Ophthalmology - Cornea Flashcards
What are the features of the cornea that cause it to stay clear?
- avascular
- non-myelinated nerves
- dehydrated
- ordered cell arrangement
Describe how epithelial ulcers heal
- hemidesmosomes degrade and disappear
- rapid cell division at the limbus
- epithelium slides to cover the ulcer
- epithelium becomes fixed to the stroma as hemidesmosomes form again
- takes about 7 days
Describe how stromal ulcers heal
- stromal cells transform into contractile cells
- these cells fill the defect
- epithelialization occurs over the new stroma
- stromal contracture causes disorganization of collagen, resulting in a scar
- takes days to weeks
What is a facet?
- a non-staining depression in the cornea
- forms when epithelialization occurs before the stroma becomes leveled
Describe how descemetoceles heal
- vascular ingrowth needed first to provide scaffold for cell growth
- eventually a scar forms
- takes a long time
What is indicated by blue corneal opacity?
edema
What are the causes of corneal edema?
- epithelial barrier disruption (allows tear film entry into stroma)
- endothelial barrier/pump disruption (allows aqueous humor entry)
What is indicated by red corneal opacity?
corneal neovascularization
What are the causes of corneal neovascularization?
- superficial vessels (granulation tissue or ghost vessels)
- deep vessels (ciliary flush)
When does superficial neovascularization occur?
occurs with superficial stimuli
- KCS, eyelid/hair abnormalities, superficial corneal ulcers
Describe the appearance of superficial neovascularization
- branching tree-like structure
- can be seen crossing the limbus
When does deep neovascularization occur?
occurs with deep stimuli
- uveitis, glaucoma, deep corneal inflammation/ulceration
Describe the appearance of deep neovascularization
- “hedge row”
- “crown of thorns”
- vessels cannot be seen crossing the limbus
What is indicated by white corneal opacity with a yellow or green hue?
white blood cell infiltration
What is indicated by white corneal opacity with gray or wispy features?
fibrosis
What is indicated by crystalline or chalky white corneal opacity?
mineral or lipid
Describe the features of corneal WBC infiltration
- often very painful
- associated with severe corneal disease or uveitis
- signals corneal infection
Describe the features of corneal fibrosis
- scar from previous keratitis
- dull white
- non-painful
- involves contracture of lamellar stromal collagen
What are the possible causes of mineral or lipid deposits in the cornea?
- corneal dystrophy (lipid)
- corneal degeneration (lipid or mineral)
What are the causes of brown corneal opacity?
- epithelial pigment (canine pigmentary keratitis)
- endothelial pigment (deflated uveal cysts, anterior synechia)
What is the cause of black corneal opacity?
feline corneal sequestrum
- often due to FHV-1
What is indicated by tan or greasy punctate?
keratic precipitates
- cellular and fibrinous adhesions to the endothelial surface
- due to uveitis
What is the limbus?
junction between cornea and sclera
What is ciliar flush?
360 degrees of deep corneal neovascularization
What are the brachycephalic risk factors for ulcerative keratitis?
- ocular prominence
- decreased corneal sensitivity
- adnexal abnormalities
- tear film abnormalities
What are the features of an uncomplicated/simple corneal ulcer?
- a superficial corneal ulcer that heals in 7 days or less
- crisp, sharp edges of ulcer margin
Describe the features of an indolent ulcer
- will not heal due to lack of epithelial adherence to stroma
- irregular, loose flaps of epithelium surrounding ulcer edge
- staining pattern: “halo” under/around ulcer margin
How is an indolent ulcer treated?
- debride epithelium
- if not healed: anterior stromal puncture or diamond burr debridement
- topical antibiotics and analgesics
What is the most common cause of melting ulcers?
Pseudomonas aeruginosa
What are the feature of a deep stromal corneal ulcer?
- inappropriate level of reflex uveitis
- severe corneal edema
- white blood cell infiltration
- deep corneal vessels and episcleral injection
- visible stromal loss or disruption
- malacia
What are the features of corneal perforation?
- positive Seidel test
- wrinkled corneal appearance
- shallow anterior chamber
- iris prolapse
- fibrin plug
- hyphema
When is surgery recommended for stromal ulcers?
> 50% stromal loss or severe infection
descemetocele or perforation
What surgery is done to correct stromal ulcers?
- conjunctival pedicle flap
- 360 degree conjunctival graft
What are the medical treatments for stromal ulcers?
- topical antibiotics (cephalosporins, fluoroquinolones)
- anti-collagenase therapy for melting ulcers (EDTA)
- topical atropine and systemic NSAID/tramadol
When are parenteral antibiotics indicated for stromal ulcers?
- the ulcer has become vascularized
- the cornea is close to perforation or has perforated
- iatrogenic vascularization
What is reflex uveitis?
the trigeminal nerve and certain cytokines cause direct stimulation of the ciliary body, inducing spasm, pain, and disruption of the blood ocular barrier
What is a descemetocele?
a corneal ulcer that has reached the depth of descemets membrane
What is keratomalacia?
softening of the cornea due to collagenolysis form infection and the ocular inflammatory response
What is collagenolysis?
enzymatic destruction of the corneal stroma that signals infection
