Vision screening and assessment in infants and children

INTRODUCTION — Vision assessment is an important part of the medical care of children (table 1). Eye problems that are not detected and treated in the first few months (eg, cataracts, pronounced ptosis) or years (asymmetric refractive errors) of life can lead to irreversible vision loss [1,2]. Poor vision and vision loss also may be an early indication of serious or life-threatening diseases, such as retinoblastoma, lipid storage disorders, or peroxisomal disorders (table 2) [3,4]. (See "Retinoblastoma: Clinical presentation, evaluation, and diagnosis" and "Inborn errors of metabolism: Epidemiology, pathogenesis, and clinical features".)

The development of the visual system and vision assessment in infants and children will be reviewed here. Specific pediatric ophthalmologic problems are discussed separately:

●Strabismus (see "Evaluation and management of strabismus in children" and "Causes of horizontal strabismus in children" and "Causes of vertical strabismus in children")

●Amblyopia (see "Amblyopia in children: Classification, screening, and evaluation" and "Amblyopia in children: Management and outcome")

●Refractive error (see "Refractive errors in children")

●Cataract (see "Cataract in children")

●Glaucoma (see "Overview of glaucoma in infants and children" and "Primary infantile glaucoma")

●Retinoblastoma (see "Retinoblastoma: Clinical presentation, evaluation, and diagnosis" and "Retinoblastoma: Treatment and outcome" and "Approach to the child with leukocoria")

VISUAL DEVELOPMENT — The visual system (retina, optic nerves, and visual cortex) is immature at birth. It begins to mature during the first weeks of life [5]. Myelination of the optic nerves, development of the visual cortex, and growth of the lateral geniculate body occur over the first two years [6]. The fovea, the most visually sensitive part of the retina, reaches maturity at approximately four years of age.

The period of visual maturation is a critical period during which the visual system is affected by outside influences. Visual stimuli are critical to the development of normal vision. Development of the visual pathways in the central nervous system requires that the brain receive equally clear, focused images from both eyes. Ocular processes (eg, refractive error, strabismus, cataract) that interfere with or inhibit the development of the visual pathways may result in amblyopia [1,2]. (See "Refractive errors in children" and "Amblyopia in children: Classification, screening, and evaluation", section on 'Definition' and "Evaluation and management of strabismus in children", section on 'Complications' and "Cataract in children", section on 'Complications'.)

Visual behavior and performance evolve with maturation of the visual system (table 3).

●Visual fixation can be demonstrated shortly after birth [7]. The visual acuity of a newborn infant is estimated to be approximately 20/400 [6].

●The ability to follow an object is detectable in most infants by three months of age.

●Stereopsis and binocular visual function develop between the ages of three and seven months [8].

●Visual acuity reaches the adult level of 20/20 by three to five years of age, though young children often will not perform formal visual acuity testing to this level.

VISION SCREENING — The approach to screening for vision problems depends on the age of the child.

Children <5 years — The prevalence of undetected vision problems in preschool children is estimated to be 5 to 10 percent [9]. Amblyopia occurs in 1 to 4 percent of children and usually develops between infancy and five to seven years of age [10]. Early detection and treatment of amblyopia improves the prognosis for normal eye development. (See "Amblyopia in children: Classification, screening, and evaluation", section on 'Epidemiology'.)

In accord with the American Academy of Pediatrics (AAP), American Academy of Family Physicians, American Academy Ophthalmology (AAO), and United States Preventive Services Task Force (USPSTF), we suggest screening to detect amblyopia, strabismus, and other vision problems in all children younger than five years of age (table 1) [11-14]. The AAP guidelines suggest vision risk assessment at all health maintenance visits and vision screening or referral, as indicated, if risk factors are identified [11,12]. If available, a photoscreener or autorefractor may be used for vision risk assessment in children beginning at age 12 months [15]. (See 'Instrument-based screening' below.)

Risk factors for vision problems include a history of prematurity; family history of congenital cataracts, retinoblastoma, and metabolic or genetic disease; significant developmental delay or neurologic difficulty; and systemic diseases associated with eye problems [16]. Parents/caregivers should be asked questions relevant to the child's vision as described below. (See 'Visual history' below.)

The AAP guidelines suggest vision screening at three and four years of age [11,12]. Vision screening should include tests of monocular distance acuity (table 1) [12,17,18]. (See 'Visual acuity' below.)

For children who are unable to cooperate with visual acuity screening, repeat screening should be attempted within one to six months. Referral to an ophthalmologist or optometrist who is appropriately trained and experienced in treating children is warranted for children who are unable to be tested after two attempts, or in whom an abnormality is suspected or detected. (See 'Referral indications' below.)

