We report two familial cases of occult macular dystrophy (OMD) presenting with a progressive decrease in central vision.

Both patients exhibited a normal ophthalmologic examination including slit lamp biomicroscope, fundus examination, fluorescein angiography, and full-field electroretinogram. However, there were central visual field defects on a Humphrey static visual field test (C 24-2) and abnormal multifocal electroretinogram (mfERG) findings affecting the central portion of the test field. Foveal thinning was also observed by optical coherence tomography images in 1 case. These findings are consistent with the clinical characteristics of occult macular dystrophy, and close observation was recommended.

OMD is a disease characterized by a reduction in central visual acuity without visible fundus abnormalities and full field ERG. It may be misdiagnosed as optic nerve disease, a central nervous system problem, non-organic visual disorder or malingering; therefore, mfERG is essential for the diagnosis of this rare type of macular dystrophy.