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Home , Cornea, Corneal epithelium, Corneal ulcer, Globe (human eye), Iris (anatomy), Keratomalacia

Photo by iStockphoto.com / EDUCATION Veterinary U 10 Diagnosis andTreatment VTS () Sara Grabiel-Duncan,BS,LVT, Corneal Ulceration Diagnosis andTreatmentof promote healing. treatment optionsisessentialto and surgical wound healingaswell asdifferent medical to , corneal recognition ofnormal and physiologyofthecornea, itsresponse affected . basicanatomy Understanding impaired sight, blindness, oreven lossofthe clarity,corneal andultimatelymaycause sepsis,profound effectsoncorneal healing, mayhave ulcers treatment ofcorneal An inaccurate diagnosisandimproper ulcers.identical foralltypesofcorneal ulcerationand treatment isnot ofcorneal affecting thecaninecornea. Diagnosis program’s validity orrelevancy totheveterinary profession. recognize AAVSB RACE approval. Pleasecontact theAAVSB RACEprogram ifyou have anycomments/concerns regardingthis This program wasreviewed andapproved bytheAAVSB RACEprogram for1hourofcontinuing educationinjurisdictionswhich available. potential managementoptions They willalsobeabletoidentify and diagnosingcorneal ulcers. and physiologyofthecornea understanding oftheanatomy Readers shouldgainabasic LEARNING OBJECTIVE: |THENAVTA JOURNAL |NAVTA.net most prevalent clinicalabnormalities isoneofthe lceration ofthecornea NURSING 1. iscomposedof5distinctlayers: The Anatomy • composed ofatleastthree distinctlayers: optical clarity. tearfilmis The pre-corneal of theavascular cornea, andmaintain cellsandtissues tocorneal nutrition thecornea,protect andlubricate provide is afluidlayerwhichfunctionstohydrate, layerofthecornea superficial (outermost) tearfilm—themost Pre-corneal • (aqueous) layerofthetearfilm. and prevents evaporation ofthesecond tomove inaglidingaction the eyelids. the The oillayerpermits meibomian glandslocatedwithin layer consistsofoilsproduced by the Oil layer—thesuperficial(outermost) is produced by theorbitallacrimal tear film.of thepre-corneal Thislayer layer andtheunderlyingmucus layer located between thesuperficialoil tearfilm(95%)andis pre-corneal constitutes thelargestvolume ofthe Aqueous layer—theaqueous 2. remarkable regenerative capabilities stroma.corneal The epithelial layerhas maintains relative dehydration ofthe stroma, intothecorneal entering which excessive volume oftearfilmfluids from topreventserves an asabarrier membrane—the corneal epitheliumanditsbasement Corneal • layers ofthetearfilm) layers inter-mixes thethree component surface.the corneal ( partially and bindsthemiddleaqueouslayerto This layerincreases thesurfacearea by conjunctival gobletprimarily cells. composed ofmucin andisproduced tearfilmis layer ofthepre-corneal Mucoid layer—theinnermost the epitheliumhydrated. andalsofunctionstokeep andoxygen and nutrition tothecornea This layerisresponsible forproviding of theaqueouscomponenttears. 35-65% membrane whichcontributes andtheglandofnictitating gland, 35-50%of whichcontributes Veterinary NURSING EDUCATION

Canine Corneal Ulcers

Superficial Deep

Young Middle age to older Uncomplicated Complicated

Trauma Free epithelial edges Topical tobramycin, Descemetocele , protective collar

Yes No Yes No Yes No

Normal Normal Surgical Medical Topical SCCED anatomy anatomy repair (graft) treatment tobramycin, gabapentin, protective collar Yes No Yes No Corneal debridement, Example: diamond topical ofloxacin burr, topical qid, and atropine Foreign Determine and treat ofloxacin, Treat sid, oral doxycline body underlying cause i.e. atropine, underlying bid, NSAID sid-bid, , ectopic cilia, oral NSAID, cause i.e. and gabapentin distichiasis, etc. gabapentin, entropion, bid-tid, protective protective distichiasis, collar collar Yes No etc.