Systematic reviews of vision screening tests for the detection of amblyopia found few high-quality data regarding the performance of preschool vision screening [19-23]. However, because of the importance of early detection, vision risk assessment should be performed at every well-child visit, with subsequent screening as indicated [11,12].

Children ≥5 years — In accord with the AAP guidelines, we suggest vision risk assessment at all health maintenance visits and vision screening or referral, as indicated, if risk factors are identified (table 1) [11,12]. We also suggest periodic assessment of visual acuity (vision screening) throughout childhood and adolescence. For children ≥5 years of age, the AAP guidelines suggest visual acuity measurement at ages 5, 6, 8, 10, 12, and 15 years [11,12]. These suggestions place a high value on the potential for improved outcome with early detection and intervention (compared with the cost, inconvenience, and lost time necessary for follow-up of a potentially false-positive result).

Data are limited regarding the prevalence of uncorrected refractive errors and undiagnosed vision problems in school-age children and adolescents [24]. Evidence that early detection of refractive errors is associated with important clinical benefits, compared with testing based on symptoms, is sparse [25].

The AAP, AAO, American Association of Certified Orthoptists, and American Association for Pediatric Ophthalmology and Strabismus recommend routine vision screening beginning at three to four years of age and every one to three years thereafter throughout childhood and adolescence [11,12,18]. The USPSTF does not address screening for visual impairment in children older than five years.

REFERRAL INDICATIONS — Indications for referral to an ophthalmologist or optometrist who is appropriately trained and experienced in treating children include (table 1) [18]:

●Abnormal red reflex (may indicate cataract, glaucoma, retinoblastoma, retinal abnormality, or strabismus, or unequal or high refractive error) (figure 1). Infants with a white reflex (leukocoria) should be referred immediately; the referring clinician should communicate directly with the ophthalmologist and confirm that the consultation actually occurred [18]. (See "Approach to the child with leukocoria", section on 'Referral' and "The pediatric physical examination: HEENT", section on 'Ophthalmoscopic examination'.)

●Personal history of prematurity (if not already cleared by an ophthalmologist) or metabolic or genetic disease with ophthalmologic implications.

●Family history of childhood cataract, retinoblastoma, retinal dysplasia, or childhood glaucoma. Infants with such histories should have a formal ophthalmologic examination in the first weeks or months of life, depending upon the condition. (See "Cataract in children" and "Retinoblastoma: Clinical presentation, evaluation, and diagnosis" and "Overview of glaucoma in infants and children".)

●Inability to fix and follow by age three months. (See 'Fixation reflex' below.)

●Abnormal ocular alignment in children older than four months (ie, strabismus). (See "Evaluation and management of strabismus in children".)

●Pupillary asymmetry of ≥1 mm in diameter (suggestive of neurologic condition).

●Corneal asymmetry (suggestive of glaucoma or microphthalmia) (picture 1). (See "Overview of glaucoma in infants and children".)

●Unilateral or bilateral ptosis or other lesions obstructing the visual axis (eg, eyelid hemangioma), which may cause amblyopia.

●Asymmetry of visual behavior (eye preference) or visual acuity difference of two lines or more between eyes.

●Visual acuity worse than 20/50 in a three-year-old, worse than 20/40 in a four-year-old, or worse than 20/30 in a child ≥5 years. The "rule of 8s" is a helpful mnemonic for determining the need for referral (table 4). (See 'Visual acuity' below.)

●Abnormal instrument-based vision screening. (See 'Instrument-based screening' below.)

●Nystagmus.

OVERVIEW OF VISION ASSESSMENT

Objectives — Children rarely complain of visual difficulties [18]. Vision assessment is an important component of pediatric care. It is performed to detect conditions that affect visual potential because early detection and prompt treatment of these conditions may prevent lifelong visual impairment.

Ocular and systemic conditions that may be detected through assessment of the visual system in infants and children include:

●Cataracts (see "Cataract in children", section on 'Clinical features')

●Strabismus (see "Evaluation and management of strabismus in children", section on 'Evaluation')

●Amblyopia (which should be suspected when the vision between the two eyes differs) and amblyopia risk factors (eg, cataracts, strabismus, ptosis, unequal refractive error) are present (see "Amblyopia in children: Classification, screening, and evaluation", section on 'Refractive amblyopia')

●Retinoblastoma (see "Retinoblastoma: Clinical presentation, evaluation, and diagnosis", section on 'Clinical presentation')

●Glaucoma (see "Overview of glaucoma in infants and children" and "Primary infantile glaucoma")

●Neurologic, metabolic, or genetic disorders (see "Inborn errors of metabolism: Epidemiology, pathogenesis, and clinical features" and "Peroxisomal disorders")

Optimal conditions — Assessment of vision should be performed in a room with minimal distractions; the door to the examination room should be closed. Other siblings may need to be reminded to remain silent.

