Sagittal height differences of disposable soft contact lenses
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We aim to improve contact lens fitting by using an innovative and simple photogrammetry imaging system to find the sagittal height (SAG) of soft contact lenses.
Eleven different types of commercially available soft contact lenses were measured, and five different lenses per package of each lens type were evaluated. The lenses were inserted in a polymethyl methacrylate cell with parallel faces containing a solution of saline and fluorescein to improve the contrast against the background. For every lens, two photographs from the top view and five photographs from the side view were taken. Using homothetic transformations, we calculated the sagittal height.
The SAG of all lenses ranged from 3450 to 3907 μm. Differences can be appreciated between SAG of different materials. Performing an ANOVA test, we confirm that the intra-packaging sagitta is reliable for every lens. Comparing the measured SAG with the calculated spherical one, we confirm that the majority of lenses, eight out of eleven, have a spherical geometry for the internal side. Finally, we are able to group the type of lenses that present similar SAG apart from the data reported on the blister.
Optical coherence tomography measurement of the eye sagitta over a given chord helped finding the first lens to fit, because matching contact lens sagitta and ocular sagitta is the key for a good fitting. In our work, we found that the majority of brands use single sphere geometry for internal surface of disposable soft contact lenses.
KeywordsBase curve radius Image analysis Lens fitting Sagittal height Soft contact lenses
We thank Claudio Iovine (Università degli Studi di Milano-Bicocca, Milano, Italia) and Marta Farioli (Ottica Benzoni, Malnate, Italia) for their help in finding the soft contact lenses on the market.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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