Objective—To determine tear volume, turnover rate, and flow rate in ophthalmologically normal horses by use of fluorophotometry.
Animals—12 mares free of ophthalmic disease.
Procedures—2 μL of 10% sodium fluorescein was instilled onto 1 eye of each horse, and tear samples were collected via microcapillary tubes from the inferonasal conjunctival culde-sac at 0, 2, 4, 6, 10, 15, and 20 minutes after instillation. Collected tear samples were then measured for fluorescein concentrations with a computerized scanning ocular fluorophotometer. A decay curve plot of concentration changes over time was used to determine tear flow rate and volume through 2 different mathematical treatments of the data (the including method and the excluding method).
Results—Fluorescein concentration in tears decreased in a first-order manner. The including method yielded a mean tear volume of 360.09 μL, a turnover rate of 12.22%/min, and a flow rate of 47.77 μL/min. The excluding method yielded values of 233.74 μL, 13.21%/min, and 33.62 μL/min, respectively. Mean ± SD correlation coefficients for the natural logarithm of the fluorescein concentration versus time were 0.93 ± 0.12 for the including method and 0.98 ± 0.03 for the excluding method.
Conclusions and Clinical Relevance—The excluding method yielded more accurate results. A tear flow rate of 33.62 μL/min and a tear volume of 233.74 μL imply a complete recycling of the tear volume in approximately 7 minutes and suggest that increased dosing regimens or constant infusion methods for topical administration of ophthalmic drugs may be indicated when treating horses for corneal disease in which high ocular surface concentrations are needed.
Objective—To determine aqueous humor flow rate (AHFR) in an avian species by use of anterior segment fluorophotometry.
Animals—9 healthy red-tailed hawks (Buteo jamaicensis; 4 males and 5 females) that ranged from 8 months to 8 years of age.
Procedures—A protocol was developed for fluorophotometric determination of AHFR. Topical administration of 10% fluorescein was used to load the corneas, and corneal and aqueous humor fluorescein concentrations were measured approximately 5, 6.5, and 8 hours later. Concentration-versus-time plots were generated, and slopes and cornea-to-aqueous humor concentration ratios from these plots were used to manually calculate flow rates.
Results—Mean ± SD AHFRs for the right eye, left eye, and both eyes were 3.17 ± 1.36 μL/min (range, 1.67 to 6.21 μL/min), 2.86 ± 0.88 μL/min (range, 2.04 to 4.30 μL/min), and 2.90 ± 0.90 μL/min (range, 1.67 to 4.42 μL/min), respectively. The AHFRs were similar for right and left eyes. These flow rates represented a mean aqueous humor transfer coefficient of 0.0082/min, which is similar to that of mammalian species.
Conclusions and Clinical Relevance—The AHFR in red-tailed hawks was similar to that of most mammalian species, and the fractional egress was almost identical to that of other species. This information will allow a greater understanding of aqueous humor flow in avian eyes, which is crucial when evaluating diseases that affect avian eyes as well as medications that alter aqueous humor flow.
Objective—To determine aqueous humor flow rate in
clinically normal dogs, using fluorophotometry.
Animals—20 clinically normal Beagles.
Procedure—A study was performed on 5 dogs to
establish an optimal protocol for fluorophotometric
determination of aqueous humor flow rate. This protocol
then was used to measure aqueous humor flow
rate in 15 dogs. Corneas were loaded with fluorescein
by topical application, and corneal and aqueous
humor fluorescein concentrations were measured 5,
6.5, and 8 hours after application. Concentration-versus-
time plots were generated, and slopes and ratios
of the fluorescein concentration in the cornea and
aqueous humor from these graphs were used to calculate
flow rates. Calculations were performed by
use of automated software provided with the fluorophotometer
and by manual computation, and the 2
calculation methods were compared.
Results—The protocol established for the 5 dogs
resulted in semilogarithmic and parallel decay of
corneal and aqueous humor concentrations. Manually
calculated mean ± SD aqueous humor flow rates for
left, right, and both eyes were 5.58 ± 2.42, 4.86 ±
2.49, and 5.22 ± 1.87 μl/min, respectively, whereas
corresponding flow rates calculated by use of the
automated software were 4.54 ± 3.08, 4.54 ± 3.10,
and 4.54 ± 2.57 μl/min, respectively. Values for the
left eye were significantly different between the 2
Conclusions and Clinical Relevance—Aqueous
humor flow rates can be determined in dogs, using
fluorophotometry. This technique can be used to
assess pathologic states and medical and surgical
treatments that alter aqueous humor dynamics. (Am
J Vet Res 2001;62:853–858)
Objective—To evaluate effects of topical application
of a 2% solution of dorzolamide on intraocular pressure
(IOP) and aqueous humor flow rate in clinically
Procedure—The IOP was measured in both eyes of
all dogs for 3 days to determine baseline values. In a
single-dose study, 50 μl of dorzolamide or control
solution was applied in both eyes at 7:00 AM, and IOP
was measured 7 times/d. In a multiple-dose study,
dorzolamide or control solution was applied to both
eyes 3 times/d for 6 days, and IOP was measured 4
times/d during treatment and for 5 days after cessation
of treatment. Aqueous humor flow rate was measured
for all dogs fluorophotometrically prior to treatment
and during the multiple-dose study.
