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Keywords:

  • bandage contact lens;
  • cornea;
  • debridement;
  • diamond burr;
  • horse;
  • nonhealing ulcer

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and method
  5. Results
  6. Discussion
  7. References

Objective

To review the signalment, clinical characteristics, and outcome of horses with nonhealing corneal ulcers treated with diamond burr debridement (DBD); and to evaluate the role of ulcer duration, size and location, and bandage contact lens (BCL) placement on healing.

Animals

From January 2012–April 2013, 60 horses were diagnosed with ulcers classified as nonhealing based on the presence of raised epithelial margins and duration of at least 7 days.

Procedure

Retrospective record review.

Results

Average age of included horses was 14.68 years, SD 8.17 years. There were three times as many males (45) as females (15), (inline image = 15, P = 0.001). Forty-eight horses (80%) had nonhealing ulcers uncomplicated by associated corneal disease. In the remaining horses, associated corneal disease included esinophilic keratitis (10%), calcific band keratopathy (5%), endothelial decompensation (1.67%), habronemiasis(1.67%), and lid suture abrasion (1.67%). Average corneal ulcer duration prior to diamond burr debridement (DBD) was 29.0 days (n = 56). Ulcers occurred most commonly in the axial cornea (41%). Fifty-five of 60 horses (92%) healed with DBD. Healing time, defined as time to epithelialization following DBD, averaged 15.5 days, SD 9.32 days, and was not correlated with patient age or ulcer duration, location, or size prior to or following DBD. Healing time was significantly longer for eyes in which a BCL had been placed (n = 28, 19.0 days) than for eyes without a BCL (n = 32, 12.9 days), F(1,58) = 5.543, P = 0.02. DBD was considered a failure for five horses (8%).

Conclusions

DBD may be an effective treatment for nonhealing corneal ulcers in horses.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and method
  5. Results
  6. Discussion
  7. References

Spontaneous chronic corneal epithelial defects have been well described in the dog.[1-3] In affected patients, these corneal defects are characterized by varying degrees of blepharospasm, corneal ulcers with nonadherent epithelial margins, and prolonged wound healing. These corneal defects in dogs share numerous clinical features with chronic or recurrent corneal erosions in people.[4] In both canine and human patients, a plethora of treatments are available, including epithelial debridement, needle stromal puncture or grid, and superficial keratectomy, meeting with variable success rates.[4, 5]

Diamond burr debridement (DBD) has been widely advocated in the treatment of recurrent erosions in people.[6-8] Simple epithelial debridement alone may be associated with higher recurrence rates than other therapies. Stromal puncture with a needle, in either a punctate or grid pattern, may be associated with scar formation, and carries with it a risk of corneal puncture. DBD requires only inexpensive equipment, produces no scar in the cornea, and may be safer than needle stromal puncture. Like epithelial debridement and stromal puncture, DBD is easily repeated in patients that have not healed after a single procedure. Based on results of a study of 36 dogs with nonhealing ulcers, DBD with placement of a bandage contact lens (BCL) may be a safe and effective treatment of canine superficial chronic corneal erosions[9] and may be associated with a faster healing time than grid keratotomy.[10] An advantage of DBD over superficial keratectomy in canine patients is the ability to perform DBD without general anesthesia. Other advantages in dogs are similar to those reported in people. Histological evaluation of DBD effects in dogs showed no effect on the corneal stroma, only on the epithelium, with basement membrane involvement dependent upon duration of DBD.[11]

Nonhealing corneal ulcers have been described in horses. In a series of 23 patients that were treated with debridement, grid keratotomy, or superficial keratectomy, time to healing averaged 20 days.[12] Histologic evaluation of four keratectomy specimens from that study revealed a PAS-positive zone in the stroma without an epithelial basement membrane, consistent with the superficial acellular hyalinized stromal zone in dogs with superficial chronic corneal erosions.[12] In a more recent series of 10 patients treated with grid keratotomy,[13] average healing time is reported as 8.4 days, although this average only includes seven patients that remained hospitalized until their ulcers were fluorescein-negative, so the exact date of complete epithelialization was known. However, this average includes a healing time of 9 days for one patient that had not healed after 25 days following an initial grid keratotomy and received a second grid keratotomy, with a healing time of 9 days following the second grid. It may have been a more accurate assessment of the healing time to use 34 days as the end-point for this case, which would result in an average healing time of 12 days following the first grid keratotomy. Additionally, two cases that did not remain hospitalized until their ulcers no longer took up fluorescein stain were not included in the average healing time, because the exact healing date was not known. These two patients were noted to have been healed a recheck examination at 45 days and 35 days, respectively. Inclusion of these two patients would have resulted in an average healing time of 18 days for this study.

