[Physics Class Notes] on Eye Defects and Correction Pdf for Exam

Vision is one of the most precious gifts that has been given to us by nature. The human eye is one of the five senses possessed by human beings and it is a part of the sensory nervous system, the eye reacts to light and helps humans achieve their vision. There are various accessory organs in the human eye, like the pupil, lens, retina, cornea, iris, etc. All the accessory organs of the eye work in synergy for humans to achieve their sense of vision. The human eye can see both nearby and distant objects but the working mechanism is different in both cases.  When we are looking at distant objects, the rays diverge and become parallel when they reach the eye, so to see distant objects, the concave eye lens is required because it has a large focal length, and it’s thick too. But when we are looking at nearby objects, the object rays diverge when it reaches the eye. In this case, the convex eye lens of high converging power and short focal length is required.

Most Common Eye Defects

Eye defects are a major health hazard in these times, it can be defined as the disability of ciliary muscles, these ciliary muscles are pivotal for the changing of the shape of the eye lens. The disability of the ciliary muscles can cause problems regarding image formation of any object in the retina and can lead to the defect of vision. The three most common types of eye defects seen in humans are:

• Nearsightedness or Myopia – In which distant objects are not seen clearly.

• Farsightedness or Hypermetropia – In which Nearby objects are not seen clearly.

• Presbyopia – It is generally seen in elderly age groups in which distant as well as nearby objects, both are not seen clearly.
  

What is Myopia?

When a person is not able to see distant objects clearly until the object is kept closer to the eye, it is stated as myopia. Myopia is also called nearsightedness or short-sightedness. All the nearer objects are clearly visible to myopic patients. Two issues usually cause myopia; they are:

When the image is formed in front of the retina, the person is not able to see distant objects clearly, and this happens because of the high convergence of the eye lens. 

And in the second case, that is when the eyeball gets too elongated, the retina then gets distant from the eye-lens. Over here, the eye lens has good converging power, but then also the image gets formed in front of the retina.

Because of myopia, the person gets blurry vision while driving. This defect can develop in childhood and can grow gradually or rapidly depending upon the power of the eye.  

This eye defect is overgrowing, and the most common symptoms are eye strain, fatigue, headache, and squinting. Myopia usually occurs when a person reads a book or computer closely. This can even happen to any individual who spends less time outdoors. 

How is Myopia Corrected?

If a person has nearsightedness or short-sightedness, then they are asked to wear spectacles, including a concave lens. 

A concave lens is used to treat myopic eyes because the lens diverges the parallel light rays coming from distant objects. Hence the virtual image is formed at a distant point of the myopic eye. 

And now, as the light rays are at the proper distance, the objects can be easily focused by the lens, and the image is thus formed on the retina. In simpler words, the concave lens decreases the converging power.

A myopic eye can also be treated by a refractive survey or by contact lenses. Although refractive surgeries are costly, it gives good results in the end. There are different degrees of myopia. 

The formula for calculating the power of the concave lens for correcting myopia is: 

1/image distance (v) – 1/object distance (u) = 1/focal length (f) i.e., (v-u)/f. 

Myopia Defect and Blindness

Myopia is a severe defect and can aggravate under extreme circumstances. There is a stage when myopia is at its peak, and this stage is called degenerative nearsightedness or high myopia. Although this stage is quite rare, once reached at this stage, it becomes impossible for a person to retain normalcy, and they can lose their eyesight.

The most serious complication seen in the myopic patient is cataract, retinal detachment, and glaucoma. The seriousness can be further divided into: pathological myopia, and degenerative myopia.  Among these three issues, the one which can lead to blindness is retinal detachment.

Conclusion:

The Human eye is a very sensitive organ, it has a very advanced mechanism where the human eye and its organs work in tandem with the nerves of the human mind to help with the process of image formation. There should be proper care taken of the eyes as it is the most significant sense which is necessary for our daily functioning. People who use phones and laptops for a long duration of time should use blue screens and spectacles which protect them from radiation.