Introduction

The legal definition of blindness in England and Wales is ‘so blind that they cannot do any work for which eyesight is essential’. Since 1851 the number of blind people in Britain has been counted. Reports on the causes of low vision in England and Wales began in 1950.1, 2, 3, 4, 5, 6 From the mid-1930s to November 2003, registration as blind in England and Wales was initiated by completion of a designated certificate—the BD8 which required the signature of an ophthalmologist. From 1991, the form consisted of five parts, part 5 being an anonymous epidemiological return containing data on the cause of visual impairment. Part 5's were dispatched to the Office of Population Censuses and Surveys (OPCS)—now known as the Office of National Statistics (ONS). The last analysis for all age groups was conducted by OPCS for all certificates completed during April 1990 to March 1991.7 We have previously reported on the three leading causes of certifications for blindness and partial sight in April 1999–March 2000 and commented on changes since the last analysis.8 Here we provide information on all (including rare) causes of certifications for blindness during this time period and examine variation in cause by age.

Materials and methods

Details regarding data collection and transmission have been reported previously.8

Part 5 of the BD8 form has 16 boxes in which medical information may be written, one for main cause, five for each eye for ophthalmic conditions, and five for diseases causing the ophthalmic conditions. In practice, the latter are rarely completed and here we present results from an analysis only on the main cause of blindness. For records where this field was not completed, the main cause was imputed wherever possible using the algorithm shown in Figure 1. People who had a different cause of visual impairment in each eye or had several diseases in one or more eyes and where the ophthalmologist had not recorded which disease, in his her opinion, was mainly responsible for loss of visual function are included in the category ‘Multiple Cause’.

Figure 1
figure 1

Algorithm used for imputation of main cause of blindness.

Table 1 summarises guidance provided on the BD8 as to what the legal definition of blindness relates to in terms of visual function. It is important to note that in England and Wales certification is voluntary and there is no statutory requirement for it to be offered.

Table 1 BD8 (1990) Guidelines on Blind Certifiable Visual Function (apply to the better eye)

To facilitate comparison with 1990 analysis and to provide information for ophthalmologists of varying specialties, we tabulated the number of certificates attributed to each main cause of blindness (Table 3) and show these numbers as percentages of the total number of certificates for blindness (Table 4). Data were coded using ICD-9.9 To illustrate more salient features of the data and examine variation by age, pie and bar charts of the more commonly occurring main causes of blindness are provided for different age groups (Figures 23 and 4).

Table 3 Main causes of blindness in England and Wales by age group: certifications April 1999–March 2000
Table 4 Percentage distribution of the main causes of blindness in England and Wales by age group: certifications April 1999–March 2000
Figure 2
figure 2

Causes of blindness in England and Wales ages 0–15 years: certifications April 1999–March 2000.

Figure 3
figure 3

Causes of blindness in England and Wales ages 16–64 years: certifications April 1999–March 2000.

Figure 4
figure 4

Causes of blindness in England and Wales ages 65–74, 75–84 and 85 years and over: certifications April 1999–March 2000.

Results

As reported previously of 34 410 BD8 certificates dated between April 1999 and March 2000, 13 788 (40%) were certificates completed for people newly blind and 1515 (4.4%) did not state whether the individual was blind or partially sighted.8 Table 2 shows that the proportion of certificates without specification of visual status was similar in each age group.

Table 2 Numbers of BD8 certificates dated April 1999–March 2000 by visual status

Table 3 shows that the most commonly recorded main cause of blindness was degeneration of the macula and posterior pole (ICD 362.5), which largely comprises age-related macular degeneration (AMD). AMD was stated as the main cause on 7881 certificates, which was 57.2% of the total. 1497 certificates were completed for people newly blind with glaucoma (10.9%) and 817 certificates were completed for people newly blind with diabetic retinopathy (5.9%). There were 422 individuals newly certified blind due to optic atrophy (3.1%), whereas 347 individuals were diagnosed as blind owing to cardiovascular disease/accidents (2.5%).

Figures 2 3 4 clearly illustrate that different causes predominated at different age groups.

