A retrospective study of 30 cases of frozen lamellar corneal graft in dogs and cats

Frozen lamellar corneal grafts and nictitating membrane flaps were used in 18 dogs and 12 cats to repair deep corneal defects. In all dogs either melting corneal ulcers or descemetoceles were present. In the 12 cats, nine had either a melting corneal ulcer or descemetocele, two animals had acute bullous keratopathy, and one cat had corneal sequestrum. Initial vascularization with gradual clearing of the graft occurred during the first 45 days postoperatively. At 60 days postoperatively, all eyes were visual. Frequent postoperative complications included: focal dehiscence of the wound ( n  = 9); melting of part of the graft ( n  = 7); and pigmentation of the graft ( n  = 4). The frozen lamellar corneal graft was a very safe technique, and restored the tectonic and the optical function of the cornea. It provided the best results in corneas with nonperforating corneal defects. This technique provides poorer results when the cornea was perforated prior to surgery or during the surgical procedure.     

Lamellar keratoplasty with a graft of lyophilized acellular porcine corneal stroma in the rabbit

Objective To evaluate the efficacy of lamellar keratoplasty in the rabbit using a graft of lyophilized acellular porcine corneal stroma (APCS). Animal studied Twelve adult 2–2.5 kg Zealand white rabbits were studied. Procedure The cell components of the porcine cornea were removed by the means of enzymatic digestion, freezing, and thawing and then APCS was lyophilized. The 6.5 mm diameter APCS was implanted on a 6.0‐mm diameter keratectomy wound each of 12 rabbits. The postoperative clinical and histological evaluations were performed in the early, intermediate, and late periods. Results All corneal wounds healed. Ten of the 12 grafts of APCS were integrated completely with the receptive cornea except two grafts scraped partially off by the eyelid. The blepharospasm, ocular discharge, and edema of the cornea were marked 1 week after transplantation. New vessels invaded the graft after week 2 and regressed after week 8. The cornea became transparent gradually. The histological evaluation showed that the epithelium on the graft stratified normally post surgery. The keratocytes of the recipient grew into the graft and were proliferative at week 4. The inflammatory cells and new vessels were observed before week 8. The fibrosis in the graft was revealed at week 4 and lessened at week 8. The histological structure of the cornea after surgery was similar to the normal cornea at week 32. Conclusions APCS can recover the integrity of the rabbit's cornea and become transparent in vivo. APCS is an effective graft for lamellar keratoplasty in the rabbit.     

Rat allogeneic mesenchymal stem cells did not prolong the survival of corneal xenograft in a pig-to-rat model

Objective  Recent reports have demonstrated that mesenchymal stem cells (MSCs) can modulate/suppress immunologic responses through interactions with different immune cells. We performed this study in order to investigate the immunomodulatory effects of MSCs in corneal xenotransplantation.
Animals studied  Pig and rat.
Procedures  We orthotopically transplanted pig corneas into rats and topically applied allogeneic rat MSCs to the corneas for 2 h immediately after transplantation. Graft survival was clinically assessed using slit-lamp biomicroscopy and the median survival time (MST) was calculated. The rejected grafts were histologically examined using antibodies against CD4, CD8, CD161, and CD68. The expression of IL-2, IL-6, IL-10, and IFN-γ was also evaluated in the rejected grafts using an enzyme-linked immunosorbent assay.
Results  The survival of corneal xenografts was not significantly prolonged by MSC application (MST 10.5 days) compared with the controls (MST 9.67 days) ( P  = 0.4189). Histologically, the rejected grafts in both groups were massively infiltrated with neutrophils and macrophages. Some CD8⁺ T cells and rare NK cells were found in the rejected grafts. The levels of IL-6 and IL-10 were significantly increased in the rejected grafts from MSC-treated rats compared with the grafts from MSC-untreated rats. However, the levels of IL-2 and IFN-γ were not different between the two groups.
Conclusions  Topical application of allogeneic rat MSCs was ineffective in prolonging corneal xenograft survival in a pig-to-rat model.     

