Optical Assessment of Soft Contact Lens Edge-Thickness

Abstract

Purpose: To assess the edge shape of soft contact lenses using Gabor-Domain Optical Coherence Microscopy (GD-OCM) with a 2-μm imaging resolution in three dimensions and to generate edge-thickness profiles at different distances from the edge tip of soft contact lenses.

Methods: A high-speed custom-designed GD-OCM system was used to produce 3D images of the edge of an experimental soft contact lens (Bausch + Lomb, Rochester, NY) in four different configurations: in air, submerged into water, submerged into saline with contrast agent, and placed onto the cornea of a porcine eyeball. An algorithm to compute the edge-thickness was developed and applied to cross-sectional images. The proposed algorithm includes the accurate detection of the interfaces between the lens and the environment, and the correction of the refraction error.

Results: The sharply defined edge tip of a soft contact lens was visualized in 3D. Results showed precise thickness measurement of the contact lens edge profile. Fifty cross-sectional image frames for each configuration were used to test the robustness of the algorithm in evaluating the edge-thickness at any distance from the edge tip. The precision of the measurements was less than 0.2 μm.

Conclusions: The results confirmed the ability of GD-OCM to provide high-definition images of soft contact lens edges. As a nondestructive, precise, and fast metrology tool for soft contact lens measurement, the integration of GD-OCM in the design and manufacturing of contact lenses will be beneficial for further improvement in edge design and quality control. In the clinical perspective, the in vivo evaluation of the lens fitted onto the cornea will advance our understanding of how the edge interacts with the ocular surface. The latter will provide insights into the impact of long-term use of contact lenses on the visual performance.

Figure 1

Gabor-Domain Optical Coherence Microscopy (GD-OCM) setup.

Figure 2

Detection of the contact lens boundaries. (A) Region of interest after segmenting the original image; (B) binary image of the detected peaks; (C) boundaries identification of the contact lens edge from polynomial fitting. Red solid line corresponds to the top surface of the CL and the blue solid line corresponds to the bottom surface of the CL. Yellow line shows the fluid gap.

Figure 3

Principle of the refraction effect. The difference between a GD-OCM data point and a real impact point is presented. The diagram helps derivation of the relationship between thicknesses and angles.

Figure 4

Plot of the apparent thickness from GD-OCM for (A) four different tilted angles as a function of the refractive index of the sample, and (B) for three different indices of refraction as a function of the tilted angle.

Figure 5

Experimental validation of the refraction correction with three different tilting angles (A1) 0 degrees, (A2) 12 degrees and (A3) 17.5 degrees. (B) Comparison of the GD-OCM apparent thickness and the refraction corrected thickness.

Figure 6

Results of imaging and edge-thickness measurement of a soft contact lens (CL) using GD-OCM in three different configurations: (A) CL in air, (B) CL in plastic bag filled with water, (C) CL in plastic bag filled with saline and contrast agent, and (D) CL onto the cornea of a porcine eyeball.

Figure 7

Thickness profile as a function of the distance from the edge. The thickness profile was obtained from the average of 50 successive image frames for each configuration and was corrected for refraction.