Ophthalmological and orthoptic findings in Down Syndrome: Is genotype-phenotype correlation possible?

Down syndrome (DS) is the most common chromosomal disorder. Ophthalmological symptoms are seen in up to 85% of the patients and not only cause decreased vision but also negatively affect mental development. It is known that approximately 95% of the disorder are free trisomy 21, 5% are translocation DS and 2% are mosaic DS. This study aims to conduct a preliminary study for genotype-phenotype correlation by comparing ophthalmological findings that may accompany different genotypes in DS. The study included 62 eyes of 31 DS patients between the ages of 6 and 37 who applied to the ophthalmology or pediatric genetics clinics for routine examination. All patients were evaluated in terms of visual acuity, refraction, accommodation, strabismus, biometric characteristics, and anterior and posterior segment findings. Keratometry and pachymetry indices, corneal aberrations, angle kappa, iridocorneal angle, keratoconus summary indices for front and back surfaces, and elevation indices were obtained using the Sirius Topographer. Biometric measurements were obtained using IOL Master 700. Visual acuity was lower (p=0.004) whereas accommodation lags were higher (p=0.013) in free trisomy 21 patients. Lens opacities and fundus anomalies were more common in the free trisomy 21 (p<0.001). The angle kappa was large in free trisomy 21 whereas it was smallest in the translocation DS (p=0.014). K2 and corneal apex curvature were highest in free trisomy 21 (p=0.05 and p=0.006, respectively). Ophthalmological findings were found to be more frequent, visual acuity was lower, accommodation response was reduced, lenticular opacities and fundus abnormalities were more frequent, the central cornea was steeper and the angle kappa was larger in free trisomy 21. These findings will guide the development of opthalmological diagnosis and follow-up algorithms for patients with DS.