The use of porcine small intestinal submucosa for the repair of full-thickness corneal defects in dogs, cats and horses

OBJECTIVE: To evaluate the efficacy of using a porcine small intestinal submucosa (SIS) graft covered by a conjunctival flap for the surgical repair of full-thickness corneal wounds in dogs, cats and horses. PROCEDURE: All records dating from August 1999 to February 2003 from Purdue University Veterinary Teaching Hospital of patients that had undergone ophthalmic surgical procedures and received a SIS corneal graft for a full-thickness lesion were reviewed. Fifteen cases were identified including six dogs, two cats and seven horses. Requirements for inclusion in this study were that SIS was used as a corneal graft in a full-thickness corneal defect and that the graft was completely covered with a conjunctival flap. RESULTS: Of the 15 cases, one canine patient had received SIS following removal of an epibulbar melanocytoma. The remaining five canine patients had undergone this surgical procedure for the repair of corneal perforation. The two feline patients had been presented for corneal perforation following chronic ulceration. One equine patient had been presented for a deep melting ulcer, three for stromal corneal abscesses, and three for corneal perforations. Complications encountered postoperatively included aqueous leakage, conjunctival flap dehiscence, synechia, cataract and fibrin in the anterior chamber. Fourteen out of 15 patients were visual at the final re-evaluation. CONCLUSION: SIS is an inexpensive, easy-to-handle biomaterial that appears to be suitable for the repair of full-thickness corneal wounds in dogs, cats and horses. Results of our study support the conclusion that this relatively new product is an effective alternative to traditional implantation materials utilized in veterinary ophthalmology.     

Posterior lamellar keratoplasty for treatment of deep stromal absesses in nine horses

OBJECTIVE: To describe and evaluate the use of posterior lamellar keratoplasty as a surgical treatment for deep corneal stromal abscesses in horses. Animals studied Nine horses of various breeds and ages that presented with corneal stromal abscesses located in the posterior one-third of the cornea. Procedure Retrospective medical record study. RESULTS: Nine horses had deep corneal stromal abscesses that were treated with posterior lamellar keratoplasty. Median patient age was 3 years. Six patients were females and three were geldings. Medical therapy alone had been attempted prior to surgery in all nine animals. Corneal abscess culture and histopathology were performed in 8/9 horses. Cultures were positive for an infectious etiology in 4/8 (50%). Histopathology was positive for an infectious etiology in 5/8 (62.5%). Mean surgical time was 71.0 +/- 18.8 min and the average healing time was 23.7 +/- 5.2 days. Visual outcome was positive in 8/9 cases. Conclusion Posterior lamellar keratoplasty is a promising procedure for treatment of deep corneal stromal abscesses in horses. The procedure resulted in considerable shorter surgery time and healing time than had been observed with full-thickness penetrating keratoplasty. Scar formation with this procedure was not significantly different than with penetrating keratoplasty.     

Reconstruction of corneal epithelium with cryopreserved corneal limbal stem cells in a rabbit model

The integrity and transparency of the cornea plays a key role in preserving vision. This paper reports a procedure to create an artificial sheet of corneal epithelium from cryopreserved limbal stem cells (LSCs) and to use this for corneal transplantation. Corneal LSCs were isolated from biopsy specimens of rabbit limbal lamellar and cryopreserved in liquid nitrogen at 2–4 passages. The cells were grown in culture medium for 12–14 days on top of a cell-free human amniotic membrane framed on a nitrocellulose sheet. The corneal epithelium generated was transplanted into the right eyes of 14 LSC deficient (LSCD) rabbits (seven experimental animals, seven controls) with corneal damage. The seven LSCD rabbits in the experimental group were transplanted with a corneal epithelial sheet generated from the cryopreserved corneal LSCs. Four LSCD rabbits were used as the vehicle control and were transplanted with a cell-free amniotic membrane, and the remaining three LSCD rabbits were negative controls without transplantation. Over a 2-month recovery period, 2/7 animals in the experimental group recovered completely, four recovered partially and one did not respond. In the control groups, three negative controls and three vehicle controls lost their vision completely, and one of the vehicle controls partially recovered transparency of the cornea Following treatment, corneal transparency of the experimental rabbits was significantly improved compared to controls (P < 0.05). The results indicated that cryopreserved corneal LSCs can repair damaged rabbit cornea, suggesting a possible new clinical approach to reconstruction of corneal epithelium.     

