Gonioscopy in the dog

Gonioscopy is the examination of the iridocorneal angle of the eye utilizing a corneal contact lens. The technique is extensively practised in human ophthalmology and is particularly important in the differential diagnosis of the glaucoma complex. The author has practised the technique extensively in dogs, and his findings on the appearance of the normal canine iridocorneal angle are reported in this paper.     

Pectinate ligament dysplasia and narrowing of the iridocorneal angle associated with glaucoma in the English Springer Spaniel

Objective The aim of the study was to evaluate if tonometry and gonioscopy could serve as predictors of later glaucoma development in the English Springer Spaniel, a breed prone to developing primary glaucoma. Animals studied Gonioscopy was performed on 279 English Springer Spaniel dogs, 119 males and 160 females, with clinically normal eyes. In addition, 14 dogs, five males and nine females were examined for glaucoma. Results A positive relation between pectinate ligament dysplasia (PLD) and narrowing of the relative width of the ciliary cleft (RWOCC) and also between PLD, RWOCC and age was demonstrated. The prevalence of PLD was 25.5%, which is higher than in other breeds reported. A positive association was demonstrated between PLD and glaucoma, as well as between narrowing of the RWOCC and glaucoma. Glaucoma was not observed in dogs with normal appearance of the iridocorneal angle. English Springer Spaniels related to dogs with glaucoma show more narrowing of the RWOCC and more PLD than unrelated dogs. Conclusion This study demonstrates the positive association between PLD and glaucoma, between narrowing of the iridocorneal angle and glaucoma and the effect of age on the iridocorneal angle. Mating of dogs with normal iridocorneal angles appears to reduce the presence and degree of abnormal appearance of the iridocorneal angle in the offspring. However, breeding only dogs with normal iridocorneal angles without consideration of their relationship to dogs with glaucoma is not a guarantee for preventing glaucoma in the offspring.     

Schwalbe line's cell in the normal and glaucomatous dog

Objective The canine iridocorneal angle contains an operculum, which is similar to that in nonhuman primates and consists of a peripheral extension of the inner cornea that overlies the anterior‐most portion of the corneoscleral trabecular meshwork. This region contains cells, the Schwalbe line’s (SL) cells, that have been found to have secretory and epithelial characteristics. This region of the iridocorneal angle represents the nonfiltering portion and becomes altered early during spontaneous glaucoma in the Beagle. The present study describes the SL cell for the first time in the dog and changes associated with canine primary open angle glaucoma. Procedures The iridocorneal angles from 18 Beagles with inherited glaucoma (3 months–8 years old) and 17 normal, age‐matched Beagles were placed in 10% buffered formalin for light microscopic evaluation, or 2.5% glutaraldehyde for ultrastructural evaluation. Using at least three fields from each region of the iridocorneal angle (opercular, corneoscleral, and uveal) at ×1000 magnification, trabecular cell nuclei were counted. Results The operculum in the canine iridocorneal angle consisted of the peripheral extension of the corneal endothelium and underlying anterior‐most corneoscleral meshwork, having no direct contact with the angular aqueous plexus. The SL cells associated with operculum‐retained epithelial morphology (polyhedral in shape with rER, Golgi apparatus, and secretory vesicles) in both normal, pre‐and early glaucomatous dogs. In animals with moderate and advanced stages the SL cells often became less epithelial and secretory in appearance. The number of SL cells in normal dogs declined by approximately one‐third by the end of their first year with gradual loss thereafter. In the glaucoma group the decline was more substantial and continuous through the first three years. Conclusions The SL cell is morphologically a distinct cell type within the canine iridocorneal angle that is specifically associated with the nonfiltering portion of the corneoscleral trabecular meshwork. Changes in the SL cells of the glaucomatous dog occurred with regard to age and progression of the disease.     

