Vision Defects: Myopia and Hypermetropia
If you wear spectacles or if you’ve been to an eye doctor you might have heard these terms myopia or nearsightedness, hypermetropia or farsightedness these are the most common vision defects and in this article, we’ll discuss what they mean and how they are corrected
Let’s start with some interesting facts:
Did you know that the first spectacles eyeglasses were made in northern Italy about 730 years back in 1290
Do you know that about thirty-five percent of the world’s population has nearsightedness and it’s expected to grow it’s predicted by 2050 that 50% of the world’s population so that’s half the population will have nearsightedness.
Another interesting fact is that by the age of 65 more than 90% of people have cataracts where the eye lens becomes cloudy since these vision defects are so common we need to be aware of them.
Human Eye
Our eye is like an autofocus camera which means that the eye has the ability to focus the light rays coming from far away objects and nearby objects this ability is known as the power of accommodation.
When we look at something our eye lens focuses the light rays on our retina so that we can see the object clearly so for the normal eye that is a person who does not need to wear spectacles he or she can clearly see distant objects as well as nearby objects.
for example, if he’s looking at a tree that is far away the branches and the leaves appear clear to him the tree does not look blurred and of course he can’t see every detail of every small leaf on the tree but overall the tree appears clear to him not blurred.
Similarly, if he’s sitting at the back of a big classroom he can easily read the writing on the board the letters written on the board appear clear to him not blurred.
How far can the normal eye see clearly?
The answer is infinity for example if the person is seeing very far of things like mountains and clouds even though he can’t see every detail but they appear clear to him, not blood so the far point of the normal eye is at infinity.
Now about nearby objects like reading a book a person who has a normal eye can clearly see nearby objects like a book the words and letters in the book appear clear to him so he can comfortably read the book.
Do you know how close can you bring the book and it still appears clear?
Answer: For the normal eye the closest distance is about 25 centimeters now if you bring the book closer than 25 centimeters then it will appear blurred so the near point of the normal eye is at 25 centimeters
Now let’s talk about the people who wear spectacle,
People wear spectacles so that they can see clearly because without their glasses they can’t see clearly. Things appear blurry or hazy to them but all people with glasses don’t have the same type of eye defects
Two most common vision defects:
- Myopia.
- Hypermetropia.
Myopia is commonly known as short-sightedness or nearsightedness.
A person who is myopia can see nearby objects clearly but he can’t see the distant objects clearly. That is why it’s called nearsightedness to see distant objects clearly he needs spectacles for nearby objects.
Let’s use the example of reading a book and for a faraway distant object let’s say the person is sitting at the back of a big classroom.
He’s looking at the writing on the board for a person with a normal eye both the nearby book and the distant board appear clear. But for a person with myopia, the nearby book is clear but the writing on the distant board appears hazy or blurry.
Most of the students in the school who wear spectacles have myopia shortsightedness and myopia is corrected using a concave lens.
Hypermetropia meaning: Hypermetropia is commonly known as long-sightedness or farsightedness it’s also known as hyperopia.
Let’s understand with an example, For a person with a normal eye, both the nearby book and the distant board appear clear. For a person with myopia, the nearby book is clear but the writing on the distant board appears hazy blurry.
Hypermetropia is the opposite of myopia. So for a person with farsightedness, the nearby book appears blurry but the writing on the distant board appears clear.
A person who is hypermetropia can see distant objects clearly. But he can’t see nearby objects clearly to see nearby objects clearly he needs to wear spectacles or contact lenses. Farsightedness eye defects can be corrected by using a convex lens.
