Initial Comfort With Silicone Hydrogels of Higher Modulus
BY ANTONIO CALOSSI, DIP OPTOM IT, FAILAC, FBCLA; ALESSANDRO FOSSETTI, OD; LUIGI LUPELLI, DIP OPTOM IT, FIACLE, FAILAC; & FABRIZIO ZERI, DIP OPTOM IT, BSC (PSYCHOL), FIACLE
Some practitioners have concerns about fitting higher-modulus silicone hydrogel lenses because patients may find them uncomfortable during the early stages of the fitting process. We designed a study with the aim to compare the initial comfort in neophyte subjects, all of whom were contact lens practitioners, fitted with a hydrogel and a silicone hydrogel monthly lens.
Materials and Methods
This study was a double-masked and randomized, controlled trial. We enrolled 211 subjects (72 females) ranging in age from 21 years to 65 years (mean 39.9 years, SD 9.4 years) in the study. We excluded subjects who were current contact lens wearers. All of the voluntary subjects were contact lens practitioners enrolled during a series of continuing education courses in 12 different locations across Italy.
Investigators fit each subject randomly, simultaneously and in a masked way with a lotrafilcon B (Air Optix/O2Optix, CIBA Vision) lens on one eye and a vifilcon A (Focus Monthly, CIBA Vision) lens on the contralateral eye. The back vertex power (BVP) of each lens was plano. Table 1 lists the different parameters of the lenses used in this study. One independent investigator randomized the lenses. A separate group of independent investigators fitted the contact lenses. The first lens to be applied was randomly chosen. None of the subjects either touched or observed the fitted contact lens.
Each subject had to rate the comfort of the two lenses from 0 (very poor comfort) to 10 (excellent comfort). Subjective ratings were compared between the two lenses on application and after 20 minutes and 60 minutes of wear.
We used repeated-measures analysis of variance (ANOVA) to compare the comfort and to look at changes over time. As many variables were assessed in this study, we introduced a Bonferroni correction and used a significance level of α = 5 percent for the analysis.
Figure 1 and Table 2 summarize the results. In the first 20 minutes, there was a slight increase of comfort for both lenses. We found no statistical difference between comfort of the two lenses at each paired comparison. On application the average comfort rating was 6.69 ±2.3 for the hydrogel lens and 6.74 ±2.3 for the silicone hydrogel lens (p=0.7394). At 20 minutes, the average comfort rating was 7.24 ±1.82 for the hydrogel lens and 7.55 ±1.69 for the silicone hydrogel lens (p=0.0643). At 60 minutes, the average comfort rating was 7.41 ±1.96 for the hydrogel lens and 7.68 ±1.97 for the silicone hydrogel lens (p=0.0991).
Figure 1. Comparison of subjective comfort over time. Ratings of zero represent "very poor" and 10 "excellent." Data are presented as mean ±1 standard deviation.
Initial comfort is reported to greatly influence a patient's perception of contact lenses and their ultimate success. Even though some hydrogel lens wearers may report initial discomfort when refitted from conventional lens materials into silicone hydrogels, neophytes tend to adapt without significant differences. Our findings indicate that neophytes are unable to subjectively differentiate in a significant manner between a higher-modulus silicone hydrogel lens and a monthly hydrogel lens over a one-hour wearing period. In similar studies, Fonn and Dumbleton (2003) and Dumbleton et al (2006) evaluated the initial comfort (over a seven-hour period and over an eight-week period, respectively) of silicone hydrogel contact lens wear in hydrogel contact lens adapted subjects.
Du Toit et al (2003) demonstrated that the initial comfort of two different silicone hydrogel contact lenses does not differ from some popular daily disposable hydrogel contact lenses. In this study limited to 15 subjects, current contact lens wearers wore each lens monocularly for a period of 10 minutes. Our results agree with these similar studies, despite the differences in procedure, sample type (neophytes versus current lens wearers), sample size and time course.
As the first impression is known to greatly influence patient perception of contact lenses and their ultimate success, some practitioners are concerned about fitting higher-modulus silicone hydrogel lenses because they believe patients might find them uncomfortable. Our findings, even though restricted to only one hydrogel lens and one higher-modulus silicone hydrogel lens, indicate that we may consider the physiological advantages of silicone hydrogels, whether for daily or extended wear, for new wearers without concerns about comfort and adaptation. CLS
This study was supported by CIBA Vision Italia and presented as a poster at the British Contact Lens Association's 2007 Clinical Conference and Exhibition.
For references, please visit www.clspectrum.com/references.asp and click on document #149.
Dr. Calossi is in private practice in Certaldo (FI), Italy. Dr. Fossetti works at Università di Padova, Italy. Dr. Lupelli and Dr. Zeri both work at Istituto Superiore di Stato De Amicis, Scuola di Ottica e Dipartimento di Scienze Optometriche, Roma, Italy.