Cone Dysfunction in Patients with Late-onset Cone Dystrophy and Age-related Macular Degeneration

Objectives: To determine the clinical and functional findings in patients with late-onset cone dystrophy (LOCD) (after the age of 50 years), which is rare; and to compare them with those of patients with age-related macular degeneration (AMD).

Methods: Eleven LOCD patients underwent ophthalmologic and electroretinographic examinations. Full-field electroretinograms were recorded according to the International Society for Clinical Electrophysiology of Vision standard. The results were compared with those of a group of 20 AMD patients and a group of 23 age-related control subjects.

Results: There was no difference between LOCD and AMD patients regarding the severity of visual acuity loss, color vision deficiencies, and central visual field defects. Alterations of the posterior pole were present in all LOCD and AMD patients. In contrast to the AMD group, all LOCD patients did not show drusen and 6 of the 11 LOCD patients displayed temporal optic disc pallor. The electroretinogram revealed the major functional difference, with severe reduction of cone-mediated responses and moderate reduction of rod-mediated responses in LOCD patients. Unexpectedly, the 30-Hz flicker amplitude was reduced in AMD patients compared with healthy controls.

Conclusions: Late-onset cone dystrophy and AMD have several features in common. In elderly patients with progressive visual loss and without drusen, LOCD should be considered. The electroretinographic results in a small group of AMD patients indicate a generalized cone dysfunction.