Contrast Sensitivity Mediated by ON- and OFF-Subsystems of the Magno- and Parvocellular Pathways of Asymptomatic Carries of 11778 LHON

Abstract

Purpose:: To measure contrast sensitivity thresholds of the ON- and OFF-subsystems of the parvocellular (Parvo) and magnocellular (Magno) pathways in asymptomatic carries of 11778 LHON from a large Brazilian pedigree using a computerized psychophysical task.

Methods:: Contrast sensitivity was measured in 40 carriers of 11778 LHON (mean age= 28.9 yrs; SD= 11.4; 19 males) and 41 controls (mean age= 29.9 yrs; SD= 8.4; 22 males). The measurements were performed with white on grey (ON) and black on grey (OFF) checkerboards at two spatial frequencies (Magno - 0.5 and Parvo - 4.0 cpd), presented at either 33 ms or 1500 ms duration on a uniform gray background, with an interstimulus interval of 300ms. The sensitivity was expressed as the mean of 3 ascending and 3 descending thresholds obtained for each condition (Parvo ON, Parvo OFF, Magno ON, Magno OFF).

Results:: LHON subjects differed statistically from controls at all conditions: Magno ON (p< 0.0001); Magno OFF (p< 0.0001); Parvo ON (p< 0.0002); Parvo OFF (p< 0.0001). CS losses increased with age for LHON subjects for Parvo ON (r= -0.364; p= 0.021), Parvo OFF (r= -.383; p= 0.015). Statistical difference was observed for all experimental conditions when male and female LHON carrier results were compared with their respective controls (p < 0.05). There were also differences between male vs female LHON carriers (P< 0.05) but not for male vs female controls.

Conclusions:: Losses in contrast sensitivity were non selective for either the magno- or the parvocellular functions in 11778 LHON subjects, although progression of losses with age were evident only for the parvocellular functions. Losses were more severe in males than in females. This in line with previous results obtained in the same population showing a non selective reduction in luminance and chromatic contrast sensitivity for spatial gratings (Ventura et al., IOVS 46 (12): 4809-4812, 2005) and a male prevalence for color discrimination losses (Ventura et al, IOVS in press).

Keywords: contrast sensitivity • visual impairment: neuro-ophthalmological disease • neuro-ophthalmology: optic nerve