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Correct! You cannot be faulted for judging the sensitivity to light, impaired visual acuity and color vision, and unreliable formal visual field results as manifestations of a psychogenic disorder. But organic causes could be at work! A bilateral optic neuropathy is not it because Ishihara color vision is too poor. Congenital dyschromatopsia would not cause degraded visual acuity. You must consider a diagnosis of cone dystrophy--even if the optic fundus examination appears normal, as it often does in that condition. You would settle the issue with an electroretinogram (ERG), which should show abnormalities in cone function. Optical coherence tomography might also show a disordered outer retina. Were you thrown off by the normal confrontation visual fields? Don’t be. That technique is insensitive to central scotomas. Why is he bothered by sunshine? Patients with cone dystrophy often complain of being aversive to normal daylight (“hemeralopia”) because the disordered cone function cannot transduce light into neural signals. The lack of a family history should not dissuade you from the diagnosis. For now, there are no proven treatments for cone dystrophy, which can become apparent at any age. Visual acuity will gradually decline over time. Two extremely rare conditions—autoimmune retinopathy and cancer-associated (paraneoplastic) retinopathy—should be excluded in the proper setting. Diagnosis depends on demonstrating anti-retinal antibodies in addition to the typical ERG abnormalities.

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