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Y. E. Wen, K. G. Locke, D. C. Hood, D. G. Birch; Rod Photoreceptor Temporal Properties in Retinal Degenerative Diseases. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1365.
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© ARVO (1962-2015); The Authors (2016-present)
One of the characteristic signs of retinal degenerative diseases (RDDs) is the progressive loss of night vision, typically indexed by elevations in dark adapted (DA) threshold. We have previously shown that the gain of photoreceptor activation is moderately reduced in some patients, but this decrease in activation kinetics is not sufficient to account for the elevation in DA threshold. Recently, single rod recording from animal models of RDDs showed faster than normal rod photoresponse recovery. [2,3] Using paired-flash ERG, here we determine whether rod phototransduction inactivation parameters might also contribute to elevated DA threshold.
The full time course of the rod photoresponse was derived from 13 subjects with normal vision, 17 patients with adRP, 19 patients with an isolated form of RP, and 7 patients with cone-rod dystrophy. These included 11 patients with RHO mutations, 11 patients with RDS mutations, and 5 patients with ABCR mutations. The inactivation phase was derived using a double-flash paradigm, with a test flash of 2.4 log scot td-sec followed at varying intervals by a 4.2 log scot td-sec probe flash.[4,5]
Derived rod photoresponses to a just-saturating test flash in normal subjects exhibit a critical time to the initiation of recovery (Tc) of 544 ± 92 ms (mean±SD). The values of Tc in patients were adRP: 298 ± 78 ms (p<0.0001, t-test), isolate form of RP: 283 ± 56 ms (p<0.0001, t-test), and CRD: 482 ± 212 ms (p=0.14, t-test). When Tc values were categorized by mutations, the values were RHO: 288 ± 86 ms (p<0.0001, t-test), RDS: 370 ± 89 ms (p<0.0002, t-test), ABCR: 430 ± 160 ms (p=0.19, t-test). All statistics were performed between normals and patients.
Compared to rods in normal subjects, the rods in RP patients exhibit shortened photoresponses. Faster photoresponse inactivation was evident for all RDDs with elevated rod thresholds and was not found to be mutation specific. In addition to reduced gain and reduced number of rods, these findings suggest that earlier termination of rod phototransduction may also underlie elevations in DA threshold. 1. Tzekov et al., IOVS 2003; 2. Kraft et al., Mol Vis. 2005; 3. Wen et al., ARVO 2009; 4. Birch et al., IOVS 1995; 5. Pepperberg et al., Vis Neurosci 1997.
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