Intermittent external strabismus (IXT) is the most common form of exotropia in children. Intermittent exotropia is a type of strabismus between exotropia and common exotropia. It is a strabismus that occurs intermittently when both eyes are unable to look straight at the same time and the visual axes are separated, initially when looking at a distance, and when the fused scattered amplitude exceeds the fused pooled amplitude when looking at a distance, it produces exotropia, and the occurrence of intermittent exotropia is often preceded by exotropia. Currently, there are both surgical and non-surgical conservative treatment methods. For surgical treatment, there is still controversy regarding the timing of surgery and the surgical approach. Non-surgical treatment can also control the progression of IXT and protect existing visual acuity. Conservative treatment may also delay or even eliminate surgery. Monocular or alternating masking is a common nonsurgical treatment that is thought to eliminate visual suppression and reduce the frequency and degree of separation (e.g., from constant exotropia to IXT or from IXT to exotropia). To determine the effectiveness of intermittent masking for IXT, an intentional multicenter randomized clinical trial was conducted by Jonathan et al. The study included 358 untreated (except refractive correction) pediatric patients aged 3-11 years with IXT with binocular near acuity better than 400 seconds of arc. iXT met the following conditions: (1) intermittent exotropia at distances where constant exotropia routinely occurs and IXT or exotropia at closer distances; (2) strabismus or occultation at least 15 prism degrees on the Near and Far Prismatic Neutralization Alternating Coverage Test (PACT) strabismus of at least 15 prism degrees (PD); and (3) looking at distance PACT of at least 10 PD. METHODS: Participants were randomly assigned to the observation group (untreated for 6 months) or masked for 3 hours per day for 5 months, with a one-month buffer period and no masking in the sixth month. The primary assessment indicator was the presence of worsening at 3 or 6 months, defined by the following criteria: (1) at least 10 PD of constant exotropia on the near- and far-seeing trigeminal neutral and alternating masking tests; and (2) a decrease in myopic acuity of at least 2 octaves from baseline levels. The results were confirmed by a single-blind tester and another tester. Those patients who were treated without meeting the deterioration criteria were specified as having worsened. RESULTS: 324 participants (91%) completed the 6-month primary outcome examination, with deterioration occurring in 10 of 165 participants (6.1%) in the observation group (3 of 10 started treatment without meeting the deterioration criteria) and 1 of 159 (0.6%) in the masked experimental group exhibiting deterioration. The investigators concluded that deterioration was rare in pediatric patients with IXT with or without masking treatment, and that the rate of deterioration was slightly lower in the masking group. In addition to suppressing deterioration, the investigators also followed the improvement in the degree of exotropia control and strabismus separation between the masked treatment group and the observation group in children with IXT, but the results showed no significant difference between the two groups. Taking into account the physical and mental health problems associated with covering a child’s single eye and the additional burden on family caregivers, both the masking and observation methods are reasonable for children with IXT aged 3-10 years. In conclusion, the study did not conclude that the masking treatment had significant advantages over observation, and the study was limited by the sample size and the degree of cooperation of the experimental participants, and the effect of masking treatment needs to be further studied in a more precise and large-scale manner.