Objective—To evaluate the in vitro efficacy of an ophthalmic drug combination against common corneal pathogens of horses.
Sample Population—Representative isolates of 3 bacterial and 2 fungal corneal pathogens of horses.
Procedures—Pathogens were subjected to minimum inhibitory concentration (MIC) testing of a drug combination that consisted of equal volumes of natamycin 3.33%, tobramycin 0.3%, cefazolin 5.5%, and equine serum. Proteinase inhibitory activity of the drug combination was assessed by use of a fluorescence microplate assay with gelatin and collagen I as substrates. The MICs of the drug combination were compared with those for each of the component medications and antiproteinase activity of the drug combination was compared with that of serum by use of paired t tests and a 2-way ANOVA, respectively.
Results—The drug combination was at least as effective as each medication separately for inhibiting microbial growth of all pathogens tested and was significantly more effective against B-hemolytic Streptococcus spp, Aspergillus spp, and Fusarium spp than the relevant medications separately. Serum and the drug combination both had significant antigelatinase activity, and serum had significant anticollagenase activity. Antiproteinase activity of serum was a concentration-dependent event, which enabled serum to achieve significantly greater activity than the drug combination after 3.5 and 4 hours of intubation for the gelatin and collagen I assays, respectively.
Conclusions and Clinical Relevance—Drug combinations have the attractive potential of minimizing the time, stress, and fatigue associated with topical treatment regimens consisting of multiple drugs used separately for horses with keratitis.
Objective—To determine density of corneal endothelial
cells and corneal thickness in eyes of euthanatized
Sample Population—52 normal eyes from 26 horses.
Procedure—Eyes were enucleated after horses were
euthanatized. Eyes were examined to determine that
they did not have visible ocular defects. Noncontact
specular microscopy was used to determine density
of corneal endothelial cells. Corneal thickness was
measured, using ultrasonic pachymetry or specular
Results—Mean density of corneal endothelial cells
was 3,155 cells/mm2. Cell density decreased with
age, but sex did not affect cell density. Values did not
differ significantly between right and left eyes from
the same horse. Cell density of the ventral quadrant
was significantly less than cell density of the medial
and temporal quadrants. Mean corneal thickness was
893 µm. Sex or age did not affect corneal thickness.
Dorsal and ventral quadrants were significantly thicker
than the medial and temporal quadrants and central
portion of the cornea. We did not detect a correlation
between corneal thickness and density of
endothelial cells in normal eyes of horses.
Conclusion and Clinical Relevance—Density of
corneal endothelial cells decreases with age, but
corneal thickness is not affected by age or sex in normal
eyes of horses. The technique described here
may be useful for determining density of endothelial
cells in the cornea of enucleated eyes. This is clinically
relevant for analyzing corneal donor tissue prior to
harvest and use for corneal transplantation. (Am J Vet
Objective—To determine regional and zonal variation
in sulfation patterns of chondroitin sulfate in normal
equine corneal stroma.
Sample Population—22 normal eyes from 11 horses.
Procedure—Corneas were collected within 24 hours
of death from equine necropsy specimens. After
papain-chondroitinase digestion of corneal tissue, disaccharides
ΔDi4S and ΔDi6S were quantified by use
of capillary zone electrophoresis in the superficial,
middle, and deep zones of central and peripheral
regions of the cornea.
Results—For the 2 regions combined,ΔDi6S/ΔDi4S
values were significantly lower in the deep and middle
zones, compared with that of the superficial zone.
In the central region, deep and middle zones had significantly
lower ΔDi6S/ΔDi4S values than the superficial
zone did. In the peripheral region, the deep zone
had significantly lower ΔDi6S/ΔDi4S values, compared
with superficial and middle zones. In the deep
zone, the peripheral region had significantly lower
ΔDi6S/ΔDi4S values than the central region did.
Conclusion and Clinical Relevance—Distribution
of ΔDi6S/ΔDi4S values follows a gradient across the
healthy equine cornea, being smallest in the deep and
middle zones of the central region and the deep zone
of the peripheral region. Regional and zonal differences
in the distribution of stromal ΔDi6S and ΔDi4S
may influence the role of glycosaminoglycans in
health, disease, and wound repair of the equine
cornea. (Am J Vet Res 2002;63:143–147)
Objective—To evaluate clinical characteristics and breeds affected with bacterial keratitis and compare patterns of resistance in bacterial isolates over time in dogs.
Design—Retrospective cross-sectional study.
Animals—97 dogs with bacterial keratitis.
