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FAQs: Questions that optometry has received

If a child between the ages of 3 and 6 does not pass vision screening, should I refer that child to an optometrist, an ophthalmologist, or a pediatric ophthalmologist?

You should refer the child to an eye care professional that enjoys seeing young children, is set up to see young children, and accepts the parents/caregivers insurance.

What is an ETDRS eye chart?

ETDRS refers to the format of optotypes in inverted pyramid form. ETDRS charts have 7 advantages:

ETDRS charts come in different optotypes, such as LEA Symbols, Sloan letters, and HOTV letters.

My eye chart has a 20/30 line and my colleague's eye chart has a 20/32 line. What is the difference?

20/30 is a Snellen visual acuity measurement fraction or notation (Hermann Snellen introduced letter chart in 1862). 20/30 is on charts using a visual acuity scale in Snellen notations. 20/32 is based on a more recent and accurate measurement known as logMAR.

Can I use my Snellen chart to screen the vision of preschoolers and Kindergarten children?

If you follow the guidelines of the American Academy of Pediatrics, you will want to use LEA Symbols or HOTV letters with young children. Both are evidence-based and some research suggests that LEA Symbols work better for very young children.

What does 20/100 mean?

The top number represents the testing distance in feet from the child's eyes to the eye chart. The bottom number represents the smallest line that the child can read. The higher the bottom number, the worse the eyesight. For 20/100, 20 = testing distance from child's eyes to the eye chart; 100 = smallest line child could clearly identify. The child could not clearly identify optotypes on lines below the 20/100 line on an eye chart. Think about it this way: the child must stand 20 feet from an eye chart to correctly identify what a person with "normal" vision can see standing 100 feet from the chart.

Chart NotationsMy eye chart says to screen at 10 feet, but it has 20/XX numbers on the side. What does this mean?

We are accustomed to describing visual acuity in 20 ft notations: 20/20, 20/32, 20/40 etc. Thus:

What is critical line screening?

Critical line screening represents the line on an eye chart that children should pass according to their age. According to the American Academy of Pediatrics, children aged 3, 4, and 5 must pass the majority of symbols on the 20/40 line; children 6 and older must pass the majority of the symbols on the 20/30 or 20/32 line.

What is threshold screening?

The screener begins at the top of the chart, asks child/student to identify the first optotype on each line until the child/student misses the optotype, moves up one line and asks child/student to identify the full line of optotypes beginning with the 2nd optotype on that line, and continues moving up one line until child correctly identifies the majority of optotypes on that line.

What does "crowding phenomenon" mean?

Optotypes (letters, symbols, etc.) are easier to identify when isolated, which is NOT what one wants to occur during vision screening. Crowding - an optotype flanked by an adjacent bar or letters, for example - causes an optotype to be more difficult to identify than the same optotype presented in isolation. This is known as the "crowding phenomenon".

What does "linear spacing" on an eye chart mean?

Linear spacing refers to equal spacing between optotypes on a line, but not between lines.

What does "proportional spacing" on an eye chart mean?

Proportional spacing refers to spaces between optotypes on a line equal to the size of the optotype on the line (1 letter width apart). Additionally, the space between lines is equal to the size of optotypes on the next line down.

Many options are available for vision screening charts. Is one better than another?

Some eye charts are better than others. You want to select charts that are backed by science, or evidence-based, and meet national/international guidelines for standardized eye chart design. Proportionally spaced charts in ETDRS format with LEA Symbols or HOTV letters are appropriate for children beginning at ages 3 years or 3½ years until they comfortably know their letters. For older children who know their letters, and adults, use proportionally spaced charts with Sloan Letters.

What do different charts test and what are the differences?

Visual acuity charts are recognition charts that test how well students/children can clearly identify optotypes at a certain distance. Some charts inadvertently test cognitive development instead of visual acuity. For example, the Tumbling E requires direction and orientation skills, which are developmental skills that do not emerge at the same time. Up and down makes sense; left and right is abstract. You may want to avoid Tumbling E for children younger than 3rd grade.

What is the best way to cover children's eyes during vision screening?

The child's hand is not the correct answer. When you give young children responsibility for occluding their own eyes, they are likely to peek, especially if one eye has amblyopia or blurred vision. Consider using special glasses occluders that optometry offers.

What is the difference between Snellen and Sloan letters?

Herman Snellen (Dutch ophthalmologist) introduced his block letters with SERIFS in 1862. Though considered a standard screening chart, a Snellen chart has 6 critical design flaws:

Louise Sloan, PhD (Wilmer Eye Institute at Johns Hopkins), introduced her 10 letters in 1952: C D H K N O R S V Z. Sloan letters have 5 advantages:

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