Chronic Hypoxia Associated With Reduced Conjunctival Vasculature Structure

A 50-54 year African male patient’s eye examination is done by a young male doctor with an ophthalmoscope Cape Town South Africa
A report shows the condition, which results from cyanotic congenital heart disease, can lead to reduced axial velocity, wall shear rate, and other changes in vessel microvasculature.

Patients with cyanotic congenital heart disease (CHD) are more likely to have lower axial velocity and wall shear rate compared with healthy controls, likely due to hypoxia, according to research results published in Microvascular Research.

Previous studies have reported on abnormalities in retinal microcirculation associated with cyanotic CHD, but there have been no reports discussing slit-lamp assessment of conjunctival microcirculation in this patient population. Researchers therefore evaluated microcirculatory parameters in patients with cyanotic CHD compared with healthy controls. 

The study included 11 patients with cyanotic CHD and 14 healthy controls (mean age, 35±12 years and 40±9 years; 36% women in each group). The primary defect in the cyanotic CHD group was right heart obstruction with reduced pulmonary blood flow. This group was also “markedly hypoxic,” with mean SpO2 of 84±10% and no significant differences in resting heart rate or systolic blood pressure. Mean diastolic blood pressure was lower compared with patients in the control group (68±13 mm Hg vs 79±14 mm Hg). 

Investigators were able to capture conjunctival videos for all patients with no adverse events. No significant differences in vessel diameter were noted (20.2±2.6 µm vs 20.4±2.7 µm in the CHD vs control groups, respectively. Axial velocity was lower in the cyanotic CHD group (0.47±0.06 mm/s vs 0.53±0.05 mm/s), as were blood volume flow (121±30 pl/s vs 145±50 fl/s; not statistically significant) and wall shear rate (153±27 s-1 vs 174±22 s-1) which was significantly lower. 

Vessels were classified into 4 groups based on diameter. Using these groups, researchers compared conjunctival measurements across each patient group using the average of all vessel segments (n=736; 292 cyanotic CHD with 27 per patient vs 444 controls with 32 per control). In total, 44% of these vessels fell within the group 4 diameter range (>22 µm); these were the most frequently observed vessels. Axial velocity did not differ significantly between the study groups for vessel groups 1 through 3, but for group 4 vessels, axial velocity was lower in the cyanotic CHD group (0.50±0.16 mm/s vs 0.58±0.15 mm/s).

Study limitations include the lack of differentiation of vessels into venules or arterioles, but vessel differentiation was not possible within the parameters of this study. The small study size was also noted. 

“Conjunctival microvascular and endothelial function assessment…found reduced [axial flow] and [wall shear rate] compared with healthy controls,” the research concludes. “These changes are suggestive of a microvascular response to chronic hypoxia and secondary erythrocytosis. Such assessments may have a role in the evaluation of patients with [cyanotic CHD] and other causes of hypoxia and erythrocytosis.”


Brennan PF, Jing M, McNeil AJ, et al. Assessment of the conjunctival microcirculation in adult patients with cyanotic congenital heart disease compared to healthy controls. Microvasc Res. Published online April 7, 2021. doi:10.1016/j.mvr.2021.104167