Significant chromatic dispersion exists among a variety of hydrogel and silicon hydrogel soft contact lens materials, according to a study published in Contact Lens and Anterior Eye. This dispersion exists regardless of whether the lenses are soaked in a phosphate-buffered solution or their standard packaging solutions, according to the report.
“With the emergence of the myopia epidemic, chromatic effects have been implicated to play some role in the emmetropization process,” the study authors explain. “Chromatic dispersions in soft contact lens materials had been suggested to have an impact on myopia development in contact lens wearing children.
Researchers measured chromatic dispersion in 18 different soft contact lens materials with high and low water content at a temperature of 20 °C while soaked in phosphate-buffered saline and in their respective packaging solutions. All lenses were the same power (−1.00 DS), which ensured the most uniform lens thickness at lens diameter. The team measured refractive index at 5 different wavelengths (range, 470-680 nm) using refractometry, while masked to the contact lens material.
Bland-Altman analysis with 95% limits of agreement and coefficient of repeatability (CoR) determined refractive index measurement repeatability. The investigators identified significant differences between the 5 wavelengths for each material using one-way ANOVA analysis and determined differences in refractive index or chromatic dispersion between packaging solution and the phosphate-buffered solution results using an unpaired t-test.
Among the 18 soft contact lenses, nelfilcon A (mean CoR, 0.00125) soaked in packaging solution showed the best repeatability for all wavelengths with an average refractive index of 1.3848 for all 6 contact lenses. Comfilcon A demonstrated the best repeatability among contact lenses soaked in the phosphate-buffered solution (average refractive index, 1.4041; CoR, 0.00060).
One-way ANOVA assessment revealed significant differences in refractive index among the lens materials within the visible wavelength range (P <.001). Abbe values were not significantly different among lenses soaked in the packaging solution (range, 43.7-89.9) or the phosphate-based solution (range, 46.3-81.6; P >.05; 95 % CI, −4.8070-5.8680, t, 0.2054).
“[T]his study confirmed that significant chromatic dispersion exists in the examined
contact lens materials and that this dispersion is independent of the solution the lenses are soaked in,” according to the study authors.
Study limitations include a failure to perform in vivo assessments.
Spychala B, Ehrmann K. Chromatic dispersion of soft contact len materials. Cont Lens Anterior Eye. Published online May 26, 2023. doi:10.1016/j.clae.2023.101864