Take Diabetes Into Consideration When Assessing for Glaucoma

Miriam E. Tucker

January 10, 2019

Diabetes and hyperglycemia are associated with thicker central corneal thickness (CCT), which could lead to overestimation of intraocular pressure when assessing patients for glaucoma, new research suggests.

The findings were published online January 4 in JAMA Network Open by Xiao-Yang Luo, MD, PhD, of Guangdong Eye Institute, Guangdong General Hospital, Guangzhou, China, and colleagues.

CCT is associated with the onset and progression of glaucoma. In this study of nearly 9000 adults of Chinese, Malay, and Indian origin living in Singapore, CCT was significantly thicker in those with diabetes, higher random glucose levels, and higher HbA1c values. The latter two associations were seen only among individuals with diabetes, not those without.

"Our study showed diabetes, high serum glucose level, and HbA1c were associated with thicker cornea, which may lead to overestimation of intraocular pressure," lead author Ching-Yu Cheng, MD, PhD, of the Singapore Eye Research Institute, told Medscape Medical News.

Cheng advises that ophthalmologists "take diabetes status, serum glucose level, and HbA1c into account when interpreting intraocular pressure," as well as "monitor corneal thickness regularly in the long-term follow-up of individuals with diabetes and glaucoma or [suspected] glaucoma, in order to obtain a better interpretation of intraocular pressure measurement."

Association of CCT With Diabetes Independent of Diabetes Duration  

The investigators conducted a cross-sectional analysis of the Singapore Epidemiology of Eye Diseases study, which took place from 2004 to 2011 and involved more than 10,000 Chinese, Malay, and Indian individuals aged 40 years or older who had no prior refractive or cataract surgery or corneal disease.

Of the 8846 participants (17,201 eyes) included in the analysis, almost a third (29.4%) had diabetes.

After adjustment for age, sex, and ethnicity, participants with diabetes had a mean CCT that was 5.2-μm thicker compared to those without diabetes (P < .001). And after further adjustment for corneal curvature, axial length, and body mass index, CCT was 4.9-μm thicker among those with diabetes (P < .001).

Multivariable analyses also showed that thicker CCT was associated with higher random glucose levels (P < .001 per 10 mg/dL) and higher HbA1c (P < .001 per percentage point).

The associations of higher random glucose and HbA1c with thicker CCT were seen only in the group with diabetes. And in the diabetes group, the observed associations were independent of diabetes duration.

Results were similar among the three ethnic groups in the study.

"Generalizability of our data to other ethnic populations may be limited, especially for non-Asian populations, yet we believe that other ethnic groups will have similar findings," Cheng told Medscape Medical News.

Caveats and Next Steps

He cautioned, however, that the cross-sectional design of this study prevents any inferences about causality. "Prospective cohort data are warranted to confirm the association," he said.

Cheng also said that the next step planned for this research will involve use of confocal microscopy of the corneal endothelium, which could provide potential insights on corneal thickening changes among individuals with diabetes.

The authors have reported no relevant financial relationships.

JAMA Netw Open. Published online January 4, 2019. Full text

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