Nonhealing corneal ulcers can be a source of chronic pain in affected horses, and can be frustrating and expensive for clients. They are a frequent cause for referral to veterinary ophthalmologists. The safety and efficacy of DBD in horses with nonhealing corneal ulcers has not been reported. The objectives of this study were (i) to review the signalment, clinical characteristics, and outcome of horses with nonhealing corneal ulcers treated with DBD, with or without placement of a BCL; and (ii) to evaluate the role of ulcer duration, size and location on healing.

Materials and method

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and method
  5. Results
  6. Discussion
  7. References

Case selection

Horses that met the following criteria were included in this study: (i) presentation to one of Diplomate of the American College of Veterinary Ophthalmologists (DACVOs) participating in this study between January 2010 and April 2013; (ii) diagnosis by the DACVO with a nonhealing ulcer, which was defined as a corneal ulcer with raised epithelial margins and a duration of at least 7 days; and (iii) treatment by, or under the supervision of, the DACVO with a DBD, with or without placement of a BCL. Horses with evidence of corneal infection, such as the presence of bacteria or fungal hyphae on corneal cytology, were not considered candidates for DBD. Medical records of included patients were reviewed to identify signalment, presence of corneal disease associated with the ulcer, duration of ulcer at presentation, ulcer location, ulcer size prior to and following DBD, corneal cytology and culture results if performed, whether a bandage contact lens was placed, and healing time. Healing time was defined as the first recheck examination at which there was no corneal fluorescein uptake. This definition potentially overestimated healing time, as epithelialization of the corneal ulcer may have occurred at any point between the last examination at which fluorescein uptake was noted and the first examination without a positive fluorescein test. Fluorescein stain tests may have been performed by a veterinarian other than the participating veterinary ophthalmologist; in these cases, time to healing time was identified by phone or e-mail correspondence. No attempt was made to determine whether corneal ulcers recurred, whether new ulcers developed in the same patient, or whether a subsequent DBD was performed in the same patient if another corneal ulcer developed.

Patients

All patients underwent complete ophthalmic examination by one of the DACVOs participating in this study. Some but not all patients had corneal or conjunctival cytology performed, and had samples collected for bacterial and fungal culture. Bacterial isolates were subjected to antimicrobial susceptibility. The adnexa, anterior and posterior ocular segments of both eyes were examined with a Finoff transilluminator,1 slit-lamp biomicroscope,2 and with direct and indirect ophthalmoscopes.3 All patients underwent DBD under standing sedation and with topical anesthesia. Loose corneal epithelium was debrided with a cotton-tipped applicator. An Algerbrush II with a round 3.5 mm medium grit diamond pterygium chuck4 was used to perform the DBD (Fig. 1). For patients treated with BCL, a 34-mm diameter blue-tinted 74% hydrophilic lens with an 18-mm base curve was used.5

image

Figure 1. Diamond burr debridement of nonhealing ulcer.

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Statistical analysis

Due to the difference in number of cases contributed by the participating DACVOs, as well as other differences such as geographic location and practice characteristics that may have little to do with the disease process and therapy of interest, differences between each DACVO's patients in signalment, ulcer characteristics, and healing time were summarized using descriptive statistics but not analyzed using inferential statistics. For all inferential statistics, all DACVO's patients were pooled into a single sample. The distribution of healing time (in days) was tested for normalcy using a Kolmogorov–Smirnov test, using SAS UNIVARIATE.6Pearson's chi-square was calculated to assess the difference between expected and observed frequencies of males and females using SAS FREQ.7 A one-way ANOVA was calculated to assess differences in healing time between horses in which a BCL had and had not been placed using SAS GLM.8 Pearson product-moment correlations were calculated to assess the relationship between healing time and patient age, ulcer duration, and ulcer size using SAS CORR.9 For all analyses, values of < 0.05 considered significant.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and method
  5. Results
  6. Discussion
  7. References

Patients

Sixty horses were diagnosed with nonhealing ulcers by one of the participating DACVOs from January 2010 through April 2013 and underwent a single DBD procedure. Average age of included horses was 14.68 years, SD 8.17 years. There were three times as many males (44 geldings, one colt) as females (15), (inline image = 15, P = 0.001). Breeds were representative of the hospital populations, with 18 Thoroughbreds, 18 Warmbloods, 11 American Quarter Horses, four Arabians, two Appaloosas, and one each of the Mustang, Paint, Morgan, Tennessee Walking Horse, Rocky Mountain Horse, Haflinger, and Miniature Horse breeds.

