Dynamic changes of iridocorneal angle morphology during accommodation in healthy children

Abstract

Purpose : The dynamics of the iridocorneal angle (ICA) during accommodative effort have not previously been explored, though anatomy would indicate that Schlemm’s canal (SC) morphology may be affected by ciliary muscle (CM) contraction. This work aims to describe changes in ICA morphology in children, a population with a naturally large range of accommodation.

Methods : We acquired anterior segment OCT images (Tomey SS-1000 CASIA, Nagoya, Japan) of ICA and CM of the right eye of 50 children age 4 to 16 years with healthy eyes, at 2 levels of accommodation: 2.5D (“relaxed”) and 15D (“intense accommodative effort”). We noted triplicates of semi-automated nasal ICA measurements: angle opening distance at 500/750 μm (AOD-500, -750), trabecular iris space area at 500/750 μm (TISA-500, -750) and trabecular iris angle at 500/750 μm (TIA-500, -750). One observer manually obtained triplicate measurements of SC diameter (SC-D) and cross-sectional area (SC-CSA) and CM width at 1, 2 and 3 mm from scleral spur (CM-1, CM-2, CM-3). Triplicates were summarised as means. Using SPSS24 (IBM, Armonk, USA) we calculated cohort means and standard deviations (SD). Comparisons: 1) all parameters: 2 tailed t-test with cutoff at a) age 10 years and b) spherical equivalent of 0D; 2) SC-D, SC-CSA, CM-1, 2, 3: 2-tailed paired t-test.

Results : Image quality was adequate for analysis in a high proportion (Table 1). SC parameters and CM width were not significantly different in younger versus older or myopic versus emmetropic/hypermetropic children (p>0.05). SC-D and CM-1 significantly increased with intense accommodative effort, whilst CM-3 significantly decreased (Table 1).

Conclusions : This is the first study to demonstrate dynamic changes in SC-D with accommodation in humans.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

Table 1. ICA, SC parameters and CM width on standard and high-resolution AS-OCT with relaxed and intense accommodative effort.