title: Psychophysical analysis of contrast processing segregated into magnocellular and parvocellular systems in asymptomatic carriers of 11778 Leber's hereditary optic neuropathy.
abstract: We examined achromatic contrast discrimination in asymptomatic carriers of 11778 Leber's hereditary optic neuropathy (LHON 18 controls) and 18 age-match were also tested. To evaluate magnocellular (MC) and Parvocellular (PC) contrast discrimination, we used a version of Pokorny and Smith's (1997) pulsed/steady-pedestal paradigms (PPP/SPP) thought to be detected via PC and MC pathways, respectively. A luminance pedestal (four 1 degree x 1 degree squares) was presented on a 12 cd/m2 surround. The luminance of one of the squares (trial square, TS) was randomly incremented for either 17 or 133 ms. Observers had to detect the TS, in a forced-choice task, at each duration, for three pedestal levels: 7, 12, 19 cd/m2. In the SPP, the pedestal was fixed, and the TS was modulated. For the PPP, all four pedestal squares pulsed for 17 or 133 ms, and the TS was simultaneously incremented or decremented. We found that contrast discrimination thresholds of LHON carriers were significantly higher than controls' in the condition with the highest luminance of both paradigms, implying impaired contrast processing with no evidence of differential sensitivity losses between the two systems. Carriers' thresholds manifested significantly longer temporal integration than controls in the SPP, consistent with slowed MC responses. The SPP and PPP paradigms can identify contrast and temporal processing deficits in asymptomatic LHON carriers, and thus provide an additional tool for early detection and characterization of the disease.
authors.affiliation: Departmento de Psicologia Experimental, Universidade de São Paulo, São Paulo, Brasil.
authors.forename: M
authors.initials: M
authors.lastname: Gualtieri
authors.forename: M
authors.initials: M
authors.lastname: Bandeira
authors.forename: R D
authors.initials: RD
authors.lastname: Hamer
authors.forename: M F
authors.initials: MF
authors.lastname: Costa
authors.forename: A G F
authors.initials: AG
authors.lastname: Oliveira
authors.forename: A L A
authors.initials: AL
authors.lastname: Moura
authors.forename: F
authors.initials: F
authors.lastname: Sadun
authors.forename: A M
authors.initials: AM
authors.lastname: De Negri
authors.forename: A
authors.initials: A
authors.lastname: Berezovsky
authors.forename: S R
authors.initials: SR
authors.lastname: Salomão
authors.forename: V
authors.initials: V
authors.lastname: Carelli
authors.forename: A A
authors.initials: AA
authors.lastname: Sadun
authors.forename: D F
authors.initials: DF
authors.lastname: Ventura
mesh_terms: D000293:Adolescent; D000328:Adult; D015350:Contrast Sensitivity; D004192:Discrimination, Psychological; D005260:Female; D006580:Genetic Carrier Screening; D006801:Humans; D008297:Male; D008875:Middle Aged; D029242:Optic Atrophy, Hereditary, Leber / Q000235:genetics*; D012016:Reference Values; D014787:Vision Tests; D014792:Visual Acuity; D014795:Visual Pathways