ACTA OPHTHALMOLOGICA SCANDINAVICA 1996 -

Clinical Section

Current trends in newly registered blindness in Denmark Thomas Rosenberg and Fleming Klie

National Eye Clinic for the Visually Impaired, Hellerup, Denmark

ABSTRACT. Current pattern of blindness (i.e. visual acuity I 6/60) in Denmark was studied based on 1585 application forms for new member- ship to the Danish Society of the Blind during 1993. Statistics on blind- ness are very sensitive to the definitions used. A change of blindness de- finition to visual acuity <6/60 reduced the number of formally blind subjects with 32%, and by using the definition of WHO (visual acuity < 3/60) only 562 subjects (35%) would have been considered blind. The prevailing causes of blindness were age-related macular degeneration with 1132 cases (71.4%), followed by diabetic retinopathy 133 cases (8.4%), and glaucoma 80 cases (5.0%). Among the younger subjects (133 persons) aged 20-59 years diabetic retinopathy comprised 36% and le- sions of the optic pathways 26%, while myopia and retinitis pigmentosa accounted for 5% each. The majority of the applicants (92%) were 2 60 years old. In this group, age-related macular degeneration was the main cause of blindness in 78%. Figures from 1993 were compared with six similar studies on newly registered blindness from the last 35 years. The annual number of registrations was doubled during the last 25 years. The annual number of registered blind due to diabetic retinopathy fell during the 60's and 70's followed by a constant rate during the last decades. Glaucoma blindness fell with a factor two, and declined from a relative frequency of 15% among the causes of blindness to 5%. The impact of age related macular degeneration increased from 20% to 70% during the same period.

Key words: blindness - blind register - epidemiology - visual impairment.

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n Denmark there is no registration by I national health authorities or public social institutions of adult persons with severe visual, impairment. The only source of information regarding the demographic pattern of legal blind- ness is the Danish Association of the Blind (DBS). This organization, how- ever, generally is considered to include a large proportion of the blind popula-

tion. The admission of 1000 consecu- tive new members to DBS during the years 1958 through 1960 was analysed by Vedel-Jensen (1962). In 1971, Skydsgaard published statistics on member accession from a 3'h-year period 1967-1970. Since then, annual statistics on member accession have been compiled in 1977 (Klie 1980), and in 1984 and 1988 (Klie, unpub-

lished). In this report we outline the current incidence of blindness based on an analysis of new adult members of DBS during the year 1993. The study includes figures from the above men- tioned earlier investigations. A parallel study deals with the incidence of visual impairment among children 0- 17 years of age (Rosenberg et al. 1995).

Material and Methods Legal blindness is a prerequisite for membership of the Danish Associ- ation of the Blind (DBS). The visual criterion for membership, which is the same as the national criterion for legal blindness, is a best corrected visual acuity in the better eye 56 /60 and/or visual field defects equalling the same degree of visual impairment (hemiano- pia or field diameter <40" combined withvisual acuity (VA) I 6/18, or field diameter 5 20" (Goldmann target IV)). Application forms are completed by ophthalmologists and include infor- mation on diagnoses, visual acuity, vis- ual fields, refraction, and near vision. Despite frequent occurrence of two or more potentially blinding conditions, only one diagnosis was chosen as the principal cause. In cases with different causes of visual impairment in the two eyes, the diagnosis in the least affected eye was used. All application forms were audited by the same observer (FK), who also classified the data from earlier investigations in 1977, 1984, and 1988. The following data were reg- istered: Personal ID code, sex, age (per December 31, 1993), principal diag-

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Results A total of 1611 persons were originally included in the study after auditing 1797 application forms. The main rea- son for exclusion was a visual acuity above 6/60. A further 26 persons under 20 years of age were excluded. Age and sex distribution of the remain- ing 1585 subjects is shown in Fig. 1. Fifty-seven persons were included due to visual field impairments.

In Fig. 2 the distribution among vis- ual impairment categories with regard to the above mentioned classification systems is demonstrated.

