MADISON, Wis. – Individuals with type 1 diabetes are slightly more likely to be nearsighted than those with type 2 diabetes, but overall rates of refractive error among adults with diabetes are similar to those reported in the general population, according to new research reported in the January issue of Archives of Ophthalmology.
Dr. Barbara E.K. Klein and her colleagues from the University of Wisconsin School of Medicine and Public Health, Madison, reported on the distribution of and change in refraction in the Wisconsin Epidemiologic Study of Diabetic Retinopathy, a large community-based study of persons with types 1 and 2 diabetes who were first identified in 1979-1980. They also examined risk factors for change in refraction.
Dr. Klein and her colleagues initially identified 10,135 diabetic persons, and then selected a sample of 2,990 individuals diagnosed with diabetes before age 30 for baseline examination (Arch. Ophthalmol. 2011;129:56-62).
For this latest analysis, the researchers used baseline examination and 10-year follow-up data of individuals aged 20 years or older at baseline. This group included 724 patients with type 1 diabetes, 1,370 patients with type 2 diabetes, and 269 patients in a nondiabetic comparison group.
The mean spherical equivalent at baseline was –1.24D in the patients with type 1 diabetes, +0.69D in those with type 2 diabetes, and –0.15D among the nondiabetic patients. The mean change in spherical equivalent was –0.28D among the type 1 patients and +0.48D among the type 2 patients. After adjusting for age and education, the researchers found a borderline significant difference in change in refraction between the groups.
The findings among the type 2 patients were similar to those seen during a 10-year interval in another study. "Most important, we found that refraction and its correlates in adults with diabetes, regardless of type, are similar to those reported in adults without diabetes," the researchers wrote.
Although they anticipated that glycemia would be an important determinant in refraction, this was not the case in either diabetic group. Also, there was no relationship between the severity of retinopathy and refractive error of patients in either diabetic group.
Limitations of the study included the exclusion of patients who were significantly older, had more hyperopic refraction, were more likely to have nuclear cataract, and had more severe retinopathy. "Thus, these exclusions might be expected to bias the baseline estimates of refraction toward myopia," the researchers wrote. Age adjustment in subsequent analyses would likely reduce some of these effects, they noted.
Dr. Klein and her colleagues reported no financial disclosures. The research was supported by grants from the National Institutes of Health and, in part, by senior scientific investigator awards from Research to Prevent Blindness.