Results—In the single-dose study, dorzolamide significantly
decreased IOP from 30 minutes to 6 hours
after treatment. Mean decrease in IOP during this
time span was 3.1 mm Hg (18.2%). Maximal
decrease was detected 6 hours after treatment (3.8
mm Hg, 22.5%). In the multiple-dose study, dorzolamide
decreased IOP at all time points, and maximal
decrease was detected 3 hours after treatment (4.1
mm Hg, 24.3%). Mean aqueous humor flow rate
decreased from 5.9 to 3.4 μl/min (43%) after treatment
in the dorzolamide group.
Conclusions and Clinical Relevance—Topical application
of a 2% solution of dorzolamide significantly
decreases IOP and aqueous humor flow rate in clinically
normal dogs. Therefore, topical administration of
dorzolamide should be considered for the medical
management of dogs with glaucoma. (Am J Vet Res
Procedures—Medical records of dogs with primary glaucoma that underwent unilateral gonioimplant placement (in 2000 through 2008), during which a temporalis muscle fascia graft (n = 8) or porcine intestinal submucosa (1) was used to cover the implant tube as it exited the globe, were reviewed. All dogs were treated with mitomycin C in the conjunctival pocket intraoperatively and with tissue plasminogen activator immediately after surgery; 1% prednisolone acetate was applied to the implanted eye daily until failure of the implant. Medical intervention or additional surgery was performed when intraocular pressures (IOPs) were > 20 mm Hg or progressively increasing values were detected.
Results—After gonioimplant placement, IOP was controlled for a variable period in all dogs. Subsequently, IOP exceeded 20 mm Hg in 7 dogs (median postoperative interval, 326 days). Median interval to vision loss despite interventional surgery was 518 days (range, 152 to 1,220 days). Surgical intervention was necessary in 4 dogs to maintain satisfactory IOP. Implant extrusion attributable to conjunctival dehiscence or necrosis occurred in 4 dogs. At 365 days after surgery, 8 dogs retained vision, and 5 dogs retained vision throughout follow-up.
Conclusions and Clinical Relevance—In dogs with medically refractory primary glaucoma, placement of a gonioimplant appears to be effective in maintaining vision.
OBJECTIVE To evaluate the tear film osmolality and electrolyte composition in healthy horses.
ANIMALS 15 healthy adult horses.
PROCEDURES Each horse was manually restrained, and an ophthalmic examination, which included slit-lamp biomicroscopy, indirect ophthalmoscopy, and a Schirmer tear test, was performed. Tear samples were collected from both eyes with microcapillary tubes 3 times at 5-minute intervals. The tear samples for each horse were pooled, and the osmolality and electrolyte concentrations were measured. The mean (SD) was calculated for each variable to establish preliminary guidelines for tear film osmolality and electrolyte composition in healthy horses.
RESULTS The mean (SD) tear film osmolality was 283.51 (9.33) mmol/kg, and the mean (SD) sodium, potassium, magnesium, and calcium concentrations were 134.75 (10), 16.3 (5.77), 3.48 (1.97), and 1.06 (0.42) mmol/L, respectively. The sodium concentration in the tear film was similar to that in serum, whereas the potassium concentration in the tear film was approximately 4.75 times that of serum.
CONCLUSIONS AND CLINICAL RELEVANCE Results provided preliminary guidelines with which tear samples obtained from horses with keratopathies can be compared. Measurement of tear film osmolality in these horses was easy and noninvasive. The tear film concentration of divalent cations was greater than expected and was higher than the divalent cation concentrations in the tear films of rabbits and humans. These data may be clinically useful for the diagnosis and monitoring of hyperosmolar ocular surface disease in horses.
Objective—To determine the effects of topically applied 2% delta-9-tetrahydrocannabinol (THC) ophthalmic solution on aqueous humor flow rate (AHFR) and intraocular pressure (IOP) in clinically normal dogs.
Animals—21 clinically normal dogs.