Other ocular Remove foreign abnormalities body, topical i.e. Dry Eye ofloxacin, (KCS), corneal atropine, calcium gabapentin, degeneration, protective collar etc.

Yes No

Treat underlying Treat, topical cause, topical tobramycin, tobramycin, gabapentin, gabapentin, protective collar protective collar

VETERINARY NURSING IN ACTION | June/July 2019 | 11 Veterinary NURSING EDUCATION

and re-epithelialization occurs rapidly “dehydrated” to maintain optimal optical the corneal stroma. Depending on the under normal circumstances. If the clarity for of light entering the amount of epithelial cellular loss, entire epithelial layer is removed, it eye. The cornea is highly innervated by the may still enter the corneal stroma. Full- takes approximately 11-14 days to re- ophthalmic branch of the trigeminal , thickness loss of corneal stoma exposes epithelialize under normal circumstances. thus its exceptional sensitivity. Sensory Descemet’s membrane which does not retain receptors are concentrated in the superficial fluorescein dye. 3. Corneal stroma—the third layer of (anterior) third of the corneal stroma and Corneal ulcers are categorized by their the cornea is the corneal stroma which in the . The epithelium topographic location, depth and etiology. is located just underneath the basement contains the greatest density of sensory Location of an ulcer is important because membrane of the epithelial layer. The per square millimeter than any other it often provides clues to determine the stroma accounts for approximately tissue in the body. It is for this reason that underlying cause. When an ulcer is located 90% of the corneal thickness and is superficial ulcerations or abrasions are more in the superior portion of the central cornea, composed mostly of uniformly arranged painful than deep ulcerations. detailed examination of the palpebral parallel bundles of fibers. The surface of the upper may reveal transparency of the cornea is achieved by Corneal Erosions and Ulcers ectopic cilia or embedded foreign body. A this precise arrangement of collagen and Corneal erosion is defined as loss of corneal horizontally-oriented ulcer located in the prevents scattering or refraction of 99% of epithelial cells without the loss of the central cornea is suggestive of exposure from light entering the cornea. The stroma is epithelial basement membrane. Corneal incomplete blinking (). Most extremely hydrophilic (water loving), but ulceration is defined as a loss of the corneal traumatic ulcers also occur in the central absorption of fluids by the stroma is limited epithelium and its basement membrane. or paracentral region. If an ulcer is located by the hydrophobic (water repelling) Ulceration can also include loss of part in the inferior-nasal region, examination corneal epithelium (preventing absorption or the entire corneal stroma. Solubility behind the nictitating membrane may reveal of tear film) and the corneal properties of the epithelium and stroma an embedded or retained foreign body. (preventing absorption of aqueous humor). help differentiate between ulcerations and Ulcers located in the paralimbal region Dysfunction or loss of either the corneal erosions. The epithelium acts as a barrier are suggestive of an eyelid conformational epithelium or endothelium may permit to water-soluble solutions, whereas the abnormality or an abnormality. over-hydration of the corneal stoma and hydrophilic stroma acts as a “sponge” Limbal-based ulceration is suggestive of an result in corneal edema. to water-soluble solutions. Fluorescein immune-mediated etiology. sodium dye is water-soluble—therefore, if The depth of an ulcer is much more 4. Descemet’s membrane—The fourth an ulcer is present the stroma will retain important than the geographic size of an layer of the cornea is Descemet’s the dye. If a corneal erosion is present, the ulcer when determining the severity of membrane, which is the basement fluorescein stain will be partially repelled corneal ulceration. A superficial ulcer is an membrane of the . by the remaining epithelial layers. ulcer only involving the epithelium and Descemet’s membrane is composed of The basement membrane of the corneal its basement membrane. When an ulcer collagen, is highly elastic, and continues to epithelium is a weak barrier to prevent involves less than one third of the stroma, thicken with advancing age. water-soluble compounds from entering it is classified as a superficial stromal ulcer, and if it involves more than one third of 5. Endothelium—The innermost layer of Corneal erosion is the stroma, it is classified as a mid to deep the cornea is the corneal endothelium stromal ulcer. Full-thickness loss of corneal which lines the inner surface of defined as loss of corneal stoma exposes Descemet’s membrane and is Descemet’s membrane and is in direct epithelial cells without called a descemetocele. A perforated corneal contact with aqueous humor. This layer ulcer occurs when Descemet’s membrane consists of a monolayer of cells that have the loss of the epithelial ruptures, resulting in leakage of aqueous a poor regenerative capacity. Endothelial basement membrane. humor from the anterior chamber. cells are the predominant barrier to Indisputably, there is always an the movement of aqueous humor into Corneal ulceration is underlying cause of corneal ulceration— the corneal stroma and are essential to defined as a loss of the determining the primary origin may maintain the transparency of the cornea. be difficult, but is an absolute necessity. The cornea is approximately 0.5 mm corneal epithelium and Besides using location and depth to help thick, is normally avascular, and is relatively its basement membrane. determine the primary cause of ulceration,

