Trace element status and free radical defense in elderly rhesus macaques (Macaca mulatta) with macular drusen.

Research into the mechanisms underlying the development of age-related macular degeneration (AMD), the leading cause of visual loss in the United States and Europe in people over 60 years old, has been limited in part by the lack of animal models for this disease. In the current study, we examined 62 elderly (> or = 20 years old) rhesus macaques (Macaca mulatta) for the presence and severity of macular drusen. Drusen were observed in 47% of the macaques; they were similar histologically and in clinical appearance to the drusen observed in humans with AMD. It has been proposed that excessive tissue free radical damage may contribute to the development of AMD. Thus, circulating levels of select components of the free radical defense system and plasma thiobarbituric acid reactive substances (TBARS), an estimate of lipid peroxides, were measured in the above animals. Macaques diagnosed with drusen were characterized by alterations in concentrations and activities of several components of the free radical defense system. Alterations were most evident with respect to those enzymes associated with copper. The concept that excessive oxidative lipid damage might be a factor contributing to the occurrence of this disease is suggested by the findings of higher plasma TBARS concentrations in animals with > 10 drusen compared with animals without drusen.

Fluorophotometric evaluation of experimental blood-aqueous barrier disruption in dogs.

A protocol for performing slit-lamp fluorophotometry of the anterior chamber in dogs was established. The technique was then used to develop a model of blood-aqueous barrier disruption that can be used for comparative testing of ophthalmic anti-inflammatory drugs. It was determined that barrier disruption induced by a slow, controlled paracentesis of a small volume of aqueous humor may provide the most reliable model for drug testing. Additionally, fluorophotometry proved to be a sensitive and accurate means of detecting breakdown of the blood-aqueous barrier.

Nutritionally variant streptococci associated with corneal ulcers in horses: 35 cases (1982-1988).

Nutritionally variant streptococci (NVS) are nutritionally deficient viridans streptococci that require pyridoxal for growth. Although NVS are pathogenic in human beings, they have not been considered to be pathogenic in domestic animals. In 1982 and 1983, 24 isolates of NVS were recovered from horses with ulcerative keratitis. A retrospective study was done to determine the incidence of NVS in horses with corneal disease. The medical records of 249 horses (259 eyes) examined for clinical signs of corneal disease were reviewed. Nutritionally variant streptococci were isolated from approximately 13.5% of horses with ulcerative keratitis.

Effect of high PaCO2 and time on cerebrospinal fluid and intraocular pressure in halothane-anesthetized horses.

The effects of different arterial carbon dioxide tensions (PaCO2) on cerebrospinal fluid pressure (CSFP) and intraocular pressure (IOP) were studied in 6 male halothane-anesthetized horses positioned in left lateral recumbency. Steady-state anesthetic conditions (1.06% end-tidal halothane concentration) commenced 60 minutes following anesthetic induction with only halothane in oxygen. During atracurium neuromuscular blockade, horses were ventilated, and respiratory rate and peak inspiratory airway pressure were maintained within narrow limits. The CSFP and IOP were measured at 3 different levels of PaCO2 (approx 40, 60, and 80 mm of Hg). The PaCO2 sequence in each horse was determined from a type of switchback design with the initial PaCO2 (period 1), established 30 minutes after the commencement of steady-state anesthesia, being repeated in the middle (period 3) and again at the end (period 5) of the experiment. Measurements taken from the middle 3 periods (2, 3, and 4) would form a Latin square design replicated twice. The interval between each period was approximately 45 minutes. Data from periods 2, 3, and 4 indicated that CSFP (P less than 0.05) and mean systemic arterial pressure increased significantly (P less than 0.05) with high PaCO2. Mean central venous pressure, heart rate, and IOP did not change significantly during these same conditions. Measurements taken during periods 1, 3, and 5 were compared to assess the time-related responses to anesthesia and showed a significant increase in CSFP, a significant decrease in mean central venous pressure, and a small (but not statistically significant) increase in mean systemic arterial pressure.

Refractive state, ocular anatomy, and accommodative range of the sea otter (Enhydra lutris).

Sea otters are carnivorous, amphibious mammals that are active both above and under water. Accordingly, it might be expected that their eyes are adapted for both aerial and aqueous vision. We examined the anatomy and physiological optics of the sea otter eye with a view towards describing and explaining its amphibious visual characteristics. We employed photokeratoscopy to measure the refractive power of the sea otter cornea, which we found to be 59 D. Using video dynamic photorefraction, we found that sea otters can focus targets clearly both in air and water, relying on accommodation to compensate for the refractive loss of their corneas upon immersion in water. Our anatomical investigations revealed that the anterior epithelium of the cornea is extensively developed, as is the iris musculature, meridional ciliary muscle, and the corneoscleral venous plexus. The first feature is most likely an adaptation to the salinity of the marine environment. We believe the latter features are part of a novel, well-developed lenticular accommodative mechanism.

