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What tool measures visual acuity?

Snellen Chart
The Snellen Chart Each row of letters gets progressively smaller. The optometrist uses this tool to measure your visual acuity, which refers to how clearly you can see objects a distance. Your optometrist may ask you to put a hand over your right or left eye and read out some letters, then switch eyes.

How should you conduct a Snellen visual acuity test?

You will be asked to cover one eye with the palm of your hand, a piece of paper, or a small paddle while you read out loud the smallest line of letters you can see on the chart. Numbers, lines, or pictures are used for people who cannot read, especially children. If you are not sure of the letter, you may guess.

How do you make a visual acuity chart?

  1. In the same way, the size of other optotypes can also be constructed.
  2. Usually, 9 lines are taken on the Snellen chart. ( 6/60, 6/36, 6/24, 6/18, 6/12, 6/9, 6/6, 6/5, 6,4)
  3. Letters should be evenly spaced on each line.
  4. The space between two consecutive lines should be 20mm (approx)

How do optometrists measure visual acuity?

Your eye doctor will measure if you have 20/20 vision using a letter chart, also called a Snellen chart, which is posted on the wall 20 feet away from the examination chair. If you have 20/20 vision, you are able to clearly see the letters that are ⅜ of an inch (or 9 mm) in size, while sitting in the chair.

How do you examine visual acuity?

Viewed from 14 to 20 feet away, this chart helps determine how well you can see letters and shapes. During the test, you’ll sit or stand a specific distance away from the chart and cover one eye. You’ll read out loud the letters you see with your uncovered eye. You’ll repeat this process with your other eye.

Which tools or equipment would you use to test near and far visual acuity?

Snellen Chart The Snellen Chart is one of the most common tools used by an optometrist. It is a physical or digital chart that is placed around 20 feet or 6 meters away from the patient and has alphabets in decreasing order of size.

How do you write a Snellen chart results?

Recording Snellen Results Top number equates to the distance (in metres) at which the test chart was presented (usually 6m), Bottom number identifies the position on the chart of the smallest line read by the ‘patient’. Eg; 6/60 means the subject can only see the top letter when viewed at 6m.

What is Snellen acuity?

The visual acuity test is used to determine the smallest letters you can read on a standardized chart (Snellen chart) or a card held 20 feet (6 meters) away. Special charts are used when testing at distances shorter than 20 feet (6 meters). Some Snellen charts are actually video monitors showing letters or images.

How do I report a Snellen chart?

Recording Snellen Results

  1. Results are recorded as a fraction.
  2. Top number equates to the distance (in metres) at which the test chart was presented (usually 6m),
  3. Bottom number identifies the position on the chart of the smallest line read by the ‘patient’.

How do you find the Snellen chart?

This is done by assessing visual acuity while looking through a pinhole. Test the eyes one at a time, beginning with the worse eye while covering the good eye. Ask the patient to begin reading letters from the top. The smallest line read represents the visual acuity.

How does the Snellen chart work?

The chart consists of 11 lines of block letters, beginning with a large single letter on the top row. The number of letters on each row increases moving from top to bottom. The size of the letters progressively decreases, allowing for more letters on each subsequent line.

What are the advantages of using a Snellen chart?


  • The eyes and visual system.
  • Headache and the Eye.
  • Neurologic Examination of the Older Child.
  • Neuro-ophthalmology of brain tumors.
  • Visual Impairment and Eye Problems.
  • Neuro-Otology.
  • Nonfunctioning and Gonadotrophin-Secreting Adenomas.
  • Ophthalmology in the Tropics and Sub-tropics
  • How do you measure visual acuity?

    Visual acuity is measured by a psychophysical procedure and as such relates the physical characteristics of a stimulus to a subject’s percept and his/her resulting responses. Measurement can be by using an eye chart invented by Ferdinand Monoyer, by optical instruments, or by computerized tests like the FrACT.

    What is the Snellen chart?

    A Snellen chart is an eye chart that can be used to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen , who developed the chart in 1862. [1] Many ophthalmologists and vision scientists now use an improved chart known as the LogMAR chart .

    What does the Snellen eye chart exam test?

    He is an active member of the American Optometric Association. The Snellen eye chart is the eye testing chart used by eye care professionals to measure visual acuity, or how well a patient can see without assistance. Dr. Hermann Snellen developed the eye chart in 1862. What Is a Snellen Eye Chart?