Squint ASSIST: A Novel Application Program for Detecting Strabismus and Measuring Angle of Deviation

To develop and validate Squint ASSIST (Squint Automatic Strabismus Sizing using Image Sensing Technology), an application program for strabismus detection and angle measurement, using corneal light reflex deviation in eye photographs.

This prospective cross‑sectional clinic‑based study enrolled 136 patients and 1384 photographs. Two analytic methods were evaluated: Method 1 (inter-ocular comparison; comparing corneal light reflex positions between both eyes in one image) and Method 2 (intra‑ocular comparison; comparing the same eye in a straight vs deviated image). Photographs were processed with standardized processing images. The participants' angles of deviation were measured using this program, which converts the light reflex deviation to misaligned angles in prism diopters. The main outcome was the sensitivity, specificity, and accuracy of the program for detecting strabismus. The agreement between the angles measured by the program and those measured by pediatric ophthalmologists using the Krimsky test and the Alternate Prism Cover Test (APCT) was analyzed using the Bland-Altman plot. Intra-observer and inter-observer reproducibility were also evaluated.

Of those 136 patients with strabismus, eighty‑seven patients had esotropia, 43 had exotropia, and six had orthophoria after strabismic surgery. The mean age was 12.8 (1-69) years. Squint ASSIST detected strabismus with high performance. Method 1: sensitivity 96.39%, specificity 94.34%, accuracy 95.59%; Method 2: sensitivity 96.83%, specificity 90.48%, accuracy 94.29%. Pearson r versus clinician measures were 0.962 (Method 1) and 0.955 (Method 2) (P < 0.001). When compared the program with ophthalmologists, the Bland-Altman analysis showed that the mean biases were small (Method 1: -1.23 PD; Method 2: -2.00 PD), but the 95% limits of agreement were wide (-29 to +27 PD overall). Repeatability and inter-observer reproducibility was strong.

The Squint ASSIST offers a reliable method for detecting and measuring strabismic angles in clinical settings. The small mean bias and strong intra-observer and inter-observer consistency support substantial clinical utility for screening, standardized photographic documentation, and telemedicine follow‑up. However, due to its wide limits of agreement for absolute angle estimates, pediatric ophthalmologists remain the reference for situations that demand maximal precision such as pre‑surgical planning.