We read the article entitled “Choroidal Thickness in Non-Arteritic Anterior Ischemic Optic Neuropathy” by Schuster and associates, and would like to offer our comments. The authors, in this hospital-based case-control study, demonstrated that patients with non-arteritic anterior ischemic optic neuropathy (non-arteritic AION) in the affected eyes and in the unaffected contralateral eyes had a significantly thinner macular choroid after adjusting for age, optic disc diameter, sex, and refractive error in comparison to the individuals of a control group without fundus or optic nerve disorders. The authors suggest that a thin choroid may be added to the diagnostic features of non-arteritic AION. We congratulate and applaud their interesting and important work on this topic; however, some important issues need to be addressed.
As the choroid is a highly vascular tissue, choroidal thicknesses are known to vary with intraocular pressure, blood pressure, smoking, and the use of certain drugs, such as phosphodiesterase inhibitors. The choroid also suffers from microvascular changes and dyslipidemia. However, the authors did not exclude the subjects having systemic diseases such as diabetes, hypertension, hypercholesterolemia, and obstructive sleep apnea. Also, the authors did not indicate whether they had any smokers or subjects with vascular medications, although both of them were shown to affect choroidal thickness. As systemic diseases are often comorbid with non-arteritic AION, expecting diabetes mellitus, obstructive sleep apnea, or hypertension more in the non-arteritic AION group is reasonable. Inclusion of these kinds of patients obviously affect the choroid and may change the results. Therefore, it should be kept in mind that choroid thinning seen in Schuster and associates’ study might be attributable to the underlying systemic diseases and concomitant interventions in patients.
The authors stated that age and refractive error were corrected before comparing choroidal thickness between the groups. However, they did not adjust the axial length, which is known to be among the most important confounding factors for the interpretation of the choroidal thickness. Although refractive error is associated with axial length, it is not stable throughout life. Myopic shifts can occur, especially in elderly patients, because of nuclear cataract progression. In this study, non-arteritic AION patients tended to be older than controls, although not significantly (66.9 vs 71.9, P = .07). Therefore, adjusting axial length instead of refractive error would be more accurate, particularly in this older population. In contrast to this study, a very recent study demonstrated an increase in choroidal thickness in eyes with chronic non-arteritic AION.
Moreover, further large-scale, high-quality studies to confirm these preliminary results would be worthwhile. We congratulate the authors on their informative article and hope our remarks will contribute to more accurate elaboration of the results.