A novel quantitative evaluation of deposits adhered to worn orthokeratology contact lenses

Abstract

Purpose: Total deposition and deposition along the reverse curve of heavily deposited worn orthokeratology (OK) lenses were quantitatively evaluated using two novel imaging methods. In addition, the cleaning efficacies of a contact lens cleaning solution for daily use and an intensive cleaner and protein remover solution were evaluated using the same two methods.

Study design: Experimental study.

Methods: Twenty-six worn reverse-geometry OK lenses (MY Emerald, Technopia) were photographed for use in three experiments: (1) total deposition was assessed before and after cleaning with two cleaning solutions; (2) in addition to assessing total lens deposition, the feasibility of measuring the thickness of lens deposits along the reverse curve was assessed; and (3) after confirming it was possible to assess the thickness of lens deposits, the thickness of deposits was assessed before and after cleaning with a daily contact lens cleaning solution (O₂ Care^®, Menicon Co., Ltd.) and an intensive cleaner and protein remover (Progent^®, Menicon Co., Ltd.). Total lens deposition was assessed as the total volume of cloudiness over the lens surface in terms of volume per unit pixel. Cross-sectional images were taken from worn OK lenses to assess the thickness of lens deposits on the reverse curve as the area of deposits/horizontal length.

Results: Significant differences in total deposition were found between the three cleaning conditions for the twenty worn OK lenses (mean total deposition ± SD for pre-cleaning = 0.209 ± 0.076; post-daily cleaning = 0.124 ± 0.078; and post-intensive cleaning = 0.045 ± 0.046) (p < 0.001). Mean total deposition and thickness of the deposits along the reverse curve for the three lenses from the second experiment were 0.310 and 6.0 mm, respectively. The mean thicknesses of lens deposits found in the third experiment under the 3 conditions were as follows: pre-cleaning = 3.4 µm; post-daily cleaning = 2.3 µm; and post-intensive cleaning = 0.0 µm.

Conclusion: The two novel imaging methods used in this study detected significant amounts of deposits attached to worn OK lenses and were sensitive enough to detect a reduction in deposition following the use of the two cleaning solutions tested. Furthermore, these methods could visualize and quantify the thickness of lens deposits along the reverse curve.

Keywords: Cleaning; Cleaning solution; Image analysis; Orthokeratology lens; Scanning electron microscope.