A Novel Method for Measuring Anterior Segment Area of the Eye on Ultrasound Biomicroscopic Images Using Photoshop

<div><p>Purpose</p><p>To describe a novel method for quantitative measurement of area parameters in ocular anterior segment ultrasound biomicroscopy (UBM) images using Photoshop software and to assess its intraobserver and interobserver reproducibility.</p><p>Methods</p><p>Twenty healthy volunteers with wide angles and twenty patients with narrow or closed angles were consecutively recruited. UBM images were obtained and analyzed using Photoshop software by two physicians with different-level training on two occasions. Borders of anterior segment structures including cornea, iris, lens, and zonules in the UBM image were semi-automatically defined by the Magnetic Lasso Tool in the Photoshop software according to the pixel contrast and modified by the observers. Anterior chamber area (ACA), posterior chamber area (PCA), iris cross-section area (ICA) and angle recess area (ARA) were drawn and measured. The intraobserver and interobserver reproducibilities of the anterior segment area parameters and scleral spur location were assessed by limits of agreement, coefficient of variation (CV), and intraclass correlation coefficient (ICC).</p><p>Results</p><p>All of the parameters were successfully measured by Photoshop. The intraobserver and interobserver reproducibilities of ACA, PCA, and ICA were good, with no more than 5% CV and more than 0.95 ICC, while the CVs of ARA were within 20%. The intraobserver and interobserver reproducibilities for defining the spur location were more than 0.97 ICCs. Although the operating times for both observers were less than 3 minutes per image, there was significant difference in the measuring time between two observers with different levels of training (<i>p</i><0.001).</p><p>Conclusion</p><p>Measurements of ocular anterior segment areas on UBM images by Photoshop showed good intraobserver and interobserver reproducibilties. The methodology was easy to adopt and effective in measuring.</p></div

Bland-Altman plots of interobserver reproducibility of UBM measurements using Photoshop software by observer 1 and observer 2.

<p>Measurements of anterior chamber area (ACA) (a), posterior chamber area (PCA) (b), iris cross-section area (ICA) (c), and angle recess area (ARA) (d). The difference is observer 2’s measurement minus observer 1’s measurement. The grey dashed line represents regression line of difference between the measurements of observer 1 and observer 2.</p

Illustration of the anterior chamber area (ACA), which was defined by the borders of the corneal endothelium, angle, iris surface, and the anterior lens epithelium.

<p>Illustration of the anterior chamber area (ACA), which was defined by the borders of the corneal endothelium, angle, iris surface, and the anterior lens epithelium.</p

Bland-Altman plots of intraobserver reproducibility of UBM measurements using Photoshop software by observer 2.

<p>Measurements of anterior chamber area (ACA) (a), posterior chamber area (PCA) (b), iris cross-section area (ICA) (c), and angle recess area (ARA) (d). The difference is calculated as the 2nd measurement minus the 1st measurement. The grey dashed line represents regression line of difference between 1st and 2nd measurements.</p

Illustration of the iris cross-section area (ICA), which was bound by the anterior and the posterior surfaces of the iris and the root of the iris.

<p>Illustration of the iris cross-section area (ICA), which was bound by the anterior and the posterior surfaces of the iris and the root of the iris.</p

Illustration of the angle recess area (ARA).

<p>Define the borders of the corneal endothelium and the anterior iris surface, and define the scleral surface junction point as the spur, then draw a circle centered on the spur with diameter of 750 μm (154 pixels) (a). The enclosed area is the ARA (b).</p

Illustration of the posterior chamber area (PCA), which was defined by the borders of the posterior iris surface, lens zonules, and the posterior border of the lens.

<p>Illustration of the posterior chamber area (PCA), which was defined by the borders of the posterior iris surface, lens zonules, and the posterior border of the lens.</p