This study is to investigate protective effect of biodegradable collagen implant in scleral showing after lateral rectus recession in patients with exotropia.

Inclusion Criteria:

1. Patients with intermittent exotropia or constant exotropia
2. Alternate prism cover test showed 20 prism diopters or more than 20 prism diopters exotropia
3. Subjects who want to do strabismus surgery

Exclusion Criteria:

1. Subject who had previous strabismus surgery or other ocular surgery history
2. Thyroid eye disease or other connective tissue disease
3. Significant bleeding or scleral perforation during operation
4. Subjects who need to do medial rectus resection, not lateral rectus recession
5. Subjects who had a plan to do other intra or extraocular surgery within 3 months

no plan to share individual participant data