Contrast Sensitivity to Achromatic Spatial Drifting Gratings in Asymptomatic Carriers of the MtDNA 11778 Mutation Leber's Hereditary Optic Neuropathy (LHON)

Abstract

Purpose: : To determine contrast sensitivities in LHON carriers for drifting gratings of spatial frequencies and velocities presented in parameter combinations designed to activate selectively either the magno- or the parvocellular pathways.

Methods: : Thirty LHON carriers (20 women) and 32 age-matched controls (17 women), with best-corrected 20/20 Snellen VA or better were tested monocularly in a darkened room. Contrast sensitivity to drifting spatial frequency gratings of functions was measured with the computerized software PSYCHO for Windows v 2.36 (CRS Ltd., Cambridge, England), with a VSG 2/4 graphic board and a Sony FD Trinitron monitor. Gratings of .5 and 9 cpd were drifted upward at temporal frequencies of .5, 7.5, and 15c/sec. Factorial ANOVA was run considering group and gender effects.

Results: : Average contrast sensitivity in carriers was uniformly lower for all conditions, compared to controls for .5 cpd (1.5 c/sec, p=.004; 7.5 c/sec, p= .033; 15c/sec, p<.001) and 10 cpd (1.5 c/sec, p<.001; 7.5 c/sec, p=.001; 15c/sec, p<.001). Gender difference was significant for 0.5 cpd (7.5 c/sec, p=.037; 15c/sec, p<.042). Comparing the proportion of LHON carriers with lower values than control’s percentile 5% for contrast sensitivity a statistical higher number of carriers with results below this value was measured for 7.5 (p= .004) and 15 c/sec (p= .001).

Conclusions: : Recent evidence from several studies has shown that clinically asymptomatic LHON carriers present losses in several visual functions. In the present study, losses in contrast sensitivity to a drifting grating were found. The magnocellular activating stimulus (grating with high temporal frequency and low spatial frequency) was associated with losses with short magnitude from those found for the parvocellular activating stimulus (grating with low temporal frequency and high spatial frequency. These results are complementary to those previously reported for stationary conditions showing a magnocellular impairment in addition to a stronger parvocellular damage.

Keywords: visual impairment: neuro-ophthalmological disease • retina • contrast sensitivity