Keratitis In Horses Research Articles

Low-dose intravitreal injection of 4 mg preservative-free gentamicin and superficial lamellar keratectomy combined with modified Gundersen grafts to control chronic heterochromic iridocyclitis and secondary keratitis in horses.

To describe a combined treatment approach for heterochromic iridocyclitis and secondary keratitis (HIK) in horses. A total of 15 horses (16 eyes). Sixteen eyes from 15 horses (mean age 14.1 years, range 6-26 years) received low-dose (4 mg) intravitreal preservative-free gentamicin injection (IVGI) and modified Gundersen grafts with standing sedation and local anesthesia following a clinical diagnosis of HIK. Additional therapies of suprachoroidal triamcinolone (8 mg) injection, episcleral bromfenac implants, and suprachoroidal cyclosporine implants were performed in individual cases. Leptospira titers were also reported when available. The most frequent ophthalmic findings were pigmented keratic precipitates (n = 15/16 eyes, 94%), corneal edema (n = 14/16 eyes, 88%), and pigmented cells suspended in the anterior chamber (n = 7/16 eyes, 44%). Postoperative treatment generally consisted of topical and systemic NSAIDs, topical antibiotics, and a topical mydriatic agent. Complications included persistent corneal edema (7/16, 44%), corneal ulceration (6/16, 38%), graft failure requiring revision (2/16, 13%), stromal abscess (1/16, 6%), surgery site infection (1/16, 6%), and suspected retinal degeneration following IVGI (1/16, 6%). One case was enucleated 6 months after treatment (1/16, 6%). Of the 12 eyes with at least 3 months of post-treatment follow-up, 10 were comfortable and visual with static or improved symptoms of HIK. This multimodal treatment approach aims to address both the anterior uveitis and endothelial decompensation frequently seen in horses with HIK. The surgery can be performed under standing sedation. Continued evaluation and long-term follow-up is necessary in all horses with HIK.

Eosinophilic keratitis in horses in the United Kingdom

Eosinophilic keratitis in horses in the United Kingdom

Features of the clinical picture of keratitis in horses with different forms of the course of the disease.

Keratitis is a common cause of eye diseases in horses, often resulting in complete loss of vision. The purpose of this article is to study the features of the clinical picture of primary and secondary keratitis in horses, depending on the form of the course of the disease. The study was conducted in 2019 at 22 private horse breeding farms. The study involved 80 horses with keratitis, which were divided into two equal groups depending on the diagnosis of primary or secondary keratitis. The effectiveness of the therapies was compared 1, 3, and 6 months after the start of treatment. Following a 1-month therapy, only a minority of horses with primary keratitis had their eye functions fully restored, the number of horses with macula was two times higher (p ≤ 0.05), the number of horses with nebula was seven times higher (p ≤ 0.001), and leukomas were reported in most of the cases ( p ≤ 0.0001). The effectiveness of the therapy for keratitis is directly related to the peculiarities of treatment and adherence to the regimen.

Outcome of superficial keratectomy without conjunctival graft as a surgical technique for immune‐mediated keratitis in horses: Four cases

Summary This case report describes four horses with unilateral superficial or mid‐stromal immune‐mediated keratitis (IMMK) treated with a superficial keratectomy (SK) without a conjunctival graft. In two horses, the surgery was performed under general anaesthesia, and in two horses standing with sedation and local blocks. Results of this report show that SK is a viable treatment option in horses with chronic superficial and/or mid‐stromal IMMK that can even be performed in the standing, sedated horse. When sufficient corneal tissue is removed, no recurrence is to be expected in the long‐term follow‐up (up to 31 months). In two horses, healing occurred without complications. Two horses developed a secondary bacterial infection post‐operatively (Enterococcus faecalis and Staphylococcus aureus). In one case, this resulted in a pre‐perforating melting corneal ulcer necessitating conjunctival pedicle graft surgery 13 days post keratectomy. In three horses, there was no recurrence of the IMMK with a long‐term follow‐up of 6–31 months. One case showed recurrence of IMMK in the cornea region surrounding the keratectomy 9 months after surgery.

