The mechanism in the pathogenesis of diabetic corneal disease is unclear, but aldose reductase may be involved in the corneal disease. We studied the effects of an aldose reductase inhibitor (ARI) on the ocular surface of diabetic patients. Fourteen aphakic or pseudophakic patients with diabetes were treated with orally administered ONO-2235 (150 mg/day). Corneal sensation, vital staining of ocular surface, and tear production were examined before and 3 months after the administration. After a 3-month period of oral ARI, corneal sensation recovered significantly (from 4.1 +/- 4.8 to 3.0 +/- 3.1 g/mm2; p = 0.015), with parallel improvements in rose bengal and fluorescein staining scores (p < 0.05). Tear break-up time had also improved (p = 0.003). Results of Schirmer's test (p = 0.03) and the cotton-thread test (p = 0.0001) showed significant improvement in tear production. Improvement in the dynamics of tear production may be due to an improvement in corneal sensitivity. An oral ARI can improve corneal epithelial changes caused by diabetes, probably through recovery of corneal sensation and tear production.