Interesting facts about Eyes

Interesting Facts about Eyes

The eye is known as a window to the brain and some people call it to the window to the soul even. There are many interesting facts and observations about eyes which may be of interest to anybody interested to more about “the Eyes”.

• In a very basic form, eyes are thought to have first developed in animals around 550 million years ago!

Eye don’t see what mind does not know

 

• We actually see with our brain, not our eyes. Our eyes function as a camera, capturing light and sending data back to the brain.
• We see things upside down – it is our brain which turns the image the right way up.

The Eyes and Blinking

• In a single second, it’s possible to blink five times.
• We are likely to blink more often when we are talking.
• The eye is the fastest muscle in our body – hence why when something happens quickly, we say ‘in the blink of an eye!’
• A blink typically lasts 100-150 milliseconds.
• On average, we will blink approximately 4,200,000 times in a single year.
• The human eye can function at 100% at any given moment, without needing to rest.

The Eyes and seeing Experience

• Red-eye in photos is caused by light from the flash bouncing off the capillaries in our eyes.
• If the human eye was a digital camera, it would have 576 megapixels.
• We have two eyeballs in order to give us depth perception – comparing two images allows us to determine how far away an object is from us. 
• In the right conditions and lighting, humans can see the light of a candle from 14 miles away.
• Blind people can see their dreams as long as they weren’t born blind.
• 80% of our memories are determined by what we see.
• Reading in dim lighting does not damage our eyes, but it may tire them out.

Healing

• Eyes heal quickly. With proper care, it takes only about 48 hours to repair a minor corneal scratch.

Interesting Facts about Eyes and Pupils

• IF A PT SHOWS NORMAL PUPILLARY REACTIONS NO ADDITIONAL INFORMATION IS TO BE GAINED BY CHECKING NEAR RESPONSE
• PUPILS ARE NEVER AFFECTED IN MYAESTHENIA GRAVIS
• LOSS OF BIL VISION WITH NORMAL FUNDI AND INTACT PUPILLARY RESPONSES POINT TOWARDS ONLY TWO CONDITIONS CORTICAL BLINDNESS OR HYSTERICAL BLINDNESS
• IN LEVERS CONGENITAL AMAUOROSIS THE PUPILS ARE SLUGGISH WHILE IN LEVERS HEREDITARY OPTIC NEUROPATHY THE PUPILLARY RESPONSES ARE RELATIVELY WELL PRESERVED
• BILATERAL COMPLETE BLINDNESS IS ALSO ONE OF THE CAUSE OF LIGHT NEAR DISSOCIATION
• MACULOPATHY OR AMBLYOPIA WILL NOT CAUSE A RELATIVE AFFERENT PUPILLARY DEFECT UNLESS VERY EXTENSIVE
• MEDIA OPACITIES DO NOT CAUSE RAPD IF STRONG LIGHT IS USED
• In POSNER SCHLOSMAN SYND PUPILLARY RESPONSES ARE GOOD
• UNILATERAL BLINDNESS DUE TO RETINAL OR OPTIC NERVE DISEASE DOES NOT CAUSE A DILATED PUPIL
• ISOLATED PUPILLARY DILATATION IS NEVER DUE TO ANEURYSM OR OTHER COMPRESSIVE LESIONS
• THE NEW ONSET OF HORNERS SYND IN KIDS SHOULD PROMPT WORK UP FOR NEUROBLASTOMA
• IN HORNER SYNDROME THE PUPILLARY REFLEXES ARE NORMAL

Eye and Colours

• The world’s most common eye colour is brown.
• The first blue-eyed person is said to have lived 6,000-10,000 years ago.
• Even if no one in the past few generations of our family had blue or green eyes, these recessive traits can still appear in later generations.
• Blue-eyed people share a common ancestor with every other blue-eyed person in the world.
• Heterochromia refers to a condition where eyes are two different colours.
• All babies are colour blind at birth.
• Colour blindness is more common in males.

The Eye and General Health

• During a sight test, health conditions including diabetes and high blood pressure can be detected.
• Diabetes is the number one cause of blindness in adults in the UK.
• Research has found that a tie tied too tightly can increase the risk of glaucoma in men.
• Contrary to urban myth, contact lenses cannot become ‘lost’ behind our eye due to the structure of our eyeball.

