Strabismus is the leading risk factor for amblyopia, which should be early detected for minimized visual impairment. EyeTurn is a smartphone application that can detect ocular misalignment by a computerized Hirschberg test. In a recent study, researchers have reported that it is feasible for non-eye care professionals such as a school nurse to perform strabismus school screening using this smartphone application. The research has been published in BMC Ophthalmology on March 25, 2021.
Early detection of strabismus in young children is important to ensure that treatment is administered as soon as possible. In 2002, the American Academy of Pediatrics strongly endorsed the development of cost-effective image-based screening (photo screening) as a means to extend screening to all children. The red reflex (Bruckner) and the corneal reflex (Hirschberg) techniques are the two most common strabismus photo screening methods. Traditional school screening for strabismus can be challenged due to several factors, most notably training, mobility and cost. Therefore, Dr Wenbo Cheng and his team conducted a study to evaluate the feasibility of using a smartphone application, EyeTurn in-school vision screening for detection of strabismus.
It was a cross-sectional study in which the EyeTurn application was used by a school nurse in a routine vision screening for 133 elementary school children. An ophthalmologist reviewed all app measurements to assess the rate of successful measurement and flagged for in-person verification with a prism alternating cover test (PACT) using a 2.4Δ threshold (root mean squared error of the app). The researchers used a receiver operating characteristic (ROC) curve to determine the best sensitivity and specificity for an 8Δ threshold (recommended by AAPOS) with the PACT measurement as ground truth.

Courtesty by Wenbo Cheng et al. BMC Ophthalmology
In a, the distances between limbus center and corneal reflection (DLR) of each eye are equal and small (0.38 mm for OD and 0.49 mm for OS). Both corneal reflections are located nasal to the limbus centers with no obvious strabismus measured. In b and c there are substantial differences in DLR. In b, 0.28 mm OD and 0.83 mm OS, with a strabismus angle calculated at 10.51△ (exodeviation). In C the corneal reflection is located in different sides of the iris center and the strabismus angle is calculated at 20.19△ (esodeviation). b shows a suspected exotropia while (c) is a suspected esotropia.

Key findings of the study were:
The researchers noted that the nurse obtained at least one successful app measurement for 93% of children (125/133).
They found 40 children 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, they reported that the optimum threshold for the app to detect strabismus was to be 3.0△, with the best sensitivity (83.0%), specificity (76.5%).
They noted, "With this threshold the app would have missed one child with accommodative esotriopia, whereas conventional screening missed 3 cases of intermittent extropia."
The authors concluded, "Results support feasibility of use of the app by personnel without professional training in routine school screenings to improve detection of strabismus."
For further information:
DOI: https://doi.org/10.1186/s12886-021-01902-w