• Background and study aims : The investigators conducted this study to compare the movement of extraocular muscle after two types of recession surgery with non-invasive tool called AS-OCT.
• Who can participate? patients who will undergo two types (conventional method and hang-back method) of typical bilateral lateral rectus recession surgery for correcting intermittent exotropia
• What does the study involve? Volunteers will attend a clinic for four visits over three months. They will undergo AS-OCT at every visits during follow up period. AS-OCT is non-invasive test to evaluate operation site. The test only requires their cooperation when they undergo AS-OCT.
• What are the possible benefits and risks of participating? This is non-invasive test for your postoperative follow up. Therefore, there will be no risks about this test.
• Where is the study run from? Samsung Medical Center
• When is the study starting and how long is it expected to run for? From April 2015 to Dec 2015

This study is a following study of our prior study about AS-OCT in strabismus. The aim of this study is to compare the longitudinal changes of lateral rectus (LR) muscle insertion between two types of bilateral recession surgery. An AS-OCT scan of the LR muscle was performed every visits. Data on gender, age, degree of deviation (prism diopter), and spur-LR insertion distance using AS-OCT were collected at postoperative months 1,3 in each group.

Inclusion Criteria:

• patients who will undergo bilateral lateral rectus recession surgery for correcting intermittent exotropia

Exclusion Criteria:

• previous ocular surgery
• other ocular diseases except intermittent exotropia
• amblyopia

60 patients

: 30 for conventional recession surgery 30 for hang-back recession surgery