Eyes facet: how are they different from simple?

In the evolution of vision, some animals have rather complicated optical instruments. To such, certainly, it is possible to carry eyes фасеточные. They formed in insects and crustaceans, some arthropods and invertebrates. What distinguishes the faceted eye from simple, what are its main functions? We'll talk about this in our today's material.

Eyes Faceted

This is an optical system, raster, where there is no single retina. And all the receptors are combined into small retinules (groups), forming a convex layer that does not contain any more nerve endings. Thus, the eye consists of a set of separate units - ommatidia, united in a common system of vision.

Eyes facet, inherent, for example, insects, differ from binocular (inherent, including in humans) poor definition of small parts. But they are able to distinguish between light vibrations (up to 300 Hz), whereas for humans, the limiting possibilities are 50 Hz. And the membrane of this type of eye has a tubular structure. In view of this, faceted eyes do not have such features of refraction as hyperopia or nearsightedness, for them the concept of accommodation is inapplicable.

Some features of structure and vision

In many insects, the organs of vision occupy most of the head and are actually immobile. For example, faceted eyes in a dragonfly consist of 30 000 particles, forming a complex structure. The butterflies have 17 000 ommatidia, the fly has 4 thousand, the bee has 5. The smallest number of particles in the worker's ant is 100 pieces.

Binocular or facet?

The first type of vision allows you to perceive the volume of objects, their small details, evaluate the distances to objects and their location relative to each other. However, binocular vision of a person is limited to an angle of 45 degrees. If the review is needed more complete, the eyeball moves at the reflex level (or we turn our head around the axis). Faceted eyes in the form of hemispheres with ommatidia allow to see the surrounding reality from all sides, without turning the organs of vision or the head. And the image that transmits the eye is very similar to a mosaic: one structural unit of the eye perceives a separate element, and together they are responsible for recreating the full picture.

Varieties

Ommatidia have anatomical features, as a result of which their optical properties (for example, in different insects) differ. Scientists define three kinds of facets:

1. Apposition. Such complex facetted eyes are present in daytime insects. The pigment, which does not have transparent properties, separates the facets - the particles that are near. And the eye receptors can only perceive light that coincides with the axis of a certain ommatidia.
2. Optosuperpositional. Such complex faceted eyes have some crustaceans, as well as nocturnal and twilight insects. The pigment contained in the eye alternately isolates the ommatidia, moving, which increases the sensitivity of the eye in low light.
3. Neurosuperpositional. Different ommatidia sum up the signal coming from one point in space.

By the way, some insect species have a mixed type of faceted vision organs, and many, besides those we are considering, have also simple eyes. For example, the fly has, for example, paired facet organs of rather large sizes on the sides of the head. And on the crown there are three simple eyes, performing auxiliary functions. The same organization of the organs of sight and the bee - that is, only five eyes!

In some crustaceans, the facetted eyes seem to sit on mobile stems-stems.

And some amphibians and fish have an additional (parietal) eye, which distinguishes light, but has objective vision. The retina is composed only of cells and receptors.

Modern scientific developments

Recently, faceted eyes are the subject of study and enthusiasm of scientists. After all, such visual organs, in view of their original structure, give the ground for scientific inventions and research in the world of modern optics. The main advantages are a wide overview of the space, the development of artificial facets used primarily in miniature, compact, secret surveillance systems.