The growth of the Eyes

• Although our nose and ears keep growing throughout our lives, our eyes do grow but very slowly.
• A newborn baby will cry, but not produce any tears. Babies do not produce tears until they are around six weeks old.
• Newborn babies can see objects about 8-15 inches away from most clearly.
• The older we get, the feour tears we produce.
• The only cells that survive from the time we are born until death are in our eyes.

The Eye Lids, Lashes and Brows

• Eyelashes have an average lifespan of five months. 
• If we lined up all the eyelashes shed during one human life, they would measure 98 feet long.
• Our eyelashes keep dirt out of our eyes.
• We have all have unseen, harmless microscopic creatures living in our eyelashes.
• Our eyebrows prevent sweat dripping into our eyes.
• The space between our eyebrows is called the Glabella.
• It’s impossible to sneeze with our eyes open.

The Natural Eye Protection and Common Injuries

• One of the most common cosmetic injuries is poking the eyeball with a mascara wand.
• Our eyes close automatically to protect us from perceived dangers.

The Eyes and Ageing

• 94% of visible premature-aging around the eyes is caused by UV damage.

Animal Eyes

• Dogs can’t distinguish between red and green.
• An ostrich’s eye is bigger than its brain.
• A shark’s cornea is used in human eye surgery, as it is the most similar to the human cornea.
• Scorpions can have as many as 12 eyes and the box jellyfish has 24!
• Camel’s eyelashes can measure up to 10cm long to protect its eyelashes from blowing sand and debris in the desert.
• As well as super long eyelashes, camels also have three eyelids to protect their eyes from sand.
• Bees have 5 eyes.
• The eyes of a chameleon are independent of each other, allowing it to look in two different directions at once.
• Geckos can see colors around 350 times better than a human, even in dim lighting.
• Dolphins sleep with one eye open.
• The largest eye on the planet belongs to the Colossal Squid, and measures around 27cm across.
• Snakes have two sets of eyes – one set used to see, and the other to detect heat and movement.
• A dragonfly has 30,000 lenses in its eyes, assisting them with motion detection and making them very difficult for predators to kill.
• The four-eyed fish can see both above and below water at the same time.
• Snakes have no eyelids, just a thin membrane covering the eye.
• Goats have rectangular pupils to give them a wide field of vision.
• Owls are the only bird which can see the color blue.
• Most hamsters only blink one eye at a time.
• Guinea pigs are born with their eyes open!
• A worm has no eyes at all.
• An owl can see a moving mouse more than 150 feet away.
• A scallop has an average of 100 eyes around the edge of its shell to detect predators.
• Owls cannot move their eyeballs – which has led to the distinctive way they turn their heads almost all the way around.
• Some people have a fear of eyes; it’s called emetophobia.

The Eyes and Computer working

• When working at a computer, we should follow the 20-20-20 rule – look at something twenty feet away from our computer every twenty minutes for twenty seconds.

The Peculiarities of the Eyes

• The whole Eye transplants are currently impossible due to the sensitivity of the optic nerve and retina.
• Everyone has one eye that is slightly stronger than the other.
• While a fingerprint has 40 unique characteristics, an iris has 256. This is why retina scans are increasingly being used for security purposes.
• Astigmatism refers to a curvature of the cornea or lens and toric lenses are prescribed to aid the individual’s vision.
• When our eyes are watering it may be a sign of dry-eye, and our eyes are producing more moisture to compensate.
• Oily fish, vitamin A and vitamin C can all help to preserve good eyesight.
• Although the function of tears is to keep eyes clean, scientists don’t understand why we cry when we are upset.
• Albinism affects melanin production; perhaps resulting in extra sensitivity to light and a red-eyed appearance.
• Our nose gets runny when we cry as the tears drain into our nasal passages.
• The Mayans believe that cross-eyes are attractive and so they would make efforts to ensure their children became cross-eyed.
• Pirates believed that wearing gold earrings improved their eyesight.
• The phrase ‘it’s all fun and games until someone loses an eye’ comes from Ancient Rome, as the only rule for their bloody wrestling matches was ‘no eye gouging’.

