Usher syndrome-related visual impairment in Finland: A 35-year nationwide register-based study (1985-2019)

To investigate visual impairment (VI) associated with Usher syndrome (USH), a syndromic form of retinitis pigmentosa.

This register-based study used data from the Register of the Finnish Federation for Visual Impairment for persons registered with USH-related VI from 1985 to 2019. Temporal trends in incidence, prevalence, recorded age at onset of VI, severity of registered VI, and sex distribution were analysed.

The mean annual incidence of USH-related VI remained relatively stable across decades (p > 0.05), ranging from 0.19/100000 in 1985-1989 to 0.09/100000 in 2010-2019. In contrast, prevalence increased significantly over time (p < 0.001), from 0.70/100000 in 1985-1989 to 2.84/100000 in 2010-2019. The mean recorded age at onset of VI remained relatively stable. A significant shift in severity distribution was observed (p = 0.041), with fewer registrations classified as Near-Total Blindness and Total Blindness. In the 2010s, the severity distribution of VI differed between women and men.

As the first nationwide, long-term register-based study of USH-related VI, this 35-year analysis demonstrates stable incidence alongside increasing prevalence, with an observed redistribution of registered VI severity away from Near-Total Blindness and Total Blindness. These findings reflect both the expected natural disease course and broader system-level influences on registration patterns, underscoring the value of long-term register data for monitoring rare disease epidemiology when interpreted in light of established clinical characteristics of USH, VI classification criteria, and the healthcare system context. Together, they support the need to refine approaches to VI classification, rehabilitation and public health planning for people with USH.