Definition of visual acuity

To answer these questions, let's take a look at vision related terminology to understand how eye doctors measure vision quality.

Visual acuity, sight and visionVisual acuity.

 Literally, it is the sharpness of vision. Acuity is measured by the power to spot letters or numbers on a uniform chart from a selected viewing distance. Visual acuity is a static measure and it means that the person is not moving during the test, and that the letters or numbers they are viewing are also still.

Additionally, visual acuity is tested under high contrast conditions: the letters or numbers that appear on the eye chart are black and the background is white.

Although the acuity test is extremely useful in determining the relative clarity of vision under standardized conditions, it's not a diagnosis of the standard of vision altogether situations.

What determines visual acuity?

There are three major physical and neurological factors that determine visual acuity:

1.   The precision with which the cornea and lens of the eye focus light on the retina.

2.   The sensitivity of the nerves of the retina and the centers of vision in the brain.

3.    The power of the brain to interpret information received from the eyes Only light that's focused on a really small and sensitive central portion of the retina (called the macula) influences the acuity measurements obtained during the attention exam. View.  It is difficult to pin down the exact definition of 'sight'. Depending on the dictionary or other resource you review, it may mean 'ability to see', 'sense of seeing', 'vision', 'range of vision', or 'seeing'. Often the terms 'sight' and 'visual acuity' are used interchangeably.

What is 20/20 vision?

The term "20/20" and similar fractions (such as 20/40, 20/60, etc.) are measurements of visual acuity. They are also called Snelling fractions, after Herman Snelling, the Dutch ophthalmologist who created this measurement system in 1862.

In the Snelling visual acuity system, the top number of the Snelling fraction is the viewing distance between the patient and the eye chart.

At this test distance, the size of the letters on one of the smaller lines (near the bottom of the eye chart) has been standardized to correspond to 'normal' visual acuity, this is the "20 /twenty". If the person can identify the letters on this line, but none smaller, they are said to have normal visual acuity (20/20).

The increasing font sizes of the lines above the 20/20 line in the Snelling table correspond to the worst visual acuity measurements (20/40, 20/60, etc.); lines with smaller letters below the 20/20 line correspond to visual acuity measurements that are even better than 20/20 vision (egg, 20/15, 20/13, 20/10).

The large letter 'E' at the top of most Snelling eye charts corresponds to a visual acuity of 20/200.

In most Snelling charts, the smallest letters correspond to a visual acuity of 20/10. If a person has 20/10 visual acuity, the vision is twice as sharp as that of a person with normal vision (20/20).

Is it possible to see even better than 20/20?

Yes, it is possible to have a sharper vision than 20/20 vision. In fact, most of the people with healthy, young eyes are ready to identify a minimum of a number of the letters on the 20/15 line or maybe smaller letters on the Snelling chart. Which may be due in part to the better printing methods available today versus those that existed in the 19th century, when Snelling set out which were the smallest letters that a person with normal vision should be able to distinguish. So it could be argued that today's 'normal' visual acuity is the ability to identify letters that are slightly smaller than those on the 20/20 line of a traditional Snelling eye chart.

On the other hand, people are living longer today than they used to in Snelling’s day. Changes due to normal aging in the eye, such as the early development of cataracts, could somehow justify larger letters on the 20/20 line as indicative of 'normal' vision among adults over 60 years of age.

Regardless of these considerations, for example, if your eye doctor tells you that you have 20/20 vision — or more accurately, that you have 20/20 visual acuity — and you happen to want sharper vision, what can be done?

If your 20/20 vision doesn't seem clear enough, it might be that your eyes have higher order aberrations (HOAs), which can't be corrected with regular glasses or soft contact lenses. The eye specialist can check for these aberrations with wave front technology that is available in some ophthalmic offices.

Even if you see 20/20, you may feel that your vision is not as good as you would like it to be. That has a remedy.

If higher order aberrations are caused by small irregularities in the shape of the front surface of the eye, many times, putting on gas permeable contact lenses (PG lenses) can improve visual acuity compared to wearing glasses or spectacles. soft contact. This is because PG lenses are rigid and replace the irregular front surface of the eye with a perfectly smooth, curved surface to focus light more precisely.

Another option may be custom wave front LASIK surgery. This personalized laser vision correction surgery provides vision that's like the utilization of rigid gas permeable contact lenses (which is usually sharper than the acuity provided by glasses or soft contact lenses), without the daily hassle of contact care.

If you prefer to wear glasses to correct refractive errors, there are glasses with special high definition lenses that can give sharper vision than regular glasses.

What is perfect vision?

It's nearly impossible to quantify what perfect vision is. Also, the interesting question would be: perfect for what?

For example, if you are driving your vehicle on a sunny day, the number one satisfaction factor with your vision could be your excellent visual acuity based on the Snelling eye chart. But your girlfriend, who has poorer visual acuity than yours, may be happier with her vision than you are and under the same circumstances, which is because she wears polarized sunglasses with an anti-reflective coating that improves vision. Contrast and blocks glare.

Another example would be the athlete who has vision much better than 20/20 and who may have difficulties with his performance because he does not have certain dynamic visual skills that allow him to react to objects by moving as quickly as a teammate whose acuity does. Visual static is not as good as yours.

Where to get professional advice?

The first step in optimizing vision clarity and comfort in all situations is to see a qualified optometrist or Ophthalmology Expert Witness.  If you are interested in whether laser vision correction could give you sharper vision compared to glasses or contact lenses, ask for a referral for a consultation with an experienced LASIK surgeon.

If you want to maximize your dynamic vision abilities for sports and other activities, find an eye doctor who is a sports vision specialist and ask about sports vision training.