Owl Monkey Eyes Research Articles

Wound healing after filtering surgery in owl monkeys.

We performed posterior lip sclerectomies in 29 owl monkey eyes to determine the natural history of wound healing after filtering surgery without adjunctive antimetabolite therapy. We noted three phases of wound healing during clinical and histologic examination: early healing (days 2 to 6), intermediate healing (days 7 to 9), and late healing (days 10 to 14). In the early healing phase, all limbal fistulas except one remained open gonioscopically, but by day 6, fibroblasts had proliferated along the walls of the opening. Proliferation and migration of fibroblasts continued during the intermediate healing phase to completely occlude four and to partially occlude two of the ten fistulas in the eyes studied during this time. In the late healing phase, the limbal fistula was completely closed by granulation tissue in four of five eyes and was slitlike open in one eye. In this model of filtering surgery, wound healing at the sclerectomy site with obliteration of the limbal opening by proliferating fibroblasts occurred within the first 14 postoperative days. We believe that the short-term effects of newer treatments designed to alter wound healing after filtering surgery may be assessed in this model, which is characterized by predictable and prompt wound healing.

The role of the vitreous in the intraocular pressure rise after neodymium-YAG laser capsulotomy.

Autologous liquid vitreous injected into the anterior chamber of the phakic owl monkey eye leads to markedly increased intraocular pressure (IOP) peaking at one to two hours. In contrast, neodymium-YAG laser shock waves focused in the center of the anterior chamber of the same animal led to a mild decrease in IOP. Debris produced by laser pulses focused on the residual cortex of owl monkey eyes that had undergone extracapsular surgery failed to increase the IOP. Similarly, injection of dialyzed vitreous did not have any significant influence on IOP. We conclude that the disruption of the integrity of the anterior cortical gel and the subsequent release of a dialyzable intravitreal substance with a molecular weight of less than 10,000 daltons into the anterior chamber may contribute to the IOP rise after surgical discission, including neodymium-YAG laser posterior capsulotomy.

Transplantation of cultured human retinal epithelium to Bruch's membrane of the owl monkey's eye.

Human retinal epithelial cells dividing in culture have been radiolabelled with tritiated thymidine and subsequently transplanted and identified on Bruch's membrane of owl monkey by autoradiography. Such cells have been followed from 2 hours to 7 days after transplantation. The transplant cells reattach within 2 hours to the basement membrane left on Bruch's membrane after the host epithelial cells have been removed by suction after trypsinization. Within 6 to 24 hours they form a layer on Bruch's membrane with junctional complexes between cells and an apical-basal polarity characteristic of such cells in culture or after retinal detachment. After 2 to 7 days multilayers form by continued mitosis but no transplant cells invade the choroid as long as Bruch membrane is intact. Within this time macrophages begin to appear in the choriocapillaris under the transplant. These cells migrate through Bruch's membrane and between the transplant cells but have not been seen phagocytizing transplant cells. Reattachment of the neural retina to the transplant layer has not been attempted but seems technically possible.

In vivo evaluation of ocular inserts of hydrogel impregnated with antibiotics fop trachoma therapy

Sustained release of antibiotics from hydrogel matrices in the eye was studied for the purpose of developing a new method for trachoma therapy. Copolymers of N-vinylpyrrolidone were moulded into an ocular insert and impregnated with erythromycin or erythromycin estolate. The antibiotic-hydrogel inserts completely supressed the chlamydia trachomatis infection in the owl monkey eyes. The drug elution rates were a little lower in vivo than in vitro. By comparison of the drug elution rate in the human eye with that in the owl monkey eye, similar therapeutic effect is expected in the treatment of human trachoma.

Outer Retina Ischemic Infarction—A Newly Recognized Complication of Cataract Extraction and Closed Vitrectomy: Part 2. An Animal Model

Intraocular pressure was artificially elevated above systolic blood pressure in 40 owl monkey eyes. Diffuse retinal whitening of the posterior pole and subsequent retinal pigment epithelial disruption were produced in nine of ten eyes with high pressure for 90 minutes or longer, but also in a few eyes with high pressure for a shorter duration. Fluorescein angiography and histologic examination demonstrated damage of the photoreceptors and retinal pigment epithelium with sparing of the inner retinal layers. This animal model duplicates the acute visual loss due to outer retinal infarction that sometimes occurs after closed vitrectomy or after continuous external ocular compression in preparation for surgery.

Modification of Corneal Curvature Following Radial Keratotomy in Primates

Radial keratotomy was performed on six stumptail monkey eyes (Macaca speciosa) and 22 owl monkey eyes (Aotus trivirgotus). Changes in keratometry, pachometry, specular microscopy, and tonometry have been studied postoperatively for three to six months. Sixteen radial incisions in stumptail monkey eyes resulted in a significant mean corneal flattening of 2.75 diopters (P <; 0.005). This effect was stable with a mean 2.50 diopters flattening remaining six months after surgery. Sixteen radial incisions in ten owl monkey eyes resulted in a much greater short-term effect, with a mean 10.50 diopters of flattening present at two weeks postoperatively. This flattening deteriorated over the observation period, and no significant effect was noted three months after surgery. A comparison of 8 vs 16 incisions on owl monkey eyes demonstrated that these two procedures are equally effective in initially flattening the cornea. Complications and side effects encountered included perforations, irregular astigmatism, corneal neovascularization, transitory increase in pachometry, and decrease in central corneal endothelial cell density in isolated cases.

