Question

Which of the following regulates the amount of light entering the eye?
A. Iris
B. Lens
C. Retina
D. Cornea

Answer 1

The human eye is a photoreceptor. Humans have a pair of spherical eyes which are located in the socket/notch of the lacrimal bone of the skull called as orbits. Only ${\dfrac{1}{5}^{th}}$ part of the eye is visible from outside between the lashes. The eye has three layers, the outermost being the sclera, is made of dense connective tissue. The middle layer is choroid, ${\dfrac{2}{3}^{rd}}$ posterior part of which is thin and the anterior ${\dfrac{1}{3}^{rd}}$ portion is thick and forms the ciliary body. The innermost layer is the retina.

Complete answer:
A. Iris: It is the extension of choroid and is the pigmented and opaque tissue surrounding the pupil. The iris is a visible portion of the eye and varies in color. It regulates the amount of light entering the eye through the pupil. It decreases the diameter of the pupil, when there is bright light outside and lets less light pass through it. But when the outside light is dim and it opens up the pupil, to let more amount of light enter the eye. Option (a) is correct

B. Lens: it is the transparent, crystalline structure found in the eye and is held by suspensory ligaments that connect the ciliary body to the lens. The lens changes the focal distance of the eye i.e., it focuses the light rays that pass through it (and onto the retina) in order to create clear images of objects that are positioned at various distances. Option (b) is incorrect.

C. Retina: The innermost layer of the eye is the retina. Retina itself is made of different layers namely, layers of cuboidal cells. Inner to which is the layer of the receptors rods and cones, followed by the layer of bipolar neurons and innermost being the layer of ganglion cells. All the nerve fibers passing from ganglion collectively make the optic nerve which goes to the brain. Option (c) is incorrect.

D. Cornea: It is the outermost transparent and avascular structure of the eye. It is the anterior portion of the outermost layer sclera. It works as a protective layer for the eye.Option (d) is incorrect.

Hence, the correct answer is (a).

Note: The space between the eye and the cornea is filled with aqueous chamber which is watery, alkaline and is formed and absorbed daily. The space between the lens and retina has vitreous chamber and is jelly-like and is formed only once in life time and helps in maintaining the intraocular pressure.