A Botany graduate, Nithya Venkat enjoys researching and writing about topics that interest her.
Eyesight is all about how well your eye can see and the distance you can see clearly. These two parameters play a significant role in determining the clarity of vision.
Structure of the Human Eye
The eyeball is similar to the shape of a rubber ball. The eyeball should have a smooth curvature of the cornea and lens for clear vision.
The human eye has two parts that help to focus – the cornea and lens -
Cornea – The cornea is the transparent front part of the eye that transmits light into the eye.
Lens – The lens is a transparent structure inside the eye. The lens helps to focus light onto the retina. The retina is a layer of nerves at the back of the eye that senses light and creates impulses sent to the brain through the optic nerve.
The optic nerve is the nerve that connects the eye to the brain. The optic nerve carries impulses from the retina to the brain. The brain then interprets them as images.
The following are conditions that can affect the eye -
Myopia or Shortsight
A person affected by myopia or short sight can see objects near clearly than objects far away from the eye.
When a person has short sight, the eyeball changes shape, and it becomes egg-shaped and elongated. Due to this change in shape, the rays of light entering the eye do not fall on the retina; instead, the light rays are focused in front of the retina that causes blurry vision.
Change in the eyeball shape may be due to genetics, any illness, or due to eyes' over-exertion.
Hypermetropia or Longsight
Long sight is also called hyperopia or hypermetropia. A person with this disorder cannot focus on objects near the eye but can see objects that are far away from the eye very clearly. This condition often starts during childhood.
Long sight occurs when the eyeball is too short or when the cornea does not have the proper curvature.
Long sight can also occur when the lens is not thick enough for clear vision. When the lens is not sufficiently thick, the light rays fall on the retina's back, making the object look blurred.
Astigmatism is a disorder of the eye that occurs when the lens's surface inside the eye is not even and smooth. Astigmatism blurs eye vision at all distances (near, far, or mid-distance). Astigmatism is often present at birth or can be the combination of short sight and long sight.
Presbyopia is a disorder of the eye that occurs with age. As you grow old, the lens in the eye thickens and loses elasticity. The muscles surrounding the lenses become very weak. These changes decrease the ability of the eye to focus clearly. Presbyopia can be detected by routine eye examination.
Types of Spectacles
Spectacles help to correct eye disorders and aid clear vision. There are different types of spectacles -
Bifocal Spectacles – The lens in the bifocal spectacles is divided into two by a demarcating line. The demarcating line is aligned to the lower eyelid. The portion of the lens above the demarcating line helps to correct distant vision, and the portion below the demarcating line helps to correct near vision.
Trifocal Spectacles or Progressive Spectacles – Trifocal spectacles, the lens has three portions. The upper part corrects long-distance vision, the middle part corrects median distance vision, and the lower part corrects near vision.
Monovision Spectacles - Monovision spectacles help to correct long-distance vision or short-distance vision but not both.
You can opt for separate spectacles, one for short-distance vision and another for long-distance vision.
The human eye can be affected by disorders such as Short sight, Long sight, Astigmatism, Myopia, and Hypermetropia. These eye disorders can be corrected by wearing spectacles or through corrective surgery.
© 2012 Nithya Venkat
Nithya Venkat (author) from Dubai on July 17, 2018:
Eye surgery is one option but glasses are just fine. I wear them too.
Mary Norton from Ontario, Canada on July 16, 2018:
I had been wearing glasses for years. My sister had eye surgery but I hesitate to have one. I am just fine with the glasses.
Nithya Venkat (author) from Dubai on February 16, 2013:
Jools99 thank you for stopping by and reading. Much appreciated.
Jools Hogg from North-East UK on February 16, 2013:
Very comprehensive and useful hub - thankfully, I had my glasses on (I am long-sighted) and was able to read it very clearly :o)
Nithya Venkat (author) from Dubai on June 18, 2012:
jpmc thank you, optometrist and opticians are the best people to get advise from for eye care.
JP Carlos from Quezon CIty, Phlippines on June 17, 2012:
I used to work for an eye care and eye wear company in the Philippines. I got to spend time with optometrist and opticians and get lots of advise on eye care. It pays to have an optometrist and optician as friends. :)