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Clinical trials are often used to evaluate the efficacy of a given treatment. The results of clinical trials however do not always agree with a clinician's experience or intuition. The merits and demerits of Clinical Trials versus Intuition are discussed by using the laser photocoagulation trials of Proliferative Diabetic Retinopathy, Central serous retinopathy, Branch Vein Occlusion (treatment for macular oedema), Senile Macular Degeneration, and Pigment Epithelial Detachment. A model based on Intuition is used to explain the discrepancy between the results of the British and American trials of Branch Vein Occlusion and Senile Macular Degeneration. Proposals on the presentation of Clinical Trials and the place of Intuition are made.

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.

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.

Established neovascular glaucoma in the presence of clear media can be treated by panphotocoagulation followed by drainage surgery. Three cases are described, and the advantages of this procedure as opposed to others available are discussed. Photocoagulation must be performed early before the development of opaque ocular media obscures the retina.

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.

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.

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.