Inverse association between breast cancer incidence and degree of visual impairment in Finland.

A total of 10935 women with visual impairment were identified from the Finnish Register of Visual Impairment and followed up for cancer through the Finnish Cancer Registry for years 1983-1996. Breast cancer risk decreased by degree of visual impairment (P for trend 0.04) which suggests a dose-response relationship between visible light and breast cancer risk.

Visual impairment and cancer: a population-based cohort study in Finland.

OBJECTIVES: To describe the cancer risk pattern of Finnish persons with visual impairment. METHODS: A cohort of 17,557 persons identified from the Finnish Register of Visual Impairment was followed-up for cancer through the Finnish Cancer Registry from 1983-95. The degree of visual impairment ranged from moderate low vision with visual acuity less than 0.3, to total blindness with no perception of light. The standardized incidence ratios (SIR) and 95% confidence intervals (CI) were calculated by primary site; the expected rates were based on national cancer incidence rates. RESULTS: The SIR for overall cancer among totally blind men was 2.2 (CI = 1.3-3.5) while in the entire cohort the incidence was increased by only 15% (1,255 cancers observed cf 1,093 expected). Excesses were observed in both genders in cancers of the liver (SIR = 1.8, CI = 1.2-2.5) and lung (SIR = 1.5, CI = 1.3-1.7); in females in cancers of the stomach (SIR = 1.5, CI = 1.2-1.9) and the colorectum (SIR = 1.3, CI = 1.1-1.6); and in males in cancers of the kidney (SIR = 1.8, CI = 1.1-2.6) and the eye (5.8, CI = 1.9-13). The excess in lung cancer was entirely attributable to age-related macular degeneration (which is most common among smokers). CONCLUSIONS: Cancer incidence among the visually impaired tended to be increased for most cancer types. Attention should be paid to lifestyle factors underlying the observed risk increases, such as unbalanced diet.

Incidence of registered visual impairment in the Nordic child population.

A collaborative, population based, prospective register study on the incidence of visual impairment in children during the year 1993 was carried out in five Nordic countries with a total population of 17 million inhabitants. The child population was 3.8 million individuals aged 0-17 years. The following variables were taken into account: nationality, age, sex, diagnoses, aetiology, degree of visual impairment, and additional impairments. Classification routines from an earlier prevalence study were used. The present study included 304 children corresponding to an incidence of notification of 8/100,000 children, varying from 5.7 to 11.1 in the five countries. Fifty per cent of the visually impaired children were reported before they were 3 years of age. In approximately 45% of the children, visual impairment was due to various brain disorders, with cerebral amblyopia and secondary optic atrophy as the two leading causes. The relative impact of retinopathy of prematurity had decreased from the third most frequent cause (10%) in the prevalence study to seventh place (4%) in the incidence study. Two thirds of the children had additional impairments and these children also suffered from the most severe visual impairments. Among aetiological factors the majority (64%) were prenatal. The overall male:female ratio of 1.4:1 was identical to the sex ratio of the prevalence study.

Visual impairment in Nordic children. V. X-linked juvenile retinoschisis.

In a study on 2,527 visually impaired children from four Nordic countries X-linked juvenile retinoschisis was diagnosed in 35 male children. Striking differences in frequency between the four countries were found, with 26 cases reported from Finland, 5 cases from Denmark, and 4 cases from Norway. None was reported from Iceland. The corresponding age and sex-specific prevalence rates of X-linked juvenile retinoschisis (N:1,000,000) were 44.5 in Finland, 8.8 in Denmark, and 7.9 in Norway. The uneven geographical distribution is possibly attributed to a 'founder effect' due to the settlements in Finland by European immigrants in the 17th century. The visual impairment of the registered cases was usually mild with 91.4% falling into WHO category 1. However, one child was totally blind, demonstrating large phenotypic heterogeneity. None of our cases had additional impairments. The majority were more than five years old, indicating a progressive course during childhood. Nevertheless, two children were diagnosed at the age of one. The most common age at registration was seven years, coinciding with the beginning of school attendance.

Visual impairment due to retinopathy of prematurity in Nordic children.

The registers of visually impaired children in Denmark, Finland, Iceland and Norway have been compiled into a common database by a Nordic study group of ophthalmologists, NORDSYN. The database contains information on 2527 children aged 0-17 years. The total number of children with visual impairment due to retinopathy of prematurity (ROP) is 247. ROP is the 3rd most common single diagnosis in the database. The age-specific national prevalence of registration (N/100 000) of visual impairment due to ROP varies from 12 in Denmark to 5 in Finland and Norway and 4 in Iceland. The differences can partly be explained by varying efficiency of registration. The age-distribution indicates that visual impairment due to ROP is not decreasing. Of the 247 children 175 had a visual acuity less than 1/60 and 58 had one or more additional impairments. Incidence studies on visual impairment in Nordic children are being prepared.

