Abstract
A study of all the schools for the blind in the West Bank and Gaza Strip was undertaken during 1991-2. 

Impaired visual function in childhood may result from genetic, intrauterine, perinatal and postnatal factors. In industrialised countries, genetic factors are the most important cause of visual impairmentl,2 accounting for approximately 50% of childhood blindness. In developing countries, corneal pathology, often associated with mal nutrition or measles, is the most important cause,3--{j accounting for up to 60% of blindness.

The West Bank and Gaza Strip is home to 1.9 million Palestinian Arabs, the majority of whom are Muslim. The per capita Gross National Product is US $1500-2000. 7 Using United Nations definitions, the territories are econ omically one of the 'least developed' areas of the world. Correspondence to: Mark Elder, FRACS, FRACO, Moorfields Eye Hospital, City Road, London EC1V 2PD, UK.
Eye (1993) 7, 580-583
Data on the causes of childhood blindness in the West Bank and Gaza Strip have not been available because there is no fonn of blind registration or data collection system. This study presents the findings of a study of all children aged 5-15 years attending the schools for the blind within the territories.
PATIENTS AND METHODS
The six academic blind schools of the West Bank and Gaza Strip were visited and 205 children aged from 5 to 15 years were examined. The schools catered for both resi dential and day students. Thirteen children were unavail able for examination; otherwise there were no exclusion criteria.
PATIENTS AND METHODS
Each school was visited by the 'Outreach' facility of the St. John Ophthalmic Hospital, Jerusalem, which is a well· equipped mobile clinic. The schools' locations and patient numbers are given in Table I . Two schools had only one student each included in this study because they catered for older students. Each child was seen and examined by at least one author (M.J.E. and R.DeC.). A complete history was taken, with particular reference to family history, and previous medical and social work records were reviewed. A full ocular examination was conducted including best corrected visual acuity with Sheridan-Gardner test charts, colour vision assessment with coloured blocks, visual field testing by confrontation, slit lamp biomicroscopy, cycloplegic refraction and fundoscopy. When indicated, children were sent to the base hospital for further investi gations such as ultrasound, Goldmann visual fields, Farns worth-Munsell tests and electrodiagnostic testing. Where possible, family members were examined on the same day. We used Gilbert and Foster's classification8 and coding instructions to define the causes of childhood blindness according to anatomical categories. Among those diseases that are less easy to categorise, the following definitions were used: corneal scar included corneal dystrophies; ret ina included albinism, degenerative myopia, retinoblas toma and retinopathy of prematurity; optic nerve included optic nerve hypoplasia; whole eye included glaucoma and microphthalmos. The results presented are those for the child. Where there was a difference in the anatomical diagnoses between each eye the diagnosis of the best see ing eye was used. Results of visual acuity measurement were categorised according to WHO definitions, which use the best corrected acuity of the better seeing eye. The aetiologies were classified according to the WHO/PBL criteria but were only specified if the examiner was defi nite about the cause.
PATIENTS AND METHODS
Because of a general lack of resources within the West Bank and Gaza Strip no child had been adequately assessed for low vision aids (LVA s). Therefore, as part of this study, all children were screened for full LVA assessment.
RESULTS
1Wo hundred and five children were examined in this study of which 109 (53%) were female. The mean age was 9.1 years. Of the 205 children, 2.9% had a visual acuity of 6/18 or better, 12.7% had visual impairment, 21% had severe visual impairment (SVI) and 63.4% were blind (BL). Good visual acuity per se was not necessarily asso ciated with good visual function, as two-thirds of the chil dren with 6/18 vision, or better, had significantly reduced visual fields due to glaucoma or retinitis pigmentosa.
RESULTS
The anatomical sites of abnormality leading to SVI or blindness in the 173 children are given in Table II . Retinal diseases were responsible for 52%, pathology of the whole globe accounted for 23% (of which 9% was due to glau coma), optic nerve disease for 12% and cataract 7%. The aetiology of the causes of SVI/BL is given in Table III .
RESULTS
Parental consanguinity was present in 62% (107/173) of children with SVI/BL: 85% (64/75) in the Gaza Strip and 44% (43/98) in the West Bank. Parental consangui!1ity was defined as the union of first-degree relatives and was usually the marriage of first cousins. The prevalence of consanguinity and a family history of the same ocular diagnosis (involving a first-degree relative, usually a sib ling or a parent) is detailed for each of the common diag noses for the 173 children with SVI/BL in Table IV . Fourteen blind children were identified as having definite non-hereditary causes of blindness (trauma, toxoplasmo sis, retinopathy of prematurity, infection) and 4 of these also gave a history of parental consanguinity.
RESULTS
There were only 3 children with a possible diagnosis of congenitally acquired rubella and one with measles associated blindness. One child was referred for retinal detachment surgery. Forty one per cent of children (85/ 205) were deemed suitable for formal LVA assessment.
DISCUSSION
The admission criteria for the schools for the blind in the West Bank and Gaza Strip are essentiallY'an inability for the child to function and obtain a sighted education in a normal school. Referral can be made by a social worker or an ophthalmologist but there are no quantitative admission criteria such as a specific visual acuity or specific visual field loss.
