Subjective Refraction Test Using a Smartphone for Vision Screening
October 18th, 2024
This paper presents the protocols and clinical validation data for using a smartphone app to subjectively measure refractive error.
We have been developing mobile health technology to address the accessibility, disparity, and equality issues in vision care. In this paper, we demonstrate how to use our mobile app to measure inter-pupillary distance, spherical equivalent refraction, and stigmatism. Uncorrected refractive error is a major cause of vision impairment in the world.
In underserved areas, rural areas, low-income areas, many people do not have access to routine eye care. With our app, we want to empower people who are not eye care professionals to help address some of the basic vision care needs. Our vision screening app can be used once installed, in general, smartphone.
There is no need to purchase any special phone attachments. This feature makes the screening tool easily accessible, even from many rural areas. To begin, launch the app and tap the IPD button on the homepage.
Place the phone approximately 40 centimeters away from the patient at eye level and ask the patient to look at the flashlight on the phone screen. Tap the round button on the right to take a picture of the patient's face. The app will then start processing the image automatically.
When two green crosshairs appear on the screen, check if they are aligned with the center of the patient's eyes. If the crosshairs are correctly positioned, tap the SAVE button. Launch the app and tap the REFRACTION button on the homepage.
Place the phone at least two meters away from the patient. Select E for tumbling E stimuli. Then select the eye to be measured and ask the patient to cover the other eye.
Now, hold the phone with the screen facing the patient and tap the START button. Ask the patient if they can identify the orientation of the letters displayed on the phone screen. If the patient cannot identify the letter orientations, gradually move the phone towards them while asking if they can see the letter orientations.
Then tap the VERIFY button to display the correct letter orientations on the screen. Compare the correct letter orientations with the patient's responses. If all three answers match, tap the CORRECT button to conclude the test.
Launch the app and tap the REFRACTION button on the homepage. Start by placing the phone at least two meters from the patient and select the Astigmatism1 stimulus. Select the eye to be measured and ask the patient to cover the other eye.
Hold the phone with the screen facing the patient and tap the START button. Ask the patient if the line group appears as three separate lines in any direction. Stop as soon as they can see the separated lines in at least one direction.
Now, select the Astigmatism2 stimulus. Rotate the phone around the axis perpendicular to the screen until the grading aligns with the clearest line group of Astigmatism1. Fine-tune the phone's rotation to find the best angle where the patient can see the red and green grading patches equally clearly.
Once found, tap the POINT 1 button to record the first far point. Note that POINT 1 is recorded, the astigmatism two stimulus is rotated 90 degrees automatically. From the first far point position, maintain the phone orientation and gradually move it closer to the patient until they can see the red and green grading patches equally clearly and identify the wider end.
Then tap the POINT 2 button to record the second far point. Based on the two far points, the app will calculate the spherical refractive error and astigmatism and display the results on the screen. On the result message box, tap the SAVE button to save the results.
The app measurement of spherical equivalent was highly consistent with clinical auto-refractor measurements with a regression line slope of 1.018 and an R squared value of 0.965. The Bland-Altman plot for the spherical equivalent shows 95%limits of agreement. The app measurement of cylinder power was consistent with standard subjective refraction with a mean error of 0.08 diopter and a standard deviation of 0.41 diopter.
This Bland-Altman plot for astigmatism measurement shows 95%limits of agreement. The error of inter-pupillary distance measurements with the app had a mean error of minus 0.55 millimeters and a standard deviation of 1.4 millimeters.
Overview
This paper presents a mobile app designed to measure refractive error, addressing accessibility issues in vision care. The app enables non-professionals to perform basic vision screenings, particularly in underserved areas.
Key Study Components
Area of Science
- Vision care
- Mobile health technology
- Refractive error measurement
Background
- Uncorrected refractive error is a leading cause of vision impairment globally.
- Many individuals in rural and low-income areas lack access to routine eye care.
- Mobile health solutions can help bridge the gap in vision care accessibility.
- The app aims to empower users without professional training to conduct vision screenings.
Purpose of Study
- To validate a smartphone app for measuring inter-pupillary distance, spherical equivalent refraction, and astigmatism.
- To improve accessibility to vision care in underserved populations.
- To provide a tool for non-professionals to assist with basic vision care needs.
Methods Used
- Development of a mobile app for vision screening.
- Clinical validation of the app's measurement capabilities.
- Testing in various demographic settings to assess usability.
- Comparison of app measurements with standard clinical methods.
Main Results
- The app successfully measures inter-pupillary distance and refractive errors.
- Results indicate high accuracy compared to traditional methods.
- User feedback highlights ease of use and accessibility.
- The app shows potential for widespread adoption in underserved areas.
Conclusions
- The smartphone app is a viable tool for measuring refractive error.
- It can significantly improve access to vision care in low-resource settings.
- Empowering non-professionals can help address basic vision care needs.
Frequently Asked Questions
Executive Industry Relevance
Accessible, quantitative vision screening is critical for large-scale population health studies and early detection of refractive errors. Smartphone-based subjective refraction enables scalable data collection and standardization in both clinical research and decentralized screening initiatives. This approach supports portfolio-wide efforts to reduce barriers in vision care and generate reproducible, device-independent measurements.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables hypothesis-driven evaluation of visual function in diverse populations.
- Supports validation of digital biomarkers for refractive error and visual acuity.
- Facilitates mechanistic de-risking by quantifying vision endpoints in real-world settings.
Screening & Assay Development
- Provides standardized, reproducible measurement protocols for vision screening assays.
- Delivers quantitative outputs for spherical equivalent, astigmatism, and inter-pupillary distance.
- Enables scalable deployment and cross-site comparability without specialized hardware.
Translational & Preclinical Research
- Aligns digital vision endpoints with clinical standards for translational continuity.
- Supports risk-adjusted advancement of digital health tools in vision research portfolios.
- Facilitates integration of real-world data into preclinical and population studies.
Pipeline & Workflow Integration
This smartphone-based subjective refraction test fits within the early discovery to translational research continuum, enabling hypothesis testing, digital endpoint validation, and scalable screening.
- Discovery Biology: Quantifies visual function for hypothesis-driven studies and pathway analysis.
- Screening: Standardizes vision assessment protocols for reproducible, quantitative outputs.
- Analytics: Provides device-independent measurements for robust statistical comparison across cohorts.
- Translational Research: Bridges digital screening data with clinical vision endpoints for biomarker alignment.
- Enterprise Reuse: Offers a reusable, scalable platform for vision screening across diverse research settings.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence in digital vision endpoints and reduces measurement variability.
- Operational Value: Enables standardized, reproducible, and scalable vision screening without specialized equipment.
- Strategic Value: Supports efficient go/no-go decisions for digital health tool development and deployment.
- Portfolio Impact: Facilitates risk-adjusted prioritization of digital screening technologies in vision research pipelines.
Implementation Considerations
- Requires basic training for lay personnel to ensure protocol adherence.
- Needs smartphones with adequate camera and display capabilities.
- Demands cross-team standardization for data collection and analysis workflows.
- May require adaptation for use in pediatric or special populations.
- Accuracy is subject to user compliance and environmental conditions as supported by pilot data.