Infants and young children are best examined while being held upright in the arms of their caregivers. In children younger than two to three years of age, visual behavior (table 3), rather than visual acuity, is assessed. (See 'Infants and children <3 years' below.)

Children usually are able to follow directions required for visual acuity testing starting around age three to four years. Patient cooperation is essential to an optimal examination. Accurate assessment of visual acuity can be made in almost all cooperative verbal children. (See 'Children three years and older' below.)

VISUAL HISTORY — The importance of the vision history cannot be overemphasized. Parents/caregivers often are aware of vision problems in their child before the problem is readily apparent to the clinician. The examiner should ask the parents/caregivers relevant questions. Suggested questions may include [16,18,26]:

●Does your child seem to see well?

●Have you noticed anything unusual about your child's vision?

●Does your child's vision seem similar to his/her siblings at the same age?

●Does the child have any difficulty seeing objects that are nearby (eg, arm's length) or further away (eg, more than several feet)?

●Does your child hold things close when trying to focus?

●Do the eyes appear to cross or wander?

●Does your child squint?

●Do your child's eyelids droop, or does one eyelid tend to close?

●Do the child's eyes appear unusual?

●Have your child's eyes been injured?

The child's past medical history should be reviewed because many medical conditions have associated ophthalmologic findings (eg, lipid storage disorders, peroxisomal disorders). Children with a history of severe prematurity, for example, are at higher risk for developing amblyopia, high myopia (nearsightedness), and strabismus. Among children with severe visual impairment, 70 percent have additional handicaps and 10 percent have impaired hearing [5].

The family history should be reviewed for serious childhood eye disease (eg, childhood cataracts, strabismus, amblyopia, glaucoma, retinal problems, nystagmus). Many ophthalmologic conditions are familial; a positive family history increases the likelihood the child may have similar problems. (See 'Referral indications' above.)

VISUAL ACUITY

Infants and children <3 years — In children younger than two to three years of age, visual behavior (table 3), rather than visual acuity, is assessed. The goal is to determine whether visual behavior is normal for age and whether behavior is similar between the two eyes. Visual behavior can be tested in virtually all children. Newborn infants can demonstrate visual fixation if an appropriate target (eg, the human face) is used [7].

Observation — The assessment of visual behavior begins with the observation of the child's reaction as the examiner enters the room. The child's ability to see the examiner, to visually track the examiner, and to respond to the examiner's smile should be noted. Visual behavior varies with the age of the child (table 3):

●One-month-old infants make eye contact and begin to look at objects that are close to their faces. They appear serious as they fixate.

●Two-month-old infants begin to display facial expression as they fixate.

●Three-month-old infants begin to observe their hands while holding them close to their faces.

●Three- to four-month-old infants begin to watch activity that occurs around them.

●Six-month-old infants observe their surroundings and recognize favorite people, toys, or foods at a distance.

Fixation reflex — The quality of the fixation reflex is a good marker of visual function in most preverbal children [18].

●Performing the assessment – The choice of target varies depending upon the age of the child. Objects with spatial orientation are essential:

•The human face, for which there may be a genetic fixation preference [27], is the ideal target for children younger than three to four months of age.

•Small, colorful toys or stickers placed on the end of tongue depressors are good targets for infants older than three to four months. More than one target may be necessary for these children because they rapidly lose interest.

•White light (eg, from a pen light) should be avoided because it lacks spatial orientation.

•Targets that make noise should be avoided because they provide both visual and auditory cues, and distinguishing which cue(s) the child is using to track the object is difficult.

In testing fixation, the target is moved from side to side while the child remains still. False-positive results may be obtained if the child, rather than the target, is moved. Movement of the child may activate the vestibulo-ocular reflex (VOR), which causes the eyes to move; this reflex is not a measure of visual behavior. (See 'Vestibulo-ocular reflex' below.)

Both eyes are assessed together, and then each eye is tested separately by occluding one eye at a time. Accuracy is improved if the fixation test is repeated several times. The eye movements of infants are expected to be somewhat uncoordinated. The ability to follow past midline develops at approximately three to six months of age; vertical eye movements develop around three months.