Ulcer etiology and characteristics

Ulcers included in this study had a characteristic appearance with a raised epithelial margin (Fig. 2). Prior to DBD, corneal ulcers were an average of 39.5 mm2 in surface area (SD 44.0, range 1–270 mm2), and their average duration was 29.0 days (SD 35.7, range 7–180 days). Ulcer location was categorized into one of five locations: axial, temporal, nasal, inferior, and superior. Among the 58 ulcers for which corneal location was recorded, ulcers occurred most commonly in the axial cornea (24, or 41%), followed by temporal (15, or 26%), nasal (10, or 17%), inferior (9, or 16%), and superior (0). Forty-eight horses (80%) had nonhealing ulcers uncomplicated by associated corneal disease. In the remaining horses, associated corneal disease included esinophilic keratitis in six (10%), calcific band keratopathy in three (5%), and one each (1.67%) with endothelial decompensation secondary to glaucoma, habronemiasis, and suture abrasion following lid laceration repair. Following DBD, average wound size was 123.5 mm2 (SD 95.9, range 9–500 mm2).

image

Figure 2. Nonhealing ulcer.

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Medical treatment

Although treatment protocols were variable, most patients were treated postoperatively with a topical antibiotic solution twice daily, 1–2 doses of atropine solution as needed to achieve mydriasis, and a short course of oral flunixin meglumine to treat inflammation associated with the procedure. However, in some cases subpalpebral lavage catheters were placed, either because the patient was intolerant of topical medication administration, or because medical therapy was more aggressive. Patients treated more aggressively were those considered high risk for complications, such as aged horses with poor corneal sensitivity and presumed impaired healing or horses with pituitary pars intermedia dysfunction (PPID) that may have impaired ability to fight infection, or patients for whom a complication in the affected eye had grave implications, such as a horse with only one eye.

Healing time

Fifty-five of 60 horses (92%) healed following DBD, without complication or adjunctive treatment. Healing time, defined as time to epithelialization following DBD, for these 55 horses averaged 15.5 days, SD 9.3 days, and was not correlated with patient age, ulcer duration, ulcer location, or ulcer size prior to or following DBD. Healing time was significantly longer for the 28 eyes in which a BCL had been placed (19.0 days) than for the 32 eyes without a BCL (12.9 days), F(1,58) = 5.543, P = 0.02 although horses with a BCL were subjectively more comfortable following DBD.

Due to the small number of horses that had developed nonhealing ulcers associated with underlying corneal disease or mechanical trauma (12/60, or 20%), and because these accompanying conditions were quite different from each other, healing time for these patients was recorded but not analyzed as a distinct group. Of the twelve horses treated with DBD that had associated corneal disease, healing time was longer than the mean of 15.5 days only for the six horses with esinophilic keratitis (19.0 days). Three horses with calcific band keratopathy healed in 13.7 days. The horse with endothelial decompensation secondary to glaucoma healed in 10 days, and the horse with habronemiasis healed in 13 days. The horse with a corneal abrasion following lid laceration repair developed complications that led to enucleation, resulting in classification of DBD as a failure for her.

DBD was considered a failure for five horses total (8%), whose healing times were not included in calculations involving healing time. The first case was a 20 year old Quarter Horse gelding with PPID that was enucleated after failure to heal 14 days following DBD. Prior to DBD in this patient, corneal cytology revealed only epithelial cells and corneal culture was negative for bacteria or fungi. Three weeks following DBD, this patient developed increased ocular pain evidenced by severe blepharospasm and epiphora. Corneal cytology and culture were again negative for infectious agents. Enucleation was elected due to economic constraints, as well as due to humane concerns about chronic pain and poor wound healing in an aged horse with PPID retired to pasture who would likely tolerate loss of an eye. The time that would have been required for his ulcer to heal was therefore unknown. The second case was a 10 year old Warmblood gelding who was diagnosed with fungal keratitis based on cytology 8 days following DBD, following progression of the ulcer and with a report of the horse rubbing his eye repeatedly. Cytology and culture had not been performed prior to DBD. Healing time was not recorded for this patient. The third case was a 15-year-old Arabian mare that was treated with systemic dexamethasone for skin allergies for 5 weeks following DBD, at which point dexamethasone was discontinued. Cytology and culture had not been performed prior to DBD for this patient. This mare healed by granulation rather than just re-epithelialization after an extended period, 25 days after discontinuation of systemic dexamethasone and 60 days post-DBD. The fourth case was an 8-year-old Thoroughbred gelding that had not healed by 11 days following DBD and underwent a superficial keratectomy combined with amnion graft. His cornea was fluorescein negative 16 days following amnion graft, which was 27 days following DBD. Cytology and culture had not been performed prior to DBD for this patient. The fifth patient for whom DBD was considered a failure was a 3-year-old Miniature Horse mare that underwent DBD for a nonhealing ulcer caused by corneal contact with a suture placed to repair an eyelid laceration. Cytology and culture had not been performed prior to DBD for this patient. This mare's corneal ulcer progressed to perforation, and the affected globe was enucleated.

