Short-sightedness is more common in first-born children

First-born children have a 10 per cent greater risk of developing myopia compared to their siblings, according to research undertaken in Wales. The researchers point to a possible connection with parental investment in education.

Myopia in children is becoming increasingly prevalent in most countries and is proving to be a major challenge in public health terms.

While certain factors have been identified as triggers for this condition, such as genetics and the amount of time spent outdoors and indoors, a new study highlights a link between myopia and birth order.

Researchers at Cardiff University in Wales undertook a study using data from the UK Biobank database involving 89,000 participants aged between 40 and 69. None of them had had a family history of myopia, thereby removing any genetic factor which could affect their sight.

The researchers compared the participants' vision assessment and their risk of myopia by studying their birth order in the family.

Their findings, which were published in the October 8 edition of the journal JAMA Ophthalmology indicated that compared to their last-born and younger siblings, first-born children had a 10 per cent greater risk of becoming short-sighted and a 20% greater risk of developing a severe form of myopia.  

Taking their work a step further, the team then took account of environmental factors associated with the noted difference. The researchers used two criteria: the highest educational qualification obtained and the age of completion of full-time education, in order to evaluate the degree of exposure to education depending on birth order.

Greater parental investment and the increased influence of educational criteria in the early childhood of first-born children could mean they are more exposed to factors triggering myopia, say the researchers. The more studying the first-born children do compared to their siblings, the greater the difference in sight between them, reports the study which points to the role of parental investment in children's school life, particularly first-born children, as a potential explanation for this phenomenon.

Previous studies have shown that myopia is accentuated by intense reading, writing, and working at screens at school, university and in professional life.

The researchers suggest that reduced parental investment with siblings who follow the first-born could be linked to the lower risk of myopia in the younger and youngest siblings in a family.