Serious visual disorders may be indicated by asymmetry or abnormality in the fixation reflex. One limitation of the fixation-and-follow test is that it uses the presence of a motor function (eye movement) as a marker of vision. Thus, false-negative results may be obtained if the child has a condition that prevents normal eye movement. (See "Third cranial nerve (oculomotor nerve) palsy in children" and "Fourth cranial nerve (trochlear nerve) palsy" and "Sixth cranial nerve (abducens nerve) palsy", section on 'Clinical manifestations'.)

●Documentation – Two methods are commonly used to document the fixation reflex: the central-steady-maintained (CSM) method and the fix-and-follow (F+F) method. Both methods provide useful information; the choice of one over the other is a matter of personal preference.

In the CSM notation, with one eye occluded (the cover test), several characteristics of fixation are noted:

•Is the fixation central (C) or eccentric/noncentral (NC)?

•Is the fixation held steadily on the target as it is held still and slowly moved (S), or is it unsteady (eg, nystagmus) (US)?

•Is the child able to maintain fixation with the viewing eye when the other eye is uncovered or through a blink (M), or not (NM)?

In the F+F notation, the child's ability to fixate on and follow a target as it is slowly moved through his or her visual space is noted. Each eye is tested separately. Notation also should be made of the child's ability to maintain fixation with the viewing eye when the other eye is uncovered. Special techniques available to the ophthalmologist may be required to determine if an eye is able to maintain fixation after the other eye is uncovered. In children with strabismus, however, movements to refixate the eye can be appreciated without these special techniques. (See "Evaluation and management of strabismus in children", section on 'Cover/uncover test'.)

Preferential looking — The forced preferential looking method uses grating (eg, Teller) cards to test visual acuity and relies upon the preference of children to look at patterns of alternating contrast rather than homogeneous targets. Grating cards typically have one target area with alternating light and dark stripes and another that is homogeneously gray. The examiner, observing through a small hole in the center of the card, notes the direction of the child's gaze as each card is presented. Targets with thinner and thinner stripes are presented until the child no longer has a preference. Visual acuity is estimated by the thinnest target lines that the child is able to detect. Accuracy is improved with test repetition. This technique has several limitations (ie, it is time consuming, it tends to overestimate vision, accuracy depends on the examiner's skill level) and it is used infrequently in the primary care setting, though it may sometimes be used by the ophthalmologist or optometrist [28-30].

Children three years and older — Accurate assessment of visual acuity can be made in almost all cooperative verbal children. Visual acuity testing with optotypes should be attempted in all children ≥3 years [18]. It should be repeated periodically throughout childhood. (See 'Vision screening' above.)

Optotype tests — Optotype recognition tests assess the child's ability to see and recognize an optotype (eg, figure or letter) and to communicate that recognition to the examiner. There are several such tests (figure 2). The Snellen acuity test (the standard letter test) is the preferred test for cooperative children who can identify all the letters of the alphabet. The HOTV and LEA tests are preferred tests for preverbal children and those who cannot readily identify letters. Selection of age-appropriate optotypes is key in accurate determination of visual acuity [18].

●Letter charts – The Snellen acuity test (the standard letter test) is the gold-standard test and is typically used for children who can identify the letters of the alphabet. When using the Snellen chart, the examiner should listen for letters that are consistently misnamed (eg, "E" for "F"); such misnamings may indicate lack of familiarity with the alphabet rather than an inability to distinguish the letter [8].

The HOTV chart is easier for young children to understand as it uses a limited number of letters which are symmetric and therefore not susceptible to letter reversal [18]. For children who are unable or unwilling to provide a verbal response, visual acuity can be assessed with a matching test as described below.

●Picture and shape optotype tests – Picture and shape charts (eg, the LEA chart) can be used to test visual acuity in children who do not know the letters of the alphabet (figure 2). For children who are unable or unwilling to provide a verbal response, visual acuity can be assessed with a matching test as described below.

Allen cards are another example of a picture optotype test; however, Allen figures are not recommended for use, because they are not standardized and they frequently overestimate visual acuity in children with amblyopia [18].

Limitations of picture optotype tests include:

•Dependence on the child's familiarity with the pictured objects

•Cultural and social factors affect results [31]

•Many picture tests cannot test acuity better than 20/30 (table 5)

•Picture tests (particularly Allen figures) may overestimate visual acuity in children with amblyopia

●Directional optotype tests – Directional optotype tests (eg, the tumbling E game, Landolt rings) (figure 2) require the child to identify the direction the optotype is facing and to express (by pointing or verbally stating) the direction. These tests are not recommended for preschool children who may have difficulty comprehending right versus left and coordinating, pointing, or communicating the correct direction [8,18,31].

