The human eye is a lot like a camera. When you take a picture, the lens in the front of the camera allows light through and focuses that light on the film in the back of the camera. When the light hits the film, a picture is taken. This same process takes place in our eyes, too. The front parts of the eye (the cornea, pupil, and lens) are clear and allow light to pass through. The light also passes through the large space in the center of the eye called the vitreous cavity. The vitreous cavity is filled with a clear, jelly-like substance called the vitreous gel. The light is focused by the cornea and the lens onto a thin layer of tissue in the back of the eye called the retina. The retina is like the film in a camera. When the focused light hits the retina, a “picture” is taken. Messages about this picture are sent to the brain through the optic nerve. This is how we see.
Adult eye examinations should be performed, by an eye doctor, on a regular basis.
Adults with high-risk conditions that can lead to eye disease should be seen at least once a year. High-risk adults include:
Visual acuity is the measure of the eye’s ability to distinguish the smallest identifiable letter or symbol, its details and shape, usually at a distance of 20 feet. Traditionally a Snellen eye chart is used. This measurement is usually given in a fraction. The top number refers to how far away, in feet, the object being viewed is located. The bottom number is the distance from which a “normal” eye should see the letter or shape. So, 20/20 vision is considered perfect. If your vision is 20/60, that means what you can see at a distance of 20 feet, someone with perfect vision can see at 60 feet.
You are legally blind, or visually impaired, when the best-corrected visual acuity (i.e., your vision with glasses or contact lenses) is less than 20/200 in your better seeing eye. You are also legally blind if your side vision is narrowed to 20 degrees or less in your better eye. Even with legal blindness, you may still have some useful vision. If you do experience visual impairment, you may qualify for some government benefits.
Low vision is a term describing a level of vision below normal (20/70 or worse) that can’t be corrected with conventional glasses or contact lenses.
Low vision is not the same as blindness. People with low vision can use their sight. However, low vision may interfere with the performance of daily activities, such as reading or driving. A common cause of acquired low vision is cataracts.
A cataract is a clouding of the lens in the eye that affects vision. Most cataracts are related to aging. Cataracts are common eye disorders, and are very prevalent in older people. By age 80, more than half of all Americans either have a cataract or have had cataract surgery. A cataract can occur in either or both eyes, and can be diagnosed during an eye exam by an eye doctor. It cannot spread from one eye to the other.
Age-related cataracts develop in two ways:
Clumps of protein reduce the sharpness of the image reaching the retina.
The clear lens slowly changes to a yellowish/brownish color, adding a brownish tint to vision.
The lens consists mostly of water and protein. When the protein clumps up, it clouds the lens and reduces the light that reaches the retina. The clouding may become severe enough to cause blurred vision. Most age-related cataracts develop from protein clumpings.
As the clear lens slowly colors with age, your vision gradually may acquire a brownish shade. At first, the amount of tinting may make it more difficult to read and perform other routine activities. This gradual change in the amount of tinting does not affect the sharpness of the image transmitted to the retina.
If you have advanced lens discoloration, you may not be able to identify blues and purples. You may be wearing what you believe to be a pair of black socks, only to find out from friends that you are wearing purple socks.
When a cataract is small, the cloudiness affects only a small part of the lens. You may not notice any changes in your vision. Cataracts tend to "grow" slowly, so vision gets worse gradually. Over time, the cloudy area in the lens may get larger, and the cataract may increase in size. Seeing may become more difficult. Your vision may get duller or blurrier.
The most common symptoms of cataracts are:
The symptoms of early cataract may be improved with new eyeglasses, brighter lighting, anti-glare sunglasses, or magnifying lenses. If these measures do not help, cataract surgery is the only effective treatment. Cataract surgery involves removing the cloudy lens and replacing it with an artificial lens implant.
A cataract needs to be removed only when vision loss interferes with your everyday activities, such as driving, reading, or watching TV. You and your ophthamologist (eye surgeon) can make this decision together. Once you understand the benefits and risks of cataract eye surgery, you can make an informed decision about whether cataract removal is right for you.
Sometimes a cataract should be removed even if it does not cause problems with your vision. For example, a cataract should be removed if it prevents examination or treatment of another eye problem, such as age-related macular degeneration or diabetic retinopathy.
Yes, there are a number of options that are available for cataract surgery. Some lens implants correct only for your distance vision, which means that you will still be dependent on glasses for your reading vision. Other lens implants correct for both distance and near vision, which gives you more freedom from glasses. There are also lens implants that correct for astigmastism.
The ability to focus on near objects decreases steadily with age and is referred to as presbyopia. Presbyopia is a natural aging of the lens. It usually begins near the age of 40, when eye glasses or bifocals are prescribed to correct this condition.
There is no predetermined schedule for changing eyeglasses or contacts. It is necessary to change your prescription glasses only when it no longer provides adequate correction. A good rule of thumb is the following: when your vision prevents you from doing all of the things you like to do (driving, watching TV, reading, knitting, etc) in the way you like to do them, that is when it is time to get your eyes checked and your prescription updated.
No, but most people are more comfortable reading with proper lighting, which is bright enough to provide good illumination but not so bright as to cause glare. Light bulbs that provide “natural light” or simulate sunlight are good options, and they are available at most hardware stores.
There is a benefit to wearing UV protective lenses. Wearing them may protect against cataract formation and protect the eyes against some forms of macular degeneration. Polarized sunglasses are the most effective at reducing glare.
No, because it does not provide the specifications for lens diameter, thickness, and base curve. A new prescription must be carefully fitted by an eye care specialist to avoid serious adverse reactions.
Yes, contact lenses are made to correct the majority of refractive errors, including presbyopia. In addition, there are contact lenses that correct for astigmatism.
Yes, contact lenses provide excellent vision for most sports. However, they do not protect the eyes from injury. Therefore, contact lens wearers should use polycarbonate sports safety goggles or glasses when participating in sports.