Investigation of transient eye closure evoked with bright light in the patients with intermittent exotropia

Abstract

Background: This study aimed to present a simple method for evaluating transient eye closure (TEC) evoked by bright light and find the agreement between TEC and photosensitivity. We also assessed the associated factors with TEC in the patients with intermittent exotropia (IXT).

Methods: In this retrospective study, IXT patients were exposed to different brightness: darkness, low-intensity white light, and high-intensity white light using a near-infrared camera vision monitor system (Mon CV3, Metrovision, France). TEC was considered to be present if the subject closed his or her eyes immediately, and for more than half of the scotopic lid fissure distance in response to the high-intensity or low-intensity photopic stimulus of light, compared with lid fissure distance in the scotopic phase. We assessed the presence of photosensitivity using a questionnaire and evaluated the agreement between TEC and photosensitivity. We also investigated the sensory fusion, motor fusion, and pupil dynamic components for the existence of TEC in IXT patients.

Results: Sixty-one patients with IXT were included. With the new method to evaluate TEC under different light intensities, 27 (44.3%) of the 61 IXT patients showed TEC, and 34 (55.7%) did not demonstrate TEC. TEC under high-intensity white light had a strong correlation with self-reporting photosensitivity (r = 0.77). The smaller angle of deviation at near was associated with the presence of TEC, with statistical significance (p = 0.04). Normal sensory status at a distance was significantly associated with TEC (p < 0.01). Multivariate analysis using multiple logistic regression analysis showed that normal sensory status was significantly associated with TEC (p = 0.02).

Conclusions: The test using a near-infrared camera vision monitor system was a simple and objective tool in identifying TEC evoked by bright light. The presence of TEC strongly correlated with self-reporting photosensitivity in patients with IXT. However, TEC may be an independent phenomenon with motor alignment, stereopsis, and pupil reflex pathway in patients with IXT.

Keywords: Eye closure; Intermittent exotropia; Photophobia; Photosensitivity; Squint.

Fig. 1

We captured snapshots of reflexive eye closure and pupil changes from a live video feed using a near-infrared vision monitoring system (Mon CV3, Metrovision, France) under different light intensities. Scotopic phase (darkness) for 3300 ms, mesopic phase (under room light without light stimulation) for 200 ms, scotopic phase for 3300 ms, low-intensity white light phase (10 cd/m²) for 200 ms, scotopic phase for 3300 ms, and high-intensity white light phase (100 cd/m²) for 200 ms.