How The Eye Works

4 Types of Vision Impairment

There are many reasons why our eyes might not focus the way we want them to. Here are 4 primary causes.

How the Eye Works


In the nearsighted eye (myopia), near objects are seen more clearly and far objects appear blurry. This is because images focus in front of the retina. Myopia occurs when the curvature of the cornea is too steep, or the eyeball is too long.


In the farsighted eye (hyperopia), far objects can be seen more clearly and near objects appear to be blurred. This is because images focus behind the retina. Hyperopia occurs when the curvature of the cornea is too flat, or the eyeball is too short.


With astigmatism, all images, whether near or far, may be blurred. Astigmatism can occur in conjunction with nearsightedness or farsightedness. Here, images focus on more than one point in front of or behind the retina. It occurs when the cornea is irregularly shaped.


Presbyopia – When you are young, the lens inside your eye is extremely flexible and allows you to easily focus on close objects. Over time, the lens gradually loses its flexibility, making it difficult to focus on close objects. This condition is called Presbyopia (prez-bee-OH-pee-ah) and is a normal, natural part of the aging process that happens to everyone, even those who have never needed glasses before. Most people notice this when they’re between the ages of 40 to 65.

You may find yourself needing to hold books and cell phones farther away from your face to be able to see them more clearly. Many people experience headaches, eye pain, or fatigue after trying to read small print.

What does 20/20 mean?

Your vision by numbers

Eye Chart

You’ve probably heard about 20/20 vision, but do you really know what it means? It’s actually a measure of your visual acuity, where your vision is placed on a numeric scale.

You know the vision chart? The one with the big “E” at the top? It’s called a Snellen chart, and we’ve been using it to measure visual acuity since the 1800s.

If your visual acuity is determined to be 20/20, it means that at 20 feet, you can see what a person with normal vision can see at 20 feet. But, if you have 20/40 vision, it means that what a person with normal vision can see at 40 feet you will only be able to see at 20 feet. Of course, if you’re one of the lucky ones with 20/15 vision, it means that you can see at 20 feet what others would have to move closer (15 feet) to see.

Your visual acuity is an important measure of your vision. It can help identify common vision problems like nearsightedness, farsightedness and astigmatism.

Beyond the numbers: There’s more to good vision than “20/20.”

In addition to visual acuity, there are other important measures of your vision, for example your ability to see subtle contrast changes, especially in low-light situations. Contrast sensitivity is important for many routine visual tasks, like recognizing a face. Taken together, these measures determine the overall performance of your vision.

So, to really understand your vision, both quantitative and qualitative measures are important. It is possible to have very good visual acuity (20/20 vision) yet have poor visual quality and vice versa. It’s important to consider both as you make your decision about laser vision correction. At LaserVue, we can help you with this decision at our convenient locations in Silicon Valley, San Francisco Bay, San Jose, and Santa Rosa.

But what if I have low-light vision problems?

In addition to vision difficulties with contrast sensitivity and visual acuity, for example nearsightedness and farsightedness (also known as lower-order aberrations), there are other common vision problems known as higher-order aberrations. They are widely believed by ophthalmic experts to contribute to night vision problems, including glare and halos.

Glasses and contact lenses are unable to help with higher-order aberrations. Furthermore, they cannot be corrected with traditional LASIK procedures. But, an exciting new procedure called Wavefront LASIK is capable of correcting both lower and higher-order aberrations.

What is a Wavefront map?

Higher-order aberrations are diagnosed and measured using Wavefront maps. These maps are plotted by passing a narrow ray of eye-safe light through the optical system and measuring the optical distortions as the light exits the eye. These patterns are then compared with the flat Wavefront associated with normal vision. An ideal Wavefront map would be perfectly flat.

Our commitment to you

When it comes to your eyes, you can count on LaserVue Eye Center. We know you rely on your eyes and we are committed to providing you with the highest-quality, most technologically advanced vision care in our state-of-the-art eye surgery centers.

From the beginning, we have been at the forefront of technology, using Custom Wavefront LASIK. We are committed to using the most advanced, precise, and reliable LASIK equipment available in San Jose, Santa Rosa and the San Francisco Bay Area.

We are proud to have been the first center in the United States to offer the VISX™ STAR S4 laser, uniquely featuring three-dimensional eye tracking and auto-centering, making the LASIK procedure safer and more precise. Because our number one focus is on quality and safety, we continue to reinvest in the technology as it evolves.

Since 1996, thousands of Bay Area residents, including countless doctors, have entrusted LaserVue with their eye care. Our expertise, clinical excellence, and specialized focus of our fellowship-trained surgeons have made us recognized cataract and LASIK surgery specialists in San Jose, Santa Rosa and the San Francisco Bay Area.

Your patient experience is important to us. That’s why you can trust that your LaserVue doctor will be there for you throughout all phases of your care—from the exam to surgery, and through all phases of follow-up. We believe that the continuity of care ensures the best possible outcome.

At LaserVue there is a difference. A difference you will see.

Find out if you are a candidate, schedule a free screening with us today at 800-527-3745 or request an appointment online.

San Francisco

LaserVue LASIK and Laser Eye Surgery Center San Francisco
711 Van Ness Ave Suite 320,
San Francisco, CA 94102
Location & Map 1-800-527-3745 1-415-346-5500

Santa Rosa

Santa Rosa Business Location
3540 Mendocino Ave. #200,
Santa Rosa, CA 95403
Location & Map 1-800-527-3745 1-707-522-6200

Santa Rosa

Santa Rosa Business Location
3540 Mendocino Ave. #200,
Santa Rosa, CA 95403
Location & Map 1-800-527-3745 1-707-522-6200

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