●Matching tests – Matching tests can be performed with letter or shape optotypes (eg, HOTV and LEA charts) (figure 2) to test the visual acuity of children who are unwilling or unable to communicate verbally. Matching tests are particularly useful for children who are shy or who have a speech impairment. The examiner indicates an optotype on the vision chart, and the child points to the optotype that matches it on his or her own sample card of the optotypes. Children will often perform better on vision testing in the office if they have the opportunity to practice at home (figure 3).

Crowding phenomenon — "Crowding" refers to simultaneous presentation of multiple visual targets. Crowding has minimal effect on visual acuity testing in normal eyes. However, it creates significant distortion in amblyopic eyes and its impact must be considered for accurate testing of visual acuity [32]. Thus, using a row of figures or letters rather than a single optotype provides a more accurate assessment of visual acuity and improves detection of amblyopia. For children who find it easier to understand the vision testing process when single optotypes are presented, crowding bars can be placed around the optotype (figure 2) [31].

Administration — Vision testing performance can be improved by pre-teaching children how to do the test [33,34]. Teaching typically is performed by holding the test targets close to the child or using large optotypes; both of the child's eyes should be used during practice [8]. Parents/caregiver can practice with the child at home before the vision evaluation if they are provided with a copy of the test optotypes and instructions for practicing (figure 3).

Optotype recognition tests are designed to test the vision in each eye individually. For children who wear glasses, vision should be assessed with and without glasses. If the child is known to have poor vision in one eye, that eye should be tested first to minimize poor performance from loss of attention and to avoid memorization artifact [8]. (See 'Testing artifacts' below.)

In the United States, testing in a primary care setting at a distance of 10 feet is recommended and should be performed with an eye chart that is calibrated for this distance [18]. In other countries, the distance may be 4 or 6 meters (table 5). In the primary care setting, testing at 10 feet is preferred over 20 feet because often the only 20-foot distance may be in an active, noisy hallway full of distractions. In addition, many children perform better with the test target at 10 feet [31,33,35]. A Snellen chart specifically designed for use at 10 feet must be used for accurate testing at this distance.

Visual acuity testing should be performed efficiently since the child may quickly lose interest; the child need not identify every optotype on the chart. If the child appears to see normally, the examiner should begin with the "critical line" (ie, the line a child is expected to see normally and pass) and adjust up or down as needed. The "critical line" varies with age (36 through 47 months 20/50, 48 through 59 months 20/40, and ≥60 months 20/30) [18].

The visual acuity often can be determined using only two or three lines of optotypes.

It may be easier to keep the child on task if the examiner performs the testing in a game-like manner. Encouragement and positive reinforcement from the parents/caregivers and the examiner are critical, particularly for the shy child.

Interpretation — The child must identify the majority of optotypes of a visual acuity line correctly to be scored with that acuity. When unequal visual acuity is detected, the eye with worse acuity should be retested.

Measured visual acuity varies with the age of the child. The "rule of 8s" is a helpful mnemonic for determining the need for referral (table 4). The patient's age plus the tens digit of the denominator of his or her visual acuity should be ≤8. Referral is generally warranted if the sum is >8. For example, a five-year-old with visual acuity of 20/30 (5 + 3 = 8) does not need to be referred; however, a five-year-old with visual acuity of 20/50 (5 + 5 = 10) should be referred [26,36].

Many children actually have better visual acuity than is recorded, but they are not able to maintain attention for the testing of very small letters. The author of this topic review often tells parents/caregivers that their child probably has 20/20 vision, but only a 20/40 attention span, for example.

Amblyopia should be suspected if acuity differs by two or more rows between eyes. (See "Amblyopia in children: Classification, screening, and evaluation", section on 'Definition'.)

Testing artifacts — Children may squint, peek, or memorize the chart in an effort to do a good job, any of which may falsely improve the recorded visual acuity. In addition, in children with amblyopia, visual acuity may falsely appear to improve if optotypes are presented in isolation rather than in a row (the crowding phenomenon, described above). The recorded visual acuity may be falsely low in children who have nystagmus unless efforts are made to compensate for it using techniques that typically are available only to the ophthalmologist. (See 'Vision assessment in children with nystagmus' below.)

●Squinting – Squinting creates a "pinhole" effect, limiting the number of light rays that enter the eye, and thereby minimizes the blur that is present without squinting.

●Peeking – Peeking can be eliminated by using a patch for occlusion of one eye (or, if a patch is not available, the examiner can ask the parent/caregiver to place the palm of his or her hand over the child's eye). Peeking occurs frequently and can be overlooked if the examiner is not paying close attention to the child. The child can peek around a handheld occluder if the examiner turns around to verify the optotype.

