Abstract
Purpose::
Study retinal signals in children with achromatopsia using contemporary ERG procedures to evaluate photoreceptor and post-receptor function. The molecular basis of achromatopsia is typically a channelopathy due to mutations in genes coding for cone photoreceptor cGMP-gated channels.
Methods::
Subjects were 11 children with achromatopsia (median age 2.3 years; range 1-7 years). Electroretinographic (ERG) responses to full-field stimuli were obtained in scotopic and photopic conditions. Rod sensitivity (SROD) was calculated from the ERG a-wave, as was saturated amplitude (RROD), which represents circulating current of the rod. Post-receptor sensitivity (log σ) and saturated amplitude (VMAX) were calculated from the b-wave. The ERG records were digitally filtered to demonstrate the oscillatory potentials (OPs). The amplitudes and implicit times of OP2 to OP5 were examined as a function of stimulus intensity. Response parameters were compared to those of 12 normal control subjects.
Results::
Significant deficits in the amplitude of the saturated rod photoresponse (RROD) and post-receptor response (VMAX) were found. RROD and VMAX were, on average, about half that in controls. Furthermore, deficits in RROD predicted deficits in VMAX. There were no significant deficits in SROD or log σ. Amplitudes of OP3 to OP5 were approximately half that in normal controls; OP2 was even smaller (~20%). Saturated rod and post-receptor response amplitude were not correlated with the amplitude of any OP. As expected, photopic responses were absent in subjects with achromatopsia.
Conclusions::
The significant attenuation of the saturated amplitude of the rod response in children with achromatopsia indicates that rod function is affected by the cone channelopathy that characterizes achromatopsia.
Keywords: electroretinography: clinical • photoreceptors: visual performance