How Does Myopia Occur? Understanding the Physics Behind It
The eyes are the sense organs of sight in our body. Each eye is a spherical-ball like structure and is referred to as the eyeball. The ability of the eye to see the object equally clear from various distances is called the power of accommodation. However, this power of accommodation can get defective at times. Like some times the eye is not able to see distant objects for eg. Highway signs clearly while sometimes it is not able to see near objects clearly. Here we are going to learn about the defect of the eye where distant vision is blurred while near vision is clear. Such a condition or abnormality of the eye is known as myopia. Let's study this defect of the eye (myopia)in detail.
What Is Myopia?
Myopia is an eye defect or common abnormality of the eye in which the near vision is clear while distant vision is blurred. This condition is known as myopia also it is called near or short-sightedness.
Retina is that part of the eye which provides a surface for image formation. In myopia what happens is light rays entering the eyes converge too soon and are brought to focus before reaching the retina hence the image cannot be formed on the retina.
Causes Of Myopia
This eye defect called myopia can be caused basically due to the defected eye structure.
Structure of the eye causing myopia can have two defects:.
The eye lens becomes too convex or curved
Depth of the eyeball is too much i.e. eyeball lengthened from front to back. When the length of the eyeball is too long as compared to the focusing power of the lens of the eye and cornea. Because of this, the light rays focus at a point in front of the retina and not on the retina itself.
Because of the above mentioned defects in the eye structure, the light that enters our eye doesn't focus correctly. Hence, images are formed in front of the retina which is the light-sensitive part of our eye instead of being formed directly on the retina which causes blurred vision.
Myopia is also referred to as the refractive error.
In the above diagram, we can see that due to the eye lens being too convex or curved the image formation that should happen on the retina is happening in front of the retina. Thus, causing blurred vision of distant objects known as myopia.
Types of myopia:
Simple Myopia - In this, the eye of a person is almost healthy, wearing glasses or contact lenses of suitable power can easily correct the defect and can correct the issue of a person's eye vision.
High Myopia - High myopia is a severe form of myopia. When a person is diagnosed with myopia at a young age then with the growing age this defect becomes worse. High myopia increases the chances of development of other eye problems such as cataract, glaucoma etc.
Pathological Myopia - This condition is also called degenerative myopia. It can also cause blindness and cannot be cured by lenses or glasses.
Myopia Correction
Myopia isn't a very complex disability. It can be corrected easily by wearing concave lenses. Concave lenses cause parallel rays of light to diverge before they converge and focus on the retina.
Let's understand it more easily through a diagram:
Whenever asked what lens is used in myopia or what lens is used to correct myopia the answer should be the concave lens.
Now we will talk about the symptoms and also the treatment of this eye defect known as myopia.
Myopia Symptoms And Treatment
Symptoms of Myopia:
If a person is myopic he or she will not be able to see the road signs and distant objects clearly but the nearer object will be visible to him/her clearly.
Feeling of fatigue while playing sports or driving is also a symptom of myopia.
When there is a need to close eyelids partially to see clearly or there is a need to squint is also a symptom of myopia.
Eyestrain is caused due to myopia
Headache is another symptom of myopia
squinting and frowning.
complications as a result of eyestrain.
Treatment of Myopia
After a person is diagnosed with myopia he can have the following ways to treat this eye defect.
Glasses and Contact Lenses - Most common treatment options for myopia is the usage of glasses and contact lenses with suitable power. The eye power for a myopic person is in negative numbers.
The custom lenses fit into frames and are worn as specs while the contact lenses are discs that sit on the surface of eyes.
Orthokeratology - Orthokeratology is using overnight rigid contact lenses to reshape the cornea. It really works with the aid of pulling down the significant cornea, thinning the central corneal epithelium, thickening the mid-peripheral cornea, and producing a myopic shift in peripheral vision. This quickly reduces or eliminates refractive errors and decreases the want to put on contact lenses or spectacles in the daylight hours. Researchers observed that orthokeratology is as effective as atropine in delaying myopic progression.
