Vision is obviously an essential sense to do everything in our days and we usually take it for granted. So a question I get asked all the time is “How do we actually see? What is the process of vision?”
Well the comprehensive answer is really complicated and involves lots of brain stuff but the straight forward summary is as follows:
Vision begins when light rays are reflected off an object and enter the eyes through the cornea, the transparent front window into the eye. The cornea helps focus the light rays that pass through a round hole called the pupil. The iris, or coloured portion of the eye that surrounds the pupil, opens and closes (making the pupil bigger or smaller) to regulate the amount of light passing through. The light rays then pass through the lens, which actually changes shape so it can further bend the rays and focus them on the retina at the back of the eye. The retina is a thin layer of tissue at the back of the eye that contains millions of tiny light-sensitive nerve cells called rods and cones, which are named for their distinct shapes. Cones are concentrated in the centre of the retina, in an area called the macula. In bright light conditions, cones provide clear, sharp central vision and detect colours and fine details. Rods are located outside the macula and extend all the way to the outer edge of the retina. They provide peripheral or side vision. Rods also allow the eyes to detect motion and help us see in low light and at night. These cells in the retina convert the light into electrical impulses. The rods and cones are connected to other nerve cells, which eventually feeds into the optic nerve, the eye’s “HDMI cable” that connects the eye to the brain. The optic nerve sends these impulses to the brain where an image is produced in the visual cortex, and then the fun part of interpreting shapes, colours, objects, movement etc really begins.