Squint, aka strabismus, is to be evaluated as per the following (ICAO Manual on Medical Assessment refers):-
"Screening: The applicant who is asymptomatic and has no past history of strabismus treatment with patching, orthoptics or surgery should be evaluated with regard to visual acuity, refraction, ocular motility and general health of the eyes. Ocular alignment should be tested with cover testing using the appropriate spectacle correction or contact lens correction. Sensory testing with the Worth four-dot test, measurement of stereopsis and measurement of fusional amplitudes are useful in evaluation of the binocular status.
Assessment: Applicants who do not normally pass the screening tests mentioned ought to be examined by an eye specialist. Based on a full sensory and motor evaluation of the applicant, the specialist may be able to estimate the risk of diplopia or shift in location. Symptoms of diplopia or location shift or a high risk of these would disqualify the applicant for class 1 and 2 certificates. Moderate risk of these symptoms may be acceptable for class 2 certificate. Minor risk of these symptoms may be acceptable for class 1 certification."
Hope this helps, or you may PM in case of any clarifications.