Abstract
Purpose :
Ocular aberrometry is becoming more closely integrated into clinical practice, and one important use is the derivation of refractive corrections, a form of objective refraction. It is important to understand the effects of pupil size and position on refractive error correction.
Methods :
Twenty-one normal subjects age 18+ participated in this research. Aberration measurement was performed without and with cycloplegia, and refractive corrections were generated using four methods: 1) meridional refraction that maximizes grating contrast at multiple orientations; 2) maximizing the VSX visual quality metric; 3) from the 2nd order Zernike terms; 4) from the 2nd, 4th, and 6th order Zernike terms. Each of these were computed for centered 6 mm and 3.5 mm diameter pupils, and for 3.5 mm pupils displaced by up to 1.0 mm. Comparisons of the refractive results were computed, and only right eyes were used in this analysis.
Results :
Aberrometry-based refractive corrections for 6 mm compared to 3.5 mm pupils for methods 1 through 3 were more negative by an average of -0.24 D. Method 4 showed nearly identical results for large and small pupils. Astigmatic changes were small; mean change values were less than 0.035 D.
Decentration of the pupil produced changes in the spherical equivalent (M) and astigmatic components. Vertical decentration produced about 2x the effect of horizontal: 1 mm vertical produced a ΔM ranging from -0.30 D to -0.41 D for the four methods. Mean changes in J0 ranged from +0.20 D to +0.28 D. H/V changes had the greater effect on J0 compared to J45, while diagonal decentration affected J45. Decentration of 0.5 mm produced intermediate changes. A decentration of 1.0 mm approximately doubled the mean high-order RMS value.
Conclusions :
The size and position of the pupil aperture influences the sphero-cylindrical result. A large pupil produces a mean refractive correction that is more minus than a small pupil, a consequence of the higher-order terms. Changes in astigmatism resulting from pupil size changes are typically much smaller than changes in sphere. Pupil displacement produces changes in sphere and astigmatism, and these changes can be large enough to be clinically meaningful. It is expected that these effects will be amplified in more highly aberrated eyes. These results illustrate the impact of positioning errors and pupil size in computing a refractive correction from aberrometry.
This is a 2020 ARVO Annual Meeting abstract.