The Human Eye
The eye focuses light on the retina with a flexible lens.
About this topic
The eye focuses light through the cornea and a flexible lens onto the retina, where rods (dim light) and cones (colour) send signals along the optic nerve to the brain. The iris adjusts the pupil size. The ciliary muscles change the lens shape to focus at different distances, called accommodation.
Most of the bending of light happens at the cornea, and the lens does the fine focusing. The image on the retina is inverted, and the brain flips it. In short sight (myopia) the image forms in front of the retina, corrected by a diverging lens; in long sight (hypermetropia) it forms behind, corrected by a converging lens. Ageing makes the lens stiffer, which is why many people need reading glasses after 45.
Worked example: a person whose far point is 2 m instead of infinity needs a diverging lens of focal length 2 m, so power −0.5 D, which makes distant objects appear to be at 2 m for the eye to focus on. The normal near point is about 25 cm.
The eye adapts to dim light over about 20 to 30 minutes by building up rhodopsin in the rods. The blind spot, where the optic nerve leaves, has no receptors, yet we do not notice it. A misconception is that the lens does most of the focusing; the cornea does, and the lens only adjusts. Another is that we see colour in dim light; rods do not detect colour.
Key ideas
- Cornea and lens refract
- Rods and cones detect light
- Glasses correct focus
Quick check
Use cases: where The Human Eye helps
- Homework: review the key idea behind The Human Eye before you start a problem set.
- Exam revision: use the quick check to test whether you can recall The Human Eye without notes.
- Visual learning: play with the interactive lab to see how The Human Eye changes when you adjust its inputs.
- Teaching a friend: explain The Human Eye in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is The Human Eye?
The eye focuses light on the retina with a flexible lens.
What will I learn in The Human Eye?
Cornea and lens refract. Rods and cones detect light. Glasses correct focus.
Is The Human Eye part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the The Human Eye lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study The Human Eye?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.