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A retrospective study found that in both patients with type 2 diabetes and non-diabetics, average central macular thickness was lower in Asians than Caucasians. Why is this significant for clinicians?
This article was reviewed by Gloria Wu, MD.
Findings of a retrospective study comparing Asian and Caucasian patients with type 2 diabetes mellitus suggest that it may be important to consider ethnicity-related differences when interpreting macular thickness data, according to researchers from the University of California San Francisco.
Analyzing data from 96 subjects, including 24 Asian non-diabetics, 24 Caucasian non-diabetics, 24 Asian diabetics, and 24 Caucasian diabetics, the investigators found that average central macular thickness (CMT) was lower in Asians than Caucasians in both the diabetic and non-diabetic cohorts. While HbA1c levels were similar comparing Asian and Caucasian diabetics, the Asians were less likely than Caucasians to have diabetic macular edema (DME) as defined by a central macular thickness (CMT) >250 μm.
A difference in body mass index (BMI) between Asians and Caucasians may account for some of the difference as the study also found lower BMI in Asians than Caucasians and an association between lower BMI and less DME.
“Asians are the fastest-growing ethnic group in the United States and are at an increasing risk of developing type 2 diabetes,” said Gloria Wu, MD, adjunct clinical instructor, Department of Ophthalmology, University of California San Francisco School of Medicine, San Francisco, CA. “Our study suggests there is a need for more research to evaluate ethnicity-related differences in the macula of patients with diabetes to determine whether we should consider ethnicity in the context of diagnosis and management of DME.”
Subjects were identified for inclusion in the study through a review of electronic health records for the years 2017 to 2020. Eligibility criteria included Asian or Caucasian ethnicity, age range >18 to 95 years, visual acuity 20/20 to 20/50, and having a CMT measured by spectral-domain OCT (Spectralis, Heidelberg Engineering) plus an HbA1c measurement within 3 months of the OCT imaging. Control patients were selected using an HbA1c cutoff of 6.0% and diabetic patients were identified based on having an HbA1c >6.1%. A CMT >250 μm was used to define DME.
The Asian and Caucasian subgroups within both the control and diabetic cohorts were similar with respect to age and HbA1c levels. The average visual acuity was also similar for the Asian and Caucasian controls, but was poorer for the Asians than the Caucasians within the diabetic cohort (20/31 and 20/23, respectively). Average CMT was lower for the Asians than the Caucasians in both the control group (265 versus 285 μm) and among the diabetics (286 versus 290 μm).
The same patterns were seen using data from the eye with the higher CMT (“maximum CMT”). The percentage of patients with a maximum CMT ≥276 μm was significantly greater among Caucasians than Asians in both the control cohort (P=.0039) and the diabetic cohort (P=.0066). Among diabetics, a significantly greater percentage of Caucasians than Asians had a BMI ≥32 kg/m2 (4.2% versus 33.3%).
An analysis categorizing subjects by BMI and maximum CMT found a statistically significant correlation for having a CMT >281 μm among Caucasian diabetics with a BMI ≥26 kg/m2. Among Asian diabetics, having a BMI ≥22 kg/m2 correlated with having a maximum CMT >254 μm.
“In fact, six Asian diabetics but none of the Caucasian diabetics had an average CMT ≤265 μm,” said Jonathan Wong, medical student, Medical College of Wisconsin, Milwaukee. “The finding was the same in an analysis using the maximum CMT reading instead of the average.”