Miscoded Visual Processing in Degenerative Retinal Disorder?

Standard electrophysiological procedures for visual testing were applied to record the retinal and cortical electrophysiological responses to contrast stimulation from 35 subjects with unambiguously diagnosed retinitis pigmentosa and severe impairment of visual acuity and field. Stimuli (central 9 degrees of visual field) were sinusoidal bars with spatial frequencies of 0.6-1.2 cycle/degree and 1.3-5.0 cycle/degree for the retinal (pattern-ERG) and cortical (pattern-VEP) responses, respectively; contrast was 80%; reversal at 2.13 Hz. Structured pattern-ERG above noise level was recorded from 29 subjects at 0.6 cycle/degree and from 24 subjects at 1.2 cycle/degree; latencies were increased and amplitude reduced. Pattern-VEP responses above noise level, with increased latencies and reduced amplitude, were observed in 92% of subjects with unilateral and in all subjects with bilateral retinal response. Both responses were phase-locked to stimulus. No correlation with the residual visual acuity or field was detected. The observation is consistent with evidence of the disease sparing the neuroretina and with unconscious visual processing and suggests miscoding of visual information processing.