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other important considerations include exposed stroma retains fluorescein dye whether the cause could be sharp or blunt and is highlighted, however an enlarging trauma, (foreign body, exposure, eyelash or area of fluorescein dye retention can be eyelid abnormalities), infectious (bacterial, observed around the periphery of the ulcer viral, fungal), chemical (soaps, flea sprays, as fluorescein undermines the non-adherent etc.), associated with cellular or metabolic epithelial edges. Many SCCED’s are never corneal stromal infiltrates (calcium, accompanied by stromal vascularization, but neutrophils) endothelial abnormalities if vascularization occurs the corneal stroma (endothelial cell dystrophy, bullous may or may not develop granulation tissue. keratopathy), or immune mediated (Dry Medical treatment alone is unlikely eye, , Terrians Marginal to result in healing of a SCCED since degeneration). the epithelium generally will not adhere completely to the underlying stroma Spontaneous Chronic while this HAZ is present. Treatment Corneal Epithelial Defect for a SCCED requires surgical removal A spontaneous chronic corneal epithelial of or penetration through the HAZ. defect (SCCED) previously referred to as Numerous techniques have been described indolent ulcer, “Boxer ulcer,” refractory to treat a SCCED including epithelial corneal erosion, or rodent ulcer, is known debridement, linear or grid keratotomy, as a superficial that heals multiple punctate keratotomy, superficial poorly or slowly and tends to recur lamellar keratectomy, thermokeratoplasty despite conventional treatment. By clinical (heat treatment), chemical debridement, definition, an indolent ulcer is a corneal cyanoacrylate tissue adhesive, and diamond ulcer that has been present for a duration of burr debridement keratectomy. at least three weeks. A SCCED invariably Diamond burr debridement is a very occurs in middle-aged to elderly dogs, effective and beneficial method to remove and can develop in all breeds, although the HAZ. The diamond burr debridement some breeds are more frequently affected, technique is a more contemporary and including the Boxer (the breed in which this preferred method of treatment for SCCED condition was initially described) and the because it does not result in stromal scar Golden Retriever. With advancing age, a formation, unlike other treatment methods. hyalinized acellular zone (HAZ) develops The procedure is performed using topical in the superficial portion of the anterior anesthetic with the patient awake. Non- corneal stroma which prevents proper adherent epithelial edges are debrided using adhesion of the epithelial layer of cornea to a dry cotton swab—it is important that all the underlying stroma, a predisposing factor loose epithelium be removed (Figure 2). It is for development of a SCCED. important to note that normal epithelium A SCCED is described clinically as overlying normal corneal stroma cannot be Figure 1 (top): Image of an eye with a spontaneous chronic corneal epithelial defect (SCCED) stained a superficial corneal defect involving easily debrided because it is firmly adhered with fluorescein dye. Note the fluorescein dye only the corneal epithelium (there is to the underlying corneal stroma. If the undermining the edges of the epithelial layer and the diagnostic “lip” of loose epithelium. no loss of corneal stromal tissue). This epithelium can be easily debrided, it is not Figure 2 (bottom): Image of an eye with a chronic superficial corneal ulceration normal and should be removed. Following spontaneous chronic corneal epithelial defect has a peripheral edge of poorly adherent debridement with a cotton swab, a battery (SCCED) stained with fluorescein dye. Corneal debridement is being performed with a sterile epithelial tissue, which is easily identified powered, high-speed, low-torque rotating cotton swab prior to performing diamond burr by examination. A SCCED is typically shaft instrument fitted with a mild diamond keratotomy. located in the central or paracentral cornea, burr is used to perform the procedure and has a characteristic non-adherent “lip” (Figure 3). The rotating burr is pressed of epithelium located at the periphery of lightly against the affected ulcerated cornea the ulcer (Figure 1). When fluorescein dye and is moved back and forth to remove is applied to the cornea, immediately the the HAZ. Post-operative care involves

