Early Screening, Treatment of Vision Problems Important for PWS Patients
Vision problems such as lazy eye, farsightedness, and strabismus — when the eyes don’t line up in the same direction — are more common in people with Prader-Willi syndrome (PWS) than among their healthy peers, a study shows.
These findings, along with data showing that vision problems may negatively affect physical activity and learning in a patient population that already faces impairments in such areas, highlight the importance of early screening and treatment of vision problems in children with PWS, the researchers noted.
Particularly, strabismus was mostly diagnosed before age 5, and the majority of patients also underwent corrective surgery before that age.
The study, “Incidence of strabismus, strabismus surgeries, and other vision conditions in Prader-Willi syndrome: data from the Global Prader-Willi Syndrome Registry,” was published in the journal BMC Ophthalmology.
PWS is caused by the loss of genes (or of their activity) that normally reside in a particular region of chromosome 15, called the PWS locus. The disorder often is caused by the loss of or defects in paternal genes; this PWS locus typically is “silenced” in the chromosome inherited from the mother.
People with the disorder, who usually are diagnosed in childhood, have low muscle tone, insatiable hunger, developmental delays and learning difficulties, temper outbursts, and difficulties adapting to changes.
While a variety of eye and vision problems have been reported in PWS patients, few studies have assessed their frequency, and none has provided information regarding corrective vision surgeries.
To address this knowledge gap, the Foundation for Prader-Willi Research (FPWR), in collaboration with other U.S. researchers, retrospectively analyzed vision-related data from 908 PWS patients participating in the Global PWS Registry.
The registry is a comprehensive database of people with PWS with yearly surveys about their experiences. Vision data was based on the Vision Survey, which was completed by patients’ caregivers between May 2015 and March 2020.
At the time of the survey’s completion, the patients had a mean age of 14.5 (range of 0–62 years). About half were female, 81.9% lived in the U.S., and 93% had seen an ophthalmologist at some point in their life.
The results showed that the most common vision problems included nearsightedness (41%) and strabismus, or improper eye alignment (40%). Farsightedness was reported in 25% of patients, astigmatism in 25%, and lazy eye in 16%.
Astigmatism comprises imperfections in the eye curvature that cause blurred distance and near vision, while lazy eye (amblyopia) is a condition in which vision does not develop well in one of the eyes.
Most of these vision problems were far more common among PWS patients than reported in the general pediatric population. For example, the rates of strabismus were 40% versus 2.1–3.6%, while those of farsightedness were 25% versus 1–8.4%, and lazy eye were 16% vs. 1.5–2.6%.
“There are several hypotheses for the high rates of strabismus and other vision problems in PWS, including as a consequence of [low muscle tone], or alterations in typical facial morphology” or, broadly, facial structures, the researchers wrote.
There were no significant associations between most eye/vision problems and genetic subtypes. Nearsightedness and astigmatism were the exceptions, with a significantly higher frequency among patients with a missing PWS locus in their paternal chromosome 15 relative to those who inherited two chromosomes 15 from their mother.
The frequency of vision issues was not significantly different comparing participants who used growth treatment with those who did not.
When focusing on patients with strabismus, the team found that the majority (91%) were diagnosed before age 5, and 42% underwent corrective surgery, most (86%) when they were younger than 5. Also, 10.1% of PWS patients had more than one strabismus surgery.
Notably, the rate of corrective strabismus surgery in these PWS patients was much higher than that reported for the general population, “where only 5 % of people with a strabismus diagnosis received strabismus surgery,” the team wrote.
Given that lazy eye is typically considered an avoidable complication if strabismus is diagnosed and corrected early, these results raise questions “about the utilization and efficacy of [eye] patching in this population, and whether PWS alone predisposes or increases the risk of [lazy eye],” the researchers wrote.
The team also noted that vision problems can exacerbate the physical and learning challenges that people with PWS already face due to obesity and cognitive and developmental delays.
These findings highlight that “strabismus in PWS starts at an early age” and that PWS patients “should be screened early and regularly for vision problems” to help their families and practitioners to determine an effective treatment plan, the team concluded.