Visual Impairment Scotland Report
Chapter 4 General Notification Information
Notification and return rates of information
- Visual function
- Ascertainment rates
- Age distribution
- Gender ratios
- Additional disabilities
- Distribution of children by deprivation category
436 children were notified to VIS between march 21 2001 and September 21 2002.
333 of these children were under 16 years of age and met the criteria for ‘significant visual impairment’.
Complete educational information was available on 67% (224/333) of these children.
Children have been notified from all parts of Scotland.
Only 6% of children notified to VIS are ‘blind’ with acuity of no perception of light.
One in five children were described as having some form of visual field loss.
Most children with visual impairment (57%) had another disability in addition to visual impairment.
13.8% (46/333) of children were reported to have hearing impairment in addition to visual impairment.
4.1 Number of Children Notified & Return Rates of Information
436 children were notified to VIS between 21 March 2001 and 21 September 2002. Of these children, 94% (409/436) were under 16 years of age on 21 September 2002. Of the children under 16 years of age information on visual function was available on 95% (389/409) and educational information on 73% (297/409). Where information on visual function was available 86% (333/389) met the criteria (as described in section 4.2) for ‘significant visual impairment’. Complete educational information was available on 67% (224/333) of these children. Throughout this report medical information relates to the group of 333 children under the age of 16 years with significant visual impairment while information on educational provision relates to a smaller subgroup of 224 (from the group of 333 children with significant visual impairment) for whom complete educational information is available. Figure 4.1 summarises notification information datasets.
Figure 4.1 Number of Children Notified & Return Rates of Parental, Health and Educational Information (n=436)
The project uses the visual impairment classification system described in Table 4.1. This system was developed in Scandinavia and is used in this report for the following two reasons:
- It includes children with a visual acuity of 6/18.
- It takes into account additional forms of visual dysfunction by reclassifying children into a worse group if they have additional functional impairment due to visual field loss (as described below).
This type of classification system is consistent with the most common visual function thresholds used for identifying children eligible for special educational provision in the UK.
If a child has one of the following visual field defects then strictly they should be reclassified as follows:
- Total hemianopic defect to the same side (homonymous) shifts category 0 to A, category A to B, and category B to C.
- Tunnel vision (< 10¡ radius measured with Goldmann target IV/4e) is classified with category C irrespective of visual acuity
- Concentric constriction of visual fields < 20¡ shifts category 0 to A and A to B.
Detailed information on the size of visual field defects was rarely available to VIS. To acknowledge the additional impact of visual field loss upon overall visual function we reclassified children into the next higher group if they had any type of visual field loss but did not move any child from Group C (Near Total Blindness) to D (Total Blindness).
The VIS project further modified this system by classifying children from group O (with a visual acuity of better than 6/18 and no visual field loss) into Group A if they suffered from symptoms of cerebral visual impairment. This further modification acknowledges the growing awareness of cerebral visual impairment in children amongst educational and health professionals and the major impact it may have on a child’s education, even if the child’s visual acuity is good.
Despite recognition as an international standard for scientific and statistical purposes the WHO classification for visual impairment45 was not used in this report for the following two reasons:
- It does not include children with a visual acuity of 6/18.
- It does not take account of additional visual impairment such as visual field loss or symptoms of cognitive visual dysfunction when classifying children into visual impairment groups.
Visual Acuity Groups
There were 285 children (Groups A, B, C and D) with a visual acuity of equal to or worse than 6/18. More than half of these children (152/285) were found in NORDSYN visual acuity group A. It was striking to note that very few children (16) with visual impairment are actually ‘blind’ with a visual acuity of no perception of light (NPL).
Visual Field Loss
Information on visual field function was available on 29% (113/389) of children. The most commonly reported finding was a ‘full field’ (36/389). Overall 20% (77/389) of children were described as having some form of visual field loss. The percentage and types of visual field loss recorded are described in Table 4.3.
The brain was the most common site of pathology (49/77) leading to visual field loss.
NORDSYN Visual Function Groups
After analysing visual acuity, visual field loss and symptoms of cognitive visualimpairment, 333 children were identified who met the VIS criteria for significant visual impairment. Table 4.3 illustrates the distribution of children within the NORDSYN Visual Function Groups.
* Children with visual field loss are reclassified into the next higher group but are not moved from Group C to D. A further VIS modification to this system is to move children with cognitive visual dysfunction in Group O into Group A.
It is generally acknowledged that the true prevalence of childhood visual impairment, including children with cerebral visual impairment and additional disabilities, in a developed country is at least 20 per 10,00011,46. There are currently estimated to be 970,374 children under the age of 16 years residing in Scotland47. Of these children therefore at least 1,941 are likely to be visually impaired. By identifying 333 children in 18 months VIS has identified 17% (333/1941) of the estimated population of children with visual impairment in Scotland.
