The eye is a complex mechanism which should enable a lifetime of vision. It is dependent on external structures such as muscles, blood supply and nerves which all contribute to what we know as seeing, and as each year passes we understand a little more as to how these each interplay.
The eye ball is surrounded by muscles which move your eyelids, and those which rotate your eye in the direction you require. The centre of the front of your eye is the cornea which is transparent and very sensitive to touch. It is surrounded by protective sclera covered in conjunctiva (the white of your eye).
Behind the anterior chamber is the iris which regulates the amount of light getting through its centre by changing shape. Brown eyes have more pigment in their iris than blue ones, and have better adapted to brighter environments.
Then there is the crystalline lens which further bends light toward your macula. It’s shape is changed when the ring of muscle surrounding it is contracted and this mechanism is called accommodation. From your teens this reduces and in your forties it causes presbyopia which prevents sustained near focus in those who can clearly see in the distance. This lens slowly yellows with time, and opacities which then develop are called cataract.
The vitreous chamber is made of transparent gel, extends from the lens to the retina, and this contracts and creates floaters with time.
The macula is the posterior area of your retina, and the fovea is the spot within it where your central sight is focused.
The optic nerve is to its side, bringing with it from behind the blood supply to the retina, and forming your natural blind spot. This may change shape in glaucoma or in other neurological problems so is also carefully monitored.