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What vision does

Sight is several abilities working together. Start with one of them, then follow the links to a lab, an everyday scene or a condition guide.

These links organise learning. They do not show which condition is likely, how severe anything is, or everything a person may experience.

Central and side vision

Finding a face and noticing the edge of a step make different demands on sight. One uses the centre of your view. The other uses the edges.

Condition guides linked to this

Glaucoma Macular degeneration Diabetic retinopathy Flashes & floaters Retinal detachment Retinitis pigmentosa Rod-cone dystrophy Cone-rod dystrophy Stargardt disease Usher syndrome Choroideremia

Try this: Try a central patch and an outer mask on the same living room. What happens to the clock, the door and the coffee table?

Comfortable light and glare

Glare can be uncomfortable and can wash out detail. Where the light comes from matters as much as how much light there is.

Condition guides linked to this

Cataracts Uveitis Retinitis pigmentosa Rod-cone dystrophy Cone-rod dystrophy Stargardt disease Usher syndrome Achromatopsia Choroideremia

Try this: Move the lamp to the side and try diffusing the light. Compare how readable the page is as the reflection moves.

Rods, cones and dim light

Rods work in dim light. Cones handle colour and fine detail in brighter light. Adjusting to darkness is a separate problem from discomfort in bright light.

Condition guides linked to this

Retinitis pigmentosa Rod-cone dystrophy Cone-rod dystrophy Usher syndrome Choroideremia

Try this: Compare the day and evening rooms. Look at the rug and the doorway. These scenes cannot test dark adaptation.

Colour and other clues

Colour helps you tell things apart. Clear labels and patterns make the same information readable without relying on colour.

Condition guides linked to this

Rod-cone dystrophy Cone-rod dystrophy Stargardt disease Achromatopsia Colour vision deficiency Red-green colour vision deficiency Blue-yellow colour vision deficiency

Try this: Turn the route map to grey, then add words and line patterns. Can you still follow the route?

Detail against a background

Sharp edges only help when they stand out from the background. Contrast, print size and blur each change how easy a task is.

Condition guides linked to this

Cataracts Macular degeneration Diabetic retinopathy Keratoconus Rod-cone dystrophy Stargardt disease Achromatopsia

Try this: Change print size, contrast and blur one at a time. Which change makes the appointment card easier to read?

Focus and the optics of the eye

The cornea and lens focus light onto the retina. A focusing problem is different from damage to the light-sensitive cells or the optic nerve.

Condition guides linked to this

Cataracts Dry eyes Blepharitis Keratoconus Uveitis Short-sightedness Long-sightedness Astigmatism Presbyopia Amblyopia (lazy eye)

Try this: Compare near and distant targets in the focus model. Notice where the light meets, compared with the retina.

Two eyes working together

Your brain combines the view from each eye with perspective, size and movement. Judging depth uses several clues at once.

Condition guides linked to this

Amblyopia (lazy eye)Strabismus (squint)

Try this: Move the foreground post between the two viewpoints. Nearby and distant objects shift by different amounts.

Compare the vision functions in two guides