BiologyICSE Class 10 · Nervous System and Sense Organs

The Human Eye: Structure, Accommodation and Defects (ICSE Class 10 Biology)

Updated 16 October 2026 · Fact-checked

The eyeball has three coats: the sclera (with the transparent cornea in front), the choroid (forming the ciliary body and iris), and the light-sensitive retina with rods and cones. Ciliary muscles change the lens's curvature to focus near and far objects. Myopia is corrected by a concave lens, hypermetropia by a convex lens, and cataract by surgery.

Understand The Human Eye and Its Defects

Three coats of the eyeball.

Coat	Front part	Role
Sclera (outer, white, tough)	cornea: transparent bulge	protects; cornea lets light in and bends it
Choroid (middle, dark, with blood vessels)	ciliary body (with ciliary muscles) and iris with the pupil	nourishes the eye, stops internal reflection; iris controls light entering
Retina (inner)	—	light-sensitive layer with rods and cones

A thin transparent conjunctiva covers the front of the eye. The ciliary body lies at the junction of the choroid and iris and is itself part of the choroid.

Inside the eye.

Lens: transparent, biconvex, held by suspensory ligaments attached to the ciliary body.
Aqueous humour: watery fluid in front of the lens; vitreous humour: jelly behind it. Both keep the eyeball's shape.
Rods: work in dim light; contain the pigment rhodopsin (visual purple); give black-and-white vision. Owls and other night animals have many rods.
Cones: work in bright light; give colour vision.
Yellow spot (fovea): most cones, sharpest vision. Blind spot: where the optic nerve leaves; no rods or cones.

Accommodation. Focusing objects at different distances by changing the focal length of the lens, done by the ciliary muscles (not the iris).

Object	Ciliary muscles	Suspensory ligaments	Lens
Near	contract	slacken	thicker, more convex (shorter focal length)
Far	relax	tighten	thinner, flatter (longer focal length)

Adaptation. Bright light: pupil constricts, cones active. Dim light: pupil dilates, rhodopsin builds up in the rods, so vision improves slowly (dark adaptation).

Stereoscopic vision. Both eyes face forward; their fields overlap, and the brain merges two slightly different images into one three-dimensional image, letting us judge depth and distance.

Defects and corrections.

Defect	Cause	Image of the problem object	Correction
Myopia (short sight): far objects blurred	eyeball too long or lens too curved	in front of the retina	concave lens
Hypermetropia (long sight): near objects blurred	eyeball too short or lens too flat	behind the retina	convex lens
Presbyopia	ageing: lens less elastic, ciliary muscles weaker	near objects blurred	convex or bifocal lens
Astigmatism	uneven curvature of cornea (or lens)	parts blurred	cylindrical lens
Cataract	lens becomes opaque (cloudy), usually with age	dim, blurred vision	surgery: remove the lens, implant an artificial lens

Flow chart: path of light. Light → conjunctiva → cornea → aqueous humour → pupil → lens → vitreous humour → retina (rods and cones) → optic nerve → cerebrum (sight).

Draw-and-label checklist: V.S. of eye. Labels: conjunctiva, cornea, aqueous humour, iris, pupil, lens, suspensory ligament, ciliary body, sclera, choroid, retina, vitreous humour, yellow spot, blind spot, optic nerve. The blind spot sits where the optic nerve leaves, slightly off the axis.

Draw-and-label checklist: myopia and hypermetropia (only these two need diagrams). Myopia: parallel rays from a distant object meet in front of the retina; corrected diagram adds a concave lens so rays meet on the retina. Hypermetropia: rays from a near point meet behind the retina; corrected diagram adds a convex lens. Show arrows on rays and a dot at the focus.

The Human Eye and Its Defects: key facts

Coats of the eye: Sclera cornea in front
Choroid ciliary body and iris in front
Retina rods (dim, rhodopsin) and cones (bright, colour); Ciliary body is part of the choroid.
Accommodation: Near: ciliary muscles contract, ligaments slack, lens thicker | Far: ciliary muscles relax, ligaments tight, lens thinner; Ciliary muscles focus; iris controls light.
Defects: Myopia image in front, concave lens
Hypermetropia image behind, convex lens
Presbyopia convex or bifocal
Astigmatism cylindrical
Cataract opaque lens, surgery; Far blurred = myopia; near blurred = hypermetropia.

Sclera	cornea in front
Choroid	ciliary body and iris in front
Retina	rods (dim, rhodopsin) and cones (bright, colour)

Myopia	image in front, concave lens
Hypermetropia	image behind, convex lens
Presbyopia	convex or bifocal
Astigmatism	cylindrical
Cataract	opaque lens, surgery

How to answer The Human Eye and Its Defects questions

ICSE gives a case (a student who cannot read the board, an old man with cloudy vision, an owl at night) or a labelled eye, and asks for the defect, the part involved, the cause, the correcting lens or a diagram.

1Decide which objects are blurred: far → myopia; near → hypermetropia or presbyopia (if elderly).
2State where the image forms: in front of or behind the retina.
3Give the lens: concave for myopia, convex for hypermetropia, cylindrical for astigmatism.
4For focusing questions, name the ciliary muscles and describe the lens shape.
5For dim-light questions, name rods and rhodopsin.

