Two highly intelligent siblings suffered from a relatively mild type of Hunter Syndrome (mucopolysaccharidosis II). Their external appearance as well as the histological and biochemical findings were characteristic of this disorder. Visual acuity, visual fields, color vision, corneas, ocular mediae, and retinas were normal in both siblings. A complaint of nyctalopia was confirmed in both patients by means of psychophysical tests and electroret inography. The latter test exhibited subnormal values for all components and deteriorated, moreover, during the four years of observation of these patients, possibly as a result of progressive mucopolysaccharidosis infiltration or of other involvement of retinal structures. The electro-oculogram, however, proved to be subnormal in only one case, and the visual evoked potential was normal. There were no abnormal ophthalmological and electrophysiological findings in the remainder of the family, except for the mother's nyctalopia.
Abraham FA, Yatziv S, Russell A, Auerbach E. Electrophysiological and Psychophysical Findings in Hunter Syndrome. Arch Ophthalmol. 1974;91(3):181–186. doi:10.1001/archopht.1974.03900060189006