●Memorization – Memorization of a row of optotypes is difficult to prevent but is easily overcome by asking the child to read the optotypes in reverse or random order. Computer-generated eye charts provide an unlimited array of letter combinations that can be used to prevent memorization. These systems also facilitate vision testing using a strict protocol that may improve accuracy. However, their cost typically precludes their use in the primary care setting.

Smart phone applications — Applications that assess visual acuity are available for use on smartphones and other devices [37-39]. These tools can provide an accurate assessment of visual acuity in older children.

INSTRUMENT-BASED SCREENING — Instrument-based vision screening devices (eg, photoscreening and autorefraction) can identify ocular risk factors that lead to vision loss in children, though they do not directly assess visual acuity. These methods are endorsed by the American Academy of Pediatrics (AAP) and the United States Preventive Task Force for screening in young children [14,18,40].

Photoscreening devices use optical images of the red reflex to detect refractive errors (anisometropia, high hypermetropia, high astigmatism), media opacities (eg, cataracts), strabismus, or adnexal deformities (eg, ptosis), each of which is a risk factor for amblyopia [41]. Autorefractors use automated retinoscopy or wave-front technology to evaluate refractive error and are therefore limited in their ability to detect strabismus in the absence of refractive error.

Instrument-based screening is relatively quick and requires minimal cooperation of the child. These methods are particularly useful in preverbal, preliterate, or developmentally delayed children. If available, instrument-based screening can be performed beginning at age 12 months. Once children can read an eye chart easily, optotype-based testing should be used instead of instrument-based testing [18]. (See 'Optotype tests' above.)

In observational studies, vision screening of preschool children with photoscreening or autorefraction has been associated with early detection of risk factors for amblyopia [42-53]. In some of the studies, earlier detection was associated with improved visual acuity outcomes [43,45].

NEAR VISION TESTING — Near vision testing should be performed in children who have the following complaints:

●Decline in school performance

●Reading difficulty

●Eye strain (asthenopia)

●Headaches

●Double vision

●Blepharospasm

●Blurred or distorted near vision

In an ophthalmologist's office, near vision testing is also often performed in children with nystagmus. Testing of near vision in the primary care setting can be helpful in providing an initial explanation of school-related difficulties prior to formal eye evaluation. (See 'Vision assessment in children with nystagmus' below.)

Near vision testing is performed much the same as is that for distance vision. A near vision testing card is used to present optotypes that are appropriately sized for the testing distance that is printed on the card, typically 14 inches. Near vision is tested with each eye individually. The distance at which the test is performed must be recorded because the testing distance alters the size of the image projected on the retina and, hence, the test results.

COLOR VISION TESTING — Proper color discrimination requires normal cone function. Most color vision abnormalities in children are congenital. Acquired color vision deficits are much less common and can be caused by optic nerve or retinal disease, among others.

Opinion varies on the value of routine color vision testing in otherwise asymptomatic children. We generally reserve color vision testing for children who have an indication such as a family history of color vision deficits, problems with color discrimination, or a condition (eg, optic neuritis, Turner syndrome) or exposure to a medication associated with color vision abnormality (eg, ethambutol). Some eye specialists routinely test color vision on new patients who are old enough to cooperate for testing (usually around four to six years old [54]).

The prevalence of color vision deficiency in childhood was evaluated in a population-based cross-sectional study (the Multi-Ethnic Pediatric Eye Disease Study), which involved 4005 children (37 to 72 months of age) who were able to complete color vision testing [54]. The overall prevalence of color vision deficiency was 1.6 percent. Color vision deficiency was far more common in males compared with females (3 versus 0.02 percent). Rates of color vision deficiency among boys varied by race/ethnicity (5.6 percent among non-Hispanic White males, 3.1 percent among Asian males, 2.6 percent among Hispanic males, and 1.4 percent among Black males).

Color vision testing can be achieved with a variety of tests. Pseudo-isochromatic plates, such as those available with the Ishihara and the Hardy-Rand-Rittler tests, are commonly used color vision screening tests. More advanced tests, such as the Farnsworth D-15 and Farnsworth-Munsell 100 Hue tests, may be used to better characterize a deficit noted on screening tests.

Additional information about color blindness is available through the American Association for Pediatric Ophthalmology and Strabismus and Colour Blind Awareness.

VISION ASSESSMENT IN CHILDREN WITH NYSTAGMUS — Nystagmus, a rhythmic to-and-fro movement of the eyes, can be horizontal, vertical, rotary, or a combination of these. Nystagmus may be present all the time (manifest) or only when one eye is covered (latent). Children in whom nystagmus is detected should be referred for ophthalmologic evaluation. (See "Overview of nystagmus".)

