Abstract
Purpose: :
To characterize the visual phenotype of asymptomatic Leber’s hereditary optic neuropathy (LHON) associated with mtDNA 11778G>A mutation in carriers from the same pedigree.
Methods: :
Computerized psychophysical assessment methods (CCT - Cambridge Colour Test and CSF - Metropsis Contrast Sensitivity Function Test) were used to evaluate visual function in a population of 17 subjects of two generations of the family mentioned above (mean age ± SD = 27.94±12.97 years; mean visual acuity ± SD = 1.25±0.11) which was compared with an age-matched control group (n=18; mean age ± SD = 33.29±14.22 years; mean visual acuity ± SD = 1.09±0.14). This evaluation was completed with electrophysiological assessment (Multifocal ERG, Pattern ERG and Pattern VEP). Stratus-OCT3 was used for structural evaluation.Statistical analysis at a significance level of p<0.05 was performed using ANOVA.
Results: :
CCT showed evidence for damage of all cone populations (R: p=0.0002; G: p<0.0001; B: p=0.01), implying concomitant damage of parvo and koniocellular pathways. No significant damage occurred in the achromatic contrast sensitivity across the spatial frequency channels studied, suggesting a relatively preservation of achromatic pathways.PERG results were normal, while mfERG (testing preganglionic pathways) showed a decrease in central ring amplitudes (P1-wave: p=0.006; N1-wave: p=0.02), corroborating pre-ganglion lesion. Retinal thickness was decreased in the inner rings (R1:p=0.012; R2:p=0.04), irrespective of changes in macular nerve fiber layer thickness.Cortical responses (VEP) were delayed (60':p=0.002 / 15’:p=0.02) with normal amplitudes.
Conclusions: :
Our results suggest that, besides the classical concept of ganglion cell dysfunction, damage to outer retinal circuits could also contribute to subclinical impairment in LHON carriers.
Keywords: electrophysiology: clinical • neuro-ophthalmology: optic nerve • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)