Incidence of canine glaucoma with goniodysplasia in Japan : a retrospective study

The incidence of primary and secondary glaucoma in dogs was investigated. A total of 1244 dogs received ophthalmologic examinations, including tonometry and gonioscopy. Goniophotographs were taken using a goniolens to evaluate the iridocorneal angle (ICA) as well as pectinate ligament (PL). The anterior width of the ciliary cleft and the total distance from the origin of the PL to the anterior corneal surface were measured from the goniophotographs. Glaucoma was diagnosed based on the cupping of the optic nerve head, clinical signs, ocular changes, and high IOP, and it was synchronized with gonioscopic grades to differentiate between primary and secondary glaucoma. We investigated 1244 dogs of 29 breeds, including the mixed breed; among these, glaucoma was diagnosed in 127 dogs (162 eyes). Of 162 eyes, primary glaucoma was diagnosed in 129 eyes and secondary glaucoma in 33 eyes. Shiba Inu dogs (42 dogs, 33%) showed the highest incidence of glaucoma, followed by Shih-Tzu (21 dogs, 16.5%). Furthermore, all the glaucomatous Shiba Inu dogs had primary glaucoma with abnormal ICA grades and dysplastic PLs. The findings of our study reveal that the Shiba Inu breed in Japan may have a hereditary predisposition to glaucoma.     

Correlation of morphologic features of the iridocorneal angle to intraocular pressure in Samoyeds.

The iridocorneal angle of the left eye was investigated in 203 Samoyeds. Comparison was made of judgements of the width of the anterior opening of the ciliary cleft when performing gonioscopy with an objective method of estimation based on measurements on goniophotographs. Results indicated high degree of correlation. Various degrees of narrowness of the iridocorneal angle width were revealed and clinical glaucoma with total-angle closure was found in 6 of 203 dogs. The intraocular pressure was significantly (P less than 0.01) higher in eyes with closed iridocorneal angles than in eyes with any other width of the angle. Appearance of the structures of the iridocorneal angle, particularly the pigment bands, indicated extensive individual variation. In approximately 25% of the eyes, dysplasia of the pectinate ligaments of variable degree existed, indicating that this anomaly is common in the Samoyed breed. Significant difference was not evident in intraocular pressure in eyes with different degrees of dysplasia of the pectinate ligaments.     

Possible association of glaucoma with pectinate ligament dysplasia and narrowing of the iridocorneal angle in Shiba Inu dogs in Japan

The purpose of the study was to describe the shape of the pectinate ligament (PL) and to estimate the width of the iridocorneal angle (ICA) in glaucomatous and non-glaucomatous eye of Shiba Inu dogs in Japan. One hundred fourteen Shiba Inu dogs were presented to the Veterinary Medical Center at the University of Tokyo between June 1998 and June 2003. Among these, 46 dogs had glaucoma; the remaining 68 dogs were presented for routine vaccinations or heartworm testing and were used as a control population. Complete ophthalmic examination and gonioscopy were performed in all the dogs. PL and ICA were evaluated by gonioscopy and goniophotographs. Of the 46 dogs with glaucoma, 17 (37%) were affected bilaterally, and 29 (63%) were affected unilaterally. Of the 29 dogs with unilateral glaucoma, the ICA of the normotensive eye was slightly narrow in 2 eyes (7%), narrow in 12 eyes (41%), and closed in 15 eyes (52%). Among the normotensive control group, the ICA was open in 13 dogs (19%), slightly narrow in 29 (43%), narrow in 22 (32%), and closed in 4 (6%). In dogs with narrow and slightly narrow ICAs, the PLs were thickened, and in some cases, formed a solid sheet. The majority of dogs with glaucoma had changes in both ICA and PL. A narrow or slightly narrow ICA was also detected in the majority of normotensive control dogs. This study suggests that ICA narrowing and PL thickening is a common abnormality in Shiba Inu dogs in Japan and may predispose those dogs to glaucoma.     

