Real life examples of vision
Measuring visual acuity
Visual acuity is often measured by the Optometrist, Optician or Orthoptist by asking the patient to read progressively smaller letters presented on a wall chart six meters (20 feet) away.
Resolution acuity tests only require the patient to look towards the black and white target. The patient doesn’t need to verbally communicate with the examiner or necessarily understand the test.
When vision is reduced and when there is disease present in the eye or the visual system resolution acuity tests may overestimate vision.
Measures of resolution acuity made with techniques such as preferential looking and the visual evoked potential should be interpreted with this in mind.
Sometimes visual acuity is recorded in other notations e.g. logMAR or cycles per degree.
These other notations can (with care) be converted to a Snellen fraction for comparison. This web page will deal only with acuities recorded in Snellen fractions.
If acuity has been recorded using logMAR or cycles per degree the tables below can be used to approximate the Snellen fraction.
Also available in the tables is a conversion from metric (UK standard) to Imperial (US standard) recording.
NOTE: tests which use logMAR or cycles per degree to record acuity may not be measuring the same type of visual acuity as a Snellen test and conversions must be treated with caution.
|Snellen equivalent||LogMAR||Cycles per degree (cpd)|
The images in these pages can be used to give an indication of the detail and size of image a child with a given visual acuity should be able to see.
It is tiring and frustrating to work with images that are only ‘just visible’ so we advise that children work with images that are at least twice their visual acuity.
You may have Visual Acuity measures for the right eye and left eye separately (monocular) or together (binocular). Generally it is the eye with the best acuity (smallest number at the bottom of the fraction if written in Snellen convention) or the binocular acuity that should be used to decide on suitable image sizes.
To find out what size of image should be seen easily at different distances click on the visual acuity below which matches or approximates to the one you have been given. Picture and letter images are available. Choose the image that is most appropriate for the individual.
For each acuity level several pages of images are presented. The text at the top of the page details whether these images are the minimum size that is likely to be seen or a size that should be easily seen.
Please click on relative links for the Snellen/logMAR numbers below to obtain Picture and Letter downloads.
Before printing images representing different acuities please print THIS page and check the scale for gross distortion. The scale on this page has been provided as a check for distortion of images during downloading. When the box is printed it should be 80mm by 80mm (8cm by 8cm).
|Snellen/logMAR Value||Picture Downloads||Letter Downloads|
|Snellen 6/480 or 1.9logMAR||Pictures||Letters|
|Snellen 6/360 or 1.8logMAR||Pictures||Letters|
|Snellen 6/240 or 1.6logMAR||Pictures||Letters|
|Snellen 6/180 or 1.5logMAR||Pictures||Letters|
|Snellen 6/120 or 1.3logMAR||Pictures||Letters|
|Snellen 6/90 or 1.2logMAR||Pictures||Letters|
|Snellen 6/72 or 1.1logMAR||Pictures||Letters|
|Snellen 6/60 or 1.0logMAR||Pictures||Letters|
|Snellen 6/48 or 0.9logMAR||Pictures||Letters|
|Snellen 6/36 or 0.8logMAR||Pictures|
|Snellen 6/24 or 0.6logMAR||Pictures|
|Snellen 6/18 or 0.5logMAR||Pictures||Letters|
|Snellen 6/12 or 0.3logMAR||Pictures|
These images are made available with permission from Kay Pictures Ltd and may only be used as described on this website. For further information on visual acuity tests visit www.kaypictures.com.