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The sclera's blood vessels are mainly on the surface. Along with the vessels of the conjunctiva (which is a thin layer covering the sclera), those in the episclera render the inflamed eye bright red. [6] In many vertebrates, the sclera is reinforced with plates of cartilage or bone, together forming a circular structure called the sclerotic ring.
A thin layer called the conjunctiva sits on top of this. The front part is also called the anterior segment of the eye. The eye is not shaped like a perfect sphere; rather it is a fused two-piece unit, composed of an anterior (front) segment and the posterior (back) segment. The anterior segment is made up of the cornea, iris and lens.
Eye and detailed ray path including one intraocular lens layer. In humans the widely quoted Helmholtz mechanism of focusing, also called accommodation, is often referred to as a "model". [27] Direct experimental proof of any lens model is necessarily difficult as the vertebrate lens is transparent and only functions well in the living animals.
Image of a human eye showing the blood vessels of the bulbar conjunctiva Hyperaemia of the superficial bulbar conjunctiva blood vessels. In the anatomy of the eye, the conjunctiva (pl.: conjunctivae) is a thin mucous membrane that lines the inside of the eyelids and covers the sclera (the white of the eye). [1]
The functional unit of the eye is the photoreceptor cell, which contains the opsin proteins and responds to light by initiating a nerve impulse. The light sensitive opsins are borne on a hairy layer, to maximise the surface area. The nature of these "hairs" differs, with two basic forms underlying photoreceptor structure: microvilli and cilia. [26]
Sheep eye lens capsule with ligaments attached. The capsule is lifting off the lens showing cell fiber ends beneath. Microscope image of lens capsule in relation to lens cell types. The lens capsule is a component of the globe of the eye. [1] It is a clear elastic basement membrane similar in composition to other basement membranes in the body.
The episclera is the outermost layer of the sclera (the white of the eye). [1] It is composed of loose, fibrous, elastic tissue and attaches to Tenon's capsule. [1]A vascular plexus is found between the bulbar conjunctiva and the sclera consisting of two layers of vessels, the superficial episcleral vessels and the deep episcleral vessels.
The uvea (/ ˈ j uː v i ə /; [1] derived from Latin: uva meaning "grape"), also called the uveal layer, uveal coat, uveal tract, vascular tunic or vascular layer, is the pigmented middle layer of the three concentric layers that make up an eye, precisely between the inner retina and the outer fibrous layer composed of the sclera and cornea.