Randomised controlled study comparing comfort-related outcomes between two rigid gas permeable (RGP) lenses with different sessile drop contact angles

P>Purpose: To compare comfort-related outcomes when wearing rigid gas permeable (RGP) contact lenses made of two different materials and using two cleaning regimes. Methods: In a double-masked lens material cross-over study, subjects (n = 28 who completed the study) were refitted with new lenses made from (A) Boston XO material in one eye and made from (B) ONSI-56 material in the other eye. The lenses made from materials A and B were worn on the right eye and the left eye following the pattern AB-BA-AB (or vice versa) during the first, second, and third 5 week trial periods respectively. Miraflow cleaner (1st and 2nd period) was replaced by Boston Advance cleaner in the 3rd period. Comfort-related outcomes were assessed by a numerical rating scale (NRS) after each period. Subjects rated six comfort-related factors: satisfaction, sharpness of vision, end of day comfort, maximum comfortable wearing time, maximum wearing time and foreign body feeling. Additionally we obtained subjects' preferences for type of lens and lens cleaner during an exit interview. The sessile drop method was used to measure static contact angles. Results: The mean of the contact angle measured for the Boston XO material was 93.3 degrees and for the ONSI-56 material was 75.8 degrees. Mean 'end of the day comfort', 'satisfaction' and 'lens feeling' scores reached statistical significance (anova periods 1, 2 and 3, p's: 0.005, 0.028, 0.046, n = 23) with marginal differences in favour of those eyes that had worn lenses made of the ONSI-56 material (differences in mean scores on a 1-10 NRS never exceeded 0.7, 0.5 and 0.2 points in periods 1, 2, 3 respectively). At the exit interview 60% of the subjects (n = 17) were not able to express a preference for wearing either of the lenses, while 29% reported some preference for lenses made of the ONSI-56 material (n = 8) and 11% for wearing lenses made of the Boston XO material (n = 3) within one or more periods. Conclusions: The differences in comfort-related outcomes between contact lenses made from two different materials, with sessile contact angles that differed by 17.5 degrees, were small. Although some observed comfort differences reached statistical significance, none of these differences were sufficiently large to support a clinically significant difference in comfort between the two materials. We recommend that both the sessile drop and the captive bubble contact angles, measured according to current standards, are made available to practitioners.