The Effect of Lens Wear on Higher-order Aberrations
Does wearing a contact lens have an effect on higher-order aberrations? If so, is it beneficial or detrimental to vision? Does it make a difference whether the contact lens is a GP or a hydrogel?
The following studies provide some answers to these and other questions.
Choi et al (2007) evaluated ocular aberrations in 22 eyes of myopic patients and 14 eyes of keratoconic patients. In each group, they obtained measurements both during GP contact lens wear and without lenses on the eye and compared the differences. The researchers noted no significant differences in total higher-order aberrations in myopic patients both with (0.33 �0.14) and without (0.33 �0.12) GP lens wear (p=0.952).
Likewise, when broken down into specific types of higher-order aberrations, they detected no significant differences for coma, trefoil or spherical aberrations when comparing myopic eyes with and without GP lenses.
Although the total higher-order aberrations were not significantly different with and without GP lenses in the keratoconic group (p=0.056), the researchers detected a significant difference in vertical coma. Without a GP lens, the mean RMS for vertical coma in the keratoconic group was -0.185 �0.228. With a GP lens, the mean RMS for vertical coma was 0.134 �0.148 (p=0.024).
Interestingly, when they compared individuals who had initially low ocular aberrations with those who had initially high ocular aberrations, they found that GP contact lenses reduced higher-order aberrations in patients who had initially high ocular aberrations. Conversely, GP lenses increased aberrations in patients who had initially low ocular aberrations.
Hiraoka et al (2007) evaluated ocular higher-order aberrations in eyes treated with overnight orthokeratology. They tested 46 eyes of 23 myopic patients and found that treatment with overnight orthokeratology lenses significantly increased total ocular higher-order aberrations from an RMS of 0.085 �0.032 to an RMS of 0.297 �0.152 (p<0.0001). More specifically, they detected significant increases in third-order and fourth-order aberrations.
Berntsen et al (2005) have reported similar results with overnight orthokeratology treatment.
The previous studies evaluated patients wearing GP contact lenses. Roberts et al (2006) conducted a study to determine the effect of spherical soft contact lenses on higher-order aberrations. They obtained measurements from 30 eyes of 15 patients wearing their habitual soft contact lenses and observed a significant increase in total higher-order aberrations. The researchers reported a mean RMS of 0.364 �0.129 in eyes without lenses and an RMS of 0.456 �0.175 with lenses (p=0.01). When broken down into coma, trefoil and spherical aberrations, they detected no significant differences with and without soft contact lenses (p=0.51, 0.06 and 0.36, respectively).
No Simple Answer
From these studies it's evident that the effect of contact lenses on higher-order ocular aberrations is a complicated issue. Several factors are involved such as patients' higher-order aberrations before lens wear, the design of the contact lens (spherical GP vs. orthokeratology) and whether patients wear a soft or GP contact lens.
Dr. Rah is an assistant professor at the New England College of Optometry where she works primarily in the Cornea and Contact Lens Service in patient care, teaching and research.
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