Randi Patterson

Formation of Drusen in the Human Eye

Light and electron microscopy of drusen formation in the human eye showed yellow-white spots in the fundus with two morphologic patterns: that of typical drusen and a nodular accumulation of cellular components beneath the retinal pigment epithelial cells. By electron microscopy, the progression of drusen formation could be classified into four stages. Stage I showed budding or evagination of retinal pigment epithelial cells into the subpigment epithelial space. This evaginated portion was connected to the retinal pigment epithelial cell cytoplasm and was surrounded by its basement membrane. In Stage II the evaginated portion of the cell was completely separate from the cytoplasm of its parent retinal pigment epithelial cell. In Stage III, the evaginated portion showed degeneration and disintegration. Finally, in Stage IV, an accumulation of vesicular, granular, tubular, and linear material was seen free within the nodular space beneath the retinal pigment epithelial cell.

Daunomycin in the treatment of experimental proliferative vitreoretinopathy: retinal toxicity of intravitreal daunomycin in the rabbit

The retinal toxicity of daunomycin, a drug that effectively suppresses experimental proliferative vitreoretinopathy (PVR), was studied in the rabbit by clinical examination, electroretinography (ERG), light microscopy, and electron microscopy. Although no toxicity was observed at the therapeutically effective dose of 10 nmol per eye, the safety margin is too small to recommend this drug for therapy of proliferative vitreoretinopathy in man.

Aging Changes in Bruch's Membrane of Monkeys: An Electron Microscopic Study

Bruchs membrane from monkeys of various ages was studied by electron microscopy. In monkeys under 15 years of age, Bruchs membrane rarely contained a small amount of polymorphous material that did not appear to increase with advancing age up to 15 years. However, the polymorphous material did increase over 20 years of age. The accumulation of vesicular, granular, tubular and linear polymorphous material in Bruchs membrane was though to be a result of evagination of a minimal portion of a retinal pigment epithelial (RPE) cell between adjacent basal infoldings, and its subsequent degeneration. The plasma membrane of the evagination seemed to be the primary source of the tubular or linear material, vesicles the main source of vesicular material, and cytosol and basement membranes to be the source of the granular material. The fibrous long-spacing collagen was associated with the basement membrane of the choriocapillaris and RPE cells. The granular deposits between the plasma infoldings and the basement membrane of RPE cells may originate from the basement membrane of the RPE, and could be the initial lesion of basal linear deposits.

Effect of the vitreous on retinal wound-healing

The healing process of experimental retinal wounds in nonvitrectomized and vitrectomized rabbit eyes was compared. Using light, transmission and scanning electron microscopy, a significant difference was observed at the late stages of the healing process. The retinal wounds in the nonvitrectomized eyes healed properly, forming regular and smooth scars, while the scars that developed in the vitrectomized eyes were irregular and hypertrophic. Our observations suggest that the vitreous plays a role in normal healing of retinal wounds.

Fibronectin of the chorioretinal interface in the monkey: immunohistochemical and immunoelectron microscopic studies.

The distribution of fibronectin in the chorioretinal interface of the monkey eye was studied by indirect immunofluorescent and immunoelectron microscopic techniques. Immunofluorescent staining revealed fibronectin in Bruchs membrane and the choriocapillaris. Immunoelectron microscopic techniques revealed fibronectin associated with basement membranes, collagen fibers and elastic fibers in Bruchs membrane; the stromal side of the basement membrane of the choriocapillaris also showed staining. This study thus demonstrates that fibronectin is an integral component of Bruchs membrane in the monkey eye.

Morphologic evaluation of vitreous collagen after penetrating ocular injury

Condensation and contraction of the vitreous have been implicated in the development of vitreoretinal traction and traction retinal detachment after penetrating ocular injury. In this study, using the inorganic dye ruthenium-red, we studied ultrastructural changes in vitreous in the rabbit eye after standard penetrating injury and intravitreal blood injection. In normal rabbit vitreous the collagen fibrils have a regular arrangement. In contrast, after a penetrating injury the collagen fibrils appear focally condensed. While it appears unlikely that such a network could alone produce tractional or directional forces, these alterations along the collagen fibrils could provide a scaffold along which contractile cells migrate into the vitreous.

An intravitreal cannula system: long-term follow-up study.

An intravitreal cannula for chronic drug delivery was implanted in the eyes of two rabbits and one monkey. The rabbits were followed up for three years after surgery and the monkey was followed up for two and one-half years. Clinical observations did not reveal any adverse effects from the cannula implantation. Patency of the cannula was demonstrated by using sodium fluorescein. Histopathological studies with light and electron microscopy revealed the scar tissue around the cannula to be minimal and localized to the wound site. The optic nerve and the retina and choroid at the posterior pole did not show any abnormalities. These results suggest that this system can be used for repeated or continuous drug delivery to the vitreous over a long period of time in experimental models.

An indwelling cannula system for the primate eye

An indwelling cannula system was designed as an instrument for chronic drug infusion into the vitreous cavity and tested in the cynomolgus monkey eye with repeated injections or continuous infusion using a pumping device. The cannula was passed through the pars plana and its tip situated in the vitreous cavity close to the macular area. Clinical observations up to 18 months did not reveal any adverse effects due to implantation. Histopathological observations from 1 week to 18 months after surgery revealed tissue proliferation around the cannula was minimal and localized only at the wound site, where proliferative tissue originated from the episclera and ciliary epithelium. Retina and choroid at the posterior pole showed normal morphology. Light microscopic autoradiograms demonstrated the function of this system. Injections of tritiated leucine through the cannula resulted in narrow bands of radioactive labelling of the photoreceptor outer segments corresponding to each injection. In contrast, chronic delivery using the pumping device resulted in a diffuse and wide band of labelling. These results strongly suggest that this system did not adversely affect the eye and that repeated intravitreal injections or chronic drug delivery into the vitreous are feasible using this system. Furthermore, autoradiographic results suggest that the drugs infused into the vitreous cavity spread readily into the retina.

Pathogenesis of Drusen in the Primate

Two monkey eyes that showed clinical evidence of drusen were studied by light and electron microscopy. The drusen-like spots had several different morphological patterns: the appearance of typical drusen, budding retinal pigment epithelial (RPE) cells, and vacuolation of retinal pigment epithelial cells. Several stages of budding were seen. In some lesions, part of the RPE cell protruded into the sub-RPE space. The upper portion of the budding cell was connected to the cytoplasm of the parent RPE cell and was surrounded by basement membrane of the RPE cell. These budding cells had plasma membranes, cytoplasm that contained organelles, and a nucleus. Disconnected buds, separate from the parent RPE cell, were also seen; these showed degeneration. Finally, an accumulation of vesicular, granular, tubular and linear material was found in the nodular space beneath the RPE cell. It is suggested that this budding of RPE cells is the initial event in drusen-formation.