Visual Acuity

Dr. Deborah Hatton, an investigator on the CFXP, also does research on visually impaired children. Therefore, she was interested in the reported high incidence of strabismus and other visual impairments in the population of persons with fragile X syndrome. Her clinical experience and research confirmed the impact of visual impairment on development in early childhood, and provided the impetus for a study on the vision of young children with FXS. Funding from the FPG Small Grant Competition and collaboration with Ave Lachiewicz, Director of the Fragile X Clinic at Duke University Medical Center, and Ed Buckley, Director of Pediatric Opthamology at Duke, made it possible to conduct the largest prospective study of the ocular status of young males to date.

Research Goals

Assess the visual status of boys with fragile X syndrome
Identify the percentage of boys with FXS who have visual abnormalities
Identify the types of visual problems and abnormalities that are present
Describe the visual acuity of boys with FXS

Methods

Participants

48 participants were recruited from the CFXP Longitudinal study and the Duke University Medical Center Fragile X Clinic.

Data Collection

Visual acuity was assessed by one of three methods:
- 1) standard Snellen charts;
- 2) picture cards (Light House or Allen); and
- 3) the Teller Visual Acuity Cards, a variation of forced-choice preferential looking assessments, often used with very young children or children with multiple disabilities. Acuity was assessed either during the eye clinic visit or during a home or school visit in conjunction with an assessment for the longitudinal study.
Eye evaluations by Dr. Buckley were performed at the Duke Eye Center or at one of the three satellite clinics held for distant families.

Results

Out of the 48 subjects that were examined, numeric visual acuities were obtained on 42, a gross measure of acuity on 5, and no measure on 1.Due to their short attention spans and some "autistic-like" behaviors, boys with FXS were challenging to examine. Results indicate that:
1. the prevalence of significant visual abnormalities is not as high as has been reported in previous studies. Ocular abnormalities occurred in 25% of the sample and only 8% had ever been diagnosed with strabismus;
2. four of the participants (8%) had strabismus (misalignment of the eyes), a prevalence that is still higher than the general population (0.5 - 1%), but much lower than the 30% to 40% reported in earlier studies. Because the prevalence is at least ten times higher than that of the normal population, it is safe to say that the FXS population is at risk for strabismus. Refractive errors (astigmatism, near- or far-sightedness), were seen in the group of participants, but they were relatively mild and probably not clinically significant. A total of 8 participants (17%) had refractive errors that were clinically significant; and
3. only 1 participant had visual acuity results that were clinically significant and thought to be the result of nystagmus (involuntary rapid eye movement).
Visual problems are not as prevalent in the population of young boys with fragile X syndrome as earlier studies indicate. However, our findings suggest that strabismus and refractive errors are more common in this population than in the general population, and optical examinations should include evaluation for these problems.