Cognito · AQA Biology 2026/27The Eye — structure and accommodation
Key facts
Structure of the eye
Cornea — transparent front of eye. Refracts (bends) most of the light entering the eye.
Iris — coloured muscle ring. Controls the size of the pupil (the hole through which light passes).
Lens — focuses light onto the retina. Changes shape (accommodation) to focus near/far objects.
Retina — contains light-sensitive cells: rods (sensitive to dim light, black and white) and cones (colour vision, need bright light).
Optic nerve — carries impulses from retina to brain.
Blind spot — where optic nerve joins retina. No rods or cones here.
Accommodation and common defects
Accommodation — ciliary muscles and suspensory ligaments change lens shape to focus on near/far objects.
Near object: ciliary muscles contract → suspensory ligaments relax → lens becomes fat/curved → more refraction.
Far object: ciliary muscles relax → suspensory ligaments tighten → lens becomes thin/flat → less refraction.
Short sight (myopia) — eyeball too long or lens too curved. Light focuses in front of retina. Corrected by concave (diverging) lens.
Long sight (hyperopia) — eyeball too short or lens too flat. Light focuses behind retina. Corrected by convex (converging) lens.
Exam questions — 3 questions · 9 marks
⚡ Extended questions included. Read the hint. Write in full sentences. AI marks against the AQA mark scheme.
1 markAccommodation — near objectAQA 8461 P2 style
What happens to the ciliary muscles and lens when focusing on a near object?
A Ciliary muscles relax, suspensory ligaments tighten, lens becomes thin
B Ciliary muscles contract, suspensory ligaments relax, lens becomes fat and curved giving greater refraction
C Ciliary muscles contract, suspensory ligaments tighten, lens becomes thin
D Ciliary muscles relax, suspensory ligaments relax, lens becomes fat
1 markShort sight correctionAQA 8461 P2 style
A person is short-sighted. What type of lens corrects this and why?
A A convex (converging) lens — to add extra bending power to a weak lens
B A concave (diverging) lens — to diverge the light rays slightly before they enter the eye so they focus on the retina rather than in front of it
C A flat lens — to stop any refraction occurring in the cornea
D A convex lens — to shorten the focal length of the image
4 marksCompare rods and conesAQA 8461 P2 style
Compare the distribution and function of rods and cones in the retina. Explain why humans see colour poorly in dim light. (4 marks)
Hint: Rods: where, what light needed, what they detect. Cones: where, what light needed, what they detect. Then explain why dim light = no colour vision.