Hypersensitivity Reaction in the Eye

Question 1

describe what sympathetic ophthalmia is

Answer 1

rare, bilateral, granulomatous uveitis due to trauma(more common) or surgery to one eye
injured eye is called ‘exciting eye’, fellow eye called ‘sympathising eye’

Question 2

what is the mechanism behind sympathetic ophthalmia

Answer 2

autoimmune reaction of ocular antigens

Question 3

what cells are involved in the pathophysiology of sympathetic ophthalmia

Answer 3

primary mediators are CD4+ helper T and CD8+ killer T cells

Question 4

what is the definition of a hypersensitivity reaction

Answer 4

immune response that results in bystander damage to self

Question 5

what are type I and II hypersensitivity reactions in Gel and Coomb’s classification

Answer 5

Type I = Immediate hypersensitivity(allergy)

Type II = Direct cell killing

Question 6

what are type III and IV hypersensitivity reactions in Gel and Coomb’s classification

Answer 6

Type III = Immune complex mediated

Type IV = Delayed type hypersensitivity

Question 7

give an examples of a type I hypersensitivity reaction of the eye

Answer 7

acute allergic conjunctivitis

Question 8

describe what happens when an allergen is encountered for first time in a type I hypersensitivity reaction

Answer 8

B cells produce antigen-specific IgE antibodies and allergen is cleared
residual IgE bind to circulating mast cells
no great consequence

Question 9

how does re-encounter with the allergen cause type I hypersensitivity reaction

Answer 9

allergen binds to IgE coated mast cells disrupting cell membrane, release of vasoactive mediators, cytokines and leukotrines

Question 10

in type II hypersensitivity what cells are responsible for direct cell killing

Answer 10

macrophages/NK cells or Complement system(membrane attack complex)

Question 11

give an example of a type II hypersensitivity reaction of the eye

Answer 11

ocular cicatricial pemphigoid, type of autoimmune conjunctivitis

Question 12

give an example of a type III hypersensitivity reaction of the eye

Answer 12

autoimmune corneal melting, outer layer melts and inner bulges forward with possible perforation

Question 13

what are the different aspects of the type IV hypersensitivity mechanism

Answer 13

T helper cells, clonal expression, exaggerated immune response

Question 14

give an example of a type IV hypersensitivity reaction of the eye

Answer 14

corneal graft rejection