Vision is usually decreased in children with nystagmus. However, near vision may be better than distance vision. Visual acuity in children with nystagmus should be checked with both eyes open to best ascertain how the child sees in the real world. Visual acuity is often better when tested with both eyes open than each eye individually. Both near and distance visual acuity testing are often indicated in children with nystagmus.

Manifest nystagmus — Manifest nystagmus is present all the time. Many children with manifest nystagmus can improve their vision by assuming an abnormal head posture. Nystagmus may be damped when the eyes are directed in a particular field of gaze (eg, up gaze, side gaze, etc), prompting the abnormal head posture. This quiet eye position is called the null zone.

Children with manifest nystagmus should have visual acuity tested initially with both eyes open and the head erect, then with both eyes open and the head in the preferred posture. As an example, the results of testing for a child who holds the head to the left would be documented as follows:

Vision tested with both eyes open:

●With head straight – 20/80

●With head turned to left – 20/25

Vision then is tested in each eye separately, and the head posture the patient adopts should be noted.

Latent nystagmus — Latent nystagmus is present only when one eye is covered. Children who have latent nystagmus should be tested initially with both eyes open; in this situation, the eyes are quiet and motionless. Abnormal head posture should be noted if present. Vision should then be tested in each eye individually. In the pediatric ophthalmology office, the eye that is not being tested is covered with a +5.00 to +10.00 lens to "fog," but not occlude, the vision. Monocular visual acuity can be more accurately assessed because fogging does not induce the same degree of latent nystagmus as occurs with occlusion. The results of testing are recorded in the medical record as in the following example:

●Both eyes open – 20/20 (table 5)

●Right eye – 20/30 (+5 to +10.00 fogging lens)

●Left eye – 20/30 (+5 to +10.00 fogging lens)

VISION ASSESSMENT IN CHILDREN WITH SPECIAL HEALTH CARE NEEDS — The population of children with special health care needs includes children who have known or suspected visual impairment, cerebral palsy, developmental delay, or other neurologic abnormality. (See "Children and youth with special health care needs", section on 'Terminology'.)

The goal of vision testing for children with special health care needs is to determine whether they see and, if so, to estimate the level of vision. This goal is often best met with involvement of the child's parents/caregivers, teachers, primary care clinician, neurologist, ophthalmologist, counselor, physical or occupational therapist, and others who can provide information about the child's visual performance.

The examiner should have an understanding of the effects of the child's medical problems on the child's behavior so that testing conditions can be optimized. Some children perform better at certain times of day (eg, in the morning or when most awake); others are on medications that may affect their ability to perform. Visual assessment is feasible in the majority of children with special health care needs under the right circumstances (eg, suitably adapted methods, familiar environment, patient and skilled examiner). In a cohort of 240 children attending schools for children with special educational needs, 95 percent were able to cooperate with assessment of visual function, and visual acuity could be reliably assessed in 83 percent [55]. Approximately one-half had a refractive error that required correction, and one-half of these required a new prescription.

Observation — Important clinical signs of severe visual impairment include:

●Manifest nystagmus (present all the time), which may result from abnormalities of the eyes, optic nerves, or brain.

●"Blindisms" or behaviors that occur in children with severe visual impairment. Examples include repeated poking of the eyes (oculodigital reflex), repetitive rocking of the head or trunk, and repetitive hand waving.

Vision tests — Some rudimentary tests of vision can be used to assess the visual performance of children with special health care needs who cannot perform conventional optotype testing and in whom visual behavior is otherwise difficult to assess:

●The normal response to a bright pen light is eye closure or withdrawal; ignoring the light is a cause for concern.

●Constriction of the pupils to light indicates that the afferent and efferent pupillomotor pathways are intact and increases the likelihood that the child sees. However, the test must be interpreted with caution because children with cortical blindness may have normal pupillary responses.

●The threat response is a learned reflex in which the child withdraws when an object (or the examiner's hand) is moved rapidly into the child's visual space. It indicates the presence of at least rudimentary vision and is reliable in children older than six months of age.

Other means of testing the vision of children with special health care needs include the vestibulo-ocular reflex (VOR) and use of optokinetic drums.

Vestibulo-ocular reflex — The VOR is a normal reflex in people who have an intact neurologic system. The examiner, while holding the child, rotates 360 degrees to stimulate the semicircular canals in the inner ear and cause a temporary nystagmus. The presence of normal vision inhibits VOR nystagmus within three to five seconds after the rotation stops. Nystagmus may continue for 15 to 30 seconds in children who have severe visual impairment [56].

