introduction to pathology of the eye Flashcards
what is inflammation?
- the body’s response to potentially damaging stimuli
what are the causes of inflammation in the eye ?
- infection with pathogen
- hypersensitivity reactions ( inappropriate inflammatory response )
- autoimmunity
- trauma ( including iatrogenic)
- chemical/toxic
- radiation
what are the two types of inflammation ?
1- acute inflammation
. short duration ( minutes or days )
. usually resolves but sometimes progresses to chronic inflammation
2- chronic inflammation
. weeks or months
. may be secondary to acute
. can also develop without acute inflammation
what are the signs of acute inflammation?
- rubor - redness
- calor - warmth
- dolor - pain
- tumor - swelling
what are the major features of acute inflammation ?
1- vascular events
2- cellular events
what are vascular and cellular events triggered by ?
- triggered by chemical mediators also referred to inflammatory mediators such as ( histamine )which also perpetuate the inflammatory process
describe the vascular events of acute inflammation ?
. vasodilation
- blood vessels get bigger
. increased blood flow to a tissue which generates warmth as more blood is coming into the area
. blood vessels change their characteristics and become more leaky and gives rise to more swelling
. increased vascular permeability
. movement of inflammatory cells from blood vessels to site of injury
describe the cellular events of acute inflammation ?
- cellular events are cells that have a particular role in the inflammatory response and several of those cells are circulating in the blood
- a classic example would be neutrophils
- when you have a site of inflammation the neutrophils can leave the vascular system and migrate towards the site of inflammation
- they go through a process where they align with the wall and roll along and squeeze there way through the endothelial wall and then migrate to the tissue
- there are chemical mediators that are produced at the site of inflammation that are attracted to the phagocyte and work their way towards the chemical as a concentration gradient
- then process of phagocytosis
. extravasation of leukocytes into tissues ( exudate )
. margination
. rolling
. diapedesis
describe the process of phagocytosis ?
- phagocytes arrive at the site of inflammation by chemotaxis
- phagocytes attach to microorganisms, cell debris or foreign material via surface receptors
- material internalised and destroyed
- phagocytosis is enhanced by the antibodies and the complement system of proteins ( opsonization )
what is the inflammatory response controlled by ?
- controlled by inflammatory mediators
examples include - vasoactive amines e.g. histamine , serotonin
- plasma proteases e.g. complement, kinins
- arachidonic acid and metabolites ( eicosanoids )
- cytokines
what are the mast cell mediators ?
- mast cell mediators include pre-formed and newly formed mediators
- pre-formed mediators include : histamine , heparin and neutral protease
- newly found mediators include leukotrienes ( LTD4, LTC4), prostaglandin D2 and platelet activating factor
what are the outcomes of acute inflammation ?
- completer resolution
- scar formation
- progress to chronic inflammation
what is the ocular response to inflammation ?
- redness- due to the vascular events, so blood vessels that are normally fine , suddenly dilate and everything becomes red
redness can be diffused or localised
e.g. episcleritis or acute closed angle glaucoma
what is episcleritis ?
episclera - which is one of the layers of the surface of the eye becomes inflammed
what is acute closed angle glaucoma ?
- acute closed angle glaucoma - drainage angle for aqueous humour has become narrowed
what is another response to inflammation ?
- oedema
e. g conjunctival oedema
can be localised or diffused
what is another response to inflammation ?
- exudate
. increased vascular permeability
. rich in protein
. rich in inflammatory cells
e.g. uveitis - proteins leak into the aqueous humour , proteins are big molecules which scatter light
what is another response to inflammation ?
cellular infiltration
e. g. bacterial keratitis - which is a bacterial infection of the cornea - which is a bacterial infection of cornea - you can see a circular white patch - which is a collection of inflammatory cells where bacteria are growing in that lesion and cells migrate to that lesion to stop the damage caused by the bacteria
- marginal keratitis - which is peripheral infiltrate
- chalazion - where the meibomian glands within the eyelids become blocked and secretion starts to build up
- cell type would depend if it was acute ( neutrophils) or chronic ( lymphocytes, macrophages )
what is another response to inflammation ?
- discharge
- eye can become watery
- over production of mucous
- sign of infection
what is another response to inflammation ?
- conjunctival response
e. g. formation of conjunctival papillae and follicles - papillae common in allergic eye disease
- follicles characteristic of viral infection or toxic reactions
what are examples of inflammation of the posterior segment of the eye ?
- anterior ischaemic optic neuropathy
- optic disc isn’t receiving enough oxygen because blood vessels that supply oxygen to the disc have become blocked through an inflammatory response
- sarcoidosis - is an example of chronic inflammation
what is autoimmunity ?
- autoimmunity represents the immune attack of normal body tissues
- breakdown of self-tolerance
- characterised by immune cell infiltration and inflammation of the target tissues
- tend to be associated with particular HLA haplotypes
e. g. HLA B27 - ocular autoimmunity can occur in the presence or absence of systemic autoimmune disease
what are examples of ocular autoimmune diseases in the absence of systemic involvement ?
- moorens ulcer - cornea has become thinner and is at risk of breaking through - loss of corneal tissue
- sympathetic ophthalmia - in damaging an eye certain antigens are exposed to the immune system, you then have immune cells that are directed to target that particular pathogens , you also get immune attack of normal healthy eye
how are autoimmune diseases in the eye mediated ?
- autoreactive T-helper cells ( CD4 ) are often responsible for initiating the tissue damage via the production of cytokines
- autoreactive cytotoxic T cells ( CD8) can also cause tissue damage
- autoantibodies cause tissue damage via a type 2 mechanism ( antibody-dependent cell killing )
