Effects of topical ophthalmic application of 0.5% proparacaine hydrochloride on aerobic bacterial culture results for naturally occurring infected corneal ulcers in dogs

Katelyn E. Fentiman Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

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Amy J. Rankin Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

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Jessica M. Meekins Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

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James K. Roush Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

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Abstract

OBJECTIVE To evaluate the effects of topical ophthalmic application of 0.5% proparacaine hydrochloride solution (PHCL; containing 0.01% benzalkonium chloride as preservative) on aerobic bacterial culture results for naturally occurring infected corneal ulcers in dogs.

DESIGN Clinical trial.

ANIMALS 25 client-owned dogs with infected corneal ulcers (24 unilaterally affected and 1 bilaterally affected; only 1 eye included/dog) examined between June 2008 and May 2011.

PROCEDURES Swab samples for aerobic bacterial culture were collected from the periphery of each corneal ulcer before and approximately 1 minute after topical ophthalmic application of 1 drop of PHCL. Numbers of aerobic bacterial species isolated from affected eyes were compared between sample collection points and between other variables (ie, side [left or right] of affected eye, prior treatments, and patient age, sex, and neuter status).

RESULTS There was no significant difference between numbers of aerobic bacterial species isolated per eye or overall aerobic bacterial culture results (positive or negative) before versus after PHCL application. Similarly, prior treatment had no significant effect on aerobic bacterial culture results for samples collected at either point. The most commonly isolated bacteria before and after PHCL application were Staphylococcus spp (40% and 48%, respectively), followed by Streptococcus spp (23% and 22%, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE Topical ophthalmic application of PHCL did not significantly affect aerobic bacterial culture results for naturally occurring infected corneal ulcers in dogs as assessed in this study. Therefore, topical ophthalmic PHCL application could be useful in clinical settings prior to sample collection to relieve patient discomfort and to aid in sample acquisition without compromising aerobic bacterial culture results.

Abstract

OBJECTIVE To evaluate the effects of topical ophthalmic application of 0.5% proparacaine hydrochloride solution (PHCL; containing 0.01% benzalkonium chloride as preservative) on aerobic bacterial culture results for naturally occurring infected corneal ulcers in dogs.

DESIGN Clinical trial.

ANIMALS 25 client-owned dogs with infected corneal ulcers (24 unilaterally affected and 1 bilaterally affected; only 1 eye included/dog) examined between June 2008 and May 2011.

PROCEDURES Swab samples for aerobic bacterial culture were collected from the periphery of each corneal ulcer before and approximately 1 minute after topical ophthalmic application of 1 drop of PHCL. Numbers of aerobic bacterial species isolated from affected eyes were compared between sample collection points and between other variables (ie, side [left or right] of affected eye, prior treatments, and patient age, sex, and neuter status).

RESULTS There was no significant difference between numbers of aerobic bacterial species isolated per eye or overall aerobic bacterial culture results (positive or negative) before versus after PHCL application. Similarly, prior treatment had no significant effect on aerobic bacterial culture results for samples collected at either point. The most commonly isolated bacteria before and after PHCL application were Staphylococcus spp (40% and 48%, respectively), followed by Streptococcus spp (23% and 22%, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE Topical ophthalmic application of PHCL did not significantly affect aerobic bacterial culture results for naturally occurring infected corneal ulcers in dogs as assessed in this study. Therefore, topical ophthalmic PHCL application could be useful in clinical settings prior to sample collection to relieve patient discomfort and to aid in sample acquisition without compromising aerobic bacterial culture results.

