Describe what presbyopia (old sight) is and how that is corrected
During middle age, usually beginning in the 40s, people experience blurred vision when doing things close up. This happens to everyone, even those who have never had a vision problem before.
Currently an estimated 90 million people in the United States either have presbyopia or will develop it by 2014.
Presbyopia Symptoms and Signs
When people develop presbyopia, they find they need to hold reading materials at arm's length in order to focus properly. When they perform near work, such as embroidery or handwriting, they may have headaches or eyestrain, or feel fatigued.
Presbyopia Treatment: Eyewear
Glasses with bifocal or progressive addition lenses (PALs) are the most common correction for presbyopia. Bifocal means two points of focus: the main part of the spectacle lens contains a prescription for nearsightedness or farsightedness, while the lower portion of the lens holds the stronger near prescription for close work.
Bifocal lenses offer a more gradual visual transition between the two prescriptions, with no visible lines between them.
Reading glasses are another choice. Unlike bifocals and PALs, which most people wear all day, reading glasses are typically worn just during close work.
There are contact lenses for presbyopes, called multifocal lenses. You can obtain multifocal contact lenses in gas permeable or soft lens materials. Another type of contact lens correction for presbyopia is monovision, in which one eye wears a distance prescription, and the other wears a prescription for near vision. The brain learns to favor one eye or the other for different tasks. But while some people are delighted with this solution, others complain of dizziness or nausea, or miss the depth perception they once had.
Because the human lens continues to change as you grow older, your presbyopic prescription will increase over time as well. You can expect your eyecare practitioner to prescribe a stronger correction for near work as you need it.
Presbyopia Treatment: Surgery
New surgical options to treat presbyopia are being researched and are already available in many countries. One example is Refractec Inc.'s conductive keratoplasty, or CK, treatment, which uses radio waves to create more curvature in the cornea for a higher "plus" prescription to improve near vision. The method was FDA-approved for the temporary reduction of presbyopia in April 2004. (In 2002 it had been approved for mild farsightedness.) Read more about how CK works.
A highly experimental treatment is a soft, elastic polymer gel that researchers say would be injected into the capsular bag, the cavity that contains the natural lens. In theory, the gel would replace the natural lens and serve as a new, more elastic lens. Animal testing may begin in 2004.
See if you can find out how bifocal and varifocal lenses work
Bifocal lenses
Bifocal lenses are effectively two lens powers combined together to assist with both near and distance vision. The most common use of bifocals is for reading correction in the lower lens together with a modest distance correction in the upper lens, giving sharp vision at two distinct distances. Bifocals can also be supplied with a clear (upper) lens for those requiring reading glasses but not wanting the inconvenience of removing their spectacles every time they look up.
Varifocal lenses
Varifocal lenses provide the wearer with a multifocal capability over all distances from near to far, thus restoring, to a certain extent, the vision of youth! So the varifocal lens designed to give you the sharpest vision for most things that you do.
What is astigmatism and how is that corrected
Astigmatism is the most common vision problem among people. Astigmatism may accompany nearsightedness or farsightedness. It's caused by an irregularly shaped cornea and is corrected with eyeglasses, contact lenses or refractive surgery.
How is it treated?
Astigmatism can be corrected with glasses or contact lenses. Now there are soft lens designs that correct astigmatism; they are called toric contact lenses.
Overview
Astigmatism means that the cornea is oval like a football instead of spherical like a basketball. Most astigmatic corneas have two curves – a steeper curve and a flatter curve. This causes light to focus on more than one point in the eye, resulting in blurred vision at distance or near. Astigmatism often occurs along with near-sightedness or farsightedness.
Detection and Diagnosis
Astigmatism can be detected and measured with corneal topography, keratometry, vision testing and refraction.
Treatment
Astigmatism can be corrected with glasses, contacts, or surgically. The most common surgeries used to correct astigmatism are astigmatic keratotomy and LASIK. The objective of these procedures is to reshape the cornea so it becomes more spherical or uniformly curved.
What is red-green colour blindness and what is its cause?
Red, green colour blindness is usually inherited. It occurs in about 8 per cent of males and only about 0.4 per cent of females. The son of a woman who carries the gene has a 50 per cent chance of being colour blind. Unless her mother is a carrier and her father is colour blind. However, colour blindness is not always inherited. It can also be due to a change in the chromosome during development.
Why does it happen?
To see colours properly, colour detecting vision cells, called cones, are needed in the retina of the eye. Three types of cone cell exist, each being sensitive to red, blue, or green light. If one or more of these types of cells are faulty then colour blindness results.
Sometimes colour blindness occurs because of diseases such as macular degeneration or from side effects of medicines.
What are cataracts and how are they treated?
Introduction:
Most people think of the elderly when they think about cataracts, but cataracts can also occur in babies and children. They are a leading preventable and treatable cause of blindness in children.
What is it?
The lens of the eye is our window to the world. Normally, this lens is crystal clear, transmitting and focusing light. A cataract is cloudiness of the lens.
HOW ARE CATARACTS TREATED?
Once a clouded lens develops, surgical removal is the only remedy. Each year about 1.3 million cataract operations are performed, making it the most common operation in the country in people over 65.
Cataract surgery is improves vision in up to 95% of cases. Newer techniques, however, have made it safer and even more efficient to operate in earlier stages. There is, in fact, considerable evidence that, because of the ease and relative safety of the procedure, it may be performed more often than needed. Patients having operations now tend to have better preoperative vision than those operated on ten or 20 years ago. In a study of 800 cataract operations, a quarter of the patients said that clouding had had no obvious effect on their lives before the procedure.
What is Glaucoma?
Glaucoma is a group of eye diseases that gradually steals sight without warning and often without symptoms. Vision loss is caused by damage to the optic nerve. This nerve acts like an electric cable with over a million wires and is responsible for carrying the images we see to the brain.
It was once thought that high intraocular pressure (IOP) was the main cause of this optic nerve damage. Although IOP is clearly a risk factor, we now know that other factors must also be involved because even people with "normal" IOP can experience vision loss from glaucoma.
