تاثیر انحراف کروی سلبی در عملکرد بینایی لنزهای تماسی دید فردی Effects of relative negative spherical aberration in single vision contact lens visual performance

Introduction Optical aberrations arise because of the innate imperfections of the ocular surface and refractive media that degrade the retinal image quality. Overall, ocular aberrations can be divided into lower- and higher-order aberrations and are commonly represented by Zernike polynomials.1 Clinicians primarily confront the lower-order aberrations because of their significant impact on vision (eg, defocus and astigmatism) and the ability to easily correct them with spectacles, contact lenses, or refractive surgery.2 However, higher-order aberrations have gained increasing interest in the recent past, primarily driven by the advances in wavefront aberration measurement technology.3–5 Various combinations of lower- and higher-order aberrations, in magnitude and sign, and their effects of visual performance have become of clinical interest, particularly for presbyopia applications.6–8 As this paper only relates to spherical aberration (SA) observed in single vision contact lenses, findings on through-focus visual performance improvements with deliberate introduction of SA for presbyopic applications will not be discussed. The SA refers to the phenomena arising from the geometry of lens surfaces in which images appear blurred because peripheral light rays focus at a different point from those originating centrally. Population studies report that the mean SA measures are about 0.10±0.15 µm and its value increases with age. As SA is rotationally symmetric, spherical contact lenses have been considered for SA correction because of their distinct advantage of maintaining alignment with the optical axis with eye movements. Contact lens manufacturers have thus targeted SA correction in soft contact lenses to improve vision.9,10 Three recent studies examined the optical power profiles of commercial single vision contact lenses from major manufacturers and found the majority incorporated negative SA.11–13 This is in an attempt to compensate for the mean SA values observed in the population.14–17 However, in light of theory and findings related to the influence of peripheral hyperopia on the rate of myopia progression, the introduction of deliberate negative SA to improve the visual performance with single vision contact lenses could have a negative consequence on the myopia progression.