Subjective Refraction Test Using a Smartphone for Vision Screening

Summary

This paper presents the protocols and clinical validation data for using a smartphone app to subjectively measure refractive error.

Abstract

To improve access to vision care and to enable mass vision screening, a smartphone app has been developed to measure refractive errors. Without needing any external attachment, the app running on a standalone phone can be used by lay personnel to measure subjective refraction. Its validity has been pilot-tested in clinical settings and underserved communities. The app estimates the refractive error by measuring the distances of far points for discerning visual stimuli. Spherical equivalent refraction and astigmatism can be measured using Tumbling E letters and grating patterns, respectively. The purpose of this paper is to describe the measurement protocols for performing subjective refraction using the app. Experimental results with 34 subjects (30 eyes for spherical equivalent and 38 eyes for astigmatism assessment) are presented. Measurement with the app was compared with standard clinical methods. The average absolute error of spherical equivalent refraction was 0.63D, and the average absolute error of astigmatism measurement was 0.28D. In addition, 22 subjects were enrolled to evaluate inter-pupillary distance (IPD) measurement with the app. The average absolute error in IPD measurement with the app was 1.2 mm. The protocol for measuring IPD with the app is also described.

Introduction

Uncorrected refractive error (URE) is a major cause of blindness and vision impairment in the world, affecting 86¹ to 116 million individuals², although it is treatable with glasses. Studies have shown that the prevalence of URE in remote areas is primarily driven by the low number of eye care professionals and the lack of an adequate health infrastructure to dispense glasses³. For instance, the prevalence of vision impairment due to URE among adults above 50 years of age in Sub-Saharan Africa is 10 times higher than that in high-income countries¹.

Protocol

The study was conducted in accordance with the tenets of the Declaration of Helsinki at Mass Eye and Ear Infirmary (Boston, MA). Informed consent was obtained from all the participants. The study was approved by the local institutional review boards of Mass Eye and Ear (Boston, MA). Subject inclusion criteria were diagnosis of myopia and no other eye conditions, such as cataracts and retinal disease, according to an optometrist.

1. Measuring spherical equivalent

1. Launch the app and tap the Refraction button on the home page (Figure 1). Place the phone at least 2 m aw....

Results

For this study, the interface of the refraction test is shown in Figure 2. Depending on the selected stimuli, the app performs a spherical equivalent or full refraction test. When Tumbling E is selected, the app measures the spherical equivalent (Figure 2). When grating stimuli Astigma 1 or 2 is selected, the app measures refractive error, including astigmatism (Figure 3).

To demonstrate the app's eff.......

Discussion

Using the app, it is feasible for a person without professional optometry training to perform subjective refractive error tests. Its application in vision screening has been demonstrated in a recent eye screening study among school-aged students in a rural area⁹. Compared to the other mass vision screening methods that are solely based on visual acuity testing²¹, this app can provide measurement of refraction in terms of spherical and cylindrical error values typically used.......

Materials

Name	Company	Catalog Number	Comments
Smartphone	Samsung	Galaxy	commercially available smartphone