There were 328 blind certificates completed for children (aged 0–15 years). Cerebral visual impairment and disorders of the optic nerve (particularly optic atrophy) together accounted for 41.2% of certifications (Figure 2). Hereditary retinal disorders were cited as the main cause of blindness in 13.1% of certificates. Congenital anomalies of the eye accounted for 13.4% of certificates completed for children, whereas perinatal conditions including retinopathy of prematurity were also an important cause (8.8%).

There were 1637 certificates completed for blindness for people of working age (aged 16–64 years). The leading cause was diabetes—290 certificates (17.7%) were completed citing diabetic retinopathy as the main cause whereas four people were certified blind with a cause of diabetes. Hereditary retinal conditions accounted for 15.8% of certificates and optic atrophy accounted for 10.1% of certificates. Degeneration of the macula and posterior pole was the cause in 7.7% of certificates. Glaucoma accounted for 5.4% of certificates.

Figure 4 shows that in the older age groups, degeneration of the macula and posterior pole accounted for increasing proportions of blind certifications—41.6% of those aged 65–74 years, 66.1% of those aged 75–84 whereas 74.3% of people newly blind aged 85 years or more were so because of AMD. Glaucoma was the leading cause in 11.6, 11.9, and 12.3%, respectively, of blind certifications for the 65–74, 75–84, and 85 and over age groups. Diabetic retinopathy accounted for 15.1% of certificates for the 65–74 age group and 4.2% of those aged 75–84 years.

Discussion

The aim of this paper is to provide updated estimates on causes of certifiable blindness in England and Wales. There has been much criticism regarding the validity and coverage of the data collected during BD8 certification.10, 11, 12, 13, 14, 15 It is almost certainly true that many people who are eligible for certification are not certified and that many people who are certified may not always satisfy the criteria for certification. It is important to note, however, that measures of vision are subject to considerable variability and there is often a very necessary delay between the onset of certifiable visual loss and the offer of certification. These figures surely give some indication of the burden of vision impairment on the eye health services and provide a degree of insight into the relative burden of different eye diseases.

To facilitate comparison with the 1990–1991 data, we have presented the number of certificates attributed to each main cause of blindness and shown these numbers as percentages of the total number of certificates for blindness. There are similarities in this analysis and the previous. AMD is by far the leading cause of all-ages certifications for blindness. In 1990/1991 this condition accounted for 48.5% of certifications for blindness, whereas in 1999/2000 it accounted for 57.2%. Diabetic eye disease has remained the leading cause of blindness among people of working age (aged 16–64)—in 1990/1991, 11.9% of blindness certifications in this age group were for diabetic retinopathy—in 1999/2000 this figure was 17.7%. Proportionately, glaucoma has decreased slightly over the time period for blindness (11.9–10.9%) but increased for partial sight (9–10.2%). Cataract as a cause of certifiable blindness has decreased over the time period from 3.3 to 1%. It is important to note, however, that a proportional comparison requires caution since an increase in one cause can result in a proportionate decrease in another cause.

This is likely to be the final complete analysis of data from BD8 forms from England and Wales. At the end of October 2000, a bulletin was circulated to all Directors of Social Services in England and Chief Executives of Health Authorities and Trusts by the Department of Health. This bulletin included a statement indicating that the Department of Health no longer required part 5 of the form to be sent to ONS and that part 5 was to be omitted for future reprint. In November 2003, following extensive consultation with service users and key stakeholders, form BD8 was replaced in England by the Certificate of Vision Impairment (CVI). CVI-W, the Welsh Version of the CVI, is to be launched in Wales later this year (2007).

The CVI has some advantages over the BD8. It records measures of visual function so that one can assess whether or not there is a shift in what is considered certifiable visual loss. It uses terminology found more acceptable by the sight impaired—no longer labelling people blind. Section C contains a list of the more commonly sight-impairing eye conditions to hopefully reduce transcription error when coding data. The CVI is not, however, without its problems. Causes of certifiable vision impairment in children are not well represented and some conditions have been included without reference to common causes (neoplasia). The CVI, like the BD8, was not piloted before being introduced, but with a move in the National Health Service (NHS) to increasing use of IT, it is hoped that the diagnostic sheet might be dynamic. Guide Dogs for the Blind Association are currently funding a 3-year project which hopes to develop an electronic CVI. Widespread use of this would hopefully improve data collection and allow users to have a greater role in determining the contents of the CVI.