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An eye chart is a chart used to measure visual acuity
Visual acuity

Visual acuity is acuteness or clearness of visual perception, especially form vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain....
. Types of eye charts include the Snellen chart
Snellen chart

A Snellen chart is an eye chart used by eye care professionals and others to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the chart in 1862....
, Landolt C
Landolt C

A Landolt C, also known as a Landolt ring or Landolt broken ring, is an optotype, i.e. a standardized symbol used for testing vision....
, and the Lea test
Lea test

A Lea test is a visual acuity test tailored for children who do not know the alphabet normally used in eye charts. The optotypes are outlines of an apple, a house, a Square , and a circle....
.

ts usually display several rows of optotype
Optotype

An optotype is a standardized symbol for testing Visual perception. Optotypes can be specially shaped letters, numbers, or geometric symbols. For instance, to determine visual acuity, optotypes of different sizes are presented to a person and the smallest size is determined at which the person can reliably identify the optotypes....
s (test symbols), each row in a different size. The person is asked to identify the numbers or letters on the chart, usually starting with large rows and continuing to smaller rows until the optotypes cannot be reliably identified anymore.

Technically speaking, testing visual acuity with an eye chart is a psychophysical
Psychophysics

Psychophysics is a subdiscipline of psychology dealing with the relationship between physical stimulus and their subjectivity correlates, or percepts....
 measurement that attempts to determine a sensory threshold
Sensory threshold

Sensory threshold is a theoretical concept used in psychophysics. A stimulus that is less intense than the sensory threshold will not elicit any sensation....
 (see also psychometric function
Psychometric function

A psychometric function describes the relationship between a parameter of a physical stimulus and the responses of a person who has to decide about a certain aspect of that stimulus....
).

ts are available for very young children or illiterate adults that do not require letter recognition.






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Encyclopedia


An eye chart is a chart used to measure visual acuity
Visual acuity

Visual acuity is acuteness or clearness of visual perception, especially form vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain....
. Types of eye charts include the Snellen chart
Snellen chart

A Snellen chart is an eye chart used by eye care professionals and others to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the chart in 1862....
, Landolt C
Landolt C

A Landolt C, also known as a Landolt ring or Landolt broken ring, is an optotype, i.e. a standardized symbol used for testing vision....
, and the Lea test
Lea test

A Lea test is a visual acuity test tailored for children who do not know the alphabet normally used in eye charts. The optotypes are outlines of an apple, a house, a Square , and a circle....
.

Procedure

Charts usually display several rows of optotype
Optotype

An optotype is a standardized symbol for testing Visual perception. Optotypes can be specially shaped letters, numbers, or geometric symbols. For instance, to determine visual acuity, optotypes of different sizes are presented to a person and the smallest size is determined at which the person can reliably identify the optotypes....
s (test symbols), each row in a different size. The person is asked to identify the numbers or letters on the chart, usually starting with large rows and continuing to smaller rows until the optotypes cannot be reliably identified anymore.

Technically speaking, testing visual acuity with an eye chart is a psychophysical
Psychophysics

Psychophysics is a subdiscipline of psychology dealing with the relationship between physical stimulus and their subjectivity correlates, or percepts....
 measurement that attempts to determine a sensory threshold
Sensory threshold

Sensory threshold is a theoretical concept used in psychophysics. A stimulus that is less intense than the sensory threshold will not elicit any sensation....
 (see also psychometric function
Psychometric function

A psychometric function describes the relationship between a parameter of a physical stimulus and the responses of a person who has to decide about a certain aspect of that stimulus....
).

Variations

Charts are available for very young children or illiterate adults that do not require letter recognition. One version uses simple pictures or patterns. Others are printed with the block letter "E" turned in different orientations, the so called . The patient simply indicates which direction each "E" is facing. The Landolt C
Landolt C

A Landolt C, also known as a Landolt ring or Landolt broken ring, is an optotype, i.e. a standardized symbol used for testing vision....
 chart is similar: rows have circles with different segments missing, and the test-taker describes where each broken piece is located. The last two kinds of charts also reduce the possibility of the patient guessing the images. Another option are the Hanks Paediatric Eye Charts
Hanks paediatric eye charts

The Hanks Paediatric Test Cards were developed by an optometrist, Dr Anthony Hanks, and are designed for use when evaluating the vision of young children....
. These use symbols that were selected based upon the results of recognition trials with young children (heart, apple, house & flower) and then calibrated for the testing distances.

Alternatives

Computer-based semi-automatic alternatives to the eye chart have been developed (e.g. ), but are not very common. They have several potential advantages, such as a more precise measurement and less examiner-induced bias. Some of them are also well suited for children since they resemble a video game.

While visual acuity charts are usually designed for use at 6 metres or 20 feet, there is often also a need to test a subject's vision at near or occupational tasks (like reading or computer use). For these situations near-point charts have been created. For example, the Hanks Near-Point Eye Charts include a typical range of text sizes and also a selection of contemporary near tasks; like music, VDU display, newsprint, telephone book, etc.