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Study: OCT imaging may aid in contact lens fitting
Researchers recently reported in Optometry & Vision Science that they identified an effective method of quantifying the topographical characteristics of the corneoscleral junction.
Tan and colleagues developed and tested the method, which included "metrics that reflect both the angle and topography in this region of the ocular surface," according to the study.
Researchers took optical coherence tomography (OCT) images in 48 participants who had not worn contact lenses for at least 12 months. The participants were equally divided into three ethnic groups of Caucasian, Asian and Latino participants in an effort to evaluate different eye types.
"First, the interface between the air and the ocular surface in the OCT image was located automatically by a custom edge-detection program written in Matlab," the authors stated. "The next step was the selection of a point at the center of the CSJ region on this interface by a trained observer. Once the center point was specified, 20 points along the interface were determined by 10 automatically generated concentric circles spanning a 2-mm region. A linear regression was then performed based on the Cartesian coordinates of the 21 points (the center point and the 20 evenly distributed points).
"Five metrics were derived from the regression output: the R2 of the regression, the sum of the squared residuals (SSR), the sum of the squared orthogonalized residuals (SSRo), and the standard deviations of the residuals (SDR) and orthogonalized residuals (SDRo)," they continued.
Results showed that the SSRo was unaffected by image orientation and was the most repeatable measurement. The researchers noted that SSRo was greatest in the nasal quadrant and flattest in the temporal quadrant. Caucasian participants were found to have higher SSRo than both Latino and Asian participants.
"Quantitatively describing the corneoscleral junction (CSJ) in terms of angle can give highly variable estimates owing to the arbitrary selection of tangential lines," the authors concluded. "In addition, the important characteristics (e.g., for contact lens wear) of the regional topography of the CSJ cannot be described by angle alone. The method in the present study provides a metric (SSRo) that quantifies the characteristics of the CSJ region more comprehensively and with good repeatability for a trained observer.
"We have shown that the SSRo in the nasal quadrant is significantly greater than that in the other three quadrants, and we have presented quantitative evidence that suggests that different ethnic groups may have significantly different CSJ topographies," they continued. "The SSRo will be particularly applicable for future studies assessing the relationships among ocular characteristics, contact lens fitting parameters and subjective comfort."