The Human Eye and Its Defects in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Blurred road signs

Suppose a boy who spends hours on video games finds that road signs look blurred while he is cycling, though he reads comics easily.

Identify the defect, explain it and suggest the correction.

Try it first, then show the solutionSolution

Distant objects are blurred while near ones are clear: myopia.
His eyeball is slightly too long (or the lens too curved), so light from far objects focuses in front of the retina.
A concave lens spreads the rays slightly before they enter the eye.
The image then falls on the retina.

Answer: Myopia; image in front of the retina; corrected with concave lenses.

Memory hook: My-opia: I see only what is near me.

Entering a dark cinema

Suppose you walk from a sunny street into a dark cinema hall. At first you cannot see the seats, but after a few minutes you can.

Explain the adjustment.

Try it first, then show the solutionSolution

In sunlight the pupil was small and cones were doing most of the work.
In the dark the iris widens the pupil to let in more light.
Rhodopsin, bleached in bright light, slowly builds up again in the rods.
As rods become sensitive, dim shapes become visible: dark adaptation.

Answer: The pupil dilates and rhodopsin is rebuilt in the rods, so vision slowly returns.

Memory hook: Rods rule the dark.

Tricks to remember The Human Eye and Its Defects

Short memory aids. Say each one aloud once, then use it on a question the same day.

SCR from outside in
Sclera, Choroid, Retina: 'Some Cats Run'.
Use it when: Order of the three coats.
Near = Ciliary Contract
Near work makes muscles work: contract, lens bulges.
Use it when: Accommodation.
MCC and HVX
Myopia: Concave lens, image in front (Close). Hypermetropia: conVeX lens.
Use it when: Matching defect and lens.

The Human Eye and Its Defects: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Seeing at night · 1 mark · MCQBoard level

Which statement about the retina is correct?
(a) Cones contain rhodopsin and work best in dim light. (b) Rods contain rhodopsin and work best in dim light. (c) Rods give colour vision in bright light. (d) The blind spot has the largest number of cones.
(A night-vision idea was asked with owls in 2025.)

Try it first, then show the solutionSolution

Rods work in dim light and contain rhodopsin; cones give colour vision in bright light; the blind spot has no rods or cones (the yellow spot has the most cones).

Answer: (b) Rods contain rhodopsin and work best in dim light.

Example 2: Focusing muscle · 2 marks · Short answerBoard level

Name the structure that changes the curvature of the lens, and the part of the choroid it lies in. State what it does when you read a book.

Try it first, then show the solutionSolution

Ciliary muscles, in the ciliary body of the choroid (1 mark).
For reading (near), they contract, the suspensory ligaments slacken and the lens becomes thicker (1 mark).

Answer: Ciliary muscles in the ciliary body; they contract so the lens thickens for near vision.

Example 3: Phone at arm's length · 3 marks · Short answerHarder board level

A 45-year-old who has always had normal vision now holds his phone at arm's length to read it. (a) Name the defect. (b) Explain its cause in terms of the lens and ciliary muscles. (c) His sister, who is myopic, develops the same problem. Why may she need bifocal lenses?

Try it first, then show the solutionSolution

(a) Presbyopia (1 mark).
(b) With age the lens loses elasticity and the ciliary muscles weaken, so the lens cannot become thick enough to focus near objects (1 mark).
(c) She needs a concave part for distant objects (myopia) and a convex part for reading (presbyopia), combined in bifocals (1 mark).

Answer: (a) Presbyopia. (b) Less elastic lens and weaker ciliary muscles. (c) Concave upper part for distance, convex lower part for reading.

Example 4: Rods versus cones · 2 marks · Short answerHarder board level

Give two differences between rods and cones.

Try it first, then show the solutionSolution

Rods work in dim light; cones in bright light (1 mark).
Rods contain rhodopsin and give no colour; cones give colour vision (1 mark).

Answer: Dim versus bright light; rhodopsin, no colour versus colour vision.

Example 5: One-eyed catch · 2 marks · Short answerHOTS / competency

Suppose a cricketer who loses sight in one eye finds it much harder to catch high balls, although he sees the ball clearly. Explain using stereoscopic vision.

Try it first, then show the solutionSolution

With two eyes, overlapping fields give two slightly different images that the brain combines into a 3-D image (1 mark).
With one eye, depth and distance are hard to judge, so he misjudges where the ball will arrive (1 mark).

Answer: Loss of stereoscopic vision makes judging depth and distance difficult.

Example 6: Two myopia remedies · 3 marks · Case-basedHOTS / competency

Suppose a myopic student is offered either glasses or an operation that slightly flattens the cornea. (a) Where does the image of a distant object form in her eye now? (b) How does the concave lens correct this? (c) Why might flattening the cornea also work?

Try it first, then show the solutionSolution

(a) In front of the retina (1 mark).
(b) A concave lens diverges the rays so that, after refraction by the eye, they meet on the retina (1 mark).
(c) A flatter cornea bends light less, moving the focus back on to the retina (1 mark).

