What is Myopia?
Myopia or short (near) sightedness is an eye condition where a person is unable to see the objects clearly which are kept far away but have no trouble seeing objects which are kept nearby. A person with myopia would have blurry vision when they would see objects kept far away. Generally, it starts to develop during childhood, and its effect increases gradually or rapidly. Its symptoms vary from person to person. If you squint your eyes often while seeing some object which is kept far away or have headaches frequently, then you might have myopia or short-sightedness. It is advised to visit the eye doctor as soon as possible if you experience any of these symptoms often. Eye strain is another symptom of short-sightedness.
What Causes Myopia?
The causes of myopia are as follows:
Myopia occurs when there is the elongation of the eyeball along the axis, and because of it, the cornea and eyeball get affected. Hence, the light rays which are supposed to fall on the surface of the retina, are focusing at the front of it, which results in blurry vision. However, the cause of eyeball elongation is unknown to date.
Shortening the focal length of the eye lens is another cause of myopia.
The overstretching of ciliary muscles beyond its elastic limit can also cause myopia.
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What is High Myopia?
High myopia is a severe case of myopia where a person has nearsightedness of -5.00 to -6.00 D (Diopters). It generally happens to people who have a family history of having the same eye condition and affects about two per cent of the population. Therefore, it is an inherited genetic condition. A person having high myopia becomes susceptible to having glaucoma (open-angle), cataract (nuclear, cortical, and posterior subcapsular), retinal tears which might lead to retinal detachment and myopic macular degeneration. In order to correct high myopia, a person can opt for laser eye surgery since it is the safest option that can correct up to -10 dioptres.
How to Correct Myopia?
Myopia or short-sightedness can be corrected by wearing corrective glasses or contact lenses. In the case of myopia, a concave lens (curved inwards) is used in corrective glasses that correct myopia when placed in front of a myopic eye. It helps in moving back the image to the retina, where it was originally supposed to be, and results in clear vision. A person who is over 18 years of age can undergo laser eye surgery to correct myopia.
Ways to Prevent Further Progression of Myopia
A person with myopia should avoid reading, writing, or operating phones and tablets for too long. He/She should get sunlight very often at a young age because it will lead to lesser chances of having myopia. People having a lack of vitamin D are more prone to having myopia; hence sunlight is a good source of Vitamin D. Healthy food enriched with vitamin A should be eaten to stop short of delaying myopia progression, and it can also be consumed to maintain a healthy eye in general.
Did You Know?
You have a high chance of having myopia, if both parents have myopia or if even one of them has myopia. You are more likely to develop myopia if you spend a lot of time reading, writing, or operating phones and tablets, which are usually kept near your eyes. Generally, it starts around puberty and proceeds to get worse with time until the eye is fully grown. It can also occur in children who haven’t reached puberty yet.
FAQs on Eye Defects Myopia
1. What exactly is myopia and how does it affect a person's vision?
Myopia, commonly known as nearsightedness or short-sightedness, is a refractive error of the eye. A person with myopia can see nearby objects clearly, but distant objects appear blurry. This happens because the eye incorrectly focuses the light from distant objects in front of the retina, instead of directly on it, leading to a blurred image.
2. What are the primary physical changes in the eye that cause myopia?
Myopia is primarily caused by structural changes in the eye's anatomy. The two main causes are:
- Elongation of the eyeball: The distance from the eye lens to the retina becomes too long along the principal axis.
- Excessive curvature of the eye lens: The eye lens becomes too curved, or its converging power increases, causing its focal length to decrease.
3. How does a concave lens work to correct the vision of a myopic eye?
A concave lens is a diverging lens, which means it spreads out light rays. When placed in front of a myopic eye, it diverges the incoming light rays from a distant object before they enter the eye. This effectively moves the focal point backward, allowing the eye's natural lens to then converge the rays precisely onto the retina, resulting in a clear, sharp image.
4. What is the key difference between myopia and hypermetropia?
Myopia and hypermetropia are opposite refractive errors. In myopia (nearsightedness), distant objects are blurry because the eyeball is too long and the image forms in front of the retina; it is corrected with a concave lens. In hypermetropia (farsightedness), near objects are blurry because the eyeball is too short and the image forms behind the retina; it is corrected with a convex lens.
5. Why does the image in a myopic eye form in front of the retina instead of directly on it?
The image forms in front of the retina due to an imbalance between the eye's focusing power and its length. In a myopic eye, the converging power of the cornea and lens combination is too strong for the length of the eyeball. This causes parallel light rays from distant objects to be focused too sharply, meeting at a focal point before they can reach the light-sensitive surface of the retina. By the time the light reaches the retina, the rays have already crossed and are diverging again, forming a blurred circle of light instead of a sharp point.
6. Can myopia worsen over time, and what factors might contribute to its progression?
Yes, myopia often progresses, especially during childhood and adolescence when the eye is still growing. The primary reason for this progression is the continued elongation of the eyeball. While genetics play a major role, environmental factors are also believed to contribute. Prolonged periods of near-work, such as reading, writing, or using digital screens, can increase the risk of myopia developing and progressing.
7. What does the power of a corrective lens, measured in Diopters (e.g., -3.0 D), actually signify?
The power of a lens in Diopters (D) quantifies the degree of correction required. For myopia, the power is always negative (-). The number itself indicates the lens's strength; a higher number like -5.0 D signifies a stronger lens is needed compared to -2.0 D. Technically, the diopter is the reciprocal of the lens's focal length in meters (P = 1/f). For a myopic person, this value also corresponds to the location of their far point—the furthest point they can see clearly without correction.
8. Besides glasses, what is the basic principle behind other common myopia correction methods like LASIK?
While glasses and contact lenses use an external concave lens to correct vision, methods like LASIK alter the eye itself. The principle of refractive surgery (LASIK) is to reshape the cornea. For a myopic eye, a laser is used to slightly flatten the central part of the cornea. This reduces the cornea's converging power, effectively weakening the eye's overall lens system so that it focuses light correctly onto the retina without the need for external lenses.
