senses three types of senses: 1. somatic senses: light touch (being touched by a feather), heat,...

SENSESSENSES

Three types of senses:Three types of senses: 1. SOMATIC SENSES1. SOMATIC SENSES: : Light touch Light touch

(being touched by a feather), heat, cold, (being touched by a feather), heat, cold, vibration, pressure, painvibration, pressure, pain. .

These are routinely tested by doctors in a These are routinely tested by doctors in a physical exam, especially for people with physical exam, especially for people with diabetes and lupus.diabetes and lupus.

SENSESSENSES

2. PROPRIOCEPTORS2. PROPRIOCEPTORS are found in the muscles, are found in the muscles, joints, and tendons. They measure the amount of joints, and tendons. They measure the amount of movement, force, and position of the body. movement, force, and position of the body.

Proprioception is often tested by having the Proprioception is often tested by having the patient close their eyes and saying if their fingers patient close their eyes and saying if their fingers are up or down.are up or down.

Proprioceptors send information to the cerebellum. Proprioceptors send information to the cerebellum. That’s how you know your legs are crossed before That’s how you know your legs are crossed before you stand up. you stand up.

Somatic senses (including pain) and Somatic senses (including pain) and proprioception are NOT considered special proprioception are NOT considered special senses.senses.

SENSESSENSES

3. SPECIAL SENSES3. SPECIAL SENSES: : Smell, taste, Smell, taste, vision, hearing, equilibrium (balance).vision, hearing, equilibrium (balance).

OLFACTORY SENSEOLFACTORY SENSE (smell) (smell) Olfactory receptors are Olfactory receptors are CHEMORECEPTORSCHEMORECEPTORS; a special ; a special

type of neuron which senses particular chemicals and type of neuron which senses particular chemicals and triggers an action potential.triggers an action potential.

Chemoreceptors are at the roof of the nasal cavity. Chemoreceptors are at the roof of the nasal cavity. There are hundreds of thousands of types, and they can There are hundreds of thousands of types, and they can smell a wide variety of substances. smell a wide variety of substances.

They are extremely sensitive, and can detect parts per They are extremely sensitive, and can detect parts per billion, as in the scent of natural gas…just a few billion, as in the scent of natural gas…just a few molecules! molecules!

The olfactory nerve goes through the cribiform plate to The olfactory nerve goes through the cribiform plate to the the OLFACTORY BULBOLFACTORY BULB (one of the shortest nerves in (one of the shortest nerves in the body) and into the limbic system.the body) and into the limbic system.

OLFACTORY SENSEOLFACTORY SENSE (smell) (smell)

Scientists who are trying to find a way Scientists who are trying to find a way to make neurons divide to heal nerve to make neurons divide to heal nerve injuries often study the body’s only injuries often study the body’s only mitotic neurons. mitotic neurons.

These neurons are the olfactory These neurons are the olfactory receptors. receptors.

People who experience imaginary People who experience imaginary odors have what are called “unicate odors have what are called “unicate fits”.fits”.

Olfactory Receptors

Figure 16.3a, b

Some towns are old factory towns.Some are ol’ factory towns!

GUSTATORY SENSEGUSTATORY SENSE (taste) (taste) Sensed on taste buds, which are located mostly on the Sensed on taste buds, which are located mostly on the

tongue surface, but are also on the palate, pharynx, and tongue surface, but are also on the palate, pharynx, and a few on the lips. a few on the lips.

Taste buds have specialized cells, which increase Taste buds have specialized cells, which increase surface area and have chemoreceptors. surface area and have chemoreceptors.

They are surrounded by support cells (like glia). They They are surrounded by support cells (like glia). They synapse on sensory neurons, which go to the facial synapse on sensory neurons, which go to the facial nerve. nerve.

Someone with a damaged facial nerve can not easily Someone with a damaged facial nerve can not easily taste sweet, sour, or salty substances.taste sweet, sour, or salty substances. Taste buds Taste buds are the only parts of the nervous system that can are the only parts of the nervous system that can regenerate completely. regenerate completely.

