The eye is one of the most complex organs in the human body and is composed of over 2 million working parts. These individual structures must work together to produce clear vision. ?
As you’re reading this, light first enters your eye through the cornea, a clear curved layer, found in front of the iris and pupil. It acts as a protective covering and is the most powerful structure in the eye for focusing light.
From the cornea, light is directed through the pupil.
The iris controls the amount of light that enters the eye by changing the diameter of the pupil. These actions are regulated by two involuntary muscles; the sphincter papillae and dilator papillae muscles. ?
Behind the iris is the lens, a biconvex transparent structure regulated by the ciliary muscles. The convexity of the lens fine-tunes the focus of the objects onto the retina, and allows us to see things that are both up close or at a distance. ?
The retina forms the inner layer of the eyeball. It is a thin, delicate transparent sheet containing photoreceptors and blood vessels.
The most sensitive part of the retina is the macula, which contains the cones (a type of photoreceptor). Cones are responsible for sharp, detailed central vision and colour vision. Rods are another type of photoreceptor which are found clustered in the peripheral areas of the retina. These are more numerous and much more sensitive to light, but do not register colour or contribute to detailed vision. ?
Each photoreceptor is linked to a nerve fibre. These fibers are bundled together to form the optic nerve. The photoreceptors are responsible for translating light photons into electrical action potentials, which are passed along the optic nerve to eventually reach the occipital lobe of the cerebral cortex. This is where visual information is processed by the brain. ?
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