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chewables CAUTION: Federal (U.S.A.) law restricts this drug to use by or on the order of a licensed veterinarian. INDICATIONS: For use in dogs to prevent canine heartworm disease by eliminating the tissue stage of heartworm larvae (Dirofilaria immitis) for a month (30 days) after infection and for the treatment and control of ascarids (Toxocara canis, Toxascaris leonina) and hookworms (Ancylostoma caninum, Uncinaria stenocephala, Ancylostoma braziliense). DOSAGE: HEARTGARD® Plus (ivermectin/pyrantel) should be administered orally at monthly intervals at the recommended minimum dose level of 6 mcg of ivermectin per kilogram (2.72 mcg/lb) and 5 mg of pyrantel (as pamoate salt) per kg (2.27 mg/lb) of body weight. The recommended dosing schedule for prevention of canine heartworm disease and for the treatment and control of ascarids and hookworms is as follows:

Color Coding 0n Dog Chewables Ivermectin Pyrantel Foil Backing Weight Per Month Content Content and Carton Up to 25 lb 1 68 mcg 57 mg 26 to 50 lb 1 136 mcg 114 mg Green 51 to 100 lb 1 272 mcg 227 mg Brown

HEARTGARD Plus is recommended for dogs 6 weeks of age and older. For dogs over 100 lb use the appropriate combination of these chewables. ADMINISTRATION: Remove only one chewable at a time from the foil-backed blister card. Return the card with the remaining chewables to its box to protect the product from light. Because most dogs find HEARTGARD Plus palatable, the product can be offered to the dog by hand. Alternatively, it may be added intact to a small amount of dog food. The chewable should be administered in a manner that encourages the dog to chew, rather than to swallow without chewing. Chewables may be broken into pieces and fed to dogs that normally swallow treats whole. Care should be taken that the dog consumes the complete dose, and treated animals should be observed for a few minutes after administration to ensure that part of the dose is not lost or rejected. If it is suspected that any of the dose has been lost, redosing is recommended. HEARTGARD Plus should be given at monthly intervals during the period of the year when mosquitoes (vectors), potentially carrying infective heartworm larvae, are active. The initial dose must be given within a month (30 days) after the dog’s first exposure to mosquitoes. The final dose must be given within a month (30 days) after the dog’s last exposure to mosquitoes. When replacing another heartworm preventive product in a heartworm disease preventive program, the first dose of HEARTGARD Plus must be given within a month (30 days) of the last dose of the former medication. If the interval between doses exceeds a month (30 days), the efficacy of ivermectin can be reduced. Therefore, for optimal performance, the chewable must be given once a month on or about the same day of the month. If treatment Figure 3: Image of the same eye shown in Figure 2 while performing diamond is delayed, whether by a few days or many, immediate treatment with HEARTGARD Plus and resumption of the burr keratotomy. recommended dosing regimen will minimize the opportunity for the development of adult heartworms. Monthly treatment with HEARTGARD Plus also provides effective treatment and control of ascarids (T. canis, T. administration of a topical broad-spectrum antibiotic, systemic and leonina) and hookworms (A. caninum, U. stenocephala, A. braziliense). Clients should be advised of measures to be taken to prevent reinfection with intestinal parasites. topical nonsteroidal anti-inflammatory medications, and topical and EFFICACY: HEARTGARD Plus Chewables, given orally using the recommended dose and regimen, are effective against the tissue larval stage of D.immitis for a month (30 days) after infection and, as a result, prevent the development systemic pain medications. of the adult stage. HEARTGARD Plus Chewables are also effective against canine ascarids (T. canis, T. leonina) and hookworms (A. caninum, U. stenocephala, A. braziliense). As with treatment of all corneal ulcers, the exception being ACCEPTABILITY: In acceptability and field trials, HEARTGARD Plus was shown to be an acceptable oral dosage form immune-mediated ulcers, use of topical should be that was consumed at first offering by the majority of dogs. PRECAUTIONS: All dogs should be tested for existing heartworm infection before starting treatment with avoided. Topical Atropine may be