Enforcement Officer / Accounts Officer (EO/AO) 2020 recruitment test, advertisement 421. Transcribed from the Commission's own booklet (series A, NMJX-U-GTA); answer as per the official UPSC final answer key. This question is in Part B. Answer last reviewed 24 August 2026.

Which one of the following statements is true with regard to the image formation by two eyes of a person ?

(a)Both the eyes see exactly the same image.
(b)One eye sees half portion of the object.
(c)Both the eyes combine the two images seen by them.
(d)Each eye sees a slightly different image.

Answer

Why

Correct — D, (d) Each eye sees a slightly different image. The two eyes are set side by side in the front of the head, separated by roughly six centimetres, so they look at the same scene from two slightly different positions. Each therefore forms its own image on its own retina, and the two images are not identical: nearer objects shift their position against the background more than distant ones do between the left view and the right view. That small difference is called binocular or retinal disparity, and it is easy to demonstrate — hold a finger up at arm's length and close one eye, then the other, and the finger appears to jump against the far wall. The disparity is not a defect. It is the raw material of depth perception: the brain measures it and converts it into a judgement of how far away each object is, which is why binocular vision gives a solid, three-dimensional sense of space that one eye alone cannot. This option states the physical fact about image formation exactly, which is what the stem asks for.

Why the others are wrong

(a)Both the eyes see exactly the same image. — If the two retinal images were exactly the same, the second eye would add nothing at all, and stereoscopic depth perception could not exist. Because the eyes are separated horizontally, they view every scene from two different vantage points, and the resulting images differ — slightly for far objects, markedly for near ones. The reason this option feels right is that we EXPERIENCE one seamless picture rather than two, so it is natural to assume the eyes are receiving identical inputs. The single picture is the product of processing in the brain, not evidence that the inputs were the same. Anything built on two viewpoints, from a stereoscope to a 3-D film, depends on the two images being different.
(b)One eye sees half portion of the object. — This describes something the visual system does not do. Each eye sees the whole object, not one half of it, and the two visual fields overlap over a wide central region — which is precisely why closing one eye does not remove half of what is in front of you but only narrows the field at the edge and flattens the sense of depth. The option seems to be reaching for the genuine fact that the two fields are not identical and that each eye contributes an extra sliver on its own side, but it misstates that as a fifty-fifty division of the object. Splitting an object between the eyes is not how binocular vision works.
(c)Both the eyes combine the two images seen by them. — The combining is real, but the eyes are not what does it. Each eye is an optical instrument that forms one image on its own retina and sends the signal down its own optic nerve; the two signals are then brought together in the brain, where the visual cortex fuses them into a single perception and reads the disparity between them as depth. As printed, this option credits the eyes with a task performed downstream of them, and the stem asks specifically about IMAGE FORMATION BY THE EYES. It is the most attractive of the wrong options because it names a genuine phenomenon — binocular fusion — and misplaces it.

Concept

Each human eye works as a camera: light is refracted mainly at the cornea and further by the lens, and forms a real, inverted, diminished image on the retina, which the brain interprets the right way up. Focusing on objects at different distances is done by ACCOMMODATION, the ciliary muscle changing the curvature of the lens. What two eyes add to one is depth. Because the eyes are about six centimetres apart, they occupy two different viewpoints, and the two retinal images differ by an amount that depends on how far away the object is — large disparity for near objects, almost none for distant ones. The brain fuses the pair into a single percept and uses the residual disparity to compute distance; this is STEREOPSIS or stereoscopic vision, and it is why predators, including humans, have forward-facing eyes with widely overlapping fields while many prey animals have eyes on the sides of the head, trading depth perception for a much wider field of view. Depth is not judged by disparity alone. Convergence (how far the two eyes turn inward to fixate an object), accommodation, and a set of monocular cues — relative size, overlap, texture gradient, linear perspective, motion parallax and haze — all contribute, which is why a person with sight in one eye can still judge distance reasonably well. Stereoscopes and 3-D cinema simply feed each eye an image made from a slightly different viewpoint, exploiting exactly the mechanism this question is about.

This opens the physics block of Part B, and it is physics of the applied, everyday kind that general ability papers favour — optics of the eye rather than formulae. All four options are statements about the same familiar experience, and only one is a correct statement of fact, so the item rewards a candidate who can separate what the eyes DO from what we experience as a result. The habit worth building is to read each option as a claim and ask which organ or stage of the process it is really describing; two of the three wrong options here go wrong by assigning the right phenomenon to the wrong stage.

