The anterior segment which lies between the cornea and lens is filled with a clear watery fluid called the aqueous humor or simply aqueous. The aqueous humor is the sole source of nutrients and oxygen for the lens as well as the endothelium layer of the cornea. Therefore, the proper flow is critical for the health of these structures.

The sclera is the white outer wall of the eye. It is a tough, fibrous tissue that extends from the cornea (the clear front section of the eye) to the optic nerve at the back of the eye. The sclera gives the eye its white colour.

The transparency of the cornea is due to the fact that it contains hardly any cells and no blood vessels. However, blood vessels can creep in from around it if it is constantly irritated or infected which can interfere with vision.

The sclera is a typical, fibrous connective tissue containing collagen and elastic fiber. Collagen is a protein that naturally occurs in the body and is found in cartilage, bones, tendons and skin. In mammals, this protein accounts for as much as 90% of the scleral dry weight.

The external most layer of the tear film is the lipid or oil layer. This layer prevents the lacrimal layer beneath it from evaporating. It also prevents the tears from flowing over the edge of the lower eyelid.

The meibomian glands or tarsal glands are a special kind of sebaceous gland at the rim of the eyelids inside the tarsal plate, responsible for the supply of meibum which is an oily substance that prevents evaporation of the eye's tear film.

It is the inner layer of wall of the eye ball containing visual receptors, rods and cones. It is the inner layer of the wall of eyeball, which stops anteriorly near the ciliary body.

The meibomian glands or tarsal glands are a special kind of sebaceous gland at the rim of the eyelids inside the tarsal plate responsible for the supply of meibum, which is an oily substance that prevents evaporation of the eye's tear film. Meibum prevents tear spillage onto the cheek, trapping tears between the oiled edge and the eyeball, and makes the closed lids airtight.

The iris appears as the colored part of the eye, and is responsible for regulating the size of the pupil which in turn influences the amount of light that enters the eye. Melanin is responsible for the color of our eyes. The iris is made up of blood vessels and connective tissue in addition to melanocytes and other pigmented cells that are responsible for its distinctive color. The melanocytes contain melanin, a brown or black pigment.

Rhodopsin, also known as visual purple, is a biological pigment in photoreceptor cells of the retina that is responsible for the first events in the perception of light. Rod cells detect the degree of lightness entering the eye, and their sensitivity is dependent on the amount of rhodopsin present. This pigment is sensitive to red light in the retinal rods of the eyes consisting of opsin and retinene.

People with albinism have no melanin in their irises, and their eyes may appear pink because the blood vessels in the back of their eyes reflect light.

The lacrimal glands secrete lacrimal fluid, which flows through the main excretory ducts into the space between the eyeball and lids. The brown or black pigment, melanin, present in melanocytes of the iris of the eye is not carried by the lacrimal fluid. So, this is not done by lacrimal fluid.

Excessive tearing, also known as epiphora, is due to a disruption in the balance between tear production and tear loss. Numerous etiologies lead to an excess of tears, and there are a number of ways to diagnose and treat this condition.

Keratoconus is degeneration of the structure of the cornea. The cornea is the clear tissue covering the front of the eye. The shape of the cornea slowly changes from the normal round shape to a cone shape.

The caruncle is a modified cutaneous tissue located at the inner canthus that contains hair follicles, accessory lacrimal glands, sweat glands and sebaceous glands. The little reddish-pink fleshy substance on the inside corner of our eye is called a caruncle.

Hordeolum or styes is an infection of the sebaceous glands of zeis usually caused by Staphylococcus aureus bacteria. It is characterized by an acute onset of symptoms, and it looks like a red bump placed underneath the eyelid. The main symptoms of styes include pain, redness of the eyelid and sometimes swollen eyelids.

The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil.

The sclera is a typical fibrous connective tissue containing collagen and elastic fiber. Collagen is a protein that naturally occurs in the body, and is found in cartilage, bones, tendons and skin.

The choroid is the layer of blood vessels and connective tissue between the sclera (white of the eye) and retina. It is part of the uvea, and supplies nutrients to the inner parts of the eye.

The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It can control the illumination in the eye, and can improve the optical quality of the image on the retina.

Rhodopsin, also known as visual purple, is a biological pigment in photoreceptor cells of the retina that is responsible for the first events in the perception of light. Night blindness or nyctalopia occurs in persons with severe vitamin A deficiency. Non-availability of this vitamin leads to the decreased formation of rhodopsin.

This is the most common cause of a white reflex or white pupil in a photo. Light entering the eye at a certain angle may be reflected from the optic nerve. It becomes magnified, and the white eye effect may be seen.

Hemianopia or hemianopsia is a type of anopsia where the decreased vision or blindness takes place in half the visual field of one or both eyes. In most cases, the visual field loss respects the vertical midline. The most common causes of this damage include stroke, brain tumor and trauma.

Ciaccio glands or wolfring glands are small, tubular, accessory lacrimal glands found in the lacrimal caruncle of the eyelid. They are located in the upper border of the tarsus approximately in the middle between the extremities of the tarsal glands. Sometimes, they are situated slightly above the tarsus.