eye lens (lat. lens ) is a transparent body located in the eye directly behind the iris, in front of the vitreous body, and occupies most of the posterior chamber.
Seen from the front, it is round, and seen in cross-section, oval (biconvex). It is built, looking from the outside in, from the capsule, epithelial cells and lens cells (fibrils), which in the anatomical sense make up the core (nucleus) and cortex (cortex) of the lens, and in total it consists of 65% water and 35% proteins and very little other substances.
The lens represents the main optical “device” of our eye due to its two properties.
First, it is completely transparent, so it easily passes light to the retina.
Second, since the lens is elastic, by stretching the zonules that are attached to its equator, the lens changes its shape and thus focuses the dioptric power of the light rays on the retina.
When seeing near, accommodation is used. Ciliary muscle and zonular fibers relax. The capsule, due to the elasticity of the lens, changes shape and increases its refractive power depending on age.
Over the course of life, the accommodation power of the lens weakens, the lens loses its elasticity and there are difficulties when looking at close-up ( Presbyiopia ).
Physical properties of the eye lens:
The refractive power (dioptric power) of the lens at rest is +19 D.
During accommodation, the diopter of the lens changes up to a maximum of +33 D.
Other lens parameters:
- diameter – 10 mm
- thickness – 4 mm
- radius of curvature of the front surface at rest – 10 mm
- radius of curvature of the front surface in accommodation – 6 mm
- radius of curvature of the rear surface at rest – 6 mm
- radius of curvature of the rear surface in accommodation – 5.5 mm
- refractive index – 1.42
The lens itself does not contain blood vessels or nerves, and is nourished by the aqueous humor.
With aging, the lens loses water, thickens, increases the specific gravity, becomes more rigid, the nucleus of the lens increases, and the cortex shrinks, which causes myopia.
We call an eye with a lens phakic, without a lens aphakic, and with an artificial lens a pseudophakic eye.
Eye lens search
Pathological changes of the eye lens occur in the form of clouding (cataract), disturbed position (subluxation and luxation) and accommodation disorders.
When the lens loses the support normally provided by the zonular fibers, it moves forward or backward. Such conditions are called subluxation.
When the lens is completely displaced forward into the anterior chamber or backward into the vitreous, it is a luxation.
The lens can be inspected:
- Using a magnifying glass
- Using a biomicroscope
- By illuminating the pupil with an ophthalmoscope
- With an ultrasound machine
Every clouding of the eye lens can be divided according to the time and cause of its occurrence.
According to the time of creation:
- Innate
- Mladenačka
- An old woman
According to the cause of occurrence:
- Traumatic
- Electric
- Thermal
- Radiation
- Diabetic
- Cortisone
- Cataracts in Down’s syndrome
Cataract treatment:
Surgery is the only and completely successful method of treatment. It is mostly performed under local, and rarely under general anesthesia.
Autor:
bc. Livio Svržnjak, optometrist
