A review of higher order aberrations of the human eye

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 ( 2 0 Z ) and astigmatism ( − and 2 2 2 2 Z Z ) 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 ( 4 0 Z ). 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.

A Systematic Review on the Association Between Tear Film Metrics and Higher Order Aberrations in Dry Eye Disease and Treatment

“…One way to address the symptoms and reported impaired optical quality of dry eyes is to use lubricating eye drops that have been shown to improve optical quality and significantly decrease aberrations associated with irregular tear films and dry eyes [2,[10][11][12]. Another strategy or intervention for dry eyes is punctal plugs to block the puncta allowing for increased tear fluid accumulation, thus keeping the tear film intact [13].…”

“…The formation of optical images on the retina marks the beginning stages of vision processing [ 1 ]. However, there are many possible avenues of error either through diffraction, errors of focus, and wavefront aberrations [ 1 , 2 ]. When optical systems are in “perfect” settings, rays emanating from an object are refracted to converge to the unique image point as expected from Gaussian theory [ 1 ].…”

“…An important factor that affects HOAs includes the tear film [ 2 , 4 , 5 ]. The tear film is the first refracting surface that light comes into contact with and thus has a crucial role in maintaining a smooth corneal surface [ 2 , 4 , 5 ]. Changes to the tear film thickness and regularity can introduce additional aberrations [ 4 ].…”

“…Changes to the tear film thickness and regularity can introduce additional aberrations [ 4 ]. As the eyes remain open, the tear film eventually breaks up and this also causes irregularity and increased aberrations [ 2 , 4 , 5 ]. Dry eye can be defined as a tear deficiency disorder of the ocular surface [ 6 ].…”

“…Dry eyes are one of the most common ocular disorders and a complication of many common laser and refractive surgeries, including cataract surgeries [ 1 , 2 , 13 ]. Therefore, it is important to understand any potential association or pathophysiology of HOAs and dry eyes, as well as whether interventions that improve dry eyes reduce HOA severity.…”