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Livia Teo, Carol Cheung, Wan Ting Tay, Tien Yin Wong; Associations between Thyroid Dysfunction and Retinal Microvascular Changes. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5106.
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Thyroid dysfunction has been associated with cardiovascular diseases but there are limited data on its effects on the retinal microvasculature. The aim of this study is to examine the associations between thyroid function and retinal vascular caliber and geometric patterns.
This was a population-based, cross-sectional study using data from the Singapore Malay Eye Study (SiMES). Thyroid status was assessed from questionnaires. Retinal vascular caliber and network geometry were quantified from retinal fundus photographs using a semi-automated computer-assisted program according to a standardized protocol. The central retinal arteriolar and venular equivalents (CRAE and CRVE) were calculated, representing the average arteriolar and venular calibers, and the arteriole:venule ratio (AVR) was the ratio of CRAE to CRVE. Retinal vascular network geometry was expressed as branching angles, tortuosity and fractal dimensions.
Of 2841 participants, 75 (2.64%) persons self-reported to have thyroid dysfunction. Subjects with thyroid dysfunction were more likely to be female (76.5% vs. 51.0%, p<0.001) and less likely to smoke (11.3% vs. 21.1%, p=0.03), and had lower diastolic blood pressures (76.60 (standard error 11.06) vs. 79.64 (11.03) mmHg, p = 0.015). After adjustment for age and gender, subjects with thyroid dysfunction had wider CRAE than the subjects without thyroid dysfunction (143.74(1.74)µm vs. 139.40(0.29µm, p =0.014). The association between thyroid dysfunction with wider CRAE persisted after further adjustments for body mass index, systolic blood pressure, HDL cholesterol and current smoking (143.66 (1.78)µm vs. 140.10(0.42)µm, p = 0.041 respectively). There were no significant associations between thyroid dysfunction and CRVE, or any measures of retinal vascular geometry including vessel tortuosity, branching angle and fractal dimension.
Subjects with thyroid dysfunction have wider retinal arterioles, independent of effects on blood pressure. This may reflect local alterations in orbital blood flow or a direct effect of thyroid hormones on the microvasculature, and suggests a novel role for retinal arteriolar caliber as a biomarker of thyroid dysfunction.
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