# An Open-Source Horizontal Strabismus Simulator as an Evaluation Platform for Monocular Gaze Estimation Using Deep Learning Models

## TL;DR

A low-cost strabismus simulator is developed to evaluate monocular gaze estimation models, revealing significant errors in current AI systems for detecting eye misalignment.

## Contribution

An open-source horizontal strabismus simulator is introduced to evaluate monocular gaze estimation models with known ground-truth angles.

## Key findings

- The simulator achieved a mechanical accuracy of less than 0.1° mean absolute error.
- AI models showed estimation errors of 6.44–8.75°, exceeding the clinical target of 2.8°.
- Accuracy degraded rapidly beyond ±15° gaze angles, missing small-angle strabismus.

## Abstract

Strabismus affects 2–4% of the global population, with horizontal cases accounting for more than 90%. Automated screening using monocular gaze estimation technology shows promise for early detection. However, existing models assume normal binocular vision, and their applicability to strabismus remains unvalidated due to the lack of evaluation platforms capable of reproducing disconjugate eye movements with known ground-truth angles. To address this gap, we developed an open-source, low-cost (approximately 200 USD) horizontal strabismus simulator. The simulator features two independently controllable artificial eyeballs mounted on a two-axis gimbal mechanism with servo motors and gyro sensors for real-time angle measurement. Mechanical accuracy achieved a mean absolute error of less than 0.1° across all axes, well below the clinical detection threshold of 1 prism diopter (≈0.57°). An evaluation of three representative AI models (Single Eye, GazeNet, and EyeNet) revealed estimation errors of 6.44–8.75°, substantially exceeding the clinical target of 2.8°. At this error level, small-angle strabismus (<15 prism diopters) would likely be missed, underscoring the need for strabismus-specific model development. Moreover, rapid accuracy degradation was observed beyond ±15° gaze angles. This platform establishes baseline performance metrics and provides a foundation for advancing gaze estimation technology for strabismus screening.