Abstract
Purpose :
While higher order aberrations (HOAs) can have a profound effect on visual acuity, both from a subjective and objective standpoint, they also can affect the accuracy of determining a correct low order refraction. These aberrations are typically associated with ectatic conditions such as keratoconus, pellucid marginal degeneration, etc. Many of these patients wear specialty contact lenses to reduce the effect of these aberrations. However, finding the appropriate manifest refraction for these patients can be quite difficult, as traditional refraction is only capable of including 1st and 2nd order aberrations (spherocylinder)
Methods :
This study compared three different methods for calculating the refraction from a wavefront aberration map. This map was fitted with Zernike polynomials through the 6th order, and the refraction was calculated from the polynomial coefficients. The Max Pupil method (MP) used only the 2nd order terms to calculate the refraction over the full pupil. The analysis Pupil method used the 2nd order terms to calculate over a 4 mm pupil, and the Seidel method used the 2nd and 4th order terms to calculate the refraction over the full pupil. For comparison, a standard commercial autorefractor (without HOA capabilities) was included
Results :
This study shows 17 eyes and compares the objective HOA autorefraction to the subjective manifest refraction (see figure 1 below). All the methods were plotted against the spherical value of manifest refraction. The data represents a spherical range from -11 to +2 D. The max pupil sphere to the manifest regression (MR) was 1.083 MR -0.329 with R2 value of 0.974, the analysis pupil was 1.014 MR – 0.159 with R2 of 0.967 and the Seidel 0.997 MR + 0.255 with R2 of 0.951. For comparison, the standard commercial auto refractor showed 1.005 MR + 0.550 with R2 of 0.960
Conclusions :
The analysis pupil and Seidel method showed slightly less offset (0.14 vs. 0.33) and had slope closer to 1. This is likely due to the aberrations near the edge of the optic zone– the area within the pupil, which more strongly affects the objective refraction calculation. Patients often try to minimize the effect of these aberrations by improving lighting or squinting. However, with an accurate objective refraction, it can be much more efficient to fit the patient with lenses and reduce the number of iterations (i.e. patient follow-ups/lens refinement), particularly those with visually significant HOAs
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.