Tolerance of the rabbit cornea to an n-butyl-ester cyanoacrylate adhesive (Vetbond)

Objective An n‐butyl‐ester cyanoacrylate adhesive available for veterinary surgery (Vetbond^®, 3M) was tested in rabbits for corneal irritation. Procedures Two experimental procedures were used on 24 rabbits: injection of the adhesive into an intralamellar corneal pocket (n = 10) and application of the glue to a mid‐stromal corneal defect (n = 14). In both experiments the eyes were examined for 20 days for evidence of corneal irritation and tolerance. At the end of each experiment, histopathologic studies were performed on all corneas. Results The corneal reaction to the intrastromally injected cyanoacrylate was characterized clinically by slight edema and vascularization localized to the vicinity of the adhesive. A moderate foreign body‐type reaction was found histologically. Following application of the adhesive to a central stromal defect, the treated corneas remained totally clear and histopathologic examination showed that the healing process was not altered compared to the controls. The mean retention time of the glue patch was 14 days. Conclusions Intrastromal injection and surface application to a corneal defect of n‐butyl‐ester cyanoacrylate to a corneal defect induced only a mild inflammatory response and did not interfere with the reparative process. These findings suggest that this surgical adhesive would be acceptable for treating corneal ulcerations in animals.     

The use of xenologous amniotic membrane to repair canine corneal perforation created by penetrating keratectomy

This study was performed to evaluate the use of glycerol-preserved equine amniotic membrane as replacement for full-thickness corneal defects in dogs. Eighteen mixed-breed dogs were used. A perilimbal, full-thickness, 5 mm square corneal defect was created surgically, and a donor implant of equine amniotic membrane of the same size and shape sutured in place with 10–0 nylon simple interrupted sutures. Corneal edema was observed near the implant 24 h after surgery, but was absent after 1 week. Granulation tissue and corneal vascularization superficial to the implant were noticed on postoperative day 7, but were absent on day 30. Corneal vascularization persisted until the end of the experiment. There was no fluorescein retention by postoperative day 30. There was slight clearing of the corneal implant by postoperative 30, and slight pigmentation of the donor implant observed at postoperative day 180. An acute inflammatory process as well as fibroblasts were present at early postoperative stages. At postoperative day 60 there was no inflammatory cellular infiltrate, but fibroblasts and fibrosis were present. Corneal architecture was restored at the end of the experiment, with a layering of the epithelium–stroma–debris of amniotic membrane–stroma–endothelium present, and pigmentation and vascularization present in the deep layers of the cornea. Although vascularization indicated some degree of graft rejection, the clinical and histological evidence indicates that the xenologous amniotic membrane can be useful as a tectonic graft in the repair of full-thickness lesions of the cornea of dogs.     

Acellular dermal graft for repair of abdominal wall defects in rabbits

Sixteen clinically healthy New Zealand white rabbits of either sex were divided into 2 equal groups (I and II) of 8 animals each. Under thiopental sodium (2.5%) anaesthesia a 2 x 3 cm full-thickness abdominal wall defect in the mid-ventral abdominal wall was created and repaired with an acellular dermal graft (ADG) in all the animals of group I (test group). In animals of group II (control group) a full-thickness linear midline abdominal muscular wall incision was made and repaired with a continuous suture pattern using 2-0 nylon.     

Effect of D-mannitol on feed digestion and cecotrophic system in rabbits

This study aimed to evaluate the effect of sugar alcohol as an energy source for cecal microbes on digestibility, cecotrophy (i.e. reingestion of microbial products of cecum, cecotrophs) and performance in rabbits. Thus, we fed rabbits an experimental diet that included 5% of D-mannitol, and collected hard feces and cecotrophs to be analyzed for crude protein (CP), acid detergent fiber (ADF), ether extract (EE), crude ash (CA) and dry matter (DM). Cecotrophic behavior of the rabbits was also observed. Feeding D-mannitol increased ( P  < 0.01) digestibility of ADF, resulting in a decrease ( P  < 0.05) in the concentration in hard feces. The increase ( P  < 0.05) in CP concentration was attributed to lower ( P  < 0.05) digestibility. D-mannitol had a similar modulatory effect on CP and ADF concentrations in hard feces and cecotrophs. Accordingly, estimations of the proportion of nutrients recycled by cecotrophy to dietary intake (PR), obtained by the two calculation methods, showed an increase ( P  < 0.01) in PR of CP and a decrease ( P  < 0.05) in that of ADF. Daily weight gain and feed efficiency increased ( P  < 0.05) for D-mannitol-fed rabbits, while daily feed intake decreased ( P  < 0.05). These results suggest the possibility of using D-mannitol as a stimulator of cecal microbial growth and cellulolytic activity, and therefore, improved rabbits performance.     

