Tag: the structure and function of the eye

Questions Related to the structure and function of the eye

Which of the following statements about rods and cones is true?

  1. Rods are responsible for photopic vision and cones are responsible for scotopic vision.

  2. Rods are responsible for scotopic vision and cones are responsible for photopic vision.

  3. Rods and cones both are responsible for photopic vision.

  4. Rods and cones are responsible for scotopic vision.


Correct Option: B
Explanation:

Rods and cones are photoreceptors in the human retina. Rods are responsible for vision at low light levels (scotopic vision). They do not mediate colour vision and have a low spatial acuity. Cones are active at higher light levels (photopic vision), are capable of colour vision and are responsible for high spatial acuity. So, the correct answer is 'Rods are responsible for scotopic vision and Cones are responsible for photopic vision'.

Iodopsin is a light sensitive (photosensitive) pigment and is present in the

  1. Rods

  2. Cones

  3. Neuroglia

  4. Bipolar cells


Correct Option: B
Explanation:

Rods and cones are used to process light, in a human eye, their number is estimated to be 5-7 million cones and 110-130 million rods. Cones have iodopsin and are found mainly in the central area of the retina (fovea), while rods containing rhodopsin are found in the peripheral retina. Cones sense colour and need more light than rods to work well. Cones are most helpful in the normal or bright light. There are 3 types of cones - red, green, and blue - to help you see different ranges of colour. Together, these cones sense combinations of light waves, that enable our eyes to see millions of colours. The light-sensitive photopigments are made of the protein opsin and the chromophore retinene. Bleaching of iodopsin in cones is similar to rhodopsin in rods, only rods contain a higher concentration of visual pigment than cones, so more light is needed to cause an action potential to be fired in cones ( a threshold for cones is higher than rods). In other words, rods are mainly used for dim light vision, cones for bright light vision.

Sensory neurons of retina of eye are

  1. Rods and cones

  2. Maculae and cristae

  3. Pacinian and Ruffini's corpuscles

  4. All of the above


Correct Option: A
Explanation:

Rods and cones are the photoreceptors present in retina of the eye. They have their own bipolar neurons and photo-sensitive pigments.

Match the following and choose the correct option.

   Column I     Column II
 A  Fovea  1  Provides opening for entry of light
 B  Iris  2  Maximum visual acuity
 C  Pupil  3  Transmits information to CNS
 D  Lens     4  Controls amount of light entering
 E  Optic nerve     5  Focuses light on the retina
  1. (A)- 4, (B)- 1, (C)- 5, (D)- 2, (E)- 3

  2. (A)- (5), (B)- (1), (C)- (4), (D)- (3), (E)- (2)

  3. (A)- (3), (B)- (1), (C)- (4), (D)- (5), (E)- (2)

  4. (A)- (1), (B)- (2), (C)- (3), (D)- (4), (E)- (5)

  5. (A)- (2), (B)- (4), (C)- (1), (D)- (5), (E)- (3)


Correct Option: E
Explanation:

The fovea centralis is the central portion of the human retina, that has the most acute vision and the best color perception. The cones have 3 types of specific photopigments - red, green and blue, or RGB. Most of the color sensitive cones are packed in the fovea centralis.
The colored part of the eye is called as the iris. It controls light levels inside the eye similar to the aperture on a camera. The round opening in the center of the iris is called as the pupil. The iris is embedded with tiny muscles, that dilate (widen) and constrict (narrow) the pupil size.
The lens, by changing shape, functions to change the focal distance of the eye, so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina, which is then transmitted to the brain by the optical nerve.

Acute vision is found in which of the following?

  1. Vulture

  2. Frog

  3. Shark

  4. Bat


Correct Option: A
Explanation:

Vultures are highly reliant on their sensory systems for the rapid detection and localization of carrion before other scavengers can exploit the resource. Vulture has acute vision. Retina has a comb like pectin in birds.

The human eye is sensitive only to light having wave length ranging from 

  1. 80 to 280 nanometres

  2. 380 to 760 nanometres

  3. 780 to 870 nanometres

  4. 880 to 980 nanometres


Correct Option: B
Explanation:

The human eye is sensitive to violet (400 nm) to red (700 nm ) light only that can generate photometric effect i.e. visual sensation on an eye. So, the correct answer is option B.

Retina is most sensitive at

  1. Optic disc

  2. Periphery

  3. Macula lutea

  4. Fovea centralis


Correct Option: D
Explanation:
A minute yellowish area containing the fovea centralis located near the center of the retina of the eye at which visual perception is most acute is called as yellow spot or macula lutea. When an eye is looking directly at an object, light rays from that object are focused on the macula lutea, a yellow oval spot at the center of the retina. It is the part of the retina, that is responsible for sharp, detailed central vision also called as visual acuity.
So, the correct answer is 'Fovea centralis'

If the circular ciliary muscles of the eye are unable to contract, the 

  1. Lens will become more convex

  2. Lens will be thin and stretched

  3. Vision will be lost completely

  4. Bright light will have no adverse effect on retina


Correct Option: B
Explanation:

Ciliary body and the attached suspensory ligament change the shape (flattened or round) of the lens through relaxation and contraction of ciliary muscles and thereby the focal length to focus on the distant and near object. Contraction of ciliary muscles releases the suspensory ligaments and allow the lens to become round (convex) while relaxation of these muscles makes the lens taut. Since ciliary muscles are involved in accommodation required for close vision, loss of their contraction would not cause loss of vision but would affect the close vision only. The amount of light entering retina is controlled by the iris. 

So, the correct answer is option B.

Choroid is

  1. Middle layer of ear

  2. Innermost layer of eye

  3. Innermost layer of ear

  4. Middle layer of eye


Correct Option: D
Explanation:

The choroid is a layer of eyeball. The eyeball has three coats namely sclera, choroid, and retina. The choroid is middle dark pigmented thin vascular layer of the eyeball and is characterized by the presence of many blood vessels. Retina forms the innermost layer of the eye. 

Which of the following have "ommatidia" as unit of eye?

  1. Pheretima

  2. Housefly

  3. Pila

  4. Sepia


Correct Option: B
Explanation:

Compound eyes are the characteristic feature of insects. The compound eye of insects consists of many ommatidia, each of which is a separate visual unit that portrays each object into several broken pieces. This type of vision is called as mosaic vision. Among the given options, housefly is an insect and has ommatidia as a unit of an eye. Pheretima (annelid) and pila and sepia (molluscs) do not have compound eyes. 

So, the correct answer is option B.