The taste information is sent to the primary The taste information is sent to the primary gustatory (taste) cortex, located in the parietal lobe gustatory (taste) cortex, located in the parietal lobe of the brain.of the brain.

Taste Buds

Figure 16.1a, b

Taste Bud

GUSTATORY SENSEGUSTATORY SENSE (taste) (taste)

How many different tastes are there? How many different tastes are there? Dozens. Salt, sweet, bitter, and sour are Dozens. Salt, sweet, bitter, and sour are only a few. only a few.

Where are they located on the tongue? All Where are they located on the tongue? All tastes are located all over the tongue. tastes are located all over the tongue.

The picture in the book was drawn 120 The picture in the book was drawn 120 years ago by an anatomist that knew his years ago by an anatomist that knew his drawing was not right; he just wanted to drawing was not right; he just wanted to use it as a starting point for further use it as a starting point for further experimentation.experimentation.

GUSTATORY SENSEGUSTATORY SENSE (taste) (taste) Taste appreciation is also involved in texture (a mealy Taste appreciation is also involved in texture (a mealy

apple is not as good), temperature (cold pizza tastes apple is not as good), temperature (cold pizza tastes different than warm), and smell (perfume or cigarette different than warm), and smell (perfume or cigarette smoke clog the senses and decrease taste). smoke clog the senses and decrease taste).

There are dozens of taste receptors, hundreds of There are dozens of taste receptors, hundreds of thousands of smell receptors, so the subtly of taste is thousands of smell receptors, so the subtly of taste is from smell. from smell.

Foods people like are in opposite proportion to the Foods people like are in opposite proportion to the numbers of taste receptors for that. People that love numbers of taste receptors for that. People that love sweets have FEWER taste receptors for sweets, so they sweets have FEWER taste receptors for sweets, so they crave more taste of sweet things. If you dislike crave more taste of sweet things. If you dislike something, it’s because you have lots of receptors for it. something, it’s because you have lots of receptors for it. Also, as you get older, you become less tolerant of Also, as you get older, you become less tolerant of sweets and more tolerant of bitter tastes (like beer and sweets and more tolerant of bitter tastes (like beer and coffee). coffee).

Fun FactsFun Facts

The catfish has over 27,000 taste buds. The catfish has over 27,000 taste buds. (What could be so tasty on the bottom of a (What could be so tasty on the bottom of a pond?)pond?)

Flies taste with their feet.Flies taste with their feet.

Tongue with bacteriaTongue with bacteria

• What did the right eye say to the left eye?

• Between you and me, something smells!

THE EYETHE EYE Structures Surrounding the EyeStructures Surrounding the Eye The eye is in the orbit of the skull for protection.The eye is in the orbit of the skull for protection. Within the orbit are 6 extrinsic eye muscles, which move Within the orbit are 6 extrinsic eye muscles, which move

the eye. the eye. There are 4 cranial nerves: Optic (II), Occulomotor There are 4 cranial nerves: Optic (II), Occulomotor

(III), Trochlear (IV), and Abducens (VI). (III), Trochlear (IV), and Abducens (VI). Eyelids are Eyelids are PALPEBRAPALPEBRA, and eyelashes are , and eyelashes are CILIACILIA..

Fun fact: there is a new medicine to make you grow longer Fun fact: there is a new medicine to make you grow longer eyelashes!eyelashes!

People of Asian descent have an People of Asian descent have an EPICANTHIC FOLD EPICANTHIC FOLD in in the upper eyelid; no functional difference. the upper eyelid; no functional difference.

Around the eyeball are glands.Around the eyeball are glands.

Surface Anatomy of Eye

Extrinsic Eye Muscles

Figure 16.6a, b

FUN FACTSFUN FACTS

Do eyelashes grow back?Do eyelashes grow back? Eyelashes take about four to eight weeks to Eyelashes take about four to eight weeks to

grow back.grow back. What purpose do eyebrows serve?What purpose do eyebrows serve? To keep the sweat and rain out of our eyes. The To keep the sweat and rain out of our eyes. The

arch shape of the eyebrow diverts rain or sweat arch shape of the eyebrow diverts rain or sweat down our cheeks, keeping our eyes dry. down our cheeks, keeping our eyes dry. Eyebrows also help us to communicate. Eyebrows also help us to communicate. Sometimes a raised eyebrow is more effective Sometimes a raised eyebrow is more effective than words.than words.

