Clinical comparison of optimum and large diameter soft contact lenses

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

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.

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).

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.