Survey of bacterial microorganisms in the conjunctival sac of clinically normal dogs and dogs with ulcerative keratitis in Fortaleza, Ceará, Brazil

OBJECTIVE: The ocular microflora in dogs has not been established in north-east Brazil. Thus, the main aim of this research was to determine the bacterial microorganisms in the conjunctival sac of clinically normal dogs and dogs with ulcerative keratitis in Fortaleza, Ceará, Brazil. ANIMALS STUDIED: This study included 60 healthy dogs, 15 dogs with unilateral corneal ulcer, and three dogs with bilateral corneal ulcers. Procedure Samples were taken by a calibrated platinum loop (1 microL) placed directly onto the conjunctival sac and on sterile blood agar. The clinical specimens were incubated at 37 degrees C in an atmosphere of 5% CO2 for 48 h. RESULTS: Of the 120 samples from healthy dogs, only 47 (39%) had positive culture for bacteria, while all of the specimens from eyes with corneal ulcer were positive for bacterial growth. The group of dogs with corneal ulcer had a higher (P < 0.05) number of colony-forming units (CFU) per plate than the group of healthy animals. Of the 59 isolates from healthy eyes, only nine (15.3%) had more than 50 CFU per plate, while in the group of dogs with corneal ulcer, 23 (62.2%) of the 37 isolates presented more than 50 CFU per plate. In both groups Gram-positive bacteria (86.5%) predominated over Gram-negative (13.5%). Staphylococcus spp. was the most frequently isolated genus and S. intermedius predominated in both groups. CONCLUSION: The results of our study are directly applicable to initiate rational, preventive and therapeutic measures with greater accuracy in dogs with corneal ulcer.     

Pectinate ligament dysplasia (PLD) and glaucoma in Flat Coated Retrievers. I. Objectives, technique and results of a PLD survey

Pectinate ligament dysplasia (PLD) in dogs is a congenital ocular abnormality affecting the iridocorneal angle, the presence of which may be associated with adult-onset primary glaucoma. This paper describes the objectives, methods and results of a survey of PLD in Flat Coated Retrievers in the UK, including the technique used for gonioscopic assessment of the degree of PLD. In a random sample of 389 Flat Coated Retrievers, 34.7% were found to have a degree of PLD. In a 'target' sample of 48 Flat Coated Retrievers (close relatives of dogs from the random sample with high degrees of PLD, or dogs presented with primary glaucoma), 83.3% were found to have a degree of PLD. The percentage of animals with a degree of PLD was only 6.0% in a 'control' sample of 100 dogs from other breeds. The relationship between PLD and canine glaucoma is discussed.     

Iridocorneal angle measurements in mammalian species: normative data by optical coherence tomography

Objective Gonioscopy provides limited quantitative information to compare the iridocorneal anatomy across different species. In addition, the anatomic relationships by histologic examination are altered during processing. As a result, the comparative anatomy of the iridocorneal angle across several mammalian species was evaluated by Optical Coherence Tomography (OCT). Methods Cats, beagle dogs, minipigs, owl monkeys, cynomolgus monkeys, and rhesus monkeys (n = 6 or 7 per species) were evaluated. Imaging was performed using the OCT. The anterior chamber angle (ACA), angle opening distance (AOD), and the angle recess area (ARA) were evaluated. Results AC angle: cat (63 ± 6°) > owl monkey (54 ± 4°) > beagle dog (42 ± 4°) > minipig (40 ± 3°) > rhesus monkey (36 ± 1°) > cynomolgus monkey (34 ± 2°). AOD: cat (3.3 ± 0.5 mm) > owl monkey (2.05 ± 0.2 mm) > beagle dog (1.08 ± 0.1 mm) > rhesus monkey (0.92 ± 0.06 mm) > minipig (0.64 ± 0.04 mm) > cynomolgus monkey (0.43 ± 0.03 mm). ARA: cat (3.5 ± 0.1 mm²) > owl monkey (1.41 ± 0.2 mm²) > dog (0.88 ± 0.1 mm²) > rhesus monkey (0.62 ± 0.06 mm²) > minipig (0.21 ± 0.05 mm²) > cynomolgus monkey (0.15 ± 0.01 mm²). Conclusions This study benchmarks the normative iridocorneal angle measurements across different mammalian species by OCT. These data can be useful to compare iridocorneal angle measurements in disease states as OCT evolves as a common diagnostic tool in veterinary ophthalmic research and practice.     

