very useful in assessing vitreo-retinal 64 interface at macula in differentiating Vitreo retinal attachment from vitreo retinal traction, such as viteo macular traction (VMT). 7.18 RETINAL THICKENING Retinal thickening can result from vitreo-macular traction, glycation of the nerve fibre layer, intra-retinal oedema/cysts and sub-retinal fluid. Vitreo-retinal traction may occur with or without epiretinal membrane formation and with or without intra-retinal fluid. Its identification is important as it may be amenable to surgery. Thickening of the nerve fibre layer occurs early and results in a different normal reference range for people with diabetes. This does not affect vision. Intra-retinal oedema/cysts in the absence of retinal thickening occur more frequently than previously appreciated, although it has been known for some time that fluorescein angiography may show leakage in the absence of retinal thickening. Ophthalmic management in such cases is uncertain as all clinical trials, whether of laser or intra-vitreal therapy, has used increased retinal thickness as an entry requirement. Neurosensory retinal detachments with subretinal fluid accumulation may be revealed on OCT scans. Optical coherence tomography readily shows the consequence of prolonged oedema on the retinal structure in the form of large cysts with thin intervening pillars, ruptured cysts and pseudo hole formation; however OCT changes do not always correlate with the effect of oedema on visual function. 7.19 FUNDUS AUTOFLUORESCENCE The role of fundus autofluorescence has yet to be fully elucidated in diabetic retinopathy. Unlike other modalities, autofluorescence is a form of functional imaging, giving insights into the metabolic activity of the retinal pigment epithelium. Autofluorescence may have a role in laser retreatment of diabetic macular oedema, particularly with sub-threshold laser where burns may not be clinically discernible yet easily apparent with autofluorescence. Although autofluorescence can identify areas of the cysts with cystoid macular oedema, it is unlikely to replace the role of optical coherence tomography. Autofluorescence may, however, have a role in judging the visual potential of patients, with long standing diabetic macular oedema, by assessing the health of the underlying retinal pigment epithelium, and by inference, the health of the adjacent photoreceptors. 65 SECTION 8: SCREENING FOR DIABETIC RETINOPATHY 8.1 INTRODUCTION National screening programmes for diabetic retinopathy based on digital retinal photography were developed and implemented in England1 , Scotland2 , Wales3 and Northern Ireland4 between 2002 and 2007. This section of the revised RCOphth guidelines covers background issues in screening and makes specific recommendations of relevance to ophthalmologists. It does not cover detailed differences between UK screening programmes and expects ophthalmologists involved in the screening and assessment of screen positive patients to be familiar with the relevant detail (e.g. the National Grading form) of their own National Programme. 8.2 DEVELOPMENT OF SCREENING IN THE UK The development of screening in Europe was first encouraged by the St. Vincent Declaration5which, in 1989, set a target for reduction of new blindness by one third in the following 5 years. In 2002, the Health Technology Board for Scotland6 recommended that a National Diabetic Retinopathy Screening Programme for Scotland be established to detect referable (sight-threatening) retinopathy using a three-stage process based on singlefield non-mydriatic digital photography, with the use of mydriasis and slit-lamps, where necessary. The National Institute of Clinical Excellence (NICE) recommended that those with type 2 diabetes(2002 guideline7 and type 1 diabetes (2004 guideline8 have their eyes screened at the time of diagnosis and at least annually thereafter. NICE reviewed their guideline9 for type 2 diabetes in 2008 and produced a similar recommendation. In 2002, Wales announced a National Screening Programme based on two field digital photography after mydriasis and Northern Ireland announced a National Screening Programme using the same methodology with selective mydriasis for those under age 50 years. In 2003, the National Service Framework for Diabetes: Delivery Strategy10 announced the introduction of a National Screening Programme for Sight-Threatening Diabetic Retinopathy in England using two field digital photography after mydriasis with tropicamide. A consensus grading protocol has been developed in England1 , Scotland2 , Wales3 and Northern Ireland4 and details are available on the relevant websites. 8.3 EVIDENCE FOR THE EFFECTIVENESS OF SCREENING The definition of screening that was adapted by the WHO11 in 1968 was ‘the presumptive identification of unrecognised disease or defect by the application of 66 tests, examinations or other procedures which can be applied rapidly. Screening tests sort out apparently well persons who probably have a disease from those who probably do not. A screening test is not intended to be diagnostic. Persons with positive or suspicious findings must be referred to their physicians for diagnosis and necessary treatment.’ The principles for screening for human disease derived from the public health papers produced by the WHO11 in 1968 were: 1. The condition sought should be an important problem. 2. There should be an accepted treatment for patients with recognised disease. 3. Facilities for diagnosis and treatment should be available. 4. There should be a recognisable latent or early symptomatic stage. 5. There should be a suitable test or examination. 6. The test should be acceptable to the population. 7. The natural history of the condition, including development from latent to declared disease should be adequately understood. 8. There should be an agreed policy on whom to treat as patients. 9. The cost of the case-finding programme (including early diagnosis and treatment of patients diagnosed) should be economically balanced in relation to possible expenditure on medical care as a whole. 10.