Conjunctival microvascular haemodynamics in sickle cell retinopathy

Abstract

Purpose: To determine alterations in bulbar conjunctival microvascular haemodynamics in sickle cell retinopathy (SCR) subjects with focal macular thinning (FMT).

Methods: Conjunctival microcirculation imaging and spectral domain optical coherence tomography (SD-OCT) were performed in 22 subjects (eyes) diagnosed with SCR. Based on evaluation of SD-OCT retinal thickness maps, eyes were assigned to one of the two groups: with or without FMT. Conjunctival venular diameter and axial blood velocity were measured in multiple venules in each eye by customized image analysis algorithms. Measurements were then categorized into two vessel size groups (vessel size 1 and 2) and compared between FMT groups. A Pearson correlation coefficient was computed to assess the relationship between retinal thickness and axial blood velocity.

Results: Mean age, haematocrit, sickle cell haemoglobin type and median retinopathy score were not significantly different between the two groups (p ≥ 0.1). Retinal thickness in parafoveal and perifoveal temporal subfields was significantly lower in eyes with FMT as compared to eyes without FMT (p ≤ 0.04). There was a significant effect of FMT on axial blood velocity (p = 0.04), while the effect of vessel size was not significant (p = 0.4). In vessel size 1, axial blood velocity was lower in eyes with FMT than in eyes without FMT (p = 0.03), while in vessel size 2, there was no statistically significant difference between FMT groups (p = 0.1). In vessel size 1, there was a significant positive correlation between axial blood velocity and retinal thickness in the perifoveal (r = 0.48, p = 0.02) and parafoveal (r = 0.43, p = 0.04) temporal subfields.

Conclusion: Conjunctival axial blood velocity in small venules is reduced in SCR subjects with focal macular thinning.

Keywords: bulbar conjunctiva; haemodynamics; retina; sickle cell disease.

Figure 1

Examples of retinal thickness maps obtained in two sickle cell retinopathy subjects without (Left) and with (Right) focal macular thinning (FMT). The Early Treatment Diabetic Retinopathy Study (ETDRS) macular subfields are displayed on each thickness map. Macular thinning is observed in perifoveal temporal and inferior subfields in the subject with FMT.

Figure 2

Examples of conjunctival microcirculation images obtained in two sickle cell retinopathy subjects without (Left) and with (Right) focal macular thinning (FMT). The outlined edges of two selected conjunctival venules (red lines) were automatically identified for diameter measurements (19 μm in both subjects). Space time images (inserts) were derived based on the movement of red blood cells or plasma gaps along the vessel lengths, depicting prominent diagonal bands. Axial blood velocity was measured as the slope of the overlaid red line which represents the prominent bands. Axial blood velocity was lower in the subject with FMT.