Isolated Cone Dystrophy With Secondary Macular Involvement Mimicking Vascular Insult and Optic Atrophy: A Case Report.

Isolated cone dystrophy is a rare retinal degenerative disorder characterized by selective dysfunction of cone photoreceptors, with relatively preserved rod function. Clinical presentation can be variable and, in rare cases, may mimic retinal vascular injuries or optic neuropathies, leading to diagnostic uncertainty. We report the case of a 32-year-old male patient with gradual, painless, asymmetric vision loss predominantly affecting the left eye. Fundus examination revealed optic disc pallor, arteriolar narrowing, macular pigmentary changes, and absence of the foveal reflex, raising initial concerns for retinal vascular insufficiency or optic atrophy. Multimodal imaging showed widespread macular thinning, photoreceptor layer disruption, and an enlarged foveal avascular zone, complicating the diagnostic evaluation. Full-field electroretinography demonstrated preserved scotopic responses but markedly reduced photopic responses, confirming selective cone dysfunction and establishing a diagnosis of isolated cone dystrophy with secondary macular involvement. The absence of systemic vascular risk factors, a routine neurological examination, and characteristic electrophysiological findings were pivotal in differentiating this condition from vascular or optic nerve disorders. This case highlights the importance of considering cone dystrophy in the differential diagnosis of painless, progressive vision loss with optic disc pallor and macular changes. It underscores the critical role of electrophysiology and multimodal imaging in accurate diagnosis.