Eyes

By Dr. Veena G.D., MBBS, DOMS

“Sarve-indriyanam Netram Pradhanam” (in Sanskrit) meaning out of the five Sense Organs (Indriyas), that we have, eyes are the most precious ones. Eyes are the windows of one’s soul. Sparkling eyes always make a person look more beautiful. It strikes us only when we see a blind person across the street and we thank God for we are blessed with vision. Eye Care is a serious concern that is often neglected by people who lack health consciousness. We surely need to protect and take good care of our eyes.

As eyes are the sense organs connecting you to the outer world, humans learn to react to any stimulus by first visualizing them. Eyes are fully developed at the time of birth. The pair of eye works in tandem (together) so that right and left eye vision are fused in the brain level and perceived as one single image. A normal human being has a good day and night vision.

Section of Human Eye                                                                Normal Retina

Eye is a Spheroid structure with Cornea as the transparent part. Underneath the cornea the aperture like structure Iris is situated which gives color to the eyes. The crystalline natural lens is situated behind the iris which is suspended by Zonules or suspensory ligaments. Zonule helps in supporting the lens and changing the curvature depending upon the focus. If the image is near, the pupil (iris aperture) will dilate and if the image is far it constricts. This further falls on sensory screen called retina. Retina is a network of millions of minute visual sensory nerve cells which are regrouped and the optic nerve is formed which carries the visual stimulus to brain to be perceived. It is similar to optic fiber carrying images. Eyes are composed of more than two million working parts. An eyeball measures about 1 inch (2.5 cm) in diameter of which only the front portion is exposed. Eyeball is encased in a boney socket called orbit in the skull. It is provided with two lids, the upper lid is strong and muscular and broader in the center while the lower lid is hemispherical, smaller and weaker than the upper lid. Both the lid margins have eyelashes which helps protecting the eye.

Seeing the light or color - The physical stimulus that is responsible for the sensation of color is the wavelength of the radiation. Wavelength in the region around 460 nm produces blue color, around 520 nm green while around 650 nm red. A mixture of wavelengths such as which occurs in sunlight, produces a white hue. It is also worth noting that object appear as a particular color because they preferentially reflect wavelength of that color and absorb the other wavelengths.