Subtle Vertical Deviation in Intermittent Exotropia

Abstract Background：To detect the subtle vertical deviation in patients with intermittent exotropia (IXT) by using prism and alternate cover test, synoptophore and perceptual eye position (PEP) test. Methods: An observational cross-sectional study was conducted of 104 IXT patients and 128 controls. A detailed ophthalmic examination was conducted on each participant. Eye position was evaluated by prism and alternate cover test, synoptophore and PEP test. Stereoacuity was measured by the Randot stereoacuity test for both near and medium distances. Results: The abnormality ratio of subtle vertical deviation was significantly higher as measured by the PEP test than by synoptophore, prism and alternate cover test (PEP: 47.12%, synoptophore: 2.88%, prism and alternate cover test: 1.92%, ????< 0.001). Furthermore, medium distance and near stereopsis were better in patients with normal vertical eye position than those with abnormal vertical eye position (P = 0.004 and P=0.017, respectively). No statistic differences were found between two groups both in near and far horizontal deviation measured by prism and alternate cover test (P=0.527, P=0.376). There were no significant differences in age, interocular difference in spherical equivalent (SE) between two groups (P=0.186 and P=0.117, respectively). Conclusions: An abnormal subtle vertical deviation is detected by PEP test in some patients with IXT, which is difficult to be measured by prism and alternate cover test, synoptophore. The stereoacuity is impaired by the abnormal subtle vertical deviation, rather than other factors such as age, horizontal deviation and anisometropia.