Everything about Compound Eye totally explained
A
compound eye is a visual
organ found in
arthropods such as
insects and
crustaceans. It consists of one to thousands of
ommatidia which are tiny independent photoreception units that consist of a
cornea,
lens, and
photoreceptor cells which distinguish brightness and color. The image perceived by the arthropod is a combination of inputs from the numerous ommatidia, which are oriented to point in slightly different directions. Compared with single-aperture
eyes, compound eyes have poor
image resolution; however, they possess a very large view angle and the ability to detect fast movement and, in some cases, the
polarization of light.
Types
Compound eyes are typically classified as either apposition eyes, that form multiple inverted images, or superposition eyes, that form a single erect image.
Apposition eyes
Apposition eyes can be divided into two groups. The typical apposition eye has a lens focusing light from one direction on the
rhabdom, while light from other directions is absorbed by the dark wall of the ommatidium. The
mantis shrimp is the most advanced example of an animal with this type of eye. In the other kind of apposition eye, found in the
Strepsiptera, each lens forms an image, and the images are combined in the brain. This is called the schizochroal compound eye or the neural superposition eye (which, despite its name, is a form of the apposition eye).
Superposition eyes
The second type is named the superposition eye. The superposition eye is divided into three types; the refracting, the reflecting and the parabolic superposition eye. The refracting superposition eye has a gap between the lens and the rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it to the same angle on the other side. The result is an image at half the radius of the eye, which is where the tips of the rhabdoms are. This kind is used mostly by nocturnal insects. In the parabolic superposition compound eye type, seen in arthropods such as
mayflies, the parabolic surfaces of the inside of each facet focus light from a reflector to a sensor array. Long-bodied decapod crustaceans such as
shrimp,
prawns,
crayfish and
lobsters are alone in having reflecting superposition eyes, which also has a transparent gap but uses corner
mirrors instead of lenses.
Other
Good fliers like flies or honey bees, or prey-catching insects like
praying mantis or
dragonflies, have specialized zones of ommatidia organized into a fovea area which gives acute vision. In the acute zone the eye are flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution.
There are some exceptions from the types mentioned above. Some insects have a so-called single lens compound eye, a transitional type which is something between a superposition type of the multi-lens compound eye and the single lens eye found in animals with simple eyes. Then there's the
mysid shrimp
Dioptromysis paucispinosa. The shrimp has an eye of the refracting superposition type, in the rear behind this in each eye there's a single large facet that's three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an upright image on a specialized retina. The resulting eye is a mixture of a simple eye within a compound eye.
Another version is the pseudofaceted eye, as seen in
Scutigera. This type of eye consists of a cluster of numerous
ocelli on each side of the head, organized in a way that resembles a true compound eye.
The body of
Ophiocoma wendtii, a type of
brittle star, is covered with ommatidia, turning its whole skin into a compound eye.
Further Information
Get more info on 'Compound Eye'.
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