What are refractive errors, and what causes them?
A variety of inheritance patterns have been observed, including dominant (when one gene is passed from a parent with a refractive error to a child), recessive (caused by two genes, one inherited from each parent who may or may not have a refractive error), and multifactorial (a combination of genes and environment).
Refractive errors are also common in children with certain genetic disorders, such as Marfan syndrome and Down syndrome.
Astigmatism, Hyperopia and Myopia are the most common refractive errors, all of which affect vision and may require corrective lenses.
Astigmatism is a condition in which an abnormal curvature of the cornea can cause two focal points to fall in two different locations, making objects up close, and at a distance, appear blurry.
- Astigmatism may cause eye strain and also may be combined with nearsightedness or farsightedness.
- Astigmatism can start in childhood or in adulthood.
- Some symptoms include headache, eye strain and/or fatigue.
- If correction of the condition is needed, vision tends to be sharper and more consistent with spectacles than contact lenses.
Commonly known as farsightedness, hyperopia is the refractive error in which an image of a distant object becomes focused behind the retina, either because the eyeball axis is too short, or because the refractive power of the object is too weak.
This condition makes close objects appear out of focus and may cause headaches, eye strain and/or fatigue. Squinting, eye rubbing, lack of interest in school and difficulty in reading are often seen in children with hyperopia.
Eyeglasses or contact lenses may help to correct or improve hyperopia by adjusting the focusing power to the retina.
Commonly known as nearsightedness, myopia is a condition in which an image of a distant object becomes focused in front of the retina, either because the eyeball axis is too long or because the refractive power of the object is too strong. This is the opposite of hyperopia.
- Myopia is the most common refractive error seen in children.
- This condition makes distant objects appear out of focus and may cause headaches and/or eye strain.
- You may notice that your child sits close to the television and often squints to better see distant objects.
Eyeglasses or contact lenses may help to correct or improve myopia by adjusting the focusing power to the retina.
Astigmatism, Hyperopia and Myopia in the premature infant
In the short-term, it’s important to look for Retinopathy of prematurity (ROP), a disorder of the blood vessels of the retina (the light sensitive part of the eye). There are a few babies whose blood vessels are still growing and need to be followed within the first two to three weeks of going home, sometimes requiring an eye exam every other day. It’s absolutely critical that they have that close follow-up to make sure they don’t have any severe disease that might require laser therapy. For long-term follow-up, premature infants are at risk for myopia, amblyopia and strabismus. We recommend a repeat ophthalmologic exam at 9 to 12 months old for babies born at less than 32 weeks gestation. That’s not something that is done in the general population.