A distinctive form of congenital stationary night blindness with cone ON-pathway dysfunction.
OBJECTIVE
To characterize a distinctive form of congenital stationary night blindness (CSNB).


METHODS
Observational case report.


METHODS
A 30-year-old male with a history of night blindness, several members of his family, a patient with "complete" congenital stationary night blindness (CSNB1), and groups of age-similar control subjects.


METHODS
Rod-system function was evaluated by measuring psychophysical dark-adapted thresholds, by recording dark-adapted electroretinograms (ERGs), and by fundus reflectometry. Cone-system function was evaluated by recording light-adapted ERGs, including those to sawtooth flicker, and by recording light-adapted visually evoked potentials (VEPs) to luminance increments and decrements.


METHODS
Dark-adapted thresholds, ERGs, rhodopsin double densities, Goldmann visual fields, and VEPs.


RESULTS
The patient's visual acuity, visual fields, and color vision were normal. His peripheral dark-adapted thresholds were rod-mediated but elevated by approximately 3 log units above normal. Rhodopsin double density and bleaching recovery were normal. His dark-adapted maximal-flash ERG showed a "negative" waveform, in which the b-wave was more reduced in amplitude than the a-wave, although the a-wave amplitude was also reduced. The rod photoreceptors contributed to the patient's dark-adapted ERGs, as illustrated by the unequal responses to cone-matched stimuli. The patient's cone-mediated thresholds for long-wavelength stimuli were within the normal range. However, his light-adapted brief-flash b-wave was abnormal in amplitude and implicit time. Selective abnormalities of the ON responses of the cone system were apparent in the patient's reduced b-wave amplitude to rapid-on flicker with a normal response to rapid-off flicker, and his prolonged VEP latencies to increments but not to decrements.


CONCLUSIONS
The overall pattern of findings distinguishes this patient from previously described forms of CSNB. The results suggest that two factors likely contribute to the patient's night blindness: (1) a rod phototransduction defect and (2) a postreceptoral defect. The results also indicate dysfunction within the cone ON pathway.
Barnes
Claire S
CS
Department of Ophthalmology and Visual Science, University of Illinois at Chicago, 1855 West Taylor Street, Chicago, IL 60612, USA.
Alexander
Kenneth R
KR
Fishman
Gerald A
GA
D000328:Adult; D003623:Dark Adaptation; D004596:Electroretinography; D005074:Evoked Potentials, Visual; D006801:Humans; D008297:Male; D009755:Night Blindness / Q000151:congenital* / Q000503:physiopathology; D010375:Pedigree; D017949:Retinal Cone Photoreceptor Cells / Q000503:physiopathology*; D017948:Retinal Rod Photoreceptor Cells / Q000503:physiopathology*; D014785:Vision, Ocular / Q000502:physiology; D014792:Visual Acuity; D014794:Visual Fields; D014795:Visual Pathways / Q000503:physiopathology*