Tag: the structure and function of the eye

Umbraculum is a modification of iris which serves to reduce the excessive glare in daytime. It is found in animals like camels. It is also known as corpus nigra.

Many suspensory ligaments are attached radially around the lens that serve to pull the edges of lens edges toward the outer circle of the eyeball. They maintain the relatively flat shape of the lens under normal conditions of the eye.

The horse has the largest eye of any land mammal. Its visual abilities are directly related to the animal's behavior and the fact that the horse is a flight animal.
Thus, the correct answer is option B.

Supporting cells of the retina is Muller cells also known as Muller glia. They are a type of retinal glial cells, first recognized and described by Heinrich Muller. They are found in the vertebrate retina, which serves as support cells for the neurons of the retina.

The retina makes up the inner layer and occupies only the posterior two-third of the eye. The retina consists of several layers of cells, including the rods and cones, the sensory cells, that respond to light. The tips of the rods and cones are embedded in a pigmented layer of cells on the back of the retina. The pigment helps prevent light from scattering in the back of the eye. 

Ostriches have the biggest eyes of all land mammals. The ostrich needs large eyes for its terrestrial lifestyle sharing the savanna as it does with an alarming army of fearsome predators. It is a flightless bird with strong hindlimbs to run.

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, 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. There are approximately 50 glands on the upper eyelids and 25 glands on the lower eyelids. Dysfunctional meibomian glands often cause dry eyes.

Retina is the light-sensitive tissue lining the back of our eye. It is the black pigment in the eye, which reduces the internal reflection. Thereby, it controls the impact of the bright light entering our eye. Function of retina is to receive light that the lens has focused, convert the light into neural signals, and send these signals on to the brain for visual recognition. Hence option A is correct.

The almond-shaped glands in the eyes present above each eyeball are called lacrimal glands. Thes glands are called tear gland because they secrete the fluid called tears. These glands have their openings between the eyelashes. Water, salts and bactericidal protein such as lysozyme are components of tear. The secretion of this glands is involved in the clearance of dust, grit and microorganisms in the cornea. They are also involved in the lubrication of eyes and eyelashes. Thus the correct answer is option C.

Glands of Zeis are modified sebaceous gland located on the margin of eyelids and produces oil into the follicles of eye lashes.