Procedure—Dogs with bacterial keratitis were identified from teaching hospital medical records at the Universities of Tennessee and Florida during the years 1993 to 2003. Data were collected pertaining to breed, Schirmer tear test results, treatments administered at the time of initial examination, bacterial species isolated, and resistance to selected antimicrobials.
Results—66% of the dogs were brachycephalic, 54% had tear production < 15 mm/min, and 29% were receiving a corticosteroid at the time of initial examination. The most common bacteria isolated were Staphylococcus intermedius (29%), β-hemolytic Streptococcus spp (17%), and Pseudomonas aeruginosa (21%). Staphylococcus intermedius isolates had limited resistance to certain antimicrobials. More than 80% of β-hemolytic Streptococcus spp isolates were resistant to neomycin, polymyxin B, and tobramycin. Isolates of P aeruginosa were susceptible to tobramycin and gentamicin and had limited resistance to ciprofloxacin and enrofloxacin. Among bacterial species isolated, there was no evidence of development of antimicrobial resistance over time.
Conclusions and Clinical Relevance—Data suggested that administration of ciprofloxacin or a combination of a first-generation cephalosporin and tobramycin may be used in the treatment of bacterial keratitis while awaiting results of bacterial culture and susceptibility testing. Evidence suggests that current methods of medical management of bacterial keratitis are not associated with increased antimicrobial resistance.
Objective—To examine postoperative ocular hypertension
(POH) and other variables as predictors of the
risk of developing glaucoma after cataract surgery in
Animals—220 dogs that had cataract surgery.
Procedure—Medical records of 220 dogs (346 eyes)
that had extracapsular cataract removal or phacoemulsification
of cataracts were reviewed. With
respect to glaucoma development, 8 variables were
analyzed, which included development of POH,
breed, sex, age at time of surgery, eye (right vs left),
phacoemulsification time, intraocular lens (IOL) placement
(yes or no), and stage of cataract development.
Eyes developed glaucoma within 6 or 12 months of
surgery or did not have signs of glaucoma at least 6
or 12 months after cataract surgery.
Results—Of 346 eyes, 58 (16.8%) developed glaucoma
after surgery. At 6 months, 32 of 206 (15.5%)
eyes examined had glaucoma; at 12 months, 44 of
153 (28.8%) eyes examined had glaucoma. Median
follow-up time was 5.8 months (range, 0.1 to 48
months). Mixed-breed dogs were at a significantly
lower risk for glaucoma, compared with other breeds.
Eyes with IOL placement were at a significantly lower
risk for glaucoma, compared with eyes without IOL
placement. Eyes with hypermature cataracts were at
a significantly higher risk for glaucoma, compared
with eyes with mature or immature cataracts.
Conclusions and Clinical Relevance—Multiple factors
appear to contribute to the onset of glaucoma in
dogs after cataract surgery. Complications prohibiting
IOL placement during cataract surgery may lead to a
high risk of glaucoma development. (J Am Vet Med
Objective—To examine in vitro effects of various
antiproteolytic compounds on activity of matrix metalloproteinase
(MMP)-2 and -9 in the tear film of horses
with active corneal ulcers.
Sample Population—Samples of tear film obtained
from the eyes of 34 horses with active ulcerative keratitis.
Procedure—Horses were sedated, and tear samples
were collected from the lower fornix of 34 ulcerated
eyes by use of capillary tubes. The protease inhibitors
0.2% EDTA, 0.1% doxycycline, 10% N-acetylcysteine
(NAC), 0.1% solution of a modified dipeptide that contains
hydroxamic acid (ie, ilomostat), 0.1% α1-proteinase
inhibitor (PI), 0.5% α1-PI, and 100% fresh
equine serum (ES) were used to treat pooled samples.
Amount of latent and active MMP-2 and -9 was
measured by optical density scanning of gelatin
zymograms of treated and untreated tear samples.
Results—Pooled tear samples obtained from ulcerated
eyes contained the latent and active forms of
MMP-2 and -9. Compared with MMP activity in
untreated samples, total MMP activity (sum of all
bands detected) observed on the gelatin zymogram
gels was reduced by 99.4% by EDTA, 96.3% by doxycycline,
98.8% by NAC, 98.9% by ilomostat, 52.4%
by 0.1% α1-PI, 93.6% by 0.5% α1-PI, and 90.0% by
Conclusions and Clinical Relevance—We documented
that EDTA, doxycycline, NAC, ilomostat, α1-
PI, and ES inhibited MMP activity in vitro. Because
these compounds use different mechanisms to inhibit
various families of proteases in the tear film of horses,
a combination of these protease inhibitors may be
beneficial for treatment of corneal ulcers in horses.
(Am J Vet Res 2003;64:1081–1087)