Abstract
BackgroundStrabismus is the leading risk factor for amblyopia, which should be early detected for minimized visual impairment. However, traditional school screening for strabismus can be challenged due to several factors, most notably training, mobility and cost. The purpose of our study is to evaluate the feasibility of using a smartphone application in school vision screening for detection of strabismus.MethodsThe beta smartphone application, EyeTurn, can measure ocular misalignment by computerized Hirschberg test. The application was used by a school nurse in a routine vision screening for 133 elementary school children. All app measurements were reviewed by an ophthalmologist to assess the rate of successful measurement and were flagged for in-person verification with prism alternating cover test (PACT) using a 2.4Δ threshold (root mean squared error of the app). A receiver operating characteristic (ROC) curve was used to determine the best sensitivity and specificity for an 8Δ threshold (recommended by AAPOS) with the PACT measurement as ground truth.ResultsThe nurse obtained at least one successful app measurement for 93% of children (125/133). 40 were flagged for PACT, of which 6 were confirmed to have strabismus, including 4 exotropia (10△, 10△, 14△ and 18△), 1 constant esotropia (25△) and 1 accommodative esotropia (14△). Based on the ROC curve, the optimum threshold for the app to detect strabismus was determined to be 3.0△, with the best sensitivity (83.0%), specificity (76.5%). With this threshold the app would have missed one child with accommodative esotriopia, whereas conventional screening missed 3 cases of intermittent extropia.ConclusionsResults support feasibility of use of the app by personnel without professional training in routine school screenings to improve detection of strabismus.
Highlights
Strabismus is the leading risk factor for amblyopia, which should be early detected for minimized visual impairment
School nurses are able to check for amblyopia using visual acuity and stereopsis, but they are not trained to conduct a cover test, which is the standard means of diagnosing and directly measuring strabismus
At the troubleshooting session, the main issue addressed was that the images were off center due to centering of the phone to the student’s face rather than the camera, which can cause the image size to vary across the horizontal axis and may induce measurement error
Summary
Strabismus is the leading risk factor for amblyopia, which should be early detected for minimized visual impairment. Traditional school screening for strabismus can be challenged due to several factors, most notably training, mobility and cost. Strabismus develops during childhood in an estimated 3– 8% of the U.S population and is the leading risk factor for amblyopia [1, 2]. School nurses are able to check for amblyopia using visual acuity and stereopsis, but they are not trained to conduct a cover test, which is the standard means of diagnosing and directly measuring strabismus. It would be challenging to train all the nurses and pediatricians to perform a cover test for strabismus detection and so screening protocols opt for the simpler stereo testing (typically Randot), which can miss cases of intermittent strabismus. Direct evaluation of strabismus (rather than relying on a stereopsis test) is important in intermittent strabismus, where stereopsis can be normal or near normal causing most cases to be missed [5, 6]
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