[Fluorescein angiographic observation of cellular changes in the retinal pigment epithelium after laser photocoagulation]

Lesions in the retinal pigment epithelium (RPE) of 16 pigmented rabbits were produced by dye laser photocoagulation using with three different wavelengths: 514, 577 and 630 nm. The power setting and exposure time was the same throughout. The size of the coagulation spot was set either at 500 or 1,000 microns. The retinal lesions were examined by high resolution fluorescein angiography on day 2, 7 and 30 after photocoagulation. Scanning electron microscopic examination of RPE was also performed in selected cases. On fluorescein angiography, the damaged RPE cells appeared as negative fluorescent spots with intense fluorescent margins, throughout the period of observation. The size of the lesion also remained constant. There were no difference in the damage or recovery of RPE cells in relation to the 3 different laser wavelengths. In some area of lesion, the fluorescein angiographic findings closely matched those observed by scanning electron microscopy.

Retinal and vitreal neovascularization in retinopathy of prematurity. A scanning electron microscopic study in the kitten

The angioarchitecture of vitreal and retinal neovascularizations produced experimentally in the eyes of kittens aged 2 to 9 weeks was studied with scanning electron microscopy. Various forms of new retinal and vitreal vessels were observed depending on topographic locations. Intraretinal neovascularization was observed at the retinal periphery as it grew toward the avascular zone in forms of short vascular buds, aneurysmal outgrowths, and neovascular loops. Posterior or to this frond of neovascularization, intertwining intraretinal telangiectasia was observed. At the posterior pole, capillaries with microaneurysms extended posteriorly toward the deeper layers of the retina from the vascular trunks at the nerve fiber layer. Vitreal neovascularization broke through the internal limiting membrane and exhibited aneurysmal outgrowths, clusters of glomerular swellings, and sinusoidal vascular channels. At the optic disc, vitreous neovascularization took the form of aneurysmal outgrowths and long vascular buds. Vitreal neovascularization showed different characteristics from the intraretinal neovascularization. We hypothesize that the topographic variation of the angioarchitecture of retinal and vitreal neovascularizations depends on the maturity of the vessels and might be related to the hemodynamics at each site.

[Effects on the retina and choroid of transpupillary diode laser photocoagulation]

A transpupillary retinal photocoagulator utilizing GaAlAs diode laser which emits an 810 nm beam has been constructed. It has a continuous-wave mode with a maximum output of 400 mW at the cornea. Animal experiments with monkeys were carried out successfully at various intensities to produce controlled coagulations. Observation by ophthalmoscopy, light and electron microscopes at different time intervals proved diode laser photocoagulation produced more intensive effects in choroid than krypton red laser (647 nm). However, due to the greater absorption of the choroid, there is a tendency to over-coagulation unless conditions are carefully set. No serious side effects in the retina and choroid were observed during the experiments.

[Morphology of live retinal pigment epithelial cells]

We attempted to observe, by means of fluorescein angiography, the retinal pigment epithelial cells in pigmented rabbits. Fluorescein angiography was performed in 31 pigmented rabbits, after intravenous injection of 14mg/kg fluorescein sodium. The angiograms were evaluated as prints and as negative film under a light microscope. Animals were sacrificed and submitted to studies by scanning electron microscopy and fluorescein light microscopy. On fluorescein angiograms, we observed mosaic pattern which consisted of numerous polygonal spots overlying choroidal vasculature. Each polygonal spot showed central hypofluorescent area surrounded by hyperfluorescent rim. They were seen in all the eyes except 4 lightly pigmented eyes. They seemed to correspond, in size, to each retinal pigment epithelial cell. This pattern appeared from the early choroidal phase on, to become more distinct 5 to 15 minutes after dye injection. A hexagonal pattern was regularly seen away from the medullary rays by 3 or more disc diameters. The pattern became larger in the periphery than in the posterior pole. These angiographic findings closely matched those of retinal pigment epithelial cells as seen by scanning electron microscopy and fluorescein light microscopy in sizes and shapes. The findings indicate that it is possible to identify retinal pigment epithelial cells in pigmented rabbits by conventional fluorescein angiography.

Angioarchitecture of the human choroid

The angioarchitecture of the human choroid was studied by corrosion vascular casts and scanning electron microscopy. The relationship of the large choroidal arteries and veins, medium-sized arteries and veins, precapillary arterioles and postcapillary venules, and the choriocapillaris is described. At the posterior pole, a lobular arrangement of the choriocapillaris is seen. At the equatorial area, the capillaries run a more direct course, joining the precapillary arterioles to the capillary venules in a spindle-shaped segment of the choroidal vasculature. At the periphery, the choroidal arterioles and venules take a parallel course, with the choriocapillaris joining the adjacent arterioles and venules at a right angle and appearing in a ladder pattern. The regional variation of the angioarchitecture of the human choroid provides supporting evidence for the unique regional characteristics of choroidal blood flow.

Epivascular glia and paravascular holes in normal human retina

We examined the retinal surface of 28 autopsy eyes by scanning electron microscopy (SEM). Glialike cells or their processes, arranged in rows, were observed along retinal vessels in 22 eyes. Additionally, there were clusters of glialike cells over retinal vessels in 8 eyes. These proliferations ranged from focal to extensive ones, the latter resulting in distinct preretinal membranes. Focal defects of the superficial retina along the vessel were noted in 6 of 28 eyes. Transmission electron microscopic study in 2 surgically enucleated eyes with normal retinae revealed epivascular retinal degeneration and thinning of Müller cells. Glial processes appeared to be covering the defect of the internal limiting membrane and some projections of these cells continued inwards. These findings were consistent with the SEM findings of epivascular glialike structure. Our conclusions are that epivascular glialike structures and paravascular surface defects appear as a common finding in normal senile eyes, and that occasionally membranous formations arise from the epivascular area.

Patterns of the choriocapillaris. A method to study the choroidal vasculature of the enucleated human eye

We examined the architecture of the choriocapillaris in enucleated human eyes by flat preparation using trypsin digestion and corrosion cast technique by injecting methacrylate into the vortex vein. The choriocapillaris in the posterior fundus had a distinct lobular pattern of about 600 mu in diameter. An arteriole entered the lobule at its center, and a ring of collector capillaries surrounded the lobule. In the equatorial and more peripheral fundus, arterioles and veins were located in the plane of the choriocapillaris, and the choriocapillaris was segmental in arrangement.

Fundus photocoagulation with the argon and krypton lasers: a comparative study

Photocoagulation of the monkey fundus with an argon-krypton laser photocoagulator was performed. Lesions produced by argon and krypton wavelengths were compared at various power settings, spot sizes, and exposure durations. At low energy levels argon laser lesions appeared clinically stronger than those produced by the krypton mode. Lesions in the foveal area produced with the argon laser demonstrated more extensive microscopic damage to the inner retinal layers than did those produced with the krypton laser. Histologically, both modalities affected the outer layers of the retina. However, the krypton wavelength affected more of the choriocapillaries and the larger choroidal vessels than the argon wavelengths. Conversely, argon laser coagulation of the retinal vessels damaged the perivascular tissue in the nerve fiber layer more than the krypton laser did. Rupture of Bruch's membrane and choroidal hemorrhage occurred frequently with the krypton laser at low energy levels when a small spot size and a short coagulation time were used. Both complications were less likely to occur with argon burns at similar dosage parameters. By choosing larger spot sizes and longer coagulation times for the krypton laser, these complications were prevented.