Use of thermokeratoplasty for treatment of ulcerative keratitis and bullous keratopathy secondary to corneal endothelial disease in dogs: 13 cases (1994-2001)

OBJECTIVE: To evaluate the outcome of thermokeratoplasty for treatment of ulcerative keratitis and bullous keratopathy secondary to corneal endothelial disease in dogs. DESIGN: Retrospective study. ANIMALS: 13 dogs. PROCEDURES: Medical records from 1994 to 2001 for dogs evaluated because of ulcerative keratitis and bullous keratopathy and treated with thermokeratoplasty were reviewed. RESULTS: There were 7 spayed females, 5 castrated males, and 1 sexually intact male, ranging from 6 to 16 years of age. Ten dogs had endothelial degeneration, and 3 dogs had breed-related endothelial dystrophy. All dogs had bullous keratopathy, characterized by microbullae formation that was detected via biomicroscopy. Recurrent or nonhealing corneal ulcers were detected unilaterally in 5 dogs and bilaterally in 8 dogs. Mean +/- SD duration from thermokeratoplasty until ulcerations were healed for all dogs was 2.2 +/- 1.1 weeks. All dogs that underwent thermokeratoplasty for nonhealing corneal ulceration secondary to endothelial disease and corneal edema had epithelial wound healing and resolution of corneal ulceration. Mean duration of treatment (ie, topical treatment required until resolution of ulceration) was significantly less after thermokeratoplasty than duration of treatment (with multiple treatments) prior to referral. CONCLUSIONS AND CLINICAL RELEVANCE: It may be necessary to perform thermokeratoplasty of the entire cornea to prevent recurrence of ulcerations in areas that have not been treated with thermokeratoplasty.     

Morphologic studies of uveoscleral outflow in normotensive and glaucomatous beagles with fluorescein-labeled dextran

Aqueous humor leaves the anterior chamber through 2 pathways: the trabecular meshwork of the iridocorneal angle and the unconventional uveoscleral route. In the latter route, aqueous humor leaves the anterior chamber, passes caudally through the trabecular meshwork and sclerociliary cleft to enter the supraciliary and suprachoroidal spaces. The fluid is absorbed by the choroidal and scleral circulation. Fluorescein-labeled dextran was slowly infused into the posterior chamber of healthy and glaucomatous Beagles for 30 minutes. The eyes were fixed in a mixture of 70% alcohol and formalin, placed in epoxy resin for histologic evaluation, and examined by fluorescent microscopy. Fluorescence was detected in the healthy dogs throughout the uveoscleral pathway. In the glaucomatous dogs, the uveoscleral outflow was decreased or completely absent.     

Primary lens luxation in the Chinese Shar Pei: clinical and hereditary characteristics

A pedigree analysis of a family of 15 related Chinese Shar Peis was conducted. This pedigree analysis, including affected and nonaffected dams, sires and offspring, was compiled to document and characterize the occurrence, common clinical signs, and age of onset of primary lens luxation while suggesting a possible mode of inheritance in this breed. Of the five offspring from the mating of an affected dam to two unrelated affected males, 100% of offspring were affected with bilateral primary lens luxations. Of the four viable offspring from the mating of the same affected dam to an unrelated, unaffected male, two dogs (50%) were affected. The average age of onset of affected animals (seven) in this first generation was 4.9 years (range 3–6 years). The six dogs in the second generation of the same pedigree line were 2-years-old at examination with none of these animals affected at the time of this study. The most common presenting complaints were a unilateral change in ocular appearance (5 of 7 dogs) and subjective vision impairment (4 of 7 dogs). The most common clinical sign upon ophthalmic examination was iridodonesis (unilateral 4 of 7 dogs; bilateral 3 of 7 dogs) and the presence of an aphakic crescent (3 of 7 dogs). Gonioscopy and tonometry of severely affected eyes revealed a narrow or closed iridocorneal angle and ocular hypertension. This study suggests that primary lens luxation does occur in the Chinese Shar Pei, resembling the clinical condition (age of onset, clinical signs) previously described in the terrier breeds, the Border Collie, and the Tibetan Terrier. Application of the phenotypic findings in this study to a Mendelian genetic model of inheritance suggests that primary lens luxation in the Chinese Shar Pei is inherited as a simple autosomal recessive trait.     