Reduction of intraocular pressure in normal and glaucomatous primate (Aotus trivirgatus) eyes by topically applied prostaglandin F2 alpha.

Topical application of a single dose of 1.0 mg prostaglandin F2 alpha (PGF2 alpha) onto the cornea of five trained owl monkeys (Aotus trivirgatus) caused a prolonged and highly significant ocular hypotony. The intraocular pressure (IOP) of the treated eye was 4.7 +/- 0.9 mm Hg below that of the control eye 18 to 24 hr after PGF2 alpha application and remained significantly reduced for over 72 hr. Miosis, aqueous flare, and accumulation of cells in the anterior chamber were minimal in extent. The hypotensive effect of PGF2 alpha was even more pronounced when applied to a glaucomatous owl monkey eye with angle recession, which had IOPs consistently in the 45 to 55 mm Hg range (mean: 47.2 +/- 0.7) as measured periodically over a one-year period. The application of a single dose of 1.0 mg of PGF2 alpha to this hypertensive eye reduced IOP by over 25 mm Hg within 4 hr, with a relative hypotony lasting for at least 6 days. These results show that topical application of certain PGs to normotensive or hypertensive primate eyes can cause a long lasting and highly significant decrease in IOP, and suggest that prostaglandins or their analogues may aid in the therapeutic control of ocular hypertension and glaucoma.

Retinal damage produced by intraocular fiber optic light

We exposed the maculas of owl monkey eyes to light from an intraocular fiber optic light source similar to that used for human pars plana vitrectomy. Retinal irradiance was calculated at 0.22 W/cm2. Eyes were exposed for time intervals ranging from 30 minutes to five minutes and were observed after light treatment by fundus photography and fluorescein angiography. Tissue was obtained for light and electron microscopy by animal killing at one hour, 24 hours, one week, and four weeks. Fundus lesions were seen ophthalmoscopically as early as five hours following 30 minutes of light exposure. Significant damage to the photoreceptor layer and less damage to the pigment epithelium was present by light and electron microscopy as early as one hour after 30 minutes of light exposure. By one month complete loss of photoreceptors with Muller cell junctions between inner retina and flattened abnormal retinal pigment epithelium cells was observed. Fluorescein angiography revealed significant staining of the pigment epithelium and outer retina 24 hours after 30 minutes of light exposure. No leakage from retinal vessels occurred. At one month following light treatment, transmission of choroidal fluorescein through window defects in the pigment epithelium was present with no retinal staining. The threshold for ophthalmoscopically visible fundus lesions in this study was 15 minutes of light exposure. Ten minutes of light treatment was the threshold for microscopic changes. Short light exposures damaged the outer retina and spared the pigment epithelium. Removing a substantial amount of the infrared light from our light source did not protect the retina from damage. Removal of light between 400 and 500 nm is probably more helpful in protecting the retina. Intermittent light exposure of the retina seemed as harmful as uninterrupted illumination for the same cumulative period of time. We speculate that the retinal damage caused by intraocular fiber optic light has primarily a photic mechanism. Damage to the retinal pigment epithelium may be secondary to outer retinal damage. The present levels of intraocular light used for human pars plana vitrectomy are probably safe in most instances. Lengthy preretinal membrane stripping procedures during vitrectomy, however, may pose a threat of light damage to the retina. This damage must be appreciated as continued efforts are made to produce brighter sources of intraocular light for human pars plana vitrectomy.

Retinal Ganglion Cell Degeneration in Experimental Optic Atrophy

By ophthalmoscopic and histopathologic examinations at various intervals after retinal injury, we studied progressive ganglion cell atrophy following retinal photocoagulation in 25 owl monkey eyes. A reduced ganglion cell population was apparent within three to four weeks after the photocoagulation and was maximal by six weeks.

