Refractive Error

Refractive Error: Excerpt from The 5-Minute Pediatric Consult

Monte D. Mills, MD

Refractive Error - BASICS

Refractive Error - description

To allow vision, light coming into the eye must focus on the retina. Refractive errors are aberrations in the optic components of the eyes that cause the eye to lose focus. Uncorrected refractive error blurs vision in 1 or both eyes, and may also cause strabismus and amblyopia in children (see “Amblyopia” and “Strabismus”).

Refractive Error - general prevention

• Early detection and correction of refractive errors is important to prevent amblyopia and strabismus. Recognition visual acuity testing using charts should start by age 4 years.
• Children with significant refractive errors are not necessarily symptomatic. All children should be screened for visual acuity in each eye.
• Glasses may not reverse amblyopia, even if the refractive error is appropriately corrected. Patients with suspected amblyopia (i.e., anisometropia, unilateral poor vision, and strabismus) should be rechecked often even if wearing glasses.

Refractive Error - epidemiology

Because of the age-related growth of the optic components of the eye, prevalence of refractive errors varies during childhood. At birth, usual median refractive error is low hyperopia, approximately +2.00 diopters. In adults, the median is emmetropia. The incidence of refractive error requiring correction increases with age.

Refractive Error - prevalence

• In school-aged children in the US, 7–25% have refractive error significant enough to affect visual acuity. ~25% of the adult population of the US have myopia, and ~5% have hyperopia.
• Some ethnic groups have increased prevalence of myopia, including people of Native American, Chinese, and Japanese descent.

Refractive Error - risk factors

Refractive Error - genetics

• Both genetic and environmental factors are important in refractive status. ~60% of myopia can be predicted by parental degree of refraction, although inheritance seems to be polygenic in most cases.
• Some genetic syndromes associated with refractive errors include:
  • Myopia:
    • Stickler syndrome
    • Albinism
    • Marfan syndrome
    • Down syndrome
    • Ehlers-Danlos syndrome
  • Hyperopia:
    • Senior-Loken syndrome
    • WAGR (Wilms tumor, aniridia, genitourinary malformations, and mental retardation) syndrome
  • Astigmatism:
    • Down syndrome
    • Crouzon syndrome
    • Albinism
• Environmental:
  • Environmental factors associated with refractive error in childhood include premature birth, eye surgery, and eye trauma.

Refractive Error - pathophysiology

• The most important optic components of the eye are the cornea and the lens, which refract light coming into the pupil to focus an image on the retina. The cornea and lens determine the focal length of the eye, which must match the actual eye length (distance from cornea to retina). A sharply focused image on the retina is necessary for recognition of small objects and normal visual acuity; refractive errors cause blurring.
• Refractive errors can be classified in three groups based on the optic effects:
  • Myopia, also called “near-sightedness,” is correctable with concave lenses with negative diopteric power. Myopic eyes may be in focus for closer targets, but blurred for more distant.
  • Hyperopia, correctable with convex lenses with positive diopteric power.
    • Although hyperopia is sometimes called “far-sightedness,” this is a misnomer in children.
    • Small hyperopic refractive errors are easily overcome by focusing the eye, or accommodation, and many hyperopic children have no difficulty seeing near or distant targets.
    • Larger amounts of hyperopia may blur both near and distant targets, or cause eye strain or esotropia because of the focusing effort required for focusing (see “Strabismus”).
  • Astigmatism, correctable with toric lenses, is caused by aspheric aberration. Uncorrected astigmatism creates images that are not focused for near or distant targets.
    • Astigmatism may occur simultaneously with myopia and hyperopia.
• Other terms related to refractive error include:
  • Emmetropia, or neutral refraction (no refractive error)
  • Anisometropia, or unequal refractive error between the 2 eyes
  • Accommodation, the ability to refocus eyes for near targets, and to overcome hyperopia
• In children <8 years of age, because of visual development and plasticity, uncorrected refractive errors may have a significant effect on life-long vision. Amblyopia, which may cause permanent uncorrectable vision loss, and strabismus are among the risks of untreated refractive errors in young children (see “Strabismus” and “Amblyopia”).

Refractive Error - pathophysiologys

• The refractive components of the eye (e.g., cornea, lens, eye length) normally develop simultaneously during early childhood to allow focused images. Factors determining the relative growth and development of these ocular features are not completely understood, and abnormal growth of any component may result in refractive error.
• High myopia (>5 diopters in children) is associated with pathological thinning of the retina and sclera, and is associated with an increased risk of retinal detachment later in life.

