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Mirella Gualtieri, Russell D. Hamer, Marcio L. Bandeira, Daniela M. Bonci, Solange R. Salomao, Adriana Berezovsky, Valerio Carelli, Alfredo A. Sadun, Dora F. Ventura; Contrast sensitivity, but not contrast gain, is affected in asymptomatic carriers of 11778 Leber’s Hereditary Optic Neuropathy (LHON) as assessed with the pedestal--pedestal protocol. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4808.
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Contrast gain (CG) is a fundamental mechanism affecting cellular operating range and sensitivity at all levels of the visual system, starting at the retina. Psychophysical signatures of CG changes have been found in a ganglion cell-based disease - glaucoma - by Sun et al. (2008). LHON is also characterized by a retinal ganglion cell loss and even asymptomatic carriers of the disease exhibit significant losses in contrast sensitivity and color vision (Ventura et al., 2005, 2007; Gualtieri et al., 2008). However, carriers’ CG has not yet been evaluated. In this study we assessed the magno- (M) and parvocellular (P) CG signatures in LHON carriers using the pedestal-Δ-pedestal (PDP) test introduced by Pokorny & Smith (1997) as modified by Sun et al. (2008).
24 LHON carriers and 9 controls were tested. A 30 cd/m2 achromatic 4-square (1o x 1o each) pedestal (P) is presented continuously on a 19 cd/m2 background. During each trial, the P is incremented transiently for 225 ms to a new (delta-pedestal, DP) level. Observers had to identify which of the 4 squares (the test square, TS) had been incremented above the 3 neighboring squares during the 1st 25 ms of the DP presentation. Thresholds (Thd) were measured for 10 values of the DP spaced linearly on log cd/m2 axis over 0.36 log units. Thds were measured using a 4AFC staircase utilizing unequal up- and down steps sizes (Garcia-Perez, 1998) with a minimum of 14 reversals.
The mean Thds for the carriers were significantly elevated above the control’s for all values of DP. The shape of the PDP functions were similar in the LHON patients and the controls.
The data are consistent with a significant loss of achromatic contrast sensitivity in both M and P channels without concomitant changes in the contrast gain of either.
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