administered once daily for HEARTGARD Plus which is not effective against adult D. immitis. Infected dogs must be treated to remove adult 3-5 days to reduce ocular pain, but is contraindicated in patients heartworms and microfilariae before initiating a program with HEARTGARD Plus. While some microfilariae may be killed by the ivermectin in HEARTGARD Plus at the recommended dose level, with Sicca (Dry Eye) and patients with or HEARTGARD Plus is not effective for microfilariae clearance. A mild hypersensitivity-type reaction, presumably due to dead or dying microfilariae and particularly involving a transient diarrhea, has been observed in clinical trials with predisposed to develop . A protective collar should also ivermectin alone after treatment of some dogs that have circulating microfilariae. be worn by the patient at all times to prevent self-trauma to the Keep this and all drugs out of the reach of children. In case of ingestion by , clients should be advised to contact a physician immediately. Physicians may contact a healing cornea until the ulcer has healed. Since SCCED is an age- Poison Control Center for advice concerning cases of ingestion by humans. Store between 68°F - 77°F (20°C - 25°C). Excursions between 59°F - 86°F (15°C - 30°C) are permitted. Protect related ulcer, owners should be informed that SCCED is usually a product from light. bilateral condition, and the fellow eye usually develops a SCCED ADVERSE REACTIONS: In clinical field trials with HEARTGARD Plus, vomiting or diarrhea within 24 hours of dosing was rarely observed (1.1% of administered doses). The following adverse reactions have been reported within one year. following the use of HEARTGARD: Depression/lethargy, vomiting, anorexia, diarrhea, , ataxia, staggering, convulsions and hypersalivation. Other surgical treatment alternatives include grid keratotomy SAFETY: HEARTGARD Plus has been shown to be bioequivalent to HEARTGARD, with respect to the bioavailability and multiple punctate keratotomy which are performed using a 25 of ivermectin. The dose regimens of HEARTGARD Plus and HEARTGARD are the same with regard to ivermectin (6 mcg/kg). Studies with ivermectin indicate that certain dogs of the Collie breed are more sensitive to the effects of gauge needle, and involve creating superficial linear incisions in a ivermectin administered at elevated dose levels (more than 16 times the target use level) than dogs of other breeds. At elevated doses, sensitive dogs showed adverse reactions which included mydriasis, depression, ataxia, tremors, crosshatch grid pattern (linear grid keratotomy) or creating multiple drooling, paresis, recumbency, excitability, stupor, and death. HEARTGARD demonstrated no signs of toxicity at 10 times the recommended dose (60 mcg/kg) in sensitive Collies. Results of these trials and bioequivalency studies, punctures (multiple punctate keratotomy) through the basement support the safety of HEARTGARD products in dogs, including Collies, when used as recommended. membrane and into the anterior corneal stroma. Superficial lamellar HEARTGARD Plus has shown a wide margin of safety at the recommended dose level in dogs, including pregnant or breeding bitches, stud dogs and puppies aged 6 or more weeks. In clinical trials, many commonly used flea keratectomy can also be performed but is infrequently necessary collars, dips, shampoos, anthelmintics, antibiotics, vaccines and steroid preparations have been administered with HEARTGARD Plus in a heartworm disease prevention program. due to the high success rate of the diamond burr debridement. In one trial, where some pups had parvovirus, there was a marginal reduction in efficacy against intestinal nematodes, possibly due to a change in intestinal transit time. Lamellar keratectomy removes the superficial layers of the anterior HOW SUPPLIED: HEARTGARD Plus is available in three dosage strengths (See DOSAGE section) for dogs of different corneal stroma and is generally recommended as a last resort weights. Each strength comes in convenient cartons of 6 and 12 chewables. For customer service, please contact Merial at 1-888-637-4251. treatment for SCCED’s that fail to heal with other therapies. This procedure requires general anesthesia, and is a more expensive and ®HEARTGARD and the Dog & Hand logo are registered trademarks of Merial. ©2015 Merial, Inc., Duluth, GA. All rights reserved. demanding micro surgical procedure. Both the diamond burr and

