Question

Blind spot is the region where
A. Image is formed
B. Cones are numerous
C. The optic nerve leaves the eye
D. Image is formed in the dark

Answer 1

Hint: Eye is the only sense organ that can perceive light. It helps living organisms to view their surroundings. The eyes are composed of photoreceptor cells present on the inner side. However, there are places in the eye where the photoreceptor cells are few or even absent.

 Complete step by step answer: Eyes are a part of the visual system in animals. They enable us to see our surroundings. There are two eyes located in skeletal orbits. Anatomically an eye has an anterior part and a posterior part. The anterior part comprises the cornea, iris and lens, while the posterior part has the vitreous humor, retina, choroid and the sclera. The cells of the retina can perceive light. They are called rod cells and cone cells and are responsible for vision. Retina has a huge number of rods and cones. However, a region on the retina where the cell fibers of the ganglion cells form the optic nerve lacks photoreceptor cells. This region is known as the Blind spot. No image formation takes place here. It is from this region the optic nerve leaves the eyes.
Light enters the eye through the cornea. The pupil dilates or contracts to control the amount of light entering the eye. The shape of the lens is altered in response to a process called accommodation. This process enables the eye to change the focus from distant objects to near objects. The lens then directs the light to the retina. The photosensitive cells of the retina are activated and send electrical signals to the brain via the optic nerve which results in vision. Therefore, the image is formed on the retina and not on the blind spot.
Rod cells and cone cells – the two photoreceptor cells of the eye are present in the retina. The center of the eye, a region called Fovea centralis contains only cone cells. The rest of the retina has a mixed number of rods and cones. Therefore, blind spots do not contain cone cells.
Since, the rods and cones are sensitive to light, they do not get activated in absence of light. Therefore, no image is formed in the dark.
Therefore, to conclude the discussion, we can say that the blind spot is the place where the optic nerve leaves the eye.
Hence, option (c) is correct.

Note: The photoreceptor cells of the eye are sensitive to light. They are able to convert light into neural impulses and send the same to the visual cortex of the brain that results in vision. These cells are present in the retina. The region of the eye that lacks photoreceptors and hence does not contribute to image formation is known as the blind spot. It is the region from where the optic nerve exits the eye.