Opal Optometry
536a 6th St New Westminster BC V3L 3B5 (604) 522-4007
(604) 227-2926


New Westminister, BC/ (604) 522-4007

How Visual Acuity Is Measured

How is visual acuity measure? This is one of the most common questions our New Westminster Optometrist gets asked. Read on to find out the answer.

Visual Acuity is the clarity of your vision. Your Optometrist measures this by asking you to read letters on the Snellen Chart as part of your eye exam. We all recognize the chart with it’s black letters on a white background with each row of letters gradually becoming smaller in size. The results of this test can be impacted by how sensitive your brain’s interpretative faculty is, the functionality of the retina and just how sharp is the retinal focus of the eye. The Optometrist then can determine whether there are any vision concerns at the present time or if any may develop in the future.

Some additional things that may be determined when you have your eye exam are:

While the contrast of the black symbols known as optotypes on the white background is effective in determining clarity of your vision, other useful information is gathered using the Snellen Chart. Optotype images include letters that have been stylized, Landolt broken rings (rings that have a gap – the person being tested must indicate in which side the gap is located) and other symbols used for those that are illiterate. Symbols are typically place on a printed chart but other formats are also used. Charts with optotypes must be placed at specific distances when being read depending on the type of test.

The measurement of your eyesight is a psychophysical procedure. What this means is the results are determined by your perception of the physical characteristics of the symbols and the resulting response you make. If you’ve taken this type of eye exam you will understand what’s meant by this statement. To this end various elements in the room must be controlled to ensure the most accurate results possible. To avoid distractions the chart and the room must have just the right lighting, the person must be given the appropriate amount of time for responding and allowances are made for errors.

So that is how visual acuity and eyesight is measured. If you have any other questions, please contact our Optometrist.