2 6 10 23 31 36 9 13 18 26 32 37 16 17 19 25 29 21 24 27 29 33 15 11 11 4 5 Subjects and methods Five healthy Caucasian subjects (two males and three females) were recruited for this study. Mean age was 24.8 years (SD ±4.6 and range 21.2–32.6) and mean body mass index (BMI) was 24.2 kg/m2 (SD ±3.2 and range 21.4 - 29.7). The Medical Ethics Committee of the VU University Medical Center in Amsterdam approved the study protocol, and written informed consent was obtained from all subjects after the nature of the study had been explained. Subjects with a history of diabetes mellitus (or a fasting plasma glucose >5.5 mmol/l), a BMI of >30 kg/m2, visual acuity of <0.5 (Snellen), or a history of ocular pathology were excluded from the study. Procedure to induce hyperglycemia After a 10-hour overnight fast, the subjects received a subcutaneous injection of 100 µg synthetic somatostatin (Sandostatin, Novartis, Basel, Switzerland) in order to suppress the endogenous insulin secretion during glucose loading. Each subject had an oral glucose tolerance test (OGTT) (glucose 75 g) 30 minutes after the somatostatin injection. Blood glucose levels were measured with a blood glucose analyzer (HemoCue Diagnostics BV, Oisterwijk, the Netherlands). Endogenous insulin levels were determined with immunometric assays (Luminescence, Bayer Diagnostics, Mijdrecht, the Netherlands) in the Laboratory of Endocrinology of the Department of Clinical Chemistry in the VU University Medical Center. The subjects remained in a fasting state during the entire procedure. Measurement of ocular parameters 4 5 lens 5 8 22 34 3 30 lens 4 P Results 1 Fig. 1 Changes in blood glucose (BG) levels in the five subjects after the administration of somatostatin and glucose; the oral glucose load (75 g) was administered at time = 0 minutes  p lens 2 lens 3 Fig. 2 lens lens p  Fig. 3 a solid line b line of dashes c line of dashes solid line  Discussion 11 7 12 11 3 30 35 14 38 21 29 21 24 27 29 33 20 23 28 37 It is surprising that a change in refraction and ocular parameters could be determined in only one subject. It must be noted that the procedures for inducing hyperglycemia and monitoring blood glucose were, to some extent, different for subject 1 compared to the other subjects. Because of a delayed elevation in blood glucose level, a second oral glucose load (150 g instead of 75 g glucose) was administered. Nevertheless, the maximum blood glucose value of subject 1 did not exceed that of the other subjects, and the endogenous insulin level was adequately suppressed during the glucose loading. Furthermore, in order to obtain sufficient blood samples, 0.9% saline had to be administered to keep the antecubital vein open. Therefore, it could not be excluded that the administration of saline contributed to the refractive change and alterations in the lens of subject 1. However, no studies have yet reported any refractive change due to saline administration. 10 24 29 32 1 In sum, the results of this study show that induced hyperglycemia generally does not cause changes in the refractive properties of the healthy human eye. However, there were interindividual variations, as illustrated by subject 1, who had a hyperopic shift of refraction and a change in shape and equivalent refractive index of the lens during hyperglycemia. This could provide an explanation for the mechanism underlying the refractive changes often experienced by patients with DM and hyperglycemia.