Keratoconus is an eye condition with distinctive corneal characteristics, including thinning and a conical shape of the cornea. Keratoconus was previously considered rare; however, in recent studies, a prevalence of 0.2% to 0.3% has been reported¹ and, in some studies, an even higher prevalence. An association of keratoconus with Down syndrome has been shown,^2,3 although the exact reason remains unknown. In some studies, investigators have reported frequencies of keratoconus in persons with Down syndrome of 0% to 71%^2-5; however, most have been limited by small sample sizes and biased patient selection. The aim of the present study was to estimate the prevalence of keratoconus among persons with Down syndrome in Norway.

In this cross-sectional study, data were obtained from the Norwegian Patient Registry, which gathers information from all publicly funded specialist care provided in Norway. All patients who received the International Classification of Diseases and Related Health Problems, Tenth Revision diagnosis codes Q90 for Down syndrome and H18.6 for keratoconus from January 1, 2010, to December 31, 2019, were included. The prevalence is presented as per 100 000 population, with 95% CIs, which were calculated using SPSS, version 26 (IBM Corp). The ethical committee and data protection officer of Oslo University Hospital determined waiver of further review, study approval, and informed patient consent because the data were anonymous and reported on an aggregated group level. The research adhered to the Declaration of Helsinki. This study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline.

Of the 238 patients with Down syndrome who had keratoconus, 122 (51.3%) were men, and 116 (48.7%) were women; the mean age was 37.1 years. A total of 4342 persons were registered as having Down syndrome in Norway during the study period. This corresponded to 0.08% of the population of Norway in the same period (mean [SD], 5 118 664 [161 758] inhabitants). Among the persons with Down syndrome, 238 (5.5%) had keratoconus, yielding an estimated prevalence of 5481 per 100 000 population (95% CI, 4834-6188 per 100 000 population).

圆锥角膜是一种眼病，具有独特的角膜特征，包括角膜变薄和圆锥形。圆锥角膜以前被认为是罕见的。但是，在最近的研究中，据报道患病率为0.2％至0.3％¹，在某些研究中，患病率甚至更高。已显示圆锥角膜与唐氏综合症的相关性[ ^{2,3] ，}但确切原因尚不清楚。在一些研究中，研究者报告唐氏综合症患者圆锥角膜的发生率为0％至71％^{2 -5}；然而，大多数都受到样本量小和患者选择偏倚的限制。本研究的目的是评估挪威唐氏综合症患者圆锥角膜的患病率。

在这项横断面研究中，数据来自挪威患者登记处，该登记处收集了挪威提供的所有公共资助的专科医疗服务中的信息。接受《国际疾病和相关健康问题分类》第十次修订的所有患者纳入了2010年1月1日至2019年12月31日唐氏综合症的诊断代码Q90和圆锥角膜的诊断代码H18.6。呈现的患病率是每10万人口中95％的CI，这些CI是使用SPSS 26版（IBM Corp）计算的。奥斯陆大学医院的伦理委员会和数据保护官决定放弃进一步的审查，研究批准和患者知情同意，因为这些数据是匿名的，并且是在汇总组级别上报告的。该研究遵守了《赫尔辛基宣言》。这项研究遵循了加强流行病学观察性研究报告（STROBE）的报告指南。

在238例唐氏综合征的圆锥角膜患者中，男性为122例（51.3％），女性为116例（48.7％）。平均年龄为37.1岁。在研究期间，挪威总共登记了4342人患有唐氏综合症。这相当于同期挪威的人口的0.08％（平均[SD]，5 118 664 [161 758]居民）。在唐氏综合症患者中，有238例（5.5％）患有圆锥角膜，估计患病率为每100000人口5481例（95％CI，每10万人口4834-6188例）。