The Basics of Vision Screening
The purpose of vision screening
In the childhood years it is important to detect any vision problems that may impair a child’s ability to learn. The screening process can help determine which infants and children may need further diagnostic assessment, or an educational evaluation.
Screening goals for children under age 8 years:
Typically, in children in this age category, before the eye is fully developed and matured, the primary goal is to screen for amblyogenic risk factors. These are conditions that may result in amblyopia (lazy eye) if not detected and treated early. These include organic defects (congenital cataracts, ptosis), strabismus (muscle imbalance) or anisometropia (a difference in visual acuity of each eye) and refractive errors. The earlier these problems are detected and treated, the better the outcome.
Screening Goals for Children over age 8 years:
The primary goal of screening (if they have been screened for amblyogenic risk factors) is to detect any refractive errors.
The prevalence of various vision problems in the pediatric population by age group:
Age 0-2: Astigmatism is common [30-70%], however most outgrow. Strabismus (esotropia) occurs at a prevalence of 1-2% in infants. Children in this age group are normally farsighted.
Preschool age: strabismus, asymmetric refractive errors and farsightedness is common, yet the prevalence of high myopia (nearsightedness) is less than 1 %. Amblyopia occurs 3-5% in this population, strabismus 2-4%.
Older children: Myopia (average age of onset 7 to 10 years, with plateau at age 14 to 18 years, females plateau earlier than males, the prevalence of this is 20% of children in this age range and the incidence is around 7 % of children screened each year are referred).
Eye Conditions age 0-2 Years
Congenital Cataracts: untreated bilateral congenital cataracts can cause nystagmus within 3 months and a unilateral cataract should be removed by 17 week, & occlusion started for 20/20 vision to be regained.
Retinoblastoma: A tumor in the retinal of the eye. 3% cancer in children < age 15, 93% survival rate. Affects 300 children annually, 2/3 cases are diagnosed before age 2, 1/3 of cases are diagnosed before age 5. Of these, 75% are unilateral, 25% are bilateral and 90% are usually confined to the orbit.
To detect cataracts and retinoblastoma, the American Academy of Pediatrics recommends that the eyes of the full-term child should be assessed within the first 2 months of life with red reflex screening (AAP). This red reflex evaluation checks for abnormalities that block the flow of light within the eye by observing the reflected light from the retina.
Eye Conditions in Childhood Years
Amblyopia: Prevalence 2.9%-3.9% Any condition that prevents the transmission of two clear, aligned, fusible images along the central visual pathways during the first decade of life can cause amblyopia. Causes: Strabismus (48%), Unequal refractive errors between 2 eyes (anisometropia) (20%), mixed strabismus/refractive errors (32%), Droopy eyelids (ptosis) (rare), Cataracts (rare).
Strabismus: Eyes that are out of alignment: Types: Congenital Esotropia, most common in infants, 1%, onset usually age 6 mos. Accommodative Esotropia, Onset children aged 2 to 4 years-eye turns when trying to focus, at distance, up close or both. In both these types, the eye turns inward. Exotropia, Onset: Age 2 to 8, most often occurs when a child is focusing on distant objects or when tired. The eye turns outward.
Refractive Errors: A defect of the eye that prevents light rays from being focused on the retina. The three most common types are; Myopia (nearsightedness), Hyperopia (farsightedness), this is a normal state of eye in children, newborns: 20/400, by Five Months: 20/100. Usually 20/20 by age 5 years, only 1% of school age children are farsighted enough to need glasses (called plus lens), and Astigmatism (oval, rather than round cornea).
Three with a light, six without, that’s what’s screening’s all about.
- Light: retinal reflex, pupillary response, corneal light reflex
- Without: Hx, observe, ext inspect (with screeners eyes) , cross cover, fix and follow (occluder and small toy) and visual acuity (HOTV/LEA/Snellen or Sloan charts)
For More Information: MDH (Maternal Child Health Section) provides training and consultations to C&TC, Head Start and School providers. www.health.state.mn.us/divs/fh/mch/hlth-vis/vision.html 651-201-3760