Visual acuity (clearness of vision) usually is measured by an eye doctor using an eye chart. It measures the smallest letters that can be reliably identified by the patient at a specified distance. The traditional test requires the patient to look and report which letters they see.
This invention provides an automated system to estimate visual acuity based on objective measurements of the eye optics and wavefront aberrations (WAs). WAs are represented in a particular form known as the Zernike polynomials. A typical measurement on the eye of a patient will consist of a list of about 16 numbers that constitute the coefficients of the polynomials. The WFAMetric is an algorithm that converts the list of numbers into an estimate of the visual acuity of the patient. If changes are planned to the WA of the patient through surgery or optical aids, the predicted change in acuity can be calculated.
The wavefront aberrations are a collection of different sorts of optical defects, including the familiar defocus and astigmatism that are corrected by eyeglasses, but also more complex “higher order” aberrations such as coma, spherical aberration, and others. The WA provide a comprehensive description of the optics of the eye, and thus determine the acuity. Until recently, a practical method of computing this relationship did not exist.
This innovation simulates the observer performing the acuity task with an eye possessing a particular set of WA. When a letter from an eye chart test is presented, a digital image of the letter is at first distorted by the specified WA, and noise is added to mimic the noisiness of the visual system. From previous research, the appropriate noise level to match human performance has been determined. Next, an attempt is made to match the blurred noisy image to similarly blurred candidate letter images, and to select the closest match. This is repeated for many trials at many letter sizes, thereby determining the smallest letter that can be reliably identified—the visual acuity. This simulation may seem complex and cumbersome, but it has been streamlined and simplified at all the key steps. The entire process is now robust, accurate, simple, and fast, with results being returned in typically a few seconds.
This work was done by Andrew B. Watson and Albert J. Ahumada Jr. of Ames Research Center.
NASA invites companies to inquire about licensing possibilities for this technology for commercial applications. Contact the Ames Technology Partnerships Office at 1-855-NASA-BIZ (1-855-6272-249). Refer to ARC-16331-1.
This Brief includes a Technical Support Package (TSP).
Prediction of Visual Acuity from Wavefront Aberration
(reference ARC-16331-1-) is currently available for download from the TSP library.
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Overview
The document outlines a NASA-developed technology for predicting visual acuity based on wavefront aberration (WA). WA refers to various optical defects in the eye, including common issues like defocus and astigmatism, as well as more complex "higher order" aberrations such as coma and spherical aberration. These aberrations affect the clarity of vision and are crucial for understanding overall visual acuity.
The innovative approach described involves simulating an observer's performance in identifying letters under specific WA conditions. The process begins by distorting a digital image of a letter according to the defined WA and adding noise to replicate the variability of human vision. By matching this blurred and noisy image to a set of similarly distorted candidate letters, the system determines the smallest letter that can be reliably identified, thus calculating the visual acuity. This method is noted for its robustness, accuracy, simplicity, and speed, typically yielding results in just a few seconds.
The technology has been patented (U.S. Patent 8,408,707) and is part of NASA's Technology Transfer Program, which aims to bring aerospace innovations to commercial applications. Potential applications for this technology include automated vision testing, automatic prescriptions for eyeglasses and contact lenses, custom optical implants, predicting acuity after laser surgery, refining laser eye surgery methods, and developing ophthalmic aberrometers.
The document also discusses prior art in the field, noting that while several formulas have been proposed to calculate acuity from WA, they often lack representation of the human neural contrast sensitivity function and do not adapt to different optotypes used in acuity measurement. In contrast, the WFAMetric method incorporates these elements, providing a more accurate simulation of the optotype recognition process.
For further inquiries or licensing opportunities, the document provides contact information for NASA's Technology Partnerships Division, emphasizing the potential for collaboration in advancing this technology for broader use in the healthcare and optical industries. Overall, this document highlights a significant advancement in the field of vision science, with implications for improving visual health assessment and treatment.
