Semiautomatic Extraction Algorithm for Images of the Ciliary Muscle

Abstract

Purpose To development and evaluate a semi-automatic algorithm for segmentation and morphological assessment of the dimensions of the ciliary muscle in Visante™ Anterior Segment Optical Coherence Tomography images. Methods Geometric distortions in Visante images analyzed as binary files were assessed by imaging an optical flat and human donor tissue. The appropriate pixel/mm conversion factor to use for air (n = 1) was estimated by imaging calibration spheres. A semi-automatic algorithm was developed to extract the dimensions of the ciliary muscle from Visante images. Measurements were also made manually using Visante software calipers. Interclass correlation coefficients (ICC) and Bland-Altman analyses were used to compare the methods. A multilevel model was fitted to estimate the variance of algorithm measurements that was due to differences within- and between-examiners in scleral spur selection versus biological variability. Results The optical flat and the human donor tissue were imaged and appeared without geometric distortions in binary file format. Bland-Altman analyses revealed that caliper measurements tended to underestimate ciliary muscle thickness at 3 mm posterior to the scleral spur in subjects with the thickest ciliary muscles (t = 3.6, p < 0.001). The percent variance due to within- or between-examiner differences in scleral spur selection was found to be small (6%) when compared to the variance due to biological difference across subjects (80%). Using the mean of measurements from three images achieved an estimated ICC of 0.85. Conclusions The semi-automatic algorithm successfully segmented the ciliary muscle for further measurement. Using the algorithm to follow the scleral curvature to locate more posterior measurements is critical to avoid underestimating thickness measurements. This semi-automatic algorithm will allow for repeatable, efficient, and masked ciliary muscle measurements in large datasets.

Quantification of the ciliary muscle and crystalline lens interaction during accommodation with synchronous OCT imaging

“…However, our preliminary findings suggest that caution must be exercised when evaluating time constants and latencies of the ciliary muscle thickness during accommodation if manual segmentation is used, especially if the image contrast over the ciliary muscle apex is low [26,27]. Semiautomatic segmentation algorithms and analytical methods for morphological data extraction from OCT images of the ciliary muscle have been recently proposed [19,35], which may help reduce the variability and subjectivity of the analysis.…”

“…In this study, we used the maximal ciliary muscle thickness to quantify the change in ciliary muscle dimensions in the accommodation diagram. However, a different metric, such as thickness at multiple positions, length, or cross-sectional area [19,23,24,34,35], may be used to generate accommodative diagrams.…”

Observation of Ciliary Body Changes during Accommodation Using Anterior OCT

“…This was the main cause of incomplete available data about the morphological changes of the ciliary muscles during accommodation, especially in children. So, OCT seems to be the most suitable imaging technique for this purpose (5). A study of the accommodation in adults by OCT demonstrated that most of the anatomical changes occur in the anterior part of the ciliary muscles which includes the circular fibers with anterior and inward shift during accommodation (6).…”

The Influence of the Autonomic Nervous System on the Human Choroid

“…As the Copernicus SOCT software applies a uniform tissue refractive index of 1.343 to all structures posterior to the back surface of the cornea the use of individual refractive indexes (1.38 for conjunctival/episcleral thickness and 1.41 for the scleral thickness and Schlemm's canal measures (Nemati et al, 1996)) allowed us to calculate thickness values more comparable to the true anatomical thickness. Additionally, to minimise optical distortions produced by artificially increased the path length of the infrared light due to the tissue tilt, the corneal limbal region was positioned orthogonal to the instrument's scanning beam (Kao et al, 2011).…”

“…Schwalbe's line represents the termination of Descemet's membrane and is located approximately 500 -750 μm from the scleral spur (Cheung et al, 2011;Usui et al, 2011, Qin et al 2013). The distance of 1.75 mm posterior to the Schwalbe line was selected as the location of a vertical reference line for thickness measurements (Kao et al, 2011;Cheung et al, 2011;Qin et al 2013).…”