The purpose of this study is to determine the long-term effect and security of the surgical treatment and observation only on ocular alignment, binocular stereopsis, and quality of life in children with moderate intermittent exotropia.

Inclusion Criteria:

1. To correspond the definition of IXT: monocular or binocular alternative exotropia, exodeviation at distance for 15 prism diopters at least, can control the normal ocular alignment, normal ocular movements.
2. Simultaneous perception and fusion point in synoptophore, but no normal function of fusion and stereopsis.
3. Age at from 5 to 18 years, sex unlimited.
4. No treatment for IXT previously (including surgical and non-surgical treatment).
5. No amblyopia.
6. Signed informed consent form voluntarily.

Exclusion Criteria:

1. Accompanied with ocular organic diseases.
2. Accompanied with systemic diseases (e.g. nervous system disease).
3. Unable to regular follow-up (e.g. from countryside and outlying district).
4. Investigators concluded that should be excluded.