A review of higher order aberrations of the human eye

Ayesha Suliman,Alan Rubin

doi:10.4102/aveh.v78i1.501

Abstract

Background: This literature review is part of a research study for aberration-correcting soft contact lenses, where wavefront aberrometry was utilised. Aim: This study was conducted as part of a postgraduate research degree by the first author with particular relevance to spherical aberrations in relation to myopia and soft contact lenses, both aberration control and non-control types. Setting: This study reports on a literature review of higher order aberrations. Methods: A comprehensive review of various databases was performed, including PubMed and Google Scholar in terms of aberration control contact lenses and particular customised contact lenses for compensation of spherical aberration in myopia, was performed. Results: Wavefront sensing and Zernike polynomials are increasingly used in optometry and ophthalmology to quantify the wavefronts for an optical system such as the eye, using either lower order (LOA) or higher order aberrations (HOA). Although other mathematical methods are available, zero, 1st and 2nd orders of the Zernike polynomial expansion are LOA. Defocus ( ) and astigmatism ( and ) are 2nd-order modes that usually can be corrected by clinicians using ordinary sphero-cylindrical compensations such as spectacle lenses. Until recently, only LOA were easily correctable by clinicians in optometry and ophthalmology. Higher order aberrations are those modes in the third radial order, n = 3 and higher, which in the past were not correctable. However, HOA contribute to only about 7% of retinal image quality and often go unnoticed by individuals, although in some instances, for example, with keratoconus or after refractive surgery, such aberrations can become more problematic. Today, new treatments are available via specially designed or customised (to an individual) rigid or soft contact lenses that are claimed to reduce or eliminate HOA such as spherical aberration ( ). Conclusion: Although such specially designed or customised contact lenses have some effect on HOA, there are conflicting reports and so further investigation of this intriguing aspect remains necessary.

Highlights

The optics of the human eye and the potential correction or compensation of its errors of refraction have been studied for at least the past 700 years
Prior to modern-day refractive surgery, the wavefront aberrations (WA) of the eye were sometimes considered as relatively insignificant when thinking about the optics and image processing of the eye
Aberrometry is useful in post-operative evaluation of both lower (LOA) and higher order aberrations (HOA) where asymmetry, decentration and irregularity of the corneal surface can be well described by aberration terms or modes

Summary

Introduction

The optics of the human eye and the potential correction or compensation of its errors of refraction have been studied for at least the past 700 years. Prior to modern-day refractive surgery, the wavefront aberrations (WA) of the eye were sometimes considered as relatively insignificant when thinking about the optics and image processing of the eye. The reason for this is that some, higher order, WA do not necessarily cause any noticeable degradation in visual acuity (VA) below 20/20 vision, generally considered as the criterion standard for a healthy eye. Aberrometry is useful in guiding wavefront error modification, especially in naturally aberrated eyes.[3] Modern wavefront-guided refractive surgery is claimed to reduce sphero-cylindrical errors http://www.avehjournal.org without inducing excessive HOA, reducing patient dissatisfaction or complaints.[4,5] The possible role of SA in terms of myopia development, progression and prevention has become an interesting concern both clinically and in research. This literature review is part of a research study for aberration-correcting soft contact lenses, where wavefront aberrometry was utilised

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