Eyeball
Each eyeball is a cystic structure kept distended by the pressure inside it. Although, generally referred to as a globe, the eyeball is not a sphere but an ablate spheroid, consisting of two modified spheres fused together. Cornea is a part of the anterior lamellar sphere with a radius 7.8 mm and sclera is part of the posterior larger sphere with a radius of about 12 mm.
Anatomy of eyeball
Dimensions of an adult eyeball
They are follow as-
1- Anteroposterior diameter - 24 mm
2- Horizontal diameter - 23.5 mm
3- vertical - 23 mm
4- Circumference - 75 mm
5- Volume - 6.5 ml
6- Weight. - 7 gm
Poles and equators of the eyeball
POLES - the central point on the maximal convexities of the anterior and posterior curvature of the eyeball is called the anterior pole and posterior pole .
EQUATORS - they are follow as -
Geometric equator of the eyeball lies at the mid plane between the two poles .
Anatomical equator of the eyeball is tilted slightly backward on the temporal side and slightly forward on the nasal side.
Surgical equator refers to the greatest circumferences of the globe approximately in the coronal plane.
AXES AND ANGLES OF THE EYEBALL
AXES OF THE EYE
1- Optical axis - it is line passing through the centre of the cornea, centre of the lens and meet the retina on the nasal side of the fovea.
2- Visual axes - It is the line joining the fixation point, nodal point and the fovea.
3- Fixation axis - it is the line joining the fixation point and centre of the rotation.
VISUAL ANGLES
1- Angle alpha - it is the angle formed between the optical axis and visual axis at the nodal point.
2- Angle gamma - it is the angle between the optical axis and fixation axis at the centre of the rotation of the eyeball .
3- Angle kappa - it is the angle formed between the visual axis and pupillary line.
Coats of the eyeball
They are follow as -
1- Fibrous coat - it is a dense strong wall which protect the intraocular content. Anterior 1/6th of this fibrous coat is transparent and is called cornea. Posterior 5/6th opaque part is called sclera. Cornea is set into sclera like a watch glass junction of the cornea and sclera called limbus is marked at the surface by the external sclera sulcus . Conjunctiva is firmly attached at the limbus.
2- Vascular coat - it supplies nutrition to the various structure of the eyeball. It consists of the three parts which from anterior to posterior are; Iris, Ciliary body and choroid.
3- Nervous coat - It is concerned with visual functions and projects to the visual cortex through visual pathway.
Segments and Chambers of the eyeball
The eyeball can be divided into two segments -
Anterior segments - It includes crystalline lens and structure anterior to it , viz. iris, cornea and posterior chambers .
Anterior chamber - it is bounded anteriorly by the back of cornea, and posteriorly by the iris and part of the ciliary body. The anterior chamber is about 30 mm deep I the centre in normal adults.
Posterior chamber - it is a triangular space containing 0.06 ml of aqueous humour. It is bounded anteriorly by the posterior surface of iris and the part of ciliary body, posteriorly by the crystalline lens and its zones and laterally by the ciliary body.
2- Posterior segment - it includes the structure posterior to lens, viz. vitreous humour, retina , choroid and optic disc.
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