Comparing habitual and i. Scription refractions

Beyond traditional subjective refraction

PURPOSE OF REVIEW

The evaluation of refractive error is probably the most important and common procedure in eye care. The gold standard method for evaluating refractive error is subjective refraction, a process that has not significantly changed in 200years. This article aims to review recent technologies and novel approaches attempting to improve this traditional procedure.

RECENT FINDINGS

From laboratory prototypes to commercial instruments, the proposed methods aim to perform reliable and fast subjective refractions, following different approaches: using motorized phoropters in combination with automatic algorithms or even self-refraction, hybridizing objective and subjective measurements within the same instruments, or using new visual tasks beyond letter identification of blur estimation to obtain the refractive error subjectively.

SUMMARY

The current trend in subjective refraction is to overcome the traditional manual blur reduction method, using automatic and self-refraction instruments, which can provide faster measurements with lower variability. Many of the technologies reported here are already in the market, and some have the potential of becoming the new standard in subjective refraction.

Repeatability of i.Profiler for measuring wavefront aberrations in healthy eyes

PURPOSE

To evaluate the repeatability of wavefront aberration measurements and the correlation between corneal aberration and pupil size in normal eyes using a wavefront-based autorefractor (i.Profiler^Plus; Carl Zeiss Vision, Germany).

METHODS

A prospective cross-sectional study. Wavefront aberrations, including spherical aberration (SA) (Z₄⁰), coma (Z₃^-1, Z₃¹), trefoil (Z₃^-3, Z₃³) and total higher-order aberrations (tHOA), were measured at different pupil diameters. The repeatability was evaluated using one-way ANOVA method, and statistical indicators including within-subject standard deviation (S_w), test-retest repeatability (TRT), and intra-class correlation coefficient (ICC). The correlations between corneal aberrations and pupil sizes were evaluated by Pearson correlation analysis.

RESULTS

A total of 96 healthy young volunteers were enrolled. Corneal and ocular higher-order aberrations (HOA) measured by i.Profiler showed S_w < 0.01 μm, TRT < 0.10 μm, ICC > 0.90. There was a linear positive correlation between the corneal HOA and pupil size. The correlation coefficient between SA and tHOA was the largest (r = 0.996, P < 0.001).

CONCLUSIONS

The measurements of wavefront aberrations by i.Profiler are highly repeatable. Corneal HOA was significantly dependent on pupil size. SA was the most influential aberration for visual quality in this study.

Predicting subjective refraction with dynamic retinal image quality analysis

The aim of this work is to evaluate the performance of a novel algorithm that combines dynamic wavefront aberrometry data and descriptors of the retinal image quality from objective autorefractor measurements to predict subjective refraction. We conducted a retrospective study of the prediction accuracy and precision of the novel algorithm compared to standard search-based retinal image quality optimization algorithms. Dynamic measurements from 34 adult patients were taken with a handheld wavefront autorefractor and static data was obtained with a high-end desktop wavefront aberrometer. The search-based algorithms did not significantly improve the results of the desktop system, while the dynamic approach was able to simultaneously reduce the standard deviation (up to a 15% for reduction of spherical equivalent power) and the mean bias error of the predictions (up to 80% reduction of spherical equivalent power) for the handheld aberrometer. These results suggest that dynamic retinal image analysis can substantially improve the accuracy and precision of the portable wavefront autorefractor relative to subjective refraction.

Effects of varying illumination on ocular aberrations and aberration compensation before and after small incision Lenticule extraction: a prospective cohort study

BACKGROUND

There are few reports regarding the influence of varying illumination on the compensation effect before and after corneal refractive surgery. We aimed to evaluate the changes in refraction, higher-order aberrations, and aberration compensation between mesopic and photopic illumination before and after small incision lenticule extraction.

METHODS

In this prospective cohort study, only the right eyes of patients who underwent small incision lenticule extraction for the correction of myopia and myopic astigmatism at the Tianjin Eye Hospital were included. Wavefront refraction and higher-order aberrations were measured preoperatively and 3 months postoperatively under mesopic and photopic illumination. Compensation factors were calculated as 1 - (aberration of the whole eye/aberration of the anterior corneal surface).

RESULTS

Forty patients undergoing small incision lenticule extraction were enrolled. All surgeries were completed without postoperative complications. Preoperatively, the eyes only had a statistically significantly higher (t = - 4.589, p < .001) spherical refractive error under mesopic vs. photopic illumination (median [interquartile range], - 6.146 [2.356] vs. - 6.030 [2.619] diopters [D]), whereas postoperatively, the eyes also exhibited statistically significantly higher (t = - 3.013, p = .005) astigmatism (- 0.608 [0.414] vs. - 0.382 [0.319] D). Differences in spherical refraction between the two illuminations were the highest in postoperative eyes (Δ > 0.5 D). Only postoperative eyes exhibited statistically significant elevations (t ≥ 4.081, p < .001) in higher-order aberrations under mesopic illumination, and only preoperative eyes exhibited statistically significantly enhanced (χ² = 6.373, p = .01 for fourth-order and χ² = 11.850, p = .001 for primary spherical aberrations) and decreased (χ² = 13.653, p = .001 for horizontal trefoil) compensation factors under mesopic illumination.

CONCLUSIONS

Exaggerations in higher-order aberrations and myopic shift after small incision lenticule extraction became apparent under mesopic illumination. Slight undercorrection may have an enhanced effect under low illumination and may reduce night vision. The specific changes in compensation effects in preoperative eyes may improve optical quality under mesopic illumination. Postoperative eyes have reduced compensation ability, specifically for spherical aberrations, under mesopic illumination, which may diminish night vision. Further studies that include the measurement of subjective night vision parameters should be conducted.