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* Attention! contains optical terms and concepts.
The cornea is part of the optical system of the eye. And that means it plays an important role in what and how we see.
Today's topic is a little more complicated, but an invariable part of the life of every optician, and also a person.
Through knowledge of the structure of the human eye, we can understand why some users feel bad when wearing contact lenses or cannot see clearly enough without glasses.
Main characteristics of the cornea
- The cornea is 1/6 of the outer shell of the eyeball.
- It is the more prominent part of the eye and is transparent.
- Its radius is about 8 mm.
- The thickness of the cornea along the axis is 0.8 mm, and in the periphery 1.2 mm.
- There are no blood vessels. It feeds on the vascular network located around it.
- Provides mechanical protection of adjacent tissues.
- The refractive power of the cornea is 45 dpt
- The cornea protects the eye from UVB rays, which have a wavelength of 280-318 nm.
- The place where the cornea passes into the sclera is called the limbus.
Structure of the cornea
The cornea consists of 5 layers: epithelium, Baumann's membrane, stroma, descement membrane and endothelium.
The outermost layer of the cornea consists of 5-7 layers. The epithelium is made up of several types of cells. Two types of these surface cells have been proven - small and light, and large and dark.
The corneal epithelium renews itself in about 7 days.
If you wear contact lenses, this is the layer that is in direct contact with them. Defects on the epithelium are restored for a certain time. For example, 6 square millimeters - in 48 hours.
The epithelium consumes 10 times more oxygen than the stroma.
This second layer is of small thickness. Through it pass the superficial nerve fibers that spread in the epithelial layer. If Baumann's membrane is injured, it cannot be repaired.
It represents 90% of the thickness of the cornea. If its integrity is violated, full recovery is impossible.
According to modern theory, the stroma is a refraction grating, the components of which are commensurate with lambda (a unit for measuring wavelength in physics).
At birth, this membrane is at its thinnest. It thickens with age. The greatest thickness is in the periphery. Descement membrane is very resistant.
The correct functioning of the endothelium ensures the transparency of the cornea. If injured, he fully recovers.
The cornea has a high sensitivity, which decreases with age.
The necessary oxygen was obtained from the atmosphere, through the tear film.
At aphakic eyes (absence of the eye lens in the eye) the level of oxygen in the anterior chamber fluid is significantly increased. Therefore, in such conditions, the lenses may be of lower oxygen permeability.
It is important to know that contact lenses reduce the sensitivity of the cornea. This is what is considered adaptation to contact lenses. Accordingly, people with sensitive corneas are unlikely to get used to contact lenses.
It is curious to know that corneal astigmatism exists. It is due to different refraction of the cornea in its sections. The cause may be corneal deformation or intraocular pressure.
Deformation of the cornea occurs, sometimes, as a consequence of blinking movements.
So now that we've learned all that, it's time to let the information sink in a bit, and read it again if needed.
And if you are not an optician and you came across our article, you can easily use the knowledge to enrich your general culture or to solve a crossword puzzle.
However, does a person know when, what he will need.
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