Pediatric Visual Acuity Assessment

Key Points at a Glance

Key Points of This Disease

• Visual acuity in children develops rapidly from birth to age 3 and is nearly complete by age 6 to 8.
• Because cooperation is difficult to obtain in infants and young children, selecting an appropriate test method according to age is essential.
• In infancy, evaluate fixation and pursuit or use Teller Acuity Cards (TAC); at 2–3 years, use the Morizumi dot card; from age 3 onward, use LEA symbols or Landolt rings.
• Crowding phenomenon is observed until 6–8 years of age, causing a difference between single optotype and crowded line acuity.
• Unilateral anisometropia or microstrabismus is often diagnosed late, making regular screening important.
• Since measurement values vary by test method, visual acuity should be evaluated together with the test method used.

1. Pediatric Visual Acuity Assessment

Visual acuity is the assessment of visual resolution by the smallest identifiable object at a specific distance. Accurate visual acuity assessment is essential for early detection of refractive errors, amblyopia, and other eye diseases.

Infants and young children are difficult to cooperate and have limited comprehension, making assessment by the same methods as adults challenging. It is necessary to select age-appropriate test methods and adapt the testing environment.

The AAO and AAPOS recommend visual acuity assessment in the newborn period, at 6/12 months, 1–3 years, 3–5 years, and after age 5. Optotypes should be high-contrast and standardized ¹⁾.

Age	Normal visual acuity reference
3 months	0.05
1 year	0.1–0.2
2 years	0.3–0.5
3 years old	0.5–0.8
6 years old	1.0

Since results vary depending on the testing method, visual acuity values are only reference values. Unilateral anisometropia and microstrabismus have few subjective symptoms and are often diagnosed late.

Q At what age is a child's vision fully developed?

A

Vision develops rapidly from birth to age 3 and is nearly complete by age 6–8. This period is called the visual sensitive period, and it is also the most effective time for amblyopia treatment. Approximate normal values by age are: 0.05 at 3 months, 0.1–0.2 at 1 year, 0.5–0.8 at 3 years, and 1.0 at 6 years.

2. Main Assessment Methods and Applicable Ages

Under 2 years (Infancy)

Qualitative Assessment

Blink reflex: If the child closes the eyelids in response to light stimulation, light perception can be confirmed.

Fixation and following: Possible from around 3 months of age. Record using the CSM notation (Central, Steady, Maintained).

Aversion response: The child resists when the amblyopic eye is covered during monocular occlusion. Note that the child may also dislike an obstacle in front of the face.

Threat reflex: Develops by 5 months of age.

Brückner reflex: Using a direct ophthalmoscope in a dark room, observe the red reflex at 1 m and 3 m. A lower crescent suggests myopia, and an upper crescent suggests hyperopia.

Quantitative Assessment

OKN (Optokinetic Nystagmus): Induces eye movements with black-and-white stripes. 6/120 or better in newborns. May be false positive even in cortical blindness.

PL (Preferential Looking): Includes FPL (2 months to 1.5 years) and OPL. Takes 40-60 minutes and is cumbersome. Assesses as 20/600 in newborns, 20/120 at 3 months, 20/60 at 12 months.

Teller Acuity Cards (TAC): Clinical application of FPL. Can be performed in a lit room, takes about 10 minutes. May overestimate grating acuity in amblyopic children¹⁾.

VEP (Visual Evoked Potential): Directly measures occipital cortex activity in response to pattern stimuli. Shows higher values than PL and OKN. Can be measured even with cataracts or vitreous opacities.

Q What is the difference between Teller Acuity Cards (TAC) and standard PL method?

A

TAC (Teller Acuity Cards) is a clinical application of the FPL method, can be performed in a lit room, and takes about 10 minutes. In contrast, the PL method requires a dark room and takes 40-60 minutes. However, caution is needed because grating acuity tests including TAC tend to overestimate visual acuity in amblyopic children.

2 to 3 Years

• Morizuka Dot Card: Points to the eyes of an animal face. Tested at 30 cm. Can be performed from around 2 years old. Measurement based on minimum visible threshold.
• Picture/Figure Optotypes: Uses animal pictures or ○△□. From around 2 years old. Start at a test distance of 2.5 m.
• Cardiff Acuity Cards: Based on vanishing optotype principle. Assesses 20/20 to 20/200 at 1 m.
• Worth’s Ivory Ball Test: Uses 5 balls of 0.5 to 2.5 inches. Performed at a distance of 18 feet.
• Beck’s Candy Test: Uses candy beads of various sizes at 40 cm.

