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Editors Selection IGR 15-2

Anatomical Structures: Schlemm's Canal

Comment by Alex Huang on:

78884 Schlemm's canal measured by optical coherence tomography and correlation study in a healthy Caucasian child population, Fernández-Vigo JI; Kudsieh B; De-Pablo-Gómez-de-Liaño L et al., Acta Ophthalmologica, 2019; 97: e493-e498

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In this paper, the authors evaluate oft studied anterior segment optical coherence tomography (AS-OCT) endpoints in a frequently unstudied population, children. Using Fourierdomain AS-OCT, cross-sectional acquisition of angle images were obtained from 290 healthy Caucasian subjects (10.7 ± 3.4 average years of age) in the nasal/temporal quadrants of the eyes. Angle, Schlemm's canal (SC), and trabecular meshwork measurements were made and compared temporal vs. nasal, between eyes, and across age. The results showed that SC measurements were only possible in ~70% of eyes due to poor image quality per the authors. Intra- and inter-reproducibility of capable measurements were performed showing good intra-class correlation coefficients ~0.94. Quantitative measurement did not differ much between eyes and between the nasal/temporal quadrants of each eye. However, multivariate analyses did yield a statistically significant positive correlation between age and SC size (p ≤ 0.041).

Anterior segment OCT is limited by the lack of a reference function where OCT can be performed in the same location across visits

The primary limitation of this paper was that only one image per quadrant was analyzed for each quadrant. This makes analyses difficult given known segmental aqueous hour outflow (AHO) patterns seen in aqueous angiographic studies^1,2 and in structural evaluation of AHO pathways in adults.³ Further, anterior segment OCT is limited by the lack of a reference function where OCT can be performed in the same location across visits. In a cross-sectional study this is not critical, but this is a key future challenge.

Ultimately, the key finding was the positive relationship between SC size and age. Potential explanations include passive change to SC as the eye grows and changes to SC size that is somehow connected to age-related AHO alterations. As the authors mentioned, they did not have IOP to add to their results. The next steps could be longitudinal evaluation of SC size with age to confirm findings here which ultimately would be best accomplished with an AS-OCT reference function.

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