The Human Eye: Structure & Conditions

The Human Eye: Structure & Conditions

Understanding vision and eye health AQA GCSE Biology Year 11

Learning Objectives

Identify the main structures of the human eye Explain how the eye focuses light to form images Describe common eye conditions and their causes Understand how corrective lenses work

The Eye as a Sense Organ

Detects light and converts it to electrical signals Part of the nervous system Works with the brain to create vision Most complex sense organ in the human body

Eye Structure Overview

The Cornea

Transparent front layer of the eye Provides most of the eye's focusing power No blood vessels - gets oxygen from tears First structure light passes through

The Iris and Pupil

Iris is the colored part of the eye Contains muscles that control pupil size Pupil is the opening in the center of the iris Regulates amount of light entering the eye

Pupil Response Activity

Work in pairs Observe your partner's pupils in normal light Cover one eye for 30 seconds, then uncover Record what happens to pupil size

The Lens

Transparent, flexible structure Changes shape to focus light precisely Controlled by ciliary muscles Becomes less flexible with age

The Retina

Light-sensitive layer at the back of the eye Contains photoreceptor cells (rods and cones) Rods detect light intensity (black and white) Cones detect color (red, green, blue)

Rods vs Cones Comparison

{"left":"Rods: 120 million in each eye\nCones: 6 million in each eye\nRods: Work in dim light\nCones: Work in bright light","right":"Rods: No color detection\nCones: Detect red, green, blue\nRods: Located throughout retina\nCones: Concentrated in fovea"}

The Optic Nerve

Bundle of nerve fibers carrying signals to brain Contains about 1 million nerve fibers Creates the 'blind spot' where it connects Signals travel to the visual cortex

Find Your Blind Spot

Draw an X and O about 8cm apart Close your right eye, focus on the O Slowly move the paper closer to your face Notice when the X disappears