The diabetic patient presenting with changing refractive error is not uncommon. We are taught to check for diabetes mellitus if a patient presents with rapidly changing refraction and advise them that spectacles should not be prescribed until the refractive state has stabilised.

A low degree of myopia (in the order of −2D) is more common in metabolically stable adult diabetics1 and is understood to be due to an increase in lens thickness2 and surface curvature.3 4 Although it is well recognised that transient refractive changes are common during periods of hyperglycaemia, or falling blood glucose during intensive glycaemic control, there has been some controversy about the nature of the changes and the underlying causes. It has been considered that myopia develops in hyperglycaemia,5 6 and that following therapy there is an hyperopic shift.7-11 Some investigators have suggested that acute changes may cause either myopia or hyperopia.12 13 Most of these studies have been retrospective and the study by Okamoto et alin this issue of the BJO (p 1098) is helpful in clarifying some of these issues. In monitoring a group of poorly controlled diabetic patients during intensive glycaemic control there was an increase in hyperopia in all patients studied. The degree of hyperopia correlated with the level of hyperglycaemia and the rate of plasma glucose reduction.

The refractive power of the eye depends on the anterior and posterior corneal curvature, the corneal thickness, the anterior chamber depth, the lens thickness, the anterior and posterior curvature of the lens, the axial length of the eye, and the refractive index of the cornea, aqueous, lens, and vitreous. Okamoto et alreport that there was no evidence of a change in lens or corneal …