Corneal ulceration is one of the most common ocular surface diseases encountered in veterinary ophthalmologic practice.1–3 Infected corneal ulcers can rapidly progress and result in loss of vision if not treated appropriately.2 Clinical signs of bacterial ulcerative keratitis include blepharospasm, purulent ocular discharge, conjunctival hyperemia, corneal edema, neovascularization, stromal loss, cellular infiltrate, malacia, and reflex anterior uveitis.1,3 When infection is suspected, the best course of treatment is commonly determined on the basis of results from corneal cytologic examination combined with bacteriologic culture and antimicrobial susceptibility testing.1–4

The cornea is innervated by the long posterior ciliary nerves, which are branches from the ophthalmic division of the trigeminal nerve. The epithelium and anterior stroma are highly innervated, making the cornea one of the most sensitive tissues in the body.3,5 To minimize discomfort and aid in sample collection, a topical anesthetic product is routinely applied prior to swab sample collection from corneal ulcers for cytologic examination or bacterial culture.

It has been proposed that commonly used topical anesthetic products may inhibit bacterial growth6–13; however, findings are varied. One study14 revealed an increase in bacterial culture yield following application of topical anesthetic products to corneas, whereas other studies7,9–13 have shown a decrease in bacterial growth in the presence of various topical anesthetic products. To the authors' knowledge, no peer-reviewed study has been reported regarding the clinical effects of topical ophthalmic PHCL application in veterinary patients with naturally occurring bacterial ulcerative keratitis.

The purpose of the study reported here was to evaluate the effects of topical ophthalmic application of PHCL on aerobic bacterial culture results for naturally infected corneal ulcers in dogs. We hypothesized that topical ophthalmic PHCL application would have no effect on numbers of aerobic bacterial species isolated or overall aerobic bacterial culture results (positive or negative) for naturally occurring infected corneal ulcers in dogs.

Materials and Methods Animals

All client-owned dogs examined by a board-certified veterinary ophthalmologist at the Veterinary Health Center of Kansas State University for an infected corneal ulcer between June 2008 and May 2011 were eligible for inclusion in the study. Dogs were included only if their owner permitted a swab sample of the ulcer to be obtained for bacterial culture. For bilaterally affected dogs, a random number generator was used to determine which eye to include in the study, such that only 1 eye of each dog was included.

Clinical procedures

All procedures conformed to the Association for Research in Vision and Ophthalmology Statement for the Use of Animals in Ophthalmic and Vision Research.15 All dogs included in the study underwent a complete ophthalmic examination, including slit-lamp biomicroscopy,a corneal fluorescein stainingb (after bacterial culture sample collected), and indirect ophthalmoscopy.c Rebound tonometryd and Schirmer tear testinge were also performed when ulcer depth did not preclude these tests, as determined by the attending veterinary ophthalmologist. A corneal ulcer was considered infected if signs of corneal stromal loss, cellular infiltrate, or malacia were detected. Data were also collected pertaining to prior treatments administered for corneal ulcers of dogs included in the study.

Aerobic bacterial cultures

All swab samples were collected prior to ophthalmic application of fluorescein dye. Special swabsf were used to collect the first sample for aerobic bacterial culture from the periphery of the corneal ulcer in each dog. Next, 1 drop of PHCLg (stored at 4°C between uses) was instilled in the affected eye. Approximately 1 minute later, a second swab sample was collected from a different area of the ulcer periphery.

Paired corneal swab samples for each dog were submitted to the bacteriology laboratory of the Kansas State Veterinary Diagnostic Laboratory for aerobic bacterial culture. Per standard protocols of the laboratory, all swab samples were applied to blood agar and MacConkey agar plates that were then incubated at 37°C in 5% CO2 overnight. After plate application, each swab sample was placed into a tube of enrichment brain-heart infusion broth that was then incubated at 37°C in 5% CO2 overnight. The following day, agar plates were evaluated for growth, and observed colonies were replated for species isolation and identification. If no growth was present on an agar plate, the corresponding sample in enrichment broth was used to inoculate blood agar and MacConkey agar plates, and the process was repeated as described.

