AS we grow older, our eye lens loses its elastic nature and becomes relatively a solid mass, a condition which eye doctors often referred to as presbyopia.
When this happens, the eyes are more or less permanently focused and are no longer able to accommodate both near and far vision. This is one of the reasons an older person often needs to wear eye glasses with bifocal lenses, with the lower portion of the glasses being of stronger power for close vision, while the upper portion allows him to see more freely at a distance.
The iris is a beautiful circular curtain like structure lying in front of the lens of the eyes. Orientals (Asians) generally have brown eyes, but the western people may have brown, blue, green, grey, or black, depending on their family background.
The iris, according to eye doctors, has a very important function, for it controls the amount of light that enters the eyes. The central black spot, or what is commonly called pupils, opens up wide in darkness, but becomes narrowed and small in bright light. This widening and narrowing is done by Iris which acts like the diaphragm on the camera, allowing just the right amount of light to enter the eye, and at the same time, giving a greater depth of focus when the opening is small. Thus, the size of the pupil is automatically adjusted according to the amount of light and sharpness of vision.
•Colour vision—In the retina, or screen, at the back of the eye, ophthalmologist explained that there are two types of nerve cells—the rods and cones, and both are said to be sensitive to light, with the rods being especially important in a dim light, while the cones react to colour and fine detail. You are using your cone cells as you read the words in this article. If you tried to see this whole page at a glance, in doing so, you are using the rod cells which are widely spread. Throughout the retina. But in reading the fine print, expert says you have to focus down on a small central spot, or fouea, on the retina where the cones are very numerous. The retina is well supplied with an important chemical substance called rhodospin, or “visual purple.” light falling on the retina brings about certain chemical changes in the rhodopsin and other substances present in the rods and cones. All these changes occur very rapidly, but large quantities of vitamin A are needed to make this happen. That is why we need to take good amount of vitamin A, yeast and other vision—enhancing medication supplements, fruits and vegetables as may be prescribed by our eye doctor. Some people even say they eat carrots a lot in order to get good amount of vitamin A and carotene, needed for good vision.
If there is any marked deficiency of vitamin A, especially from childhood, night blindness may occur, and that is why parents are advised to give Vitamin A drops to their infants in order to prevent eye trouble and to enhance good vision. Vitamin A can also be got from certain fruits and vegetables.
The importance of vitamin A in our diet cannot be under estimated. For example, vitamin A is called the “beauty vitamin” as it helps to keep the skin smooth and soft apart from boosting good, bright vision.
Vitamin A is also needed for the mucous membranes lining the nose, throat, and bronchial tubes, as well as the entire digestive tract, the bladder, kidneys, and pelvic organs. This “beauty vitamin” also aids in the normal growth of bones and teeth, particularly in children and young people.
If one take it as a duty to regularly eat green and yellow vegetables and fruits, then one need not worry about getting too much or too little of vitamin A. This is because vitamin A is formed from a chemical substance known as carotene, which is present in all green leafy vegetables, especially amaranth leaves, carrots, sweet potatoes, squash, pumpkins, apricots, payaya (pawpaw), mangoes, avocados (butterfruit), melons and nearly all yellow fruits. Any diet containing an abundance of fresh fruits and vegetables will also be rich in vitamin A.
This vitamin helps to fight infections diseases and keeps our eyes bright and also helps us to see in a dim light. Remember, without vitamin A, our vision would soon be impaired, smaller than the other.
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