Abstract
Purpose: To determine (1) luminance contrast sensitivity functions (CSF) in the spatial (SCSF) and temporal domains (TCSF) and (2) chromatic red/green (R/G) and blue/yellow (B/Y) CSFs in 11778 LHON carriers with no visual complaints.
Methods: The subjects, carriers (n= 27) and age–matched controls (n = 30), were tested monocularly in a darkened room. CSFs were measured with PSYCHO for Windows v 2.36 (Cambridge Research Systems), with a VSG 2/4 graphic board and a Sony FD Trinitron monitor, calibrated with a CS1000 Minolta spectrophotometer. The SCSF was measured with horizontal sinusoidal gratings at 0.3, 2, 6 and 12 cpd; the TCSF at 2, 10, 20 and 33 Hz using sinusoidal modulation of a 30 degree field with a superimposed spatial Gabor function. R/G and B/Y CSFs were determined with horizontal sinusoidal gratings of 0.3, 0.7 and 2 cpd, after equiluminance correction. The u'v' (CIE 1976) chromaticity coordinates were: D6500: 0.198, 0.468; Red: 0.258, 0.454; Green: 0.133, 0.469; Blue: 0.210, 0.397 and Yellow: 0.188, 0.551. A non–parametric statistical analysis (Mann–Whitney Rank Sum test with alpha= 0.05) was performed.
Results:Differences between the carriers and controls were statistically significant for all spatial frequencies of both chromatic and luminance spatial contrast modulation tests, but not for the temporal CSFs. R/G equiluminance settings of carriers differed from controls (p<0.001), requiring higher luminance in the green. However, the B/Y equiluminance settings of carriers and controls were not statistically different.
Conclusions:Pre–clinical functional losses have been shown to exist in LHON carriers (Sadun and cols., ARVO 2002). In the same line, we now report luminance and chromatic CS losses in the carriers of the MtDNA 11778 mutation. The CS losses affected all spatial frequencies, without preferential impairment of either the magno– or parvocellular pathways. An important finding is that the blue system is spared in LHON, as indicated by the equiluminance data.
