Corpus: Choroid

In veterinary medicine, the term choroid refers to a pigmented and highly vascularised section of the tunica vasculosa bulbi (middle eye skin), which is located between the sclera (sclera) and the retina (retina).

The choroid is the posterior and largest part of the middle membrane of the eye. It is located in the posterior two-thirds of the eye between the sclera and the retina. From the outside in, it is composed of the following three layers:

• Lamina suprachoroidea
• Lamina vasculosa
• Lamina choroideocapillaris

The outer, pigmented lamina suprachoroidea contains large vessels and nerves. This layer is loosely connected to the outer sclera. Embedded in a highly pigmented connective tissue framework, smaller arteries and veins run in the lamina vasculosa. The innermost layer (lamina choroidocapillaris), on the other hand, is a flat and dense capillary network that lies on the retina and nourishes it. This layer is connected to the outer layer of the retina via the so-called Bruch membrane.

A special feature of many animal species is the tapetum lucidum. This triangular and downwardly limited area is not developed in humans and pigs. The tapetum lucidum lies between the lamina vasculosa and the lamina choroideocapillaris. In this area, the pigment sheet of the retina in front of it has little or no pigment, which reflects the light falling into it. The photoreceptors are thus additionally stimulated, which leads to optimum utilisation of the incident light at dusk. Due to the diffraction of the light, this section glows blue-green, in carnivores golden yellow or orange.

The vascular supply of the choroid is ensured by the arteriae ciliares posteriores longae, arteriae ciliares posteriores breves and the arteriae ciliares anteriores. Venous drainage is provided by the venae vorticosae, venae ciliares anteriores and venae ciliares posteriores.

• Salomon FV, Geyer H, Uwe G. 2008. anatomy for veterinary medicine. 2nd, updated and expanded edition. Stuttgart: Enke Verlag in MVS Medizinverlage Stuttgart GmbH & Co. KG. ISBN: 978-3-8304-1075-1
• Sabine Breit, Wolfgang Künzel. 2016/17 Morphology and Function Neurology/Sense Organs II.