Procedures—A randomized longitudinal crossover design was used. Following acquisition of baseline IOP (morning and evening) and AHFR (afternoon only) data, dogs were randomly assigned to 2 treatment groups and received 1 drop of either 2% THC solution or a control treatment (olive oil vehicle) to 1 randomly selected eye every 12 hours for 9 doses. The IOPs and AHFRs were reassessed after the final treatment. Following a washout period of ≥ 7 days, dogs were administered the alternate treatment in the same eye, and measurements were repeated.
Results—Mean ± SD IOPs in the morning were 15.86 ± 2.48 mm Hg at baseline, 12.54 ± 3.18 mm Hg after THC treatment, and 13.88 ± 3.28 mm Hg after control treatment. Mean ± SD IOPs in the evening were 13.69 ± 3.36 mm Hg at baseline, 11.69 ± 3.94 mm Hg after THC treatment, and 12.13 ± 2.99 mm Hg after control treatment. Mean IOPs were significantly decreased from baseline after administration of THC solution but not the control treatment. Changes in IOP varied substantially among individual dogs. Mean ± SD AHFRs were not significantly different from baseline for either treatment.
Conclusions and Clinical Relevance—Topical application of 2% THC ophthalmic solution resulted in moderate reduction of mean IOP in clinically normal dogs. Further research is needed to determine efficacy in dogs with glaucoma.
Objective—To determine effects of commonly used
ophthalmic antibiotics on cellular morphologic characteristics
and migration of canine corneal epithelium in
Sample Population—Corneal epithelial cells harvested
from corneas of 12 euthanatized dogs and propagated
in cell culture.
Procedure—Cells were treated with various antibiotics
after a defect was created in the monolayer.
Cellular morphologic characteristics and closure of
the defect were compared between antibiotic-treated
and control cells.
Results—Cells treated with ciprofloxacin and cefazolin
had the greatest degree of rounding, shrinkage,
and detachment from plates. Cells treated with
neomycin-polymyxin B-gramicidin and gentamicin sulfate
had rounding and shrinkage but with less
detachment. Cells treated with tobramycin and chloramphenicol
grew similarly to control cells. On the
basis of comparisons of defect circumference
between control cells and cells exposed to antibiotics,
tobramycin affected cellular migration the least.
Conclusion and Clinical Relevance—Effects of
ciprofloxacin and cefazolin on morphologic characteristics
of canine corneal epithelial cells in vitro should
be taken into consideration before using these antibiotics
for first-line of treatment for noninfected ulcers.
Of the antibiotics tested that have a primarily gramnegative
spectrum of coverage, gentamicin inhibited
corneal epithelial cell migration and had greater
cytopathologic effects than tobramycin did. For antibiotics
with a gram-positive coverage, chloramphenicol
had no cytopathologic effects on cells in comparison
to cefazolin, which caused most of the cells to shrink
and detach from the plate. Polymyxin B-neomycingramicidin
was midrange in its effects on cellular morphologic
characteristics and migration. (Am J Vet Res
Objective—To evaluate the effects of deracoxib and aspirin on serum concentrations of thyroxine (T4), 3,5,3′-triiodothyronine (T3), free thyroxine (fT4), and thyroid-stimulating hormone (TSH) in healthy dogs.
Procedure—Dogs were allocated to 1 of 3 groups of 8 dogs each. Dogs received the vehicle used for deracoxib tablets (PO, q 8 h; placebo), aspirin (23 to 25 mg/kg, PO, q 8 h), or deracoxib (1.25 to 1.8 mg/kg, PO, q 24 h) and placebo (PO, q 8 h) for 28 days. Measurement of serum concentrations of T4, T3, fT4, and TSH were performed 7 days before treatment (day −7), on days 14 and 28 of treatment, and 14 days after treatment was discontinued. Plasma total protein, albumin, and globulin concentrations were measured on days −7 and 28.
Results—Mean serum T4, fT4, and T3 concentrations decreased significantly from baseline on days 14 and 28 of treatment in dogs receiving aspirin, compared with those receiving placebo. Mean plasma total protein, albumin, and globulin concentrations on day 28 decreased significantly in dogs receiving aspirin, compared with those receiving placebo. Fourteen days after administration of aspirin was stopped, differences in hormone concentrations were no longer significant. Differences in serum TSH or the free fraction of T4 were not detected at any time. No significant difference in any of the analytes was detected at any time in dogs treated with deracoxib.
Conclusions and Clinical Relevance—Aspirin had substantial suppressive effects on thyroid hormone concentrations in dogs. Treatment with high dosages of aspirin, but not deracoxib, should be discontinued prior to evaluation of thyroid function.