Basics
Description
- Refractive errors are abnormalities in the optical components of the eyes that cause light not to be focused on the retinal plane. In order for a person to have clear vision, light entering the eye must precisely focus on the retina.
- Uncorrected refractive errors blur vision in one or both eyes.
- If left untreated in children, uncorrected refractive errors may cause permanent vision loss from amblyopia and strabismus (see "Amblyopia " and "Strabismus " ).
- Refractive errors are measured in diopter units.
- Refractive errors can be classified in three groups based on the optic effects (Appendix, Figure 1):
- Myopia (near-sightedness): Objects are focused in front of the retinal plane. Near vision is clearer and distance vision is more blurry. Optical correction is with concave lenses (negative power).
- Hyperopia (far-sightedness): Objects are focused behind the retinal plane and optical correction contains convex lens (plus power).
- Astigmatism: Unequal curvature of the cornea causing the cornea to be more curved in one direction than another (aspherical). The shape of the cornea is more like a football than a basketball in astigmatism.
- Images are blurred at near and far distances.
- Astigmatism can occur concomitantly with myopia and hyperopia.
- Other terms related to refractive error include the following:
- Emmetropia: No refractive error. Objects are focused on the retinal plane.
- Anisometropia: Unequal refractive error between the two eyes that increases the risk of amblyopia
- Accommodation: the changing of the shape of the eye 's lens to focus clearly at near or all of the time in hyperopes
Epidemiology
Prevalence of refractive errors varies during childhood as the optical components change with development. At birth, usual median refractive error is low hyperopia, approximately +2.00 diopters. In adults, the median is emmetropia; approximately 30% require optical correction.
Prevalence
- In children aged 5 " 17 years, the prevalence of visually significant refractive error varies on type.
- Myopia = 0.7 " 5.0%
- Hyperopia = 4.0 " 9.0%
- Astigmatism = 0.5 " 3%
- The prevalence and type of refractive error varies among ethnic groups. For example, people of Native American, Chinese, and Japanese descent have an increased prevalence of myopia.
Risk Factors
Genetics
- Both genetic and environmental factors are important in refractive status. ’ Ό60% of myopia can be predicted by parental degree of refraction.
- There is an increased prevalence of visually significant refractive errors in individuals with prematurity, autism, and cerebral palsy.
- Some genetic syndromes or medical problems associated with refractive errors include the following:
- Myopia is associated with Stickler, Marfan, Down, and Ehlers-Danlos syndromes.
- Hyperopia is associated with Senior-Loken syndrome, WAGR (Wilms tumor, aniridia, genitourinary malformations, mental retardation) syndrome, and Down syndrome.
- Astigmatism is associated with Down syndrome, craniofacial abnormalities, and albinism.
- Environmental factors associated with refractive error include prematurity, eye surgery, and trauma.
General Prevention
- Early detection and correction of refractive errors is important to prevent amblyopia and strabismus. A child should be able to perform a visual acuity examination by age 4 years.
- Children with significant refractive errors are often asymptomatic. All children should be screened for visual acuity in each eye.
- Glasses may not improve vision alone because of amblyopia (maldevelopment of the brain 's ocular cells). Patients with suspected amblyopia should be rechecked even if wearing glasses.
Pathophysiology
- The three most important determinants of refractive error include the cornea, lens, and axial length of the eye. The cornea and lens bend light to meet the retina in order to create a sharply focused image. The optical power of the cornea and lens must match the actual eye length (distance from cornea to retina). If the cornea and lens do not bend light to hit the retina, there is a refractive error and can blur the vision.
- Small amounts of hyperopia are normal for children. With small hyperopic errors, a child 's eye can easily bring objects into clear focus by adjusting the shape of the lens (accommodation). These children have no problems seeing at far or near distances.
- With larger amounts of hyperopia (greater than +3.50 diopters), a child 's vision may be blurred at distance and near because accommodation may be limited or cause esotropia (see "Strabismus " ).
- The refractive components evolve as the eye develops over childhood. The cornea, lens, and eye length should simultaneously develop to lead to emmetropia. Factors determining the normal and abnormal growth of eye are not completely understood.
- There are likely genetic and environmental factors determining the growth of the eye. There may be an association with increased level of education and increased incidence of myopia. Epidemiologic data suggest that increased amount of time spent outdoors protects against the development of myopia.
Commonly Associated Conditions
Refractive errors are frequently associated with other ocular conditions.
- Anisometropia is associated with nasolacrimal duct obstruction.
