Cornea

cornea

Cornea is the  clear window that lets light into the front of your eye. we are  going to explore several of its amazing properties first it is made out of the  same tissue as your skin so how is it  the cornea can be so clear second optically speaking the cornea supplies more than half of the focusing power of  the eye third the shape of the cornea has to be  perfectly smooth and properly curved to make the high quality image that falls  on the retina we will explore all these features in detail looking at the front of the eye .

Some parts are easy to identify you can see the iris the colored part and the pupil the round  hole in the middle of the iris the  cornea however is so clear it can only  be seen by the light reflecting off its surface this is the view we get looking through the microscope that we use to examine the eye the pupil is widely dilated with a slit beam of light passing through the cornea and lens each is outlined with dashed lines to make them easier to identify in diagram view the cornea is like the crystal of a watch arching over the iris in the center of the iris is the pupil which changes size to regulate the amount of light entering the eye and behind the iris is the natural lens like the lens in a camera  if the slit beam view was confusing at  first it should now make more sense you  can see the curved shape and thinness of  the cornea separated by a space then the rounded shape and thickness of the normal lens in the adult the average  cornea is 12 millimeters wide thickness  in the centre is half a millimeter at the edge 0.7 millimeters think about  that only half a millimeter thick  looking closer at the cornea we are taking a section and magnifying it  showing it has three distinct layers on  the outer surface is the epithelium a  lot like the surface layer of your skin  The middle layer the stroma occupies  most of the thickness of the cornea providing its shape and structural  integrity lining the inside is the  endothelium a single layer of cells that  pump fluid out of the cornea keeping it  dry and clear looking through a regular microscope you can see the actual  corneal layers and the fine cellular details we will now work our way from  front to back in detail the first thing that light encounters as it reaches your  eye is the tear film on the surface of the cornea a good-quality tear film is  important for clear vision comfort and  corneal health the tear film needs to be smooth and even say glassy as the first step of making a clear image if it is  not smooth then light is scattered and vision is reduced the tear film is more complicated than you might guess magnifying the section in the orange circle shows the tear film has three layers on the surface of the cornea is a  layer of mucus that allows the watery part to spread out over the cornea in the middle is the aqueous or watery layer on the outer surface is a layer of  oil which helps reduce evaporation so  the tear layer is more complicated and more important than you might have thought back at the microscope view we  see the outer surface layer of the cornea the epithelium in this closer  view you can see the individual cell layers which are labeled epithelial  layers typically rest on a basement  membrane that is important because that is where the epithelial layer makes its attachment to the cornea the epithelial layer is derived from the same tissue as  your skin so it behaves much like your  skin how is that  the action begins in the column shaped basal layer of cells these cells divide  and move upward into the middle layer where they take on a more flattened  wing-like shape then they reach the surface and after a short while they are Slough tauf just like dead skin cells this process takes about seven to ten days meaning the surface cells are replaced just about every week.