Radiotherapy for canine chronic superficial keratitis using soft X-rays (15 kV)

Objective  To evaluate the effect of soft X-ray therapy in the treatment of refractory chronic superficial keratitis (CSK).
Animals studied  Thirteen dogs with severe CSK, that had been refractory to prior medical and/or surgical therapy were treated with soft X-ray therapy.
Procedures  Both corneas of each dog were irradiated with soft X-rays (15 kV), to a total dose of 30 Gy, administered as two fractions over 48–96 h. Treatment was carried out under deep sedation in all dogs. Three dogs were treated by superficial lamellar keratectomy 48 h prior to radiotherapy. Changes in the extent of corneal pigmentation, pigment density and corneal vascularization were documented using a semi-quantitative grading scheme, schematic drawings and clinical photographs.
Results  Only minor, transient adverse effects of treatment, such as photophobia, epiphora and blepharitis were noted. Overall the effect of soft X-rays on the course of the keratitis was superior when compared to the effect of Sr-90 irradiation that had been determined in a previous study.
Conclusion  Soft X-ray irradiation combined with keratectomy is a safe and effective new treatment option for severe and advanced CSK with significant visual impairment due to corneal pathology.     

Comparative observation of freeze–thaw-induced damage in pig, rabbit, and human corneal stroma

Objective  Although variations exist between species with respect to outcomes after cryopreservation, little is known about the differences in the susceptibility of the corneal stroma to cryoinjury. We performed this study to investigate freeze–thaw-induced damage in keratocytes and collagen in rabbit, pig, and human corneas.
Animals studied  Rabbit, pig, and human.
Procedures  We prepared 250-μm-thick anterior stroma from rabbit, pig, and human corneas after scraping off the epithelium and endothelium. Each 250-μm-thick corneal stroma without epithelium was placed in a 50-mL tube, frozen with liquid N₂ for 15 min and taken out to thaw rapidly at 37 °C. This procedure of rapid freezing and thawing was repeated three times. Differences between the species with respect to cells and collagen structures were examined using hematoxylin–eosin (H&E) staining, terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) assay, and transmission electron microscopy (TEM). We orthotopically transplanted the pig and rabbit corneal transplants after the triple freeze–thaw cycle into rabbit eyes and evaluated graft survival.
Results  On gross examination, rabbit corneas became opaque after the triple freeze–thaw procedure, while pig and human corneas remained transparent. Histologically, keratocytes were apoptotic on TUNEL assay and TEM in rabbit, pig, and human corneas. Collagen fibrils were fragmented and the arrangement of collagen fibrils was severely disturbed in rabbit corneas on H&E staining and TEM; collagen was well preserved in pig and human corneas. Rabbit corneal stroma underwent autolysis after transplantation, whereas the pig corneal stroma remained clear for 1 month.
Conclusions  Our study showed that rabbit corneal stroma was more susceptible to freeze–thaw injury than pig and human corneas.     

Lamellar keratoplasty for the treatment of feline corneal sequestrum

A lamellar keratoplasty was used to treat corneal sequestrum in four Persian cats (six eyes). Following a superficial keratectomy, lamellar corneal allografts (feline corneal tissue) or heterografts (canine corneal tissue) which had been preserved at –20 °C were placed in the recipient cornea. All grafts became optically transparent within 2 months following surgery and no recurrences of the sequestrum have been noted during the follow-up period (4–30 months). We conclude that feline corneal sequestrum may be successfully treated with feline or canine donor corneal tissue using this technique.     

