Eye Defect -Processes vision takes place, 10 causes of eye defect, 12 signs and symptoms of eye defect
The eye gives the human body light and direction for proper functioning. The eye enables the body to sight things, in turn allows the body to either approach or divert from the object. (Vision)
Process which vision takes place
Before vision takes place, the following must take place. They are reflection, refraction, accommodation, stimulation or transmission, interpretation or perception.
Reflection – This is the process which the object before the eye throw back light rays into the eye. In refraction, certain parts of the eye are involved i.e the lens, the cornea, the aqueous humour, the conjunctiva.
Refraction – The are two major organs in the eye that perform refracture. They are the cornea and the lens. It is the ability of the light rays to bend. Errors in refraction occurs when there is interfere with the ability of the eye to focus light rays on the retina resulting in impaired vision.
Near Point: This is used to refer to the nearest point which an object can be viewed clearly. The near point for anyone without a defect is 25cm from the eye. 25cm is the limit to which the eye (ciliary muscle) can reach. Therefore, they are greatly strained and the accommodation is great.
Accommodation is when the eye can alter itself to produce clear images of objects at a particular distance and angles on the retina.
Far Point: This is the longest point which an object can view clearly. For an eye without defect, the far point is infinity. The ciliary muscles are relaxed and the lens is slim. Here, accommodation is at the lowest range.
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CAUSES OF EYE DEFECT:
3. Vitamin A deficiency
4. Chemical irritants
10. Poor hygiene habit
DEFECTS OF VISION:
This occurs when refraction cannot occur thereby creating an error in vision. The following are eye defects:
HYPERMETROPIA (LONG SIGHT)
Another name for hypermetropia is long sightedness. A person suffering from long sightedness can only see distant or far objects clearly but cannot see close object clearly. The near point for this eye defect is more than the normal 25cm. Instead of the ray of light to appear on the retina, it appears behind the retina. Hence, the eye becomes too short.
Correction of this defect can be done by using a convex lens. The lens will help to reduce the ray and make the object to appear on the retina. It will make the near point to stay at its normal level which is 25cm. It will help the person to see close objects clearly.
Myopia can also be called short sightedness. Myopia makes one see close object clearly but cannot see far object clearly. Hence, near point is at infinity. The far point becomes shorten. The object to be viewed now falls in front of the retina. The eyeballs become too long. This defect is corrected with the use of a concave lens or diverging lens. The light rays is diverted from penetrating the eye for a distant object. Concave lens produces divergence of light rays thereby making distant object clear and not blur.
Here, refraction is scattered. The light ray does not go its normal way but forms short lines on the retina because the curvatures of the cornea are uneven.
This defect can be associated with aging because the lens loses it’s elasticity and the ciliary muscle weak. It further becomes thinner and flatter. This makes the level of refraction to reduce. It can be corrected with the use lens which will enable the person see near and far objects called bifocals.
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This condition occurs mainly in old people. The lens becomes cloudy. Sufficient light cannot pass through it so that the affected person cannot see clearly. It can be corrected through surgery.
This is a discomfort experienced when exposed to light. It can be the intolerance to light. It can occur in many eye conditions and is caused by ocular inflammation, decreased ocular pigmentation and neurologic disorder.
GENERAL SIGNS AND SYMPTOMS OF EYE DEFECT
1. Difficulty in reading or seeing objects clearly.
2. Photophobia (sensitivity to light) caused by the inflammation of the eye.
4. Straining of the eyes in any effort to see.
5. Errors are made because of misread information or direction.
6. Redness of the eye.
7. Discharge from the eye.
8. Severe headache.
9. Dryness of the eye.
10. Itching in the eye.
11. Flash of eye.
12. Discomfort of the eye as the lens becomes less spherical with age, becomes opaque and nucleus harden.
Impaired innervation of the eyes due to a neurological disorder (brain tumor or injury).
Systematic disease like hypertension, diabetes.
Inadequate knowledge about the factors that contribute to the preservation of good vision e.g. nutritional requirement, protection of the eye in hazardous situation.
Do not read under poor or dim light.
Put on screen guard when using the computer system.
Wear protective goggles if working in a welding workshop.
Consume enough fruits that contains vitamin A,B complex and C. A deficiency in vitamin A may cause drying, change of the cornea and conjunctiva and decreased in the production of the retina pigment (rhedopsin) leading to night blindness. A deficiency in vitamin B complex may predispose to retina changes. Vitamin C plays a role in resistance to infection.