Evaluation of the distance between Schwalbe’s line and the anterior lens capsule as a parameter for the correction of ultrasound biomicroscopic values of the canine iridocorneal angle

Objective To determine whether the distance between Schwalbe’s line (the peripheral termination of Descemet’s membrane, i.e., the borderline between the cornea and sclera) and the anterior lens capsule (SLD) is an applicable parameter for correcting raw ultrasound biomicroscopic values of the canine iridocorneal angle (ICA) and to establish a comparative system for the ICA values in different canine breeds with varied body sizes/weights. Animal studied The dogs were divided into four groups based on body weight (BW): <4 kg, 4–8 kg, 8–20 kg, and >20 kg, and 180 normotensive eyes were studied. Procedures The ICA microstructure was examined by ultrasound biomicroscopy (UBM) using 40‐MHz probes in dogs with or without anesthesia/sedation. Linear regression analysis and correlation coefficients were evaluated between SLD or SLD² and UBM measurements; subsequently, noncorrected and SLD‐corrected UBM values were statistically assessed. Results Significant linear correlations were detected between SLD and the ciliary cleft width, the minimum distance between the angle recess and the scleral venous plexus, and the scleral thickness. Positive linear correlations were also demonstrated between SLD² and the ciliary cleft area as well as the scleral venous plexus area. Raw UBM measurements were corrected by using a ratio with SLD on the distance or SLD² on the area. Although noncorrected UBM measurements increased with canine BW, SLD‐corrected UBM values remained similar with no significant statistical differences in any of the dogs. Conclusions Correction with SLD would be clinically useful for comparing UBM measurements of the ICA in dogs with different body sizes/weights.     

Effects of intracameral injection of viscoelastic solutions on corneal endothelium in dogs

Contact in vivo wide-field specular microscopy was performed on right eyes of 20 healthy dogs after sodium hyaluronate (1%, n = 5), sodium chondroitin sulfate (4%) and sodium hyaluronate (3%, n = 5), hydroxypropyl methylcellulose (2%, n = 5), or balanced salt solution (control, n = 5) was injected into the anterior chamber. Using computerized morphometric analysis and pachymetry, changes in endothelial cell density, cell morphologic features, and corneal thickness from baseline values were evaluated at postinjection hour (PIH) 72 and PIH 168. Changes were not seen in endothelial cell density or cell morphologic features in any treated eye. The mean corneal thickness of all treated eyes at PIH 72 increased 6%, significantly greater than that of the nontreated eyes (P = 0.03). Mean corneal thickness of treated and nontreated eyes was similar at baseline and PIH 168 in all treatment groups.     

Ultrasound biomicroscopic findings of the iridocorneal angle in live healthy and glaucomatous dogs

