Purpose: Some knowledge of the orientation position of toric soft lenses is required as part of the fitting process. Although it is known that factors such as lid anatomy, lens design, and fit are important, there is little detailed understanding of how these relate to toric lens orientation. The purpose of this study was to evaluate various patient and lens factors that might influence toric soft lens fit and to determine the predictor variables for lens orientation.
Methods: This was a clinical study in which 45 subjects were fitted with a prism-stabilized, mid-water, cast-molded, back surface toric soft lens. The lens was representative of commonly used designs for frequent replacement toric soft lenses. Patient and lens fit variables were assessed, including a range of lid topography features, which were measured using a digital photographic technique.
Results: The main patient factors associated with lens orientation and stability were degree of myopia, palpebral aperture, and several angles relating to lid anatomy. Greater upward incline of the temporal lids was associated with increasing inferior-temporal lens orientation; lower myopia and smaller palpebral aperture size were associated with more stable lens orientation. The principal lens fit characteristics affecting lens orientation were postblink movement and lens tightness. Less movement was associated with more stable lens orientation, and increased tightness was associated with slower reorientation speed. Weaker but significant correlations were also shown between a number of other patient and lens variables.
Conclusions: A number of patient factors and lens fit characteristics influencing toric soft lens orientation were identified. The findings fall short of allowing practitioners to accurately predict toric lens orientation; however, they do provide some factors to consider when fitting toric soft lenses.