The incidence, presenting clinical findings and treatment patterns of Birdshot Retinochoroiditis in a high-prevalence region: findings from Northern Ireland, England and Wales.

Background: Birdshot Retinochoroiditis (BSRC) is a rare, chronic posterior uveitis that is strongly associated with HLA-A*29.2 positivity. To date, no robust incidence studies of BSRC have been undertaken. We present the first epidemiological study of BSRC in a high-prevalence region.

Methods: In collaboration with the British Ophthalmological Surveillance Unit, all new cases of BSRC between May 2017 and June 2019 were prospectively collected. Presenting demographics, symptoms, signs and treatment modalities were collected. A follow-up questionnaire twelve months later was also sent.

Results: Thirty-seven confirmed cases meeting the reporting criteria were identified. Twenty-three cases had both baseline and follow-up data. The total population incidence of BSRC was 0.035 cases per 100,000 person-years [95% CI 0.025-0.048 cases per 100 000 people]. 97.3% were HLA-A*29 positive. The median age was 46 years, with females making up 78% of patients. There were no significant differences in the latitudinal incidence of BSRC. At presentation, floaters were the most common symptom. Optic disc swelling was the most common sign. Mean presenting visual acuity was independent of symptom duration. Combined systemic corticosteroids and immunomodulatory therapy were the most common treatments at baseline and follow-up. Intravitreal steroids were equally popular at follow-up.

Conclusions: This study provides the first nationwide estimate of the incidence of BSRC in a high-prevalence region. Cases were more common in females, with a broad range of presentation ages. No significant latitudinal effect of incidence was identified. Systemic therapy with steroids and IMT remain the most common treatments.