Relationship Between Retinal Vessel Tortuosity and Oxygenation in Normal Control and Sickle Cell Retinopathy Subjects

Abstract

Purpose : Increased retinal vessel tortuosity is among early abnormalities that occur due to many retinopathies. Previous studies have shown increased tortuosity of retinal microvessels due to sickle cell retinopathy (SCR). The purpose of the current study is to investigate the relationship between retinal vessel tortuosity and oxygenation in normal control (NC) and SCR subjects.

Methods : Scanning laser ophthalmoscopy (Optos 200TX) at laser wavelengths of 532 nm and 633 nm was performed in both eyes of 15 NC and 13 SCR subjects. Oxygen saturation (SO₂) was measured in retinal arteries and veins within a circumpapillary region centered on the optic nerve head (ONH) and extended between 1 and 2 ONH radii using a previously published custom software, and oxygen content (O₂= O_2max×H_gB×SO₂/100) was determined. Retinal vessel tortuosity index (VTI) and number of inflection points (IP) were measured based on a previously established method applied to vessels within a circumpapillary region that extended between 1.5 and 5 ONH radii. Measurements of O₂, VTI and IP were averaged in retinal arteries and veins per eye. Compiled data were submitted for linear mixed model analysis, with diagnosis (NC, SCR), vessel type (artery, vein) and eye (right, left) as fixed effects and subject as a random effect, with and without adjusting for covariates, age and mean arterial pressure (MAP). Significance was accepted at P≤0.05.

Results : NC subjects (49±7 years) were older than SCR subjects (39±15 years) (P=0.02). MAP was higher in NC (96±11 mmHg) than SCR (81±10 mmHg) subjects (P=0.001). Vessel type had a significant effect on O₂ and IP (P≤0.009), but not on VTI (P=0.9). O₂ was lower in SCR (10±3 mLO₂/dL) compared to NC (15±5 mLO₂/dL) (p≤0.001), with and without covariates adjustment. VTI was higher in SCR (0.22±0.15) compared to NC (0.15±0.05) without adjusting for the covariates (P=0.01), but the difference became less significant after covariates adjustment (P=0.06). IP was higher in SCR (10±1) compared to NC (8±2) with and without adjusting for the covariates (P=0.003). There was a negative linear relationship between IP and O₂ (p=0.02), but no significant relationship between VTI and O₂ (P=0.5).

Conclusions : Reduction in vascular oxygen content was associated with increased number of vessel inflection points, suggesting the retinal vessels become more twisted in response to hypoxia.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.