Efficacy of riboflavin/UV-A corneal phototherapy as stand-alone treatment for ulcerative keratitis in horses

The purpose of this study was to assess the efficacy of riboflavin/UV-A corneal phototherapy in comparison with topical antimicrobials for the treatment of corneal ulcers in horses. Nineteen horses with a diagnosis of corneal ulceration were randomised to receive either corneal phototherapy (11 horses) or topical antimicrobial therapy (8 horses). The corneal phototherapy consisted in the application of a riboflavin-enriched ophthalmic solution onto the cornea for 20 min followed by cornea UV-A irradiation at 30 mW/cm<sup>2</sup> for 3 min using a point-of-care UV-A device. A complete ophthalmological examination was performed at enrolment and then at day 1, 3, 7, 14, 21, 28, 35, 42, and 49 after treatment. The corneal ulcer was considered healed when the fluorescein staining was negative. The corneal phototherapy succeeded in the complete corneal wound healing in 91% cases (10/11 horses) by 12.7 ± 5.5 days. In the topical antimicrobial group, no horse showed improvement of the corneal ulceration (0/8; 0%) and two eyes had a corneal perforation. Six horses, due to an enlarged corneal lesion, underwent corneal phototherapy at day 14 and achieved complete wound healing by 17.2 ± 5.5 days in 83% cases (5/6). The corneal phototherapy was shown to be an effective and safe treatment for equine corneal ulcers.

Use of bacteriophage cocktails for ulcerative keratitis in horses, clinical and ophthalmological justification

In the presented work, the authors assessed the possibility of using the drug from bacteriophage cocktails for the treatment of ulcerative keratitis in horses. The study was carried out on 30 horses (30 eyes), which were previously treated with antibiotics empirically, which resulted in the development of complications in the form of keratolysis and corneal abscess. On admission, horses were examined using a forehead magnifier and a portable slit lamp, and the cornea was stained with fluorescein to assess the diameter and depth of the corneal ulcer. For the treatment of horses with ulcerative keratitis and their complications, a bacteriophage was prescribed 3-5 times a day, depending on the severity of the disease. After using the bacteriophage drug, the authors noted a positive dynamics of the inflammatory process in a short period of time: vascularization and the formation of a granulation barrier with further restoration of the integrity of the cornea.

Paper spray high-resolution accurate mass spectrometry for quantitation of voriconazole in equine tears.

Paper spray high-resolution accurate mass spectrometry is a fast and versatile analysis method. This ambient ionization technique enables the quantitation of xenobiotics in complex biological matrices without chromatography or conventional sample extraction. The simplicity, rapidity, and affordability of the paper spray mass spectrometry (PS-MS) method make the technique especially attractive for clinical investigations where fast and affordable sample analysis is crucial. A new PS-MS method for the quantitation of voriconazole in equine tears was developed and validated. For a concentration range of 10 to 1000ng/mL, good linearity (R2 > 0.99), inter- and intra-run precision (coefficient of variation (CV) max. 11.9%), accuracy (bias of the nominal concentration ± 13.9%), and selectivity (signal areas of the double blanks represent 0.13 ± 0.05% of the lower limit of quantitation (LLOQ) signal in equine tears) were observed. The quantitation of voriconazole was based on three product ions and calculated relative to the isotope-labeled internal standard, voriconazole-d3, which had a final concentration of 250ng/mL in the standards and samples. The matrix effect of the method showed an ionization suppression by reduction of the voriconazole response to 63.6%, 70.2%, and 81.9% for 30ng/mL, 450ng/mL, and 900ng/mL in equine tears compared with voriconazole in solvent (methanol:water, 50:50, v:v). The method was used to analyze 126 study samples collected for a pharmacokinetic study investigating a novel approach for treatment of fungal keratitis in horses. Therefore, the integrity of the sample dilution (n = 6, CV 6.90%, and bias of nominal concentration + 8.40%) and the carryover effect (increase from 0.33 ± 0.21% to 1.33 ± 0.89% of the signal of the LLOQ) was further investigated. To our knowledge, this method is the first application of PS-MS for quantitation of drug concentrations in tears from any species.