By using ultrasound biomicroscopy (UBM), the cross-sectional structures of the entire iridocorneal angle (ICA) which are unable to assess with gonioscopic examination were evaluated objectively and quantitatively in live healthy and glaucomatous dogs. The ICAs of normotensive eyes in healthy dogs with normal open angle (NOR), a predisposition to primary closed angle glaucoma (PCAG) (PREDIS) and suffering from unilateral PCAG (UNI), as well as the ICAs of hypertensive eyes with acute and chronic PCAG (ACG and CRG), were assessed. The opening of the ciliary cleft in PREDIS was smaller than that in NOR. In UNI, the opening and area of the ciliary cleft were significantly decreased compared with those of NOR and PREDIS. ACG had widespread structural abnormalities including marked decrease in the ciliary cleft and scleral venous plexus, and a thinner sclera than those in normotensive eyes, whereas the ICA collapsed in CRG with the thinnest sclera. Medical therapy-responsive glaucomatous cases had wider ciliary cleft and scleral venous plexus than unresponsive ones. These findings suggest that the ciliary cleft and scleral venous plexus of the ICA are key structures contributing to not only the pathophysiology of canine glaucoma but also the responsiveness to medical therapy in glaucomatous eyes, and cross-sectional entire structures of the ICA should be evaluated quantitatively with UBM when diagnosing and managing canine glaucoma.     

Ultrasound biomicroscopy of the iridocorneal angle of the eye before and after phacoemulsification and intraocular lens implantation in dogs

OBJECTIVE: To compare the iridocorneal angle (ICA) and angle opening distance (AOD) in dogs with cataractous and noncataractous lenses; evaluate cataractous eyes ultrasono-graphically for association of postoperative ocular hypertension (POH) with the ICA, AOD, and postoperative echogenic anterior chamber debris; and evaluate intraobserver reliability associated with ICA and AOD measurements. ANIMALS: 56 dogs with 102 cataracts, and 23 clinically normal dogs. PROCEDURES: Ultrasound biomicroscopy was performed on 102 eyes of 56 dogs before and after cataract surgery and on 46 nondilated and dilated eyes of 23 clinically normal dogs. Cataract stage, ICA, AOD, and association with POH were assessed. RESULTS: Cataract stage and ICA or AOD were not significantly associated; however, ICA and AOD typically decreased with increasing cataract maturity. Before and after pupillary dilation, AODs were significantly smaller in cataractous eyes than in noncataractous eyes. Before surgery, ICA and AOD in eyes without pupillary dilation were significantly associated with POH. At > 13 degrees , odds of developing POH increased by 11% for each degree increase in the ICA. Postoperative anterior chamber debris was not associated with POH. Coefficient of variation for repeated measurements was 10% for the ICA and 9.5% for the AOD, suggesting good intraobserver reliability. CONCLUSIONS AND CLINICAL RELEVANCE: In this study, dogs with larger ICA and AOD measurements before surgery were at greater risk of developing POH. This information may be useful for future studies to determine whether preventative treatment for POH administered prior to surgery may be beneficial.     

Keratoprosthesis with retrocorneal fixation: preliminary results in dogs with corneal blindness

Objective To evaluate the use and complications of a penetrating keratoprosthesis implantation in the management of corneal opacification in dogs. Methods A retrospective clinical study describes the indications for the surgical technique utilized and the outcomes of this procedure in 20 eyes of 19 dogs with blindness of corneal origin. A successful surgical outcome was defined as a clear keratoprosthesis optic and improvement or restoration of functional vision over a follow‐up period ranging from at least 8 months to a maximum of 7 years. Results Eyes with total corneal opacification resulting from chronic superficial keratitis (n = 11), keratoconjunctivitis sicca (n = 5), endothelial dystrophy (n = 3) and chemical burn (n = 1) were treated by unilateral (n = 18) or bilateral (n = 1) full‐thickness implantation of a keratoprosthesis. Keratoprostheses were retained in 15 eyes (75%) which regained vision to the date of reporting. Among these eyes, six had uncomplicated postoperative course, five developed retroprosthetic membranes and four developed granulation tissue over the optic of the keratoprostheses. These complications were successfully removed surgically in the nine eyes. The five remaining eyes (25%) developed serious early postoperative complications, for which enucleation had to be performed. Conclusion In keratopathies in which the corneal opacification could not be treated by standard medical or surgical procedures, this keratoprosthesis appears to be promising to restore vision in chronic superficial keratitis and deep corneal dystrophy. It appears to have a poor prognosis in keratoconjunctivitis sicca in brachycephalic dogs. The post operative complications retro‐prosthetic membranes and granulomatous overgrowth could be treated well.     

