
* Attention! contains optical terms and concepts.
The optical system of the eye
It consists of the cornea, intraocular fluid and lens. After the lens, the light rays spread into the vitreous body and give an image on the retina. The resulting images are real and inverted. The straightening of the image is done with the help of the brain. When an imperfection appears, the need for glasses also appears in some of the elements. Therefore, we will introduce you to these three main elements.Cornea
It represents 1/6 of the outer shell of the eyeball, it lacks blood vessels. It is nourished by the vascular network located around it. It is transparent and provides mechanical protection to the adjacent tissues. It is formed in the fifth month of intrauterine development. It has a refractive power of 45 diopters. The cornea protects us from UVB rays. The most important part of it is the middle 1/3, since the optical and visual axes of the eye pass through there. The refractive index of the cornea is 1.37, and the radius of curvature is approximately 7.8mm. The curvature of the cornea plays an important role in your choice of contact lenses. It is good that your curvature matches that of the lenses, so that you feel maximum comfort. There are devices in optics that, with the help of doctors, can measure this value. In corneal diseases such as keratoconus (the cornea progressively deforms and thins, taking on an irregular cone-shaped shape), hard contact lenses are used to maintain its correct shape.Intraocular fluid
It fills the eye chambers. Its refractive power is related to that of the cornea. These two elements are the first part of the optical system of the eye.The intraocular lens
is transparent and biconvex, with different radii of curvature, its flatter side facing the iris. Made of band-shaped cells, it has a weight of about 180 g and the highest protein content (~ 35%). It is rich in calcium and phosphorus. It has a refractive power of about 19 diopters. It absorbs UVA rays. In young people, the lens is more elastic. With age, this elasticity decreases. An interesting fact is that our eye remains the same size as at birth, but it still ages and changes constantly. There are people who are born without an intraocular lens, this disease is called aphakia. The optical system of the eye is not ideal. It has small defects that are usually not corrected.Optical defects of the eye
- Deviations in the sphericity of the surface of the cornea and lens. In these deviations, the centers/vertices of the optical surfaces do not lie exactly on the optical axis.
- Astigmatism of oblique rays. It is due to the fact that the optical and visual axes do not coincide, as a result of which the images on the retina are deformed and unclear.
- Spherical aberration. This defect occurs with a wider pupil. It is compensated by the flatter peripheral part of the cornea.
- Chromatic aberration. It is due to the dispersion of light. It is compensated by the pigment of the "yellow spot". It absorbs blue-violet rays.
- Irradiation, as a result of which the images on the retina are not sharp. There are two types: positive (in this case, dark objects on a light background appear smaller) and negative (here, light objects on a dark background appear smaller)