Early detection of glaucoma.

Primary open-angle glaucoma (often loosely called "chronic glaucoma") is one of the main causes of preventable loss of sight in Britain1 2 and throughout the world. All too often it is diagnosed only when loss ofthe visual fields is advanced and the condition is resistant to treatment.3 Early detection is therefore of the highest importance, especially with recent evidence that appreciable neuronal damage has occurred even before tests show impairment of the visual fields and before the optic disc shows glaucomatous change.4 After diagnosis careful lifelong monitoring is essential.5 The identification of primary open-angle glaucoma depends on three tests. Ophthalmoscopy detects glaucomatous cupping and pallor of the optic disc, tonometry measures the intra-ocular pressure, and perimetry permits detection of the characteristic visual-field defects.6 Both tonometry and peri-metry require special skill and apparatus, and testing the visual fields in particular is often time consuming. This type of glaucoma is found in about 1% of the population aged over 40.7-9 Surveys have shown that at this level of prevalence no one test provides a cost-effective screening measure: the sensitivity and specificity of each test individually are not good enough to prevent an unacceptably high yield of false-negative and false-positive results.9 10 Any screening procedure which has a high probability of either missing the disease or overloading the hospital services with suspects who prove to be normal will rapidly come into disrepute.9 How then can the ophthalmic services be so organised that the three essential tests are carried out in a cost-effective manner? In Britain we are fortunate in having an existing National Health Service framework within which this objective can be achieved progressively. We need to-make staff, time, and instruments available for the tests when in the examiner's judgment they are necessary. It is crucial to recognise factors which indicate the high-risk subgroup-namely, increasing age over 40; a family history of glaucoma, particularly in siblings11-13; diabetes mellitus14 15; high myopia16; haemorrhages on the optic disc; the presence of coronary disease; and a history of a bleeding episode requiring blood transfusion (M Schultzer and S M Drance, personal communication). In the presence of such factors the possibility of chronic glaucoma must be considered if patients with early disease are not to be missed. In any endeavour rules and check lists have far less influence on the result than the morale of those actually carrying out the work. High morale depends on the aims …