Characterization of soft contact lens edge fitting using ultra-high resolution and ultra-long scan depth optical coherence tomography

Abstract

Purpose: To characterize the edge fitting of soft contact lenses using ultra-high resolution optical coherence tomography (UHR-OCT) and ultra-long scan depth optical coherence tomography (UL-OCT).

Methods: A total of 20 participants (11 men, 9 women; mean age, 32.3 years) were recruited. Four different types of soft contact lenses were randomly fitted to both eyes of each subject on two separate visits. After 30 minutes, the horizontal meridians of the corneal center, midperiphery, and limbus were imaged by UHR-OCT. UL-OCT imaged each lens in vitro and the ocular surface of a physical model eye.

Results: Angle-edged lenses had significantly less conjunctival buildup than did round-edged lenses (P = 0.008). Limbal post-lens tear film gaps were present in 42% of the eyes, with the round-edged lenses having the most at 68%. Similarly, post-lens tear film gaps at the corneal mid-periphery were present in 47% of all eyes, with the round-edged lens having the most at 75%. Mismatches between the lens and the ocular surface were simulated based on UL-OCT images of the in vitro lenses and the model eye. The existence of tear film gaps and touching points were predicted in the simulation.

Conclusions: The soft contact lens edge fitting was characterized by the conjunctival buildup and tear film gaps. Different types of contact lenses presented different levels of conjunctival buildup as well as different frequencies of tear film gaps. The findings by UHR-OCT were predicted in the simulation by UL-OCT. The application of these new technologies may open new ways of designing lenses and evaluating their fit.

Figure 1.

In vivo UHR-OCT images of soft contact lens edges. (A) PureVision. (B) Acuvue 2. The PureVision lenses had a rounded edge, and the Acuvue 2 lenses had an angled edge. All images were corrected for optical distortion. Conjunctival buildup at the lens edge varied from 0%, indicating nearly no buildup, to 100%, indicating nearly full conjunctival buildup. Scale bar, 500 μm.

Figure 2.

Edge ranking among lenses. Conjunctival buildup on the lens edge was ranked on an analog scale at 0%, 25%, 50%, 75%, and 100%, indicating the degree of buildup around the lens edge. Rankings were assigned after the image was optically corrected. (A) Distribution of the edge ranking among the four lenses. Approximately 75% of all lenses were covered between 25% and 50% at the edge. In the Biomedics 55 lens, the conjunctiva did not remain flat (0%). (B) Comparison of edge ranking among lenses. The Biomedics 55 lens with the rounded edge had significantly more covering than did the Acuvue Advance lens with the angled edge (Mann-Whitney U test; *P = 0.008 for Biomedics 55 vs. Acuvue Advance). There were no significant differences in conjunctival buildup among the other lenses.

Figure 3.

Visualized tear film gaps underneath the lens. Tear film gaps between the lens and the ocular surface were clearly visualized. The limbal gap was located at the corneal-scleral transition, and the corneal gap was located at the midperiphery. These two gaps did not appear to be connected. Scale bar, 500 μm.

Figure 4.

Occurrence frequencies of tear film gaps. (A) Tear film gap at the limbus. The round-edged PureVision lens had the highest percentage of post-lens tear film gap at the limbus (68%; χ² test; †P < 0.001 for PureVision and *P < 0.001 for Biomedics 55 compared with the two angle-edged lenses, respectively). There was no significant difference in the frequency between the two round-edged lenses or between the two angle-edged lenses (χ² test; P > 0.05). (B) Tear film gap over the cornea. The round-edged Biomedics 55 lens had the highest percentage of post-lens tear film gap on the cornea (75%; χ² test; *P < 0.001 compared with the angle-edged Acuvue 2 and the Acuvue Advance; †P < 0.05 compared with the round-edged PureVision). There was no significant difference between the two angle-edged lenses (P > 0.05). Bars denote 95% confidence intervals.

Figure 5.

In vitro UL-OCT images of entire contact lenses and a model eye. Four study lenses were immersed in contact lens solution and imaged using UL-OCT. A model eye was also imaged in air. (A) Biomedics 55. (B) PureVision. (C) Acuvue 2. (D) Acuvue Advance. (E) Ocular surface of the model eye. The Acuvue 2 lens image was enhanced by liquid droplets added in the solution. Scale bar, 500 μm.

Figure 6.

Simulations of surface mismatches between the contact lenses and the model eye. The simulation matching the back surface of each contact lens and the front surface of the model eye demonstrated the gaps and touching points. The first touching point was predicted at the limbus when the lens first contacted the surface of the model eye (A). When the apex touched the surface of the model eye, the second touching point was located on the apex of the model eye (B). Meanwhile, the third touching point was apparent at the midperiphery of the model eye. Clearly, the post-lens tear film gaps were located between the touching point at the lens edge and the apex (A).