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A new technique for the treatment of certain types of cardiac arrhythmias was used in a 3-year-old dog that was evaluated for incessant supraventricular tachycardia (220 to 280 beats/min), which had been refractory to several treatment regimens. The mechanism of supraventricular tachycardia was atrioventricular (AV) reentry, using a dorsoseptal accessory pathway (AP) for retrograde ventriculoatrial conduction (concealed AP). With the dog under general anesthesia and with fluoroscopic monitoring, electrode catheters were introduced into the heart via peripheral vessels. Electrical recordings allowed localization of the accessory AV pathway. Programmed electrical stimulation was used to verify the function of the abnormal AV connection. At the atrial insertion site of the AP, 2 applications of radiofrequency current (45 V, 21.6 W) were delivered to the dorsoseptal right atrium (near the coronary sinus ostium), which eliminated AP conduction and AV reentrant tachycardia. The dog has remained free of tachycardia and has not required medication during more than 1 year of follow-up.

Glaucoma in the beagle is an inherited disease that is exhibited clinically in dogs of 6 to 18 months of age. The genealogy, clinical signs, gonioscopy, tonometry, tonography, water provocative response, and scanning electron microscopy of the iridocorneal angle of the glaucomatous beagle are summarized.

Ophthalmic nodular fasciitis in 5 dogs was often manifested as subconjunctival masses of variable growth rate. Each mass was raised, pink, and hyperemic. Five masses involved the bulbar conjunctiva, and 2 masses involved the eyelids. Local excision of each mass successfully resolved the condition.

Lipid infiltration of the corneal stroma, sclera, and uvea occurred in a 2-year-old cottontail rabbit that had been fed an all-milk diet for 20 months. Superficial keratectomy was performed on the left eye but the rabbit died. Histologically, lipid deposits were most extensive in the anterior corneal stroma and posterior iridal epithelium.

The Schiøtz tonometer with 5.5-, 7.5-, and 10-g weights was calibrated for the normal canine eye, using a transducer with open and closed reservoir systems. The line of best fit for the observations was determined, and the equation of this line was utilized to derive a calibration table for the conversion of tonometer scale readings to mm of Hg intraocular pressure.

Topical 1, 2, and 4 percent pilocarpine were evaluated in the normotensive and glaucomatous beagles, comparing intraocular pressure (IOP), pupillary size, and time. In normotensive beagles pilocarpine produced maximal decreases of 25 percent (5.5 mm. Hg) at 1 percent concentration; 34 percent (7.26 mm. Hg) at 2 percent concentration; and 25 percent (6.9 mm. Hg) at 4 percent concentration. The maximum reductions in IOP after pilocarpine instillation in the glaucomatous beagle were 30 percent (9.1 mm. Hg) at 1 percent concentration; 44 percent (14.92 mm. Hg) at 2 percent concentration; and 31 percent (10.89 mm. Hg) at 4 percent concentration. The glaucomatous beagles responded with a greater reduction of IOP than did the normotensive beagles.

Fifty-nine normal dogs, ranging in age from 6 weeks to 132 months were examined with contact specular microscopy to determine the relationship of age to corneal endothelial cell density, morphology, and corneal thickness. Canine corneal endothelial cells appear quite similar to those of other species studied, including man. The hexagonally shaped canine endothelial cells tend to enlarge with age, with the population in young animals averaging around 2500 cells/mm2 and the number of cells in older dogs being frequently below 2100 cells/mm2. A significant increase in corneal thickness was observed with age. Healthy canine corneal endothelial cells appear to maintain a functional monolayer by enlargement and migration and represent a reasonable model for future endothelial cell study.

Conjunctival swab specimens were obtained from both eyes of 43 horses, 25 cows, 50 dogs, and 25 cats without keratitis or other ophthalmologic problems. Fungi were isolated from 95% of the horses, 100% of the cows, 22% of the dogs, and 40% of the cats. Aspergillus spp were isolated from 56% of the horses, 12% of the cows, 8% of the cats, and none of the dogs. Penicillium spp and Cladosporium spp were isolated ubiquitously. Collectively, 28 species from 209 isolants were identified.

In two cases of naturally occurring disseminated histoplasmosis, multifocal inflammatory lesions were seen in the posterior segment of the eyes. Histologic examination of both animals revealed lesions of active choroiditis (cat) and retinitis (dog) in association with numerous Histoplasma capsulatum.