3 to 6 Years

• LEA Symbols: Uses 4 optotypes: apple, pentagon, square, circle. With 4 choices, easy for young children to perform¹⁾.
• HOTV test: Uses the four letters H, O, T, V. Matching cards eliminate the need for reading ¹⁾
• Landolt C ring: Tested at near (30 cm) and distance (5 m). Can be performed from around age 3. Matching with a handheld Landolt C ring is useful
• Tumbling E chart: Conceptually difficult for young children, with a high rate of inability to test ¹⁾
• Allen picture test: Uses seven black-and-white line drawings, but has standardization issues ¹⁾
• Sheridan letter test: Uses the letters V, T, O, H, X, A, U

School age (6 years and older)

• Crowded visual acuity test (Landolt C ring) can be performed almost as in adults
• Snellen visual acuity chart: ETDRS logMAR arrangement is preferable ¹⁾

3. Factors affecting the test and points to note

Visual acuity test results vary depending on the following factors.

• Child’s condition: Greatly influenced by developmental stage, stranger anxiety, unfamiliarity with the place, health status, and mood
• Test environment: A quiet and calm environment is necessary ¹⁾. The test should be conducted in a fun atmosphere without forcing
• Near and distance vision: Near visual acuity develops earlier than distance visual acuity
• Crowding phenomenon: Observed until ages 6–8, causing a difference between single optotype (single letter acuity) and line optotype (crowded acuity). In amblyopia, visual acuity is overestimated with single optotypes ¹⁾
• Difficulty with monocular occlusion: Children may dislike covering one eye. It is effective to reduce the adhesive strength of the eye patch beforehand
• Children with nystagmus: Assess visual acuity in one eye using blurring with plus lenses or a translucent occluder¹⁾
• Differences in test methods: Picture visual acuity of 0.7 is rated lower than Landolt ring visual acuity of 0.7. Record the test method clearly.

Q What is the difference between single optotype acuity and crowded acuity?

A

Single optotype acuity uses a single optotype, while crowded acuity uses multiple optotypes arranged in a line. Due to the crowding phenomenon, which is observed until 6–8 years of age, single optotype acuity shows better results. In amblyopia treatment, if single optotype acuity improves but crowded acuity does not, it indicates residual visual immaturity.

4. Clinical Application and Guidance for Parents

Recommended Tests by Age

Age	Recommended Test	Notes
Newborn	Blink reflex, red reflex check	Rule out congenital cataract
3–6 months	Fixation and pursuit, aversion response	Record using CSM notation
6–18 months	TAC, PL method	Measurement of grating acuity
2–3 years	Morizumi dot card, picture optotypes	Matching method
3–5 years	LEA symbols, HOTV, Landolt C	Single optotype → crowded optotype transition
6 years and older	Landolt C (crowded), Snellen	Testing similar to adults

Testing Tips

• Test the worse-seeing eye first (to avoid fatigue)
• If a difference between eyes is found, schedule a follow-up early
• For children with developmental delays, select an examination method according to their developmental age, not chronological age.

Guidance for Parents

Age	What can be checked at home
Under 2 years	Presence of aversion reaction when one eye is covered (video recording is useful)
2 years and older	Practice covering one eye, home training using copies of picture visual acuity charts

• Explain that normal visual acuity differs by age.
• Inform that results may vary depending on the examination method and the child’s mood.
• Explain in advance that if visual acuity is poor, a refraction test under cycloplegic medication is necessary.

Q Is there a way to check a child's vision at home?

A

For children under 2 years, observe whether they show an aversion reaction when one eye is covered by hand. Video recording to show at the clinic is also useful. For children 2 years and older, home practice using copies of picture visual acuity charts is possible. However, home checks are only supplementary; an ophthalmology visit is necessary for accurate assessment.

6. Physiological Background of Visual Development

The sensitive period for vision is from birth to around 6–8 years of age, with the most rapid development occurring especially before 3 years of age. If appropriate visual input is not obtained during this period, amblyopia may develop.

Mechanism of Crowding

Crowding phenomenon (difficulty in reading isolated letters) is due to immaturity of the visual system. Interference effects from surrounding optotypes are observed until 6–8 years of age. In amblyopia treatment, if single-letter visual acuity improves but crowded visual acuity does not, it indicates residual visual immaturity.

Differences in Visual Acuity Values by Testing Method

The reason VEP visual acuity shows higher values than PL or OKN visual acuity is that VEP directly evaluates electrical activity from the occipital cortex. Since it does not require eye movements, it is less affected by immaturity of the motor system or cooperation issues. With VEP, visual acuity equivalent to 20/20 is measured at 6–12 months of age.

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8. References

1. American Academy of Ophthalmology Pediatric Ophthalmology/Strabismus Panel. Amblyopia Preferred Practice Pattern. San Francisco, CA: American Academy of Ophthalmology; 2024.
2. Birch EE. Amblyopia and binocular vision. Prog Retin Eye Res. 2013;33:67-84. PMID: 23201436.
3. Birch EE, Jost RM, Hudgins LA, Morale SE, Donohoe M, Kelly KR. Dichoptic and Monocular Visual Acuity in Amblyopia. Am J Ophthalmol. 2022;242:209-214. PMID: 35738394.