7 min readConcept sheetA 3-mark or 5-mark question with a labelled diagram; near point and far point come as 1-mark MCQs

The human eye and power of accommodation

The eye lens forms a real, inverted image on the retina. Ciliary muscles change its focal length so we see near and far: this is the power of accommodation.

Near point (normal eye)About 25 cm, the least distance of distinct vision

Far point (normal eye)Infinity

Image on the retinaReal and inverted

Most bending of lightAt the outer surface of the cornea

Parts of the eye and their jobs

Part	What it does
Cornea	The thin, clear bulge at the front of the eyeball. Light enters here, and most of the refraction happens at its outer surface
Iris	A dark muscular ring behind the cornea. It controls the size of the pupil
Pupil	The opening in the iris. It controls the amount of light that enters: small in bright light, wide in dim light
Eye lens	A clear, jelly-like convex lens. It fine-tunes the focal length so the image falls on the retina
Ciliary muscles	Hold the eye lens and change its curvature (how curved it is)
Retina	The light-sensitive screen at the back. Its cells make electrical signals when light falls on them
Optic nerve	Carries the signals from the retina to the brain, which makes sense of them

How the eye sees and adjusts its focus

1
Light from an object enters through the cornea and passes through the pupil.
2
The cornea and the eye lens together form a real, inverted image on the retina.
3
Retina cells turn the light into electrical signals. The optic nerve carries them to the brain, which lets us see the object as it is.
4
Looking far away: the ciliary muscles relax. The lens becomes thin, its focal length increases, and distant objects come into focus.
5
Looking at something near: the ciliary muscles contract. The lens becomes thick (more curved), its focal length decreases, and near objects come into focus.
6
This ability of the eye lens to adjust its focal length is the power of accommodation. The focal length cannot go below a certain minimum, so objects held very close look blurred.

Near point vs far point

Near pointThe closest distance at which the eye sees clearly without strain. It is also called the least distance of distinct vision. For a young adult with normal vision it is about 25 cm.

Far pointThe farthest point up to which the eye sees clearly. For a normal eye it is infinity.

So a normal eye sees clearly anything between 25 cm and infinity. Hold this page 10 cm from your eye: it blurs, because it is closer than your near point.

How to draw the human eye

1
Draw a large circle for the eyeball (in real life it is about 2.3 cm across).
2
On the left, draw a small curved bulge outside the circle. Label it cornea.
3
Just behind the cornea, draw two short dark bands, one from the top and one from the bottom, with a gap between them. Label the bands iris and the gap pupil.
4
Behind the iris, draw an upright convex lens shape. Label it eye lens (the textbook figure calls it the crystalline lens). Join its top and bottom to the eyeball wall with short lines and label them ciliary muscles.
5
Shade a thin layer along the inside of the back wall. Label it retina.
6
From the back of the eyeball, draw a thick cord going out to the right. Label it optic nerve.
7
Label two more parts, as the textbook figure does. The space between the cornea and the lens is the aqueous humour (a clear, watery fluid). The large space behind the lens is the vitreous humour (a clear jelly).

In real life

Reading a phone or a book for a long time keeps the ciliary muscles contracted. Looking up at something far away, like the trees outside the classroom window, now and then lets them relax.

Exam angle

1 marks: “What is the near point of the normal eye of a young adult?” About 25 cm.

2 marks: “Define the power of accommodation. What do the ciliary muscles and the eye lens do when we look at a distant object?” The ability of the eye lens to adjust its focal length. For a distant object the ciliary muscles relax, the lens becomes thin and its focal length increases.

3 marks: “Draw a labelled diagram of the human eye and state the functions of the iris and the retina.” Diagram with cornea, iris, pupil, eye lens, ciliary muscles, retina and optic nerve. Iris: controls the size of the pupil. Retina: light-sensitive screen whose signals go to the brain through the optic nerve.

Remember it

Far = flat: for far objects the muscles relax and the lens stays thin. Near = thick: for near objects the muscles contract and the lens bulges.