Low-energy, Q-switched ruby laser iridotomies in Macaca mulatta.

Laser iridotomies have been pursued as a means of performing anterior segments surgery as a virtually noninvasive procedure. An ideal single laser pulse technique has been elusive. In this study, iridotomies in rhesus monkeys were produced with a single exposure to a Q-switched ruby laser pulse. The iridotomy formation was accompanied by acoustic wave generation, bubble formation, and explosive tissue disruption, evidence of a nonlinear laser-iris interaction. The average energies at which these iridotomies were produced ranged between 18 and 48 mJ, some of the lowest energies reported for a laser iridotomy. Corneal changes were observed both at the epithelium and at the endothelium in some, but not all, of the eyes exposed. The epithelial changes morphologically resembled nonlinear damage reported for transparent solids. Damage to physical materials has been attributed to stimulated Brillouin scattering, a mechanism that may also play a role at the cornea. Consideration of such phenomena should be a part of the clinical evaluation prior to exposure of a cornea to high-power laser pulses. Although the endothelial change was more difficult to analyze, a shock-wave effect could not be discounted.

Long-term effects of Q-switched ruby laser on monkey anterior chamber angle.

In an attempt to clarify whether pulsed lasers might be able to cause permanent fistulas from the anterior chamber to the interior of the canal of Schlemm, slightly suprathreshold, low energy, small diameter Q-switched ruby laser pulses were applied to the trabecular meshwork of nine eyes of six rhesus monkeys. Clinical examinations during the next 2 months disclosed no adverse effect on the cornea, iris, lens, or retina. There was transient mild inflammation in five eyes. Intraocular pressure was not changed significantly; the facility determined by perfusion of the anterior chambers at 2 months was normal. Light microscopy and scanning electron microscopy show localized trabecular lesions; some are slightly indented, but there is no persistent penetration to Schlemm's canal. Endothelial cells, confluent with those of the cornea, cover the inner (anterior chamber) surface of the lesions. Cross-sections through the center of a lesion show that trabecular meshwork and Schlemm's canal have been obliterated by the treatment and healing; these changes are similar to those previously seen after argon laser monkey trabecular treatment. In the untreated areas, between pulsed laser application sites, trabecular meshwork and Schlemm's canal are normal by light microscopic and scanning electron microscopic examination. Any effect on IOP from this particular type of pulsed laser treatment of the trabecular meshwork is probably not due to trabeculopuncture and flow of fluid through the fistula.

Short-term effects of Q-switched ruby laser on monkey anterior chamber angle.

Three Q-switched ruby laser pulses were applied to the trabecular meshwork of 10 monkey eyes. Pulse energies ranging from 20 to 110 mJ were studied. The spot size ranged from 100 to 200 micrometer (in air), and the pulse durations was 28 sec. Gonioscopic examinations showed a graded response from no appreciable change at 20 mJ per pulse to marked disruption of anterior chamber angle structures at 100 mJ or more per pulse. Perfusions done within an hour of treatment showed no consistent alteration of the outflow facility. Scanning electron microscopy demonstrated the graded anterior chamber angle response. No disruption of the angle structures was seen after the 20 mJ treatment, but discrete trabecular damage occurred after treatments with 25 mJ. After pulses equal to or greater than 45 mJ the anterior chamber angle structures were markedly altered. The power density causing extensive tissue disruption was equal to or greater than 150 X 10(8) watts/cm2. In each specimen with an identifiable trabecular lesion, tissue debris and endothelial edema were found on the adjacent inner surface of the cornea. Tearing of Descemet's membrane next to the trabecular meshwork occurred with the 100 mJ pulses.

Papillomatosis of conjunctiva and adnexa in dogs.

Ocular or periocular papillomatosis was diagnosed in seven dogs. The periocular tumors (in 4 dogs) were located on the eyelids or the mucocutaneous junctions of the eyelids. Six of the tumors were removed surgically, using either superficial keratectomy and conjunctival dissection or lid resection techniques; the seventh was biopsied but not removed. In all cases, confirmation of the clinical diagnosis was made by light microscopy. The differential clinical considerations included squamous cell carcinoma, basal cell carcinoma, histiocytoma, and mastocytoma. In all cases of surgical removal, the dogs were free of recurrence 6 months following surgery.

An endemic focus of Trypanosoma cruzi infection in a subhuman primate research colony.

Leishmanial forms of Trypanosoma cruzi with multifocal pseudocysts were identified in a deceased adult female rhesus monkey (Macaca mulatta) that had been maintained in an outdoor primate colony in southern Texas. Subsequent clinical investigation of the remainder of the colony identified 20 additional monkeys seropositive for T cruzi. Concurrent epizootiologic surveys confirmed the presence of sylvatic reservoirs and triatomine vectors of T cruzi infection and identified a natural T cruzi transmission cycle. Veterinarians associated with the research colony were informed of the potential for further T cruzi transmission and appropriate insect vector and reservoir animal control programs were implemented..