Refractive Error - associated conditions

Refractive errors are frequently associated with other ocular conditions. These include:

• Myopia:
  • Childhood glaucoma
  • Retinitis pigmentosa
  • Coloboma
  • Microphthalmia
  • Retinopathy of prematurity
  • Congenital cataract
  • Achromatopsia
  • Retinal detachment
  • Retinal hole
• Hyperopia:
  • Esotropia
  • Leber congenital amaurosis
  • Surgically treated cataracts (aphakia)
• Astigmatism:
  • Congenital ptosis
  • Coloboma
  • Forceps birth injury
  • Glaucoma
  • Retinopathy of prematurity

Refractive Error - DIAGNOSIS

Refractive Error - signs & symptoms

• Loss of vision
• Blurred vision
• Headache
• Squinting

Refractive Error - history

• Age of onset of vision loss
• Associated ocular abnormalities, trauma, injury, or surgery
• History of strabismus, amblyopia
• History of prematurity, genetic disorders, collagen disorders (e.g., Ehlers-Danlos, Marfan syndromes)
• History of headaches, squinting, or subjective vision problems
• Family history of glasses or refractive error, amblyopia, strabismus

Refractive Error - physical exam

• Visual acuity is the most effective diagnostic tool for detecting refractive errors.
• Vision must be tested with each eye separately, using a patch, opaque card, or plastic occluder.
• Testing charts are available with letters as well as pictures and for children who cannot yet read figures (Es). In children who are too young to test with charts, the Bruchner simultaneous red reflex examination can detect high refractive errors and anisometropia, which appear as an asymmetric or distorted red pupillary reflex using the direct ophthalmoscope.
• Strabismus is frequently a secondary sign of refractive error in children and can be detected by cover test, Hirschberg corneal light reflex test, or Bruchner test. Photoscreening, which uses the principle of red reflex testing, is also effective in detecting high or asymmetric refractive errors.

Refractive Error - differencial diagnosis

• Any cause of monocular or binocular vision loss can simulate refractive error. Because refraction is not easily measured without eye drops and special equipment, possibility of refractive error must be considered in all children with reduced visual acuity and should also be considered in children with strabismus and normal vision. Cycloplegic refraction (measuring refraction after the use of eye drops to relax accommodation), and, in younger children, a trial of correction with glasses, is necessary to eliminate the possibility of residual amblyopia or other cause of poor vision.

Refractive Error - TREATMENT

Refractive Error - general measures

• Refractive errors are treated by corrective lenses. In young children, this is usually glasses, although contact lenses are frequently used in teenagers.
• Unlike adults, children with neglected refractive error are at great risk for significant long-term complications, including amblyopia and strabismus. Hyperopia and anisometropic hyperopia pose the greatest risk for amblyopia. Therefore, smaller amounts of hyperopia and anisometropia are generally corrected with glasses. Glasses are prescribed to improve vision and treat or prevent amblyopia in children for:
  • Myopia, −3.00 diopters or more in infants and young children, −1.00 diopter or more in school-age children
  • Hyperopia, +4.00 diopters or more in infants, +3.00 diopters or more in school-age children, or +1.50 diopters or more anisometropia (difference between eyes)
  • Any hyperopia in accomodative esotropia. Bifocals may also be prescribed to treat residual esotropia for near targets (high AC/A ratio).
  • Astigmatism of >3.00 diopters in infants and young children, or >1.50 diopters in school-age children
• In general, children accept full correction of all refractive error, although undercorrection of hyperopia by 0.50–1.00 diopter may enhance the acceptance of new glasses. Occasionally, if hyperopic correction is not well accepted, a brief period of cycloplegia with topical atropine can reinforce use of the glasses.
• In suspected amblyopia, vision should be retested to measure visual improvement after glasses have been worn for several weeks. Children wearing glasses must be remeasured regularly, usually at least annually, until they have reached visual maturity and the risk of amblyopia has passed (i.e., 8–10 years of age).
• Hyperopic patients may develop accommodative esotropia when their glasses are off, after wearing the glasses for some time. Full correction of hyperopia and continuous correction are key approaches to this unusual complication.

Refractive Error - FOLLOW UP

Refractive errors change over time due to growth of the eye and its optic components. In general, younger children will need rerefraction and new glasses more frequently. All children wearing glasses should have acuity tested and be rerefracted at least annually.

Refractive Error - complications

In children, the most significant complications of uncorrected refractive errors are strabismus and amblyopia.