Statistical analysis

All statistical comparisons were performed with commercially available software.h The number of bacterial species isolated from corneal swab samples from affected eyes before and after PHCL application was compared with the paired t test, whereas the independent t test was performed to compare mean numbers of isolated bacterial species at each sample collection point according to prior treatments (yes vs no), sex of the patient (male vs female), and side (left vs right) of the affected eye. In addition, effects of sex and neuter status on the number of isolated bacterial species before and after PHCL application were evaluated by ANOVA with the Newman-Keuls post hoc test, and correlations with age were evaluated through Pearson correlation analyses. Proportions of eyes with a positive aerobic bacterial culture result were compared between sample collection points with the χ2 test. For all statistical comparisons, values of P ≤ 0.05 were considered significant. Lastly, post hoc power analyses of treatment effects on numbers of isolated bacterial species were performed with an online statistical calculator.i

Results

Animals

The study included 25 dogs, of which the Pug (n = 5 [20%]) was the most commonly represented breed, followed by the Boston Terrier (3 [12%]), Shih Tzu (3 [12%]), Japanese Chin (2 [8%]), and American Staffordshire Terrier, Basset Hound, Boxer, English Bulldog, Chihuahua, Chinese Shar-Pei, Chow Chow, English Cocker Spaniel, German Shepherd Dog, Miniature Schnauzer, Pekingese, and Yorkshire Terrier (1 [4%] each). Fifteen of the 25 (60%) dogs were spayed females, 7 (28%) were castrated males, 2 (8%) were sexually intact males, and 1 (4%) was a sexually intact female. Ages ranged from 3 months to 12 years.

Of the 25 dogs, 24 (96%) dogs had a unilateral infected corneal ulcer and 1 (4%) had bilateral infected corneal ulcers. Only data pertaining to the left eye of the bilaterally affected dog were included in statistical analyses, resulting in inclusion of data for 15 (60%) right eyes and 10 (40%) left eyes.

Prior treatments

Information regarding medical treatments administered prior to initial ophthalmic examination at the Veterinary Health Center was available for 24 dogs. Twelve of the 24 (50%) dogs were not receiving antimicrobials at the time of initial examination, and 12 (50%) were receiving at least 1 topical ophthalmic antimicrobial (gentamicin [n = 1]; a combination of neomycin, polymyxin B, and bacitracin [6]; neomycin and polymyxin B in combination with dexamethasone [2]; tobramycin [4]; ciprofloxacin [1]; and cefazolin [1], alone or in combination). Four (17%) dogs were receiving an oral antimicrobial in addition to a topical antimicrobial product, including amoxicillin (27 mg/kg [12.3 mg/lb], PO, q 12 h) combined with topical gentamicin; amoxicillin-clavulanate (11 mg/kg [5 mg/lb], PO, q 12 h) combined with a topical product containing neomycin, polymyxin B, and bacitracin; ciprofloxacin (10 mg/kg [4.5 mg/lb], PO, q 12 h) combined with topical ciprofloxacin; and enrofloxacin (6 mg/kg [2.8 mg/lb], PO, q 24 h) combined with topical tobramycin.

Thirteen of 24 (54%) dogs were not receiving any anti-inflammatory medications for their corneal ulcers at the time of initial examination at the Veterinary Health Center. Eight (33%) dogs were receiving topical anti-inflammatory products, including 7 (29%) dogs treated with topical corticosteroid medications (a product containing neomycin, polymyxin B, and dexamethasone [n = 2] or prednisolone acetate [5]), 2 dogs treated with compounded topical 1% cyclosporine drops, and 1 dog treated with an NSAID (flurbiprofen). One of these 8 dogs was receiving 3 topical anti-inflammatory products (prednisolone acetate, flurbiprofen, and 1% cyclosporine) at the time of initial examination. Six dogs were receiving orally administered NSAIDs. Four of these dogs received an oral NSAID in combination with a topical antimicrobial, including meloxicam (0.07 to 0.1 mg/kg [0.03 to 0.04 mg/lb], PO, q 24 h) with a topical ophthalmic product containing neomycin, polymyxin B, and bacitracin (n = 1) or tobramycin (1); carprofen (2.2 mg/kg [1 mg/lb], PO, q 12 h) with topical cefazolin and a topical ophthalmic product containing neomycin, polymyxin B, and bacitracin (1); or firocoxib (5 mg/kg [2.3 mg/lb], PO, q 24 h) with topical tobramycin (1). Two dogs received deracoxib (2 mg/kg [0.9 mg/lb], PO, q 24 h) in combination with a topical corticosteroid (dexamethasone in an ophthalmic product also containing neomycin and polymyxin B [n = 1] or prednisolone acetate [1]).

