Ophthalmology - Cornea

Question 1

What are the features of the cornea that cause it to stay clear?

Answer 1

• avascular
• non-myelinated nerves
• dehydrated
• ordered cell arrangement

Question 2

Describe how epithelial ulcers heal

Answer 2

• 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

Question 3

Describe how stromal ulcers heal

Answer 3

• 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

Question 4

What is a facet?

Answer 4

• a non-staining depression in the cornea

- forms when epithelialization occurs before the stroma becomes leveled

Question 5

Describe how descemetoceles heal

Answer 5

• vascular ingrowth needed first to provide scaffold for cell growth
• eventually a scar forms
• takes a long time

Question 6

What is indicated by blue corneal opacity?

Answer 6

edema

Question 7

What are the causes of corneal edema?

Answer 7

• epithelial barrier disruption (allows tear film entry into stroma)
• endothelial barrier/pump disruption (allows aqueous humor entry)

Question 8

What is indicated by red corneal opacity?

Answer 8

corneal neovascularization

Question 9

What are the causes of corneal neovascularization?

Answer 9

• superficial vessels (granulation tissue or ghost vessels)

- deep vessels (ciliary flush)

Question 10

When does superficial neovascularization occur?

Answer 10

occurs with superficial stimuli

- KCS, eyelid/hair abnormalities, superficial corneal ulcers

Question 11

Describe the appearance of superficial neovascularization

Answer 11

• branching tree-like structure

- can be seen crossing the limbus

Question 12

When does deep neovascularization occur?

Answer 12

occurs with deep stimuli

- uveitis, glaucoma, deep corneal inflammation/ulceration

Question 13

Describe the appearance of deep neovascularization

Answer 13

• “hedge row”
• “crown of thorns”
• vessels cannot be seen crossing the limbus

Question 14

What is indicated by white corneal opacity with a yellow or green hue?

Answer 14

white blood cell infiltration

Question 15

What is indicated by white corneal opacity with gray or wispy features?

Answer 15

fibrosis

Question 16

What is indicated by crystalline or chalky white corneal opacity?

Answer 16

mineral or lipid

Question 17

Describe the features of corneal WBC infiltration

Answer 17

• often very painful
• associated with severe corneal disease or uveitis
• signals corneal infection

Question 18

Describe the features of corneal fibrosis

Answer 18

• scar from previous keratitis
• dull white
• non-painful
• involves contracture of lamellar stromal collagen

Question 19

What are the possible causes of mineral or lipid deposits in the cornea?

Answer 19

• corneal dystrophy (lipid)

- corneal degeneration (lipid or mineral)

Question 20

What are the causes of brown corneal opacity?

Answer 20

• epithelial pigment (canine pigmentary keratitis)

- endothelial pigment (deflated uveal cysts, anterior synechia)

Question 21

What is the cause of black corneal opacity?

Answer 21

feline corneal sequestrum

- often due to FHV-1

Question 22

What is indicated by tan or greasy punctate?

Answer 22

keratic precipitates

• cellular and fibrinous adhesions to the endothelial surface
• due to uveitis

Question 23

What is the limbus?

Answer 23

junction between cornea and sclera

Question 24

What is ciliar flush?

Answer 24

360 degrees of deep corneal neovascularization

Question 25

What are the brachycephalic risk factors for ulcerative keratitis?

Answer 25

- ocular prominence - decreased corneal sensitivity - adnexal abnormalities - tear film abnormalities

Question 26

What are the features of an uncomplicated/simple corneal ulcer?

Answer 26

- a superficial corneal ulcer that heals in 7 days or less | - crisp, sharp edges of ulcer margin

Question 27

Describe the features of an indolent ulcer

Answer 27

- 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

Question 28

How is an indolent ulcer treated?

Answer 28

- debride epithelium - if not healed: anterior stromal puncture or diamond burr debridement - topical antibiotics and analgesics

Question 29

What is the most common cause of melting ulcers?

Answer 29

Pseudomonas aeruginosa

Question 30

What are the feature of a deep stromal corneal ulcer?

Answer 30

- inappropriate level of reflex uveitis - severe corneal edema - white blood cell infiltration - deep corneal vessels and episcleral injection - visible stromal loss or disruption - malacia

Question 31

What are the features of corneal perforation?

Answer 31

- positive Seidel test - wrinkled corneal appearance - shallow anterior chamber - iris prolapse - fibrin plug - hyphema

Question 32

When is surgery recommended for stromal ulcers?

Answer 32

> 50% stromal loss or severe infection | descemetocele or perforation

Question 33

What surgery is done to correct stromal ulcers?

Answer 33

- conjunctival pedicle flap | - 360 degree conjunctival graft

Question 34

What are the medical treatments for stromal ulcers?

Answer 34

- topical antibiotics (cephalosporins, fluoroquinolones) - anti-collagenase therapy for melting ulcers (EDTA) - topical atropine and systemic NSAID/tramadol

Question 35

When are parenteral antibiotics indicated for stromal ulcers?

Answer 35

- the ulcer has become vascularized - the cornea is close to perforation or has perforated - iatrogenic vascularization

Question 36

What is reflex uveitis?

Answer 36

the trigeminal nerve and certain cytokines cause direct stimulation of the ciliary body, inducing spasm, pain, and disruption of the blood ocular barrier

Question 37

What is a descemetocele?

Answer 37

a corneal ulcer that has reached the depth of descemets membrane

Question 38

What is keratomalacia?

Answer 38

softening of the cornea due to collagenolysis form infection and the ocular inflammatory response

Question 39

What is collagenolysis?

Answer 39

enzymatic destruction of the corneal stroma that signals infection