Abstract
Visual acuity measurement is an essential component of any eye exam. In adults and older children, letter-based acuity (i.e., recognition acuity) is commonly used to measure vision. However, in infants and toddlers, performing traditional visual acuity testing is nearly impossible. Instead, modified optotypes such as gratings and pictures are shown to observe the young child's visual behavior. Additionally, there are objective visual acuity methods that negate the need for observing visual behavior. For the practicing clinician, the choices are many and can be confusing. With new commercial products coming into the market every day, it is nearly impossible to comprehensively cover each one of them. Instead, in this chapter, commonly used and/or studied visual acuity tests are covered. For each test, the set-up, procedure, documentation, and scientific evidence supporting or negating its use are discussed.
TopVisual Acuity Testing In Infants And Toddlers
Tests that are suitable for infants and toddlers require minimal or no verbal response from the child and depend on either the clinician’s observation of visual behavior to the stimulus presented, or the utilization of instrumentation to measure visual acuity (e.g., VEP). While most tests allow the clinician to make qualitative measures of visual acuity, some do not and are qualitative.
Key Terms in this Chapter
LogMAR: Logarithm of the Minimum Angle of Resolution (logMAR). LogMAR charts have logarithmic progression of optotype spacing within each line and between lines.
Minimum Angle of Resolution (MAR): Angular size of a letter in minutes of arc. It is calculated by dividing the Snellen denominator by the numerator. The MAR conversion for 20/20 is 1’ (1 minute of arc).
Amblyopia: Unilateral or bilateral reduction in vision in an otherwise structurally intact eye caused by abnormal visual experience in early life.
Recognition Acuity: The ability to recognize optotypes such as letters, numbers or pictures.
Crowding: The impaired ability to visually detect objects in a clutter as opposed to when presented in isolation.
Resolution Acuity: The ability to resolve spatial details within a target, such as detecting the gap in a Landolt C.
20/20 Vision: The ability to see a target clearly at 20 feet which an average person can also see at 20 feet. Similarly, 20/40 vision means that the target was seen clearly at 20 feet whereas an average person can see that same target from 40 feet distance. This is the Snellen denomination.