Question
Identify the structure marked as “B” in the picture below ?
A. Optic nerve.
B. Cilliary nerve.
C. Lacrimal nerve.
D. None of the above.
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Correct Answer » A Explanation |
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Ans:A. Optic Nerve.
The structure marked as
A- Eyeball.
B- Optic nerve.
Layers of the Eyeball
The eye is made up of three coats.The outermost layer, known as the fibrous tunic, is composed of the cornea and sclera. The middle layer, known as the vascular tunic or uvea, consists of the choroid, ciliary body, pigmented epithelium and iris. The innermost is the retina
Parts of the Eye
Extraocular Muscles:
- Six muscles :Superior rectus, Inferior rectus ,Medial rectus ,Lateral rectus, Superior oblique ,Inferior oblique .
Conjunctiva:
- It is a transparent mucous membrane that covers the inner surface of the eyelids and the surface of the eye.
Lacrimal Gland:
- It produces tears that lubricate the eye. It is located under the lateral edge of the eyebrow in the orbit.
Tenon’s Capsule:
- Tenon’s capsule is a layer of tissue that lies between the conjunctiva and the surface of the eye.
Cornea
- It is the clear, transparent front part of the eye that covers the iris, pupil and anterior chamber and provides most of an eye’s optical power .
Anterior Chamber
- The Anterior Chamber is filled with Aqueous Humor. The eye receives oxygen through the aqueous. It’s function is to nourish the cornea, iris, and lens by carrying nutrients, it removes waste products excreted from the lens, and maintain intraocular pressure and thus maintains the shape of the eye.
Iris
- It is the pigmented tissue lying behind the cornea that gives color to the eye and controls the amount of light entering the eye by varying the size of the pupillary opening.
Pupil
- It is a variable-sized black circular opening in the center of the iris that regulates the amount of light that enters the eye.
Lens
- Transparent, biconvex intraocular tissue that helps bring rays of light to focus on the retina
Ciliary Body
- The circumferential tissue (a ring of tissue between the end of the choroids and the beginning of the iris) inside the eye composed of the ciliary muscle (involved in lens accommodation and control of intraocular pressure and thus the shape of the lens) and ciliary processes that produce aqueous fluid.
Vitreous Humour
- It is the transparent, colorless gelatinous mass that fills rear two-thirds of the eyeball, between the lens and the retina.
Retina
- It is the light sensitive nerve tissue in the eye that converts images from the eye’s optical system into electrical impulses that are sent along the optic nerve to the brain, to interpret as vision. Forms a thin membranous lining of the rear two-thirds of the globe; consists of layers that include two types of cells: rods and cones. There is no retina over the optic nerve which causes a blind spot
Cones
- They are the light-sensitive retinal receptor cell that provides the sharp visual acuity (detail vision) and color discrimination; most numerous in macular area. Function under bright lighting.
Rods
- The light-sensitive, specialized retinal receptor cell that works at low light levels (night vision). The rods function with movement and provide light/dark contrast. It makes up peripheral vision.
Macula
- It is the “yellow spot” in the small (3 °) central area of the retina surrounding the fovea. It is the area of acute central vision (used for reading and discriminating fine detail and color). Within this area is the largest concentration of cones
Fovea
- It is the central pit in the macula that produces the sharpest vision.
Choroid
- The vascular central layer of the eye lying between the retina and sclera. It’s function is to provide nourishment to the outer layers of the retina through blood vessels.
Sclera
- It is the opaque, fibrous, tough, protective outer layer of the eye (“white of the eye”) that is directly continuous with the cornea in front and with the sheath covering the optic nerve behind. The sclera provides protection and form.
Optic Nerve
- It is the largest sensory nerve of the eye. It carries impulses for sight from the retina to the brain.