Structure of the Human Eye - UNSOLVED PRACTICE SET

Q7. Draw (or describe) a labelled diagram of the human eye. Label at least six parts: cornea, iris, pupil, lens, retina, optic nerve.

Q8. What is the function of the iris and pupil? How do they work together to protect the eye from excessive light?

Q9. Describe the function of the retina. What are rods and cones, and how do they contribute to vision?

Q10. What is the blind spot? Why can we not see objects whose image falls on the blind spot? How can you demonstrate its existence?

Q11. What is the role of the crystalline lens of the eye? How is it different from the lenses used in spectacles or cameras?

Q12. Compare the human eye to a photographic camera. Name and match at least four corresponding parts and their functions.

Q13. Describe the structure of the human eye in detail. Your answer must cover:
(a) the roles of the cornea, iris, and pupil in controlling light entry,
(b) the function of the crystalline lens in focusing light,
(c) how an image is formed on the retina,
(d) the roles of rods and cones in light and colour vision respectively, and
(e) the function of the optic nerve in transmitting visual information to the brain.

Q14. You enter a dark cinema hall from bright sunlight and initially cannot see clearly, but after a few minutes your vision adjusts.
(a) What is this phenomenon called?
(b) Which part of the eye is responsible for this adjustment?
(c) Describe the process: what happens to the pupil and the photoreceptors during adjustment?
(d) Explain the reverse situation: stepping out of a dark room into bright sunlight — what happens and why?
(e) Why do people sometimes wear sunglasses during this transition?

Q15. The human eye is often compared to a camera, but it is far more advanced.
(a) Compare the cornea to a camera lens, the iris to an aperture diaphragm, the retina to the film/sensor, and the optic nerve to the data cable.
(b) What critical ability does the human eye have that a fixed camera does NOT have?
(c) What part of the eye performs this adjustment and how?
(d) Why does the brain need to receive the image from both eyes for depth perception?
(e) What is the approximate field of view of the human eye, and how does it compare to a standard camera?

Q16. The diameter of the human eyeball is approximately 2.3 cm. The crystalline lens forms a focused image on the retina.
(a) If an object is placed 25 cm from the eye (near point), estimate the image distance (≈ diameter of eyeball = 2.3 cm). Using the lens formula 1/v − 1/u = 1/f with u = −25 cm and v = +2.3 cm, calculate the focal length of the eye lens.
(b) Calculate the power of the eye lens in this situation.
(c) What does this value tell you about the strength of the eye lens compared to typical spectacle lenses?

Q17. The angle subtended by an object at the eye determines how large it appears.
(a) A book page is 20 cm × 15 cm and held 30 cm from the eye. Estimate the angle (in radians) subtended by the longer dimension using: angle = size/distance.
(b) The same page is held 60 cm away. Calculate the new angle.
(c) How does moving the page closer improve readability - connect this to the concept of near point of the eye.

Q18. The retina contains approximately 120 million rod cells and 6 million cone cells.
(a) What percentage of photoreceptors are cones?
(b) Cones are concentrated in a region called the fovea (yellow spot). If the fovea covers a 1 mm² area and contains about 147,000 cones, calculate the cone density (cones per mm²).
(c) Why is the fovea the region of sharpest vision?
(d) In dim light, we sometimes see objects better by looking slightly to the side — explain this using the distribution of rods and cones.