Normal features of superficial nondesquamating cells of the rabbit corneal epithelium assessed by scanning electron microscopy

Objective To quantitatively assess surface features of corneal epithelial cells with particular emphasis on regional differences in cell size or shape. Animals studied Female New Zealand White rabbits, aged 11–12 weeks. Procedures Animals were exposed to a light : dark cycle of 14 : 10 h for 2 weeks and then the corneas prepared for scanning electron microscopy (SEM) at 1500 h. Images were taken at central location (C), mid‐periphery (MP), and periphery (P) of the cornea. On prints at 5000×, cell–cell borders were marked, and long (L) and short (S) dimensions measured, and the surface ring‐shaped features outlined and counted. Results Across the epithelial surface cells had from 3 to 11 bordering cells (sides), with 5‐sided cells being more common (mean 32.7 ± 11.3%, SD). L dimensions averaged 26.7, 30.9, and 33.9 µm at the C, MP, and P locations, while S dimensions were 18.5, 21.8, and 24.0 µm, respectively. The L : S ratio was1.523, with averages of 1.567, 1.501, and 1.487 at the three locations. Using an averaged cell dimension, cell density was estimated and found to be 7376, 4405, and 3071 cells/mm² at C, MP, and P locations. Almost all cells were decorated with ring‐shaped features (craters), with the number increasing in relation to cell size and were much higher on more peripheral cells. Conclusions The non‐exfoliating corneal epithelial surface is composed of flat polygonal cells often with 5‐sides cells, which are progressively larger towards the peripheral cornea and more decorated with ring‐shaped features.     

Corneal transplantation for inflammatory keratopathies in the horse: visual outcome in 206 cases (1993-2007)

Objective To evaluate the visual outcome of three techniques of corneal transplantation surgery in treating severe inflammatory keratopathies in the horse. Design Retrospective medical records study. Animals studied Medical records of 206 horses that received corneal transplantation surgery at the University of Florida Veterinary Medical Center from 1993 to 2007 were reviewed. Procedure Data collected from the medical records included signalment, types of ocular lesions, type of transplant surgery performed, length of follow‐up, complications, and visual outcomes. Results Full thickness penetrating keratoplasty (PK) was performed in 86 horses for melting ulcers, iris prolapse/descemetoceles, and medically nonresponsive full thickness stromal abscesses (SA). Posterior lamellar keratoplasty (PLK) and deep lamellar endothelial keratoplasty (DLEK) are split thickness penetrating keratoplasties that were utilized for medically nonresponsive deep stromal abscesses (DSA) in 54 and 66 eyes, respectively. The most common postoperative surgical complication was graft rejection and varying degrees of graft opacification. Wound dehiscence and aqueous humor leakage was also a common postoperative problem. A positive visual outcome was achieved for PK, PLK, and DLEK in 77.9%, 98.1%, and 89.4%, respectively. Conclusions Corneal transplantation is a tectonically viable surgery in the horse with an overall success rate of 88.5% in maintaining vision when treating vascularized and infected corneal disease in the horse.     

Effect of bovine freeze-dried amniotic membrane (Amnisite-BA™) on uncomplicated canine corneal erosion

Objective   To evaluate the effectiveness of bovine freeze-dried amniotic membrane (FD-AM) (Amnisite-BA™) in the surgical treatment of corneal ulceration in dogs.
Animals studied   Eight normal Shih-tzu dogs.
Procedures   The corneas of 16 eyes were scored with an 8.0-mm trephine under general anesthetic and 100% ethanol was applied to remove a standardized button of corneal epithelium. The eyes were treated as described below and the corneas were evaluated 48 h later. The dogs were divided into four treatment groups: (i) control, (ii) amniotic membrane transplantation (AMT), (iii) nictitating membrane flap and (iv) contact lens. The proportion of the corneal wound that healed was calculated and all eyes were enucleated. Histological sections of cornea were assessed with the proliferating cell nuclear antigen (PCNA) assay.
Results   The proportion of corneas healed in the different treatment groups was (i) 38.02%, (ii) 89.15%, (iii) 52.31%, and (iv) 60.56%. Epithelial healing was significantly increased in the AMT group (ii) ( P  = 0.001) while groups (iii) and (iv) were not significantly different from the control group ( P  = 0.537 and P  = 0.198, respectively). The number of PCNA positive cells was (i) 275.00, (ii) 740.50, (iii) 285.75 and (iv) 420.59, these varying compared with the control group with statistical significance of (ii) P  = 0.002, (iii) P  = 0.999, and (iv) P  = 0.467. The greatest healing rate and epithelial cell proliferation was achieved with AMT compared to the other treatment regimes.
Conclusions  The results of this study show that FD-AM transplantation is an effective treatment for enhancing canine corneal wound healing and suggest that the approach will provide superior results compared to conventional treatments for the condition.     

