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Abhishek Bhat, Kenneth Duy Tran, Christine W Sindt, Klara Barbarossa, Megan Bauer, Raymond Lum, Kuangmon Ashley Tuan; Objective method for limbus detection of anterior segment topography. Invest. Ophthalmol. Vis. Sci. 2021;62(8):665.
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© ARVO (1962-2015); The Authors (2016-present)
Successful contact lens designs are predicated on the accurate identification of the limbus. Custom scleral lens designs can now be fabricated using 3D ocular surface maps from scanning and impression-based methods. Utilizing 3D topography maps, an objective method of defining the limbus was developed.
Thirty impression-based 3D topography maps were selected based on ocular conditions that do not affect the limbal region.Subjective Detection: An expert clinician identified at least 5 points on the topography map using the EyePrint Designer (EPD) software to represent the limbal margin. Visual selection of points was guided by known anatomical features such as expected curvature change and limbus size.Objective Detection: A custom algorithm in MATLAB detects changes in 3D ocular surface profile at the limbal region. An initial estimate of candidate limbal points represent locations with large gradient magnitudes. An adaptive varying threshold is applied since the gradient magnitude of the limbus is not constant across all meridians. Candidate points away from the probable limbal region are rejected. Further testing for outliers using Random Sample Consensus (RANSAC) is done to remove points that do not fit an elliptical profile. The detected limbal points tend not to be planar, resulting in a best fit hyperbolic paraboloid shape.Comparison: Limbal parameters from subjective and objective methods collected using the EPD software were compared. All objective limbus designs were reviewed by another expert clinician. Lens designs with >75% similarity of the limbal region between the two methods were clinically acceptable.
Limbal parameters were reported as: major diameter, minor diameter, and axis of major diameter. The average difference between the two methods were 0.16mm, 0.07mm, and 1.92 degrees, respectively. The median difference between the two methods were 0.05mm, 0.03mm, and 2.95 degrees, respectively. Review of objectively determined limbal points found 80% of designs to be clinically acceptable.
This objective method of identifying the limbus may be an effective way of guiding novice contact lens designers to create custom scleral lenses. Further investigation of irregular ocular surfaces is necessary to address the broader ocular demographic who wear scleral lenses.
This is a 2021 ARVO Annual Meeting abstract.
Comparison of limbus detection methods
Candidate and selected limbal points on surface gradient profile
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