Best note|Functional anatomy of the human eyeball:

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Morphology of the eyeball :

Human eyeball is also known as bulbus oculi . The eyeball of the human being is approximately globe shaped. The diameter of the eyeball of the human being is about 24mm.

Human eyeball

This is slightly flattened from above downwards. There is present two segments in the eye ball.The segments which are present in the eyeball are :an anterior part and a posterior part.

The anterior part of the human eyeball is small in structure,and it forms one sixth of the eyeball. Posterior part of the this structure is larger and the posterior part of the human eyeball forms five sixth of the eyeball.

Radious of this part is approximately 8 mm. Posterior wall of this part is lined by the light sensitive structure known as retina.

Anterior pole is regarded as the center of anterior curvature of the eyeball.On the other hand posterior pole is regarded as the center of posterior curvature of the eyeball.

The line which is involves in the joining of the anterior pole and the posterior pole is regarded as the Optical axis .

The line joining a point in cornea little medial to anterior pole and fovea centralis, situated lateral to posterior pole is regarded as visual axis. Through the visual axis of the eyeball of the eye light rays pass.

Best image for exam on the structure of human eyeball

Human eye with the eyeball and other parts,Image by-OpenStax College,Source,License- CC BY 3.0

Orbital cavity:

Orbital cavity is known as the eye socket. Except anterior one sixth the eyeball of the human eye is present in a bony cavity,which is regarded as the orbital cavity.

Between bone and eyeball of the human eye a thick layer of areolar tissue is present. Because of the presence of this structure, external force can't do any loss of the eyeball.

With the help of the ocular muscles eyeballs are attached to the orbital cavity.

Eyelids:

Eyelids protect the eyeball from foreign particles coming in contact with its surface and cutoff the light during sleep.

There is no need of any mechanical action to open and close the eyelids. They are also opens by reflex action .

There is present sensitive hair in the margins of eyelids which are known as cilia.From a follicle each cilium arises,which is surrounded by a sensory nerve plexus.

These sensory nerves are activated when dust particle comes in contact with cilia,which in turn results in rapid blicking of eyelids.

In the upper eyelid there is present almost 100 to 150 cilia ,and in the lower eyelid there is present almost 50 to 75 cilia. Opening between the upper eyelid and lower eyelid is known as palpebral fissure.

Conjunctiva:

Conjunctiva is a thin mucus membrane,which helps in the covering of the exposed part of the eye.Conjunctiva is reflected into the inner surfaces of the eyelid after covering the anterior surface.

Bulbar portion is the part of the conjunctiva which covers the eyeball of the human eye.

Part of conjuctiva which helps in covering of the eyelid is regarded as the palpebral portion. The opposed portions of this structure slide over each other ,during closure or opening of eyelids.

Lacrimal gland and tear:

In the shelter of the bone this gland is present. Lacrimal gland forms the upper and outer border of wall of the orbital cavity.Tear flows over the surface of the conjunctiva from this gland .

And drains into the nose via lacrimal ducts,lacrimal sac and nasolacrimal duct. Tear is a fluid ,which is hypertonic in nature.

The conjunctiva is kept moist and is protected from infection due to the endless washing and lubrication .

There is present lysozyme in the tear which can kill bacteria.

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