Photocoagulation and diabetic retinopathy.
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Biomedical subjects
Publications and source records attributed to E M Kohner.
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Branch and hemisphere vein occlusion were produced in rhesus monkeys by argon laser photocoagulation. The following observations were made: (1) Immediately after occlusion there was venous dilatation, delayed filling of the artery, delayed drainage by the occluded vein, and capillary leakage. (2) Two patterns of evolution were identified within the first week. In some animals the fundus changes resolved and the retina returned to normal, while in others there was progressive retinal capillary closure. (3) Those animals destined to have capillary closure had diffuse or cluster retinal haemorrhages at 24 hours. (4) Capillary closure took place over 1 week and was usually complete over large areas of retina. (5) Retinal atrophy and major vessel changes occurred over several weeks. (6) Retinal revascularisation occurred in those areas of closure, though this was often limited. It was concluded that the early changes mimicked those seen in human retinal vein occlusion, though persistent retinal oedema and preretinal neovascularisation were not identified.
Experimental branch vein occlusion by laser photocoagulation in the rhesus monkey leads to early, marked, and lasting reduction of blood flow to the affected retinal region. The radioactive microsphere method demonstrates this reduction of blood flow in both gamma counting and autoradiography. The reduction of flow becomes evident as early as 2 hours after occlusion and persists up to 1 week. The mechanism of the altered flow is discussed.
Four cases of diabetic maculopathy with excessive permeability are described. Fluorescence angiography is distinctive, showing profuse early leakage from the entire capillary bed of the posterior pole. Careful studies have failed to reveal any cause for this excessive permeability response at the macula or any constantly associated medical abnormality. The prognosis for visual acuity is poor, and photocoagulation has only rarely been successful in maintaining or improving vision in these patients.
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The role of pituitary hormones in the aetiology of diabetic ketoacidosis was examined by withdrawing insulin from five pituitary-ablated diabetics for a 12-hour period. The rise in blood glucose and ketone-body concentrations was markedly retarded in these patients when compared with five matched juvenile-type diabetic controls with normal pituitary function. When cortisol replacement in the pituitary-ablated patients was increased to reproduce the high plasma concentrations found in severe ketoacidosis, blood ketones and glucose were increased but were still significantly lower than in the control diabetics. It is concluded that pituitary hormones may be important in the development of diabetic ketoacidosis.
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Diabetic retinopathy was found to be present in 12 out of a group of 67 diabetic patients supervised by us during 92 pregnancies, and 3 further pregnant diabetics were referred to us because of retinopathy. The mean duration of diabetes was 13 years (range 3--25 years). Nine patients had minimal retinopathy, 2 had background retinopathy, and the remaining 4 proliferative retinopathy. The cases with minimal retinopathy showed no progression during pregnancy. In 1 patient with background retinopathy there was deterioration. Of the 4 patients with proliferative retinopathy 1 showed regression during the pregnancy, 2 showed advance and were treated with photocoagulation (these 2 patients now have normal vision), while the patient with extensive retinitis proliferans, with retinal detachment in both eyes and previous photocoagulation remained unchanged. The prognosis during pregnancy for patients with diabetic retinopathy is reasonable and has been improved by the advent of photocoagulation.
A patient with temporal arteritis developed a variety of ischaemic lesions in the eyes. Infarction of the inner retina and optic nerve head was delineated on presentation by white swelling in the retinal nerve fibre layer. The role of interrupted axoplasmic transport in the production of this sign is discussed. Outer retinal infarction was also noted on presentation and subsequently gave rise to striking pigmented scars.
Diabetic retinopathy is now a treatable condition, in which blindness can be prevented in a large number of patients. To achieve this, physicians have to screen patients for retinopathy and control diabetes adequately. Ophthalmologists should acquire the expertise of photocoagulation and instruct others in the assessment of retinopathy. Regional centres (one or more per Region) should be set up around interested individuals. These centres' main function is to give prompt treatment facilities to patients and to educate ophthalmologists and physicians in the management of retinopathy. They should also be the centres of advances in treatment. If physicians and ophthalmologists work together, blindness may indeed be prevented in diabetic patients.
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Two patients with Waldenström's macroglobulinemia (WM), which had become resistant to cytotoxic drugs, were treated for features of the hyperviscosity syndrome by repeated plasma exchange with the continuous-flow blood-cell separator over periods of 36 and 28 months, respectively. After four initial weekly plasma exchanges the procedure was carried out every 4 to 6 weeks and both patients tolerated it well. Relative viscosity of the serum was maintained within the normal range in one patient, and both patients remained free of symptoms of the hyperviscosity syndrome. The results suggest that treatment of WM by long-term "maintenance" plasma exchange alone should be considered in any patient with complications due to chemotherapy or whose disease fails to respond to chemotherapy.