May 01, 2014
Childhood strabismus has been well-characterized by epidemiologic studies worldwide, but published reports of strabismus among adults are uncommon — and almost exclusively institution-based series of patients referred solely for surgical intervention.
"Existing reports provide very little data on the true incidence and demographics of strabismus in adults," says Brian G. Mohney, M.D., with the Department of Ophthalmology at Mayo Clinic in Rochester, Minn. Dr. Mohney led a team that used Rochester Epidemiology Project data to study the incidence of new-onset strabismus and its types in a geographically defined adult population diagnosed over a 20-year period. Results were published in Ophthalmology online in December 2013.
Ocular misalignment among adults differs significantly from pediatric strabismus, a well-characterized disorder. "Nearly 90 percent of children with strabismus are diagnosed by their sixth year of life, two-thirds display an esotropic deviation, many have amblyopia, and diplopia is rare," says Dr. Mohney. "In contrast, new-onset ocular misalignment among adults is significantly associated with increasing age. Esotropia, exotropia and hypertropia occur with similar frequency. Adult-onset strabismus is not associated with amblyopia or decreased vision. Instead, it is more likely to be the result of a paralytic disorder or small but troubling deviations with persistent double vision."
Adults develop strabismus secondary to a variety of conditions, including trauma, surgical procedures, thyroid dysfunction, cranial nerve palsies and other neurological diseases.
1 in 25 adults may develop strabismus
The research team's retrospective study identified 753 cases of new-onset strabismus among residents 19 years or older in Olmsted County, Minn., diagnosed from Jan. 1, 1985, through Dec. 31, 2004, an annual age- and sex-adjusted incidence rate of 54 cases per 100,000 individuals. The four most common types of new-onset strabismus were:
- Paralytic (44 percent of cases)
- Convergence insufficiency (16 percent)
- Small-angle hypertropia (13 percent)
- Divergence insufficiency (11 percent)
"For paralytic strabismus, the association between age and the incidence may be related to the age-dependent increase of diseases such as hypertension and diabetes," says Dr. Mohney. "Paralytic strabismus was also significantly more common in males, due primarily to the higher incidence of fourth nerve palsy. Head trauma is often reported as the most common identifiable cause of fourth nerve palsy, and the reported incidence of closed-head injury is higher in males than females."
The incidence of adult-onset strabismus overall and its four most common forms significantly increased with age, with peak incidence in the eighth decade of life. "There were no significant gender differences or changes in the incidence of adult-onset strabismus over the 20-year study period," says Dr. Mohney. "This trend of increasing incidence with age was seen in each of the major forms of adult-onset strabismus. Based on the age- and gender-adjusted annual incidence rate of 54 cases per 100,000 people, about 1 in 25 adults would be expected to develop strabismus during their lifetime, with a significant higher risk with increasing age."
Extrapolation of the results is limited by the lack of access to records from optometrists practicing in Olmsted County and the racial and ethnic composition of the county, which was 90 percent white during the years of the study. "Recognizing these weaknesses and assuming a population of 209,129,000 individuals 19 years or older, we estimate that approximately 113,000 new cases of adult-onset strabismus will develop each year in the United States. Roughly 50,000 adults will have some form of paralytic strabismus," says Dr. Mohney.
For more information
Martinez-Thompson JM, et al. Incidence, types, and lifetime risk of adult-onset strabismus. Ophthalmology. In press.