Eye Defects and Correction

Hypermetropia and Myopia Defects

Light helps us to see things. The human eye is a part of the sensory nervous system, and it reacts to the light and helps humans to see. There are different accessory organs in the human eye, like the pupil, lens, retina, cornea, iris, etc. All these accessory organs work together to provide vision to human beings. Through the eye, a human can see both nearby and distant objects. But working is totally different in both cases.  

While looking at distant objects, the rays get diverged and become parallel when they reach the eye. Hence to see distant objects, the concave eye lens is required, as it has a large focal length, and it's thick too. 

But in the case of nearby objects, the object rays get diverged when it reaches the eye. Over here, the convex eye lens of high converging power and short focal length is required to focus on the image.


What is an Eye Defect?

An eye defect can be defined as the disability of ciliary muscles, which helps in changing the shape of the eye lens.  These changes can cause problems regarding the image formation of any object in the retina and can lead to the defect of vision. 


Most Common Eye Defects

There are three common types of eye defects seen in humans; they are:

  • Nearsightedness or Myopia - Distant objects are not seen clearly in this eye defect.

  • Farsightedness or Hypermetropia - Nearby objects are not seen clearly in this eye defect.

  • Presbyopia - Presbyopia is usually seen in elderly age groups, and this happens because of the weakness of ciliary muscles. 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:

  • High converging power of the lens

  • Eye-ball elongation 

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. 

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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 eye 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. 

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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.

FAQ (Frequently Asked Questions)

1. Is Nearsightedness Genetic?

There aren't any full proof reasons behind this eye defect, but there is some evidence which clearly states that myopic is inherited. As mentioned previously, nearsightedness occurs because of two reasons, high converging power or eyeballs growing too long. Myopia is not a disease but just happens because of the error in the refractive index. Genes do have some influence on myopia, but environmental factors play an important role in the development of nearsightedness. Weak vision power because of improper diet and more consumption of phones and laptops is one of the major causes.

2. Can a Person Get Nearsightedness in One Eye and Farsightedness in Another? 

This is an unusual condition, but it is seen in many cases nowadays. A person can get hypermetropia in an eye and myopia in the other one. In medical science, this condition is described as anisometropia. In anisometropia, both the eyes have different refractive powers. Both the term technically means the same. 

This condition can be detected when a person is facing an unequal blurry image from both the eyes. And this can cause severe headaches, nausea, and sometimes dizziness too. 

As there are unequal reflective errors, this situation is treated by eyeglasses.

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