Optokinetic drum — Optokinetic drums are cylindrical devices with a recurring pattern of white and black stripes of varying thickness. Rotation of the drum in the child's visual space stimulates the development of nystagmus if the child can distinguish the black and white contrast. Gross vision (ie, 20/400) is present if the child responds to the optokinetic drum with thick stripes. Visual acuity can be estimated by using drums with thinner and thinner stripes until the response is no longer detected. False-negative tests occur in children who lack interest or who do not have normal ocular motor function [57]. False-positive results, presumably caused by the presence of other vision-related neural pathways, can occur in children who do not have a normal visual cortex [57].

VISUAL EVOKED POTENTIAL — The office eye examination is not always sufficient to determine whether a child is able to see. The visual evoked potential (VEP) test is used when other measures do not provide the necessary information. The VEP test uses electrodes that are placed on the child's scalp, over the occipital lobes of the brain, to detect electrical response in the visual cortex in response to visual stimuli.

VEP testing is not necessary in routine clinical practice and is generally obtained only in special situations, such as when office visual function testing fails to demonstrate visual function but the other clinical findings suggest the child can see, or if the clinician feels the child does not have vision but the family feels that the child can see. VEP testing may provide an answer in these situations. In addition, VEP testing is sometimes used to assess the potential for vision in a child prior to undergoing complex eye surgery to restore vision.

The visual stimuli are patterned targets (eg, checkerboards) that are presented to the child on a television monitor. Analysis of the electrical patterns that are produced permits estimation of the child's visual acuity. Close agreement between VEP testing and psychophysical testing exists [58]. However, VEP results must be interpreted with caution because variation in laboratory technique can alter the results, and normal flash VEP (VEP using a flash stimulus rather than a patterned target) can occur in the absence of a functioning visual cortex.

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or email these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword[s] of interest.)

●Basics topic (see "Patient education: Crossed eyes and lazy eye (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Visual development – Visual stimuli are critical to the development of normal vision. Any ocular process that significantly interferes with or inhibits the development of the visual pathways may result in amblyopia. (See 'Visual development' above and "Amblyopia in children: Classification, screening, and evaluation".)

Visual behavior and performance evolve with maturation of the visual system (table 3). (See 'Visual development' above.)

●Visual history – Parents/caregivers often are aware of a vision problem before it is readily apparent to the clinician. It is important to ask the parents/caregivers specific questions about the child's vision, including whether the child sees well, holds things close, or squints; the eyes appear to cross or wander; the eyelids droop; or the eyes have ever been injured. (See 'Visual history' above.)

●Vision screening – For all children, we suggest periodic vision screening aimed at detecting amblyopia, strabismus, and other vision problems (Grade 2C). In children <5 years old, vision risk assessment should be performed at all health maintenance visits with vision screening or referral, as indicated, if risk factors are identified (table 1). For older children, visual acuity should be assessed at ages 5, 6, 8, 10, 12, and 15 years. (See 'Vision screening' above.)

●Assessment of vision in children

In children younger than two to three years of age, visual behavior (table 3), rather than visual acuity, is assessed. The goal is to determine whether visual behavior is normal for age and whether vision behavior is similar between the two eyes. Visual behavior may be assessed through observation, evaluation of the fixation reflex, and forced preferential looking. (See 'Infants and children <3 years' above.)

Visual acuity testing with optotypes (figure 2) should be attempted in all children three years and older. (See 'Children three years and older' above.)

Instrument-based screening (eg, photoscreening and autorefraction), if available, can be performed beginning at age 12 months to identify ocular risk factors that may lead to vision loss. Instrument-based screening is relatively quick and requires minimal cooperation of the child. Once children can read an eye chart easily, optotype-based testing should be used instead of instrument-based testing. (See 'Instrument-based screening' above.)

●Referral indications – Indications for referral to an eye specialist include (table 1) (see 'Referral indications' above):

•Abnormal red reflex

•History of prematurity

•Metabolic disease or genetic disease with ophthalmologic implications

•Family history of childhood cataract, retinoblastoma, retinal dysplasia, or glaucoma

•Inability to fix and follow by age three months

•Abnormal ocular alignment

•Pupillary asymmetry of ≥1 mm in diameter

•Corneal size asymmetry (picture 1)

•Unilateral or bilateral ptosis or other lesions obstructing the visual axis

•Asymmetry of vision (ie, visual acuity difference of two or more lines between eyes)

•Visual acuity worse than 20/50 (table 5) in a three-year-old, worse than 20/40 in a four-year-old, or worse than 20/30 in a child ≥5 years

•Abnormal instrument-based vision screening

•Nystagmus