Retinal functions in snowflake degeneration

Retinal functions were studied in 7 patients with snowflake degeneration and correlated with fundus appearance. Despite the presence of vitreous turbidity, scotomatic glare sensitivity was slightly elevated in only one case. Retinal functions were affected more extensively in the late stages of the disease; however, abnormal retinal functions were also detected in some patients who showed only slight fundus changes on ophthalmoscopic examination. Kinetic perimetry showed peripheral defects which were more pronounced in the upper field. Flicker perimetry revealed abnormalities that kinetic perimetry could not detect. Dark-adaptation tests showed elevated rod thresholds except during the early stage of the disease. In all patients, the scotopic b-wave of the electroretinogram elicited by dim white light was low in amplitude. The photopic b-wave and the photopic flicker responses showed decreased amplitudes in some patients. The scotopic b-wave, normally recorded as a second positive peak when deep red light is used, almost disappeared, leaving only a small, single positive peak, photopic in nature, in the late stages. However, no patient had a nonrecordable electroretinogram. The electro-oculographic light peak/dark trough ratio was abnormal in only a few patients. These results indicate that in snowflake degeneration, functional abnormalities of the retina are milder than those in other progressive primary retinal degenerations typically represented by retinitis pigmentosa.