Myopia progression during three years of soft contact lens wear.

For decades myopia progression has been reported in adult low Dk/t hydrogel contact lenses wearers 1–3 and to a lesser degree in adults wearing silicone hydrogel lenses. 4–6 In a five-year retrospective study of 291 contact lens wearers aged 20 to 40 years, Bullimore and co-workers reported a mean progression of −0.44 ± 0.60 D during the 5 year period, but found a range from +1.88 to −2.75 D, indicating a high degree of individual variability. In that study myopic progression was greater in younger adult contact lens wearers and for those who began wearing spectacles at a later age.3 This and other studies also showed that the degree of myopia at baseline was not a contributing factor to the amount of myopic progression. Dumbleton and co-workers studied young adults primarily in their 20s for 9 months after initiation of extended wear and found that lower myopes showed significantly more myopic progression with extended wear of low transmissibililty hydrogel contact lenses compared with those with higher refractive error.5 Clearly, quantifying the role of factors such as lens wearing schedule (daily or extended wear), lens material, subject age and refractive status will help the research community determine the importance of each in the changing refractive error of contact lens wearers. The studies comparing myopic progression among low Dk/t hydrogel and silicone hydrogel lens wearers have shown that contact lens material also affects myopic progression, although the relative contribution of physical (lens modulus) versus physiological (corneal oxygen supply) effects are not fully understood.4–7 The most recent of these studies, a 3-year non-randomized, prospective clinical study, compared clinical signs and symptoms in patients wearing lotrafilcon A silicone hydrogel contact lenses up to 30-nights at a time with those wearing low Dk/t hydrogel contact lenses on a daily wear basis.6 Among the reported findings was a comparison of change in refractive error. Because of a substantial difference in the mean baseline age of the groups wearing silicone hydrogel contact lenses and hydrogel contact lenses (38 vs. 23 years), the investigators elected to select two age-matched subsets, each of 36 patients (mean age of 27.9 years each). The age-matched subjects were selected by a masked investigator from among the lens wearers who completed the study. Consistent with other reports among randomized subjects that did not differ in age, 5, 7 the age-matched silicone hydrogel contact lens subset had an increase in myopia of −0.03 D, whereas the low Dk/t hydrogel group increased in myopia by −0.40 D in the 3-year study (p = 0.007). Unfortunately, the two subgroups differed significantly in mean baseline refractive error as well, with the silicone hydrogel contact lens wearers entering the study with a refractive error of −3.59 ± 1.99 D compared with −2.10 ± 1.78 D for the low Dk/t hydrogel contact lens wearers. Since degree of myopia has been shown in some studies to affect myopia progression in adult contact lens wearers, an analysis is required to determine the role of lens material alone. In order to accomplish this, the data from the 3-year study 6 were reanalyzed using strategies that allowed both age and baseline refractive error to be controlled. By using a multivariate analysis, data from all subjects in the study could be used, and not just a limited subset.