Determination of the dark-adapted pupillary area (DAPA) by infrared photography revealed that some diabetic patients show corectopia (oval pupil) in addition to the small DAPA as pupillary abnormalities. The prevalence and clinical details of oval pupil were compared between diabetic patients and healthy subjects. Pupillary light reflexes were also analyzed with an infrared videopupillography in some of the diabetic patients. The healthy subjects were examined for the influence of age on the ratio of the pupillary diameter of the major and minor axes. The ratio was 1.04 +/- 0.02 (mean +/- S.D.) in the healthy subjects, and cases in which the ratio was +2 S.D. or higher than the mean ratio were defined as oval pupil. Oval pupil was observed in 21 (24%) of 86 diabetic patients, and was correlated with heart rate variation (P < 0.05) and DAPA (P < 0.01), which represent an autonomic dysfunction. Quantitative analysis of pupillary light reflexes with an infrared videopupillography revealed that the dark-adapted pupillary area before photic stimulation (P < 0.01) and the maximum %-velocity of constriction (P < 0.05) were significantly less in the oval pupil group than in the round pupil group. Cranial magnetic resonance imaging revealed no abnormalities in the oval pupil group. From these results, a peripheral autonomic disorder was implicated in the etiology of oval pupils in diabetic patients.