Lecture 4: corneal injury and wound healing

what type of wounds to the cornea cause loss of vision

scarring

what corneal injuries tend to scar and which don’t

epithelial injuries DON’T scar

stroma injuries DO

why do stroma injuries tend to scar

the fibrils that replace the damaged ones are different sizes and become placed unevenly

common signs of ocular injury

• hyperemia

• staining

• watering

• pain

• foreign body sensation

• swollen lid

• vision changes

how many days does it take the epithelium to recover

about 7 days

what does fibronectin assist with in corneal wound healing

helps cells migrate over the wounded area

what two layers of the cornea do not regenerate

endothelium

bowman’s

can descemet’s membrane regenerate

yes, it is made by the endothelium

how does corneal staining allow us to visualize injury

healthy corneal surface has tightly packed cells that repel hydrophilic dye

when abrasion, scratch, or sore breaks outer layer of cells, dye flows into and binds with exposed underlying tissue

what is the cause of meibomian related dry eye

evaporation due to lack of lipids

what is the cause behind aqueous deficiency related dry eye

less water and more salt

what causes epithelial basement membrane dystrophy

genetic condition

faulty basement membrane

cells do not attach correctly and sluff off leaving recurrent erosion

what are the classic signs of epithelial basement membrane dystrophy

Map - areas of thickened abnormal membrane

Dot - trapped cells

Fingerprint - misdirected membrane

what are the advantages of PRK (photorefractive keratectomy)

• good option if cornea is too thick for lasik

• removes epithelium and lasers stroma so lets the epithelium grow back

• no flap

what is the disadvantage of PRK

longer healing time

what is one of the first case history questions you should ask in a red eye patient

do you wear contact lenses

what is the risk of contact lens cases

microbes attach to the case and secrete proteins to protect them forming a biofilm

staph aureus, pseudomonas, and serratia can all form biofilms

what chemicals are found in contact solution

• polyquad (polyquaternium-1)

• PHMB (polyhexamethylene biguanide)

how do the chemicals in multipurpose contact solution contribute to its antibacterial properties

chemical is incorporated into the cell membrane of the bacteria to cause membrane permeability and cell death

how do hydrogen peroxide based solutions kill bacteria

use oxidizing activity to disrupt microbial DNA

what should you ask about in regards to how a patient handles their contacts

handwashing

fingernail care

what should you ask about in regards to a patient’s replacement schedule of their contacts

dailys, biweeklys, or monthlys

continuous wear

specialty lenses such as gas permeable or scleral

what are contacts typically made from

silicone hydrogels

hydrogels

what are reasons people wear contacts

refractive error

cosmetics

myopia control

keratoconus

dry eye

where does the eye get oxygen from

atmosphere when eyes are open

palpebral capillaries when closed

effects of hypoxia on the cornea

• corneal edema due to reduced metabolic activity and decreased pH

• epithelial microcysts: pockets of disorganized cellular material, appear after EW with lenses

• neovascularization

• endothelial loss

what is a major mechanical complication of soft contacts

giant papillary conjunctivitis

key signs of giant papillary conjunctivitis

• lens moves a lot

• itches when removed

• stringy mucous discharge

etiology of giant papillary conjunctivitis

• type IV hypersensitivity response to denatured proteins on CL surface

• mechanical irritation from blinking during waking hours

what kinds of contact lens are more likely to cause giant papillary conjunctivitis

• more common in nonionic low-water content lenses

• less common in gas permeable lenses

how is giant papillary conjunctivitis managed

• D/C lenses until resolution

• possibly use steroids

• change lens material to one with higher water content or change from nonionic to ionic

• enzymatic cleaning of lenses between wear cycle

what is a superior epithelial arcuate lesion

• friction response

• full thickness epithelial disruption

what should be done to treat a superior epithelial arcuate lesion

flatten the lens or reduce modulus

usually not super noticeable to the patient

signs of contact lens associated red eye (CLARE)

• usually a lot of corneal infiltrates (clusters of white blood cells)

• hyperemia

how to treat inflammatory contact reactions

discontinue lens wear until improved

change lens, case, or solution

may need steroid or antibiotic

what is a corneal ulcer

• an infiltrate with an epithelial defect over the top

• ulcers stain

• can come from infectious or noninfectious causes

• contact lens wear can lead CLPU (contact lens peripheral ulcer

what is CLPU

• contact lens peripheral ulcer

• immune response to bacterial endotoxins

• usually staph related

• small, peripheral and round

what is an infectious CL response termed

• microbial keratitis

• can happen with or without CL but CL introduce more/different bacteria

• disrupts tear immune response

types of infectious keratitis

herpes keratitis

fungal keratitis

bacterial keratitis

amoebic keratitis

where does microbial keratitis tend to be located

central cornea

affects vision

stroma and epithelium or full cornea

symptoms of microbial keratitis

• pain

• vision loss

• hyperemia

• discharge

• photophobia

clinical signs of microbial keratitis

• ulcer

• discharge

• hyperemia

• anterior chamber reaction

• conjunctival response (papillary or follicular)

• ptosis (from lid swelling)

risk factors for microbial keratitis

• contact lens wear

• abrasions and foreign bodies

• immune deficiency

• vitamin deficiency (esp vit A)

• dry eye (keratitis sicca)

• systemic diseases that change the cornea (RA and DM esp)

what key case history points should you collect in cases of microbial keratitis

• contact lens wear

• any immunosuppresion

• malnutrition such as alcohol abuse

• bell’s palsy, DM, Sjorgens, RA

• prior trauma, erosions, dystrophies

• topical steroid use or anything that regularly goes in the eye

what bacteria are common causes of bacterial keratitis

staph and strep

pseudomonas is a big concern due to its aggressive nature

what fungi are common causes of fungal keratitis

fusarium and aspergillus

key sign of fungal keratitis

feathery infiltrate

treatment for fungal keratitis

natamycin or other antifungals

can be hard to find

how long does it take for fungal keratitis to take hold

about 48 hours between trauma and infection

what is the main culprit of amoebic keratitis

acanthomeba

how does amoebic keratitis present

• usually as a ring infiltrate

• really painful

• worsens quickly

how is amoebic keratitis usually acquired

from CL wear in water sources such as lakes, hot tubs, and dirty pools

how is amoebic keratitis treated

chlorhexadine

but it is hard to find

when should you suspect herpes keratitis

whenever there is a unilateral red eye

ulcer has a dendritic pattern

when infected with herpes zoster where will the rash be

across V1 usually

how is herpes keratitis treated

antivirals (can be oral or topical)

no steroids

two types of herpes

herpes simplex (more common)

herpes zoster