The use of autorefractors using the image‐size principle in determining on‐axis and off‐axis refraction. Part 2: Theoretical study of peripheral refraction with the Grand Seiko AutoRef/Keratometer WAM‐5500

Abstract

Purpose: To determine, through simulations, the likely validity of Grand-Seiko autorefractors with annular targets in peripheral refraction.Methods: Using a physical model eye, the distance inside the eye to which the Grand Seiko AutoRef/Keratometer WAM-5500 beam was converging and the effective size of its outer diameter at the cornea were determined. Grand-Seiko refraction was calculated from R x = (θ + α)/h 1 , where θ is the angle of the ingoing radiation beam, h 1 is the height of the beam at the anterior cornea and α is the angle of the beam emerging from the eye following reflection at the retina. Two eye models were used: a Navarro schematic eye and a Navarro schematic eye with a contact lens having a highly positive aspheric front surface. Results:The instrument beam was determined to be converging towards the eye to a distance of 24.4 mm behind the corneal vertex, with a 2.46 mm effective size outer diameter of the beam at the anterior cornea. The Grand-Seiko refractions provided accurate estimates of peripheral refraction for the model eyes.The results were closer to Zernike refractions than to Zernike paraxial refraction. Spherical aberration influenced refraction by up to 0.5 D, and peripheral coma had limited influence. Conclusion:Grand-Seiko autorefractors in current use, and having a circular annulus with an ingoing effective outer diameter at the front of the eye of about 2.4 mm, are likely to give valid peripheral refractions.

Accommodation lags are higher in myopia than in emmetropia: Measurement methods and metrics matter

“…It uses approximately a 1.5-mm to 2.3-mm sampling annulus. 14,38 The dominant eye viewed the target and drove the accommodation response, while the refraction of the other eye, that is, the consensual response, was measured. This was achieved by placing a distance trial lens correction in front of the dominant eye, while an infrared pass filter (87C, Kodak, kodak.com) close to the non-dominant eye occluded its view but transmitted the instrument's infrared radiation (Figure 1a).…”

“…15 The pupil plane metrics are based directly on Zernike aberration coefficients, such as using only the second order (Zernike refraction), or using second order and one or more of the higher orders (Seidel refraction), which give greater emphasis to the more central parts of the pupil. 14 Retinal image plane metrics optimise a measure of image quality, sometimes weighted by neural sensitivity. These include the Strehl intensity ratio, the intensity variance of the point spread function, the volume under the modulation transfer function (MTF) and the volume under the contrast sensitivity function (CSF).…”

“…Instruments such as the Grand Seiko autorefractors use an annulus beam in the pupil in combination with the ‘image‐size’ principle. However, the further out the annulus, the more that higher order aberrations, such as spherical aberrations, can influence refraction 13,14 . Other autorefractors and most aberrometers use circular beams, and again, the larger the beam, the larger the influence of higher order aberrations.…”

“…Refractions using aberrometers can be determined from different metrics, based on the aberration coefficients, and classified into pupil plane and retinal image plane metrics 15 . The pupil plane metrics are based directly on Zernike aberration coefficients, such as using only the second order (Zernike refraction), or using second order and one or more of the higher orders (Seidel refraction), which give greater emphasis to the more central parts of the pupil 14 . Retinal image plane metrics optimise a measure of image quality, sometimes weighted by neural sensitivity.…”

The use of autorefractors using the image‐size principle in determining on‐axis and off‐axis refraction. Part 3: Theoretical effect of pupil misalignment on peripheral refraction for the Grand‐Seiko Autorefractor

“…A Navarro four refracting surface schematic eye 6 was used for simulations. Raytracing was done with OpticStudio version 19.4 (Zemax, zemax.com) according to the procedure of Atchison et al, 7 but with the addition of decentration of the schematic eye relative to the instrument axis (Figure 1). For into‐the‐eye raytracing, a circular annulus stop of 2.46 mm outer diameter was used.…”