Eyes Reflex
Accommodation reflex
When you look at something close, three things happen at once. The eyes turn inward, the pupils shrink, and the lens in each eye gets fatter. You do not decide any of it.
Everyone
Eyes
Things you can see that are not out there, and structural quirks of the eye.
Showing 39 oddities.
The eye is not a camera. It is a curved patch of light-sensing cells wired to a brain that edits the picture before you see it. Gaps get painted over, motion gets smoothed, and colour gets guessed where there is none.
What ties the region together is a gap between what light actually does and what you experience. Sometimes the gap is a structural quirk you can see from outside. Other times it is a construction you only notice once someone points it out.
Results narrow the list below as you type.
Mainly this region
Eyes Perception
Afterimages
An image that stays in your vision after the thing you looked at is gone. Bright things leave a same-colour copy for a moment. Long stares leave a copy in opposite colours.
Everyone
Eyes Perception
Blue arcs of the retina
Look at a small red light in a dark room and two faint blue arcs curve away from it towards your blind spot. The arcs follow the paths of the nerve fibres in your own retina.
94% of healthy eyes in one clinic test
Eyes Perception
Blue field entoptic phenomenon
Tiny bright dots that dart along wiggly paths when you look at a clear blue sky. They are your own white blood cells moving through the capillaries of the retina.
Most people
Eyes Perception
Closed-eye hallucinations
Close your eyes and you do not see nothing. You see speckle, drifting colour, and, as you fall asleep, moving patterns and even scenes. Almost everyone sees the speckle, and many people see more. Almost nobody talks about them.
Almost everyone
Eyes Trick
Crossing your eyes
Turning both eyes inward toward the nose on purpose. Most people with normal two-eyed vision can do it. Your eyes will not get stuck that way.
Most people (no formal count)
Eyes Variation
Distichiasis
A second row of eyelashes growing from the oil-gland openings along the inner edge of the eyelid. It is rare. It can be inherited or acquired. Elizabeth Taylor was born with it.
About 1 in 10,000 people
Eyes Perception
Eigengrau
The colour you see in total darkness is not black. It is a very dark grey, most likely because the light-sensing cells in your eyes fire a little even when no light reaches them.
Everyone
Eyes Reflex
Emotional tears
Humans are the only animals known to weep from feeling. Emotional tears have a different chemistry from the tears that wash the eye, and babies cannot make them until one or two months after birth.
Almost everyone
Eyes Trick
Eyelid flipping
Turning the upper eyelid inside out so the pink inner surface shows. Nobody has counted how many people can do it. Eye doctors do it to patients to look for grit.
No formal count Icky
Eyes Involuntary
Floaters
Small grey threads, dots, or cobwebs that drift across your vision and dart away when you look at them. They are shadows of tiny clumps inside the eye. They are common and usually harmless.
76% in one survey of 603 people
Eyes Perception
Foveal tritanopia
The very centre of your vision cannot see blue. The middle of the fovea has no blue-sensitive cones at all. You never notice, because the brain fills the colour in from the surrounding area.
Everyone
Eyes Perception
Haidinger's brush
Humans can see the polarization of light without any tool. It appears as a faint yellow bow-tie in the middle of your vision when you look at a white screen or a blue sky.
Most people, with practice
Eyes Variation
Heterochromia
Eyes of two different colours, or one eye with two colours, in fewer than 1 in 100 people. When it is present from birth it is usually harmless.
Fewer than 200,000 people in the US
Eyes Trick
Independent eye movement
Moving one eye while the other stays still, or moving the two eyes in different directions. Few people seem to manage it, and nobody has counted them. Chameleons do it all day.
No formal count
Eyes Perception
Palinopsia
An image that keeps appearing after the thing you saw is gone. A faint afterimage after a bright light is normal and harmless. Copies that persist or return later need a doctor.
Not counted in the general population
Eyes Involuntary
Phosphenes
The flashes, rings, and patterns of light you see when you rub or press your closed eyes, or after a knock on the head. Pressure on the eye makes the retina fire without any light.
Anyone with a working retina
Eyes Reflex
Pupillary light reflex
Shine a light into one eye and both pupils shrink, even the eye in the dark. The wiring crosses in the midbrain so that the two pupils react together. You can watch it in a mirror.
Everyone
Eyes Perception
Purkinje effect
As the light fades at dusk, red things go dark first and blue things stay bright. Your eyes switch from colour-sensing cones to blue-favouring rods, and the whole world shifts towards blue.
