Pigment loss and pseudo-albinism in Birdshot chorioretinitis.

Objectives

To describe a rare phenotype of birdshot chorioretinitis (BSCR) characterised by diffuse retinal depigmentation and to evaluate its relationship with disease chronicity and visual outcomes.

Methods

This observational study included patients from the CO-BIRD cohort with ultra-widefield fundus imaging. Retinal depigmentation was graded using the albinism scale by Kruijt et al. (grades 0-3). Eyes with a grade ≥ 2 in at least one image were included. Disease activity and severity were assessed using best-corrected visual acuity (BCVA), vision-related quality of life (VFQ-25), visual field testing and multimodal imaging.

Results

Among 1016 eyes (508 patients), 52 eyes (26 patients, 5.1%) had depigmentation grade ≥ 2; 22 eyes (2.2%) reached grade 3. Fifteen years after symptom onset, BCVA worse than 0.7 logMAR occurred in 42.1% of grade 3 versus 5.0% of grade 2 eyes (p = 0.014). VFQ-25 scores were similarly reduced in both groups. Grade 3 was associated with a lower risk of optic disc oedema (HR = 0.38; p = 0.028) and a non-significant reduction in macular oedema risk. Choroidal neovascularisation occurred only in grade 3 (40.9%). Grade 3 was linked to worse BCVA (p = 0.012), higher pattern standard deviation (p = 0.011), and a history of active disease. Compared with previously published CO-BIRD data, grade 3 showed faster BCVA decline (p = 0.044) and greater cumulative loss (p = 0.001).

Conclusion

Diffuse retinal depigmentation resembling albinism is an uncommon but severe expression of BSCR, indicative of chronic disease and associated with poorer visual outcomes.