[Comparative measurements of exodeviations in intermittent exotropia]

To compare the results of 4 methods for measuring angle of exodeviation including when fixating at indoor distance target of 6m, fixating at outdoor far distance target, after 1 hour diagnostic occlusion test (1h-DOT), and prism adaption test (PAT), in patients with intermittent exotropia.

Prospective case series study. Inpatients with intermittent exotropia was recruited from Sep 2011 to May 2012 in the Eye Center of Provincial Hospital Affiliated to Shandong University. Fifty involved patients included 26 males and 24 females with average age (10.1 ± 6.9) years. Prism and alternative cover test was used to evaluate the exodeviation on the primary position in patients with intermittent exotropia. All the patients were measured when fixating at indoor distance target of 6m and near target of 33 cm, fixating at outdoor far distance target, after 1h-DOT, and PAT. The mean deviations measured with 4 methods for distance and 3 methods for near were analysed statistically with levene test. LSD test was applied to compare the differences between each two methods. Positive increased angle of exodeviation was defined as equal to and more than 10 prism diopters (PD) when tested with fixating at outdoor far distance target, after 1h-DOT, and PAT, compared with the results of primary measurement of fixating at indoor distance target of 6 m and near target of 33 cm. A Chi-square test was applied to compare the distribution of sub-types of intermittent exotropia in 4 methods of measuring angle of exodeviation.

(1) The exodeviations tested with fixating at indoor distance target of 6 m, after 1h-DOT, fixating at outdoor far distance target, and PAT were (28.2 ± 8.4), (30.8 ± 9.7), (32.3 ± 8.8), (36.5 ± 9.5) PD, respectively (F = 7.235, P = 0.000) . The exodeviation tested with fixating at outdoor far distance target (P = 0.027) and PAT (P = 0.000) were greater than that tested with the primary measurement of fixating at indoor distance target of 6m. There are no significant difference between the exodeviation tested after 1h-DOT and that tested with fixating at indoor distance target of 6 m (P = 0.164) . Compared with the primary measurement of fixating at indoor distance target of 6 m, the increased angles of deviation measured with the methods of after 1 h-DOT, fixating at outdoor far distance target, and PAT were (2.5 ± 3.7), (4.1 ± 3.7), and (8.3 ± 4.3) PD, with positive rate of increased angles of deviation 8%, 16%, and 44%, respectively. The exodeviations tested with the primary measurement fixating at near target of 33 cm, after 1h-DOT, PAT were (29.7 ± 8.0), (35.3 ± 9.5) and (41.6 ± 10.5) PD, respectively. The exodeviations tested with fixating at near target of 33 cm after 1h-DOT (P = 0.003) and PAT (P = 0.000) were greater than that tested with the primary measurement. (2) Compared with the primary measurement of fixating at indoor near target of 33 cm, the increased angles of deviation measured with the methods of after 1h-DOT and PAT were (5.6 ± 4.7) and (11.8 ± 6.7) PD, with positive rate of increased angles of deviation 38% and 66%, respectively. (3) The distributions of intermittent exotropia sub-types tested with evaluation of fixating at indoor targets of 6 m and 33 cm, outdoor target of far distance and indoor target of 33 cm, indoor targets of 6 m and 33 cm after 1h-DOT, and indoor targets of 6 m and 33 cm with PAT have significant difference (χ(2) = 18.53, P = 0.001).

Both the measurement with fixating at outdoor far distance target and the measurement with PAT can elicit larger angle of exodeviations for distance, while both the measurement after 1h-DOT and the measurement with PAT can elicit larger angle of exodeviations for near in patients with intermittent exotropia. The measurement with PAT can elicit the maximal angle of exodeviations both for distance and for near in patients intermittent exotropia.