Slit Lamp Biomicroscopy Can Predict Vascular Complications of Diabetes

Young optometrist
young optometrist
The noninvasive exam may estimate the burden of vascular complications in diabetes.

Bulbar conjunctival blood flow metrics as measured by functional slit lamp biomicroscopy (FSLB) may be a fast, accessible, and noninvasive way to measure and predict vascular complications of diabetes, according to research published in Cornea.

Researchers sought to use FSLB to evaluate the conjunctival vasculature in people with diabetes of varying severity — particularly patients with and without vascular complications — compared with control participants. Investigators postulated that the creation of a “quick, noninvasive, and reliable” screening test could improve the early detection of diabetic complications. 

The patients in the study group included 136 adults recruited from the Miami Veterans Affairs Health System (mean age, 60±11 years; 87% men; 74% nonHispanic). Thirty-eight participants had a diagnosis of diabetes and 4 were excluded from analyses due to missing data. The cohort also included 98 healthy controls, 13 with diabetes but no complications, and 21 with diabetes related complications. 

Researchers noted no significant differences in age, sex, ethnicity, race, or smoking status between the 3 groups. However, they did note increased percentages of individuals with hypertension and hypercholesterolemia in patients with diabetes vs those in the control group. No significant differences in conjunctival microvascular metrics were noted based on age, sex, smoking status, or hypertension or hypercholesterolemia status, but race did impact conjunctival velocities, flow rate, and complexity of morphology. 

The study shows no significant correlations between conjunctival microvascular metrics and HbA1c or diabetes duration. Comparisons of these metrics between groups did show significant differences in velocities. Post-hoc pairwise comparisons show that patients with diabetes but without complications from diabetes had significantly higher axial velocities and cross-sectional velocities than those in the control group. 

Mean velocities were lower in patients who had diabetes with complications, but these differences were not statistically significant. 

Although race and diabetes status were significantly correlated with axial velocities and cross-sectional velocities, no interactions were found between independent variables, with Black patients consistently demonstrating higher axial velocities and cross-sectional velocities compared with White participants. 

Differences in axial velocities and cross-sectional velocities by diabetes status persisted even after race was accounted for, according to the report. 

Diabetes-related complications included nephropathy (62%), cardiovascular disease (52%), neuropathy (38%), retinopathy (33%), cerebrovascular disease (19%), and peripheral vascular disease (10%). Blood flow metrics were not different in comparisons of patients with and without specific complications, but they were inversely correlated with a number of diabetes-related complications. 

All 3 hemodynamic parameters “significantly discriminate” between patients with diabetes with and without complications, the report shows.

To assess for confounders, researchers ran the model including demographics, smoking status, diabetic parameters, and comorbidities, in addition to the 3 hemodynamic parameters. In this model, all parameters were significantly associated with end-organ damage in addition to hypertension. Race did not remain significantly associated with diabetes complications. 

Study limitations include the cross-sectional design, the patient population, and the use of chart review for diagnosis. 

“Given the need for noninvasive tests to monitor vascular status, FSLB might serve as a tool to improve the detection of diabetes related complications,” according to the researchers. “Future prospective studies are needed to validate its use as a predictive tool of early and late diabetic complications in diverse populations.” 


Hwang J, Karanam V, Wang J, et al. Conjunctival vessels in diabetes using functional slit lamp biomicroscopy. Cornea. 2021;40(8):950-957. doi:10.1097/ICO.0000000000002623