The choice between eyeglasses and contact lenses depends on what sight problem you have, and the degree of the disorder.  Let's explore the advantages and disadvantages of contact lenses vs. glasses:
In glasses the lenses vary in thickness, depending on the weakness of vision.  The shape of an eyeglass lens creates distortion and the thicker the glass, the greater the distortion.  The eye, looking through the center and then suddenly switching to the edge, sees the object being looked at move.  This is called the "prism effect".

If you look through a prism you can see how a straight line becomes bent.  Even though the prism effect is gradual as the eye moves across the glasses lens and does not disturb the wearer very much, it can be a nuisance.  This distortion can also affect stereoscopic vision until the brain has had time to compensate. 
Lens Strength:
Because of its closeness to the pupil, the contact lens often does not need to be as strong as glasses.  The image formed at the back of the eye for the near-sighted is larger and less dazzling than with glasses-an effect which makes many near-sighted people who wear glasses choose lenses weaker than their full prescription, so they many not see well.

For far-sighted people the image is smaller than with glasses.  The power needed for contact lenses can be greater than for glasses.  However, when far sight is fully corrected by contact lenses close work is easier than with glasses because the wearer does not have to accommodate so much.
Eye Problems:
Some eye disorders can only be treated by contact lenses.  These are: extreme far and near sight, unequal vision and astigmatism.  People with keratoconus (a cone shaped cornea) or who have had a cataract operation are often better off with a contact lens.

Cosmetic Effect:
This is the major reason for many people trying contact lenses.  Either they feel glasses don't look good, or they find them heavy and uncomfortable.  The freedom of contact lenses is worth the effort involved in getting used to them.
To start with, wearing contact lenses is certainly more uncomfortable than glasses.  In the long term, provided you can learn to adapt, you don't notice you're wearing them.  Glasses, on the other hand, may be heavy on the bridge of the nose, steamy or sticky in wet or hot weather.  There are, however, some common eye conditions that make wearing contact lenses impossible:

Dry Eyes: If your tear glands don't make enough tears your eyes will become gritty and sore.  The discomfort is relieved with eyedrops and by avoiding a dry or rapidly ventilated atmosphere.  But contact lenses would irritate the soreness and so are unsuitable.

Wet Eyes: Too many tears can interfere with your vision.  Watering eyes may be due to a cold, a foreign body or crying.  But if your eyes are continually watery, this may be due to a blockage in the drainage channels and until it has been put right, it will not be possible to wear contact lenses.

Adapting To Lenses:
It takes some perserverance to get used to lenses and a lot of people give up in the first two or three weeks.  Motivation is of course, all important.

The cost of contact lenses are generally higher than a pair of eye glasses, when factoring in the cost of saline and cleaning solutions, lens cases, etc.  This is especially true if you are using disposable contacts, some of which are designed to be thrown away every month, week, or day.

Much depends on where you live, and whether free health care is available.  Some insurance plans will not pay for contact lenses, as they are considered cosmetic and not essential (unless of course, your eye disorder requires correction provided by contacts.)

Above all, you should heed the advice of your eye care professional when deciding on glasses or contacts.
The "Prism Effect"
Contact lenses can also have this effect, but to a lesser degree.  For anyone needing high powered correction, wearing contact lenses should be a real advantage.
Some Of Us Don't Like The Appearance Of Eye Glasses.
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Eyeglasses vs. Contact Lenses: