Patients with diabetes account for one eighth of all patients undergoing cataract surgery. Despite this, there is uncertainty over the best operative technique, and although postoperative visual acuity may be poor as a result of macular oedema, the optimal management of this entity is undefined, and natural history data on which to base management are lacking. In this thesis a prospective randomised paired-eye controlled trial comparing phakoemulsification with extracapsular cataract surgery in diabetes identified a lower incidence of capsular opacification and postoperative inflammation, and slightly better visual acuity, in eyes undergoing phakoemulsification. There was no difference in retinopathy progression or incidence of macular oedema. The principal determinants of postoperative visual acuity in each surgical group were the presence of macular oedema at the time of surgery, and to a lesser extent, the severity of retinopathy. A study directed at defining the natural history of postoperative macular oedema attempted to identify predictors of likely spontaneous resolution. Angiographic findings, in particular postoperative optic disc hyperfluorescence, were not predictive. By contrast, clinical examination was a useful predictor, since macular oedema present at the time of surgery showed no tendency to spontaneous resolution, whereas that arising after surgery resolved in three- quarters of eyes by one year. The presence of macular oedema at the time of surgery was the principal determinant of postoperative visual acuity. These findings suggest that macular oedema should be managed expectantly if it arises after surgery, and treated with laser if present at the time of surgery. Phakoemulsification appears to be the preferred surgical approach, but the choice of surgical technique may be less critical to outcome than operating early enough to ensure that cataract does not prevent identification of macular oedema, the presence of which at the time of surgery is associated with poor postoperative visual acuity.