Cytology and culture results

Thirty-six of the 60 patients had corneal or conjunctival cytology performed, and 26/60 had samples collected for bacterial and fungal culture, at the discretion of the participating DACVO. Two aged horses, a 26-year-old Thoroughbred gelding with a healing time of 7 days and a 21-year-old Thoroughbred gelding with a healing time of 32 days, had bacterial cocci noted on corneal cytology, and both of these horses had bacterial growth, both Enterococcus species, on corneal culture. Both horses had comorbidities with pituitary pars intermedia dysfunction. No other horses had findings other than epithelial cells on corneal cytology. One 2-year-old Thoroughbred filly previously diagnosed with eosinophilic keratitis grew a Penicillium species on corneal culture but healed in 14 days. No other horses had growth of bacterial or fungal organisms on corneal culture. Due to the small number of horses with bacteria or fungi on cytology and with positive bacterial or fungal cultures, healing times for these horses were not analyzed separately.

DACVO differences

Four DACVOs participated in this study. Cases contributed by each DACVO are summarized in Table 1. Average age of patients was comparable across DACVO samples. Mean duration of ulcer prior to presentation was longer (45.2 days) for patients presenting to a university teaching hospital (MLU) than to a private ophthalmology practice (19.3 days, 15 days, and 22.4 days for TJC, TMM and CMN, respectively). The average surface area of ulcers prior to DBD varied between practices, as did the surface area of the corneal wound post-DBD. The majority of patients who underwent DBD at the university teaching hospital, 19/24, had a BCL placed following DBD, whereas few if any DBD patients had a BCL placed following DBD in the three private ophthalmology practices (6/21, 0/10, and 3/5 for TJC, TMM, and CMN, respectively). Mean healing time also varied between practices, ranging from 11 days (TMM) to 18.8 days (MLU). The longer healing time in the latter case, which correlates with increased use of BCL, may be a result of longer duration prior to DBD, or delayed return for recheck examination, in that practice.

Table 1. DACVO differences
DACVONumber casesMean age (years)Mean duration (days)Mean size pre-DBD (mm2)Mean size post-DBD (mm2)Number with BCLMean healing time (days)
  1. DBD, diamond burr debridement; BCL, bandage contact lens; DACVO, Diplomate of the American College of Veterinary Ophthalmologists.

MLU2413.445.23017119/2418.8
TJC2116.219.3551336/2114.8
TMM1013.015.0n/a540/1011.0
CMN517.622.413303/516.8

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and method
  5. Results
  6. Discussion
  7. References

Diamond burr debridement, which has shown promise as a therapy for chronic and recurrent corneal ulcers in humans and dogs, was evaluated as a therapy for horses with nonhealing corneal ulcers. Horses with evidence of corneal infection were not considered candidates for DBD. The average patient was a middle-aged gelding with an axial corneal ulcer with raised epithelial margins that had been present for about 1 month. In the majority of patients, no underlying etiology for the corneal ulcer had been identified. Diamond burr debridement was associated with a healing time of about 2 weeks.

Breed of affected horses was representative of the respective DACVO patient populations. As with canine patients, chronic corneal ulceration in horses appears to be a disease of middle-aged to aged patients, with an average age of 14.68 years. There was an increased incidence of chronic corneal ulcers in male horses in this study, inconsistent with the slightly increased incidence of recurrent erosions in female humans.[4] No sex predisposition has been reported in dogs. The cause of the increased incidence of chronic corneal ulcers in male horses in this study is unknown, although it may simply represent a hospital sampling bias.

Healing time following DBD was not correlated with ulcer location, which was most commonly axial, with duration, or with size. Placement of a BCL was the only factor significantly related to healing time, with ulcers treated with a BCL taking significantly longer to heal. It is not clear that the presence of the BCL was causative in this relationship. At least two other factors confounded this result: BCLs were more likely to be placed in ulcers having a nonhealing ulcer for a longer duration than ulcers without BCLs, and BCLs were more likely to be placed following DBD performed at a University teaching hospital (by MLU). It is possible that longer duration prior to seeking treatment by a DACVO was associated with longer duration to return for recheck examination, artifacts reflecting bias of the clientele or availability of appointments in the university hospital, rather than a true delay in time to healing.

