In this study of generally healthy 7- to 9-year-old children, we showed that eyes with smaller vertical optic disc diameter had smaller retinal arteriolar and venular calibers, independent of magnification, ethnicity,
16 BMI,
20 and other potential confounding factors.
Our findings are consistent with observations in older adults (mean age, 69 years) in the Beaver Dam Eye Study, which showed that eyes with the smallest optic discs had smaller retinal arteriolar and venular calibers, as measured with similar retinal vessel measurement software.
13 However, because many ocular and systemic disease processes are associated with retinal arteriolar narrowing in older adults, the validity of these associations in the Beaver Dam Eye Study was uncertain. Although the Beaver Dam analysis controlled for some of these factors (e.g., age and blood pressure), the possibility of residual confounding from chronic blood pressure changes and other risk factors, such as smoking, medication use and diabetes, cannot be totally excluded.
11 Our present study in young, healthy children is therefore important, as it indicates that the association between optic disc size and retinal vascular caliber is very likely a true anatomic relationship. To the best of our knowledge, there are no other comparable studies (i.e., in children) in the current literature.
As hypothesized by previous investigators,
13 an association of smaller optic disc size with narrower retinal vessels could be related to the primary biological mechanism involved in the pathogenesis of nonarteritic ischemic optic neuropathy.
28 The association between smaller optic discs and narrower retinal vessels has been attributed to the crowding at the lamina cribrosa in eyes with small optic discs, which in turn may lead to compression of retinal vessels at the disc, and thereby predispose eyes to nonarteritic ischemic optic neuropathy.
13
Our findings may also have implications in future studies of retinal vascular caliber in ocular and systemic diseases. Most existing studies did not consider the ocular factors likely to influence retinal vascular caliber. Although we demonstrated in prior work that intraocular pressure is not associated with retinal vascular caliber,
29 the present study indicates that variation in optic disc dimensions may be relevant factors to be accounted for in studies of retinal vascular caliber with ocular outcomes.
Strengths of our study include its sample of healthy children, generally free of confounding factors arising from systemic and ocular diseases, and the masked evaluation of retinal vascular caliber by a previously validated retinal image-analysis program, shown to have high reproducibility. However, there are several potential limitations. First, our study population was drawn from only three schools and may therefore not truly represent the entire community. Second, although our study sample was randomly drawn from the SCORM cohort, selection bias cannot be totally excluded, as our participants had some characteristics that differed from those of the remaining cohort. Third, our findings could reflect proportional changes due to confounding from magnification or anthropometric factors, though we believe that this is unlikely to be the case, as the optic disc and retinal vessel measurements were both corrected for magnification, and BMI was included in our multivariate analysis. Finally, although our observed associations between optic disc diameters and retinal vascular caliber were significant, the magnitude of differences in retinal vascular caliber (in pixels) was small. Thus, the clinical significance of our findings remains unclear.
In conclusion, in our cohort of generally healthy 7- to 9-year-old children, eyes with smaller optic discs had narrower retinal arterioles and venules. This anatomic relationship provides additional insights into the retinal vascular pattern in relation to optic disc morphology, which may be relevant to understanding vascular changes in diseases such as glaucomatous and ischemic optic neuropathies.