Angiotensin converting enzyme system in the normal canine eye: pharmacological and physiological aspects.

The function of the renin-angiotensin-aldosterone system (RAAS) in the mammalian eye remains unclear, although alterations in the concentrations of various pathway components can influence intraocular pressure and the electroretinogram. Angiotensin Converting Enzyme (ACE) has been localized to ocular tissues and fluids. Aqueous humor and serum values of ACE are increased in sarcoid uveitis patients. We used the dog to simultaneously examine the effects of a topically administered ACE inhibitor on the intraocular pressure (IOP), on components of the renin-angiotensin pathway in the serum and aqueous humor, and to monitor any systemic effects of the ACE inhibitor. The novel ACE inhibitor, SCH 33861 (Schering Corporation), decreased IOP in amounts similar to timolol when applied topically to the canine eye. Serum ACE values significantly decreased in SCH 33861 treated dogs, while aqueous ACE values were only slightly decreased. A decrease in heart rate, and systolic and diastolic blood pressure in these dogs during the treatment period indicated probable systemic absorption. Normal values of aqueous humor and serum angiotensin-I were established for the dog. Plasma renin activity and angiotensin-I values were not significantly changed for any of the treatment groups. Topical application of SCH 33861 to the canine eye is a useful model to further evaluate the role of the renin-angiotensin system in the eye.

Nonulcerative keratouveitis in five horses.

Five horses with severe nonulcerative keratouveitis had corneal lesions characterized by a pink stromal infiltrate that initially appeared in the stroma near the limbus. Unremitting iridocyclitis also was evident. In 3 horses, microscopic lesions consisted of marked corneal stromal fibrosis, with mild to severe inflammatory cellular infiltration. Corticosteroids and mydriatic/cycloplegics applied topically and corticosteroids and nonsteroidal anti-inflammatory medications administered parenterally were used with varying degrees of success to control pain and retain vision.

Eyelid malformation in four cockatiels.

Four unrelated cockatiels had various degrees of maldevelopment of the eyelids. Only 1 eye of the 8 was normal. The condition had features compatible with ankyloblepharon or cryptophthalmos. Attempts were made to surgically establish an artificial palpebral fissure. Despite extensive surgical intervention and postoperative topical administration of corticosteroids, the skin over the orbit reverted to the preoperative state in all birds. Anecdotal information along with our findings suggest that this condition, although uncommon, is widespread in the cockatiel population in the United States.

Waveform analysis and reproducibility of visual-evoked potentials in dogs.

Visual-evoked potentials (VEP) and electroretinograms (ERG) were recorded from 10 normal light-adapted adult dogs, using a 3 x 5 matrix of light-emitting diodes as a stimulator. Visual-evoked potentials were recorded from 4 scalp electrodes overlying cortical areas, whereas electroretinographic activity was recorded by 2 scalp electrodes placed near the eye and by a conjunctivally placed electrode. The waveform of the VEP consisted of 3 major positive waves (P1 through P3), with peak latencies in the 20- to 70-ms range. Waveform reproducibility was assessed by comparing peak latencies from VEP recorded on 2 separate days approximately 1 week apart. The peak latencies for P1 through P3 did not differ (P greater than or equal to 0.05) between first and second recording sessions. To substantiate the postretinal origin of VEP, recordings were made before and after unilateral optic nerve transsections in 4 dogs. Electroretinograms were also measured before and after surgery to assess the integrity of the retina. Postsurgically, VEP were absent when the eye on the surgically treated side was stimulated. Stimulation of the contralateral eye induced VEP with the same waveform shape, but latencies were slightly prolonged (P less than or equal to 0.05) compared with presurgical recordings. The only effect of optic nerve transsection on the ipsilateral ERG was a prolongation (P less than or equal to 0.05) of the b-wave. However, when postsurgical ERG values were compared with those from the intact side after surgery, there were no differences.

Visual-evoked potentials in cats, using a light-emitting diode stimulator.

Visual-evoked potentials (VEP) were studied in 8 healthy adult cats anesthetized with xylazine HCl and ketamine HCl. Monocular visual stimulation was accomplished by a 3 x 5 matrix of light-emitting diodes. Subcutaneous needle electrodes placed in the scalp at various locations and a contact lens electrode on the cornea were used to record cortical and electroretinographic activities, respectively. Multiple electrode pairings and unilateral optic nerve transsection were used to distinguish between retinal and postretinal potentials recorded from scalp electrodes. The VEP was a robust polyphasic cortical potential, with peak latencies between 0 and 110 ms. Using the light-emitting diode method of stimulation, a VEP was recorded which was not contaminated by volume-conducted retinal activity.

Uveitis associated with poliosis and vitiligo in six dogs.

Idiopathic panuveitis with retinal detachment was associated with facial poliosis, vitiligo, and alopecia in 6 dogs; 4 were adult males. Dermatohistologic examination of affected facial sites from all dogs revealed a lichenoid dermatitis and unusual histiocytic cells. Intensive topical and systemic corticosteroid and topical mydriatic/cycloplegic therapy was successful in controlling uveitis in all dogs for variable periods. Three dogs, monitored for 12, 30, and 46 months, retained useful vision despite infrequent recurrence of uveitis. One dog was lost for subsequent examination. Two dogs were euthanatized and necropsied. Ocular histologic examination of these dogs revealed extensive granulomatous iridocyclitis and choroiditis, with retinal detachment and lenticular degeneration.

Multiple congenital ocular defects in the Akita dog.

Microphthalmia, congenital cataracts, posterior lenticonus, and retinal dysplasia were observed in members of 3 litters of Akita puppies thought to be related to a common male ancestor. The electroretinograms of 3 clinically affected puppies were normal. Histological examination of 6 microphthalmic animals revealed nuclear and cortical cataract with multiple retinal folds and rosettes predominantly overlying the tapetum lucidum. Posterior lenticonus was observed histologically in 3 of the 6 puppies.

Effect of flunixin meglumine on prostacyclin accumulation in the equine eye.

A study was performed to identify prostacyclin (PGI2) in equine aqueous humor, demonstrate an increase in PGI2 following anterior chamber paracentesis, and determine the effects of subconjunctival injection of flunixin meglumine on PGI2 accumulation. Twenty ponies were found to be normal upon ocular examination and were placed under general anesthesia. Anterior chamber paracentesis was performed in both eyes (right and left); immediately afterward, 25 mg of flunixin meglumine was injected (subconjunctivally) in the left eye. Aqueous paracentesis was performed 1.5 hours later (both eyes). Aqueous humor samples were assayed for 6-keto PGF1alpha, the stable, inactive metabolite of PGI2. Eyes treated with flunixin meglumine contained less 6-keto PGF1alpha than did control eyes.