Visual impairment in Nordic children. III. Diagnoses.

The diagnoses, according to type and site and the degree of visual impairment, responsible for severe visual impairment in children below the age of 18, were analyzed in a material compiled from the national registers of visually impaired in Denmark, Finland, Iceland and Norway. Among 2527 children the predominant causes of visual impairment are ascribed to congenital malformations, neuro-ophthalmological diseases and retinal diseases. Optic atrophy is the leading single cause of severe visual impairment when all diagnoses are compared, and this also applies when all categories of visual impairment are included. Retinopathy of prematurity is the second principal cause of severe visual impairment, while cerebral amblyopia rates as the third most significant cause. Congenital cataract is also of considerable importance when all categories of visual impairment are compared. The differences registered between the Nordic countries were found to be within reasonable limits, except for a preponderance of neuro-ophthalmological diseases in the Danish material. This could be explained by a better medical supervision of mentally retarded patients in Denmark. Additional impairments occur in a large percentage of patients, but are unevenly distributed in the disease groups. A high frequency of additional impairments are found in the neuro-ophthalmological group and in the groups with congenital malformations, emphasizing the importance of a multidisciplinary evaluation when dealing with the visually impaired child.

Visual impairment in Nordic children. IV. Sex distribution.

A Nordic study group of ophthalmologists, NORDSYN, has compiled registers in Denmark, Finland, Iceland and Norway of 2527 visually impaired children aged 0-17 years. This paper is concerned with the sex-distribution in the registers and has documented a statistically significant excess of males in two of the registers (Denmark and Finland). The dominance of males seems to be related to two main conditions: 1. Genetic factors. 2. Perinatal factors. The genetic factors are mainly concerned with X-linked inheritance. The fact that perinatal influences involve visual impairment in males more than in females is difficult to account for. It may be conjectured, that the basis for perinatal visual damage is determined by unknown prenatal, possibly genetic, factors.

Visual impairment in Nordic children. I. Nordic registers and prevalence data.

A Nordic study group of ophthalmologists, NORDSYN, has compiled data from registers in Denmark, Finland, Iceland and Norway of 2527 visually impaired children. Each record contains the following information: sex, year of birth, year of registration, classification of visual impairment, ocular diagnosis, systemic diagnosis, aetiology and evt. additional impairments. The ocular diagnoses were compiled into groups, and coding systems for aetiology and additional impairment were developed. The sex distribution revealed a dominance of males compared to the general population at the same age. Cases with non-genetic aetiology showed--through to a lesser extent--the same relative preponderance of males. The diseases in males caused by x-linked genetic factors do, therefore, not fully explain the sex distribution observed in the study. The national prevalences for registration of childhood blindness (WHO-definition: best corrected visual acuity in the best eye less than 3/60 or visual field less than 10 degrees around fixation for the ages 0-15 years) are per 100,000 child-population aged 0-15 years: Denmark 41, Finland 15, Iceland 19 and Norway 15. The differences are primarily presumed to be due to varying efficiency in registration. The proportion of visually impaired children with an additional mobility, hearing or mental impairment is between one-third and one-half of the national materials, thus indicating the need for interdisciplinary tracing of and care for the visually impaired child. This study documents the need of uniform routines for data classification of visually impaired children. The quality of the data in the present study calls for caution in the interpretation of the prevalence estimates. Incidence studies are being prepared to obtain information on whether the amount and causes of visual impairment in children with or without multiple impairments are changing.

Visual impairment in Nordic children. II. Aetiological factors.

Careful clinical-aetiological assessment of visually impaired children is one of the prerequisites for prevention of future, 'unavoidable' cases of visual impairment of children in the industrialized part of the world. In a collaborative study (NORDSYN) between four Nordic national registers of visual impairment, we analysed and classified some of the factors considered to be essential components for the development of low vision or blindness in children. We discuss the conceptual basis for aetiological classification of eye disorders and visual impairment. An aetiological classification system, based on the type and debut of an essential causal factor is introduced. We present data on 2527 visually impaired children from the Nordic countries. In accordance with several other reports from the last twenty years it is demonstrated that prenatal factors, including genetic aetiologies, were involved in a large proportion (66%) of the cases. In children without additional impairments the corresponding fraction was 74%. Genetic factors accounted for a little over half of the prenatal cases, and in a substantial number of children (40%) with visual impairments of prenatal origin, the causes were obscure. In 1/5 of the material some peri-neonatal causal or modifying factor was identified. In 7% only, the presumed aetiological factor was introduced in the infantile-juvenile period of life. Further prevention of visual impairment among children of the industrialized countries would benefit most from a more comprehensive understanding of prenatal, nongenetic causal factors, further knowledge about regulating mechanisms responsible for gene expression, and additional improvements in perinatal care.