Table 1 presents the distribution among diagnostic categories for 133 persons (8.4%) aged 20-59 and 1452

Age in five-year groups Fig. 1. Age and sex distribution of 1585 legally blind persons (VA < 6/60) enrolled during 1993.

persons (91.6%)- aged 60-103. The relative frequency of the three most common blinding conditions, i.e. age- related macular degeneration, diabetic retinopathy, and glaucoma in five simi- lar studies from the last 35 years is shown in Table 2 for comparison.

nosis, and impairment category ac- cording to both the Danish national classification (NDC) (Schider & Mos- bech 1993) and the international Statistik 1978-1994).

classification (ICIDH) (WHO 1980). Population counts were extracted from the Danish vital statistics (Danmarks

Discussion

Visual impairment Category

WHO / ICIDH

Category II Social Blindness

N = 1218

I 1/60 I N=397

Category 111 Practical Blindness

N=335 with Category 4

localization Near-total V.i. N=l55

perception Category IV without

N=32

N=10 I

Fig. 2. Distribution among vis- ual categories of 1585 legally blind persons according to two classi- fication systems. NDC = National Dan- ish classification. WHO/ICIDH = World Health Organization, International Classifi- cation of Impairments, Disabilities, and Handi- caps.

Voluntary membership of a private or- ganisation of blind persons may seem quite remote from a compulsary regis- tration by a national public authority. Nevertheless, mainly due to statutory defined visual criteria for eligibility coinciding with the official Danish de- finition of legal blindness, the member files of the Danish Society of the Blind may be considered equal to a public register. In addition, the certificate form must be completed by a specialist in ophthalmology to be considered.

Low sensitivity, i.e. only a fraction of eligible persons actually being regis- tered, is a problem shared by most blind registers (Goldstein 1980; Ro- binson et d. 1994). Among recognized reasons for non-registration are high age, the degree of visual impairment, the attitude towards registration in general and towards the word ‘blind’in particular, the access to ophthalmic and social services, the attitude of oph- thalmologists, and the patient’s benefit from registration.

The underregistration of visually impaired people in UK has been esti- mated between 10% and 85% of the visually impaired population eligible

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Table 1. Primary blinding condition in 1585 adult legally blind persons enrolled during 1993. The material is given in numbers of subjects (N) and percent (%) and furthermore divided in two age groups, below 60 and from 60 years and older, respectively.

Diagnosis

Age groups Total

20-59 2 60 20-103 N % N Y O N Yo

Age related macular degeneration Diabetic retinopathy Glaucoma Retinopathy not elsewhere specified Optic nerve atrophy Higher optic pathway lesion Myopia Evidence insufficient for diagnosis Corneal dystrophy/degeneration Age related cataract Uveitis Retinal detachment Amblyopia ex anopsia Pigmentary retinal dystrophy Miscellanous

5 3.8 1127 77.6 1132 71.4 48 36.1 85 5.9 133 8.4

5 3.8 75 5.2 80 5.0 3 2.3 45 3.1 48 3.0

25 18.8 13 0.9 38 2.4 9 6.8 21 1.4 30 1.9 7 5.3 22 1.5 29 1.8 4 3.0 20 1.4 24 1.5 0 18 1.2 18 1.1 0 8 0.6 8 0.5 5 3.8 3 0.2 8 0.5 3 2.3 4 0.3 7 0.4 3 2.3 4 0.3 7 0.4 7 5.3 0 7 0.4 9 6.8 2 0.1 11 0.7

Sum 133 100 1452 100 1585 99

for registration (Bruce et al. 1991). In Finland it is assumed that only 25% of the eligible persons are actually known by the register (The Finnish Register of Visual Impairment 199 3).

In Denmark, the effort by DBS is well recognized and appreciated by ophthalmologists, and it is generally believed that most patients are offered membership when a visual impairment 56 /60 is ascertained. In addition, a well organized local network of social workers (consultants for the welfare of the blind) are in contact with a con- siderable number of visually impaired persons. Nevertheless, it is a general impression among ophthalmologists that a significant proportion of the vis- ually impaired refuse membership of

DBS. It should be mentioned that this membership is not a precondition for receiving financial or rehabilitational support.

Despite the obvious fallacy imposed by the unknown sensitivity, we feel confident that statistics presented on the blind to a certain degree charac- terize the present situation qualita- tively. This may be ascribed to the high specificity of medical information available, i.e. nearly all registered per- sons may be considered ‘true’ blind.

The most obvious feature of the in- cidence of blindness (Fig. 1) is the well known skewed age profile sustaining the common conception of visual im- pairment being a companion of aging (Sorsby 1972; Goldstein 1974; Culli-

Table 2. Relative frequency of the 3 most common blinding conditions in six Danish studies: 1958-1960 (Vedel-Jensen 1962), 1967-70 (Skydsgaard 1971), 1977 (Klie 1980), 1984and 1988 (Klie, unpublished), and 1993 (present study).

