Diagnosing peripheral cone dystrophy

In this photo essay, my colleague and I report the case of a 19-year-old man with bilateral peripheral visual field loss, hemeralopia (day blindness) and photophobia who was diagnosed with peripheral cone dystrophy after examination and testing.

This case illustrates a striking correlation between visual field depression and multifocal electroretinography (mfERG) attenuation in the peripheral retina. The patient showed well-preserved local responses in the central retina and severely reduced responses in the perifoveal retina.

Cone dystrophy refers to a group of genetically heterogeneous disorders ranging from normal to mild pigmentary mottling to bull’s eye maculopathy. It can be subdivided into central and peripheral forms. Peripheral cone dystrophy is the rarer of the two types and involves only the perifoveal cones.

Peripheral cone dystrophy, like central cone dystrophy, presents with photophobia, hemeralopia and visual field loss. However, because the peripheral cones are affected, visual acuity and color vision are preserved.

Because of its rarity, peripheral cone dystrophy may be misdiagnosed as acute idiopathic blind-spot enlargement or functional visual loss. Technological advances, such as mfERG, have facilitated the diagnosis of peripheral cone dystrophy.