Proposing a new scoring system in intermittent exotropia: towards a better assessment of control

There is a clinical need for a valid and reliable assessment system to quantify the severity and measure the progression of intermittent exotropia. We have developed a new scoring system (Look And Cover, then Ten seconds of Observation Scale for Exotropia [LACTOSE]) based on the examinee's potential to regain the phoria for both distance and near fixation. The test takes only 1 minute to complete. The aim of this study was to evaluate the reliability and validity of LACTOSE.

The LACTOSE was created by incorporating both distance and near score (0-4 each) into a total score ranging from 0 to 8. A total of 235 consecutive patients with intermittent exotropia were prospectively evaluated using this new scoring system. Inter-rater and test-retest reliability was assessed from a cohort of 10 patients who were video recorded while undergoing the scoring testing and then scored by 10 trained ophthalmologists independently. Construct validity was studied by comparison with clinical variables indicating disease severity.

Inter-rater reliability was good for both distance and near (intraclass correlation coefficient [ICC] = 0.729 and 0.818). Test-retest reliability was excellent for both distance and near (ICC = 0.849 and 0.727). Median scores for distance, near, and total were 3, 1, and 4, respectively. A broad representation of the total scores was significantly linked to the age of onset and the amount of exotropia (r² = 0.194, p = 0.003 and r² = 0.159, p < 0.001).

We found that our newly developed scoring system is a reliable and valid tool for assessing the severity of intermittent exotropia. This new measure can be implemented easily and efficiently across diverse clinical settings.