Sight is one of the special five senses we humans are endowed with, and perhaps the most important. Most of us take this unique faculty for granted, until something affects our capacity to see well. In some situations, we can even loose this important faculty of sight that helps us see the world around us.
To understand how the eye works, think of a camera. The camera has a lens in the front that focuses the outside world on to the film in the back or on the chip inside if it is a digital camera. Similarly, the eye functions with the natural human lens that focuses light rays reflected off objects to the back of the eye, where the ‘film’ of the eye, the retina, is located. The retina, in turn, converts these light rays into electrical impulses that are sent to the parts of the brain concerned with sight. The whole process of sight is amazingly well organized and structured. Even the most technologically advanced camera in the world cannot match the capabilities of the human eye.
The eye is a very small organ compared to other organs in the human body. An average eye measures only about 2.5 cms front to back. But compared to its size, it is difficult to even comprehend the amount of work it does for us. Every waking second, the eye can send about a billion bytes of information to the brain. It can sense around tens of millions of gradations of light and around seven million different shades of colour. It is responsible for about 75 percent of what we perceive in our lives at any given moment of time.
The retina forms the anatomic and physiologic basis for the gift of sight. It supplies over 30% of the sensory input to the brain. It gives us the power to form, dissolve and create a new image every tenth of a second. But this amazing sense organ can get diseased; it can be affected by factors such as genetic and birth defects, metabolic changes, trauma and aging. And when it does get affected, either from birth or in life, a person never develops the capacity to see, as we occasionally find in patients with Retinopathy of Prematurity (ROP), or lose this capacity to see, as in cases of Retinitis Pigmentosa (RP), Diabetic retinopathy or Macular degeneration.