- Myopia is associated with childhood glaucoma, deprivation amblyopia, retinopathy of prematurity, retinal dystrophies, coloboma, and retinal detachments.
- Hyperopia is associated with esotropia, Leber congenital amaurosis, and aphakia (absence of lens).
- Astigmatism is associated with ptosis, coloboma, glaucoma, retinopathy of prematurity, lid hemangioma, nystagmus, and limbal dermoid.
Diagnosis
Signs and Symptoms
- Blurred vision
- Headache
- Squinting
- Torticollis
- Strabismus
History
- Age of onset of vision loss
- History of headaches, squinting, or subjective vision problems
- Associated ocular abnormalities, trauma, injury, or surgery
- History of strabismus, amblyopia
- History of prematurity, genetic disorders
- Family history of strabismus, amblyopia, congenital cataract, ocular or systemic genetic disease
Physical Exam
- Age appropriate vision screening is the most effective diagnostic tool for detecting refractive errors.
- Vision must be tested with each eye separately (patch or occluder over one eye).
- In children younger than 3 years of age:
- Monocular testing for fixing and following will determine visual behavior for each eye.
- Br Όckner (simultaneous red reflex) examination with the direct ophthalmoscope can objectively identify high refractive errors (distorted or darkened red reflex) or anisometropia (asymmetric brightness of red reflex).
- In children age 3 years or older:
- Subjective visual acuity should be testing with matching or identifying optotypes on a vision chart (Allen figures, HOTV, Lea, or Snellen).
- A failed vision screening or untestable vision after 2 attempts warrants a referral to an eye care provider.
- Vision screenings are important at regular intervals throughout childhood to prevent vision loss.
- Strabismus is frequently a secondary sign of refractive error in children and can be detected by cover test, Hirschberg corneal light reflex test, or Br Όckner test.
- Photoscreening, which uses the principle of red reflex testing, is also effective in detecting high or asymmetric refractive errors.
Differential Diagnosis
- Decreased binocular or monocular vision can be caused by a number of structural abnormalities of the eye as well as decreased cortical visual development. In any child with vision loss, refractive error needs to be evaluated as the cause or one of many factors contributing to decreased vision.
- True refractive error needs to be measured by only after instilling cycloplegic eye drops with retinoscopy (objective technique to measure refractive error). Without these drops, a child 's lens will accommodate (change shape) and give a false amount of refractive error.
Treatment
General Measures
- Refractive errors are treated by corrective lenses. Young children typically use glasses and teenagers may use contact lenses.
- The following guidelines for prescribing glasses have been developed to improve visual acuity and reduce the risk of amblyopia and strabismus.
- Myopia: >3.00 diopters for age 2 " 3 years and >1.00 diopter or more in school-age children
- Hyperopia: +4.50 diopters or more for age 2 " 3 years, +3.00 diopters or more in school-age children, or +1.50 diopters or more anisometropia
- Astigmatism: >2.00 diopters in age 2 " 3 years or >1.50 diopters in school-age children
- If hyperopic correction is needed for treatment but is not well accepted by the child, a brief period of cycloplegia with topical atropine can increase usage of glasses.
- In suspected amblyopia, vision should be retested to measure visual improvement after glasses have been worn for several weeks
- Hyperopic patients may develop esotropia when their glasses are taken off. Full-time glasses usage will prevent loss of vision and depth perception when children have accommodative esotropia.
Ongoing Care
Because refractive error depends on the eye 's shape and the eye 's shape changes as a child grows, the refractive error will evolve over time. Because this process is dynamic, children require at least an annual vision evaluation and refraction to assess whether they need a change in their glasses. They also need to be evaluated for amblyopia and strabismus.
Prognosis
If a child has a significant refractive error, his or her visual acuity will likely improve with optical correction. Refractive error rarely leads to significant functional limitations for daily activities and school. If refractive errors accompany other vision problems such as amblyopia or strabismus, other treatments may be needed to improve visual acuity. Special frames for athletic activities should be considered for children if standard glasses are interfering with those activities.
Complications
In children, the most significant complications of uncorrected refractive errors are strabismus and amblyopia.
- Accommodative esotropia
- For children with moderate to high hyperopia, their eyes will normally accommodate (change shape of lens) to bring objects into focus.
- This accommodative process may involuntarily cause overconvergence of the eyes and thus esotropia.
- Small amounts of convergence normally occur with accommodation so that both eyes can be looking at a near target. But in children with accommodative esotropia, they cannot control the degree of convergence and develop esotropia when focusing at both distance and near.
- Refractive amblyopia is poor cortical visual development resulting from a poorly focused image in one or both eyes.