Aerobic bacterial cultures

Corneal ulcer swab samples obtained before PHLC application yielded positive aerobic bacterial culture results for 20 of 25 (80%) eyes (11 yielded 1 bacterial species, 8 yielded 2 species, and 1 yielded 3 species) and negative aerobic bacterial culture results for 5 (20%) eyes. Samples obtained after PHLC application yielded positive results for 18 (72%) eyes (10 yielded 1 bacterial species, 7 yielded 2 species, and 1 yielded 3 species) and negative results for 7 (28%) eyes. None of the dogs with negative aerobic bacterial culture results for swab samples obtained before PHCL application had positive results of aerobic bacterial culture for corneal ulcer swab samples obtained after PHCL application. The most commonly isolated bacterial species before and after PHLC application were Staphylococcus spp (40% and 48% of all isolates, respectively), followed by Streptococcus spp (23% and 22% of all isolates, respectively; Table 1).

Table 1—

Number (%) of aerobic bacterial species isolated from corneal swab samples obtained before and approximately 1 minute after application of 1 drop of PHCL to 25 affected eyes of 25 dogs with naturally occurring infected corneal ulcers.

Bacterial speciesBefore PHCL applicationAfter PHCL application
Staphylococcus spp12 (40)13 (48)
Streptococcus spp7 (23)6 (22)
Escherichia coli2 (7)2 (7)
Pasteurella spp2 (7)1 (4)
Corynebacterium sp1 (3)1 (4)
Bacillus sp1 (3)1 (4)
Enterococcus faecalis1 (3)1 (4)
Pseudomonas aeruginosa1 (3)1 (4)
Gram negative (no ID*)1 (3)1 (4)
Enterobacter aerogenes1 (3)0 (0)
Gram positive (no ID*)1 (3)0 (0)
Total No. of isolates3027

Within each column, percentages may not total to 100% because of rounding. At least 1 bacterial species was isolated from the affected eyes of 20 (80%) dogs before PHCL application and 18 (72%) dogs after PHCL application.

No species identification (ID) was obtained.

Of the 12 dogs receiving antimicrobial products at the time of initial examination at the Veterinary Health Center, 9 had positive results of aerobic bacterial culture prior to application of PHCL, including the 2 dogs that were receiving a topical ophthalmic drug product containing neomycin, polymyxin B, and dexamethasone. Only 1 of the 4 dogs receiving both topical (tobramycin) and systemic (enrofloxacin) antimicrobial treatments had negative results on aerobic bacterial culture of corneal ulcer swab samples. All 8 dogs that received topical anti-inflammatory treatment had positive aerobic bacterial culture results prior to application of PHCL.

There was no significant (P = 0.19) difference between numbers of aerobic bacterial species isolated before (mean ± SD, 1.2 ± 0.8; range, 0 to 3) versus after (mean ± SD, 1.1 ± 0.9; range, 0 to 3) PHCL application. In addition, there was no significant (P = 0.51) difference between these sample collection points (before and after PHCL application) in proportions of dogs with a positive aerobic bacterial culture result. Further, no significant differences in the mean number of aerobic bacteria species before or after PHCL application were identified regarding ulcer treatments previously received (Table 2).

Table 2—

Mean ± SD number of aerobic bacterial species isolated per affected eye for the dogs in Table 1,* categorized according to whether dogs did or did not receive various types of treatments for their corneal ulcers prior to participation in the present study.