Anatomical Causes of Blindness
The anatomical sites of visual loss are compared with those in other countries in Table V . All children had a visual acuity less than 6/60 and this is similar to the other studies,3-6,9-12 although the studies in Lebanon and Saudi Arabia also included acuities of 6/60. The data show a pat tern of diseases similar to that found in the United States and the United Kingdom (developed countries) except that a higher proportion of visual loss is due to glaucoma (9% vs. 0 and 2% respectively). This contrasts with Africa, which has similar economic circumstances to the West Bank and Gaza Strip. Glaucoma is reported to be an important cause of childhood blindness in Saudi Arabia, Jordan and Lebanon (14%, 15% and 18%) .11-13 These are countries with predominantly Arab populations and a high degree of consanguinity.ll-13 Compared with other countries, the West Bank and Gaza Strip have a high pro portion of SVI/BL due to retinal disease (52%). The major retinal causes were Leber's congenital amaurosis (n=23), degenerative myopia (n=22), cone dystrophy (n=13), ret initis pigmentosa (n=ll) and retinopathy of prematurity (n=3). There was little SVI/BL due to rubella or measles. This contrasts with East and West Africa where the inci dence of measles-associated blindness is between 27% and 34%.3-6 This is probably due to an effective vac cination programme or to a relative lack of malnutrition. In a study in the West Bank, 49% of young children were fully vaccinated, 46% were partially vaccinated and only 5% had not been immunised.14
Consanguinity
Levels of parental consanguinity are very high in this study (62%) but are similar to studies of blind children undertaken in other Middle East countries such as Saudi Arabia (56%),12 Lebanon (56%)11 and Jordan (67%).13 These findings are in marked contrast to studies under taken in Europe and Africa where the figures are 0 in Scot-
M. J. ELDER AND R. DE COCK
land,1O 1.7% in Ireland15 and 7.8% in Malawi. 16 The prevalence of consanguinity in the general population of the West Bank and Gaza Strip is unknown, although a study of handicapped children in Gaza Strip showed a prevalence of 59% .17 In Lebanon, Abou Daoudls showed that 20% of all marriages are consanguineous, usually between first cousins. The Lebanese study of childhood blindnessll found consanguineous marriages in the parents of 28% of children with acquired SVI/BL; this compares with 14% in Saudi Arabia,12 33% in Jordan13 and 29% (4/14) in this study. Levels of consanguinity were higher in the Gaza Strip than the West Bank (85% vs. 44% ). The reasons for this are not clear but are probably multifactorial.
M. J. ELDER AND R. DE COCK
Consanguinity allows the expression of recessive genes and this may explain the high numbers of children in this study with known recessive conditions such as Leber's amaurosis (13%), cone dystrophy (8%), retinitis pigmen tosa (6%) and albinism (3%). This is in contrast to findings in Scotland where a total of 7% of childhood blindness was due to recessive genes; 10 however, it is in accordance with data from Lebanon, 11 where 65% of childhood blind ness was estimated to be autosomal recessive.
Prevalence of Blindness
The minimum prevalance of blindness in school-age chil dren can be estimated using standard demographic datal9 dating from 1992. The population of the West Bank and East Jerusalem was 1 202 000 of whom 335 358 (27.9%) were aged 5-15 years, 98 of whom had a visual acuity of less than 6/60. The population of Gaza Strip was 714 800 of whom 203 003 (28.4%) were aged 5-15 years, 75 of whom had an acuity of less than 6/60. Therefore the mini mum prevalence of school-age SVI/BL is estimated to be 0.29 and 0.37/1000 respectively with a mean of 0.32/1000 children. The above calculations assume, however, that all blind children have been identified and attend schools for the blind. The regular school screening programmes are likely to detect most children with severe visual loss who are otherwise normal. Due to the lack of programmes for integrated education and the legal requirement to attend school it is probable that most severely visually impaired children will attend schools for the blind. However, chil dren with multiple handicaps will not be represented. The prevalence of school-age blindness calculated from data obtained from this study is therefore a minimum estimate.
Possible Control Measures
To reduce the prevalence of childhood blindness in the West Bank and Gaza Strip there is a particular need to reduce the incidence of childhood blindness from heredi tary causes. This may be achieved by reducing the inci dence of consanguineous marriages and by providing genetic counselling to families with blind children or a family history of blindness. Counselling may be of par ticular benefit to parents with existing blind children with autosomal dominant or X-linked conditions.20 However, at least 29% of all children with SVI/BL had known reces sive. diseases. Counselling these families may prevent further affected siblings being conceived. However, there are currently neither the resources nor the cultural accept ability for prenatal diagnosis or termination of preg nancl1 which would justify screening programmes.
Possible Control Measures
Reducing the incidence of consanguineous marriages would also reduce the incidence of recessive blindness, but this would be difficult to achieve, mainly because it is so socially acceptable. Congenital and infantile glaucoma and congenital cataract need particular measures to ensure early identification and optimal treatment, as together they represent 16% of all children with SVI/BL.

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