Squamous cell carcinoma causing blindness and ophthalmoplegia in a cat.

Ophthalmoplegia and blindness caused by squamous cell carcinoma were reported in a cat. Unilateral functional deficits of cranial nerves II, III, IV, and VI and of the sympathetic nerve supply caused blindness, complete ophthalmoplegia, and Horner syndrome. Radiography and computed tomography revealed a proliferating bony lesion associated with the right tympanic bulla, right temporal bone, right side of the mandible, and left frontal bone. A focal area of bony destruction involved the right sphenoid bone. The cat was euthanatized and necropsied. Squamous cell carcinoma was identified invading the bones and rostral part of the right side of the skull. The tumor had extended through the sphenoid bones into the region of the cavernous sinus and had surrounded the cranial nerves passing through this region. It also had invested connective tissue surrounding the optic nerves and had invaded the right globe through the lamina cribrosa. This represents an unusual distribution for ocular cranial squamous cell carcinoma in a cat.

Disseminated adenocarcinoma with ocular involvement in a cat.

Disseminated adenocarcinoma was associated with unilateral uveitis and multiple subcutaneous nodules in an 8-year-old domestic shorthair cat. Erythroleukemia and hind limb paresis developed over a 5-month period. At necropsy, numerous sites of metastases were found that had histologic features similar to the neoplasm in the left eye. Neoplastic cells were identified in the lungs, mediastinum, muscles, subcutaneous tissues, lymph nodes, and vasculature associated with the meninges of the brain and spinal cord. Morphologic associations were not found between erythroleukemia and the neoplastic process.

Bilateral conjunctival masses in two dogs.

Bilateral conjunctival masses in 2 dogs were excised. In one dog, the masses represented hemangiomas that may have been related to exposure to UV radiation. In the other dog, they represented conjunctival inclusion cysts of probable congenital origin.

Efficacy of zinc citrate ascorbate for treatment of canine cataracts.

Efficacy of zinc citrate ascorbate was evaluated in 146 dogs (265 eyes) that had various lens opacities. Zinc citrate ascorbate or saline placebo drops were applied topically once or twice daily for 4 to 31 weeks. Of 138 eyes treated with zinc citrate ascorbate, 86 eyes (62.3%) had no change, 48 eyes (34.8%) had increased lens opacity, and 4 eyes (2.9%) had decreased lens opacity. Of 127 eyes treated with a saline placebo, 99 eyes (77.9%) had no change, 25 eyes (19.7%) had increased lens opacity, and 3 eyes (2.4%) had decreased lens opacity. Zinc citrate ascorbate drops were not significantly (P = less than 0.05) more effective in clearing cataracts than were saline drops. Seemingly, zinc citrate ascorbate drops may have caused lens opacities to increase in area and density.

Bilateral eyelid swelling attributable to lymphosarcoma in a horse.

Bilateral swelling of upper and lower eyelids was caused by lymphocytic infiltration in an 8-year-old Thoroughbred mare. The condition worsened with pregnancy and became associated with subcutaneous dissemination of lymphosarcoma at distant sites.

Cataracts and optic nerve hypoplasia in turkey poults.

Newly hatched commercial turkey poults culled because of grossly visible cataracts were studied. A total of 43 affected and 23 unaffected control poults at various ages were necropsied, and the ocular changes in affected poults were compared with those of aged-matched controls. Affected poults had consistent cataracts coupled with a marked depletion in retinal inner plexiform, ganglion cell, and optic nerve fiber layers, with a resultant reduction in the size of the optic nerves. Lesions were seen in 1-day-old poults. Lens changes included microphakia and lens fiber degeneration throughout the lens, with nuclear liquefaction. The depletion in the numbers of retinal ganglion cells did not appear to progress over several weeks time. The ganglion cell depletion was not uniform within the retina. The cause for these ocular changes is unknown.

Spontaneous corneal degeneration in the rat.

