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Masakazu Hirota, Takeshi Morimoto, Hiroyuki Kanda, Takao Endo, Tomomitsu Miyoshi, Suguru Miyagawa, Yoko Hirohara, Tatsuo Yamaguchi, Makoto Saika, Takashi Fujikado; Objective Evaluation of Characteristics of Visual Fatigue in Patients with Intermittent Exotropia. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1031. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Intermittent exotropia [X(T)] is the most common form of childhood-onset exotropia and is characterized by poor near point of convergence and low fusional convergence. The resultant vergence–accommodation conflict induces visual fatigue in these patients. Questionnaire surveys have shown that visual fatigue is one of the most prevalent symptoms in patients with X(T) and that the eyes of these patients tend to tire easily compared with those of healthy individuals. However, objective measures for the assessment of visual fatigue in patients with X(T) are not well established. Hirota et al. (ARVO 2017) reported that binocular fusion maintenance (BFM) test may be used for the objective evaluation of visual fatigue. The purpose of this study was to compare visual fatigue between patients with X(T) and healthy individuals using BFM test.
Fifteen patients with X(T) [age (mean ± SD): 30.8 ± 16.4 years] and 15 age-matched healthy volunteers (31.2 ± 9.3 years) participated in the study. The BFM was assessed by measuring the transmittance of liquid crystals placed in front of the subjects’ non-dominant eye at the instance when binocular fusion was broken and vergence eye movement was induced. A questionnaire on subjective symptoms was administered to the subjects before and after a visual task. The visual task comprised a triangle wave with an amplitude of 1-m angle and constant dioptric movement between 67 and 40 cm.
Post-visual task BFM in patients with X(T) (0.700 ± 0.267) was significantly lower than that in healthy volunteers (0.917 ± 0.081), whereas pre-visual task BFM was not significantly different between the patients (0.877 ± 0.186) and the healthy volunteers (0.947 ± 0.068; pre, P = 0.595; post, P = 0.011). The difference [post − pre] in BFM showed a significant correlation with the difference in subjective eye symptom scores in both patients with X(T) (R2 = 653, P < 0.001) and healthy volunteers (R2 = 292, P = 0.038). Moreover, the rate of reduction in BFM with increase in subjective eye symptom score was significantly higher in patients with X(T) than in healthy volunteers (P = 0.009).
The present findings indicate that the eyes of patients with X(T) tire easily compared with those of healthy individuals.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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