Key facts

The human eyes are separated by roughly six centimetres, giving each a slightly different viewpoint on the same scene.
The difference between the two retinal images is called binocular or retinal disparity, and it is greater for nearer objects.
The brain, not the eye, fuses the two images and reads their disparity as depth — the process called stereopsis.
The eye forms a real, inverted and diminished image on the retina; most of the refraction happens at the cornea, with the lens providing fine adjustment.
Accommodation is the change in the curvature of the lens by the ciliary muscle to focus objects at different distances.
Forward-facing eyes give a large binocular overlap and good depth perception; side-facing eyes give a wider total field but little stereopsis.
Monocular depth cues — relative size, overlap, texture gradient, linear perspective and motion parallax — let a person with one eye still judge distance.
Stereoscopes and 3-D films work by presenting each eye with an image captured from a slightly different position.

Two eyes, two images — and a fusion that happens downstream of both

(d) Each eye sees a slightly different image — TRUE→The eyes are set side by side about six centimetres apart, so they look at the same scene from two slightly different positions, and each forms its own image on its own retina. Nearer objects shift against the background more than distant ones do between the left view and the right. That difference is called binocular or retinal disparity, and far from being a defect it is the raw material of depth perception.

(a) Both the eyes see exactly the same image — FALSE→If the two retinal images were exactly the same, the second eye would add nothing at all and stereoscopic depth perception could not exist. The option feels right because we EXPERIENCE one seamless picture rather than two — but that is the result of fusion, not evidence that the images are identical.

(b) One eye sees half the object — FALSE→Each eye sees the whole object, and the two visual fields overlap over a wide central region. That is precisely why closing one eye does not remove half of what is in front of you: it narrows the field at the edge and flattens the sense of depth.

(c) Both the eyes combine the two images — FALSE as printed→The combining is real, but the eyes are not what does it. Each eye is an optical instrument forming one image on its own retina and sending the signal down its own optic nerve; the two signals are brought together in the visual cortex, which fuses them into a single perception and reads the disparity between them as depth.

The demonstration→Hold a finger up at arm’s length and close one eye, then the other. The finger appears to jump against the far wall, and that jump is the disparity the brain converts into a judgement of how far away each object is.

Depth is not judged by disparity alone→Convergence — how far the two eyes turn inward to fixate an object — together with accommodation and a set of monocular cues (relative size, overlap, texture gradient, linear perspective, motion parallax and haze) all contribute, which is why a person with sight in one eye can still judge distance reasonably well. Stereoscopes and 3-D cinema simply feed each eye an image made from a slightly different viewpoint.

Study next

The human eye: cornea, aqueous humour, iris, pupil, lens, vitreous humour, retina, rods and cones, blind spot and yellow spotDefects of vision and their correction — myopia with a concave lens, hypermetropia with a convex lens, presbyopia and astigmatismPower of a lens, the dioptre, and the lens formulaPersistence of vision and how motion pictures exploit itDispersion, scattering and everyday optical phenomena — the rainbow, the blue sky and the red sunsetColour vision, the three types of cone, and colour blindness

Common traps

Assuming that because we perceive one image, the eyes must receive identical images. The single percept is built in the brain from two different inputs.
Crediting the eyes with fusing the two images. Fusion happens in the visual cortex.
Believing each eye sees only part of the object. The two fields overlap over most of the central region and each eye sees the whole of it.
Thinking depth perception is impossible with one eye. Monocular cues still work; what is lost is stereopsis.
Confusing accommodation, which focuses, with convergence, which aims both eyes at the same point.

Physics on EO/AO papers is qualitative and everyday — the eye, the electromagnetic spectrum, sound, heat, simple electricity — and is set as a four-way statement comparison at least as often as a numerical item. Where a statement set is offered, the wrong options usually place a real phenomenon at the wrong stage of the process rather than inventing a false phenomenon, so testing each option for WHERE something happens is more productive than testing whether the phenomenon exists.

Related PYQs

EPFO_EOAO_2020_Q49Open & attempt →

Which one of the following statements regarding force is correct ?

(a) A positive force implies attractive nature.
(b) A negative force implies repulsive nature.
(c) A positive force can be both attractive and repulsive in nature.
(d) A negative force implies attractive nature.

Answer(d) A negative force implies attractive nature.

The other statement-comparison item in this physics block. Both offer four sentences about a familiar idea and turn on which one states the physics correctly, rather than on any calculation.

Practice

practice — not a real PYQ
The ability of the human eye to judge distance and see the world in three dimensions using both eyes together is called
- (a)accommodation
- (b)stereopsis
- (c)persistence of vision
- (d)dispersion
Answer(b) stereopsis
practice — not a real PYQ
The image formed on the retina of a normal human eye is
- (a)real, erect and diminished
- (b)virtual, erect and magnified
- (c)real, inverted and diminished
- (d)virtual, inverted and diminished
Answer(c) real, inverted and diminished

Why