What is Myopia? (near-sightedness)
Commonly referred to as short or nearsightedness, myopia causes difficulty with seeing distant objects. It is caused by either the front surface of the eye (the cornea) being too curved or the length of the eye being too long to allow light to be focused sharply at the back of the eye (the retina).
Myopia most commonly develops between the ages of 10-12 years and normally stops changing by 30. It is most commonly corrected with glasses, contact lenses, or with laser surgery.
What is Hyperopia? (far-sightedness)
This condition is more commonly known as long-sightedness and occurs mainly due to the length of the eyeball being too short. Under these circumstances visual images are focused behind the retina, causing the eye to increase its internal effort to focus the image onto the retina. This effort increases as objects are brought closer to the eye causing people with hyperopia to tire more easily while reading and to be more prone to sore eyes and headaches after close work.
Hyperopia can be present from birth and may increase or decrease as the child grows. Glasses are usually prescribed and depending on the level of hyperopia are sometimes worn full time or otherwise just for close work. It is most commonly corrected with glasses, contact lenses, or with laser surgery.
What is Astigmatism?
Astigmatism can cause blurring of vision at both long and short distances. However, unlike myopia this blurring is mainly due to distortion of the image by the eye. This distortion is caused in most cases by the front of the eye (the cornea) being irregular or uneven in shape. Light passing through this irregular cornea becomes distorted as well and no longer comes to a sharp focus at the back of the eye (the retina). This often results in headaches and sore, tired eyes.
Astigmatism in most cases develops at an early age during childhood and does not tend to deteriorate significantly with age. It is most commonly corrected with glasses, although contact lenses and laser surgery are other options.
What is Presbyopia?
Young eyes are able to change focus in order to see objects up close by contracting a muscle (the ciliary muscle) which in turn alters the shape of the lens within the eye. Presbyopia occurs as the eye ages and the lens becomes less flexible, making it increasingly difficult to focus on close objects.
The condition starts to become noticeable around the age of 40 - 45 years and people often complain of difficulty reading fine print such as the phone book or threading a needle. Reading glasses are prescribed for close work, which help to alleviate symptoms of sore, tired eyes and headaches, which are common with presbyopia.