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S Yoneya

Publications and source records attributed to S Yoneya.

50 records · Page 3Linked to original sources
PubMed1991

[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.

Animals↗
PubMed1987

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.

Aged↗
PubMed1986

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.

Adult↗
PubMed1983

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.

Animals↗
PubMed1981

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.

Animals↗
PubMedDate not supplied

Fluorescence properties of a hydrophilic sensitizer in pigmented rats, rabbits, and monkeys.

BACKGROUND AND OBJECTIVE: To evaluate fluorescence properties of mono-L-aspartyl chlorin e6 (NPe6; Meija Seika Kaisha, Ltd., Tokyo, Japan) photodynamic therapy, which allows real-time simultaneous imaging of choroidal and retinal vasculature during treatment without the addition of another dye. MATERIALS AND METHODS: Four pigmented rabbits, 4 pigmented rats, and 2 African green monkeys were administered intravenous injections of the NPe6 dye. The animals were immediately placed in front of the scanning laser ophthalmoscope and the fundus was viewed with the helium-neon laser. The resulting fluorescence was viewed and recorded on super-VHS videotape. RESULTS: Fluorescence demonstrated clearly that NPe6 entered the retinal and choroidal circulation within seconds of intravenous injection. The concentration of NPe6 was diminished over a period of 1.5 hours in the monkey and 5 hours in the rat, as evidenced by considerable diminution of the intensity of fluorescence. CONCLUSION: NPe6 fluorescence allows evaluation of drug availability within the retinal and choroidal circulation and visualization of pathological lesions before commencement of photodynamic therapy.

Animals↗
PubMedDate not supplied

Threshold power levels for NPe6 photodynamic therapy.

OBJECTIVE: To determine the threshold power levels for producing retinal and choroidal vascular occlusion using mono-L-aspartyl chlorin e6 (NPe6) photodynamic therapy; to evaluate its efficacy with longer intervals between photosensitizer injection and laser application; to determine the elapsed time between light application and appearance of angiographic changes. METHODS: Pigmented and nonpigmented rabbits were injected intravenously with 2 mg/kg of NPe6 before laser irradiation of the retina-choroid. Group 1 was treated at increasing power levels; fluorescein angiograms were obtained at each fluence. Group 2 animals were exposed to laser irradiation at 5 minutes, and 1 and 3 hours postinjection to determine (by fluorescein angiography 24 hours post-treatment) if increasing the interval affected outcome. Group 3 animals underwent fluorescein angiography at 30 minutes, 1 hour, 2 hours, and 24 hours posttreatment to document the time between laser application and subsequent vessel closure. RESULTS: Choroidal vessel occlusion was angiographically evident in all lesions at fluences of > or = 2.65 J/cm2 in pigmented rabbits and at > or = 0.88 J/cm2 in nonpigmented rabbits. Lesion diameter decreased as the time between injection and treatment increased. Vessel occlusion was documented at least 2 hours after treatment. CONCLUSION: Choroidal vessel occlusion can occur at very low fluence.

Animals↗
PubMedDate not supplied

Dome-shaped detachment of premacular vitreous cortex in macular hole development.

PURPOSE: To clarify the role of the posterior vitreous cortex in macular hole development, we evaluated the follow-up findings of clinical observations and optical coherence tomography (OCT) images of macular holes in early stage. METHODS: The vitreoretinal tomography was examined and followed in eyes with stage 1 and 2 macular holes with OCT. RESULTS: The posterior cortical vitreous was identified in 12 of 17 eyes with early-stage macular holes by OCT (71%). In these eyes, the detached posterior vitreous appeared to be merged to the fovea and the disc. The vitreoretinal separations showed typically dome-shaped. A long scan along the papillomacular axis also delineated the posterior vitreous face as dome-shaped perifoveal vitreous detachment with adhesion to the fovea and disc. Repetitive OCT examinations clearly demonstrated the course of development of the macular hole. CONCLUSIONS: The dome-shaped vitreoretinal separation seen with OCT gives rise to an idea that the posterior vitreous cortex may not be taut but slack, and would not cause a continuous tractional force even in early-stage macular holes. This finding brings us an idea that the tangential traction at the fovea may be generated by fluid movements, rather than by contraction of the cortical vitreous.

Aged↗
PubMedDate not supplied

Threshold and retreatment parameters of NPe6 photodynamic therapy in retinal and choroidal vessels.

BACKGROUND AND OBJECTIVE: To determine the threshold fluence for producing choroidal and retinal vascular occlusion with mono-L-aspartyl chlorin e6 (NPe6) photodynamic therapy (PDT) during primary treatment and the effect of retreatment. METHODS: Primary treatment: Rats, rabbits, and monkeys underwent NPe6 PDT to determine the threshold fluences for choroidal and retinal vessel occlusion. The threshold was determined by analyzing fluorescein angiograms for areas of nonperfusion. Retreatment: Dutch-belted rabbits underwent NPe6 PDT followed by fluorescein angiography. Rabbits were retreated one week later at the same parameters. RESULTS: Fluence levels and vascular damage thresholds were always higher for retinal than for choroidal vascular occlusion. Retreatment caused choroidal vessel closure at all tested fluences but retinal capillaries closed only at a fluence > 17.7 J/cm2. CONCLUSION: NPe6 PDT has a lower threshold to occlude choroidal vessels than retinal vessels. The cumulative effect of retreatment does not damage retinal vessels unless the threshold is exceeded during a single retreatment session.

Animals↗
PubMedDate not supplied

Toxicity of the photosensitizer NPe6 following intravitreal injection.

BACKGROUND AND OBJECTIVE: To determine the retinal toxicity of mono-L-aspartyl chlorin e6 (NPe6) following intravitreal injection. METHODS: Twelve Dutch-belted rabbits divided into 5 experimental groups (n=2 each) were injected intravitreally with 6.25, 12.5, 25, 50, or 100 microg of NPe6; one control group (n=2) was injected with intravitreal normal saline. One eye in each rabbit was sutured shut to test the effect of light exposure. Fundus photography and electroretinograms were performed before treatment and 2 days, 1 week, and 2 weeks after injection. Animals were euthanized and the eyes enucleated for histopathologic analysis. RESULTS: After 1 week, 4 uncovered eyes given 50 and 100 microg had central retinal vein occlusion and varying degrees of retinal hemorrhage. RPE proliferation was seen in the covered eyes given 50 or 100 microg. Electroretinograms revealed absent retinal response at 100 microg and mild toxicity at 50 microg, but no change from normal at doses of < or = 25 microg of NPe6. CONCLUSIONS: Intravitreal doses of < or = 25 microg NPe6 caused little or no apparent toxicity; however, toxicity was significant at doses of 50 microg and 100 microg.

Animals↗