Two-color pupillometry in KCNV2 retinopathy

Two unrelated patients (1 male and 1 female) with molecularly confirmed KCNV2 retinopathy underwent full-field two-color pupillometry testing in one eye, with monitoring of the stimulated eye by an infrared digital camera. Pupillometry stimuli consisted of 1-s duration, short-wavelength (465-nm, blue) and long-wavelength (642-nm, red) stimuli. Pupillometry intensity series were performed under both a dark-adapted condition and a light-adapted condition (on a 0.76-log cd m⁻² blue background). The transient PLR, defined as the maximum constriction following flash onset, was measured under all conditions. The melanopsin-mediated sustained constriction was measured 5–7 s following flash offset for the highest flash luminance presented in the dark. Both patients were also tested in one eye with the full-field ERG, including a dark-adapted intensity series and ISCEV standard stimuli.

Dark-adapted PLRs were markedly attenuated or extinguished for low-luminance stimuli, but the responses to higher-luminance blue stimuli were within normal limits. Light-adapted PLRs to blue stimuli were generally within normal limits, exceeding the responses to photopically matched red stimuli. Thus, light-adapted responses were consistent with either rod or S-cone mediation of the PLR. Melanopsin-mediated sustained PLRs were within normal limits. ERG showed the characteristic findings previously reported in this condition. Cone-mediated ERG responses were markedly decreased in amplitude. Rod-mediated ERG responses were absent for low-luminance stimuli (− 3 log cd s m⁻²), but had normal amplitude for stimuli of − 2 log cd s m⁻² and above (although none were “supernormal”). The b-wave for the dark-adapted ISCEV standard − 2 log cd s m⁻² stimulus was markedly delayed, whereas the b-wave timing was generally normal for higher flash luminances.

The abnormalities measured by pupillometry have a similar pattern to the outer-retinal abnormalities measured by ERG in KCNV2 retinopathy. These findings as well as the normal sustained PLR suggest that inner-retinal function may be preserved in KCNV2 retinopathy and highlight the potential for therapies designed to restore outer-retinal function in these individuals.