Eosinophilic keratitis in horses

Eosinophilic keratitis is an immune-mediated condition of the cornea, in which eosinophils accumulate within the superficial stroma. It is often associated with corneal ulceration. The instigating trigger for the migration...

Diagnostic Aspects of Veterinary and Human Aspergillosis.

The genus Aspergillus is composed of more than 300 species, a fraction of which are involved in animal or human infections mostly following environmental exposure. Various risk factors (i.e., immunosuppression, tuberculosis) have been recognized for human whereas for veterinary infections, unhygienic management, trauma, anatomical conformation of the skull, or suspected immunological deficiencies have been suggested. In animals, aspergillosis is mostly sporadic but in some circumstance such as infections on poultry farms may involve the whole flock. Since the high prevalence of immunosuppression in human patients has not been mirrored in veterinary medicine, and although to the best of our knowledge, no comprehensive data on the prevalence of aspergillosis in animals has been published, their epidemiology has not changed during the last decades. The impact of these infections may be economic or if they are incurable, sentimental. The objective of the first part is to describe the diagnosis of the main clinical entities caused by Aspergillus spp. in animals. It includes disseminated canine aspergillosis, canine and feline sino-nasal and sino-orbital aspergillosis, guttural pouch mycosis in horses, mycotic abortion in cattle, mycotic keratitis in horses, and avian aspergillosis. When pathogenesis and clinical aspects are relevant for diagnosis—they will be addressed as well. The second part deals with human aspergillosis, which is a multifaceted disease, manifested in a spectrum of clinical entities affecting one or more organs. Diagnosis is based on the clinical manifestation, supported and confirmed by laboratory means, involving the classical approach of demonstrating the etiological agent in the clinical specimens and in culture. Noncultural methods, such as antigen detection and/or molecular assays to detect fungal nucleic acids or protein profiles, are used as well. The isolation and identification of the fungus allows the determination of its susceptibility to antifungal drugs. Thus, antifungal susceptibility testing maybe considered as part of the diagnostic process, which is of relevance for management of the infection. In this review article, the part dealing with diagnostic aspects of aspergillosis in humans concentrates on susceptibility testing of Aspergillus spp. to antifungal drugs and drug combinations. The technologies and methods of susceptibility testing are described and evaluated.

Eosinophilic keratitis in horses

Eosinophilic keratitis has been described in horses, cats and rabbits. It can be a frustrating condition for owners, veterinarians and animals. In horses there is often a seasonal element to...

Investigation of corneal autoantibodies in horses with immune mediated keratitis (IMMK)

Immune mediated keratitis (IMMK) is primarily a non-ulcerative keratitis in horses causing intermittent ocular pain, eventually resulting in visual impairment. Affected horses typically respond to immunomodulatory treatment. However, the underlying cause of the disease remains enigmatic. The current study was undertaken to investigate the presence of autoantibodies in horses with immune mediated keratitis. Using 28 horses with IMMK and 27 healthy controls screening for serum autoantibodies against the corneal proteome using indirect immunofluorescence, one-dimensional (1DE) and two-dimensional electrophoresis (2DE) with subsequent western blot analysis was performed followed by mass spectrometric identification of bands or spots of interest. Indirect immunofluorescence did not reveal a difference in immune response towards corneal proteins between healthy horses and those with IMMK. Using western blot analysis some horses affected by IMMK (4/28) showed a single band (1D) or a single spot (2DE) (5/28) not detected in healthy controls. The corresponding spot was identified as maspin (SERPINB5), a protein responsible for the inhibition of corneal vascularisation, cell migration and cell adhesion to the extracellular matrix. Tests with a recombinant human protein commercially available did not verify blot findings, but the human protein may not be fully cross-reactive. Still, maspin might play a role in some cases of equine IMMK. Further research is needed to clarify the etiology of this disease.

