The newly-revised American National Standard ANSI Z80.28-2017: Ophthalmics – Methods of Reporting Optical Aberrations of Eyes is initiated by the short and simple scope, “This standard specifies standardized methods for reporting the optical aberrations of eyes.” This purpose is clear and succinct, yet it orients the standard guidelines that ANSI Z80.28 sets forth around a vast, complex topic.
Optical aberrations refer to the influences that cause different rays to converge at varying points in an optical system, as, in an ideal system, all rays of light would converge to the same point in the image plane. Technology for wavefront mapping, which measures and diagrams the imperfections of an optical system, has been around for over 100 years, for which it has served astronomy equipment.
The eye, just like any other optical system, is prone to optical aberrations. These adversely affect the vision of the individual with these aberrations in his or her eye or eyes, and they are actually quite prevalent in the United States, at least low-order aberrations, which include astigmatism, myopia (nearsightedness), and hyperopia (farsightedness). Astigmatism is especially common, as it appears in some form in about 1 in 3 people.
Low-order aberrations of the eye generally are remedied with corrective lenses, but higher-order aberrations, while far less common, are more complex. Primary types of higher-order aberrations include coma, spherical aberration, and trefoil.
With the indisputable importance of optical aberrations of the eye to ophthalmology, standard systems are integral for their comprehension and communication. Fundamental to this is the graduated dial scale of ophthalmology, a coordinate system, on a 360-degree scale, that is meant to be incorporated in instruments for determining optical data on human eyes or corrective lenses. It is covered by ISO 8429:1986 – Optics and optical instruments — Ophthalmology — Graduated dial scale.
This international standard is referenced in ANSI Z80.28-2017, for which it is utilized in representing wavefront surfaces of the eye. For reporting optical aberrations, the American National Standard standardizes Zernike polynomial functions, which are defined and orthogonal over the unit circle. Each Zernike polynomial function is the product of three terms: a normalization term, a radial term, and a meridional term.
ANSI Z80.28-2017 lists the many Zernike functions, as well as their common names, such as those for oblique astigmatism or horizontal coma, and it also contains a section for the representation of wavefront data.
However, it is also noted in the ANSI Z80.28-2017 document that, while the preferred method of communicating aberration data for the human eye to others for analysis is in the form of a set of gradient components for each measured location, this form is often not convenient for use in papers, displays, and other common forms of communication.
Therefore, the preferred forms of presenting aberration data of the human eye are through a list of normalized Zernike coefficients, as a bar chart showing Zernike coefficients, and in the form of a topographical map of the wavefront surface.
ANSI Z80.28-2017: Ophthalmics – Methods of Reporting Optical Aberrations of Eyes is available on the ANSI Webstore.