How the Eye is Able to See

It is really interesting how the eye is able to take light, bend it and reassemble the information into an object. Here is the basics of how it all works.

Being able to see all comes down to how the eye is able to focus light. As light enters the eye through the cornea (the outer part of the eye), light begins to bend. This is begins what is called "refraction." After light goes through the cornea, it bends one more time by a crystalline lens inside the eye as it goes to the retina, where the light is focused. Once the light is focused, it stimulates cells that send millions of electrochemical impulses along the optic nerve to the brain. The brain uses a special section near the back that interprets the signals into an image of an object. The amazing thing is that this complicated process happens automatically and in less than a blink of an eye.


However, sometimes the eye has trouble focusing light. Vision becomes blurry and objects don't appear as sharp anymore. That is where the importance of an eye exam and corrective prescription like glasses or contact lenses come to the rescue. It can adjust the focus of the light so that the eye and brain can clearly define objects. During an eye exam with an eye doctor, one of the technicians will use what is called an auto-refractor. It measures the approximate amount of correction is needed and tells the optometrist if there is an astigmatism or not.

What about animals? Well, they aren't exactly your typical eye exam patient, but I did dig up this YouTube video of what was just explained and how humans and animals see the world in sometimes different lights.



Here is a great resource for more about how the eye is able to see.

A consumer guide to eye topics such as Eye Twitching, Itchy Eyes, Conjunctivitis, Contact Lenses and more.

Astigmatisms

This five syllable word sounds a whole lot scarier than it actually is. Astigmatisms are a common diagnosis when someone comes to get an eye exam and they can be corrected. The word traces back to Greek roots with the literally meaning of "without a spot or mark." However, with astigmatisms, there are multiple points on where light focuses in the eye. Those multi focal points will cause vision to appear blurry.

The reason for this is because the cornea has an oblong shape, instead of a shape closer to a perfect sphere.

The picture above shows how the cornea is shaped in an odd way that is making the letter "A" appear to focus on two different parts of the eye. If that oddly shaped part followed the contour of the rest of the eye, there would only be one point of focus. That is where corrective lenses come into play.

Glasses are commonly thought to be the only way to correct for an astigmatism. This couldn't be further from the truth. Contact lenses are now able to fit around the astigmatism and properly correct vision, and not just the hard lenses. There are a number of soft lens options that are just as comfortable and have no discernible differences over the spherical counterparts. Refractive surgery like LASIK can also correct for astigmatism. Even if the astigmatism is severe, they can be corrected.

Astigmatisms can happen naturally or they can be caused by other factors. So if you have an astigmatism, your eye doctor will let you know and tell you about a proper course of correction.

If you want to learn more about Astigmatisms, visit All About Vision for more information.

Eye Care 101: 20/20 Vision

Eye Care is one of the most important parts in the practice of Optometry. Good eye care practices are both the responsibility of patients and doctors. This series of posts will cover the basics that highlight important topics in Optometry to show how eye care is important.

One thing most people know about optometry is that 20/20 vision is good to have. It means that at a distance of 20 feet, objects are seen clearly and crisply. If an Optometrist were to say you had 20/100 vision, that would mean that you would have to stand 20 feet away from an object while someone with normal vision could stand 100 feet to see the object just as clearly.



I tend to find pictures help explain this. In the above image, the man has 20/100 vision. He has to stand 20 feet away from the vase on the table while the woman can stand 100 feet away and see the same clarity as the man. The 20/(number) figure that is given by Optometrists part of what is known as "visual acuity."

The reason why everyone doesn't have 20/20 vision is due to a variety of reasons including nearsightedness (blurry distance vision), farsightedness (blurry close-up vision), astigmatism (non-spherical eye) or eye disease. Optometrists will be able to determine the causes during a comprehensive eye exam. The way to check distance vision is generally done by reading lines off those famous eye charts. Because of there are many factors for differences in visual acuity, that could mean that even people with 20/20 vision will note their vision could use adjustment.

The most common way to correct distance vision by prescribing glasses or contacts. There are also visual therapy programs and medications that can help improve vision, when the situation calls for them. Since the eyes are rapidly changing all the time, annual eye exams are important to make sure that visual corrections are current and aiding the health of the eye.

20/20 vision is a good barometer for healthy vision as it tests distance and clarity; however, it is only one part in the story. Saying someone has "perfect" sight when they have 20/20 vision is entirely misleading. What is missing are the other indicators of optimal vision like peripheral (side) vision, coordination of the eyes, depth perception, ability to focus and color testing. In summary, 20/20 vision is important but it isn't the end all, be all measurement for healthy vision.

Learn about eye glasses at All About Vision.