VETERINARY NURSING IN ACTION | June/July 2019 | 15 Veterinary NURSING EDUCATION

grid keratotomy procedures are performed and it is not infected, it may be treated MMP-9 activity. Topical autogenous serum with topical anesthetic only, and since the conservatively as described above for a contains alpha-2 macroglobulin, which patient is generally middle aged to geriatric, superficial stromal ulcer. also may arrest collagenolysis by blocking this eliminates risks and costs associated Stromal ulcers may have inflammatory MMP-9 activity. Topical atropine may also with general anesthesia therefore, appealing cellular infiltrates within the stroma be used to prevent spasm to owners. which produce matrix metalloproteinases which alleviates ocular pain, helps prevent (MMP’s). These are enzymes that degrade anterior , and prevents formation of Stromal Ulcers the resulting in rapid posterior . A protective collar should Determining the depth of a corneal stromal collagen degradation, or collagenolysis be placed to prevent any self -trauma to ulcer is critical since surgical treatment (a “melting” ulcer) (Figure 4). When an the . Re-evaluation is recommended is usually indicated for ulcers involving ulcer becomes infected by certain with-in 24-48 hours. It is important for the deeper layers of the corneal stroma. (especially Pseudomonas spp, Staphylococcus owners to understand the severity of deep Superficial stromal ulcers typically have spp, and Streptococcus spp.) and from MMPs or progressive corneal ulceration and if the well defined margins, with minimal changes that are over-expressed by corneal epithelial ulcer does not respond well to aggressive in corneal contour and topography. cells, keratocytes and neutrophils present medical treatment, surgery (conjunctival Superficial stromal ulcers may be treated in tear film or that have infiltrated the graft) may be required to save the globe. medically and conservatively, with a topical corneal stroma, and cause destruction Depending on the size and depth of the broad spectrum antibiotic, ocular pain of the corneal extracellular matrix, ulcer, and whether vascularization of the management, and a protective collar. Re- resulting in rapid collagen degradation corneal stroma is present, a conjunctival evaluation is recommended every 3-5 days (collagenolysis) and loss of the entire graft may be necessary to provide tectonic until re-epithelialization is complete. thickness of the stroma within 4-24 support in order to prevent rupture, and If an ulcer involves the deep stroma hours. Bacteria, specifically Pseudomonas to provide a vascular supply to favor or greater than half corneal thickness, spp, also produce MMP which degrade healing. A conjunctival graft consists of the cornea is fragile and is at risk to corneal stromal collagen. Stromal ulcers transposing a thin layer of only conjunctival perforate—therefore it should be handled that are infected and “melting” will have membrane tissue onto the cornea to provide carefully. It is critical to avoid placing gelatinous margins and the stroma may tectonic support and to provide a vascular any external pressure on the eye that have a mucoid appearance that may remain tissue supply to aid in healing. Surgically might cause the eye to rupture. If an ulcer attached to the cornea and may not be transposing a vascular supply (conjunctival is progressive, regardless of whether the easily removed (Figures 5 and 6). Treatment graft) to the ulcer also provides leukocytes stromal ulcer is superficial or deep, the ulcer with a topical antibiotic that penetrates and antibodies to provide antimicrobial should be treated aggressively, as this is into corneal tissue (a fluoroquinolone) is and anti-collagenase effects, as well as potentially a vision and globe threatening recommended every hour in an attempt delivers systemic antibiotics to the site. abnormality. If the ulcer is non progressive to cease bacterial infection. Doxycycline Third eyelid flaps are never recommended (e.g., collagenolysis [“melting”] is not or minocycline administered orally have and are contraindicated for treatment of evident) and uncomplicated (e.g., there the property to stop collagenolysis (e.g. infected, deep or complicated ulcers since are no cellular infiltrates in the cornea), “melting”) by impairing MMP-2 and they prevent direct visualization and re-

