The pupillary response to light in Type 1 (insulin-dependent) diabetes

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Abstract
The pupillary response to light was examined by infrared television-videopupillography in 93 Type 1 (insulin-dependent) diabetic patients (aged 25–42 years, duration of diabetes 0–32 years), and 37 control subjects (aged 26–41 years) with techniques ensuring equality of stimulus and retinal sensitivity, and allowing a detailed computerized calculation of the various parameters of the response. There was no difference in latency time or constriction time between diabetic patients and control subjects. The diabetic patients had a smaller initial pupil size (p=0.012) and a smaller response amplitude (pr=0.49, pr=−0.26, p=0.013 and r=−0.29, p=0.0051, respectively). As a group, the diabetic patients had a relative response amplitude that was similar to that of the control subjects. However, more detailed analysis showed that the diabetic patients with pupil size in the normal range had a small, but significant, reduction in relative response amplitude (p=0.0021). The maximal velocities of constriction and re-dilatation were reduced in the diabetic patients (pr=0.91, pr=0.79, p<0.000001, respectively), and this relationship was identical in the control subjects. Analysis of velocity-size plot for long-term diabetic patients showed no systematic deviation from that of non-diabetic subjects, indicating unaltered dynamic properties of the small pupil within the altered dynamic range in diabetic patients. The foremost change in the pupils of long-term diabetic patients is a reduction in size. Since normal iris dynamics are preserved, the small pupil must be due to loss of sympathetic tone. When diabetic patients with a normal or near-normal sensory pathway are stimulated by light, they have a normal latency time and response parameters that are normal for the size of their pupil. The only exception seems to be a minor reduction in response amplitude, possibly indicating damage to the efferent, parasympathetic pathways, as is known to develop in other organs.