Answer: (a) In front of the retina. (b) Diverging rays shift the focus back. (c) Less bending by the cornea also moves the focus back.

Where students lose marks in The Human Eye and Its Defects

The slips examiners see most often, and what to write instead.

Mistake: Iris for ciliary muscles
CISCE examiners' comments (2024): for adjusting the focal length of the lens, candidates wrote iris instead of ciliary muscles.
Do this: Ciliary muscles focus; iris controls light.
Usually costs: 1 mark.
Mistake: Myopia answered as hypermetropia
CISCE examiners' comments (2024): for a student unable to see the blackboard, candidates wrote hyperopia, said the image forms beyond the retina, and suggested a convex lens.
Do this: Far blurred = myopia, image in front, concave lens.
Usually costs: 1-3 marks.
Mistake: Cataract placed in the wrong part
CISCE examiners' comments (2025): candidates wrote cornea, retina or iris instead of lens, or the vague 'eye is weak'.
Do this: Cataract = lens becomes opaque.
Usually costs: 1 mark.
Mistake: Suspensory ligament for ciliary body
CISCE examiners' comments (2025): for the structure at the junction of the choroid and iris, part of the choroid, candidates wrote suspensory ligament.
Do this: Ciliary body; ligaments only hold the lens.
Usually costs: 1 mark.
Mistake: Rods and cones swapped
CISCE examiners' comments (2025): in the owl question, candidates confused the functions of the sensory cells in dim and bright light.
Do this: Rods: dim light, rhodopsin. Cones: bright light, colour.
Usually costs: 1 mark.

Exam tips

Ciliary muscles focus; iris controls light.
Myopia: concave; hypermetropia: convex; astigmatism: cylindrical.
Cataract: opaque lens, surgery.
Diagrams only for myopia and hypermetropia.

Practice questions on The Human Eye and Its Defects

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The defect in which the eye lens becomes opaque is:
(a) myopia (b) astigmatism (c) cataract (d) presbyopia
Hint
Cloudy lens.
Answer
(c) cataract.
Q2 · 1 mark · Very short answerBoard level
Name the part of the retina with no rods or cones.
Hint
Where the optic nerve leaves.
Answer
Blind spot.
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): A person with astigmatism is given cylindrical lenses.
Reason (R): Astigmatism is due to uneven curvature of the cornea.
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(d) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
Hint
Uneven curvature needs uneven correction.
Answer
(c).
Q4 · 2 marks · Short answerHarder board level
State the functions of (a) the iris, (b) the vitreous humour.
Hint
Light; shape.
Answer
(a) Controls the size of the pupil and so the amount of light entering. (b) Keeps the shape of the eyeball and supports the retina.
Q5 · 2 marks · Short answerHarder board level
Explain why reading a book for two hours tires the eyes more than gazing at distant mountains for the same time.
Hint
Which muscles work for near vision?
Answer
For near objects the ciliary muscles must stay contracted to keep the lens thick; for distant objects they are relaxed, the suspensory ligaments are tight and the lens is thin, so no muscular effort is needed.
Q6 · 2 marks · Short answerHarder board level
What is the yellow spot, and why is vision sharpest there?
Hint
Cones.
Answer
The yellow spot (fovea) is a small area of the retina opposite the lens; it has the greatest number of cones, so detail and colour are seen most sharply.
Q7 · 2 marks · Short answerHarder board level
Name the defect, the position of the image and the correcting lens for a person who sees far objects clearly but not near ones (not due to age).
Hint
Eyeball too short.
Answer
Hypermetropia; image of near objects forms behind the retina; convex lens.
Q8 · 3 marks · Case-basedHOTS / competency
Read and answer.
Suppose after cataract surgery a 70-year-old man has an artificial lens of fixed shape implanted in his eye.
(a) Which natural part was removed, and why? (1)
(b) Why can the new lens not accommodate? (1)
(c) What kind of spectacles will he still need for reading, and why? (1)
Hint
Accommodation needs a lens that can change shape.
Answer
(a) The eye lens, because it had become opaque and blocked light. (b) A fixed lens cannot change its curvature when the ciliary muscles contract. (c) Convex reading glasses, because the eye is set for distance and cannot focus near objects by itself.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What is the transparent front part of the sclera?Show answer
Cornea.
2.Which pigment is found in rods?Show answer
Rhodopsin (visual purple).
3.What holds the lens in place?Show answer
Suspensory ligaments.
4.Which lens corrects myopia?Show answer
Concave lens.
5.What is stereoscopic vision?Show answer
Combining images from both eyes into one 3-D image to judge depth and distance.

The Human Eye and Its Defects: frequently asked questions

Do I need ray diagrams for presbyopia or astigmatism?

No. Diagrams are required only for myopia and hypermetropia.

Is the pupil a structure?

It is the opening in the centre of the iris, not a separate tissue.

Why are eye pages in both Physics and Biology?

Physics stresses lens optics; Biology stresses parts, functions, accommodation and defects with their causes.

Why do we not notice the blind spot?

The two eyes' blind spots fall on different parts of the scene, and the brain fills in the gap.