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Complicated Corneal UlcersMicrobial KeratitisJames V. Schoster, DVM DACVO

University of Wisconsin USA

Learning Objectives

Recognize the signs of corneal infection

Recognize the signs of corneal melting

Understand the diagnostic and therapeutic options.

IntroductionA corneal ulcer is an area of the cornea that has lost its epithelium and a variable amount ofstroma. Stromal ulcers take longer to heal than simple epithelial abrasions. Uncomplicatedstromal ulcers that were trauma induced should heal in one to two weeks; as apposed to superficialcorneal abrasions that should be healed in less than one week.

DefinitionA complicated corneal ulcer is one that has additional factors present which are not only delayingthe normal healing response but have the potential to cause further deterioration of the cornea.hese factors can be intrinsic or ac!uired. Sepsis is the most common ac!uired reason which candirectly destroy the cornea as well as by stimulation of intrinsic "self destruct" mechanisms#collagenase$. %n addition& other complications of septic ulcers are uveitis and cataract.

Epidemiology'ven though corneal ulceration is one of the most common ocular disorders in dogs; the incidenceof complicated corneal ulcers is not known but is felt to be significantly less than uncomplicatedcorneal ulcers.

Etiology%n most cases the cause is corneal trauma& however considerations of foreign body& eyelidabnormalities& aberrant cilia& e(posure and )*S #keratocon+unctivitis sicca$& should be made.

Normal Corneal Defense Mechanisms,ormally the cornea is flooded with microorganisms consisting of the normal flora. ,ormal cornealdefense mechanisms provide protection from these organisms.

'yelids and intact blink refle(

'yelashes

Refle( tearing and trilaminar tear film

ear proteins with antibacterial effects

-icrobial products #bacteriocins$ from the normal flora that affect pathogenicmicroorganisms

*orneal epithelial cells

Smooth corneal surface


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Impaired Corneal Defense MechanismsWhen any of the above normal protective mechanisms are not present or if they aremalfunctioning; there is increased risk for infection. %n addition& specific risk factors such astrauma& foreign body& corneal surgery and other local or systemic factors can impair the normalcorneal defenses. -icroorganisms may adhere to the corneal tissues more readily if there is

damage to the tissue and or if the microorganisms are not swept from the surface of the corneaefficiently by the normal blink& and tear film mechanics and physiology.Systemic factors such as senility& *ushings disease& diabetes mellitus& and any other local orsystemic disease or medication can impair the immune system.

Clinical eatureshe evaluation of an animal with a stromal keratitis should include a careful history ande(amination of the corneal ulcer for signs of infection as well as the entire anterior segment to lookfor predisposing factors.-ost often the history is one of an initial acute onset of ocular discomfort& blepharospasms& tearingand rubbing at the eye.

'(amination findings that would imply a complicated stromal ulcer and possibly a microbialkeratitis/

*orneal ulcer present longer than one week with stromal loss

0rogressive stromal loss

%nfiltrate

,eovascularization 1 perilimbal flush

Anterior uveitis

Soft borders

-alacia #melting$ 2 li!uifactive stromal necrolysis

Small ulcer #pin point or dot$& minimal to no apparent stromal loss& acute onset withsignificant anterior uveitis #miotic pupil and a!ueous flare and pain$

3ypopyon *orneal edema

Sterile complicated stromal ulcerations are fre!uently encountered and usually do not haveinfiltrates or hypopyon; however they may be malacic and have secondary uveitis.


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our !teps or !uccess "hen dealing#ith Complicated !tromal Ulcers

!$E% &

'ttempt to determine the cause for the stromal ulcer and inspect the anteriorsegmentOphthalmic Examination#'specially take note of the following points$

- 4ocation of ulcer- A(ial- 0ara(ial- %nferior nasal- %nferior temporal- 0erilimbal

-Size- of the lesion is important especially from a prognostic standpoint.

- Shape of the lesion is important to note prognostically in that as the lesionheals one can identify the change in shape with healing& which is usually in theform of tongues or waves of epithelium moving toward the center.- he shapemay also infer or corroborate the etiology; e.g.& scratch would

be linear or out line the path of a foreign body attached to the underside ofthe eyelid and the path or track it makes in the cornea as the eyelidmoves.

- 0alpebral Refle(- 5lobe size and position

-Schirmer ear est #6o not perform if 6escemetocele$

- 'yelids #conformation& aberrant cilia$- 7oreign body search- 'valuation for uveitis- %ntraocular pressure measurement #do not perform if ulcer is very deep and

there is impending rupture$- %s this ulcer infected8

- %nfiltrates- %ndistinct borders- 5rey to yellow color

- %s a foreign body present8

-'vert all eyelids and e(amine the con+unctival surfaces and forni( withmagnification and good light

- What is the depth of the ulcer8 #Amount of stroma remaining at its deepestpoint$

- What is the breadth of the ulcer8- Are there other complications/ Uveitis& *ataract& 5laucoma

Essential E(aminationE)uipment

4oupes 7ocal 4ight Source Slit 4ight Source Schirmer ear est

Strips 6elicate 9 ( : rat

toothed forceps -uscle hook

onometer #do notmeasure %0 ifthere is a deepcorneal ulcer$.


