The study population consisted of 16 eyes, from five patients with RP, three patients with CRD, and eight subjects with unaffected eyes
(Table 1) . Each patient and each subject with healthy eyes underwent complete eye examination. All patients and three subjects with healthy eyes (subject ages 20, 27, and 61 years) underwent additional clinical testing that included testing of color vision, visual field, multifocal electroretinography (ERG), optical coherence tomography (OCT), and measurement of best-corrected visual acuity (BCVA) with a Snellen chart and reported as the quotient of the Snellen acuity (20/20 = 1.0). Acuities equal to or better than 20/20 were recorded as 20/20. Patients were excluded if their pupils did not dilate to at least 7 mm, they had dense cataracts or other media opacities, they had previously undergone refractive surgery, they had pseudophakia, or they were unable to maintain stable fixation on a 1° target. Color vision was assessed with the use of a color vision test (Farnsworth D-15 panel; Richmond Products, Inc., Albuquerque, NM). Subjects showing no crossing errors on the color vision test were further examined with a Lanthony 15-hue desaturated panel. Automated perimetry was completed with a visual field analyzer (Humphrey Visual Field Analyzer II; 750-6116-12.6; Carl Zeiss Meditec, Inc., Dublin, CA), 10-2 Swedish interactive thresholding algorithm (SITA) with measurement of foveal thresholds, a Goldmann III stimulus on a white background (31.5 ASB), and an exposure duration of 200 ms. Goldmann kinetic perimetry was performed with V-4e and I-4e targets. Fundus-related microperimetry was examined in a subset of subjects (MP-1; Nidek Technologies America Inc., Greensboro, NC). The central 8° visual field was tested with a Goldmann III stimulus of 200-ms duration with a 4-2 threshold strategy; subjects were instructed to fixate on the center of four crosses, each 2° in size at an eccentricity of 5°. Fixation was monitored with respect to the fovea—judged by anatomic landmarks—and stability. Numeric thresholds in decibels (dB) were exported and overlain with AOSLO images (Matlab software; Mathworks, Natick, MA). OCT images were obtained (Stratus OCT 4.0.2 software; Zeiss Instruments, Dublin, CA) to determine retinal thickness with 6-mm horizontal scans centered on the anatomic fovea. Retinal thickness was measured using calipers to mark the vitread surface of the foveal dip and the first highly reflective band sclerad to the vitread surface. Pupils were dilated with 1% tropicamide and 2.5% phenylephrine before full-field ERG, which was performed after 45 minutes of dark adaptation using a Burian-Allen contact lens electrode (Hansen Ophthalmic Development Laboratory, Iowa City, IA), according to International Society for Clinical Electrophysiology and Vision (ISCEV)
27 standards. Multifocal ERG (mfERG) testing was performed in a light-adapted state (VERIS 5.1.10×; Electro-Diagnostic Imaging, Inc., Redwood City, CA) with a Burian-Allen contact lens electrode according to ISCEV standards.
28 Responses were recorded using 16 30-second sequences in each eye. The stimulus consisted of 103 elements covering the central 40° diameter of the visual field; the flash intensity was 200 cd/m
2, the intensity of dark frames was less than 4 cd/m
2, and the average luminance was 100 cd/m
2. Fixation was monitored with the use of an infrared eye camera. The signal was amplified 100,000 times, and the bandwidth measured 10 to 100 Hz. A single iteration of 17% spatial averaging was performed (VERIS software; Electro-Diagnostic Imaging, Inc.). Response amplitudes of the first-order waveform were measured from N1-P1, and P1 response latency was reported.