Clinical performance and factors affecting the physical fit of a soft toric frequent replacement contact lens

Background: Differences in ocular parameters between Chinese and Caucasian eyes may lead to differences in the success rate of soft contact lens fittings. As most disposable or frequent replacement lenses are manufactured based on data of Caucasian eyes, the aim of this study was to investigate the clinical performance and factors affecting the preliminary fitting of a 'one-fit' bi-weekly replacement soft toric lens on Hong Kong (HK)-Chinese. Method: Forty-one HK-Chinese were fitted with Acuvue soft toric lenses (on one eye only). The success rate, the comfort, vision and the effects of central corneal curvature, horizontal visible iris diameter (HVID) and palpebral aperture size (PAS) on the physical fit of the toric lenses were determined. Results: Twenty-four of 41 eyes (58.6 per cent) attained acceptable fit and satisfactory vision with these lenses. The main reason for unsuccessful lens fit was loose fitting. Only central corneal curvatures were significantly correlated (statistically) to the looseness of the lens. Discussion: The results showed that about 40 per cent of our subjects were unable to obtain acceptable fit with this one-fit frequent replacement lens, the main reason for which was loose fit. This was expected due to the steeper corneas of the Chinese eyes and we would expect similar results with other one-fit soft lenses. Only the central corneal radii were significantly correlated with the looseness of the lens fit. However, this factor was not the main factor affecting the contact lens fitting. HVID and PAS did not appear to play any significant role in the physical fit of this lens. As there are individual variations of lens fitting behaviour, trial lens fitting assessment is the most suitable way to select the appropriate lens.