Prevention of postmetrizamide myelographic seizures in dogs, using 5% dextrose solution

Diuresis by IV administration of 5% dextrose in a balanced electrolyte solution (BES) reduced the frequency of occurrence of postmyelographic seizures in dogs. In the first study, a single myelogram was obtained in 8 dogs without dextrose diuresis. Two of these dogs weighed greater than 15 kg and both had seizures after metrizamide myelography. The remaining 6 dogs weighed less than 15 kg and only 2 had seizures. Greater body weight may have increased the risk of postmyelographic convulsions. In a crossover study, myelograms were obtained in 12 dogs weighing 20 to 31 kg. Six dogs were given 5% dextrose in BES (20 ml/kg of body weight/hr [diuresed]) and 6 were given BES alone (10 ml/kg/hr [not diuresed]). When myelography was repeated 10 days later, the 6 dogs that had been given 5% dextrose in BES were given BES only and the 6 dogs that had been given BES alone were given 5% dextrose in BES. The frequency of convulsions after metrizamide myelography was lower when dogs were given dextrose (33%) than when they were not (100%).     

A clinical evaluation of a one-piece drainage system in the treatment of canine glaucoma

A one-piece drainage implant consisting of an anterior chamber tube and an attached large surface area strap has been used to treat glaucoma in 15 dogs (21 eyes). The results obtained over a minimum period of nine months suggest that the technique offers a greater chance of long term control than other surgical therapies currently practised. In all patients in this series medical therapy was either inappropriate or had proved ineffective, and surgery to bypass the iridocorneal angle was considered essential if intraocular pressure control was to be achieved. The drainage implant allowed aqueous to be diverted from the anterior chamber and absorbed from a large sub-conjunctival scar sac which developed around the strap. Four weeks after surgery 20 eyes were normotensive and by nine months after surgery only three additional eyes had become irreversibly hypertensive. No further failures have been recorded, and throughout there has been no apparent untoward reaction to the presence of the implant. Additional medical hypotensive therapy is being used in approximately 50 per cent of the controlled eyes.     

Duration of effect and effect of multiple doses of topical ophthalmic 0.5% proparacaine hydrochloride in clinically normal dogs

OBJECTIVE: To determine the duration of effect and the effect of multiple doses of topical ophthalmic application of 0.5% proparacaine hydrochloride on corneal sensitivity in clinically normal dogs. ANIMALS: 8 clinically normal dogs. PROCEDURE: Dogs were randomly allocated to treatment order in a 2 x 2 (period X treatment) crossover study. Treatments consisted of topical application of ophthalmic 0.5% proparacaine (1 drop or 2 drops at a 1-minute interval); treatments were applied to both eyes. A Cochet-Bonnet aesthesiometer was used to determine corneal touch threshold (CTT) before corneal application, 1 and 5 minutes after corneal application, and at 5-minute intervals thereafter for 90 minutes. RESULTS: The CTT value before treatment differed significantly from CTT values after treatment until 45 minutes after application in the 1-drop group and until 55 minutes after application in the 2-drop group. As determined by use of the Cochet-Bonnet aesthesiometer, a significantly greater anesthetic effect was detected for the 2-drop treatment, compared with the effect for the 1-drop treatment, at 30, 35, 40, 45, 50, and 55 minutes after application. Maximal anesthetic effect lasted for 15 minutes for the 1-drop treatment and 25 minutes for the 2-drop treatment. CONCLUSIONS AND CLINICAL RELEVANCE: Duration of corneal anesthetic effect induced by topical ophthalmic application of 0.5% proparacaine in dogs of this study is considerably longer than that reported elsewhere. Serial application of doses of 0.5% proparacaine increases the duration and magnitude of corneal anesthetic effects.