ITS2 REGION-BASED MOLECULAR IDENTIFICATION OF FUNGAL PATHOGENS IN EQUINE CORNEAL ULCERATION

This study aimed to assess the utility of polymerase chain reaction (PCR) and DNA sequencing in diagnosing fungal ulcerative keratitis in horses and compare their sensitivity with conventional microbiologic techniques used in laboratories. Conjunctival swabs from 12 horses with corneal ulcerations admitted to the Veterinary Teaching Hospital, College of Veterinary Medicine, PurdueUniversity were collected for examinations. 14 conjunctival swabs were analyzed by the conventional culture method and by generic PCR using universal fungal primers to amplify the internal transcribed spacer 2 (ITS2) genetic region followed by DNA sequencing. The conventional culture method revealed that two samples exhibited fungal growth that identified as Aspergillus sp. and Penicillium sp. while three conjunctival samples contained bacterial growth which was identified as Staphylococcus intermedius, Staphylococcus epidermidis and Streptococcus zooepidemicus. Interestingly, PCR followed by DNA sequencing of the biological specimens on the swabs identified fungal pathogens in 9/14 samples and Ascomycete species in 3/14 samples. In 2/14 samples, no fungal pathogen was identified using PCR. Fungal pathogens detected included Aspergillus sp. in six eyes, Penicillium sp. in one eye, Fusarium sp. in one eye and Cladosporium sp. in one eye. Our findings demonstrate a limitation of the conventional culture method as a diagnostic tool as a fungal pathogen was detected in only two samples by this method as compared to nine samples using PCR and DNA sequencing. Therefore, PCR followed by DNA sequencing is able to identify a greater spectrum of agents including fastidious organisms or organisms present in lower numbers within mixed infections than can be identified by culture. In conclusion, PCR combined by DNA sequencing not only proved to be an effective and rapid method for the diagnosis of fungal keratitis, but was also a more sensitive diagnostic tool compared to the conventional culture method. Our findings demonstrate that PCR, in particular semi-nested PCR, is a promising tool for faster diagnoses of fungal keratitis in affected horses.

Treatment of immune‐mediated keratitis in horses with episcleral silicone matrix cyclosporine delivery devices

To describe the use of episcleral silicone matrix cyclosporine (ESMC) drug delivery devices in horses with immune-mediated keratitis (IMMK) with evaluation of tolerability and efficacy in long-term control of inflammation. Retrospective study. ESMC implants (1.2 cm length, 30% wt/wt cyclosporine (CsA) in silicone; with approximately 2 μg/day steady-state release for at least 400 days) were used. Nineteen horses (20 eyes) received two or more ESMC implants for superficial stromal (n = 9), midstromal (n = 3), or endothelial (n = 5) IMMK. Three additional horses received two or more ESMC implants for pigmentary keratouveitis (PK). Nine eyes of eight horses with superficial and five eyes of five horses with endothelial IMMK were well controlled after placement of ESMC implants (mean follow-up 176.8 and 207.2 days, respectively). Horses with midstromal IMMK and PK were not controlled with ESMC implants alone, but instead required frequent use of other medications or surgery to control the disease. The mean duration of disease prior to ESMC implantation of horses with midstromal IMMK was 495 ± 203.9 days, compared with 121.6 ± 92.7 days with superficial IMMK. ESMC implants were well tolerated by all horses without documented loss of the device. Results from this preliminary retrospective study suggest that the ESMC implants were well tolerated and associated with treatment success with superficial and endothelial IMMK, especially if placed early in the disease process. Further study is needed to determine the duration of efficacy, number of implants required, and better therapies for chronic midstromal IMMK and pigmentary keratouveitis.

