Structural and functional evaluation of macula in a 9-year-old boy with occult macular dystrophy and his affected elder sibling

Two siblings aged 9 and 15 years with unexplained visual loss had normal pupillary reactions, unremarkable anterior and posterior segment, normal fluorescein angiography, visual evoked potential, and flash electroretinogram (ERG). Spectral domain optical coherence tomography (OCT) showed loss of normal inner segment-outer segment (IS-OS) junction line bump at fovea in one and absent IS-OS junction line at fovea in the other. Characteristic hypovoltaged responses from central macula in multifocal ERG (mfERG) confirmed the diagnosis of occult macular dystrophy (OMD) in both siblings. Marked difference in OCT findings despite same visual acuity indicate that structural changes in OCT might not always correlate with the extent of functional loss. Obvious mfERG changes and very subtle OCT defect in the younger one suggests that functional changes probably appear much earlier than the structural changes. OMD is often underdiagnosed because of lack of high index of suspicion and detailed work up. The patients presented here represent first OMD report from India, one of them being the second youngest reported so far (medline search).