In the present study, three horses had previously been diagnosed with pituitary pars intermedia dysfunction (PPID). Pituitary pars intermedia dysfunction, commonly known as Equine Cushing's Syndrome, is a disease of aged horses that is associated with decreased corneal sensitivity.[14] Pituitary pars intermedia dysfunction, caused by a pituitary adenoma, is the most common endocrine disorder in horses, and is characterized clinically by hirsutism. Decreased corneal sensitivity may be a mechanism underlying recurrent and chronic corneal ulceration in horses.[14] One 20-year-old Quarter Horse gelding with PPID was enucleated after failure to heal 14 days following DBD, associated with economic constraints, as well as with humane concerns about chronic pain and poor wound healing in an aged horse who would likely tolerate loss of an eye retired to pasture. Two other horses with PPID, both aged Thoroughbred geldings, had positive bacterial cultures, although healing duration was increased relative to the mean for only one of them. Horses with PPID may represent a group at increased risk for chronic corneal ulcers, and more extensive diagnostics (i.e., corneal cytology and culture) as well as more aggressive supportive care following DBD (e.g., the addition of an antifungal) may be warranted for these patients.

Chronic ulcers included in this study fit well with the classic clinical description of “nonhealing ulcer”. The axial location recorded most frequently among ulcers in this study is also the location reported to be the most sensitive,[15, 16] although healing time was not correlated with ulcer location. In some patients, nonhealing corneal ulcers were associated with another ocular condition, including esinophilic keratitis, calcific band keratopathy, habronemiasis, and endothelial decompensation associated with glaucoma. Large differences in healing time were not noted relative to the mean healing time for all patients, although the six patients with esinophilic keratitis did have the longest healing time (19.0 days). Esinophilic keratitis has been associated with extended healing time, as long as 3–4 months in one recent study,[17] suggesting that horses with esinophilic keratitis without secondary corneal infection may be candidates for DBD.

Complications of DBD, including infection and globe perforation, were rare. Four of 60 horses had evidence of corneal infection, three based on corneal cytology or culture collected prior to DBD and all of whom healed, and one who developed fungal keratitis post-DBD and for whom DBD was considered a failure. Only one ulcer treated with DBD, which had developed secondary to mechanical trauma from sutures placed to repair a lid laceration, progressed to perforation. Corneal ulcers associated with mechanical trauma may thus be poor candidates for DBD. In two patients for whom DBD was considered a failure, perceived delayed healing time was the basis for electing an alternate procedure (i.e., enucleation at 21 days post-DBD in a 20-year-old Quarter Horse gelding with PPID, and amnion graft at 10 days post-DBD in an 8-year-old Thoroughbred gelding), and thus actual healing time could not be evaluated. As already discussed for patients with PPID, diagnostic tests such as corneal cytology and culture may also be warranted for horses that are at risk for prolonged healing or complications, such as horses with esinophilic keratitis or horses with corneal ulcers secondary to mechanical trauma, and for horses for whom loss of an eye would be a significant impairment, such as one-eyed horses or horses required to have two eyes to compete, to rule out infection prior to DBD.

Based on results of this retrospective study, diamond burr debridement, with or without BCL placement, may be an effective treatment for nonhealing corneal ulcers in horses. The likelihood of recurrence following DBD is unknown, and would prove a valuable topic for a subsequent investigation.

Notes
  1. 1

    Finoff transilluminator, Heine USA, Dover, NH, USA.

  2. 2

    Slit-lamp biomicroscope, SL 15, Kowa, Tokyo, Japan.

  3. 3

    Direct and indirect ophthalmoscope, Heine USA.

  4. 4

    Algerbrush II with round 3.5 mm medium grit diamond pterygium chuck, The Alger Company, Lago Vista, TX.

  5. 5

    Equus 34, Keragenix, Carson City, NV.

  6. 6

    UNIVARIATE procedure, SAS, version 9.1, SAS Institute Inc., Cary, NC.

  7. 7

    FREQ procedure, SAS, version 9.1, SAS Institute Inc., Cary, NC.

  8. 8

    GLM procedure, SAS, version 9.1, SAS Institute Inc., Cary, NC.

  9. 9

    CORR procedure, SAS, version 9.1, SAS Institute Inc., Cary, NC.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and method
  5. Results
  6. Discussion
  7. References
  • 1
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    Lassaline-Utter M, Miller C, Wotman KL. Eosinophilic keratitis in 46 eyes of 27 horses in the Mid-Atlantic United States (2008-2012). Veterinary Ophthalmology 2013; DOI: 10.1111/vop.12076.