Eye Care (Part 2)

Colour Blindness

Complete colour blindness, in which you see the world in only shades of grey, black and white, is extremely rare. More common is the difficulty in distinguishing between colours, particularly red and green, although the degree of difficulty varies considerably. Colour blindness is usually an inherited defect and while it cannot be cured, it is important for those affected to be aware of it.

Colour blindness is usually discovered accidentally but it is important to have a proper diagnosis if you suspect your colour vision, or that of a child, may be defective - close relatives should then take a test. Although it is not a disease or symptoms of any other eye problem, poor colour differentiation can cause difficulties in people who are unaware of it.

Testing can be done by a doctor or ophthalmic optician using a method known as the Ishihara test, developed in Japan. The subject is shown a series of plates made up of coloured dots, in which numbers or patterns can be discerned, depending on colour perception.

Here are some Ishihara images to test colour blindness:

Answer: 8

(Shades of grey, black & white?? Complete colour blindness??!!)
*LOL~ Don't worry about it... the image is intentionally set in grey scale*

Answer: 2

*No joke this time*

Answer: Pizza? 10!

Being colour blind has little effect on everyday life, except that motorists must learn to distinguish traffic lights by position. Careers such as airline pilot or train driver may also be problematic. Coloured spectacles and contact lenses may help to enhance contrast, but cannot correct actual colour vision.


Correcting Visual Defects

Problems often become apparent at about the time of puberty as the eyeball grows too long or not long enough, or becomes misshapen - the three commonest reasons for needing to wear glasses.

(Images from www.eyesite.org)

Normal Sight - Image focused accurately onto the retina

Types of Defects:

1. Short Sight
   Distance vision is blurred as the eyeball is too long and light rays converge short of the retina. Concave lenses correct the problem.
   
   
   Short Sight - Image focused in front of the retina
   
   
   
2. Long Sight
   Close-up vision is blurred as the eyeball is short and light rays don not converge. Convex lenses can overcome the problem.
   
   
   Long Sight - Image focused behind the retina
   
   
   
3. Astigmatism
   Vision is blurred both horizontally and vertically as the eyeball is irregular in shape. Cylindrical lenses correct the defect.
   
   
   Astigmatism - Image is focused onto retina but is distorted
   
   
   

Contact Lenses

The type of contact lenses that is most suitable for you depends on several factors: your particular vision problem; whether you want to wear your lenses every day or only occassionally; and how easy you want them to be to look after. There are five main types of contact lens:

1. Hard Lenses
   These are the original contact lenses, and still offer the best vision correction for people with astigmatism and irregular corneas. They are durable (possibly giving more than five years of use) and inexpensive. However, there are drawbacks: it may be several weeks before they are comfortable to wear all day; they are not very porous to oxygen, so should not be worn for more than 20 hours at a time; and they fall out more easily than other lenses.
   
   
2. Gas-permeable Lenses
   These are rigid like hard lenses, but allow oxygen to pass through more easily and reach the surface of the eye, thereby reducing the risk of infection. They offer the sharp vision of hard lenses (though less durability - up to five years), with some of the comfort of soft lenses.
   
   
3. Soft Lenses
   Soft lenses allow oxygen to pass through them, and because of their high water content, most people find them comfortable almost immediately. Soft lenses can correct short and long-sightedness. They are also very fragile, giving about two to three years of wear, and are more expensive than hard lenses.
   
   
4. Extended-wear Soft Lenses
   These soft lenses have a very high water content, and can be worn for up to a month without removal. But they may increase the risk of infection, because they allow a contaminated lens to stay in contact with the eye for a long period of time.
   
   
5. Disposable Soft Lenses
   These special soft lenses are replaced every two to four weeks. This disposability lowers the risk of eye infection and reduces the build-up of protein on lenses, which elsewhere can lead to blurred vision and eye irritation. Such lenses are increasingly popular. Disposable lenses must be cleaned in the same way as conventional soft lenses.
   

Bifocal Glasses

The key to wearing bifocal glasses successfully is to get used to looking through the appropriate section of the glasses for each task. Conventional bifocals have two distinct sections for each eye, the upper part of the lens being ground to correct for distance vision, the lower and usually smaller one for close-up vision.

Mid-range vision - the kind one relies on when descending stairs or stepping off a kerb - is sometimes blurry because it literally 'falls between the cracks' of the lenses.

The best way to adjust to bifocals is to wear them indoors at first, in safe and familiar surroundings. Practise going up and down the stairs at home until you feel confident enough to move with ease in public places.

In seamless bifocals (progressive lenses), one section of the lens blends into the other without a line in between. Some people find these glasses more attractive, but they sometimes prove difficult to adapt, and more expensive than the standard version.


Laser Eye Surgery

Any type of surgery involves some degree of risk, and laser eye surgery is no exception. On top of that, laser surgery can only help those with short-sightedness but not all of them - needs assessment by eye surgeon.

The degree of short-sightedness is a key factor in assessing your suitability. One with normal vision is said to have 6/6 or 20/20 vision. Deviation from the norm is measure in dioptres. The best candidates for laser surgery are those with up to -4 dioptres and no astigmatism or lens distortion, but surgeons will consider people with up to -6 dioptres and moderate astigmatism.

The process takes about 15 to 30 seconds for each eye. It is painless at the time, though the eyes may hurt in the following 24-48 hours. Painkillers are usually prescribed as a remedy. It takes approximately three months for the eyes to heal completely and for vision to stabilise.

After laser surgery, there is a 50-60 percent chance of perfect 6/6 vision, and an 80-90 percent chance of 6/12 vision - enough to allow you to play most sports and to drive by day without glasses.

There is a 1 to 2 percent chance that people who have undergone surgery may experience distortions in night vision, such as radiating lines from street lamps, or even experience double vision. In such cases, patients may have to wear contact lenses until a follow-up operation takes place.

Even when treatment is successful and long-distance vision is improved, glasses still may be needed for reading.

-Cartoon from www.cartoonstock.com-