Anterior Ocular Biometrics as Measured by Ultrasound Biomicroscopy

Abstract

Background: High frequency ultrasonography (ultrasound biomicroscopy; UBM) is an ophthalmic diagnostic tool that can be used to measure the depth of the anterior segment (ASD), the anterior chamber angle (ACA), as well as thicknesses of the iris and the ciliary body (CB).

Methods: The anterior segment dimensions and thicknesses were measured by Sonomed 35-MHz.

Results: Measurements for 95 eyes from 52 adults were analyzed. The mean and median ASD and ACA were 2.91, 2.92 ± 0.41 mm and 34.1, 34.3 ± 12.1 degrees, respectively. The angle superiorly was wider than inferiorly (p = 0.04). At the root of the iris, the mid of the iris, and the juxtapupillary edge of the iris, the iris thicknesses (median, mean) were 0.40, 0.41 ± 0.1, 0.50, 0.51 ± 0.1, and 0.70, 0.71 ± 0.1 mm, respectively. The thicknesses of CB and CB together with the ciliary processes (median, mean), were 0.70, 0.71 ± 0.15 mm and 1.36, 1.41 ± 0.15 mm, respectively. The upper quadrant of both the iris and the CB was significantly thicker than the lower quadrant (p = 0.04).

Conclusions: Our biometric measurements for the anterior segment can be used as normative data for anterior segment depth and angle and iris and ciliary body thickness in normal eyes.

Keywords: anterior segment; ciliary body; iris; ultrasound biomicroscopy.

Figure 1

(A) This is an illustration of both the iris and the ciliary body, as seen by ultrasound biomicroscopy (UBM) in this study. The blue line (1) represents the iris thicknesses at 0.8 mm distance from the root of the iris. The yellow line (2) represents the iris thickness halfway down the radial length of the iris. The red line (3) represents the iris thickness at the juxtapupillary edge. The blue line (4) represents the thickness of the ciliary body, and the green line (5) represents the thickness of the ciliary body and the ciliary processes. (B) The red line (1) represents the anterior chamber angle, and the green line (2) represents the anterior segment depth, all as described in the methodology section.

Figure 2

Ultrasound biomicroscopy (UBM): (A) This is an example of the UBM that shows the measured thicknesses for the iris and the ciliary body at different locations. The blue line (1) represents the iris thicknesses at 0.8 mm distance from the root of the iris. The yellow line (2) represents the iris thickness halfway down the radial length of the iris. The red line (3) represents the iris thickness at the juxtapupillary edge. The blue line (4) represents the thickness of the ciliary body, and the green line (5) represents the thickness of the ciliary body and the ciliary processes. (B) The iris thickness of one of the participants was 0.42 mm at a distance of 0.8 mm from the iris root, 0.52 mm in the mid of the radial length of the iris, and 0.7 mm at the juxtapupillary edge. The ciliary body was 0.72 mm thick, while the ciliary body with ciliary processes was 1.38 mm thick.