Ocular Anatomical Facts

• The eyeball is not resting on the maxilla rather it is suspended in the orbit. Therefore, even if maxilla is removed the eyeball will remain in position.
• Only one-sixth of the human eyeball is exposed.
• The superior and inferior recti are inserted at an angle of 23° to the long axis of the eyeball. Coincidentally planet earth is tilted in space and this tilt makes an angle of 23° to the long axis of the earth. There may be a phylogenetic relationship between these two phenomena.
• The ciliary ganglion is the only place in the autonomic nervous system where postganglionic fibres are myelinated.
• The human lens is the organ in the body with maximum protein concentration (33% by weight).
• The anterior capsule of the lens is the thickest basement membrane in the body.
• The cornea is the only tissue in the human body that doesn’t contain blood vessels.
• The muscles in the eye are 100 times stronger than they need to be to perform their function.
• Eyes are the second most complex organ after the brain.
• Our eyes are positioned in a hollowed eye socket, to protect the eye.
• 80% of vision impairment worldwide is curable.
• Our eyes are made up of over 2 million working parts.
• The eyeball weighs around 28 grams.
• The eye muscles are the most active muscles in the human body.

Ocular Embryology

• Our eyes start to develop just two weeks after conception. 
• In a very basic form, eyes are thought to have first developed in animals around 550 million years ago!
• The lens is embryologically derived from the surface ectoderm so it behaves like the skin i.e. it keeps on growing throughout life.
• Embryologically the branching pattern of the central retinal artery is not genetically determined therefore a point of forensic importance:” Identical twins will not have identical fundi”.
• The plica semilunaris is the vestigial remnant of the nictitating membrane of lower animals.
• Iris’ muscles are the only muscles in the human body derived from the ectoderm.

 

Ocular Physiology

• Eyes are able to process 36,000 pieces of information in a single hour.
• In an average life, our eyes will see 24 million different images.
• The human eye only sees three colors: red, blue and green. All other colors are a combination of these.
• The human eye can see 500 shades of grey.
• The accommodation reflex is the only reflex mediated by the cerebral cortex otherwise a reflex by definition is always subcortically elicited.
• The following organs do not require insulin for glucose uptake;
  • Retina
  • Brain
  • Liver
  • Exercising muscle
• While venous pulsations may occur as a normal phenomenon in the fundus, arterial pulsations in the fundi are always pathological.
• The branches of the central retinal arteries are anatomical end arteries, while in the choroid are functional end arteries.
• The choroid has 80% excessive blood supply that is required.
• The inferior rectus is the only extraocular muscle with a dual function. It depresses the eyeball in the abducted position and also acts as a lower lid retractor by virtue of its attachment with capsulopalpebral fascia.
• Levator palpebrae superioris muscle is the only muscle of facial expression not supplied by the facial nerve.
• Both levators are supplied by a central midline nucleus in the midbrain, therefore, lesions at this level will always produce bilateral ptosis.
• The photoreceptors in the retina fire action potential in the hyperpolarized state.

Ocular Pathophysiology

• The narrowest portion of the central retinal vein is just behind the lamina cribrosa, a frequent site for occlusion to take place.
• RPE proliferates in inflammation but choroidal melanin does not proliferate.
• Our eyes have small blind spots where the optic nerve passes through the retina, and our brains use the information from the other eye to fill this gap.
• Smoking reduces our night vision.

Glaucoma

• With reference to glaucoma, the following are genetically determined:
• C/D ratio
• Facility of outflow of aqueous
• Intraocular pressure

Neuroophthalmological Interesting Facts

• The optic nerve is not a nerve but a tract.
• Sensory deprivation nystagmus is only caused by lesions anterior to the lateral geniculate body.
• The chiasma is the only place in the CNS where a “50/50” crossing of the nerve fibers takes place.
• The fourth cranial nerve is phylogenetically a part of the third cranial nerve complex that has migrated down in the midbrain.
• The fourth cranial nerve is the only cranial nerve which comes from the dorsal aspect of the brain stem.
• All cranial nerve nuclei have bilateral supranuclear connections with the cerebral cortex except facial and hypoglossal nerve.