Everyone
Eyes Perception
Purkinje images
A candle held near someone's eye produces four tiny reflections, one from each surface of the cornea and lens. Eye trackers and eye doctors use them. In the right conditions you can see two of them inside your own eye.
Everyone
Eyes Perception
Purkinje tree
A branching shadow of your own retinal blood vessels. It is always on your retina, but you only see it when light enters the eye from an unusual angle and the shadow moves.
Everyone
Eyes Perception
Tetrachromacy
Most people have three kinds of colour-sensing cone. About 12% of women carry a fourth. In theory they can tell apart colours that look identical to everyone else. Clear cases are extremely rare, and online tests cannot detect it.
About 12% of women carry a fourth cone type
Eyes Perception
The blind spot
Each eye has a hole in its field of view where the optic nerve leaves the retina. You never notice it, because the brain paints over the gap with whatever surrounds it.
Everyone
Eyes Perception
Troxler effect
When you hold your gaze on one point, things in the edge of your vision fade out and disappear. The brain stops reporting anything that does not change.
Everyone
Eyes Trick
Voluntary nystagmus
About 8% of people can make both eyes shake rapidly from side to side on command. It looks alarming and is harmless. It is tiring and lasts only seconds.
About 8% of people
Eyes Trick
Voluntary pupil control
Changing the size of your pupils by will alone, without imagining a light or doing sums. One case has been studied with modern methods. Older reports exist, but most describe indirect tricks. Indirect control by thinking hard is possible for almost everyone.
One modern case study. No rate known
Eyes Trick
Wall-eyed divergence
Turning both eyes outward, away from the nose, on purpose. Nobody has counted how many people can do it. Most people can learn the mild version, parallel viewing, from Magic Eye pictures.
Not known
Also involves this region
These entries belong to another region first, and touch this one too.
Brain Perception
Alice in Wonderland syndrome
Objects, body parts, or the whole room suddenly look far too big, far too small, or far away. It mostly happens to children, often during a fever or infection, and it passes on its own. In adults it is usually linked to migraine.
6–7% of teenagers (size distortion)
Brain Perception
Charles Bonnet syndrome
People who lose a lot of their sight often start to see things that are not there: patterns, faces, small people in costume, whole landscapes. They know the images are not real. It is caused by sight loss, not by mental illness.
10–40% of older people with serious sight loss
Brain Perception
Chronostasis
Glance at a clock and the second hand can seem to freeze for a moment before it moves. The brain hides your eye movement and stretches the first thing you see to cover the gap.
Everyone
Brain Perception
Ganzfeld effect
Fill your whole field of view with a featureless colour and, after some minutes, your brain may start inventing shapes, lights, and scenes. Two halved ping-pong balls and a lamp are enough to do it at home.
Most people who try it, in lab tests
Brain Involuntary
Migraine aura
A shimmering zigzag or C-shaped patch of light that grows across your vision over 5 to 60 minutes and then fades. It can come before a migraine headache or, in some people, with no headache at all.
About 5% of people
Brain Perception
Motion aftereffect
Watch something move in one direction for about a minute, then look at something still. The still thing appears to drift the opposite way for a few seconds.
Everyone
Heart Reflex
Oculocardiac reflex
Pressure on the eyeball, or a pull on an eye muscle, makes the heart slow down. It matters most during eye surgery, especially in children. It is not a safe way to slow your own heart.
Found in 14–90% of eye muscle operations. Its strength varies a lot.
Nerves Reflex
Photic sneeze reflex
About one person in four sneezes when they step into bright sunlight. It runs in families, and the leading idea is a wiring mix-up between the nerve for the eyes and the nerve for the nose.
About 18–35% of people
Brain Perception
Prisoner's cinema
After hours or days in darkness, people start to see light shows: colours, geometric patterns, and sometimes figures or scenes. Prisoners, truck drivers, pilots, and meditators all report it.
77% of sighted people blindfolded for four days
Heart Involuntary
Seeing stars when standing up
You stand up fast, your vision goes grey or sparkly, and your head feels light for a few seconds. Blood has briefly pooled in your legs. It passes on its own.
Almost everyone, at some time
Brain Perception
Strange-face illusion
Stare at your own face in a mirror in dim light for a few minutes and it starts to distort. Most people see their features warp. Some see a stranger, an animal, or a monster.
66% see their face distort
Brain Involuntary
Visual snow
Tiny flickering dots across the whole field of vision, like static on an old TV, present with eyes open or closed. About 2% of people have it. The eyes are fine. The visual part of the brain is over-active.
About 2% of people