Abstract
To determine the relationships among equivalent intrinsic noise (Neq), sampling efficiency, and contrast sensitivity (CS) in patients with retinitis pigmentosa (RP), where Neq is an estimate of the amount of noise within the visual pathway and sampling efficiency represents the subject's ability to use stimulus information optimally. Participants included 10 patients with RP aged 10 to 54 years, who had visual acuities of 20/40 or better, and 10 visually normal control subjects aged 22 to 65 years. CS was measured for 2-cycles-per-degree Gabor patch targets presented in the absence of noise (CS0) and in five levels of noise spectral density. Data were fit with a standard linear amplifier model, which provided estimates of Neq and sampling efficiency. CS0 for the patients ranged from normal to as much as a factor of 3 below the lower limit of normal. All 10 patients had abnormally high Neq, including two patients with normal CS0. In comparison, only two patients had lower-than-normal sampling efficiency, and these two patients also had below-normal CS0. Log CS0 for the patients was correlated significantly with log Neq (r = -0.80, P < 0.05), but not with log efficiency (r = 0.54, P = 0.11). Low CS was associated with elevated intrinsic noise in this group of RP patients, but even patients with normal CS had elevated noise levels. The results suggest that CS measurement in both the presence and absence of luminance noise can provide important information about visual dysfunction in RP patients.
Highlights
To determine the relationships among equivalent intrinsic noise (Neq), sampling efficiency, and contrast sensitivity (CS) in patients with retinitis pigmentosa (RP), where Neq is an estimate of the amount of noise within the visual pathway and sampling efficiency represents the subject’s ability to use stimulus information optimally
Low CS was associated with elevated intrinsic noise in this group of RP patients, but even patients with normal CS had elevated noise levels
The results suggest that CS measurement in both the presence and absence of luminance noise can provide important information about visual dysfunction in RP patients
Summary
Participants included 10 patients with RP aged 10 to 54 years, who had visual acuities of 20/40 or better, and 10 visually normal control subjects aged 22 to 65 years. The characteristics given in the Table are for the tested eye, which. AD, autosomal dominant; AR, autosomal recessive; ISO, isolated; USH2, Usher syndrome type II; VA, visual acuity; P-R CS, Pelli-Robson letter contrast sensitivity; VF, visual field horizontal width using a Goldmann II/4e target. VF diameter was correlated significantly with logMAR visual acuity (r 1⁄4 À0.84, P < 0.05), consistent with previous research,[8] but there was no significant correlation between VF diameter and Pelli-Robson letter contrast sensitivity (r 1⁄4 0.19, P 1⁄4 0.63). By optical coherence tomography (OCT), six patients had a normal macula, two patients (nos. 8 and 10) had extrafoveal patchy losses of the inner segment ellipsoid region, and two patients (nos. 1 and 6) had slight extrafoveal microcystic changes, but none of the 10 patients had an epiretinal macular membrane
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