What is the difference in referral rates for children using Visual Acuity (VA) screening versus instrument-based screening?

From the Guidelines

Instrument-based screening methods have a lower referral rate compared to Visual Acuity (VA) screening, with approximately 3-15% fewer children being referred for follow-up eye examinations, as they provide objective measurements of refractive errors and eye alignment without requiring the child's active participation. This difference in referral rates is due to the subjective nature of VA testing, which relies on a child's responses to vision charts and can be influenced by factors such as attention, comprehension, and cooperation, especially in younger children 1.

Key Considerations

• The age of the child is an important consideration, as VA testing becomes more reliable in children over 3-4 years old, while instrument-based screening may be more appropriate for younger children or those with developmental delays who cannot reliably complete VA testing 1.
• Instrument-based screening methods, such as photoscreening and autorefraction, can detect risk factors for amblyopia, including strabismus, high or asymmetric refractive errors, media opacities, and retinal abnormalities 1.
• The sensitivity and specificity of instrument-based screening devices depend on the referral criteria used, and guidelines for a uniform set of amblyopia risk factors that should be detected by instrument-based screening are available 1.

Implications for Practice

• Primary care providers should consider using instrument-based screening methods for children under 3-4 years old or those with developmental delays, as they provide a more objective assessment of refractive errors and eye alignment 1.
• VA testing should be used for children over 3-4 years old, as it becomes more reliable at this age, and instrument-based screening may not be necessary 1.
• Referral criteria for instrument-based screening should be based on the manufacturer's guidelines and the child's age, and primary care providers should be aware of the limitations of these devices and the potential for false positives and false negatives 1.

From the Research

Difference in Referral Rates

• The referral rates for children using Visual Acuity (VA) screening versus instrument-based screening are compared in several studies 2, 3, 4, 5, 6.
• A study published in 2020 found that instrument-based screening referred 398 children, while traditional screening referred 287 children, with 169 children referred by both methods 5.
• The same study found that there was no statistical difference between the two methods for detecting visual acuity of <20/30 or the number of children requiring intervention 5.
• Another study published in 2002 found that a satisfactory sensitivity/specificity profile was obtained using a referral criterion of visual acuity worse than or equal to 0.28 logarithm of the minimum angle of resolution in at least one eye, with a sensitivity of 72% and specificity of 97% 4.
• A study published in 2007 found that combining screening for eye alignment with screening for refractive error or reduced VA increased sensitivity for detection of strabismus, with a statistically significant increase in detection of strabismus when a unilateral cover test was added to a test of refraction 6.

Screening Methods

• Optotype-based screening, which uses tests of visual acuity using optotypes, is a common method of vision screening for children 2.
• Instrument-based screening, which uses automated devices to measure amblyogenic risk factors, is an alternative to optotype-based screening 2, 3.
• Photoscreening and autorefraction are examples of instrument-based screening methods 3, 5.
• The American Academy of Pediatrics recommends screening starting at three years of age and at regular intervals in childhood, and supports the use of instrument-based screening as an alternative to vision charts for testing visual acuity in patients three to five years of age 3.

Screening Outcomes

• The positive predictive value for detecting a need for glasses in third-graders is not statistically significant between traditional and instrument-based screening 5.
• Instrument-based vision screening takes less time than traditional screening, with an average time to screen a child of 30 seconds compared to 120 seconds for traditional screening 5.
• The sensitivity and specificity of visual acuity screening for refractive errors in schoolchildren can be optimized using a referral criterion of visual acuity worse than or equal to 0.28 logarithm of the minimum angle of resolution in at least one eye 4.