Period 1958-61 1967-70 1977 1984 1988 1993

Subjects (N) 1000 2528 1043 1468 1560 1585

Age-related N=192 N=891 N=621 N=966 N=1132 N=1132 macular degeneration 19.2% 35.2% 59.5% 6S.8’/0 72.6% 71.4% Diabeticretinopathy N=228 N=323 N=133 N = 1 5 0 N=132 N=133

Glaucoma N=152 N=394 N=102 N=106 N = 8 1 N = 8 0

3’/2 years 3’/2 years 1 year 1 year 1 year 1 year

22.8% 12.8% 12.8% 10.2% 8.5% 8.7%

15.2% 15.6% 9.8% 7.2% 5.2% 5.0%

nan 1978; Klein et al. 1991; Salive et al. 1992). Expressed as a relative risk, the probability of being registered as blind in Denmark at age 80-84 is nearly 100 times the equivalent risk at age 40-44. Still, it should be remembered that the risk for an 80-year old person of be- coming registered as blind during the residual lifetime is no larger than about 3 per cent.

Our study illustrates the impact of different blindness definitions. Ac- cording to the current national defini- tion, 1585 persons were newly regis- tered as legally blind (social + practi- cal + total blindness) during the year of investigation. Yet, if the WHO defini- tion was applied, only 562 persons (35%) should be considered ‘blind’ (< 3/60). This example illustrates one of the difficulties involved when adopt- ing a common categorization for in- dustrialized and developing countries. If the WHO criterion for severe visual impairment (VA < 6/60) had been chosen as the inclusion criterion for this study the number of incident cases would be reduced by 32% to 1070 (Fig. 2).

Table 2 summarizes the main fea- tures from six Danish studies over the last 35 years. All the studies were based on consecutive new applications for membership in the Danish Associ- ation of the Blind. The visual inclusion criterion of the 1958-61 study was a visual acuity < 3/60. In the remaining five studies a visual acuity in the better eye I 6/60 was used as inclusion crite- rion. The same cut off between legal blindness and partial sight was em- ployed in the Model Reporting Area for Blindness Statistics in USA (Gold- stein 1974). In Great Britain, two ‘blindness’ definitions are in current use, i.e. <6/60, applied by the Royal National Institute for the Blind and <3/60, by the official certificate of blindness form, BD8 (Editorial 1994).

During the latest 25-year period the annual number of newly registered blind persons increased from 722 to 1585. This trend of increasing registra- tion of blind citizens has been ob- served in many studies and is mainly ascribed to the change in the age struc- ture of Western populations during the last decennia (Goldstein 1980).

The three most common causes of blindness constituted 63% in the

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1967-70 study and has since 1977 been a rather constant fraction be- tween 82% and 86%.

In the 1958-61 study, diabetic reti- nopathy was the leading cause of blindness among adults despite a low annual mean of 65 persons. This figure increased to a maximum of 150 in the 1984 study and decreased to the 1977 level in 1988 and 1993.

Glaucoma blindness peaked in the 1967-70 study with a mean of 113 per year. Ths figure decreased to 80 in the last two studies. In a study of glaucoma blindness in Denmark 1955-1987 in persons 2 50 years at admission to DBS, Fuchs et al. (1992) found a pre- valence rate of 45 per 100,000 and an annual incidence of 7 per 100,000 2 65 years. The incidence of glaucoma blindness among the middle aged I 65 years decreased during the period.

The increase in the occurrence of blindness from age-related macular degeneration (Table 2) is impressive, making AMD the absolute leading eye disorder among the prevailing blinding conditions. The low figure in the 1958-61 study is partly explained by a lower visual inclusion criterion, but from 1967-70 to 1988 the absolute figures increased 4-fold from 255 to 1132 per year and the relative impact of AMD from 35% to more than 70%. A similar tendency to a rise in blind- ness due to AMD has been reported in several studies (Lovie-Kitchin and Bowman 1985). This increase is gener- ally explained by the age displace- ments within the populations. Never- theless, due to the unknown fraction of non registration, an increasing in- cidence of registrable AMD as pro- posed by Evans and Wormald (1994) cannot be ruled out.

Aknowledgments The Danish Society of the Blind (DBS) gave this study support by copying all application forms. We thank Kirsten Marie Klie for her help with data processing.

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Received on August 24th, 1995.

Corresponding author: Thomas Rosenberg National Eye Clinic for the Visually Impaired 1 Rymarksvej DK-2900 Hellerup, Denmark.

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