 Before PHCL applicationAfter PHCL application
 Prior treatmentNo prior treatment Prior treatmentNo prior treatment 
Treatment typeNo. of dogsNo. of species/eyeNo. of dogsNo. of species/eyeP valueNo. of dogsNo. of species/eyeNo. of dogsNo. of species/eyeP value
Any treatment161.3 ± 0.981.1 ± 0.80.74161.1 ± 0.981.0 ± 0.90.75
Topical antimicrobial121.2 ± 0.9121.3 ± 0.80.81121.1 ± 1.0121.1 ± 0.8> 0.99
Oral antimicrobial41.0 ± 0.8201.3 ± 0.90.6040.8 ± 1.0201.2 ± 0.90.42
Any antimicrobial121.2 ± 0.9121.3 ± 0.80.81121.1 ± 1.0121.1 ± 0.8> 0.99
Topical steroid71.3 ± 0.5171.2 ± 1.00.7871.0 ± 0.6171.1 ± 1.00.77
Oral NSAID61.0 ± 0.9181.3 ± 0.80.4960.8 ± 0.8181.2 ± 0.90.43
Any NSAID71.1 ± 0.9171.2 ± 0.80.8171.0 ± 0.8171.1 ± 0.90.77
Any topical81.3 ± 0.5161.2 ± 1.00.8781.0 ± 0.5161.1 ± 1.00.75
  anti-inflammatory
  medication

Information on prior ophthalmic treatment was available for only 24 of the 25 dogs.

Mean number of bacterial species isolated before or after PHCL application did not differ significantly (P = 0.51 and P = 0.11, respectively) with sex and neuter status. Regardless of neuter status, females had significantly fewer numbers than males after (P = 0.04) but not before (P = 0.27) PHCL application. No correlation was identified between dog age and number of bacterial species isolated before (P = 0.27) or after (P = 0.26) PHCL application. Further, no correlation was identified between side (left or right) of affected eye on number of bacterial isolates before (P = 1.0) or after (P = 0.93) PHCL application.

Discussion

Findings of the present study indicated that topical application of PHCL to eyes prior to collection of corneal swab samples from dogs with infected corneal ulcers had no significant effect on results of standard aerobic bacterial culture. These results suggested that PHCL could be topically applied prior to corneal swab sample collection without the risk of impacting aerobic bacterial culture results. This is particularly relevant to clinical practice because, in the authors' experience, most animals with infected corneal ulcers have blepharospasm, and topical anesthesia could alleviate discomfort and decrease the risk of sample contamination by accidental sample contact with the eyelids or conjunctiva.16 Additionally, in patients with considerable stromal loss, topical anesthetic application could decrease the risk of globe rupture during sample collection. To the authors' knowledge, no previous peer-reviewed report exists in the veterinary literature regarding the effects of topically applied PHCL on bacterial yields from naturally infected corneal ulcers. However, an abstractj from 2 decades ago reported findings similar to those of the present study.

The most common bacterial species isolated in the study reported here were Staphylococcus spp and Streptococcus spp. In an evaluation of 97 dogs with infected corneal ulcers, the most common species were Staphylococcus intermedius (29%), Pseudomonas aeruginosa (21%), and β-hemolytic Streptococcus spp (17%).17 Similarly in horses, infections of corneal ulcers most commonly involve Streptococcus equi zooepidemicus (33.3%), Staphylococcus spp (11.8%), and P aeruginosa (11.8%).18 It was interesting to note that there was only 1 ulcer in the present study from which P aeruginosa was isolated, and this organism may have been more common had the number of included dogs been larger.

