Comparison of the Near Eye Tool for Refractive Assessment (NETRA) and non-cycloplegic subjective refraction

Abstract

ObjectiveThe NETRA (Near Eye Tool for Refractive Assessment) is a smartphone-based refractive tool that allows for self-evaluation of refractive error. This study investigates the validity of the NETRA with and without cycloplegia to non-cycloplegic subjective refractions (SR).Methods and analysisParticipants underwent NETRA measurements without cycloplegia, and again after the administration of cycloplegia (cyclopentolate hydrochloride 1%). Non-cycloplegic SR were also performed. Variation of refractive measurements in symmetric dioptric power space were investigated using stereo-pair comets, hypothesis tests for variances and means. Bland-Altman plots were applied to better understand validity of the NETRA against non-cycloplegic SR. Coefficients of repeatability and intraclass correlation coefficients were also determined.ResultsThe sample included 22 women (64.7%) and 12 men (35.3%); most were indigenous Africans (52.9%) with mean age and SD of 20.24±1.95 years. Variation of refractive measurements were mainly stigmatic (spherical), and variation of NETRA measurements decreased after cycloplegia. The pre-cycloplegia NETRA measurements (and their means) for the right and left eyes were more negative (myopic) in power than the post-cycloplegia NETRA measurements and means. On average, eyes were approximately 1.25 D more myopic with the NETRA without cycloplegia. With cycloplegia, NETRA results were in closer agreement with non-cycloplegic SR for the same eyes.ConclusionNETRA validity to SR, even in the absence of cycloplegia, suggests the instrument may be useful in geographical regions where self-refractions might be potentially helpful in addressing limitations in eye and vision care.

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

“…The specific aim below is to relate the analysis of dioptric power using both power vectors and matrices27 and to emphasise a few critical issues also such as departure from normality,21 22 138–141 outliers21 22 and transformations21 22 of data. These important issues are often ignored in analyses 64. The analysis is brief, but the key aspects, methodology and their relevance should become readily apparent.…”

“…Readers should fixate to an imaginary point beyond the figure to see the stereo-pair with an exo-posture, (B) The same sample but using power matrices (F i ), (C) the same sample but with axes rotated to look along the scalar axis (label true05I is obscured by data) to directly view the antiscalar plane, (D) Two pseudo-three-dimension plots using coordinate vector f to produce a stereo-pair for the same sample but without the SCPD. (Data courtesy of NH—see reference number 64).…”

“…Over the last three decades general analyses for dioptric power globally have improved and it is now rare that journals will readily accept papers that do not use either power vectors2–6 10–22 24 26–39 (such as those of Harris2 or Thibos et al 24 or others such as Alpins32 33 or power matrices 1 10–22 25 27–31 41–74. This section will very briefly summarise applications where such methods are used in ophthalmology and optometry.…”

“…Epidemiological studies of the relevant components of the eye in terms of refractive state (and meridional refraction130 have also improved our understanding of the nature and variation of the cornea, air-tear interface and even the retina itself. This is an area where further research with large samples remains necessary although there are studies21 22 28 56 58 62–64 66–70 73 81 82 96 97 117–120 where power vectors or matrices are used to investigate distributions of refractive behaviour but they remain relatively few in number. Often sampling is not random13 and thus clinical or other biases may be limiting factors for such studies.…”

“…Possible relationships between refractive behaviour and visual acuity are explored by Harris and Rubin but this multidimensional topic is not further considered here 54 55. Power vectors and power matrices and the analytical methods as explained and described mathematically below have been applied to a diverse range of clinical and experimental topics20–74 including autorefraction in adults,28–31 56 57 children,58 66 keratometric variation,59–61 comparisons of methods to measure refractive behaviour in relation to age62 63 and other factors including also luminance of targets within autorefractors65 and wavefront aberrometry,66 interocular mirror symmetry,67 cycloplegia,64 68 keratoconus,69 70 measurement error and uncertainty,64 71 72 anisometropia73 and refractive surgery 74…”