Eye Anatomy

Structure of the Human Eye

Key Components

Component	Function
Cornea	Clear front surface, provides most of the eye’s focusing power
Lens	Focuses light onto the retina; changes shape for accommodation
Pupil	Opening that controls light entry; dilates/contracts
Iris	Controls pupil size
Retina	Light-sensitive layer at the back of the eye
Fovea	High-resolution region at the centre of vision
Optic nerve	Transmits signals to the visual cortex

Inverted Vision

The lens forms an inverted image on the retina. The brain interprets this correctly—it is the image formed on the retina, not our perception, that is inverted.

The Lens and Accommodation

Focusing Mechanism

The lens changes shape to focus on objects at different distances:

• Near objects: Lens becomes rounder (greater refractive power)
• Far objects: Lens becomes flatter (less refractive power)

This process is called accommodation.

Refractive Errors

Condition	Cause	Effect
Myopia	Eyeball too long or cornea too curved	Distant objects blurred
Hyperopia	Eyeball too short or cornea too flat	Near objects blurred
Presbyopia	Lens loses flexibility with age	Difficulty focusing on near objects
Astigmatism	Irregular cornea shape	Distorted vision at all distances

The Fovea

The fovea is a small depression in the retina:

• Contains the highest concentration of cone cells
• Responsible for sharp central vision
• Essential for tasks requiring detail: reading, driving, recognising faces

Visual Field

• Central vision: Foveal region, high acuity, colour perception
• Peripheral vision: Outside fovea, motion detection, lower resolution

Eye Movements

Types of Eye Movements

Movement	Purpose
Saccades	Rapid movements to scan a scene
Pursuit	Smooth tracking of moving objects
Vergence	Convergence/divergence for depth perception
Vestibulo-ocular	Stabilise image during head movement

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Summary

• The eye focuses light onto the retina through cornea and lens
• The fovea provides sharp central vision with high cone density
• The lens accommodates to focus on objects at varying distances
• The retina transmits visual information via the optic nerve

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Past Paper Questions

2024 Paper 3 Question 3: Describe the structure of the human eye and the function of each component.

2022 Paper 3 Question 3: What is the role of the lens in human vision? How does it accommodate?

2020 Paper 3 Question 3: Explain the difference between central and peripheral vision.