Here is the design of a clinical trial:

Official Title: Long-term Prospective Randomized Controlled Clinical Study on Surgical Treatment of Moderate Intermittent Exotropia

Included conditions:
- Moderate Intermittent Exotropia

Study Armgroups:
- {'label': 'Surgical treatment', 'type': 'EXPERIMENTAL', 'description': 'The recession or resection of the horizontal extraocular muscles will be processed in the beginning of the trial.', 'interventionNames': ['Procedure: recession or resection of the horizontal extraocular muscles']}
- {'label': 'Observation only', 'type': 'NO_INTERVENTION'}

Interventions:
- {'type': 'PROCEDURE', 'name': 'recession or resection of the horizontal extraocular muscles', 'armGroupLabels': ['Surgical treatment']}

Primary Outcomes:
- {'measure': 'Ocular alignment (Prism alternative cover test)', 'timeFrame': '5 years'}
- {'measure': 'Binocular stereopsis at distance and near (Random dot stereopsis test)', 'timeFrame': '5 years'}

Please estimate the sample size based on the assumption: 
5% type I error, 80% power, 30% dropout rate.
Sample size
        The sample size for this study was calculated based on a standard two-sided trial with a continuous outcome, and the calculations assume 5% type I error with 80% power. According to an average 30% dropout rate in long-term follow-up period, we anticipate that we will require 280 total participants.