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A neodymium-YAG laser, operating in its free-running mode with pulse durations of 10 to 20 ms, was used to treat 63 cases of choroidal and retinal diseases. These cases included diabetic background retinopathies, thrombosis of the central retinal vein or branch retinal vein, neovascular membranes under the pigment epithelium, and retinal breaks or degenerations of the peripheral retina. Because the number of diabetic retinopathies (24) and their average follow-up time (25.5 months) are insufficient for the evaluation of irradiation effects, no definite statement as to the merits of this energy modality in such cases can be made. The irradiation of infarcted retina was followed by extensive atrophy of the involved area. No secondary glaucoma was observed during a follow-up period of 16.4 months. The irradiation in four cases of neovascular subretinal membranes was followed by disappearance of the membranes. However, relapse later occurred in all four cases. The irradiation of eight retinal breaks resulted in solid scar tissue. Two choroidal melanomas were destroyed and did not recur during a follow-up period of 22 months.

The effect on range of accommodation, size of pupil and corneal sensitivity of panretinal photocoagulations was investigated in 30 diabetic patients. Treatments with the xenon arc or the argon laser produced significant changes in the 3 parameters one month after photocoagulation, but only when retrobulbar anaesthesia was used. After 6 months the range of accommodation and the size of the pupil were almost normalized. The corneal sensitivity remained significantly reduced.

Choroidal neovascularization in rat eyes was induced by krypton laser photocoagulation. Lesions were studied weekly by ophthalmoscopy, fundus photography, and fluorescein angiography. Morphologic correlation was provided by serial sectioning of lesions for light and transmission electron microscopy. In addition, vascular casts were prepared for scanning electron microscopy. Choroidal neovascularization occurred in 25 (60%) of 42 lesions, as evidenced by growth of capillaries through breaks in Bruch's membrane. In addition, 24 (28%) of 86 lesions studied by fluorescein angiography demonstrated leakage. This study provides the most complete angiographic, histologic, and ultrastructural documentation of experimental choroidal neovascularization in the rat. This model may be useful for in vivo studies of choroidal angiogenesis and its modulation via drug therapy.

Krypton laser photocoagulation of the posterior fundus of the rat created white retinal lesions comparable with therapeutic burns in the human. Twenty-four hours after injury, the retinal pigment epithelium was destroyed and the majority of the endothelial cells survived. The choriocapillary lumen was occluded. Bruch's membrane was not fractured nor had it undergone thermal lysis in any area studied but choriocapillary endothelial cell buds invaded the choroidal side of Bruch's membrane. After seven days, cellular protrusions arising from retinal pigment epithelial cells traversed Bruch's membrane through full-thickness defects and entered the choroid. Although intense laser burns may destroy Bruch's membrane, we conclude from this data that many so-called "breaks" in Bruch's membrane following laser therapy are formed by cellular processes and are not caused primarily by laser coagulation.

The effects of the neodymium:YAG laser in the thermal mode on the subhuman primate retina were studied with ophthalmoscopy, intravenous fluorescein angiography, light microscopy, transmission electron microscopy, and scanning electron microscopy using a plastic injection-corrosion technique. Representative samples were examined at 24 hours, 14 days, and 28 days after treatment. The burns appeared to predominantly affect the outer half of the retina and the inner half of the choroid, although with higher energy levels the inner retinal layers were occasionally involved. In most instances Bruch's membrane was disrupted. The injured choriocapillaris underwent a reparative process during a four-week period in which the discrete lesions observed at 24 hours had disappeared.

Three cases of postradiation retinopathy are reported. The findings are analysed. The exudates described by many authors are really infarcts of the choroid lobules. Chorioretinopathy is proposed as a better descriptive term, and three types are suggested. Diagnosis of the condition is important to spare unnecessary enucleation, as the infarcted areas may resemble a recurrence. Predisposing factors are discussed.

The scarring process induced within the retina and choroid of pigmented rabbits' eyes following irradiation with the neodymium-YAG laser (working in the free-running mode) was examined at the ultrastructural level. Scarring of the sensory retina proceeded rapidly and was well advanced two weeks after irradiation, whereas in the choroid, signs of repair were apparent only after six weeks. This difference in the rate of repair between the two tissues has a bearing on the scarring pattern in the retinochoroid as a whole. The severity of damage to the elastic component of Bruch's membrane also has important consequences in relation to the repair processes in the retina and choroid. Microfractures within this layer, while enabling migrating cells of various kinds to penetrate into the inner collagenous zone, did not prevent complete regeneration of the retinal pigment epithelium (RPE). In instances of greater rupture, however, RPE regeneration was found to stop at the border of the break, and the discontinuity produced within Bruch's membrane and the RPE allowed the glial scar to expand into the choroid. In this region, new formation of vessels was not found.

This paper reviews the historical events leading to the development of the ophthalmic laser. The formation of the argon laser beam and its biological effects on ocular tissues are outlined, with the major emphasis on the retinal and choroidal tissues. The clinical indications, contraindications, and complications of ophthalmic argon laser photocoagulation for the anterior segment as well as the posterior segment structures of the eye are also thoroughly discussed.

The Authors were able to observe histologically the lesions induced by Argon-laser on the retina and choroid of two eyeballs that afterwards were enucleated because they developed choroid melanoma. The observations have been respectively made 10, 20 and 40 days after the beginning of the treatment and a progressive structural overturning of the retina and the choroid due to the obstruction of choriocapillary vessels, to the tendency to fusion of the various nuclear layers as well as to the connection of the layer of nerve fibres, has been observed.

The electromagnetic spectrum consists of radiant energy that is classified according to specific wavelengths. Man is constantly exposed to a portion of the electromagnetic spectrum, particularly to radiation in the ultraviolet, visible and infrared regions. The tissues of the eye and skin are particularly sensitive to the non-ionizing wavelengths of radiant energy. Although both tissues possess endogenous protective mechanisms to minimize the effects of such exposure, problems still occur due to the absorption of radiation. The cornea, lens and retina have been shown to be susceptible to damage from light in the ultraviolet, visible and infrared range. Part I of this two-part article examines the structures of the eye that are most susceptible to light damage; part II, which will be published in the next issue of the Journal, focuses on eye protection.

Metastatic carcinoma is the commonest malignant tumour of the eye and usually presents with a disturbance of vision. A rare case of choroidal metastasis secondary to adenocarcinoma of the rectum is reported to emphasize the need to investigate visual symptoms in patients with known or suspected malignant disease.

Photocoagulation was performed in pigmented and albino rabbits using four different wave-lengths of the dye laser (577 nm, 590 nm, 610 nm and 630 nm), and each photocoagulated lesion was examined histologically. The 577 nm dye laser produced chorioretinal coagulation in albino rabbits, which was almost the same as that in pigmented rabbits. This result confirmed that the 577 nm dye laser was well absorbed by hemoglobin in the choriocapillaris, and could produce the sufficient coagulation even if there was no melanin pigment. The 590 nm dye laser produced chorioretinal coagulation in albino rabbits, but it was weaker than that in pigmented rabbits. It was considered that this was because the absorption by hemoglobin of the 590 nm dye laser was less than that of the 577 nm dye laser. The 610 and 630 nm dye laser could not yield appropriate coagulation in albino rabbits under the same conditions as in the 577 nm dye laser. More intense coagulation, that is longer duration and higher power, was required to make chorioretinal coagulation in albino rabbits using the 610 and 630 nm dye laser. In photocoagulation of normal fundus, melanin is the main substance of laser absorption, but in various disorders lacking melanin, the differences of the hemoglobin absorption rate becomes important.