- Anisometropia (unequal refractive error) is the most frequent cause of unilateral amblyopia ( ’ Ό35%). The brain learns to see well from the eye that has the least amount of refractive error but does not develop equal vision from the eye that has a higher refractive error.
- Bilateral high refractive errors may cause bilateral amblyopia from chronically poor visual input from both eyes.
- High myopia (>5 diopters) can lead to retinal thinning and eventual retinal detachment. It is also associated with increased risk of glaucoma and cataracts as an adult.
Additional Reading
- American Academy of Ophthalmology. Preferred Practice Pattern: Refractive Errors. San Francisco: American Academy of Ophthalmology; 2013.
- American Academy of Ophthalmology Pediatric Ophthalmology/Strabismus Panel. Preferred Practice Pattern Guidelines. Pediatric Eye Evaluations. San Francisco: American Academy of Ophthalmology; 2012.
- Bell AL, Rodes ME, Kellar LC. Childhood eye examination. Am Fam Physician. 2013;88(4):241 " 248. [View Abstract]
- Paysse EA, Williams GC, Coats DK, et al. Detection of red reflex asymmetry by pediatric residents using the Br Όckner reflex versus the MTI photoscreener. Pediatrics. 2001;108(4):E74. [View Abstract]
- Thorn F. Development of refraction and strabismus. Curr Opin Ophthalmol. 2000;11(5):301 " 305. [View Abstract]
- Wen G, Tarczy-Hornoch K, McKean-Cowdin R, et al. Prevalence of myopia, hyperopia, and astigmatism in non-Hispanic white and Asian children: multiethnic pediatric eye disease study. Ophthalmology. 2013;120(10):2109 " 2116. [View Abstract]
Codes
ICD09
- 367.9 Unspecified disorder of refraction and accommodation
- 367.1 Myopia
- 367.20 Astigmatism, unspecified
- 367.0 Hypermetropia
- 367.22 Irregular astigmatism
- 367.31 Anisometropia
- 367.21 Regular astigmatism
- 367.89 Other disorders of refraction and accommodation
ICD10
- H52.7 Unspecified disorder of refraction
- H52.10 Myopia, unspecified eye
- H52.209 Unspecified astigmatism, unspecified eye
- H52.00 Hypermetropia, unspecified eye
- H52.01 Hypermetropia, right eye
- H52.6 Other disorders of refraction
- H52.201 Unspecified astigmatism, right eye
- H52.213 Irregular astigmatism, bilateral
- H52.202 Unspecified astigmatism, left eye
- H52.212 Irregular astigmatism, left eye
- H52.219 Irregular astigmatism, unspecified eye
- H52.203 Unspecified astigmatism, bilateral
- H52.221 Regular astigmatism, right eye
- H52.222 Regular astigmatism, left eye
- H52.229 Regular astigmatism, unspecified eye
- H52.11 Myopia, right eye
- H52.12 Myopia, left eye
- H52.13 Myopia, bilateral
- H52.211 Irregular astigmatism, right eye
- H52.02 Hypermetropia, left eye
- H52.223 Regular astigmatism, bilateral
- H52.03 Hypermetropia, bilateral
SNOMED
- 39021009 Disorder of refraction (disorder)
- 57190000 Myopia (disorder)
- 82649003 Astigmatism (disorder)
- 38101003 Hypermetropia (disorder)
- 68905002 Regular astigmatism (disorder)
- 47099006 Irregular astigmatism (disorder)
FAQ
- Q: Will my child always need glasses?
- A: Not necessarily. As children grow, the shape of the eyes change. Because the need for glasses depend on the eye 's shape, it is unclear whether the child will continue to need glasses to have normal vision as his or her eye develops. If optical correction remains necessary, contact lenses and refractive surgery are also possible in older children or adults.
- Q: Will wearing glasses weaken my child 's eyes?
- A: No. Glasses change the way light enters the eye to focus on the retina and optimize vision. Glasses do not weaken the eyes or vision. Glasses are important to prevent amblyopia and permanent vision loss.
- Q: If my child wears glasses and his or her vision improves, can my child stop wearing glasses?
- A: In the majority of children, they will need to continue to wear glasses to clarify the blur from their refractive error. The glasses are improving their visual acuity.
- Q: Is my child too young for glasses?
- A: If a child needs glasses to improve his or her visual acuity, then a child is never too young to wear them. Small frames are designed for children as young as a few months. If glasses improve vision, a child usually quickly accepts correction.
- 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. Increased hours spent outdoors may prevent myopic progression. 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.