CORNEAL SWELLING AND RECOVERY FOLLOWING WEAR OF THICK HYDROGEL CONTACT-LENSES IN INSULIN-DEPENDENT DIABETICS

Thick, 0.34 mm, 38% water hydrogel lenses were fitted, under a pressur e patch, to one eye of 18 type I diabetic patients (aged 18-40 years) to assess the acute response to hypoxia and hypercapnia; the response was compared with that in 18 healthy, aged-matched nondiabetic subject s; the closed-eye lens wear was started mid-morning. Pre-lens wear ass essments were made of acuity, intraocular pressure (IOP), central corn eal thickness (CCT) and corneal appearance by biomicroscopy. The mean duration of the diabetes was 13 +/- 7 years and the average fasting bl ood glucose was 8.7 +/- 3.3 mM l(-1) Baseline CCT values were marginal ly greater in diabetic patients (600 +/- 33 mu m) compared with a grou p of non-diabetic control subjects (584 +/- 26 mu m; P > 0.5). A 7.7 /- 2.1 % increase in CCT was measured after 3 h lens wear in the diabe tic patients while an average 10.6 +/- 2.4 % increase in CCT was measu red in the control subjects (P < 0.05). The recovery of corneal thickn ess to baseline values in diabetic patients was slower (at 44.8 +/- 2. 0 % per hour) than the control subjects (53.9 +/- 2.1 per hour; P < 0. 05) although recovery of corneal thickness occurred in both groups wit hin 2.5-3 h. IOP values (non-contact tonometry) were higher in the dia betic patients than in the controls (14.5 +/- 2.9 vs 12.4 +/- 1.7 mmHg ; P < 0.01). Overall, those corneas with greater baseline CCT values t ended to swell less than those with lower baseline CCT values (r = 0.5 82). Positive correlations were also found between corneal thickness a nd IOP and blood glucose. The diabetic patients thus tended to have sl ightly thicker corneas (but this could be related to blood glucose or IOP rather than true corneal disease) and also had corneas that tended to swell less with a contact lens stress test (but this could be cons titutively due to the slight oedema already present). The different co rneal response in diabetic patients may thus be the result of physical determinants such as initial oedema and IOP and not the result of a d isease of the cornea itself.