NDA (I & II) 2020 General Ability Test · Question 131 of 148

Correct — C, retina. In the human eye, the cornea and the lens refract incoming light to form a real, inverted image on the retina — the light-sensitive innermost layer at the back of the eyeball. The retina is packed with photoreceptor cells (rods for dim light, cones for colour), which convert the image into nerve impulses carried by the optic nerve to the brain. It therefore acts like the screen (or film) on which the picture is captured.

• (a)pupil — The pupil is only the adjustable opening at the centre of the iris that lets light in; it controls the amount of light, but no image forms on it.
• (b)cornea — The cornea is the transparent front window that does most of the initial bending of light, but it is a refracting surface, not the screen where the image is captured.
• (d)iris — The iris is the coloured muscular ring that adjusts the size of the pupil; it regulates light entry and gives eye colour, but does not receive the image.

The eye works like a camera. Light passes through the cornea, the pupil (whose size the iris controls) and the lens, which together focus it to a sharp, real, inverted image on the retina. The retina's rods and cones transduce light into electrical signals; the brain later re-inverts the image so we perceive it upright.

The trap is that the cornea and lens do the focusing, so students sometimes pick the cornea. But the question asks where the image forms, not what bends the light — and the image lands on the retina, the eye's light-sensitive screen.

• The retina is the light-sensitive inner layer at the back of the eye.
• It contains rod (dim-light) and cone (colour) photoreceptors.
• The image formed on the retina is real and inverted.
• The optic nerve carries the retinal signals to the brain.

• Choosing the cornea because it refracts the most light — but the image forms on the retina.
• Mixing up the iris (coloured ring) and the pupil (the opening it controls).

Asked as a straight recall of eye anatomy — identify the light-sensitive screen where the image lands.

• practice — not a real PYQ

  Which cells on the retina are chiefly responsible for colour vision?

  • (a)Rods
  • (b)Cones
  • (c)Ganglion cells
  • (d)Bipolar cells

  Answer(b) Cones — they detect colour and work best in bright light; rods handle dim-light vision.

• practice — not a real PYQ

  The image formed on the retina of a normal human eye is

  • (a)real and erect
  • (b)virtual and erect
  • (c)real and inverted
  • (d)virtual and inverted

  Answer(c) real and inverted — the brain later interprets it as upright.