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Can a preterm birth cause myopia? How?

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The effects of preterm birth on a baby’s vision

When a baby is born preterm, there are often concerns about the effects of prematurity. Preterm babies may not yet be fully developed, which can lead to medical and eye complications. Among these is an increased risk of myopia of prematurity (MOP) associated with low birth weight and retinopathy.

What is myopia of prematurity (MOP)?

A baby is considered preterm if they are born before 37 weeks of pregnancy. The earlier a baby is born before the 37-week mark, the higher the risk of medical complications. 

Preterm babies begin their life not yet fully mature. As a result, eye development and growth in preterm babies may not proceed as it would for a full-term baby. The eye goes through its most rapid period of growth in the first year of a baby's life. In babies born preterm, there is a higher risk of myopia development in that first year.

SEE RELATED: Baby's vision: What you need to know about your infant's eye development

How is MOP different from common myopia?

Myopia in preterm infants is caused by changes to the front of the eye — the cornea, lens and anterior chamber. It is associated with low birth weight, severe retinopathy of prematurity (ROP) and the side effects of the treatments for ROP. 

By contrast, the most common type of myopia that affects children in the first and second decades of life is axial myopia. Axial myopia results from an increase in the length of the eyeball.

MOP and low birth weight

Low birth weight leads to a number of developmental issues in a child. Among these issues is a higher risk of refractive error in the eye. Studies have found that babies with low birth weight are at a higher risk of myopia development as they grow into adulthood. They are also at a higher risk of decreased visual acuity. 

There is a correlation between the amount of myopia in a preterm infant and birth weight. 

Research has found that in preterm babies, myopia was 10% more likely for every 100g decrease in birth weight.

MOP and retinopathy of prematurity (ROP)

Although myopia of prematurity (MOP) can occur without ROP, there is a strong link between MOP and severe ROP.

ROP results in changes to the back of the eye (retina) in preterm infants born before 31 weeks. It causes leaky, abnormal blood vessels to grow in the retina of these infants. These leaky blood vessels can result in retinal detachment and vision loss.

MOP is a result of changes to the front of the eye in preterm infants. These changes include a very steep cornea, a thick natural lens and a smaller anterior chamber (area between the cornea and iris). The combined effect of these changes results in myopia. 

ROP is one of the leading factors associated with myopia progression in preterm babies. Vision scientists have found that severe ROP is linked to high myopia (refractive error > – 6.00 D). ROP that was mild or went away on its own did not cause high myopia.

In a large study of premature babies (CRYO-ROP Trial), about 20% had myopia by age one. In the group of babies who had severe ROP, about 80% had myopia. 

This study also found that high myopia was more likely in premature babies with severe ROP. In the overall study, less than one in 20 of 1-year-olds had high myopia. In the group with severe ROP, nearly one in two babies had high myopia.

Vision researchers do not know the exact process by which prematurity and ROP cause changes to the front of the eye that lead to myopia. Theories such as a limitation of the eye’s growth or bone deficiency due to preterm birth have been proposed.

MOP and ROP treatments

In most cases, preterm babies have only mild or moderate ROP. In fact, the ROP may “regress,” or go away on its own, without treatment. Some babies, however, develop advanced ROP and require medical treatments. 

The treatments for advanced ROP include cryotherapy (freezing abnormal blood vessels), laser therapy (burning abnormal blood vessels) or an injection into the eye that blocks the growth of new abnormal blood vessels in the retina. 

Laser and cryotherapy treatments are performed in the periphery of the retina where abnormal blood vessels are found. Although these treatments decrease side vision, they help to preserve central vision.

An additional side effect of ROP treatments is that they are linked with the development of myopia of prematurity. Researchers have found that the amount of myopia depends on the type of treatment.

According to the American Academy of Ophthalmology, research has shown that the more laser therapy that an infant has, the higher the risk of myopia. Cryotherapy seems to increase the risk of myopia even more than laser therapy. 

Another treatment, called intravitreal bevacizumab (IVB) blocks the growth of new, abnormal blood vessels. Researchers found that IVB treatment seems to cause less myopia than laser treatment. 

High myopia was also less common in children treated with IVB than with laser. However, laser treatment seems to be more effective in treating ROP than IVB.

Myopia and vision issues in preterm babies

A preterm birth can result in an increased risk of myopia in infants. This myopia of prematurity is associated with low birth weight and severe retinopathy of prematurity. A preterm birth can also increase a child's risk of other eye conditions such as anisometropia and astigmatism. All of these conditions may lead to a decrease in vision in a young child.

According to the American Academy of Optometry, babies born prematurely should see an eye doctor early and frequently. In general, AAO recommends that babies get their first comprehensive eye exam between ages 6 and 12 months of age. This guideline is especially critical for babies who have a preterm birth.

If poor vision issues are not detected early in a young child, they may lead to irreversible vision loss due to amblyopia. It is extremely important to monitor the vision and eye health of children who have a preterm birth. As a preterm baby grows, comprehensive eye exams will ensure that any visual issues are detected early and managed properly.

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