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Frederick Collison, Gerald Fishman, J Jason McAnany, Jana Zernant, Rando Allikmets; Psychophysical Measurement of Rod and Cone Thresholds in Stargardt Disease with Full-Field Stimuli. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3027.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate rod and cone psychophysical thresholds in Stargardt disease with the Diagnosys Full-Field Stimulus Test (D-FST) using chromatic stimuli and a dark adaptation protocol.
Twenty-two patients with Stargardt disease (age range 21-52) were categorized by fundus appearance as Stage 1 (flecks confined to the macula, n=7), Stage 2 (flecks also outside the macula, n=6), or Stage 3 (resorbed flecks, n=9). The better-seeing eye was tested with ETDRS acuity charts, SD-OCT, and full-field ERG. Using the D-FST, dark-adapted rod thresholds were measured with short-wavelength stimuli and cone thresholds were obtained from the cone plateau phase of dark adaptation using long-wavelength stimuli. Four visually normal subjects (age range 28-38) also underwent the D-FST with the same protocol. For D-FST results zero dB = 0.1 photopic cd/m2. Correlation coefficients were calculated for comparisons of D-FST thresholds to other tests.
Stargardt patient D-FST cone thresholds correlated with ETDRS acuity (r=+0.56, p<0.01), ERG light-adapted single flash b-wave (r=-0.78, p<0.001), and SD-OCT macular thickness (r=-0.62, p<0.01). For normal subjects D-FST mean rod threshold was -70.1 dB (SD 3.4), and mean cone threshold was -29.1 dB (SD 1.2). Stage 1 D-FST cone and rod thresholds were all within 3 dB of normal (mean rod and cone thresholds were -69.7 dB, SD 1.2 and -28.4 dB, SD 1.5, respectively). Stage 2 rod and cone thresholds ranged from normal to well above normal by 7 dB for rods and 9 dB for cones (rod mean -69.2 dB, SD 4.2; cone mean -25.6 dB, SD 4.5). Stage 3 rod thresholds ranged from 1.3 to 13.8 dB above normal (rod mean -63.8 dB, SD 4.9), whereas Stage 3 cone thresholds were all elevated at least 6 dB above normal (cone mean -21.3 dB, SD 1.5).
D-FST may be useful as an efficient measure of visual function in patients with macular dystrophies who have difficulty fixating during visual field tests. Various levels of threshold elevation were identified among three stages of Stargardt disease by measuring thresholds with the D-FST both fully dark adapted (for rods) and during dark-adaptation (for cones). Of particular importance, cone thresholds in Stage 3 were consistently elevated, suggesting that full-field cone thresholds may be a parameter that warrants monitoring in this subset of Stargardt disease patients in treatment trials.
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