Analysis of Contrast Processing Segregated Into Magnocellular and Parvocellular Systems in Unaffected Carriers of 11778 LHON

Abstract

Purpose:: To detect evidence of specific impairment of either parvocellular (PC) or magnocellular (MC) functions in unaffected carriers of Leber`s Hereditary Optic Neuropathy (LHON) from a large Brazilian pedigree.

Methods:: Contrast discrimination processing was measured in 18 carriers of 11778 LHON (2? women; 16? men; mean age= 35 ± 13.47 yrs) and 18 control subjects (11 women; 7 men; mean age= 40 ± 10yrs). Assessment was with a self-developed software runing the pulsed- /steady-pedestal paradigm. Thresholds were measured by presenting a luminance pedestal (four-square array, 1 degree each) on a constant 12 cdm² background in a high resolution display. The luminance of one squares in the pedestal (randomly chosen) was temporally modulated (17ms and 133ms) under different adaptation levels provided by the pedestal ( 7, 12 and 19 cdm²) and the background. In the steady paradigm, the square array stood all trials on the screen whereas in the pulsed the array consisted on pulse with the same duration of the stimulus test. Psychophysical correlate from MC and PC functions are revealed on the first and second paradigms, respectively. The six resulting combinations were presented in the pulsed and steady paradigms, in a total of 12 subsets.

Results:: Approximately 33% of the carriers had higher contrast thresholds than the 95% confidence limits based on control thresholds. This was true in both paradigms. We compared separately data from those with normal and abnormal responses. Contrast thresholds from carriers with data exceeding the upper confidence limit were significantly higher from the thresholds from controls (Mann-Whitney U test α= .05). For those carriers with responses below the upper limit, five of the twelve subsets were different from controls, including both steady and pulsed paradigms. There was no correlation between the contrast thresholds and age, visual acuity or color vision scores.

Conclusions:: We demonstrated an impairment of the temporal contrast detection function in the LHON unaffected carriers however, there was no evidence of selective damage to either the MC or PC streams which corroborates previous results on spatial contrast sensitivity function.

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