EyelashesEyelashes

GLANDS OF THE EYEGLANDS OF THE EYE

1. 1. LACRIMAL GLANDS LACRIMAL GLANDS are the largest are the largest set. They are on the superior lateral eyelid set. They are on the superior lateral eyelid and they produce and they produce tears, which drain into tears, which drain into the nasal cavity the nasal cavity via the via the LACRIMAL LACRIMAL DUCTDUCT. .

The function is to moisten and lubricate The function is to moisten and lubricate the eye surface, and it has enzymes to kill the eye surface, and it has enzymes to kill bacteria (which thrive in warm, moist bacteria (which thrive in warm, moist conditions).conditions).

Figure 16.5b


2. 2. LACRIMAL CARUNCLE LACRIMAL CARUNCLE (“little meat”) (“little meat”) is the spot on the medial corner of the eye. is the spot on the medial corner of the eye. It makes an oily secretion like a It makes an oily secretion like a sebaceous gland. sebaceous gland.

The function is to lubricate the eye a little The function is to lubricate the eye a little bit for the eyelids. When the secretion bit for the eyelids. When the secretion dries, it is called “sand” in the eyes.dries, it is called “sand” in the eyes.


3. 3. TARSAL GLANDS TARSAL GLANDS are sebaceous glands on are sebaceous glands on the inside of the eyelid, and produce sebum, the inside of the eyelid, and produce sebum, which is an oil to lubricate the eyeball. which is an oil to lubricate the eyeball.

Therefore, the oil component found in tears Therefore, the oil component found in tears is produced by the tarsal glands.is produced by the tarsal glands.

The tarsal glands and the lacrimal caruncle The tarsal glands and the lacrimal caruncle make a waterproof surface so the eye won’t dry make a waterproof surface so the eye won’t dry out. out.

When tarsal glands are clogged = When tarsal glands are clogged = CHALAZIONCHALAZION

Chalazion


4. 4. CILLIARY SEBACEOUS GLANDS CILLIARY SEBACEOUS GLANDS go go to only the cilia. to only the cilia.

When clogged = When clogged = STYSTY..

Dry Eye SyndromeSty

FUN FACTSFUN FACTS

An ostrich's eye is bigger than it s brain!An ostrich's eye is bigger than it s brain! Is the human eye fully grown at birth?Is the human eye fully grown at birth? A typical newborn's eye is around 18 millimeters A typical newborn's eye is around 18 millimeters

in diameter. A fully grown adult's eye measures in diameter. A fully grown adult's eye measures 24-25 millimeters. A fully developed eyeball is 24-25 millimeters. A fully developed eyeball is about two-thirds the size of a ping-pong ball. about two-thirds the size of a ping-pong ball.

This means a human eye grows only about 28% This means a human eye grows only about 28% over the course of its life. Fish supposedly have over the course of its life. Fish supposedly have the ability to increase their eye size "steadily the ability to increase their eye size "steadily over the course of their entire lives," a talent lost over the course of their entire lives," a talent lost on us.on us.

Rods and cones

Ora serrata

The EyeballThe Eyeball

1. 1. CONJUNCTIVACONJUNCTIVA is like a Saran Wrap covering is like a Saran Wrap covering around the eye and under the eyelids. It’s made around the eye and under the eyelids. It’s made of stratified columnar epithelium (the first time in of stratified columnar epithelium (the first time in the body we’ve seen this tissue). the body we’ve seen this tissue).

It also has lots of goblet cells to secrete moisture It also has lots of goblet cells to secrete moisture for those areas. for those areas.