The Swedish notification system achieved a prevalence rate of 11.75 per 10,000 in its first 4 years48. This would equate to 1,140 children with visual impairment in Scotland. VIS has therefore achieved an ascertainment rate of 29% (333/1140) of this potential realistic total. This has been achieved in 18 months and is comparable in success to the Swedish experience. The VIS ascertainment rates across all Health Boards are illustrated in Figure 4.2.
Children have been notified from all parts of Scotland. There was no ‘central belt’ bias despite the project office being based in Edinburgh. The two Health Board areas with the highest ascertainment rates are from geographically opposite parts of the country. The absence of notification bias to the central belt and wide and even geographical spread of notifications suggests that the promotion of VIS through the web-based information support service and the series of Scotland-wide health, educational and social service meetings have been successful.
Figure 4.3 illustrates the distribution of notifications by age group. Rates of notification rose linearly until the age of 5 to 6 years. Thereafter the rates plateau then tail off through the teens. This ‘shape’ of notification rates by age group is similar to the study carried out in Sweden48. In developed countries 80-90% of childhood visual impairment becomes evident within the first two years of life13. In Scotland however 62% of new registrations via the BP1 system occur after the age of 5 years12. The VIS notification system has also similarly failed to be notified of many of the younger children with visual impairment.
Of the 333 children under the age of 16 years notified with significant visual impairment, 175 were male and 158 female creating a male to female ratio of 1.11.
Previous studies have similarly identified a larger proportion of boys amongst children with visual impairment49-52. There is a preponderance of males in the general population under the age of 16 (1.05)47 but the ratio is not as large as that found on the VIS database (1.11). This difference was not statistically significant. This preponderance of males may be due to x-linked inherited disorders (where males are affected) and the greater susceptibility of males to brain injury from prematurity and perinatal insult.
In the VIS project the ratio of males with albinism to females with albinism was 2.67 to 1. The ratio of males to females with brain as the primary anatomical cause of impairment was 1.21 to 1.
The majority of children with visual impairment (57.1%) had another disability in addition to visual impairment. The most common combination was learning and physical impairment in addition to visual impairment (28.8%). Table 4.7 describes the combinations of additional disabilities seen in children with visual impairment. If children had any additional disability they most commonly had two additional disabilities (57.9%, Table 4.8).
Dual Sensory Impairment
Dual sensory impairment was more common than anticipated. 13.8% (46/333) of children had hearing impairment in addition to visual impairment. This is higher than in previous studies (6.2% to 12%)13,53 and very much higher than the official blind and partial sight register (1.5%) in Scotland12. Nearly all children (93.5%) had additional disabilities.
The most common combination of disabilities (63%) was learning and physical impairment in addition to dual sensory impairment (Table 4.9).
Almost one third (30%) had particularly poor visual function and met the criteria for NORDSYN visual function groups C and D with visual acuity of worse than 1/60. In most of the children with dual sensory loss the brain was the main anatomical site of impairment (59%). A wide range of visually impairing conditions (20) was described in the 46 children. Children with dual sensory impairment present a greater challenge to health, education and social services than children with isolated visual impairment. This is further complicated by the variety of impairing conditions, the presence of additional disabilities and particularly poor visual function in many cases.
NORDSYN Visual Function Groups
There is a clear and significant relationship between poorer visual function and increasing prevalence of additional disabilities. 51% (121/238) of children in groups A & B had an additional disability compared to 73% (69/95) of children in groups C & D (with poorer visual function). The groups are defined in section 4.1.
VIS uses the Carstairs & Morris Deprivation Index54 which is calculated using four indicators as follows:
- Overcrowding: persons in private homes living at a density of more than one person per room as a proportion of all persons in private homes.
- Male unemployment: proportion of economically active males who are seeking work.
- Social class 4 or 5: proportion of all persons in private homes with head of household in social class 4 or 5.
- No car: proportion of all persons in private homes with no car.
All the proportions are calculated on the households in a given postcode sector. The composite score is divided into five separate categories, ranging from very high (5) to very low (1) deprivation. 20% of the normal population should be found in each category 1 to 5. Children notified to VIS were skewed towards the least materially deprived groups. This is in contrast to the expected distribution where approximately 40% of all children with serious visual impairment have been reported to be found in the most deprived 20% of the population55 (category 5).
The ‘voluntary consent’ nature of the VIS notification system is likely to have created the relative over-representation of children from the least materially deprived areas: For a child to be notified a consent and notification form must be completed and signed by a parent then returned to VIS. It is a strong possibility that these steps are more likely to be successful in the least materially deprived families, thus skewing the database to children from more affluent areas.