Superficial punctate opacities were observed in the palpebral aperture region of the cornea of Sprague-Dawley and Wistar rats of both sexes and varying ages, but they were not observed in Lewis rats. Slit-lamp biomicroscopy localized the opacities in the subepithelial corneal stroma. Electron microscopy demonstrated 0.1-2.0 micron granules at the stromal-epithelial interface and in the adjacent stroma. Smaller granules, consisting of aggregates of amorphous granular material, were associated with bundles of filaments among collagen fibers. Larger granules were located adjacent to and sometimes straddle the epithelial basement membrane. The overlying epithelial cells were displaced, but otherwise appeared normal. Large granules consisted of layered dark and light electron dense rings and appeared in some instances to represent fusing of smaller granules. This rat keratopathy bears certain resemblance to granular dystrophy of man (Groenouw's Type I), but histochemically is dissimilar.

Melanosome abnormalities of ocular pigmented epithelial cells in beagle dogs with hereditary tapetal degeneration.

Eyes of laboratory beagle dogs with an inherited tapetal degeneration were abnormally lightly pigmented. The development of pigmentation was followed morphologically from 7 days postnatal to 9 years of age. At all postnatal ages the iris pigmented epithelia contained no normal melanosomes, only organelles resembling secondary lysosomes or residual bodies. The ciliary body pigmented epithelium contained a variety of melanosome organelles at the earliest stages examined, but in fewer numbers than in normal animals. These included premelanosomes, partially melanized and some fully melanized pigment granules. However, the melanin deposition was usually patchy and irregular. With time, many of these granules appeared to condense into residual bodies. The retinal pigmented epithelium in peripheral and inferior posterior regions of affected animals never contained normal appearing melanin granules at any stage of postnatal development. The iris and choroidal stroma had melanosomes of normal size and shape, but many fewer than in normal animals. These results imply that there is local cellular control over melanosome production and regression, since the melanosome abnormalities do not follow the anterior to posterior development of pigment in ocular epithelia. It is proposed that a defect in synthesis of the matrix component of melanosomes could result in absent or abnormal deposition of melanin and initiate a process of autophagy of these organelles.

Development of hereditary tapetal degeneration in the beagle dog.

Laboratory beagle dogs with an apparent absence of a tapetum lucidum were identified by ophthalmoscopic examination. Breeding experiments demonstrated a probable autosomal recessive mutation. Studies of the development of the tapetal abnormality showed that up to postnatal day 21 the tapetum was normal by light and ultrastructural morphology. Subsequent to that time the tapetal rodlets failed to accumulate electron-dense material, did not accumulate zinc, and degenerated primarily into spherical inclusion bodies of varying electron density. In the early phases of the degeneration the rough endoplasmic reticulum formed large whorls of membrane denuded of ribosomes. With time, the inclusions became electron lucent, and the entire tapetal cell degenerated, ending with almost total loss of the tapetum lucidum by approximately one to two years of age. The structure of the retina was normal. Retinal function measured by electroretinography was normal except for a slight elevation of dark adapted white light thresholds. It is speculated that the hereditary defect may be defective synthesis of the tapetal rodlet matrix or of the zinc-complexing substance of the tapetum.

Effect of topical phenylephrine on the equine pupil.

The mydriatic effect of 10% phenylephrine was evaluated in 9 horses. Base-line pupillary size in mesopic conditions and during light stimulation was ascertained before application of pharmacologic agents. In study 1, 10% phenylephrine was applied to each eye (n = 5 horses). After 15 minutes, the pupillary size was determined in both lighting conditions. Phenylephrine was again applied to each eye, and after an additional 15 minutes, the pupillary size was determined. In study 2, 1% tropicamide was applied to each eye (n = 4 horses), and after 30 minutes, the pupillary size was determined in both lighting conditions. Tropicamide and phenylephrine were applied to each eye immediately after determination of pupillary size, and after an additional 30 minutes, the pupillary size was determined. There was no significant change (P greater than 0.9) in pupillary size when phenylephrine was used alone or when phenylephrine was used in an eye that had been dilated with tropicamide.

Retinal degeneration in the WKY rat.

An outer retinal degeneration occurs in middle aged Wistar-Kyoto (WKY) rats, the normotensive counterpart to the spontaneous hypertensive rat strain (SHR). The degeneration, like that of other spontaneous and experimentally-induced outer layer retinopathies of rats, is characterized by a progressive loss of photoreceptor and outer nuclear layers which, in turn, leads to contact between the deep capillary bed of the retina and the retinal pigment epithelial (RPE) cells. RPE proliferation and/or migration causes a number of capillaries to become enmeshed within RPE cells, and some of those capillaries undergo morphologic and physiologic alterations such that they resemble choroidal capillaries. There is variable loss of the choriocapillaris associated with this retinopathy, but since this is also seen to some degree in normal eyes, it is not known if this is an integral part of the pathologic process.