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San Diego, CA Vision Tests: Exploring the Vision Chart


Have you ever asked yourself why 20/20 is the benchmark for ''perfect'' vision and what it actually represents? The term 20/20 vision expresses normal visual acuity or sharpness of vision. In other words an individual with 20/20 eyesight will be able to clearly see an object at a distance of 20 feet that the majority of people are expected to be able to see from that distance.

For those who don't have 20/20 vision, their visual acuity score is designated according to the distance at which they are able to see sharply, in relation to what is normally expected. As an example, if your acuity is 20/100 that means that at 20 feet you can only see an object that the standard would see at 100 feet away.

Someone whose eyesight is 20/200 or below is considered blind, legally however, they can often see normally by using prescription glasses or contacts or by undergoing LASIK if they are eligible.

Most eye care professionals employ some version of the Snellen eye chart, which was designed by Hermann Snellen, a Dutch eye doctor in the mid-1800's, to conduct a vision screening. While there are now a number of variations, the chart typically shows eleven lines with capital letters which get progressively smaller as they move toward the bottom. The chart begins with the capital letter - ''E'' with letters being added gradually as you move down the chart. During the vision screening, the optometrist will determine which is the line with the smallest lettering you can make out. Each line is assigned a distance, with the 20/20 line typically being assigned forth from the bottom. For small children, illiterate or handicapped persons who are not able to read or vocalize letters, the ''Tumbling E'' chart is used. Similar to the regular Snellen chart, this version portrays only the capital letter E in different spatial orientations. The optometrist asks the patient to point to the right, left, top or bottom according to the direction the E is pointing. Either chart must be positioned 20 feet away from the patient's eyes.

Although 20/20 visual acuity does indicate that an individual's sight for distances is normal, this test alone does not show that someone has perfect vision. Complete eyesight involves many other important competencies such as peripheral sight, depth perception, color vision, near vision and focusing and coordination between the eyes to name a few.

While an eye exam with a Snellen chart will establish if you require eyeglasses to see far away it will not provide the eye doctor a full understanding of your overall eye health. Make sure you still schedule a yearly comprehensive eye exam which can diagnose any more serious conditions. Call us now to book a San Diego, CA eye exam.