Lens of the eye

Synonyms

Lens oculi

Introduction

The lens is a part of the ocular apparatus, is located behind the pupil and, together with other structures, is responsible for the refraction of the incoming light beam. It is elastic and can be actively curved by muscles. This allows the refractive power to be adjusted to different requirements. With age, the inherent elasticity and transparency decrease.

Classification of the lens

  • Inner lens core
  • Lens Bark
  • Lens capsule
  • Suspension and accommodation apparatus

Anatomy of the lens of the eye

The lens is located behind the pupil of the eye. The lens is encased in a lens capsule. The inside of the lens is divided into a lens cortex (outside) and a lens core (inside).

Lens cortex and lens core contain the lens fibers. On the inside of the anterior lens capsule and at the lens equator are cells (lens epithelial cells) which form lens fibers for a lifetime. The fibers attach themselves from the outside in a shell-like manner to the already existing fibers, release more and more water over time and thus become thinner and thinner.

This creates the lens core, which is denser and harder. The lens is subject to age-related changes, so it becomes larger and harder. This results in a loss of inherent elasticity, which leads to a certain degree of presbyopia in every person.

In the course of life, the weight of the lens can increase fivefold. The diameter of the lens is about 8 – 10 mm, it is about 2 – 5 mm thick and transparent. It is biconvex and slightly more curved in the back than in the front. The rear part of the lens borders on the vitreous body.

Lens composition

The lens is composed of about 60% proteins, which consist of dense, stable crystals. The remaining 40% contain water. The crystallines provide stability against protein destruction (denaturation).

Furthermore, the lens has a high content of vitamin C (ascorbic acid) and certain enzymes, which provide a certain “stress resistance” (anti-oxidative). The high water content ensures transparency and, like the refractive power or elasticity, decreases over the course of life. Thus, with age, the lens also becomes cloudy.

The lens is fed by the aqueous humor. The crystals are negatively charged, so that positively charged salts (cations) are the most important. The lens epithelium has a pump that transports potassium into the lens and sodium back into the aqueous humor. The lens contains no nerves and no blood vessels.