Deep to the epithelium is loose connective tissue Deep to the epithelium is loose connective tissue with lost of small blood vessels, which are not with lost of small blood vessels, which are not seen unless the conjunctiva becomes inflamed: seen unless the conjunctiva becomes inflamed: Blood-shot eyes: just from being tiredBlood-shot eyes: just from being tired PINK EYE PINK EYE (layman’s term), known as (layman’s term), known as

CONJUNCTIVITISCONJUNCTIVITIS (from bacteria, very contagious). (from bacteria, very contagious).

The EyeballThe Eyeball 2. 2. FIBROUS TUNIC FIBROUS TUNIC is the next layer, and has 2 parts:is the next layer, and has 2 parts: A. A. SCLERASCLERA is the white of the eye, made of dense is the white of the eye, made of dense

irregular connective tissue. It is continuous with the dura irregular connective tissue. It is continuous with the dura mater of the brain. The eye is part of the brain. The mater of the brain. The eye is part of the brain. The sclera protects the eye.sclera protects the eye.

B. B. CORNEACORNEA is clear, and is clear, and avascular (no blood supply) avascular (no blood supply) except around the periphery. Therefore, there is no except around the periphery. Therefore, there is no tissue rejection when it is transplanted into another tissue rejection when it is transplanted into another person;person; there is also no need to find a donor match. It there is also no need to find a donor match. It has lots of pain receptors, so a scratched cornea is very has lots of pain receptors, so a scratched cornea is very painful. Its function is to be the main focuser of light for painful. Its function is to be the main focuser of light for the eye. If damaged, need a corneal transplant. the eye. If damaged, need a corneal transplant.

Scleritis

Conjunctivitis

The EyeballThe Eyeball 3. 3. VASCULAR TUNIC VASCULAR TUNIC is deep to the fibrous tunic. It is deep to the fibrous tunic. It

has several structures.has several structures. A. A. CHOROIDCHOROID has lots of blood vessels and pigment. has lots of blood vessels and pigment.

The function of the pigment is to make sure light does The function of the pigment is to make sure light does not enter from the sides. The blood vessels provide not enter from the sides. The blood vessels provide blood supply to the other layers.blood supply to the other layers.

B. B. CILIARY MUSCLES CILIARY MUSCLES surround the lens.surround the lens. C. C. SUSPENSORY LIGAMENTS (also known as the SUSPENSORY LIGAMENTS (also known as the

zonule) zonule) hold the lens in place.hold the lens in place. D. D. LENSLENS functions to continue to focus the light after it functions to continue to focus the light after it

passes through the cornea. It changes shape to allow passes through the cornea. It changes shape to allow you to distinguish close from far. The lens changes you to distinguish close from far. The lens changes shape by the ciliary muscles pulling on the suspensory shape by the ciliary muscles pulling on the suspensory ligaments. ligaments.

The Vascular Tunic

Figure 16.8

PLAYPLAY Vascular Tunic (Uvea)

Rods and cones

Figure 16.7a

Figure 16.9a

Ciliary MusclesCiliary Muscles

When you are looking far away, the ciliary When you are looking far away, the ciliary muscles are relaxed, the lens is stretched muscles are relaxed, the lens is stretched into a wide circle, and the suspensory into a wide circle, and the suspensory ligaments are tight. ligaments are tight.

When you look up close, the ciliary muscle When you look up close, the ciliary muscle contracts and gets smaller, to the contracts and gets smaller, to the ligaments relax. Constantly looking close ligaments relax. Constantly looking close puts strain on the ciliary muscles = EYE puts strain on the ciliary muscles = EYE STRAIN. STRAIN.

PupilsPupils

Fun Fact: -When you are looking at Fun Fact: -When you are looking at someone you love, your pupils dilate, someone you love, your pupils dilate, and they do the same when you are and they do the same when you are looking at someone you hate.looking at someone you hate.

PROBLEMS WITH THE LENSPROBLEMS WITH THE LENS

With age, the lens loses flexibility, and is With age, the lens loses flexibility, and is less likely to round up. less likely to round up.

