Vision Screening Online Training Program
Questions and Answers Regarding Visual Acuity Screening
Q. What evaluative criterion was used in the 2015 recommendations for visual acuity charts?
A. Chart selection was based on:
- Scientific research that demonstrated sensitivity, specificity, as well as testability
- Optotypes (letters or symbols)
- Distance (10 foot)
- Presence of a 10/12.5 (20/25) line
- Practicality of use and cost
- Cultural and disability bias
- State and federal regulations for screening programs
- Federal Head Start performance standards
In the spring of 2015 (April to June) a Minnesota Expert Panel on Childhood Vision screening reviewed and updated the 2006 recommendations based on national professional organization policy including the American Academy of Pediatrics (AAP) and the American Association of Pediatric Ophthalmology and Strabismus (AAPOS) in print as of January 2015.
Other considerations included in the 2006 recommendations and carried over into for the development of the 2015 Vision Screening Guidelines for Children were:
- 10-foot visual acuity charts should have a 10/12.5 line.
- Charts should only require recognition of optotypes (letters or symbols). They should not require an understanding of language or be culturally specific. This is an important consideration for conducting vision screening on culturally and linguistically diverse populations.
- Optotypes should blur equally. The symbols or letters should 'blur to zero' or transform into circle shapes when a symbol cannot be correctly identified,
- Visual acuity charts should have a proportional layout where the space between optotypes can fit one full symbol or letter, referred to as 100% spacing, and the space between lines can fit half an optotype, referred to as 50% spacing.
- To achieve both high standards of testability and sensitivity visual acuity charts for children 3-5 years of age should have a 50% spaced rectangle surrounding each line of optotypes. These rectangles create a 'crowding phenomena,' which is considered by the National Institutes of Health's Vision in Preschoolers (VIP) study as the best strategy to detect amblyopia.
Q. There seem to be so many vision charts available, which charts are recommended in the Minnesota Vision Screening Guidelines for children under age 6?
A. The 10 foot HOTV or the LEA SYMBOLS ® chart with 50% spaced rectangle boxes around each line is the MDH recommendation for children ages 3 through 5. Below are the MDH approved visual acuity charts.
Used with permission of Good-Lite company
In addition, Massachusetts Visual Acuity Test (Mass VAT) Flip charts can be used:
Used with permission of Good-Lite company
Q. Are there tools available to help me prepare the child for screening?
A. There are tools available to prepare very young children for vision screening, such as the LEA Puzzle. Young children can become familiar with the shapes used in the visual acuity charts by playing with the LEA SYMBOLS ® Puzzle prior to the vision screening. In addition, the MDH Vision Screening Procedures manual has HOTV Prescreening Practice sheets and LEA SYMBOLS ® prescreening Practice Sheets.
Q. What visual acuity charts do NOT meet the criteria for inclusion in the MDH Vision Screening Guidelines?
A. Examples of visual acuity charts not recommended by MDH for screening children in Minnesota are pictured below:
Q. What are the pass criteria for the recommended visual acuity charts?
A. The pass criteria per age are:
Age 3 years: 10/25 (20/50) line or better
Age 4 years: 10/20 (20/40) line or better
Age 5 years: 10/16 (20/32) line or better
In addition, children need to identify letters on these lines or better (lower down the chart) in order to have a PASS result. The result also must be without a 2-line difference in the passing range. This means that in the PASS range, the right eye must be able to identify letters on the same line or the line directly below or above the line where the left eye can identify letters. An example PASS result in a 4 year old would be right eye 10/20 and left eye 10/16.
Q. What is the recommended visual acuity chart for screening vision in children six years old and older?
A. The Sloan Chart 10 foot proportional (LogMar) chart is recommended as of September 2015.
Q. Why is the Snellen chart no longer recommended?
The Snellen chart does not meet our basic criteria of an acceptable chart.
- The Serif font does not blur easily and therefore a child with a borderline ability to see the letters will pass when they are not able to see the letters clearly.
- The extra spacing of the lines of letters also allow the child to identify letters they cannot see clearly.
The crowding lines of the LogMar (proportional) Sloan chart allows for easy blurring and is more likely to pick up the younger elementary school age child that is at risk of amblyopia, but did not get picked up in previous screenings.
The 10-foot distance makes it easier for a screener to catch a peeking child and keep the child engaged.
All of these aspects of the Sloan Letters 10-foot chart ensures a decrease in under referral (a child with visual deficits going undetected) in comparison to the Snellen chart.