Talk:Compound eye

From Wikipedia, the free encyclopedia

	This article is within the scope of WikiProject Arthropods, a collaborative effort to improve and expand Wikipedia's coverage of arthropods. If you would like to participate, visit the project page where you can join the project and/or contribute to discussion.
B	This article has been rated as B-class on the quality scale.
Mid	This article has been rated as Mid-importance on the importance scale.
Article Grading: The following comments were left by the quality and importance raters: (edit · refresh) I think that there should be more sections than just "Types". Maybe "structure", "evolution", etc. IronChris | (talk) 21:23, 15 November 2006 (UTC)

[edit] Aperture limitation of resolution

Unless the phases of a light wave in different ommatidia can be compared to form a phased array, which seem unlikely, diffraction limits the resolution (in radians) to about the wave length divided by twice the lens diameter. This makes this type of eye surprising in small animals. Sensitivity to ultraviolet is some help here. I am not sure that this belongs in the article at this time. David R. Ingham 01:39, 1 July 2006 (UTC)

{If any bug has clearer vision than this limit, that would seem to imply that its nervous system were something like a quantum computer. Classical descriptions do not preserve phase information of individual photons. If the output of an ommatidia is describable classically, then the photon is described as being received in only one ommatidia and relative phase is not measured. David R. Ingham 04:27, 1 July 2006 (UTC)}

[edit] Trilobite eyes

I love to see something about the eyes of trilobites or other arthopods. Right now it seems focused almost exclusively on insects. Eluchil404 07:51, 12 July 2006 (UTC)

[edit] Types of compound eyes

• Compound eyes: Compound eyes are composed of many light-sensitive elements, each having its own refractive system and each forming a portion of an image [1]. Compared with single-aperature eyes, they have poor resolution, but a very large view angle, polarization, or fast movement detection often make up for the lack of resolution [2]. Compound eyes are typically classified as either apposition eyes, that form multiple inverted images, or superposition eyes, that form a single erect image[3]. In the superposition compound eye each rhabdom (light sensitive unit) receives light through many ommatidial facets, while in the apposition compound eye every rhabdom receives light from a single facet[4]. Species: Compound eyes are found in a large number of arthropods, including various species of insects, crustaceans, centipedes, and millipedes [5] as well as a few species of annelids and mollusks [6]. Trilobites, an extinct class of arthropods, also utilized various types of compound eyes. A combination of both types of compound eyes is used in some insects [7]. The various types of compound eyes (apposition and all three superposition types) are present in all crustacean classes except Copepoda [8].

• Apposition eyes: Apposition eyes consist of an array of individual units with a single lens and photoreceptor called ommatidia. Each ommatidium gathers light from a small part of the visual field [9]. This type of eye allows for reasonably high resolution but low sensitivity[10]. There are two types of apposition eyes: the typical apposition eye and the neural superposition eye. Species: Apposition eyes are found in Drosophila, many diurnal insects, shallow-water and terrestrial crabs, lower crustacea, and the Limulus horseshoe crab [11][12] [13].

• Apposition eye (typical)

• Neural superposition eye, or schizochroal eyes: Neural superposition eyes are identical to the typical apposition eye in that each lens forms an image on the rhabdom, but the images are combined in the brain. Species: Neural superposition eyes are found in Strepsiptera and dipteran flies [14].

• Superposition eyes or clear zone eyes: In superposition eyes, the light from multiple facets combines on the surface of the photoreceptor layer to form a single erect image of the object. Compared to apposition eyes, the superposition eye is much more light sensitive [15] [16][17]. In these types of eyes, the dioptric apparatus and the rhabdom layer are separated by an unpigmented clear zone. This permits, in theory, the superposition of light from a number of corneal facets onto a single rhabdom [18]. There are three types of superposition eyes: refracting superposition eyes, reflecting superposition eyes, or parabolic superposition eyes. Many ommatidia contribute to a deep-lying erect image [19]. Species: Superposition eyes are found in nocturnal insects such as neuropteran flies and moths as well as deep-water crustaceans and crabs [20][21][22].

• Refracting superposition eyes: Refracting superposition eyes have lenses which are spherical in shape, causing the light to be bent into fewer convergence points on the retina, creating a much higher quality image[23]. Species: Refracting superposition eyes are found in insects, including the Hummingbird hawkmoth, and euphausid crustaceans (krill) [24][25].

• Reflecting superposition eyes: In reflecting superposition eyes, the lenses are rectangular in shape, so light is not bent through each of them, rather it is reflected creating multiple convergence points on the retina [26]. Species: Reflecting superposition eyes are found only in most long-bodied decapod crustaceans such as crayfish, lobsters, and shrimp [27][28][29].

• Parabolic superposition eyes: In parabolic superposition eyes, the ommatidia are shaped much like lightbulbs, with the larger end facing outward. Light is processed in a similar fashion as with the refracting superposition eye, however, not to such a precise degree [30]. Species: Parabolic superposition eyes are found in swimming crabs and hermit crabs [31][32].

---

I'm posting the above information here for future reference. I may try to work it into the article later. -AED 05:30, 29 September 2006 (UTC)