Heavy-ion-induced cataractogenesis.

Cataract formation following heavy ion exposure (O+8) was noted in three rhesus monkeys secondary to a study of retinal effects. The pathogenesis of these lens changes follows many, but not all, of the characteristics for "radiation cataracts." The ring-shaped opacity was not noted to occur. Posterior capsular changes were noted initially and followed through the formation of a mature cataract.

Fluorescein angiography and light microscopy studies of retinas irradiated by oxygen nuclei.

Fluorescein angiography and light microscopy techniques were utilized in the rhesus monkey to evaluate retinal damage following oxygen ion irradiation. Particle flux ranged from 1.3 x 10(7) particles/cm2 to 1.5 x 10(8) particles/cm2. Earliest evidence of damage was detected with fluorescein angiograms 24 h after exposures to 7.7 x 10(7) particles/cm2. No evidence of the hypothesized microlesion was found by either technique.

Relative biological effectiveness (RBE) of heavy ions (O+8) for producing retinal lesions.

The relative biological effectiveness (RBE) for oxygen ions (250 MeV/nucleon) for producing an ischemic retinal lesion in the rhesus monkey has been shown to be greater than 10. The RBE concept and the use of the standard methodology is discussed with respect to other published reports.

Radiogenic changes in the behavior and physiology of the spontaneously hypertensive rat: evidence for a dissociation between acute hypotension and incapacitation.

Immediately following exposure to a sufficiently large dose of ionizing radiation, rats and several other species experience a transient period of acute hypotension and an accompanying deficit in performance. Although significant correlations have been reported between the drop in blood pressure and the early transient incapacitation (ETI) and a causal relationship has been suggested, the extent to which hypotension precipitates the occurrence of the behavioral deficits remains uncertain. The present experiments investigated both radiogenic blood pressure and performance changes in a strain of rat bred for hypertension (spontaneously hypertensive rat: SHR) in order to determine if high blood pressure might attenuate ETI. Although male SHRs experienced a severe ETI and a drop in blood pressure, much of the data is inconsistent with the hypothesis that hypotension causes performance decrements. In an additional series of studies, blood volume and serum chemistry data were analyzed. Male SHRs were significantly higher than normotensive controls on several blood chemistry determinations. Exposure to ionizing radiation, more often than not, enhanced these differences. These results could not be explained on the basis of radiogenic blood volume fluctuations.

Integrity of the blood-aqueous barrier in hyperuricemia.

Neither the origin nor the role of high levels of uric acid, found in the aqueous humor of some human glaucomatous eyes, is known. A model of hyperuricemia in the rat was evaluated for its contribution to urate levels in the aqueous humor. Epinephrine-induced hyperuricemia in male rats was shown to increase mean serum urate levels from 1.2 mg/dL to 6.7 mg/dL. Female rats were shown to have a lower uric acid baseline and a lower absolute hyperuricemic level than males. The mean aqueous-humor urate levels were increased from 0.06 mg/dL to 0.33 mg/dL for male rats. In our studies, the blood-aqueous barrier effectively prevented equilibration between the systemic and ocular compartments. The increased aqueous-humor uric acid levels in glaucoma may arise from intraocular mechanisms.

Retinal change induced in the primate (Macaca mulatta) by oxygen nuclei radiation.

Retinas of primates (Macaca mulatta) were exposed to oxygen nuclei at the Bevatron, Berkeley, California. Color fundus photographs and fluorescein angiograms were taken of the retinas prior to irradiation and up to 5 weeks post exposure. Animals were sacrificed at post exposure intervals for histopathologic examination of the retinas. A series of animals were exposed to 200 kVp X-ray and examined on the same regime as the first series. The results showed a low rad equivalent dose for retinal damage as compared with the X-ray series, i.e., a high quality factor, and a marked compression of the latency between exposure and onset of the retinal pathology.

Ocular hyperuricosis in the rabbit following hyperuricemia and topical epinephrine.

Sources for the high levels of uric acid reported in the aqueous humor from human glaucoma eyes were studied in the rabbit model. A hyperuricemia was produced by oxonic acid blockade of uricase prior to a systemic administration of uric acid. These animals showed no increase in aqueous humor uric acid. Topical medication of eyes with 1% epinephrine produced a statistically significant (P less than 0.001) rise in the level of uric acid in aqueous humor of treated eyes. Mean urate levels increased from 0.44 mg/dl to 0.82 mg/dl. Topical glaucoma medication appears to be the source of ocular hyperuricosis.