Biomedical subjects
Publications and source records attributed to A M Hamilton.
We describe cases of haemorrhagic disciform macular detachment occurring in young adults in association with multifocal disease at the level of the retinal pigment epithelium (RPE). The cause of the original focal lesions is unknown. Our cases demonstrate a variable and unpredictable clinical course in which the disciform response may develop rapidly.
The effects of treatment by argon laser and xenon arc photocoagulation in 165 diabetic patients with optic disc new vessel formation have been studied retrospectively. Visual acuity and degree of new vessel formation have been assessed over a period of between six months and seven years of follow-up (mean 23 months). Visual acuity improved in 36% of treated eyes and remained unchanged in 34%. Improvement was most marked in those with initially poor acuity (less than 6/36). There was no association between improvement in visual acuity and regression of disc vessels, the latter occurring in 79% of treated eyes. Only 6% of eyes became blind during the period of follow-up, principally as a result of vitreous haemorrhage and retinal detachment. There was no difference between the results produced by the use of separate or combined argon laser and xenon arc photocoagulation on the regression of disc new vessels. However, our results suggest that argon laser treatment was more effective than xenon arc photocoagulation in improving visual acuity. These findings suggest that either form of treatment or a combination offers considerable benefit in the management of proliferative diabetic retinopathy, even when very severe at presentation.
We report a modification to the argon-krypton laser (Lasertek Model AK 41) which allows optional automatic operation. This is a safe, time-saving device for use in cases requiring extensive retinal laser treatment.
Angioid streaks were observed in 21 of 242 patients with homozygous sickle cell disease. Two morphological types were observed. There is no evidence that angioid streaks in Jamaican patients are related to pseudoxanthoma elasticum.
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Xenon arc and argon laser photocoagulation are equally effective in producing regression of disc neovascularization and maintaining visual acuity. Xenon has more destructive effects on the visual field and electroretinogram, but is more comfortable because retrobulbar anaesthesia is used and more convenient to the patient because fewer treatment sessions are needed.
Patients with long-standing diabetes develop acquired colour vision defects in parallel with retinal vascular changes. This may take the form of an overall loss of hue discrimination or a specific tritan (blue) defect. A battery of colour vision tests can be used to monitor the different features of diabetic retinopathy and to assess the effects of treatment. Diabetic disc new vessels form when approximately a quarter of the retina is ischaemic. The colour vision defect in these patients is usually severe and is frequently tritanopic. The effect of both argon laser and xenon arc panretinal photocoagulation is to increase the severity of the colour defect. All the eyes examined were tritanopic after treatment and did not recover during the 12-month follow-up period. The severity of this acquired colour vision defect can result in practical difficulties for the patient.
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Twelve affected members from 3 families with autosomal dominant exudative vitreouretinopathy were examined, and the following conclusions were drawn: (1) There is great variability in the phenotypic expression of the abnormal gene, such that many patients have very mild disease which can be detected with certainty only by fluorescein angiography. (2) Gene penetrance is close to 100%. (3) Progress of fundus changes and visual threat is rare after 20 years of age.
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The beneficial effect of photocoagulation in diabetic retinopathy is now established (3-7, 10). Whereas the capability of providing photocoagulation is widespread, the indications and actual technqiues are poorly defined. In an earlier paper (1) we discussed the principles of photocoagulation. In this paper the detailed techniques required for the treatment of individual lesions and of different types of retinopathy will be discussed.
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.
A comparative study of the relative efficacy of the krypton and argon lasers in the treatment of disc new vessels in diabetic retinopathy was made. Resolution of the disc new vessels was achieved in both instances. There were clinical differences in the use and effects of the 2 lasers.
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 beneficial effect of photocoagulation in diabetic retinopathy is now established (2-6, 10). Whereas the capability of providing photocoagulation is widespread, the indications and actual techniques are poorly defined. In this paper, we propose to discuss the principles of photocoagulation. In a following paper the detailed techniques required for the treatment of individual lesions and of different types of retinopathy will be discussed.