Short‐term tear film stability, optical quality and visual performance in two dual‐focus contact lenses for myopia control with different optical designs

To the Editor, We read with great interest the recent paper by GarcíaMarqués et al. regarding tear film (TF) stability, and visual and optical quality performance between two dualfocus prototype myopia control contact lenses (CL) over a short time period. We would like to congratulate the authors for the findings reported in this research since they represent an advance in the study of the visual changes and alterations at the level of the TF that these new CL designs cause on the ocular surface. At the same time, we would like to make comments that help to reinforce the results found. Concerning the technology utilised in the evaluation of TF stability, the authors used a Placido diskbased corneal topographer to measure noninvasive breakup time (NIBUT). New ocular surface analysers based on optical interferometry can be used to study the TF and ocular surface. Singh et al. assessed the repeatability and reliability of three different commercially available diagnostic platforms: LipiView® II (jnjvi sionp ro.com), IDRA Ocular Surface Analyser (sbmsi stemi.com) and the Oculus Keratograph 5M (us.oculus.de) for the objective assessment of TF parameters and to determine whether any agreement existed between them. The results obtained by Singh et al. were completed with the analysis of bulbar and limbal redness of the conjunctiva, lipid layer thickness, tear meniscus height and first/average NIBUT. Despite the fact that the instrument used by GarcíaMarqués et al. had a validated algorithm to measure the TF, the scientific literature where this technology has been used is scarce, which makes comparison of the reported findings with previous studies that investigated the ocular surface difficult. Another point to highlight was the contact lens material used. We understand that this is a limitation of the lens manufacturer. The NIBUT changed from 7.12 s to either 2.54 s (in the small centre diameter design) or 2.47 s (for the medium centre diameter design), but both values were below the normative value of 10 s. Recently, a number of water gradient CL materials (e.g., Delefilcon A and Lehfilcon A) have been developed where ≈80% water content is reached at the CL surface. Such CL display low (θ ≤ 20°) advancing and receding water contact angles immediately after removal from the blister pack, and their wettability remains significantly better than the “standard” silicone hydrogel lenses at continuous blinklike desiccation/rehydration cycling. The enhanced wettability is theoretically expected to result in: (i) an enhanced capability of the CL to acquire thicker prelens TF upon eye opening and (ii) to support a thinner and stable prelens TF concurrent with the film thinning occurring between blinks. This, in turn, will result in a longer NIBUT for a water gradient contact lens compared with silicone hydrogels with limited surface hydration. Furthermore, the enhanced hydration and wettability of the CL are assumed to ensure better lubricity and a higher overall comfort score. These theoretical predictions were recently confirmed in a clinical study, which demonstrated that Lehfilcon A wear resulted in a significant change in mean (±SD) prelens NIBUT from 15.19 ± 9.54 to 21.27 ± 11.97 s (p < 0.01). Further confirmation of these theoretical expectations was provided by Fujimoto et al., where the prelens TF with Delefilcon A (θ ≤ 20°) remained stable at 4.1 ± 2.3 s versus Narafilcon A (θ = 70°) with a value of 2.7 ± 1.6 s after ≥5 h wear for 1 month. Lateral shearing interferometry also demonstrated higher TF surface quality for Delefilcon A compared with Narafilcon A (a hydrogel lens with higher bulk water content but lacking water gradient), thus emphasising the importance of the hydration and structure of the CL surface. Thus, in order to put the effects of dual focus, prototype myopia control CL on the TF parameters into perspective, it is important that more diverse CL materials be studied in future investigations, since they may show greater comfort and biocompatibility at the ocular surface.