Children born to mothers who take the heroin substitute, methadone, during pregnancy may be at an increased risk of developing a wide range of vision problems, the results of a new study indicate.

Methadone is a synthetic substance usually prescribed as a substitute for heroin as it is much less likely to be misused. Methadone treatment has been available in Ireland for heroin addiction since the 1990s.

Among pregnant drug users, it is associated with a more stable maternal lifestyle and less likelihood of stunted foetal growth or preterm birth.

However, most babies born to mothers who are prescribed it during their pregnancy have significant withdrawal symptoms, known as neonatal abstinence syndrome (NAS). These symptoms are severe enough to warrant treatment in up to 80% of cases.

Scottish researchers assessed the eyesight of 20 children with vision problems, whose mothers had taken methadone during pregnancy. Over half of the children had also been exposed to benzodiazepines (tranquillisers), and 40% had been exposed to heroin, while in the womb.

Virtually all the children (95%) had poor eyesight, while seven out of 10 had involuntary eye movement (nystagmus). In half of the children, vision had not yet developed fully (delayed visual maturation).

Eleven out of 12 children who had been treated for NAS had nystagmus, compared with only three out of eight whose NAS had not been severe enough to warrant treatment.

One in three (35%) also had a squint (strabismus), while a similar proportion (30%) had blurred vision or long or short sightedness problems. One in four of the children had impaired brain function relating to sight.

The researchers also noted that one in four had significant developmental problems, including developmental delay and cerebral palsy.

“The underlying causes of the children’s visual problems are unclear, but the developing visual system is particularly sensitive to unexpected stressors before birth,” the team from the Royal Hospital for Sick Children in Glasgow said.

Details of these findings are published in the British Journal of Ophthalmology.

For more information on pregnancy, click here