Variation during autorefraction: influence of two different target types

Impact of Viewing Conditions and Vision Anomalies on Accuracy and Dynamics of Noncycloplegic Autorefraction

SIGNIFICANCE

This study was conducted to analyze the influence of binocular vision and accommodation anomalies on refraction dynamics. Our results may help to design more accurate autorefractors and to better understand the difficulties in prescribing an optical correction or adaptation to a correction.

PURPOSE

This study aimed to verify whether viewing conditions (open- or closed-field) or vision anomalies, such as ocular surface diseases, accommodative dysfunctions, and binocular vision anomalies, influence (1) the differences between subjective refraction and autorefraction and (2) the characteristics of the short-term refractive state variation.

METHODS

The subjective refraction of 64 subjects aged 23 to 60 years was measured during a comprehensive optometric examination, and the Ocular Surface Disease Index questionnaire was collected. Twenty successive measurements of automated refraction of each eye were obtained using a conventional autorefractor Nidek ARK-510A and an open-field autorefractor Shin-Nippon NVision-K 5001. Conventional notation of refractive error (sphere, cylinder, axis) was transformed to h-vectors, presented in scatterplots, and analyzed statistically.

RESULTS

The three-way analysis of variance tests showed that there is no influence of accommodation dysfunctions (P = .22 for ARK-510A), binocular vision anomalies (P = .97 for ARK-510A), and ocular surface diseases (P = .20 for ARK-510A) on differences between autorefraction and subjective refraction. The binocular vision anomalies affected the results from open-field autorefractor, whereas the accommodation impacted closed-field refraction measurements. Changes in short-term refractive state variation occurred in sphere power, indicating accommodative state changes; however, 30 subjects demonstrated at least one outlier and/or polymodality of refractive state distributions.

CONCLUSIONS

The study showed that the presence of accommodative dysfunctions or binocular vision anomalies might increase the range of short-term refractive state variation. The impact of vision anomalies differs between viewing conditions. The polymodal distribution of refractive state variation and the presence of outliers imply that automatic modes used typically in autorefractors with three to five readings may not accurately represent the refractive state of the eye.

Dioptric power and refractive behaviour: a review of methods and applications

Myopia is a global healthcare concern and effective analyses of dioptric power are important in evaluating potential treatments involving surgery, orthokeratology, drugs such as low-dose (0.05%) atropine and gene therapy. This paper considers issues of concern when analysing refractive state such as data normality, transformations, outliers and anisometropia. A brief review of methods for analysing and representing dioptric power is included but the emphasis is on the optimal approach to understanding refractive state (and its variation) in addressing pertinent clinical and research questions.

Although there have been significant improvements in the analysis of refractive state, areas for critical consideration remain and the use of power matrices as opposed to power vectors is one such area. Another is effective identification of outliers in refractive data. The type of multivariate distribution present with samples of dioptric power is often not considered. Similarly, transformations of samples (of dioptric power) towards normality and the effects of such transformations are not thoroughly explored. These areas (outliers, normality and transformations) need further investigation for greater efficacy and proper inferences regarding refractive error. Although power vectors are better known, power matrices are accentuated herein due to potential advantages for statistical analyses of dioptric power such as greater simplicity, completeness, and improved facility for quantitative and graphical representation of refractive state.

Accuracy and accommodation capability of a handheld autorefractor

PURPOSE

To determine the accuracy of measurement by the Nikon Retinomax handheld autorefractor and its ability to relax accommodation.

SETTING

Pediatric Section, Department of Ophthalmology, University of Mainz, Germany.

METHODS

To perform a series of comparative measurements, autorefractor readings were obtained on healthy young adults (students) and on children aged 2 to 12 years. The autorefractor readings were compared with subjective refractions of the young adults and with cycloplegic retinoscopy of the children.

RESULTS

In adults, the accuracy of the handheld autorefractor measurements was comparable to that of conventional tabletop autorefractors. In children, the autorefractor measurements performed under cycloplegia were reliable; when cycloplegic agents were not administered, 24% were overcorrected by more than -2.0 diopters.

CONCLUSION

Cycloplegia is often necessary to obtain accurate autorefractor results.