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[[Image:Panther_Chameleon.jpg|300px|thumb|right|'''Panther chameleon spectacle''' (© Tom Junek, Wikimedia Commons)]]

[[Image:Panther_Chameleon.jpg|300px|thumb|right|'''Panther chameleon spectacle''' (© Tom Junek, Wikimedia Commons)]]

[[Image:Lizard_skull_mandible.jpg|150px|thumb|right|'''Parietal eye on the dorsum of the head''' (Copyright © RVC)]]

[[Image:Lizard_skull_mandible.jpg|150px|thumb|right|'''Parietal eye on the dorsum of the head''' (Copyright © RVC)]]

Common [[Mydriatic|mydriatics]] have no effect on the reptilian eye because both the iris sphincter and ciliary muscle contain striated (or skeletal) rather than smooth muscle. This means that they are under conscious control. Therefore, unlike mammals, the consensual pupillary response is absent, the cornea does not contain a Descemets membrane and scleral ossicles are often present. This renders the ocular examination more challenging but more importantly, the parasympatholytic topical drugs (that reduce the activity of the parasympathetic nervous system) used to dilate the pupil [[Mydriatic|mydriasis]]) in mammals are totally ineffective.

Common [[Mydriatic|mydriatics]] have no effect on the reptilian eye because both the iris sphincter and ciliary muscle contain striated (or skeletal) rather than smooth muscle. This means that they are under conscious control. Therefore, unlike mammals, the consensual pupillary response is absent, the cornea does not contain a Descemets membrane and scleral ossicles are often present. This renders the ocular examination more challenging but more importantly, the parasympatholytic topical drugs (that reduce the activity of the parasympathetic nervous system) used to dilate the pupil ([[Mydriatic|mydriasis]]) in mammals are totally ineffective.

Another characteristic of the lizard eye is its ability to occupy both scotopic (light limited) and photopic (light rich) environments. Indeed, the morphology of the eye adapts and varies according to activity in these different light environments.  

Another characteristic of the lizard eye is its ability to occupy both scotopic (light limited) and photopic (light rich) environments. Indeed, the morphology of the eye adapts and varies according to activity in these different light environments.  

* '''For information on examination of the eye, see''' [[Lizard Physical Examination|Lizard Physical Examination]].

* '''For information on examination of the eye, see''' [[Lizard Physical Examination|Lizard Physical Examination]].

A well developed [[Parietal eye|parietal "eye"]] (with a rudimentary lens and retina) is found on the dorsal midline in some lizards, including the [[Green Iguana|green iguana]], [[Stump-tailed Skink|blue-tongued skink]] and [[Water Dragon|water dragon]]. This sensory organ, connected to the central [[Lizard Nervous System|nervous system]] and the pineal gland by the small parietal nerve, functions in [[Lizard Endocrine System|hormone production]] (including [[Lizard Reproduction|reproduction]]) and thermoregulation. Although sensitive to changes in light, it cannot form images. Sometimes referred to as "pineal eye" or "third eye", it it visible as an opalescent gray spot on the top of some lizard's heads.

This sensory organ is connected to the central [[Lizard Nervous System|nervous system]] and the pineal gland by the small parietal nerve. It functions in [[Lizard Endocrine System|hormone production]] (including [[Lizard Reproduction|reproduction]]) and thermoregulation (by acting as a light dosimeter). It detects both UV light and heat. Although sensitive to changes in light, it cannot form images. By detecting '''light and dark''' it allows lizards to detect the '''movement of  predators'''. Sometimes referred to as "pineal eye" or "third eye", it it visible as an opalescent gray spot on the top of some lizard's heads.

==Eyelids==

==Eyelids==

In some [[Chameleon|chameleon]] species as well as some geckos and the oscellated skink (''Ablepharus sp.'') the eyelids have fused to produce a circular, immobile and transparent dermal aperture called a spectacle. It create an impervious barrier to topically applied medications.

In some [[Chameleon|chameleon]] species as well as some geckos and the oscellated skink (''Ablepharus sp.'') the eyelids have fused to produce a circular, immobile and transparent dermal aperture called a spectacle. It create an impervious barrier to topically applied medications.

==The pupil==

==Pupil==

The pupil is usually round and relatively immobile in diurnal species and is usually slit-like in nocturnal species. Geckos, such as the [[Tokay Gecko|Tokay gecko]], have a serrated pupillary opening resembling a series of small holes when the pupil is completely closed. This specificity allows for acute vision even in dim light.

The pupil is usually round and relatively immobile in diurnal species and is usually slit-like in nocturnal species. Geckos, such as the [[Tokay Gecko|Tokay gecko]], have a serrated pupillary opening resembling a series of small holes when the pupil is completely closed. This specificity allows for acute vision even in dim light.

* '''For more information on behaviour, see''' [[Lizard Behaviour|Lizard Behaviour]].

* '''For more information on behaviour, see''' [[Lizard Behaviour|Lizard Behaviour]].

==References==

==References==

* Engbretson, G.A. & Lent, C.M. (1976). Parietal eye of the lizard: neuronal photoresponses and feedback from the pineal gland. Proceedings of the National Academy of Sciences 73, 654-657

* Engbretson, G.A. & Lent, C.M. (1976). Parietal eye of the lizard: neuronal photoresponses and feedback from the pineal gland. Proceedings of the National Academy of Sciences 73, 654-657

* Girling, S.J. (2004). ''BSAVA Manual of Reptiles''. British Small Animal Veterinary Association. pp. 350. ISBN 0905214757

* Girling, S.J. (2004). ''BSAVA Manual of Reptiles''. British Small Animal Veterinary Association. pp. 350. ISBN 0905214757

* Hall, M.I. (2008). Comparative analysis of the size and shape of the lizard eye. Zoology 111, 62-75

* Hall, M.I. (2008). Comparative analysis of the size and shape of the lizard eye. Zoology 111, 62-75

* Mader, D.R. (2005). ''Reptile Medicine and Surgery''. Saunders. pp. 1264. ISBN 072169327X

* Mader, D.R. (2005). ''Reptile Medicine and Surgery''. Saunders. pp. 1264. ISBN 072169327X

[[Category:Lizard Anatomy|E]]

[[Category:Lizard Anatomy|E]]