Percentages of corneal ulcers with positive results of aerobic bacterial culture in the present study were comparable with previous findings4,19 that suggest even when a high suspicion of bacterial infection exists on the basis of clinical appearance or cytologic examination results, aerobic bacterial culture can fail to detect and identify organisms in every case. For instance, only 68.2% of infected corneal ulcers in humans had positive results of bacterial culture in 1 study.19 Furthermore, a prospective study4 evaluating the effectiveness of bacterial culture and cytologic evaluation in diagnosing clinically infected corneal ulcers in veterinary patients showed that 29 of 48 cases had positive results for bacterial culture, whereas infected corneal ulcers were diagnosed on the basis of cytologic evaluation in 6 additional animals with negative results for bacterial culture. Many factors could have contributed to decreased sensitivity of bacterial culture in these circumstances, such as antimicrobial administration prior to sample collection, failure to obtain a sample from an area that contained viable organisms, inappropriate sample handling, and failure of the culture procedures.6

Twelve of the 24 dogs for which information on previous treatment was available in the present study were receiving topical antimicrobial treatment prior to referral, and 4 of these 12 dogs were also receiving oral antimicrobials. The effects that prior treatment had on aerobic bacterial culture results for swab samples collected before and after PHCL application were evaluated in the present study, and no significant effect was detected. These findings suggested that a history of previous antimicrobial treatment may not be a justification to forego bacterial culture of corneal ulcer swab samples.

The effects of various topical anesthetic products on in vitro growth of microorganisms have been evaluated with inconsistent results. Investigators have cultured Staphylococcus albus, P aeruginosa, and Candida albicans in the presence of several topical anesthetic products and have found that PHCL did not inhibit growth of S albus or P aeruginosa but did inhibit growth of C albicans.9 Other investigators have demonstrated in vitro inhibition of S aureus, Streptococcus pneumoniae, and S intermedius by PHCL solutions7,13 and inhibited growth of S aureus and P aeruginosa in the presence of PHCL-infused paper disks.11

In addition, when the antibacterial effects of preservative-free topical anesthetic products were compared with those of common preservatives, preservative-free PHCL was shown to have no inhibitory effect on P aeruginosa or S aureus.6 However, an inhibitory effect of benzalkonium chloride (concentration not reported) on S aureus was demonstrated, and the investigators concluded that the use of preservative-free topical anesthetics may provide improved bacterial culture results.6 In the present study, the evaluated PHCL solution contained 0.01% benzalkonium chloride as a preservative; however, no significant impact on aerobic bacterial yield was identified.

The results of the present study should not be directly compared with the results of previously published in vitro studies6,7,9–11,13 because in each in vitro study, the microorganisms were cultured in the constant presence of an anesthetic drug or preservative for 18 to 48 hours. That continuous presence of anesthetic drug or preservative could have had an enhanced inhibitory effect on bacterial growth, compared with the present study in which corneal swab samples were obtained 1 minute after 1 drop of PHCL was applied, representing a clinically relevant scenario.

In a study14 evaluating bacterial isolation from healthy conjunctiva in humans, investigators found an increase in bacterial culture yield after topical anesthetic application and concluded that this was from a washout effect leading to more bacteria present in the lower conjunctival fornix. A washout effect could presumably decrease the bacterial yield of corneal swab samples owing to removal of bacteria from the corneal surface during topical PHCL application. This effect was not noted in the present study.

Topical ophthalmic application of PHCL led to a decrease in bacterial culture yield for mice with experimentally induced corneal infection in a previous study,7 in which the posttreatment sample for bacterial culture was obtained 5 minutes after PHCL application (vs 1 minute after PHCL application in the present study). Similarly, bacterial inhibition was observed for samples collected 15 minutes after PHCL application in humans.12 It is possible that exposure to PHCL for longer than 1 minute before cornel ulcer swab sample collection could decrease bacterial culture results; however, dilution by the tear film and a normal tear film turnover rate are expected to quickly reduce the amount of PHCL present in the 1 drop of product applied to the corneal surface. In the present study, an elapsed time of 1 minute following PHCL application was used because this closely mimicked the clinical timeframe between PHCL application and corneal ulcer swab sample collection and because PHCL has been demonstrated to achieve complete corneal anesthesia within 1 minute after topical ophthalmic application in dogs.20

