Gordon-Bennett et al Table 4 Demographics of Cambridgeshire (Census 2001) Cambridge City, South and Huntingdonshire Total population 395,933 Male 49.7% Female 50.3% Ethnic group White 95.0% Mixed 1.2% Asian 1.7% Black 0.7% Chinese/Other 1.4% Age (years) 0–15 19.3% 16–74 74.2% 75+ 6.5% Note: Percentages given are proportions of the total population of the column. per year and a VI registration rate of 24 per million per year was reported for Leeds for 2002.8 The prevalence of diabetes in South Cambridgeshire, Cambridge city, and Huntingdonshire (2.74%) is less than the national prevalence estimated as 4.26%.9 The prevalence in Leeds is 2.9%.8 The region of Cambridgeshire studied has about 5% more Whites than the ethnic proﬁle of England/Wales, (Table 4). Likewise, our studied region has 2.8% less Asians and 2.3% less Blacks than England/Wales. This difference might account for the slightly lower prevalence of diabetes than the national prevalence, as there is well documented evidence of an increased prevalence of diabetes in Asians and Blacks.10,11 The severe VI and VI registration rates per million diabetic patients per year were 230 and 600 respectively. These rates are lower than the corresponding rates in the diabetic population of Leeds of 337 and 817, respectively.8 The rates of registration in our study are also lower than the severe VI registration rate of 640 per million diabetics per year reported for Fife between 1990–1999,7 and similar to the VI registration rate of 530 per million diabetics per year calculated for Tayside in 1998.12 This interregional variation may be related to differing population proﬁles.13,14 Addenbrookes Hospital is a tertiary referral hospital in Cambridge city and Hinchingbrooke Hospital is a secondary care centre which serves as a district general hospital for Huntingdonshire and other surrounding subpopulations of Cambridgeshire. We questioned whether our relatively low rates of registration of VI due to diabetes were due to the nature of these hospitals. Geographically, Addenbrookes Hospital is 78 Cambridgeshire England and Wales 552,658 49.5% 50.5% 95.9% 1.0% 1.3% 0.6% 1.2% 19.4% 73.6% 7.0% 52,041,916 48.7% 51.3% 90.0% 1.5% 4.5% 3.0% 1.0% 18.7% 74.0% 7.3% the closest hospital to patients living in Cambridge city and South Cambridgeshire and being a tertiary referral centre, it would serve all patients in Cambridge in addition to receiving referrals from outside Cambridge. Very few diabetic patients would be referred elsewhere for treatment. Our results were cross-checked with the relevant Primary Care Trusts and both sets of data correlated very well. The Primary Care Trusts had no record of any patient living in the study population, who was registered visually impaired outside of Addenbrookes or Hinchingbrooke Hospitals or from the private sector in the study period. The possibility of a large number patients being registered visually impaired in the private sector is unlikely. It is well known that there are limitations in using VI registration data to study rates of VI.15,16,17 VI registration data are hospital-based, not population-based.5 The patient must access the hospital eye service in order to be seen by a consultant ophthalmologist. Between 43% and 58% of eligible outpatients are said to remain unregistered even after consultation with an ophthalmologist,15,16 and up to 40% of registered patients are inappropriately registered.15 Patient attitudes to registration process (patients are entitled to refuse the offer), and medical attitudes to registration (there is no statutory requirement for it to be offered) also affect registration rates.5,18 There is often a delay between onset of certiﬁable visual loss and offer of registration.5 Studies have shown that certiﬁcation of VI is biased towards severe visual loss, permanent, nontreatable causes, and those that affect central rather than peripheral vision.15,17 Ethnic minorities are less likely to undergo registration.16,19 A prospective audit of Clinical Ophthalmology 2009:3