Cardiovascular and pupillary light reflexes in subjects with abnormal glucose tolerance

Abstract

It is well known that in diabetes mellitus autonomic neuropathy frequently develops. This is usually determined by the cardiovascular reflex. Furthermore, even in borderline cases that have not become overt diabetes, we have already reported the presence of autonomic neuropathy as assessed by the pupillary light reflex. However, a relationship between the impairments of the cardiovascular and pupillary light reflexes is not clear, especially in people with abnormal glucose tolerance. In the present study diabetics were divided into three groups according to the results of their cardiac beat-to-beat variation (BBV) tests and Schellong tests; group I had no abnormality of these cardiovascular reflexes, group II had abnormal BBV scores and normal Schellong test scores, and group III had abnormal responses to both tests. People with borderline diabetes (B-DM) were free from any impairment of their cardiovascular reflexes. We examined their pupillary light reflexes. Age-matched non-diabetics were also studied as a control, The following results were obtained. (1) Compared to controls, (a) diabetics, but not borderline diabetics, had smaller pupils before photic stimulation (A1) and lower maximum dilatation velocities (VD). These illustrate sympathetic function; (b) diabetics and borderline diabetics had lower amplitudes of constriction (A3) and maximum constriction velocities (VC). These illustrate parasympathetic function; (c) borderline diabetics and those diabetics belonging to group III experienced a lower pupillary constriction rate. (2) Diabetics (a) had lower A1 values than did people with B-DM; (b) in group III had lower A3, VC and VD values than did people with B-DM; and (c) in group III had lower A1 and VD values than those in group I and lower A3 and VC values than those in groups I and II. These observations support the existence of parasympathetic neuropathy in B-DM. They indicate that the pupillary light reflex worsens with the progression of cardiovascular reflex abnormalities. In particular, when the cardiovascular reflex indicates remarkable sympathetic impairment, both the sympathetic and parasympathetic components of the pupillary light reflex become more predominantly disturbed.