ABSTRACT

Conclusion:

In DS patients, the prevalence rates of refractive errors, amblyopia, and visual impairment are higher than those in non-DS individuals, and emmetropization appears to be either defective or slow. Cylinder error is stable in this age range, but the rotation of astigmatism axis is different from normal samples.

Results:

In the DS and control groups, respectively, mean age was 17.2±4.8 and 17.2±4.4 years (p=0.993) and 53.0% and 49.5% were male (p=0.473). In the DS and control groups, respectively, mean spherical equivalent (SE) was -5.13±4.47 and -4.15±3.04 diopters (D) in myopics (p=0.050) and 2.47±1.64 and 2.36±2.04 D in hyperopics (p=0.482), mean cylinder error was -2.17±1.39 and -2.05±1.57 D (p=0.451), mean J0 was -0.03±0.89 and 0.12±0.76 D (p=0.086), and mean J45 was 0.11±1.02 and -0.13±1.03 D (p=0.024). The prevalence of oblique astigmatism was higher in the DS group (20.4% vs. 6.1%) while against-the-rule astigmatism was more prevalent in the control group (84.0% vs. 71.6%) (p<0.001). The prevalence of anisometropia was not significantly different between the groups (19.4% vs. 13.8%). Visual impairment was detected in 11.7% of the DS and 0.5% of the control group (p<0.001). The prevalence of amblyopia was 36.3% and 3.8% in the DS and control groups, respectively (p<0.001). Based on the multiple model, only absolute SE inversely correlated with age and differed between males and females (all p<0.05).

Materials and Methods:

Cycloplegic refraction was tested in 213 DS patients and 184 normal age- and gender-matched controls using autorefraction followed by retinoscopy. Data from the worse eye of each case were used in the analyses.

Objectives:

To determine the prevalence of refractive errors and visual impairment in Down syndrome (DS) patients compared to normal controls.

Introduction

Refractive errors are one of the main items and the fifth priority of the 2020 Vision: Right to Sight Initiative.¹ In 2012, a systematic review of surveys in 39 countries showed that uncorrected refractive errors were the leading cause of visual impairment (43%).² A systematic review in 2018 reported the pooled prevalence of myopia, hyperopia, and astigmatism in children worldwide to be 11.7%, 4.6%, and 14.9% respectively, which are considerably high prevalence rates.³ Studies have shown a significant correlation between refractive errors, socioeconomic status, and lifestyle.⁴ In patients with Down syndrome (DS), quality of life is reduced due to medical conditions,⁵ and declines further as they age.⁶ Therefore, the identification and correction of refractive errors in this population deserves even higher priority than in normal populations.

To date, several studies have been done on the prevalence and degree of refractive errors in patients with DS.^7,8,9,10,11 These studies were mostly carried out in age groups 10 years of age and younger, and one study reported non-cycloplegic refraction in a group with a mean age of 15 years (range, 4 to 60 years).^8,9,10,11

The goal of this study was to determine the prevalence and distribution of refractive errors, type of astigmatism, visual impairment, and amblyopia in order to provide a comprehensive report on the refractive status in this particular population. We used cyclopentolate, as evidence showed that it is the gold standard for epidemiological studies of refraction and increases the reliability of findings.¹² The distribution of refraction in DS patients was compared to a group of age- and gender-matched normal controls.

Materials and Methods

Results

After applying the inclusion criteria for this report (having cycloplegic refraction results, no ectasia, and no history of corneal surgery), of the 234 patients with DS and 200 normal controls enrolled into the study, data from 213 DS cases and 184 controls were used in the analyses.

In the DS and control groups, respectively, the mean age was 17.2±4.8 and 17.2±4.4 years (p=0.993), and 53.0% and 49.5% were male (p=0.473). In the DS and control groups, mean UDVA was 0.36±0.34 and 0.86±0.62 logMAR (p<0.001) and mean CDVA was 0.20±0.11 and 0.02±0.06 logMAR (p<0.001), respectively.

Discussion

In this large comparative study, we showed the distribution and prevalence of myopia, hyperopia, astigmatism, amblyopia, and visual impairment in a sample of DS patients aged 10-30 years (when the incidence of refractive errors is highest) and compared the results to a group of age- and gender-matched controls. The strength of this study was selecting DS patients from different sources and creating a sample with diverse cases. Although several studies have been done on refractive errors in DS patients, they have often been studied in the 10-year-old age group^7,9,10,11 or a broad age range (3 months to 60 years) without cycloplegia.⁸ As emmetropization has been suggested to be incomplete in DS patients even up to 17 years of age¹⁶ and the prevalence of myopia tends to increase in non-DS individuals after the age of 9 years¹⁷ and continue up to 30 years of age¹⁸, in this study we considered the age range of 10 to 30 years.

Conclusion

Overall, in our sample of 10- to 30-year-old DS patients, the prevalence of refractive errors, astigmatism, visual impairment, and amblyopia was higher than that of their age- and gender-matched controls, and emmetropization appeared to be either defective or slow. The prevalence of refractive and visual complications was similar between males and females. Cylinder error appears to be stable in this age range in DS patients, but the rotation of its axis was different from the controls. These findings are useful for refractive errors correction services for DS patients.