BHVI disproves CL theory

Single vision contact lenses with optical designs that aim to reduce inherent spherical aberrations (SAs) of the eye are not effective in improving visual performance, according to a recent study¹ by the Brien Holden Vision Institute (BHVI).

The results of the study, published in Clinical Optometry, show the assumption among manufacturers that reducing the inherent SA of the eye will improve vision is wrong, said study co-author, Dr Cathleen Fedtke, a senior research fellow at BHVI, adding there are also no known published studies to support this assumption.

To test the assumption, BHVI researchers randomly selected non-presbyopic, adult myopes, aged between 18 and 33 years, and asked them to wear either a lens with minimal or no spherical aberration or a commercial lens designed with negative SA.

Visual acuity measures and binocular vision assessments were conducted and a questionnaire completed after the lenses were fitted. Responses on vision quality (clarity and lack of ghosting for distance, intermediate, near, and driving vision in day and night-time), vision stability, overall vision satisfaction and ocular comfort, were rated. After five days of wear, the same tests were conducted and the survey repeated.

“We found that the introduction of negative SA into contact lenses did not produce appreciable visual performance gains in terms of visual acuity or subjective metrics,” said Dr Fedtke. “This is the first study to show that inducing negative SA, as done in many commercial single vision contact lenses, does not improve visual performance.”

Furthermore, the authors warned that power profiles of soft contact lenses with negative SA “can induce measurable changes in peripheral refraction (including relative peripheral hyperopia)”, and “this could have a negative consequence on the myopia progression.” Consequently, they suggest that, “given current clinical interest in the peripheral retina in relation to myopia, clinicians should be aware of the insignificant visual performance gains when fitting soft contact lenses of this design on young and progressing myopes.”

Reference

1.    Kho D, Fedtke C, Tilia D, Diec J, Sha J, Thomas V, Bakaraju RC, Effects of relative negative spherical aberration in single vision contact lens visual performance. Clinical Optometry, 2018:10 9-17.