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

      BMJ Open Ophthalmology
      BMJ Publishing Group
      optics and refraction, telemedicine, public health

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          The 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 analysis

          Participants 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.


          The 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.


          NETRA 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.

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          Most cited references45

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          Power vectors: an application of Fourier analysis to the description and statistical analysis of refractive error.

          The description of sphero-cylinder lenses is approached from the viewpoint of Fourier analysis of the power profile. It is shown that the familiar sine-squared law leads naturally to a Fourier series representation with exactly three Fourier coefficients, representing the natural parameters of a thin lens. The constant term corresponds to the mean spherical equivalent (MSE) power, whereas the amplitude and phase of the harmonic correspond to the power and axis of a Jackson cross-cylinder (JCC) lens, respectively. Expressing the Fourier series in rectangular form leads to the representation of an arbitrary sphero-cylinder lens as the sum of a spherical lens and two cross-cylinders, one at axis 0 degree and the other at axis 45 degrees. The power of these three component lenses may be interpreted as (x,y,z) coordinates of a vector representation of the power profile. Advantages of this power vector representation of a sphero-cylinder lens for numerical and graphical analysis of optometric data are described for problems involving lens combinations, comparison of different lenses, and the statistical distribution of refractive errors.
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            Exact parametric confidence intervals for Bland-Altman limits of agreement.

            The previous literature on Bland-Altman analysis only describes approximate methods for calculating confidence intervals for 95% limits of agreement (LoAs). This article describes exact methods for calculating such confidence intervals based on the assumption that differences in measurement pairs are normally distributed.
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              Depth-of-focus of the human eye: theory and clinical implications.

              The depth-of-focus, or the perceptual tolerance of the human eye to retinal defocus, is important to and imbedded in many aspects of clinical refraction and physiological optics. Although the depth-of-focus is a common concept in classical optics, there is relatively little detailed discussion of its implications as related to normal vision function and to vision anomalies. With current advances in refractive surgery and ophthalmic lens design, the demand for knowledge in this topic is both timely and important. This review of our current understanding of the depth-of-focus should prove to be useful to clinicians, researchers, and students as an introduction to the subject. Two areas will be considered: 1) basic definitions of and factors affecting the depth-of-focus, and 2) its contemporary clinical implications.

                Author and article information

                BMJ Open Ophthalmol
                BMJ Open Ophthalmol
                BMJ Open Ophthalmology
                BMJ Publishing Group (BMA House, Tavistock Square, London, WC1H 9JR )
                1 April 2022
                : 7
                : 1
                : e000851
                [1]departmentDepartment of Optometry, Faculty of Health Sciences , University of Johannesburg , Johannesburg, Gauteng, South Africa
                Author notes
                [Correspondence to ] Dr Nabeela Hasrod; nabeelah@ 123456uj.ac.za
                Author information
                © Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

                This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

                : 12 July 2021
                : 26 August 2021
                Vision Science
                Original research
                Custom metadata

                optics and refraction,telemedicine,public health
                optics and refraction, telemedicine, public health


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