It stays in the position for seeing far, so It stays in the position for seeing far, so there is trouble focusing on things that are there is trouble focusing on things that are near = near = PRESBYOPIAPRESBYOPIA (“old eyes”). (“old eyes”).

Occurs around age 45-50.Occurs around age 45-50. The lens The lens cannot accommodate.cannot accommodate.

PROBLEMS WITH THE LENSPROBLEMS WITH THE LENS

Clouding of the lens leads to a clinical Clouding of the lens leads to a clinical condition known ascondition known as CATARACTSCATARACTS..

Treatment is to remove the lens and Treatment is to remove the lens and replace it with a plastic one (which is not replace it with a plastic one (which is not flexible either). flexible either).

If the lens yellows, you can’t see the color If the lens yellows, you can’t see the color blue. After surgery, can see blue again.blue. After surgery, can see blue again.

Cataract

Cataract Vision

IRISIRIS (the colored part of the eye) (the colored part of the eye)

The function is to constrict or dilate the The function is to constrict or dilate the pupil (opening) to allow light in. pupil (opening) to allow light in.

Therefore, it regulates the amount of Therefore, it regulates the amount of light passing to the visual receptors of light passing to the visual receptors of the eye. the eye.

If there is a lot of pigment, eye is brown; a If there is a lot of pigment, eye is brown; a medium amount = green, small amount = medium amount = green, small amount = blue, no pigment = pink (albino). blue, no pigment = pink (albino).

FUN FACTSFUN FACTSWhy are all babies born with blue eyes?Why are all babies born with blue eyes? Melanin is a brownish pigment that adds color to your Melanin is a brownish pigment that adds color to your

hair, eyes, and skin. At the time babies are born, melanin hair, eyes, and skin. At the time babies are born, melanin hasn't yet been "deposited" in the eyes' iris. Hence, they hasn't yet been "deposited" in the eyes' iris. Hence, they appear blue. appear blue.

After about six months, eyes change color depending on After about six months, eyes change color depending on the amount of melanin. If you have a lot of it, your eyes the amount of melanin. If you have a lot of it, your eyes will turn brown or black. If you have little, they'll stay will turn brown or black. If you have little, they'll stay blue. And if you have no melanin, your eyes may appear blue. And if you have no melanin, your eyes may appear pink. Interestingly, as the site notes, human beings aren't pink. Interestingly, as the site notes, human beings aren't the only creatures with freaky color-morphing eyeballs. the only creatures with freaky color-morphing eyeballs. Kittens experience the same phenomenon.Kittens experience the same phenomenon.

How can someone have two different colored eyes?How can someone have two different colored eyes? Eye color is a polygenic trait. Many babies are born with Eye color is a polygenic trait. Many babies are born with

blue eyes. Their eyes change color later as they begin to blue eyes. Their eyes change color later as they begin to produce more melanin.produce more melanin.

RETINARETINA

The retina is on top of the choroid layer.The retina is on top of the choroid layer. The retina is made up of The retina is made up of

PHOTORECEPTORSPHOTORECEPTORS, which are sensors , which are sensors for light. for light.

Rods and cones

Figure 16.7a

Fovea centralisOptic Nerve

Rods and ConesRods and Cones Two types of photoreceptors: Rods and Two types of photoreceptors: Rods and

Cones.Cones. 1. 1. CONESCONES (red, green, and blue) they have less (red, green, and blue) they have less

light sensitivity (poor at night) but see colors light sensitivity (poor at night) but see colors well. There is a well. There is a region on the retina that has region on the retina that has the highest concentration of cones; it is the highest concentration of cones; it is called thecalled the FOVEA CENTRALIS. FOVEA CENTRALIS. The fovea The fovea centralis is the very center point of a small centralis is the very center point of a small circular region called thecircular region called the MACULA. MACULA. When you When you want details, focus the light on the macula, want details, focus the light on the macula, because there are a lot of cones there. The because there are a lot of cones there. The other layers contain a mixture of both.other layers contain a mixture of both.

