Ocular Immunology

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Ocular Immune System - Eye's Tiny Defenders

  • Immune Privilege: Eye's unique defense, limiting inflammation to protect vision. Key sites: anterior chamber, vitreous cavity, subretinal space.
  • Cellular Army:
    • Antigen-Presenting Cells (APCs): Langerhans cells (cornea, conjunctiva), macrophages.
    • Lymphocytes: T-cells & B-cells.
    • Mast cells: Key in allergic reactions.
  • Soluble Weapons:
    • Tears: Contain Secretory IgA (sIgA) - first line of defense, lysozyme.
    • Complement system, cytokines.
  • Specialized Lymphoid Tissues:
    • Conjunctiva-Associated Lymphoid Tissue (CALT).
    • Lacrimal Gland Associated Lymphoid Tissue (LGALT). Ocular Immune System Diagram

⭐ Anterior Chamber Associated Immune Deviation (ACAID) is a vital mechanism of ocular immune privilege, inducing systemic tolerance to intraocular antigens via regulatory T-cells.

Immune Privilege - Eye's VIP Pass

The eye uniquely tolerates antigens without damaging inflammation, vital for vision. This "VIP pass" is a complex protective strategy.

  • Key Mechanisms:
    • Barriers: Blood-ocular barriers (blood-aqueous & blood-retinal).
    • Alymphatic: Cornea, lens, vitreous lack lymphatic drainage.
    • Soluble Factors: Immunosuppressive TGF-β, α-MSH, FasL create an anti-inflammatory milieu.
    • ACAID: Anterior Chamber Associated Immune Deviation; antigens in AC induce systemic tolerance via regulatory T cells.

Ocular Immune Privilege Mechanisms

⭐ ACAID is a major reason for the high success (>90%) of initial corneal transplants, even without HLA matching.

Ocular Hypersensitivity - Allergic Eye Alarms

Ocular damage from immune overreaction. Classified by 📌 Gell & Coombs:

TypeName (ACID)MechanismOcular Examples
IAllergic (A)IgE-mediated, mast cell degranulation, histamine releaseAllergic conjunctivitis, VKC, AKC
IICytotoxic (C)Antibody (IgG/IgM) against cell surface antigens, complement activation, cell lysisOcular Cicatricial Pemphigoid, Mooren's ulcer
IIIImmune Cmplx (I)Deposition of antigen-antibody (Ag-Ab) immune complexes, complement activation, inflammationScleritis, some Uveitis, SJS
IVDelayed (D)Delayed T-cell mediated (Th1, CTLs), cytokine release, macrophage activationContact dermatitis, Phlyctenules, Graft rejection

Key Immunopathologies & Tx - Rogue Cells & Remedies

  • Uveitis: Uveal tract inflammation.
    • Types: Anterior, Intermediate, Posterior, Panuveitis.
    • Etiology: Infections, autoimmune (HLA-B27), trauma.
    • Tx: Corticosteroids, mydriatics, immunomodulators (Methotrexate).
  • Sympathetic Ophthalmia: Bilateral granulomatous panuveitis post-trauma/surgery to one eye.
    • Autoimmune to uveal antigens.
    • Tx: Aggressive immunosuppression; enucleation of injured eye within 2 weeks may prevent.
  • Ocular Cicatricial Pemphigoid (OCP): Autoimmune conjunctivitis causing scarring.
    • Type II HSR. Leads to symblepharon, blindness.
    • Tx: Systemic immunosuppressants (Dapsone, Cyclophosphamide).
  • Mooren's Ulcer: Idiopathic peripheral ulcerative keratitis (PUK).
    • Painful, progressive. Autoimmune.
    • Tx: Steroids, immunosuppressants.

Dalen-Fuchs nodules histopathology

⭐ Sympathetic ophthalmia can occur weeks to decades after initial injury; early enucleation of a non-salvageable traumatized eye is key prevention if vision is lost in that eye within 14 days post-injury to prevent sensitization to self-antigens and subsequent attack on the fellow eye (sympathizing eye).

High‑Yield Points - ⚡ Biggest Takeaways

  • Anterior Chamber Associated Immune Deviation (ACAID) is a key mechanism for ocular immune privilege.
  • Sympathetic Ophthalmia: bilateral granulomatous uveitis post-trauma; T-cell mediated against retinal antigens.
  • Type I hypersensitivity (IgE-mediated) is common in allergic conjunctivitis.
  • Type IV hypersensitivity (cell-mediated) is involved in phlyctenular keratoconjunctivitis and contact dermatitis.
  • Corneal graft rejection involves both cellular (T-lymphocytes) and humoral immune responses.
  • Uveitis can be associated with systemic autoimmune diseases like Ankylosing Spondylitis (HLA-B27).
  • Toll-like receptors (TLRs) on ocular surface cells recognize PAMPs, initiating innate immune responses.

Practice Questions: Ocular Immunology

Test your understanding with these related questions

Which of the following findings is typically NOT seen in a patient with allergic conjunctivitis?

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Flashcards: Ocular Immunology

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_____ sensitivity of the peripheral retina is one of the natural mechanisms to decrease aberration of the eye

TAP TO REVEAL ANSWER

_____ sensitivity of the peripheral retina is one of the natural mechanisms to decrease aberration of the eye

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