Immunohistochemical and immunopathologic characterization of superficial stromal immune-mediated keratitis in horses

To describe the immunopathologic characteristics of superficial stromal immune-mediated keratitis (IMMK) immunopathologically by characterizing cellular infiltrate in affected corneas of horses. 10 client-owned horses with IMMK. Immunohistochemical staining was performed on keratectomy samples with equine antibodies against the T-cell marker CD3 and B-cell marker CD79a (10 eyes) and the T-helper cytotoxic marker CD4 and T-cell cytotoxic marker CD8 (6 eyes). Percentage of positively stained cells was scored on a scale from 0 (no cells stained) to 4 (> 75% of cells stained). Equine IgG, IgM, and IgA antibodies were used to detect corneal immunoglobulin via direct immunofluorescence (10 eyes). Serum and aqueous humor (AH) samples from 3 horses with IMMK were used to detect circulating and intraocular IgG against corneal antigens via indirect immunofluorescence on unaffected equine cornea. Percentage scores (scale, 0 to 4) of cells expressing CD3 (median, 2.35 [range, 0.2 to 3.7]; mean ± SD, 2.36 ± 1.08) were significantly greater than scores of cells expressing CD79a (median, 0.55 [range, 0 to 1.5]; mean, 0.69 ± 0.72). All samples stained positively for CD4- and CD8-expressing cells, with no significant difference in scoring. All samples stained positively for IgG, IgM, and IgA. No serum or AH samples collected from horses with IMMK reacted with unaffected equine cornea. Pathogenesis of superficial stromal IMMK included cell-mediated inflammation governed by both cytotoxic and helper T cells. Local immunoglobulins were present in affected corneas; however, corneal-binding immunoglobulins were not detected in the serum or AH from horses with IMMK.

The search for causes of nonhealing or recurrent ulcerative keratitis in horses

SummaryChronic or recurrent superficial ulcerative keratitis in horses is common and the causes of these lesions must always be searched for and identified by the clinician. Without appropriate elimination of the underlying cause, the ulcerative keratitis may not resolve, resulting in corneal scarring, decreased vision and possibly loss of the eye. Common causes of chronic or recurrent superficial ulcerative keratitis, such as infectious keratitis, should always be ruled out; however, other possible causes such as single or multiple distichiasis, should be considered.

In Vitro Evaluation of the Antibiotic Activity of Combinations of Ophthalmic Drugs Against Common Equine Ocular Pathogens

A subpalpebral lavage catheter is commonly used to administer medications in the treatment of infectious keratitis in horses. Drugs may mix in the subpalpebral lavage catheter, potentially affecting antimicrobial efficacy. The objective of this study was to determine the in vitro antimicrobial efficacy of combinations of commonly used ophthalmic preparations. An agar gel diffusion bioassay was used to determine the antibiotic activity of a number of antimicrobial, antifungal, mydriatic, and antiproteinase drug combinations. Drug mixtures were allowed to sit in a syringe at ambient temperatures and room lighting, for 1 (T1) and 6 hours (T2). The antibacterial efficacy was determined by measuring the zone of inhibition around wells containing the drug combinations after overnight incubation at 37°C and comparing them with the zone of inhibition around the antimicrobial alone. Combinations were tested against Pseudomonas aeruginosa and Streptococcus zooepidemicus. There was no significant decrease in the zone of inhibition, compared with controls, for the majority of combinations tested. Significantly smaller zones of inhibition were identified for the following combinations: (1) tobramycin, cefazolin, natamycin, and serum (T1) and (2) tobramycin, cefazolin, natamycin, serum, and atropine (T1) compared with tobramycin alone; (3) ciprofloxacin, cefazolin, natamycin (T1) compared with ciprofloxacin alone; (4) triple antibiotic ophthalmic solution (TAB) and natamycin (T6); (5) TAB, natamycin, and serum (T6); and (6) TAB, natamycin, serum, and atropine (T6) compared with TAB alone. Admixture does not affect in vitro antibacterial efficacy for the majority of ophthalmic preparations, although efficacy of TAB may be decreased compared with the drug alone.

