Correct! Look carefully at the shape of these defects, noting that they cross the vertical and horizontal meridians without a change in their width. In other words, there are no “step-offs.” These are incomplete “ring defects,” which are characteristic of outer retinal (pigment epithelium/photoreceptor) dysfunction in genetic disorders called “retinal dystrophies.” Very rarely, these defects could be caused by paraneoplastic or idiopathic autoimmune retinopathies. Electroretinography will confirm loss of rod function. For most forms of these conditions, there is regrettably no effective treatment yet. The defects become gradually more extensive over ensuing years. Patients also have impaired dark adaptation, but it develops so slowly that they make accommodations and do not suspect a disease. Ophthalmoscopy typically discloses an atrophic retinal pigment epithelium, black spicules, and attenuated arterioles. But do not be surprised if ophthalmoscopy shows a normal-appearing retina! This diagnosis is often long in coming, especially if ophthalmoscopic abnormalities are subtle or absent. In that case, the deficit is often blamed on psychogenic causes. Optic neuropathies would cause defects that have “step-offs” along the nasal horizontal meridian, a feature of nerve fiber bundle defects. Optic chiasm lesions and visual cortex lesions would show “step-offs” along the vertical meridian.

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