Eyeballs

Parts of the eye

• Sclera - The white of the eye
• Cornea is the clear outer layer of the eye through which you can see the Iris and Pupil. It has an Index of Refraction of 1.376, and a curved outer surface, contributing to the refractive state of the eye. The Cornea provides about 80% of the eye's total refracting power. If you have LASIK or PRK surgery it thins the cornea to change your refractive state.
• Aqueous humor - the fluid supporting the cornea
• Pupil - the hole where light enters the eye
• Iris - the Iris is the colored part of the eyeball that contains the muscles that control the opening size of the pupil.
• Ciliary muscle is a ring of muscle fibers in the eye that control the tendons supporting the natural lens of the eye, and controls the flow of aqueous humor behind the cornea. The Ciliary muscle is controlled by the Ciliary ganglion, which is a complex intersection of several nerve systems. The action of the ciliary muscle is the primary source of accommodation and ciliary spasm which causes pseudomyopia.
• Lens - The part that changes the focus distance of the eye
• Rods and cones - the sensory cells of the eye that see light intensity and color
• Retina - the tissue that supports the rods and cones.
• Vitreous humor is the clear gel filling the majority of the eyeball. It is where true floaters live. This gel is important for helping the eye hold its shape and maintain the correct pressures inside the eye even when air pressure changes. In adults, the gel has a complex structure, with different thicknesses in different parts.
• Vitreous detachment is attached to the outer wall of the eye in multiple locations, but can become separated. When separated from the retina it does not support the retina fully, and puts you at higher risk for retinal detachment. It can also leave behind a large floater that impairs vision.

Axial Length

The primary cause of differences in refractive state is the length of the eye, referred to as axial length, relative to the focusing power. Long eyeballs are associated with myopia, as the natural lens of the eye focuses light too far forward of the retina.