Background: Recently, novel anatomic parameters that can be measured by optical coherence tomography (OCT), have been identified as a more objective and accurate method of defining the iridocorneal angle. The aim of the present study is to measure the iridocorneal angle by Fourier domain (FD) OCT and to identify correlations between angle measurements and subject factors in a large healthy Caucasian population.
Methods: A cross sectional study was performed in 989 left eyes of 989 healthy subjects. The iridocorneal angle measurements: trabecular-iris angle (TIA), angle opening distance (AOD500) and trabecular-iris space area (TISA500) 500 μm from the scleral spur, were made using the FD-OCT RTVue®. Iris thickness was also measured. Correlations were examined between angle measurements and demographic and ocular factors. The main determinants of angle width were identified by multivariate linear regression.
Results: TIA could be measured in 94% of the eyes, and AOD500 and TISA500 in 92%. The means recorded were TIA 35.8 ± 12.2 degrees (range 1.5 to 76.1), AOD500 542.6 ± 285.4 μm (range 15 to 1755), and TISA500 0.195 ± 0.104 mm(2) (range 0.02 to 0.62). The correlation between the temporal and nasal quadrant was R = 0.902 for TIA. The reproducibility of measurements was excellent (intraclass correlation coefficient >0.947). Mean angle width measurements were smaller in women (p = 0.02). Correlation was detected between angle means and anterior chamber volume (ACV; R = 0.848), anterior chamber depth (ACD; R = 0.818), spherical error (R = -0.619) and age (R = -0.487), while no correlation was observed with Intraocular pressure (R = -0.052). ACV emerged as the main determinant of TIA (R(2) = 0.705; p < 0.001).
Conclusions: In this Caucasian population, strong correlation was detected between FD-OCT anterior angle measurements and ACV, ACD, spherical refractive error and sex, emerging the ACV as the main determinant of TIA.
Keywords: Anterior chamber; Glaucoma; Iridocorneal angle; Optical coherence tomography.