Twenty-one dogs were used to study the effects of phacoemulsification and extracapsular lens removal on corneal endothelium and corneal thickness. Specular microscopy revealed preoperative cell morphology and cell densities similar to man. After surgery endothelial cell counts significantly decreased 22% (central) and 13% (periphery) with phacoemulsification and 34% (central) and 31% (periphery) with extracapsular lens removal. Corneal thickness increased with both procedures. Endothelial cell pathology included cellular enlargement, increased pleomorphism, and focal cellular degeneration. Phacoemulsification time did not correlate with the degree of cell loss. Dog corneal endothelium responds to surgical trauma in a manner similar to man and maintains a functional monolayer via cellular enlargement and migration. The dog, therefore, represents a good animal model for the study of corneal endothelial disease in man.

A standard procedure for tonography was developed in the dog. Acepromazine, ketamine, xylazine, droperidol-fentamyl, and combinations of these drugs were evaluated for effects on blood pressure, intraocular pressure, and restraint of the dog for 4 minutes of Schiotz tonography of each eye. In dogs given a cepromazine (0.5 mg/kg intravenously) and then ketamine (10.0 mg/kg intramuscularly), the mean coefficient of aqueous humor out-flow in 24 normal Beagles was 0.24 mul/mm of Hg/minute (SD +/- 0.07). Mean coefficient of aqueous humor outflow in 35 glaucomatous Beagles, between 4 months to more than 37 months old, was 0.09 mul/mm of Hg/minute (SD +/- 0.04). Coefficient of aqueous humor out-flow was less in the older glaucomatous Beagle.

Four carbonic anhydrase inhibitors (acetazolamide, dichlorphenamide, ethoxzolamide, and methazolamide) cause ocular hypotony in normotensive and glaucomatous Beagles. Four dosages of acetazolamide and methazolamide and three dosages of dichlorphenamide and ethoxzolamide were evaluated. The extent of ocular hypotony after these carbonic anhydrase inhibitors was usually greater in glaucomatous Beagles than it was in normotensive Beagles.

Inherited glaucoma was exhibited in 55 beagles. The glaucomatous process was divided into early (6 to 12 months of age), moderate (13 to 30 months of age), and advanced (31 months of age). In early glaucoma the tridocorneal angles, as judged by gonioscopy, were open and without anomalies, intraocular pressure was elevated, and the tonographic facility of aqueous outflow was decreased. With moderate glaucoma, the tridocorneal angles were typically open; intraocular pressure was elevated, facility of aqueous outflow was decreased; and variable optic disc cupping and focal disinsertion of the zonules from the lens were seen. Advanced glaucoma exhibited narrow to closed tridocorneal angles, decreased facility of aqueous outflow, elevated intraocular pressure, lens dislocation, optic disc atrophy, and finally phthisis bulbi. The beagle in the early and moderate stages of glaucoma, before angle closure and lens dislocation, is an animal model for studies in open-angle glaucoma.

The base and pupillary zones of the iris were exposed for 10 s to a -79 C cryoprobe (iridocryothermy). The resultant iritis lasted 7 to 10 days as evidenced by aqueous flare, hypotony, and miosis. At 21 days, the iris was depigmented and had an irregular pupil. The initial histopathologic changes after iridocryothermy were iridic intrastromal hemorrhage, exudation, and neutrophil infiltration. The iridic pigmented epithelium was lyzed, and the melanin granules were liberated into the iridic stroma, posterior, and anterior chambers. Irides frozen at the pupillary zone exhibited sphincter muscle degeneration. By 21 days after iridocryothermy, the irides were depigmented and atrophic.

The Mackay-Marg, pneumatonograph, TonAir, and EMT-20 tonometers were evaluated in the normal dog eye. Tonometric scale readings were compared to the manometric recordings from the anterior chamber. The Mackay-Marg tonometer evaluated in open and closed systems was the most reliable (goodness of fit [r2] = 0.96) with intraocular pressure up to 100 mm. Hg. The pneumatonograph also exhibited high reliability (r2 = 0.92) but tended to underestimate intraocular pressures above 40 to 50 mm. Hg. The TonAir and EMT-20 tonometers were the least satisfactory for the dog, with r2 of 0.77 and 0.66 to 0.81, respectively. The Mackay-Marg is the most satisfactory tonometer for the dog.

Dipivalyl epinephrine and l-epinephrine were evaluated in various concentrations in normotensive and glaucomatous Beagles. In higher concentrations, both drugs produced significant lowering of intraocular pressure. Mydriasis and some local irritation occurred. The hypotony after drug administration tended to be greater in glaucomatous than in normotensive Beagles. The glaucomatous Beagle may be a valuable biomedical model in the investigation of various pharmacologic substances.