Neuro-ophthalmic presentation of cone dysfunction syndromes in the adult

Cone dysfunction syndromes are probably part of the spectrum of cone-rod degenerations and can present with widely varying clinical pictures. Thus, although the age of onset is usually before the third decade, patients can present at any age, and, although family history is usually positive, in typical cases it may be quite negative. Patients can have initially very subtle, bizarre, or poorly described visual complaints so that numerous examiners may label them "functional" or "malingering." They can present with the classic symptoms of hemeralopia, poor acuity, and reduced color vision, but these complaints may be absent. Visual acuity and color vision can be normal or severely reduced and the fundi may show classic changes such as bulls-eye maculopathy, macular choroidal atrophy, pigment clumping in the maculae, mild peripheral pigmentary changes, or a fundus flavimaculata-like change. The patients here reported were considered as having normal fundi by several competent ophthalmologists as a rule, however. Visual fields can vary from normal to ring scotomas, central scotomas, and other interesting types of defects, even simulating a hemianopia. Although involvement is usually symmetrical between the two eyes, this is not always the case, and one of our patients had a strictly uniocular cone dystrophy. Cone dysfunction can be considered in a patient of any age even with normal acuity, good color vision, and a normal ophthalmoscopic examination. A high index of suspicion should prompt specific questioning about hemeralopia, or reduced visual function in brightly illuminated situations, and better vision in twilight or under dim illumination. Patients may falsely describe hemeralopia as "glare" or "photophobia." Careful testing of color vision, a meticulous tangent screen examination, and specifically looking for diffuse narrowing of retinal arterioles in a patient with an otherwise normal fundus appearance will usually suffice to prompt the clinician to order electroretinography, which is the definitive diagnostic criterion for the cone dystrophies. It is important to consider this diagnosis before embarking on an otherwise fruitless and expensive neuroimaging investigation.