Figure 16.7a

Test for Colorblindness

Rods and ConesRods and Cones

2. 2. RODSRODS (chartreuse = yellowish green) (chartreuse = yellowish green) have more light sensitivity (can see well at have more light sensitivity (can see well at night) but does not see colors well.night) but does not see colors well.

Above the photoreceptors are layers of Above the photoreceptors are layers of neurons whose axons become the optic neurons whose axons become the optic nerve.nerve.

Fovea centralisOptic Nerve

Retina

Figure 16.10a

Figure 16.11

Photoreceptors

Blind Spot at the Optic NerveBlind Spot at the Optic Nerve

The region where the optic nerve and The region where the optic nerve and blood vessels goes in and out of the eye blood vessels goes in and out of the eye has no photoreceptors = has no photoreceptors = BLIND SPOTBLIND SPOT..

Hold your hands out at 45° and that’s the Hold your hands out at 45° and that’s the location of the blind spot. location of the blind spot.

You can still see your hands because the You can still see your hands because the other eye sees it. Close your right eye other eye sees it. Close your right eye and look for your right hand and you’ll find and look for your right hand and you’ll find the blind spot.the blind spot.

Figure 16.7a

Find your blind spot!Stare at the center of X and move head closer until one red spot disappears

Blind SpotBlind Spot

The light takes a path through the lens to the The light takes a path through the lens to the blood vessels, so this is the only place in the blood vessels, so this is the only place in the body where you can see blood vessels directly. body where you can see blood vessels directly.

The doctor can diagnose hypertension. The doctor can diagnose hypertension. On a clear, bright day, look at the blue sky and On a clear, bright day, look at the blue sky and

you can see the shadow of your own blood you can see the shadow of your own blood vessels on the photoreceptors as criss-cross vessels on the photoreceptors as criss-cross lines in field of vision. The little moving dots are lines in field of vision. The little moving dots are your blood cells.your blood cells.

Normal Retina

The visual information travels from the The visual information travels from the retina deep into the brain through the retina deep into the brain through the optic chiasma (not visible with an optic chiasma (not visible with an opthalmascope). opthalmascope).

From here, it goes into the occipital From here, it goes into the occipital lobe of the brain, where it is processed.lobe of the brain, where it is processed.

Cranial Nerves II, III, IV, VI

OPTHALMASCOPEOPTHALMASCOPE

An opthalmascope is the instrument An opthalmascope is the instrument used to look inside the eye.used to look inside the eye.

The doctor can see the optic disc, fovea The doctor can see the optic disc, fovea centralis, macula, the lens, retina, blood centralis, macula, the lens, retina, blood vessels, but of course, not the optic vessels, but of course, not the optic chiasma, since that is on the brain surface, chiasma, since that is on the brain surface, external to the eye.external to the eye.

PROBLEMS WITH VISIONPROBLEMS WITH VISION

FLOATERSFLOATERS are when a capillary breaks are when a capillary breaks and cells break off. Floaters don’t actually and cells break off. Floaters don’t actually move, the eye just tries to track them.move, the eye just tries to track them.

Floaters

Floaters

Floaters can best be seen when the person looks at a clear blue sky or white wall.

RETINAL DETACHMENTRETINAL DETACHMENT The retina separates from the underlying choroid. The retina separates from the underlying choroid. Retinal detachment can be caused from a blow to the Retinal detachment can be caused from a blow to the

eye, or may occur spontaneously. Usually eye, or may occur spontaneously. Usually caused by an caused by an injury like a blow to the eyeinjury like a blow to the eye with a baseball, punch, or with a baseball, punch, or airbag to the eye. airbag to the eye.

It may not cause blindness immediately. Although It may not cause blindness immediately. Although the detached portion contains capillaries, it is the detached portion contains capillaries, it is separated from the main blood supply, so if it is not separated from the main blood supply, so if it is not lasered back into place immediately, permanent lasered back into place immediately, permanent blindness can result.blindness can result.