The use of preserved equine renal capsule to repair lamellar corneal lesions in normal dogs

The purpose of this study was to evaluate the use of equine renal capsule preserved in 98% glycerine to repair lamellar corneal lesions in normal dogs. For this purpose, 12 dogs, divided into six groups ( n  = 2), were used to evaluate the 1st to 7th day, 15th day and 30th to 60th postoperative day. In order to perform the histologic study, the clinical procedures were analyzed, while the recipient's corneas were collected. The photophobia and blepharospasm also were more intense in the 1st to 7th postoperative day, and regressed in the 15th postoperative day. Therefore, the edema and the vascular events were both more frequent in the intermediary phases and regressed in the late periods. On the other hand, the morphological evaluation demonstrated an inflamatory exudate, also in the intermediary and late periods. These results suggested that the equine renal preserved capsule could be a useful alternative tissue to repair lamellar corneal lesions in dogs.     

The use of porcine small intestinal submucosa in ten cases of feline corneal disease

Porcine small intestinal submucosa (SIS) was used as a novel graft material in the management of 10 cases of feline corneal disease. Five cases had stromal ulceration associated with trauma, ocular foreign body and/or suspected infection and required a grafting procedure. Five cases had feline sequestra that were managed by a keratectomy prior to placement of SIS as a graft material. Eight eyes healed with minimal corneal scarring with a very good cosmetic and visual result. One eye with continued aqueous leakage in the immediate postoperative period required a conjunctival pedicle graft to reinforce the SIS graft site. One eye required enucleation 48 h following grafting due to progressive keratomalacia but the SIS material remained intact.     

Air assisted lamellar keratectomy for the corneal haze model

To standardize the corneal haze model in the resection depth and size for efficient corneal haze development, air assisted lamellar keratectomy was performed. The ex vivo porcine corneas were categorized into four groups depending on the trephined depth: 250 µm (G1), 375 µm (G2), 500 µm (G3) and 750 µm (G4). The stroma was equally ablated at the five measurement sites in all groups. Significant differences were observed between the trephined corneal depths for resection and ablated corneal thickness in G1 (p < 0.001). No significant differences were observed between the trephined corneal depth for resection and the ablated corneal thickness in G2, G3, and G4. The resection percentage was similar in all groups after microscopic imaging of corneal sections. Air assisted lamellar keratectomy (AK) and conventional keratectomy (CK) method were applied to six beagles, after which development of corneal haze was evaluated weekly until postoperative day 28. The occurrence of corneal haze in the AK group was significantly higher than that in the CK group beginning 14 days after surgery. Alpha-smooth muscle actin expression was significantly higher in the AK group (p < 0.001) than the CK group. Air assisted lamellar keratectomy was used to achieve the desired corneal thickness after resection and produce sufficient corneal haze.     

Superficial, nonhealing corneal ulcers in horses: 23 cases (1989-2003)

Objective To characterize superficial, nonhealing corneal ulcers in the horse and to assess the affect of age, breed, sex, inciting cause of the ulcer, and treatment on healing time of these ulcers. Design Retrospective study. Animals Twenty‐three horses with superficial, nonhealing corneal ulcerations. Procedure Medical records from 1989 to 2003 of horses diagnosed with superficial, nonhealing corneal ulcers were reviewed. Signalment, duration of clinical signs, ophthalmic abnormalities, treatment and response to treatment were recorded. Horses were treated, in addition to medical therapy, using debridement, debridement and grid keratotomy, superficial keratectomy, and superficial keratectomy with conjunctival graft placement. Results Mean age ± SD of horses was 13.7 ± 5.8 years. The mean time of presence of the corneal ulceration was 38.9 ± 21.3 days. Mean time to complete re‐epithelialization of the corneal ulcers after treatment was 20 ± 14.7 days. Horses treated with debridement alone, grid keratotomy and superficial keratectomy healed in a mean time of 15.3 ± 14.6 days, 16 ± 12.6 days, and 22.8 ± 6.7 days, respectively. Conclusions and clinical relevance Horses treated with a single debridement at initial evaluation healed in a significantly shorter time period than horses treated with grid keratotomy or superficial keratectomy. The latter two procedures may be beneficial in the treatment of nonhealing ulceration in horses, but the results of this study suggest that these procedures should only be performed following failure of the ulcer to heal after epithelial debridement.