black occluder, which reduced retinal illumination by 3.1 log units and a white occluder, which reduced illumination by 0.77 log units. Testing order was counterbalanced (ABBA).
For each subject, the results for each occluder were averaged. For the control subjects, there was a significant difference between the occluders. Foveal sensitivities were 1.86 dB higher for the translucent occluder than for the opaque one (Wilcoxon matched-pairs signed rank test, p = 0.031). When the results for all the points were included, the effect was smaller (0.43 dB) but still significant (signed rank test, p = 0.047). For the patients, there was no significant difference in sensitivity when all the points were included (difference = 0.13 dB, p = 0.438) but there was a significant difference for the fovea (difference = 1.93 dB, p = 0.031).
Foveal sensitivity was decreased for the black compared to the white occluder for both the control subjects and the patients with RP. These results have implications for studies using the HVF to evaluate the effects of therapeutic interventions, particularly for patients with ocular diseases such as RP who have decreased visual field sensitivity.1. Fuhr, et al., 1990, Arch. Ophthal, 983-82. Sreenivasan, et al., Clin. & Exp. Opt, 26-9
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