• Accommodative esotropia: Uncorrected hyperopia in young children can be overcome by focusing, or accommodation.
  • This involuntary focusing of the eyes is controlled reflexively and integrated with convergence (i.e., crossing the eyes inward).
  • Usually, accommodation is used to focus on near targets, and convergence keeps both eyes pointed at the near target.
  • If excessive hyperopia is present, or an abnormal ratio of accommodative convergence to accommodation exists (AC:A ratio), the eyes may cross with accommodation, producing accommodative esotropia (see “Strabismus”).
• Amblyopia: Poor visual development results from a poorly focused image. Anisometropia (unequal refractive error), which blurs vision in 1 eye and is the most frequent cause of unilateral amblyopia, causes ~35% of amblypia. Less frequently, bilateral high refractive errors may cause bilateral amblyopia (see “Amblyopia”).

Refractive Error - bibliography

American Academy of Ophthalmology. Preferred Practice Pattern: Pediatric Eye Examination. San Francisco: American Academy of Ophthalmology, 2002American Academy of Ophthalmology. Preferred Practice Pattern: Refractive errors. San Francisco: American Academy of Ophthalmology, 2002.Drack AV. Inheritance of refractive errors. In Traboulsi EI, ed. Genetic Diseases of the Eye. New York: Oxford University Press; 1998.
1. Kuo A, Sinatra RB, Donahue SP. Distribution of refractive error in healthy infants. J Am Assoc Pediatr Ophthalmol Strabismus. 2003;7:174–177.
2. Mills, MD. The eye in childhood. Am Fam Phys. 1999;60:907–918.
3. Paysse EA, Williams GC, Coats DK, et al. Detection of red reflex asymmetry by pediatric residents using the Bruchner reflex versus the MTI photoscreener. Pediatrics. 2001;108.
Taylor DA, Hoyt CS. Pediatric Ophthalmology and Strabismus. Malden, MA: Saunders, 2004.
4. Thorn F. Development of refraction and strabismus. Curr Opin Ophthalmol. 2000;11:301–305.

Refractive Error - CODES

Refractive Error - icd9

367.9 Unspecified disorder of refraction and accommodation

• 367.0 Hyperopia
• 367.1 Myopia
• 367.2 Astigmatism
• 367.3 Anisometropia

Refractive Error - FAQ

• Q: Will my child always need glasses?
• A: Not necessarily. Many children who wear glasses are able to see well without correction as adults. Contact lenses and refractive surgery are also possible in older children or adults, if correction remains necessary.
• Q: Will wearing glasses weaken my child’s eyes?
• A: No, wearing correction for refractive errors will not weaken the eyes or vision, and is important to prevent amblyopia and permanent vision loss. Occasionally, children with hyperopia will develop accommodative esotropia when the glasses are removed, after wearing correction for some time. This is rarely a problem as long as the glasses are worn continuously.
• Q: Is my child too young for glasses?
• A: Glasses can be worn in children as young as a few months old, with appropriate frames. Usually, children get used to glasses quickly and accept correction easily.
• Q: My child can see well, why does he need glasses?
• A: Some children with hyperopia can see charts well, but the accommodation (i.e., focusing) necessary to overcome the refractive error may cause eye strain, fatigue, and esotropia. Others may need glasses for unilateral refractive error and seem to see well with both eyes open. In these children, wearing correction may treat or prevent problems even though they may seem to see well without correction.
• Q: Everyone in my family has needed glasses for myopia in childhood. Is there anything we can do for my child that will prevent the development of myopia?
• A: Unfortunately, few environmental factors have been clearly identified to affect the development of myopia. Reading, particularly at an early age; excessively close visual targets (holding books or toys too close to the face); and light exposure during nighttime have been suggested as factors in myopia development. Avoiding long periods of reading, avoiding intensive near work, using a reasonable reading distance (i.e., 16–18 inches), and avoiding use of night lights may reduce some environmental stimuli.

Book Source Details

• Book Title: The 5-Minute Pediatric Consult
• Author(s): M. William Schwartz MD; et al.
• Year of Publication: 2008
• Copyright Details: The 5-Minute Pediatric Consult, Copyright © 2008 Lippincott Williams & Wilkins.

More About Refractive Eye Disorders

• Back to disease: Refractive Eye Disorders: Introduction
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.

More About This Book: Title: The 5-Minute Pediatric Consult Authors: M. William Schwartz MD; et al. Publisher: Lippincott Williams & Wilkins Copyright: 2008 ISBN: 0-7817-7577-9

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