Ocular Immunology and Inflammation
Core concepts
Understand the basic immune mechanisms: innate versus adaptive immunity, humoral versus cell-mediated responses, and the role of complement. Know the ocular immune privilege of the anterior chamber (ACAID) and the blood-ocular barrier. Recognise hypersensitivity types I–IV and their ocular examples: type I (allergic conjunctivitis), type II (pemphigoid), type III (Arthus, some uveitis), type IV (contact dermatitis, graft rejection).
Know the clinical approach to uveitis: anterior, intermediate, posterior, panuveitis; granulomatous versus non-granulomatous. Understand HLA associations (e.g., HLA-B27 with anterior uveitis, HLA-B51 with Behçet). Recognise that sympathetic ophthalmia is a T-cell mediated autoimmune response to uveal antigens after trauma.
Traps
- Confusing immune privilege with absence of immune response.
- Assuming all uveitis needs systemic steroids.
- Forgetting that HLA-B27 uveitis is typically unilateral and recurrent.
- Mixing up type II and type III hypersensitivity.
Rule of thumb
Granulomatous uveitis (mutton-fat keratic precipitates, iris nodules) suggests sarcoidosis, TB, or sympathetic ophthalmia; non-granulomatous suggests HLA-B27 or idiopathic.
Worked example
A patient with ankylosing spondylitis develops a painful red eye with cells and flare. Diagnose HLA-B27-associated anterior uveitis; treat with topical steroid and cycloplegic, and screen for systemic disease.