Vision ( ESSAY )

Nearly 70% of all the sensory receptors of your whole body are in the eyes, so it's important to "see" what's going on and what does our eye looks like, right? But the fascinating thing about our eye doesn't end there. In order for you to see, perceive, or recognize anything, nearly half of your entire cerebral cortex has to get involved. Vision is considered the dominant sense of humans, and while we can get along without it, and it can be tricked, what you are about to learn is NOT an illusion.
When I talk about your sense of hearing, I started with the mechanics of sound, and now is not going to be any different. Light is electromagnetic radiation travelling in waves. Remember how the pitch and loudness of a sound is determined by the frequency and amplitude of it's waves? Well, it's similar with light, except that the frequency of a light wave determines the hue, while the amplitude of the light wave determines its brightness. We register short waves at high frequency as bluish color, while long, low frequencies look reddish to us. Meanwhile that red would look dull and muted at low amplitude, while if the amplitude are high it would look bright to us. But the visible light we are able to see are only a tiny chunk of the whole electromagnetic spectrum, ranging from super tiny gamma rays, to super long radio waves. Some of the first things that you will notice if you look at an average pair of eyes, are all the outer things that are created to help protect your eyes from the outside world : the eyebrows, that help keep your sweat away from your eyes; the super-sensitive eyelashes, that trigger reflexive blinking; your eyelids; the tear-producing lacrimal apparatus. The eyeball itself are irregularly spherical, with an adult diameter of about 2.5 centimeters. It's essentially hollow, full of fluids that help keep it's shape, and you can only see about the anterior sixth of the whole ball. The rest of it is safely tucked into a pocket of protective fat, tethered down by six strap-like extrinsic eye muscles, and jammed into the bony orbit of your skull. Your eye's wall is made up of three distinct layers : the fibrous, vascular, and inner layers. The outermost fibrous layer is made of connective tissue. Most of it is that white stuff called the sclera, while the most anterior part is the transparent cornea. The cornea is like the window that lets light in. Going little deeper, there's the posterior choroid, the one that supply all the layers with blood. In the interior, there is also the ciliary body, a ring of muscle tissue that surrounds the lens, but off course the most famous part of the vascular layer is the iris, which is that distinctive colored part of the eye that makes your eye different from anybody else in the world's eye. The pupil is an opening in the iris that let's light in. The opening in the iris is controlled by sphincter muscles, that control how much light gets into your eyes. Light comes in through the cornea and pupil and hits the lens, the transparent, convex disc that focuses that light and projects it onto the retina, which makes up the inner layer at the back of the eyeball. The retina itself has two layers, the outer pigmented layer that helps absorb light so it doesn't scatter around in the eye, and also the inner neural layer.