Binocular Coordination during Smartphone Reading in Patients with Intermittent Exotropia
Masakazu Hirota; Hiroyuki Kanda; Takao Endo; Takeshi Morimoto; Tomomitsu Miyoshi; Takashi Fujikado
2-2 Yamadaoka, Suita, Osaka, Japan
Introduction: To evaluate binocular coordination during smartphone reading in q patients with intermittent exotropia [X(T)] and normal subjects using video-oculography (VOG).
Methods: Ten patients with X(T) (21.8 ± 9.8 years) and fifteen control subjects (26.6 ± 4.3 years) were examined. Eye movements were recorded during smartphone reading at 50, 30, and 20 cm using VOG. The rate of monocular viewing, reading speed, and their correlation were analyzed.
Results: The rate of monocular viewing was significantly higher in the X(T) group than in the control group (50 cm, 13.1 ± 20.0 vs. 0%; 30 cm, 21.6 ± 24.2 vs. 0%; and 20 cm, 43.0 ± 30.1 vs. 0%; P < 0.001), and was significantly higher at 20 cm than at 50 cm in X(T) group (P < 0.05). The reading speed was significantly slower in the X(T) group than in the control group at 20 and 30 cm [30cm, 7.8 ± 1.4 characters per second (cps) vs. 9.3 ± 1.7 cps; 20cm, 7.4 ± 1.1 cps vs. 9.4 ± 2.0 cps; P <0.05] and was significantly and negatively correlated with the rate of monocular viewing at 20 and 30 cm in the X(T) group (P < 0.05).
Discussion: The decrease of reading performance is presumably due to the monocular viewing at close reading distance in patients with X(T) .
Conclusion: It should be taken into account that patients with X(T) watch a smartphone monoculally with lower reading performance when they use a smartphone at close distances.