Figure 4: An image of a “melting” corneal Figure 5: An image of a corneal ulcer with Figure 6: An image of a protruding corneal bulla (a ulcer. Note deep neovascularization completely (a “melting” corneal ulcer). The blister) that is retaining fluorescein dye. This must surrounding the ulcerated cornea with degenerated corneal epithelium has been lost and the stroma, be differentiated from a protruding descemetocele stromal collagen which masquerades as a mucoid which is composed of collagen, has degenerated. which will not retain fluorescein dye. Corneal bullae discharge. are treated medically, whereas descemetocele requires surgical repair. 16 | THE NAVTA JOURNAL | NAVTA.net Veterinary NURSING EDUCATION

evaluation of the healing process. Placing a anesthetic risks, etc) the eye is very fragile third eyelid flap can also induce unnecessary and is at risk for perforation. If perforation pressure on the globe, which can result in does not occur, later in the healing process perforation of a deep stromal ulcer or a corneal epithelium migrates over the descemetocele. corneal stroma and Descemet’s membrane A descemetocele is a deep ulcer in which and forms a corneal facet (divot). This will the corneal stroma is completely absent be evident in the corneal stroma, but since and Descemet’s membrane is exposed. corneal stroma and Descemet’s membrane Descemet’s membrane will not stain positive are covered by corneal epithelium, with fluorescein dye, as there is no stroma fluorescein dye will not be retained. A Figure 7: An image of a cornea with a present in that area to retain fluorescein dye. “pooling” effect of fluorescein dye within descemetocele with loss of corneal stromal collagen. A descemetocele will have an excavated, the facet will occur, but can be washed crater-like appearance, indicating loss of away. A facet requires no treatment and will stromal tissue. However, the deepest portion continue to fill in overtime. of the ulcer (Descemet’s membrane) will appear clear (it will lack corneal edema) Medication Recommendations or will appear black over the . Note for Corneal Ulcers that the periphery of the ulcer where Ulceration of the cornea eliminates the corneal stromal tissue is present will retain corneal epithelium (barrier) and permits fluorescein dye as long as the stroma in surface bacterial attachment to the this location has not epithelialized, and corneal stroma—a necessary requisite to will appear as a “target” (Figures 7 and 8). establishing bacterial infection. Despite A descemtocele requires surgery for the corneal stromal exposure, most corneal highest success rate at saving vision. Surgical ulcers are not infected. Only two indications placement of multilaminar collagen matrix exist for administering a topical antibiotic (BioSist) with an onlay conjunctival graft when corneal ulceration exists: 1) to may be required in order to seal the tissue prevent infection from occurring, or 2) and provide vascularization to the area to treat infection. The difference between (Figures 8 and 9). When the defect occurs preventing infection and treating infection within the visual axis, and if adequate is vastly different regarding the selection normal corneal tissue is located adjacent of an appropriate topical antibiotic. Some to the ulcerated area, corneoconjunctival topical antibiotics are more toxic to the Figure 8: An image of a descemetocele stained lamellar transposition can be performed corneal epithelium and delay wound with fluorescein dye. Note the corneal stroma to restore a clear visual axis. Third eyelid healing (gentamicin, ciprofloxacin) retaining fluorescein dye and absence of fluorescein dye retention by exposed Descemet’s flaps are never indicated and often result whereas others are far less toxic and membrane. Exposed corneal stroma also retains in perforation of the globe. When a minimally delay corneal wound healing tear fluid, resulting in corneal edema. descemetocele has perforated, tissue (tobramycin, ofloxacin). When an ulcer may prolapse through the defect and is not infected or complicated, a broad- and/or fibrin may be present in spectrum topical antibiotic that does not the anterior chamber. Prolapsed iris tissue penetrate into corneal tissue (tobramycin, may require amputation before proceeding bacitracin-polymyxin-gramacidin) is with multilaminar collagen matrix and recommended to prevent infection. When placement of a conjunctival graft. Post- an ulcer is complicated or infected, a operative medications should include topical topical antibiotic that penetrates deep into and systemic antibiotics, and systemic non- corneal stromal tissue is recommended steroidal anti-inflammatories (NSAID) and (ofloxacin, marbofloxacin). Treatment of a analgesics. The pet must wear a protective corneal ulcer with a topical antibiotic will Figure 9: A descemetocele which is protruding. collar at all times and re-evaluation is not speed re-epithelialization or healing; This occurs when Descemet’s membrane is pushed outward by . Debriding an typically within 1 to 5 days. If surgery is likewise, changing topical antibiotic ulcer with a descemtocele can result in perforation not an option (due to budget constraints or treatment because an ulcer has not healed of the globe and expulsion of aqueous humor and anterior uveal tissues.