Orthokeratology is a nonsurgical method for the treatment of myopia. This can be helpful in the treatment of a mild form of myopia. This treatment involves wearing a series of rigid contact lenses to reshape the cornea.
Surgery - There are two types of surgery which can treat myopia. First one is laser surgery and the other surgery involves placing of the corrective lens inside the eye.
FAQs on Myopia in Physics: Causes, Symptoms, and Solutions
1. What is myopia, and how is it corrected using lenses?
Myopia, also known as near-sightedness, is a common vision defect where a person can see nearby objects clearly but distant objects appear blurry. This occurs because the eye focuses images of distant objects in front of the retina, instead of directly on it. This defect is corrected by using a concave lens of an appropriate power. The concave lens diverges the incoming light rays before they reach the eye's lens, effectively moving the final focal point backward onto the retina to form a clear image.
2. From a physics perspective, what are the two main causes of myopia?
In terms of the eye's optical system, myopia is primarily caused by two physical changes to the eye:
- Excessive curvature of the eye lens: The eye's lens becomes too convex, causing it to have a shorter focal length. This increased converging power bends light rays too much, causing them to focus in front of the retina.
- Elongation of the eyeball: The eyeball becomes longer than normal. This increases the distance between the eye lens and the retina, so even with a normal focal length, the image forms before reaching the retina.
3. What are the common symptoms a person with myopia might experience?
The most common symptom of myopia is blurry vision when looking at distant objects, such as a whiteboard in a classroom or road signs. Other related signs that students might notice include:
- Frequent squinting or partially closing the eyelids in an attempt to see distant objects more clearly.
- Experiencing headaches or eye strain after trying to focus on things far away.
- Needing to sit closer to the television or the front of the classroom.
4. Why does a concave lens, and not a convex lens, correct myopia?
A concave lens is used to correct myopia because it is a diverging lens. In a myopic eye, the natural lens converges light too strongly, focusing it in front of the retina. A concave lens works by spreading out (diverging) the light rays from distant objects before they enter the eye. This initial divergence reduces the overall converging effect, allowing the eye's lens to focus the light correctly onto the retina. A convex lens, which is a converging lens, would only worsen the problem by increasing the converging power and focusing the image even further in front of the retina.
5. How is myopia different from hypermetropia?
Myopia and hypermetropia are opposite refractive errors with key differences in vision, cause, and correction:
- Vision: In myopia (near-sightedness), near objects are clear while distant objects are blurry. In hypermetropia (far-sightedness), distant objects may be clear, but near objects are blurry.
- Image Formation: In myopia, the image is formed in front of the retina. In hypermetropia, the image is formed conceptually behind the retina.
- Corrective Lens: Myopia is corrected with a concave (diverging) lens. Hypermetropia is corrected with a convex (converging) lens.
6. How is the power of a corrective lens for myopia determined and expressed?
The power of a corrective lens is measured in a unit called dioptres (D). For a myopic person, the required lens power is calculated based on their far point (the farthest distance they can see clearly). Since myopia is corrected with a concave lens, which has a negative focal length, the power of the corrective lens is always negative (e.g., -1.5 D, -3.0 D). A larger negative number signifies a higher degree of myopia and the need for a stronger lens to correct the vision.
7. How would you draw a ray diagram to show both a myopic eye and its correction?
To draw the required ray diagrams as per the CBSE syllabus for the academic year 2025-26, you would create two separate figures:
- The Myopic Eye Defect: Draw an eyeball and a convex lens to represent the eye lens. Draw at least two parallel rays coming from a distant object. Show these rays converging and meeting at a focal point in front of the retina.
- Correction of Myopia: Draw the same eyeball but place a concave lens just before the eye lens. Draw the parallel rays from the distant object first passing through the concave lens, where they will diverge slightly. Then, show these diverged rays entering the eye lens, which converges them to a sharp point exactly on the retina.
