Lecture 2: Corneal Ulceration and Perforation Flashcards
Causes of Corneal ulcers
- trauma
- corneal abrasion due to adnexal disease
- tear film deficiency
- exposure keratitis
- infection
When we talk about bacterial infections of corneal ulcers, what context is this in?
generally as a complication more than a cause of corneal ulceration
Acute superficial ulcers can progress to which 3 directions
- they can spontaneously heal
- they can progress to a mid-stromal ulcer
- they can progress to a chronic superficial ulcer
At which point can an ulcer no longer heal? How do you treat this?
when it becomes a descemetocoele;
it requires surgery to treat
what is the progression from acute superficial ulcer to corneal perforation
acute superficial ulcer –> mid-stromal ulcer –> deep stromal ulcer –> descemetocoele –> corneal perforation
Under normal circumstances, how quickly to corneal ulcers generally heal? What does healing generally depend on?
7-10 days, or quicker.
ulcer size, and any inhibiting factors that haven’t been addressed
What is the best diagnostic tool for corneal ulceration diagnosis?
the eyes and brain, searching for an underlying cause
Which diagnostic techniques MUST ALWAYS be performed when looking at eyes?
- searching for the underlying cause
- schirmer tear test
When are you likely to perform a corneal cytology or culture?
when you are concerned about a bacterial infection
What are 5 risk factors to consider with corneal ulceration?
- is tear production normal?
- can and DOES the animal blink normally?
- is the animal a brachycephalic breed or is there conformational exophtalmos?
- are there any adnexal abnormalities?
- does the ulcer appear infected?
Why are we concerned about tear production?
we want to make sure that eye is properly producing tears to lubricate the eye. Also concerned that there may be blockage, leading to other ocular issues
How do we assess normal blinking in an animal?
evaluate their menace and palpebral reflexes
What is Corneal Ulceration?
a full-thickness loss of corneal epithelium
T/F
corneal epithelial loss can vary greatly
true
What can loss of the protective barrier function of the corneal epithelium result in?
- can allow resident microbial flora to colonize the exposed corneal stroma
- predominantly bacteria, but can be fungal (keratomycosis)
what is the most common complicating factor for corneal ulcers?
secondary infection
What are diagnostics generally directed at?
- identifying the cause of the ulcer
- identifying the extent of the ulcer
- further characterizing the disease process with regard to presence/absence of infection
What variables may affect your decision to perform diagnostics?
- severity of disease (how deep/extensive the ulcer is)
- duration of disease
- presence of mucopurulent or purulent discharge (may signal an infection)
What does fluoroscein stain do?
- enhances the ability to detect corneal ulcers
why doesn’t fluoroscein stain bind to the intact corneal epithelium?
its hydrophilic, so it binds to exposed corenal stroma instead
T/F
fluoroscein isn’t helpful in monitoring the healing of ulcers
false
what does fluoroscein fluoresce under?
cobalt blue light
T/F
Fluoroscein stain is always required to dx an ulcer
false
T/F
Tear Production measurement should be considered as almost routine diagnostic for corneal ulcers.
true
dry eye is a very common disorder
When might you omit an STT?
in situations with copious tearing, indicating that lacrimation is not a problem
What situations are highly recommended to perform an STT?
- dogs with mucopurulent discharge (hallmark finding for canine KCS)
- dull or lackluster appearance to the corneal surface
- chronic non-healing ulcers
- recurrent ulcers with an unknown underlying cause
Why are low STT values in a cat difficult to interpret?
cats seem to shut down tear production when stressed
T/F
Topical anesthetics and most sedatives/anesthetics will not reduce STT values
false, they will
what are the specific indications for corneal cytology?
- deepening/expanding corneal ulcers
- apparently minor ulcers with disproportionately severe anterior uveitis
- ulcers accompanied by severe mucopurulent discharge
How are specimens collected for corneal cytology?
- topical anesthetic given before scraping
- use of a kimura spatula or the blunt side of a scalpel blade or a specialized brush
Why shouldn’t you use topical anesthetic for corneal cultures?
it may reduce bacterial yield
In what order should you perform diagnostic tests for corneal ulcers
- STT
- Corneal culture
- Corneal cytology
Fluorescein stain
what are the goals of tx for corneal ulcers?
- prevention and/or treatment of infection
- prevention and/or treatment of stromal collagenolysis
- promotion of corneal healing
- maintenance of patient comfort
what must a practitioner strike a balance between when developing a patient care plan
- necessity of each med
- clinical effectiveness of each med
- owner’s ability to comply with tx plan
what factors can prevent or delay normal corneal healing?
- presence of secondary corneal infection
- continued corneal abrasion (from distichia, ectopic cilia, foreign body, etc.)
- inadequate tear production
- corneal exposure due to inadequate eyelid closure/inadequate blinking (pugs and brachycephalic conformation)
What topical antimicrobials can be given to treat corneal ulcers?
- aminoglycosides
- neomycin
- gentamicin
- tobramycin
- chloramphenicol
- tetracyclines
- fluoroquinolones
- cefazolin
In which circumstance would you use an aminoglycoside
broad spectrum use (both Gram + & -); bactericidal
what antimicrobial is an excellent first line drug for prophylaxis?
triple antibiotics like neomycin
what is combined with neomycin in triple antibiotic solutions
- polymixin B
- gramicidin
what is combined with neomycin in triple antibiotic ointments
- polymixin B
- bacitracin
when would you want to use Gentamicin or tobramycin? Why would you not want to use it as a first line abx? Which is considered more effective
- in situations where there is infection, rather than as prophylaxis
- resistance to gentamicin can rise fairly quickly
- tobramycin
T/F
chloramphenicol availability as an ophthalmic medication has been reduced in recent years
true
why are tetracyclines not considered a good first choice of tx for corneal ulcers?
- wide resistance by Pseudomonas, Staphylococcus, and Streptococcus spp.
T/F
fluoroquinolones should only be reserved for established corneal ulcer infections
true
Which drugs are considered for use as anti-proteolytics?
- autogenous serum
- acetylcysteine
- tetracycline
what is autogenous serum used for? Why is it used
- to speed corneal epithelialization via growth factors present
- contains numerous factors that theoretically reduce proteolytic degradation of the cornea
what drug classification is atropine sulfate? how does it affect the eye?
- mydriatic / cycloplegic
- provides pain relief by causing relaxation of the ciliary body musculature
- causes mydriasis
- may cause severe (but reversible) decline in tear production (can impair healing)
Acute Superficial Ulcers
- Diagnostics
- Treatment
- Follow-up
- look for underlying cause
- prophylactic topical abx BID-TID (ointment) TID (drops). Atropine SID-TID, depending on extent of reflex uveitis
- recheck 2-3 days. if no progress or worse, re-eval. recheck every 2-4 days until healed.
what does SCCED stand for
spontaneous chronic corneal epithelial defect
does a SCCED require surgical tx
typically yes
Specific causes of delayed corneal healing
- corneal infection
- unresolved source of corneal abrasion
- KCS
- exposure keratitis
- neutrophic keratitis
- SCCED
give an example of a primary infectious vector for corneal infection
herpesvirus infection in cats
what is entropion, and how does it cause corneal ulcers
- an inward rolling of eyelids, causing hairs to abrade the cornea
- can be conformational or spastic
- they keep rubbing the cornea, preventing it from healing
