Studies have found that internal strabismus is associated with farsightedness, which is common in Western populations, while exotropia is associated with myopia, which is more prevalent in Asians. The March issue of the American Journal of Ophthalmology reported on a 20-year follow-up of 135 patients with intermittent exotropia by researchers at the Mayo Clinic and the Mayo Foundation. They found that a little more than 90 percent of those patients followed developed myopia after age 20. This one of the few follow-up studies on the incidence of myopia in children with intermittent exotropia demonstrated that the prevalence of myopia in this population was 7.4% at age 5, 46.5% at age 10, and 91.1% at age 20. This data was independent of the method of observation and surgical intervention and was significantly higher than any previously reported incidence in the total population. This suggests that intermittent exotropia is clearly associated with the development of myopia. Several other studies have demonstrated the prevalence of myopia in similar age groups of 3-5%, 24%, and 45%, respectively. The study recommends that children with intermittent exotropia should be followed closely by an ophthalmologist for two reasons: the presence of misalignment in their eyes and the near certainty that they will develop myopia as they begin to enter adolescence. According to Dr. Brian G. Moni of the Mayo Clinic Ophthalmology Department, “This finding provides further evidence of the relationship between refractive error and strabismus: internal strabismus is associated with hyperopia, which is very common in Western populations; and ectropia is associated with myopia, which is more prevalent in Asians. It is unclear whether these relationships are linked to genetics, environment, or both, and merit further investigation.” More interestingly, exotropia is more common in Asian populations, with a prevalence twice as high as that of internal strabismus.