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will also not speed healing. Use of topical corticosteroids or topical anesthetics to treat a corneal ulcer is never advised and Let’s Review... is unequivocally contraindicated. Topical corticosteroids delay epithelial healing, can potentiate “melting” (collagenolysis) and cause ocular immunosuppression which can favor infection. 1. Name the layer of the cornea where a superficial ulcer occurs: Topical anesthetics can also prevent epithelial healing. In conclusion, corneal ulcers occur frequently in dogs and a. Corneal stroma although a superficial, uncomplicated ulcer may likely heal b. Tear film without medical attention, a complicated ulcer requires optimal c. Corneal epithelium knowledge and management if the affected eye is to be saved. d. Corneal endothelium Proper treatment of an ulcer requires knowledge of common causes of ulceration, expected healing times, types and severity 2. A deep divot in the cornea is observed, however of ulceration, general medical therapy for each type of ulcer, it is fluorescein negative and the patient is and knowledge of when surgery is indicated. In an ulcer that comfortable. This is because; is not healing with current medical therapy, the underlying a. Corneal epithelium has re-epithelialized over the cause may still be present or the cause of the ulcer may have deep area of ulceration and is now considered to been misdiagnosed. When an ulcer has become infected and is be a corneal facet melting, or when a superficial ulcer fails to heal, referral to a b. This is a descemetocele and requires surgical veterinary ophthalmologist is advised. The decision to refer to repair a specialist may mean the difference of preserving or restoring c. Fluorescein stain will not stain the corneal stroma vision and/or salvage of the globe. J d. This type of ulcer requires debridement

REFERENCES 3. A 10 year old boxer presents with a superficial non 1. Ramsey DT. Veterinary Ophthalmology Lecture Notes. 4th ed. healing ulcer of 3 weeks duration. This type of ulcer University Printing. 1999. requires which of the following? 2. Martin CL. Ophthalmic Disease in Veterinary Medicine. Manson Publishing Ltd; 2010 a. Medical treatment alone with a different topical antibiotic and protective collar 3. Maggs DJ, Miller PE, Ofri R. Slatter’s Fundamentals of Veterinary Ophthalmology. 4th ed. Saunders Elsevier Inc. 2008. b. A third eyelid flap 4. Gelatt KN, Gilger BC, Kern TJ. Veterinary Ophthalmology. 5th ed. John c. Corneal debridement with sterile cotton swabs Wiley & Sons Inc. 2013. 5. Spiess BM, Pot SA, Florin M, Hafezi F. Corneal collagen cross-linking d. Corneal debridement and diamond burr for the treatment of melting in cats and dogs: a pilot study. The keratotomy official Journal of the American College of Veterinary Ophthalmologists. 2014; volume 17 number 1. 4. Which type of corneal ulcer is affected negatively by MMPs? *Photo credits: David Ramsey a. A SCCED (spontaneous chronic corneal epithelial defect) b. A descemetocele SARA GRABIEL-DUNCAN, c. A “melting” corneal ulcer BS, LVT, VTS d. A corneal facet Sara Grabiel-Duncan, BS, LVT, VTS, is a Veterinary 5. Corneal debridement and/or diamond burr Technician Specialist in ophthalmology who has keratotomy should never be performed on which of been in veterinary ophthalmology exclusively the following; for over ten years. She has been a Licensed a. A deep complicated ulcer Veterinary Technician since 2010 and holds b. A young dog a Bachelor of Science degree from Michigan State University. Sara is married and has two c. A middle aged to older dog with a superficial beautiful children, a dog and two cats. She enjoys ulcer traveling, camping and hiking with her family. d. A & B

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