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PAPERS: H Dolk, A Busby, B G Armstrong, P H Walls, and Jack Cuzick Geographical variation in anophthalmia and microphthalmia in England, 1988-94 • Commentary: Clustering of anophthalmia and microphthalmia is not supported by the data BMJ 1998; 317: 905-910 [Abstract] [Full text]

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Further research on the differences in prevalence...

Jugnoo Rahi   (10 November 1998)

Further research on the differences in prevalence... 10 November 1998
Jugnoo Rahi, Clinical Research Fellow Institute of Child Health Send response to journal: Re: Further research on the differences in prevalence...	6.11.98 Dear Sir, We read with great interest the paper by Dolk et al1 regarding possible geographical variation in the combined prevalence of anophthalmia and microphthalmia in England. We agree that further research on the observed differences in prevalence of these two disorders between areas with different population densities would be of interest.2 The urban- rural gradient reported may be partly explained by factors such as differences in the population in degree of gene mix and maternal age at conception and these would need to be accounted for in future studies. We would suggest also that future research on the role of environmental factors should also aim to determine prevalence of microphthalmos and anophthalmos separately, as well as by region of residence during early pregnancy, rather than at birth alone, as the critical time when aberrant development gives rise to these disorders is between the 3rd and 5th weeks of gestation.3 In this context, it is of note that Dolk et al reported that 7.4% of cases in their study did not have a valid postcode for residence at birth compared with 0.3% of all birth notifications in the Office of National Statistics database: it would be important to know the reasons for this difference as they may have influenced the observed gradient. Finally, in a recent study undertaken in India, we observed that microphthalmos occurred more frequently amongst severely visually impaired and blind school children in rural settings than in urban settings.4 As there is evidence that the prevalence of congenital ocular anomalies may be higher in some developing than in industrialised countries,5 we would suggest that international collaboration in further research in this field may be fruitful. Yours faithfully, Dr JS Rahi 1, Dr CE Gilbert 2, Dr A Foster 2 1 Departments of Epidemiology and Ophthalmology Institute of Child Health/ Great Ormond Street Hospital, London WC1N 2 Department of Preventive Ophthalmology Institute of Ophthalmology, London EC1V References 1. Dolk H, Busby A, Armstrong BG, Wallis PH. Geographical variation in anophthalmia and microphthalmia in England, 1988-94. BMJ 1998; 317: 905-910. 2. Mariman ECM. Clustering of anophthalmia and microphthalmia. BMJ 1998; 317: 895-896. 3. McCartney AC. Embryological development of the eye. In: Garner AG, Klintworth GK, eds. Pathobiology of ocular disease, 2 ed. New York: Marcel Dekker, 1994: 1225-1284. 4. Rahi JS, Sripathi S, Gilbert CE, Foster A. The importance of prenatal factors in childhood blindness in India. Dev Med Child Neurol 1997; 39: 449-455. 5. Dandona L, Williams JD, Williams BC, Rao GN. Population based assessment of childhood blindness in Southern India. Arch Ophthalmol 1998; 116: 545-546.