The authors have nothing to declare regarding conflicts of interest or commercial relationships. Effect of spherical aberrations on aberrometer-predicted refraction and manifest refraction Jinho Jeong1, Mee Kum Kim2, Won Ryang Wee2 Department of Ophthalmology Jeju National University Hospital, Jeju, Korea1 Seoul National University Hospital, Seoul, Korea2

Backgrounds Stiles-Crawford Effect 1937, W.S. Stiles & B.H. Crawford The directional sensitivity of the cone light passing near the edge of the pupil (a marginal ray) is less efficient at evoking sensation than light passing through the center of the pupil Works on photopic condition

Backgrounds The SCE has been reported not to act on rods and its directional selectivity is considered to be least effective in the scotopic condition. Human neurons recognize central rays more selectively according to the SCE, but on the other hand, aberrometers do not have directional selectivity. Therefore, differences between manifest refraction and aberrometer predicted refraction could occur if measurements were taken in the photopic condition. However, these measurements are usually conducted in the scotopic condition, and the SCE needs evaluation under these environments. In this study, we compared refractive errors measured by manifest refraction with those predicted by an aberrometer, both measurement types were conducted in the scotopic condition, and the role of the SCE was evaluated by analyzing correlations between spherical aberrations and discrepancies between refraction results.

Purpose Purpose: To evaluate the influence of the Stiles-Crawford effect (SCE) on manifest refraction and aberrometer predicted refraction in pseudophakic eyes. Design: Retrospective review of diagnostic tests Participants: 73 eyes of 45 patients that underwent uneventful cataract surgery.

Methods The records of 73 cases with uneventful cataract surgery were retrospectively reviewed. 1 month after surgery, manifest refraction (MR) was assessed, and ocular aberrations, aberrometer predicted refraction (APR), and mesopic pupil size were measured using a Wavescan 1 (VISX, Santa Clara, CA). APR was calculated for a 4 mm pupil. Refraction gap was calculated by subtraction APR spherical equivalents (SEs) from MR SEs, and correlations of refraction gap between high order aberration, pupil size, and refractive error were analyzed.

Results

Results Paired samples t-test: Manifest refraction - Aberrometer predicted refraction

Results The mean refraction gap was -0.28 ± 0.26 D (range -0.76 to 0.44 D), and MR SEs were significantly more myopic than APR SEs (paired t test; p<0.001). APR and MR were found to be significantly correlated with each other (R=0.963), and the distribution of the refractive gap qualified 95% limit of agreement, which ranged from -0.84 D to 0.24 D.

Results Correlations between refraction gap and refractive error, pupil size, and high order RMS. Refraction gap was measured by subtracting aberrometer predicted refraction from manifest refraction.

Results According to multiple regression analysis, spherical aberrations were significantly correlated with refraction gaps (R=0.508). As spherical aberration increased, APR became more myopic than MR. Refractive error and pupil size were not found to be significantly related to refraction gap

Discussions Schematic presentation of spherical aberration effects at a focal point. Spherical aberrations are caused by peripheral rays, and the minimum circle of confusion moves in a more myopic direction in eyes with a positive spherical aberration and in a more hyperopic direction in eyes with a negative spherical aberration. When the Stiles-Crawford effect is taken into account, central rays are more weighted and the focal point remains unchanged despite the presence of spherical aberrations.

Discussions We regard that MR with the SCE may represent the refractive state of day vision and APR without SCE represents for night vision, although some modulation may be necessary to make direct comparisons. We expect that both MR and APR results should be taken into consideration when assessing a patient’s refractive status, and these results would also be useful for deciding on ablation amounts during corneal refractive surgery in the presence of a refraction gap between MR and APR. Based on our results, we would expect a 0.4 D refraction gap for a 0.2 µm spherical aberration change.

Conclusion The Stiles-Crawford effect was found to influence manifest refraction results. In terms of the interpretation of aberrometer predicted refraction, SCE and spherical aberrations should be weighted when the relationships with MR are being investigated Both MR and APR results should be taken into consideration when assessing a patient’s refractive status