Clinical comparison of optimum and large diameter soft contact lenses.

PURPOSE: To compare the clinical performance of large diameter lenses with optimally fit lenses in the same material and monocurve back surface design.

METHOD: In a four-visit, randomised, bilateral, crossover, study, 25 myopic subjects wore optimum diameter lenses (control) and large diameter lenses (test) in random succession for 1 week each. Both study lenses were made of methafilcon A and of an identical design. Trial fittings with Frequency 55 (Coopervision) lenses modified with a design algorithm were used to determine the appropriate custom-made study lenses.

RESULTS: The least squares mean scores (±SE) for overall comfort and end-of-day comfort (0-10 scale) were 7.57 ± 0.33 vs. 7.42 ± 0.33 (P = 0.59) and 7.00 ± 0.31 vs. 7.27 ± 0.32 (P > 0.05) for the optimum and large diameter lenses, respectively. There were no significant differences in mean (±SE) gradings for limbal hyperaemia (1.23 ± 0.11 vs. 1.19 ± 0.11, 0-4 scale, P = 0.60) and corneal staining (1.79 ± 0.25 vs. 2.04 ± 0.25, P = 0.39). Conjunctival staining was greater for the optimum lens: 1.80 ± 0.28 vs. 0.93 ± 0.28 (0-4 scale, P = 0.001). With regard to lens fit, the large diameter lenses showed significantly less post-blink movement (0.22 ± 0.01 vs. 0.16 ± 0.01 mm, P = 0.004), and greater total decentration (0.15 ± 0.02 vs. 0.21 ± 0.02 mm, P = 0.010). However, there was no significant difference in the key fit variable of tightness on push-up (46 ± 0.69% vs. 48 ± 0.69%, 0-100 scale, P = 0.12).

DISCUSSION: The findings suggest that larger than optimal soft lenses may be worn without detriment to either comfort or ocular physiology, provided an optimal fit is otherwise maintained.