1. The changes in the volume and depth of the anterior chamber of the eye during acute insulin-induced hypoglycaemia were examined in nine healthy non-diabetic subjects (aged 23–31 years). The dimensions of the anterior chamber of the eye were measured by a photogrammetric technique, with Polaroid photographs taken of the lower half of the mid-sagittal plane of the eye at an angle of 55° at a magnification of × 16. Photographs were taken before and at regular intervals after the induction of acute hypoglycaemia using an infusion of unmodified (soluble) insulin at 2.5 m-units min−1 kg−1. Plasma adrenaline was measured regularly throughout the study.
2. Plasma glucose fell from 4.5 ± 0.2 mmol/l (mean ± SEM) to a nadir of 1.0 ± 0.1 mmol/l (P <0.01), which coincided with the onset of the acute autonomic reaction. Plasma adrenaline rose from 0.3 ± 0.1 nmol/l to a peak of 3.2 ± 0.6 nmol/l (P <0.01) at 15 min after the autonomic reaction.
3. The volume of the anterior chamber decreased by 8.2% from 284.7 ± 21.5 μl at baseline to 264.5 ± 17.0 μl (P <0.01) at the onset of the autonomic reaction. No significant alteration in axial anterior chamber depth was evident, but peripheral anterior depth decreased from 2.25 ± 0.20 mm at baseline to 2.07 ± 0.14 mm (P <0.05) at the onset of the autonomic response. Pupillary constriction was demonstrated in all subjects, which was most marked at 10 min after the autonomic reaction (baseline 5.0 ± 0.2 mm versus 10 min after reaction 3.7 ± 0.2 mm, P < 0.001).
4. This study has demonstrated an alteration in the dimensions and a reduction in volume of the anterior chamber of the eye in humans during acute insulin-induced hypoglycaemia. These changes in the anterior segment of the eye are probably mediated by autonomic mechanisms which are stimulated by hypoglycaemia.