Nystagmus in Down Syndrome - a Retrospective Notes Review.

Introduction: Nystagmus has been reported in up to 30% of people with Down Syndrome (DS), and yet is still not well understood. Our study aims to characterise the clinical features of patients with DS and nystagmus. Methods: A retrospective medical-records review was conducted of all patients with a diagnosis of DS and nystagmus seen at Moorfields Eye Hospital over a ten-year period. Results: Fifty-one subjects were identified, with complete data in 48. The mean age at presentation was 5.1 years (range 0-26 years). The mean binocular LogMAR visual acuity was 0.55(95%CI 0.53-0.57), mean refractive error was -1.8 Dioptre Sphere, DS (95% CI - 5.251.63) with -1.2 Dioptre Cylinder, DC (95% CI - 1.6-0.7). Ocular misalignment was found in 50% of patients. A diagnosis of Fusion Maldevelopment Nystagmus Syndrome (FMNS) was made in 6.3%, Infantile Nystagmus Syndrome (INS) in 8.4% and ABducting nystagmus/Inter-Nuclear Ophthalmoplegia (INO) in 2.1%. The descriptive term 'Manifest Horizontal Nystagmus'(MNH) was used in the majority, highlighting the difficulties in clinically differentiating the subtypes of nystagmus in DS. Eleven patients had associated cataract. Additional diagnoses unrelated to DS were made in 10.4%. Conclusions: The most frequent type of nystagmus in our cohort was 'presumed' INS. This study highlights the importance of differentiating between FMNS and INS (with a latent component), so that further investigations can be performed as appropriate. Almost 25% had associated cataract, and a further 10% other diagnoses un-associated to DS. Despite INS being known to be associated with DS, further investigations may be required in a small subset with true INS after careful clinical assessment and use of eye movement recordings (where available).