Macular dystrophy with protan genotype and phenotype studied with cone type specific ERGs
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Published on: March 20, 2021
H P Scholl1, J Kremers, B Wissinger
1Laboratories of Electrophysiology, Department of Experimental Ophthalmology, University Eye Hospital Tübingen, Germany. hendrik.scholl@uni-tuebingen.de
Purpose:
To determine the L- and M-cone driven ERG responses in a male patient with macular dystrophy and a protan phenotype.
Methods:
We measured large field ERG thresholds to stimuli which modulated exclusively the L- or the M-cones or the two in various combinations (both in-phase and in counterphase). In none of the stimuli, the S-cones were modulated. Additionally, standard and multifocal ERGs were measured. Analysis of the L- and M-cone pigment genes was performed by means of PCR, RFLP analysis and DNA sequencing techniques.
Results:
Macular dystrophy was revealed by the markedly abnormal multifocal ERGs in presence of near normal standard ERGs. The large field ERG responses were exclusively driven by the M-cones with enlarged thresholds when compared with otherwise normal protanopes. In addition, the M-cone driven ERG response phases were abnormal. Pigment gene analysis confirmed a protan genotype with the presence of a single 5'red/3'green hybrid pigment gene.
Conclusions:
Our novel stimulus technique allows a reliable analysis of the separate cone pathways even in cases with macular dysfunction. The increased thresholds and the abnormal phase behavior of the M-cone driven ERGs reflect altered mechanisms of the retinal physiology in this patient. The data strongly suggest that the macular dystrophy and the protanopia have independent origins.
