We “see” things every day, from the moment we get up in the morning until we go to sleep at night. Sight is our primary sense for maneuvering around in our environment. It keeps us safe and allows us to find wherever we wish to be. Through sight, we are able to appreciate the graceful human form, a kids’ crayon drawing, a fine oil painting, swirling computer graphics, gorgeous sunsets, blooming gardens, rainbows and so much more. We rely on mirrors to make ourselves presentable, signs to give us direction, and sparkling gemstones to show affection.
But, did you ever stop to think that when we see any of these things, we are not directly connected to them? And that we are, in fact, only seeing light – light that bounces off objects far or near and into our eyes. Light is all our eyes can really see.
For people with normal vision, the following sequence takes place:
In normal vision, 20/20 vision light focuses on the center of the retina.
Where the light is focused on the retina is determined by the length and shape of the eyeball:
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When the brain perceives out-of-focus images the result is called a refractive error (that is to say, when the light came through the eye there was an “error” made in bending it correctly).
Vision or visual acuity is primarily tested using a Snellen Eye Chart. By examining lots of people, eye doctors have decided what is normal for human being to be able to see when standing 20 feet away from the eye chart.
If you have 20/20 vision, it means that when you stand 20 feet away from the chart you can see what the majority of people can see at that same distance.
If you have 20/40 vision, it means that if a normal person were standing 40 feet away from the chart, and you were standing only 20 feet away from the chart, you and the normal person would see the chart with the same level of clarity.
20/100 vision means that when you stand 20 feet from the chart you can only see what a normal person sees when standing 100 feet away.
20/200 vision and over is the qualification of legal blindness in the United States.
You can also have vision that is better than normal. If a person has 20/15 vision they would be seeing at 20 feet what a normal person sees when standing 15 feet away from the chart.
Hawks, owls and other birds of prey have much more acute vision than humans. Although a hawk has a much smaller eye than a human being, it has more cones packed into that space and two foveas. A hawk’s vision is eight times more acute than a human’s: a hawk might have visual acuity of 20/2.
However, with today’s Wavefront technology, it is possible for human eyes to achieve 20/15 or better.
At Seibel Vision Surgery, your eyes and vision are of paramount importance. To help you make the most informed decisions regarding the welfare of your vision, we are delighted to be of service and are happy to answer any questions you may have.
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