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Study links diabetes, hyperglycemia to increased IOP
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A large study based on the population of the Singapore Epidemiology Eye Disease Study showed direct association between diabetes or high long-term hyperglycemia and increased IOP, non-mediated by central corneal thickness.
The aim of the study was to confirm the association between diabetes and IOP in a large multiethnic Asian population and to determine whether this association was partly mediated by central corneal thickness (CCT) or other factors, such as axial length (AL) and spherical equivalent.
The analysis was conducted on the 2,524 subjects who were found to have diabetes in the Singapore Epidemiology Eye Disease Study. A consistent association between diabetes and higher IOP was found in this subgroup, as it was between diabetes, thicker CCT and shorter AL. High serum glucose or HbA1c levels were also significantly associated with IOP elevation. No association between serum glucose and IOP was found in patients without diabetes.
By linear regression analysis CCT was the only factor identified as a potential mediating variable in the diabetes-IOP association, because spherical equivalent was not associated with diabetes and AL was not associated with IOP. However, the indirect contribution of CCT to both the diabetes-IOP and high serum glucose-IOP association was small and not significant.
“Our findings suggest that higher IOP associated with diabetes is not primarily mediated through thicker CCT. Therefore, diabetes and poorer long-term glycemic control may potentially place one at a greater risk of glaucoma through non CCT-related mechanisms,” the authors wrote.
The physiological mechanism that underlies the association between diabetes and higher IOP remains unclear, they noted. One hypothesis is that the accumulation of advanced glycation end products might cause cell apoptosis within the trabecular meshwork. Another possible mechanism is the elevation of TGF-, reducing aqueous outflow.
Whatever the cause, elevated IOP in patients with diabetes is not to be considered as an overestimation due to thicker CCT, but as an objective measurement, which may increase the risk of glaucoma in these patients, they said. – by Michela Cimberle
Disclosure: None of the authors reported a relevant financial disclosure.
Perspective
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Lisa M. Young, OD, FAAO
It is well known that diabetes can lead to diabetic retinopathy and neovascular glaucoma, but the relationship between diabetes and other types of glaucoma is rather confusing. When I examine a diabetic patient with an increased IOP, I’m reminded of the varying study outcomes and wonder if and what I should take into consideration.
While diabetes has been associated with a thicker central corneal thickness (CCT), it has been unclear whether that association and the subsequent overestimation of IOP is directly linked to the higher IOP readings. Interestingly, Luo and colleagues in their large, population-based study found that established diabetics indeed have higher IOP, and, although the exact causative mechanism is unclear, these findings are largely unrelated to an overestimation due to CCT.
Understanding that our diabetic patients may have increased IOP that is independent of CCT sheds a ray of light on this confusing relationship between glaucoma and diabetes. This leads me to believe that diabetes deserves higher consideration as a potential risk factor for glaucoma, at least until a clearer picture of the biomechanics of this diabetes-IOP phenomenon has been uncovered.
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