The primary limitations of the present study were related to its clinical nature because there was no control over prior treatments and because the severity and type of infection varied among dogs enrolled. In addition, the present study evaluated the presence of aerobic bacteria, and it was possible that other types of infection (eg, fungal and anaerobic bacterial infections21–23) could have been present. In dogs with external ocular disease, fungi have been isolated from the cornea or conjunctiva in 4.6% of cases,23 and anaerobic bacteria have been found in 14% of infected corneal ulcers in dogs.21 It was also possible that some organisms responsible for the infections in the present study were more susceptible to inhibition by an anesthetic solution than others, as has been suggested by previous findings.6,7,9,11

Lastly, the small number of dogs with infected corneal ulcers included in the present study was a limiting factor. Results of post hoc power analyses performed to assess the likelihood of finding significant treatment effects on the number of aerobic bacterial species isolated from corneal swab samples indicated that sample sizes between 72 and > 22,700 affected eyes would have been needed to detect differences caused by prior treatments if such differences truly existed.

In the present study, topical ophthalmic application of 1 drop of PHCL did not significantly impact aerobic bacterial culture results for swab samples collected from naturally occurring infected corneal ulcers in a population of dogs. Therefore, we believe that topical PHCL application could be useful in a clinical setting to aid in sample acquisition without compromising aerobic bacterial culture results.

Acknowledgments

No third-party funding or support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.

ABBREVIATIONS

PHCL

0.5% proparacaine hydrochloride solution

Footnotes

a.

SL-15 slit lamp, Kowa Co Ltd, Tokyo, Japan.

b.

Ful-Glo fluorescein sodium ophthalmic strips, Akorn Inc, Buffalo Grove, Ill.

c.

Vantage Plus binocular indirect ophthalmoscope, Keeler Instruments Inc, Broomall, Pa.

d.

TonoVet, Jorgensen Laboratories Inc, Loveland, Colo.

e.

Schirmer tear test strips, Schering-Plough Animal Health Corp, Union, NJ.

f.

BactiSwab, Starplex Scientific Inc, Etobicoke, ON, Canada.

g.

PHCL with benzalkonium chloride (0.01%), Alcon Laboratories Inc, Fort Worth, Tex.

h.

WINKS SDA, version 7.0.9, TexaSoft, Cedar Hill, Tex.

i.

Power and sample size calculator, Statistical Solutions LLC, Beavercreek, Ohio. Available at: www.statisticalsolutions.net/pssTtest_calc.php. Accessed Feb 13, 2017.

j.

Champagne ES, Pickett JP. The effect of topical 0.5% proparacaine HCl on corneal and conjunctival culture results (abstr), in Proceedings. 25th Annu Meet Am Coll Vet Ophthalmol 1995;144.

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  • 1. Ollivier FJ. Bacterial corneal diseases in dogs and cats. Clin Tech Small Anim Pract 2003;18:193198.

  • 2. Whitley RD. Canine and feline primary ocular bacterial infections. Vet Clin North Am Small Anim 2000;30:11511167.

  • 3. Ledbetter EC, Gilger BC. Diseases and surgery of the canine cornea and sclera. In: Gelatt KN, Gilger BC, Kern TJ, eds. Veterinary ophthalmology. 5th ed. Ames, Iowa: Wiley-Blackwell Publishing, 2013;9761049.

    • Search Google Scholar
    • Export Citation
  • 4. Massa KL, Murphy CJ, Hartmann FL, et al. Usefulness of aerobic microbial culture and cytologic evaluation of corneal specimens in the diagnosis of infectious ulcerative keratitis in animals. J Am Vet Med Assoc 1999;215:16711674.

    • Search Google Scholar
    • Export Citation
  • 5. Kafarnik C, Fritsche J, Reese S. Corneal innervation in mesocephalic and brachycephalic dogs and cats: Assessment using in vivo confocal microscopy. Vet Ophthalmol 2008;11:363367.

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