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J Jason McAnany, Kenneth R. Alexander, Mohamed A. Genead, Gerald A. Fishman; Equivalent Intrinsic Noise, Sampling Efficiency, And Contrast Sensitivity In Patients With Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4361.
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To evaluate 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 is an estimate of the ability to use optimally the information contained in the stimulus.
Participants included ten patients with RP, ages 10 to 69 years, who had visual acuity between 20/20 and 20/40, and ten visually normal control subjects, ages 22 to 65 years. CS was measured for 2-cycle-per-degree Gabor patch targets presented for 100 ms in each of five levels of external noise (crms) ranging from approximately 1x10-7 to 4x10-5 deg2 s, as well as in the absence of noise. CS was converted to log threshold signal energy and plotted as a function of log crms. Data were fit with a standard linear amplifier model (LAM) that provided an estimate of Neq and sampling efficiency, as well as the predicted value of CS in the absence of noise (CS0).
The values of CS0 for the patients with RP ranged from within the normal range (N = 4) to losses that were as much as a factor of four below the lower limit of the normal range (N = 6). CS in the highest level of external noise ranged from within the normal range (N = 7) to losses that were less than 0.2 log units below the lower limit of the normal range (N = 3). All ten patients with RP had increased levels of Neq, including the four patients with normal CS0, who also had visual acuity of 20/25 or better. Only three of the ten patients had sampling efficiency that was below the range of normal, and all three had reduced CS0 and visual acuity of 20/25 or worse.
Equivalent intrinsic noise was elevated for each patient with RP, whereas sampling efficiency was reduced only in a subset of patients. The elevated equivalent intrinsic noise in RP patients provides further evidence that 20/20 visual acuity and normal contrast sensitivity in patients with RP does not necessarily indicate normal visual function.
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