ContactLens and AnteriorEye, Vol. 20, No. 1, pp. 13-21, 1997 © 1997 British Contact Lens Association Printed in Great Britain COMPARATIVE PERFORMANCE OF DISPOSABLE SOFT CONTACT LENSES Graeme Young*, Greta AllsoppJ;, Andrea Inglis:~ and Susan Watson§ (Received 28th June 1996; in revisedform 30th October 1996) Abstract--A short-term clinical study was undertaken to compare and evaluate the fit and clinical behaviour of eight disposable hydrogel contact lenses. Thirty subjects were enrolled in a 1-day, randomised, double-masked study. The lenses compared were Vistakon Acuvue (8.80), Vistakon Surevue (8.80), Aspect Frequency-55, Bausch & Lomb Medalist (SeeQuence 2), Ciba Focus (8.90), Lunelle Rythmic, Pilkington Barnes-Hind Precision-UV and Wesley Jessen Freshlook. Three of the eight designs, Acuvue (86. 7%), Precision-UV (86. 7%) and Frequency-55 (90%), achieved relatively high levels of fitting success. The Rythmic lenses achieved the lowest success rate (70%) showing significantly greater downward decentration than the other designs. Although all the lenses were designed to fit a wide variety of eyes, they exhibited widely varying fitting characteristics. Some were more successful than others. The study shows that it is necessary for practitioners to utilise a range of lens designs in order to fit satisfactorily the typical contact lens population. KEYWORDS: Disposable contact lenses, hydrogel, lens movement, lens decentrafion Introduction D isposable soft lenses used with replacement sched- ules varying from 1 day to 1 month are being pre- scribed for a steadily increasing percentage of the soft lens wearing population (65% in Europe). 1,2 With con- ventional regimens, the lens replacement period is largely dependent on the rate at which the individual patient produces significant lens spoilation. 3 There is some evidence that a wide range of corneal shapes can be fitted by a single, well-chosen design? ,5 Most disposable lenses have, at least initially, been launched as 'one-fit' lens designs. Those manufacturers who have developed a one-fit design have each attempted to achieve the same goal, to identify the single design which accommodates the widest possible range of eyes. The prime purpose of this study has been to evaluate the relative success of a range of dis- posable lens designs. Study Design and Rationale This was a 1 day, 30 subject, partially double-masked, randomised, repeated measures study. Each subject wore each of the eight test lenses, i.e. four per eye. Since previous work has shown that even high water content lenses reach equilibrium within 15min of inser- tion, 6 the settling time allowed in this study (30+min) would allow a valid test of lens fit. This period of lens wear is a reliable predictor of performance.7 The study simulated the process of a trial fitting when a similar settling time is generally given. The study compared the performance of lenses in a given eye and also between eyes. It was therefore assumed that the performance of a given lens in one eye was comparable with that of the same lens in the * BSc, MPhil, FCOptom, DCLP, optometrist. t BSc, PhD, Visioncare Research Ltd. BSc, MCOptom, optometrist. § BSc, FCOptom, optometrist. contralateral eye. In other areas of eye research correla- tions between eyes have been noted. 8 In order to min- imise these possible differences, subjects whose eyes showed a significant difference in corneal topography were excluded according to criteria given below. Some disposable products are available in more than one back optic zone radius (BOZR) (e.g. Focus, Acuvue). However, because of the practical limit on the number of lenses that can be tested in one subject, only one BOZR for each design was tested. Where more than one BOZR is available in a given design, the one selected was in the middle of a range of three (e.g. Medalist) or alternatively, that recommended by the manufacturer as the principal fitting (e.g. Focus). Method Study Population Thirty subjects were enrolled (10 males, 20 females) 17 of whom were habitual contact lens wearers. A sum- mary of the subjects' biometric data is given in Table 1. The mean horizontal visible iris diameter (HVID) and corneal curvatures were consistent with those seen in a representative population2.1° Subjects were required to have a spherical distance correction between +8.00D and -8.00D and a cylindrical correction no greater than 2.00D in both eyes. Subjects were also required to have a similar corneal topography in each eye. This was determined by three criteria: (1) a difference in mean keratometry of less than 0.20ram, (2) a difference in corneal astigmatism of less than 1.00D (0.20ram), and (3) a difference in corneal astigmatism of less than 0.30ram. Subjects were excluded from the study if they had any significant ocular abnormality or were suffering from a medical problem likely to affect their vision or successful contact lens wear. Polymethylmethacrylate (PMMA) lens wearers were also excluded owing to the likelihood of inherent corneal distortion. 13