Retinal Damage Produced by Intraocular Fiber Optic Light

We exposed the maculas of owl monkey eyes to light from an intraocular fiber optic light source similar to that used for human pars plana vitrectomy. Retinal irradiance was calculated at 0.22 W/cm2. Eyes were exposed for time intervals ranging from 30 minutes to five minutes and were observed after light treatment by fundus photography and fluorescein angiography. Tissue was obtained for light and electron microscopy by animal killing at one hour, 24 hours, one week, and four weeks. Fundus lesions were seen ophthalmoscopically as early as five hours following 30 minutes of light exposure. Significant damage to the photoreceptor layer and less damage to the pigment epithelium was present by light and electron microscopy as early as one hour after 30 minutes of light exposure. By one month complete loss of photoreceptors with Müller cell junctions between inner retina and flattened abnormal retinal pigment epithelium cells was observed. Fluorescein angiography revealed significant staining of the pigment epithelium and outer retina 24 hours after 30 minutes of light exposure. No leakage from retinal vessels occurred. At one month following light treatment, transmission of choroidal fluorescein through window defects in the pigment epithelium was present with no retinal staining. The threshold for ophthalmoscopically visible fundus lesions in this study was 15 minutes of light exposure. Ten minutes of light treatment was the threshold for microscopic changes. Short light exposures damaged the outer retina and spared the pigment epithelium. Removing a substantial amount of the infrared light from our light source did not protect the retina from damage. Removal of light between 400 and 500 nm is probably more helpful in protecting the retina. Intermittent light exposure of the retina seemed as harmful as uninterrupted illumination for the same cumulative period of time. We speculate that the retinal damage caused by intraocular fiber optic light has primarily a photic mechanism. Damage to the retinal pigment epithelium may be secondary to outer retinal damage. The present levels of intraocular light used for human pars plana vitrectomy are probably safe in most instances. Lengthy preretinal membrane stripping procedures during vitrectomy, however, may pose a threat of light damage to the retina. This damage must be appreciated as continued efforts are made to produce brighter sources of intraocular light for human pars plana vitrectomy.

Macromolecular composition of the vitreous in the aphakic owl monkey eye

The concentration of different macromolecular components of the owl monkey vitreous was investigated after surgical procedures equivalent to intracapsular and extracapsular cataract extraction. Following intracapsular extraction the concentration of hyaluronic acid decreased markedly during the early postoperative period, whereas in eyes subjected to extracapsular extraction, hyaluronic acid concentration was virtually unchanged. The molecular parameters of hyaluronic acid might change as reflected on the gel chromatographic profile. Both surgical methods were accompanied by increased concentrations of protein in the vitreous.

Small-Field Irradiation of Monkey Eyes with Protons and Photons

The relative biological efficiency (RBE) of a 7 mm diameter proton beam was compared to a 6.25 mm 2 MV photon beam by measuring their relative effects in owl monkey eyes. We chose as the endpoint the appearance of a circumscribed patch of chorioretinal edema 2 days after a single dose. Both unmodulated protons and modulated proton beams showed an RBE close to unity. Dose is critically dependent on the position of the Bragg peak relative to the retina and choroid. Irradiation with modulated protons in five fractions once per week produced a marked tissue-sparing effect; no clinical or histological effects were evident 1 yr later, until a total dose of 12,500 rad or more had been delivered. These experiments are of importance to the planning of small-beam therapy of eye tumors. Finally, they demonstrate that carefully collimated narrow beams can deliver a tissue-destroying dose to a localized area of retina and choroid, while causing minimal damage to adjacent normal tissue.

Proliferation and Metaplasia of Intravitreal Retinal Pigment Epithelium Cell Autotransplants

Pigment epithelium cells autotransplanted into the vitreous cavity of owl monkey eyes, proliferated and metaplased. The metaplastic cells looked like pigmented macrophages, membrane forming fibrocyte-like cells, and frank epithelium cells. This in vivo experiment demonstrated that the vitreous cavity is an adequate culture medium for cells deriving from the pigment epithelium and that pigment epithelium cells could be the source of intraocular proliferation seen in massive periretinal proliferation.

Pigment Epithelium Proliferation in Retinal Detachment (Massive Periretinal Proliferation)

Cell proliferation and membrane formation found in the posterior parts of the eye after production of retinal detachment in owl monkey eyes had either the characteristics of macrophages or of membrane-forming epithelial cells. The proliferating cells originated from pigment epithelium. These membranes caused folding of the retina and strand formation in the vitreous cavity. Since cell proliferation was present on all available surfaces, such as the upper and under surface of the retina, and along vitreous surfaces, we propose to call this entity "massive periretinal proliferation" (MPP).

Sulfur Hexafluoride in Owl Monkey Vitreous Cavity

Sulfur hexafluoride (SF6) gas, tested in the vitreous chamber of owl monkey eyes, remained in the vitreous cavity about twice as long as air (ten to 11 days vs. five to six days). Its volume expanded from the diffusion of other gases into the created gas pocket. Lens opacities developed when the lens was in continuous contact with SF6 or air. Sulfur hexafluoride appeared to be no more toxic to the retina than air, using electroretinographic, histologic, and electron microscopic criteria.

Experimental central retinal vein occlusion. A comparison of intraocular and extraocular occlusion.

Circulatory dynamics and pathology of occlusion of the central retinal vein was compared at two sites in the owl monkey eye. In 17 eyes, neoprene occluded the central retinal vein at the disc and, in ten eyes, the central retinal vein was tied and cut as it emerged from the optic nerve. The first group of animals demonstrated rapid ischemic and hemorrhagic infarction of the retina and obstruction of the arterial flow by fluorescein angiography. The second group demonstrated a temporary and reversible increase in venous congestion without secondary damage to the eye. Collateral circulation in the region of the disc and posterior to it explains best the difference in the two groups. Partial obstruction of the central retinal vein by neoprene approximated the central vein occlusion in man, but neither model exactly reproduced it.