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!$E% *

Laboratory Evaluations

- -icrobiological 'valuation-


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!$E% ,I $-E DE%$- O $-E CO.NE'L ULCE. I!

4ess than 9: the thickness of the normalcornea

MEDIC'L!

5reater than :> rds the normal cornealthickness

!U./IC'L!

opical herapy6rug *hoice- Antimicrobial- Antiinflammatory- -ydriatic 1 cycloplegic

0reparation 7ormA!ueous solutionSuspension'mulsion5elintment

*ollagen Shield7ortified drops6elivery


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MEDIC'L $-E.'%0 !%ECIIC!

ypically infected #septic$ corneal ulcers can have either cocci or rods& or both; septic ulcers areusually of an aerobic variety. ml of Artificialears to make concentration of >> mgml. 6o not use ears ,aturale #precipitates$.'(piration 2 9 month

Cefa2olinAdd @BB mg 9.@ ml of *efazolin #>>B mgml$ to 9>.@ ml of Artificial ears. '(p. 2 F days.Refrigerate. Shake well. he final concentration is >> mgml.

/entamicino make G mgml final concentration& add >@ mg #B.>@ ml of the 9BB mgml in+ectable$ to @ml of gentamicin ophthalmic solution. '(p./ 9 month.

InsulinRemove : ml from Artificial ears bottle. Add :BB units #U9BB 1 : ml$ regular insulin. 7inalconcentration 2 9>.@ units ml. '(p. 2 9 month Refrigerate

%enicillin /3 40enicilina 55Remove @ ml from 9@ ml Artificial ears bottle. Add 9: ml sterile water to :B million unitvial of 0enicillin 5) #concentration 2 9 million units per ml$& add @ ml 0enicillin 5) to 9B mlArtificial ears. 7inal concentration of 0enicillin is >>>&>>> unitsml. '(p. 2 F days.Refrigerate. Shake well.

$obramycino make G mg ml& add HB mg ml of obramycin in+ectable to @ cc of obramycinophthalmic solution. '(p. 2 9 month.

6Use Methylcellulose &7 for 'rtificial $ears Unless Other"ise Indicated8


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'ntimicrobial 'pplication !uggestionsAll of the above drugs are in drop form #solutions$. ne or two drops of the solution can be used ateach dosing interval. he dosing interval for bacterial stromal keratitis usually begins at one to twodrops every >B minutes for the first :H hours. %f improvement is noted after :H hours& the fre!uency

can persist for another 9: 1 :H hours or begin to taper by 9: #if ! >B minutes then go to ! 9 hour 1 if! 9 hour then go to ! :hours$.

opical application to mimic subcon+unctival in+ection can be done by instilling one drop minute for@ minutes each hour.When two or more different drugs are being used; they must be instilled at different times 1 at least@ to 9B minutes apart since the lacrimal lake in the dog and cat can not accommodate more thanone drop at a time.

!pace for NO$E!


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'nti9inflammatory $herapy

Anterior uveitis is commonly associated with corneal irritation because when the cornea isabraded& factors are released #substance 0 and likely others$ from the ophthalmic branch of the @thnerve in the cornea. hese factors enter the anterior chamber and cause the release of

prostaglandin leukotrienes& which generate the signs of anterior uveitis; break down of the blooda!ueous barrier& vasodilatation& leakage of protein& smooth muscle contraction1ciliary spasm andthe respective resulting pain and miosis$.opical or subcon+unctival steroids would be contraindicated yet topical andor systemic anti1inflammatory drugs such as one of the nonsteroidal agents would be indicated.

9D 0rofenol Suprofen/ one drop : 1 > times per dayoo fre!uent usage will cause a punctate keratitis and may also reduce cornealneovascularization

B minutes to J times per day.*are should be taken in handling this product since it could become contaminated easily.

'cetylcysteine 4Mucomyst

5is a commercially available anticollagenase agent that has beensuccessfully used as an e(tra label use drug in the eye. A @D concentration diluted with an artificialtear such as 9D methylcellulose #%soptoalkaline$ can be used. 5reater concentrations are more


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irritating. A serous collagenase corneal ulcer should be treated hourly with the @D -ucomyst dropat least for the first to 9: hours. apering of the fre!uency can occur as deemed necessary.