Cornea special edition of veterinary ophthalmology

This special issue of Veterinary Ophthalmology concentrates on a seemingly straightforward tissue: the cornea. Although a relatively simple structure when compared to other ocular tissues such as the retina, the cornea compromises a huge portion of the ophthalmic diseases that we treat as veterinary ophthalmologists. Additionally, because of the cornea’s relative similarity across species, we are in a unique position as veterinary ophthalmologists to characterize spontaneous diseases in other species that can serve as models of human disease, furthering both animal and human health. In this issue, researchers and clinicians strive to improve our understanding of normal corneal homeostasis and wound healing as well as investigate new treatments of common corneal diseases. The review of integrins in normal and abnormal corneas by Dr. Renee Carter is an excellent starting point in furthering our understanding of corneal health and disease. The role of myofibroblasts in the cornea, highlighted in the review by Dr. Kathern Myrna et al., is only just beginning to be understood in humans and will likely prove to be an important factor in modulating corneal wound healing in all species. Both of these papers highlight the amount of work that still needs to be done to fully understand both the normal and diseased cornea. In this issue, we also have the first description of the anatomy of the living equine cornea using confocal microscopy, which is an exciting addition to the advanced diagnostic tools increasingly available to us to understand corneal pathology. Drs. Brian Gilger and Andy Matthew review the classification of immune mediated keratitis in horses. In this review, various forms and treatment options are described, as well as new areas of research to improve our understanding of these sometimes frustrating entities in horses. Dr. Caryn Plummer reviews the use of amniotic membrane use for ocular reconstruction, an underutilized option to improve corneal wound healing in veterinary medicine. Other papers in this issue address methodology to culture primary equine corneal cells, which should provide an excellent foundation for future wounding healing studies. In the area of corneal transplantation, work with allogenic mesenchymal stem cells demonstrates an innovative area of research to improve outcomes in all species (Wee et al.). Wee et al. also research the effect of freezing and thawing corneal prior to transplantation, a step in increasing the possible supply of donor corneas. Other papers in this issue address new treatment techniques and critically analyze success rates of treatment modalities. The practice of evidence based medicine whenever possible should be our goal in veterinary ophthalmology, in spite of the seemingly numerous obstacles placed in our way.1 One crucial element of evidence-based medicine is the peer review process. During the editing of this journal, I have been repeatedly impressed with reviewers who take time out of their busy schedules to provide thoughtful, constructive reviews. Without reviewers generously donating their time, we could not as a profession move forward. I would like to extend my thanks and congratulations to these reviewers who make the extra effort to advance the field of veterinary ophthalmology.

Nonulcerative bullous keratitis associated with Pseudomonas alcaligenes infection in a Thoroughbred mare

SummaryA 5‐year‐old Thoroughbred mare presented with an intermittently mildly painful right eye with a nonulcerative corneal opacity of several weeks' duration that had improved with topical steroids but recurred when steroids were withdrawn. Ophthalmic examination demonstrated a focal region of moderate corneal oedema and midstromal corneal infiltrate centrally but no other significant ocular abnormalities, and suggested a diagnosis of immune‐mediated keratitis. Empirical courses of both topical and systemic anti‐inflammatory drugs, both nonsteroidal and steroidal, led to initial improvement but bullous keratopathy developed when corneal oedema became profound. Due to the rapidly progressive nature of the bullous keratopathy combined with poor response to medical therapy, a keratectomy and conjunctival graft were performed under general anaesthesia. Intraoperative corneal culture of the keratectomy site grew Pseudomonas alcaligenes, a common soil and water contaminant. Histopathology of the keratectomy specimen revealed neutrophilic inflammation. Keratectomy and conjunctival graft led to resolution of ocular pain and inflammation, with an acceptable cosmetic and visual outcome. This report describes an unusual case of a nonulcerative Pseudomonas keratitis that responded well to surgical therapy, and underscores the complicated nature of nonulcerative keratitis in horses.

