Schlemm’s Canal Size Is Associated with Axial Length, Age and Corneal Thickness in Normal Eyes

Abstract

 

Purpose

 

To assess the associations between Schlemm’s canal (SC) size with ocular and demographic factors in normal eyes.

 

Methods

 

Serial horizontal enhanced depth imaging (EDI) optical coherence tomography (OCT) B-scans were obtained in the nasal limbal area from one eye of normal subjects (21 scans per 15x5 degree rectangle; interval between scans, ~140 µm; Fig 1A and 1B). The cross-sectional area (CSA) of SC was measured in each EDI OCT B-scan (Fig 1C) by an independent observer, who was masked to the clinical information of the examined eyes. Associations between mean SC CSA and axial length, age, central corneal thickness (CCT), and intraocular pressure (IOP) were assessed using correlation analysis. Mean SC CSA was also compared between different genders and races.

 

Results

 

Thirty-six normal eyes (36 subjects) were included. Mean SC CSA, axial length, age, CCT and IOP were 4538±759 µm², 24.5±1.3 (22.7-27.6) mm, 36±13 (22-67) years, 549±37 (492-632) µm and 14.0±2.3 (10-18) mmHg, respectively. In a univariate model, SC CSA was significantly correlated with axial length, age and CCT (R=0.633, -0.500 and -0.467, respectively; all p<0.01), but not with IOP (p=0.52) (Fig 2). In a multivariate model, SC CSA still had a moderate correlation with axial length, age and CCT (R=0.529, -0.385 and -0.377, respectively; all p<0.03). Mean SC CSA was similar between males and females (p=0.22), and also among different races (11 Caucasians, 4 African-Americans, 5 Hispanics, and 16 Asians; p=0.51).

 

Conclusions

 

SC is larger in eyes with longer axial lengths and thinner corneas, and may decrease with age. This may have important implications for the glaucoma treatments that target the trabecular outflow pathway.