ED$'can also be used to inhibit the proteoglycan enzyme produced by pseudomonas. A topicalpreparation can be made by adding B.H ml of '6A #9@B mgml$ to a 9@ ml bottle of Adapt or other

artificial tear solution. ne to two drops can be delivered five times daily #


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!U./IC'L $-E.'%0

Since the cornea has a limited thickness& stromal corneal ulcers may deepen to the point whererupture of the cornea in imminent #less than 9H of corneal thickness remaining$. %t is at this timewhere procedures to provide structural support are necessary. he choices are con+unctival flaps#grafts$& Autogenous lamellar corneal grafts #transposition of ad+acent cornea$& ectonic cornealgraft #frozen corneal tissue$& corneal transplant #penetrating keratoplasty$ and *yanoacrylaterepair.

*on+unctival flaps also provide an immediate blood supply that can deliver constituents vital to

corneal healing via its blood supply.

%rinciples

Conjunctival grafts or flapshese grafts should be as small as possible while still covering the lesion. hey also should bethin and carry a blood supply so they remain viable& and they should have no holes #for a watertightseal$ nor should they be under tension #to prevent dehiscence$.Several con+unctival flaps #graft$ configurations are possible. he choice depends on the surgeonIspreference& e(perience& the condition of the cornea& and the size& depth and location of the cornealdefect.


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0ossible choices are/- 3ood or advancement #forni( based$- 0edicle- B- *orneal Scleral *on+unctival ransposition

*on+unctival flaps must be applied with the subcon+unctival surface directly against the stroma or6escemetIs membrane to create a permanent adhesion. %f the mucosal surface contacts theepithelium& stroma or 6escemetIs membrane& a secure adhesion probably wonIt develop. Also ifthe subcon+unctiva is sutured to corneal epithelium& a poor adhesion can be e(pected;

adhesion will occur only at each suture site& which would not be strong enough to hold the graft inplace. 6ebriding the epithelium for about 9 to : mm around the margin of the corneal lesion willensure that the flap adheres to the cornea. his is especially true in cases in which the corneal

epithelium is at the margin of the deep lesion or has migrated over the edge and down the walls ofthe lesion.

7laps are difficult to create from the inferiornasal bulbar con+unctiva because the con+unctivareflects on to the third eyelid a very short distance from the limbus. 7orni(1based flaps advancedfrom the inferior nasal area tend to cause partial prolapse of the third eyelid #resulting in e(cessivetension on the graft$ because the attachment of the bulbar con+unctiva is close to the third eyelid.A pedicle flap works well in this area.

When deciding where to begin a flap& consider using the con+unctiva closest to the lesion& but alsoconsider what will happen to the visual a(is. ne should minimize the amount of con+unctival

tissue that must be dissected free but prevent obstruction of the visual a(is.


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orni( based 4-ood or 'dvancement5

hese are also known as sliding or hood flaps that utilize the bulbar con+unctiva. 1 @ mm nick +ust through the con+unctiva with thetenotomy scissors pointed away from the cornea. %deally& the tenotomy scissors should be slightlycurved so the tips can be directed upward.


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%edicle lap

%edicle flapshese are the ne(t most common con+unctival flap and are also fashioned from bulbar con+unctiva.


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:ridge lap

:ridge flapshis is a variation of the pedicle flap e(cept that it is continuous from limbus to limbus . his flap ismore visually obstructive& less cosmetic& and involves more dissection and trauma to the globe. %tis however more likely to remain viable because the blood supply enters from both ends of the flap.6ehiscence is also less likely because of the union with the bulbar con+unctiva at both ends. hemain problems with this type of graft are its horizontal position and limitation on the width of thegraft.


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Island /rafts

Island graftsWith tarsocon+unctival and bulbar con+unctival island grafts& a button of con+unctiva is used to patcha thin and weak corneal area. he graft does not bring in an active blood supply. he tissue canbe obtained from either the bulbar con+unctiva or the palpebral tarsocon+unctiva. hetarsocon+unctiva provides a thicker piece of tissue than the bulbar con+unctiva& and also providesgreater support. his graft is indicated in non1infected descemetoceles where one is trying to avoidobstruction of cornea and a second surgery for graft trimming #as would be necessary with apedicle. his graft is especially effective if there is a perilesional corneal blood supply that isalready present.


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+;anas !cissors

- #escott !cissors

- !tevens $enotomy !cissors


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- !harptome :lades

- 3eratomes

- Castroviejo caliper

- Non9loc1ing needle holderi.e./ :arra)uer Curved

- Castroviejo !uturing orceps 4


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Materials- *ellulose sponges 1 spears

Lint !ree "ponges- 9H" 0enrose drain

"mall #ieces for arsorrhaphy $ubber %umpers-

=iscoelastic!or reformation of the anterior chamber an& manipulation of iris in the eventof a corneal rupture