Immune‐mediated keratitis in horses: 19 cases (1998–2004)

The purpose of this study is to describe clinical and histologic findings, treatment, and outcome of horses with suspected immune-mediated keratitis (IMMK). Retrospective study. Nineteen horses that presented to NCSU-VTH from 1998 to 2004 with IMMK. Procedures Information retrieved from the medical records included signalment, duration of clinical signs, therapy prior to initial examination, ophthalmic abnormalities, diagnostics performed, therapy instituted, and long-term vision. Nineteen horses (22 eyes) were diagnosed with IMMK. Three distinct clinical groups were identified based on the depth of the lesion in the cornea: superficial stromal (n = 11 eyes), midstromal (n = 6 eyes), or endothelial (n = 5 eyes). Horses ranged from 5 to 19 years of age, with a mean age +/- SD of 11.9 +/- 3.6 years. Eleven horses had 12 months or greater duration of clinical signs of corneal disease prior to referral. Overall there was a mean duration of 11.8 +/- SD 8.3 months. Superficial stromal keratitis appeared as a superficial stromal cellular infiltrate with diffuse vascularization. Midstromal keratitis appeared as midstromal cellular infiltrate with mild, surrounding corneal edema and vascularization. Endothelial disease appeared as endothelial cellular infiltrate with diffuse corneal edema. In all types of IMMK, signs of uveitis or severe discomfort were not observed. Horses with superficial IMMK responded to topical medical therapy, but responded best to surgical removal of the lesion. Horses with midstromal keratitis responded to topical cyclosporine therapy. Endothelial disease was the least amenable to therapy.

Profiles of matrix metalloproteinase activity in equine tear fluid during corneal healing in 10 horses with ulcerative keratitis

Levels of tear film matrix metalloproteinases (MMPs) activity are significantly elevated in horses with ulcerative keratitis and contribute to the excessive breakdown of stromal collagen. Changes in the amount of proteolytic activity in horse tear film during corneal healing and stromal remodeling have not yet been reported, but we hypothesize they should decrease. In the present study we analyzed serial tear fluid from horses with ulcerative keratitis to identify any changes in MMP activity during corneal healing and stromal remodeling. Samples of tear fluid were obtained from both eyes of 10 horses with ulcerative keratitis on the day of admission (day 1) at the hospital and then at various time points until complete healing of the cornea. Tear film MMP2 and MMP9 activity was determined by quantitative gelatin zymography. In all cases medical treatment included topical applications of equine serum, antibiotics, atropine and systemic administration of anti-inflammatory drugs. Surgical procedures were performed in several cases on day 2 in addition to the medical treatment. The mean total MMP activity (+/- SD) measured in relative standard units (RSU) in the tear fluid of the ulcerated eye (2.44 +/- 1.44) of the 10 horses was significantly higher than the mean in the contralateral eye (0.81 +/- 0.68) (P = 0.006), on the day of admission at the VMTH. The mean MMP activity in these ulcerated eyes significantly decreased (-82.4%) between the first day of admission and the day when the ulcer had completely healed (P = 0.0002). The activity level in the healed eye (0.43 +/- 0.17) was not significantly different to the one in the contralateral eye (0.36 +/- 0.18) on the day of complete corneal healing (P = 0.374). The level of MMP activity in the contralateral eye also decreased from 0.81 +/- 0.68-0.36 +/- 0.18 but this decrease (56%) was not significant (P = 0.069). Ulcerative keratitis in horses is associated with initially high levels of tear film proteolytic activity that decrease as the ulcers heal. The success of medical and surgical treatment of the corneal ulcers is reflected by the enzyme activity in tears. In horses successful treatment does lead to a rapid reduction in tear film proteolytic activity that corresponded with the improvement in the clinical signs of corneal ulceration. Measurement of MMP activity in the tear film might represent a way to monitor the progression of corneal healing in horses with ulcerative keratitis.