Cells in the retina die from lack of oxygen. Manifests as Cells in the retina die from lack of oxygen. Manifests as a shimmering light. This is a shimmering light. This is considered a medical considered a medical emergencyemergency and needs immediate treatment. Those and needs immediate treatment. Those who are most vulnerable to spontaneous detachment are who are most vulnerable to spontaneous detachment are those who are nearsighted. those who are nearsighted.

HYPEROPIA (far-sighted) eyes are too short

MYOPIA (nearsighted) eyes are too long

The Eye as an Optical Device

Figure 16.14a–c

Hyperopia and MyopiaHyperopia and Myopia

Normal eyes are perfect spheres. When the Normal eyes are perfect spheres. When the eyeball is not a perfect sphere, the lens has to eyeball is not a perfect sphere, the lens has to accommodate as much as possible, and accommodate as much as possible, and corrective glasses are usually needed. corrective glasses are usually needed.

Myopic eyes are elongated (overhead projector Myopic eyes are elongated (overhead projector is in focus, but move it backward, gets fuzzy). is in focus, but move it backward, gets fuzzy). Even badly nearsighted eyes are only 1mm from Even badly nearsighted eyes are only 1mm from normal. Treatments are glasses or Lasix, which normal. Treatments are glasses or Lasix, which is laser surgery on cornea, when it’s shaved so it is laser surgery on cornea, when it’s shaved so it focuses light farther back to reach the retina.focuses light farther back to reach the retina.

Lasik Surgery

Hyperopia and PresbyopiaHyperopia and Presbyopia

Hyperopia and presbyopia have Hyperopia and presbyopia have some features in common, but a some features in common, but a key difference between these key difference between these two conditions is that in two conditions is that in hyperopia the lens can hyperopia the lens can accommodate, but in presbyopia accommodate, but in presbyopia it cannot.it cannot.

ASTIGMATISM• ASTIGMATISM is when the cornea has

an irregular shape. Part of the field of view is out of focus.

• The eyeball changes shape until age 24.

Astigmatism Test

Astigmatism Vision

MACULAR MACULAR DEGENERATIONDEGENERATION

The size of the macula is the size of the The size of the macula is the size of the printed letter “O” in 14 pt font. When the printed letter “O” in 14 pt font. When the macula degenerates, you lose a lot of sight. macula degenerates, you lose a lot of sight. This is the most common cause of blindness This is the most common cause of blindness in the US. in the US.

It’s due to bleeding in the eye, causing scar It’s due to bleeding in the eye, causing scar tissue. The retina does not get enough tissue. The retina does not get enough oxygen, and the cells die. Macular oxygen, and the cells die. Macular degeneration allows vision in the periphery, degeneration allows vision in the periphery, but they can’t read or drive. but they can’t read or drive.

Macular Degeneration

DIABETIC RETINOPATHYDIABETIC RETINOPATHY

This is when the high sugar levels destroy This is when the high sugar levels destroy the photoreceptors in the retina. the photoreceptors in the retina.

The blood vessels also swell and rupture The blood vessels also swell and rupture and the clots block vision. and the clots block vision.

Some of this damage can be repaired by Some of this damage can be repaired by using a laser to evaporate the blood clots, using a laser to evaporate the blood clots, but any damage to the photoreceptors is but any damage to the photoreceptors is permanent. It can lead to blindness.permanent. It can lead to blindness.

Diabetic Retinopathy

Diabetic Retinopathy vision

INTERNAL STRUCTURES INTERNAL STRUCTURES OF THE EYEOF THE EYE

There are two cavitiesThere are two cavities Anterior CavityAnterior Cavity Posterior CavityPosterior Cavity

Anterior CavityAnterior Cavity

1. ANTERIOR CAVITY1. ANTERIOR CAVITY is anterior to is anterior to the lens, and is filled with the lens, and is filled with AQUEOUS AQUEOUS HUMORHUMOR, similar to plasma, supplies , similar to plasma, supplies nutrients to the cornea and lens. nutrients to the cornea and lens.

Figure 16.7a

GLAUCOMAGLAUCOMA GLAUCOMAGLAUCOMA is increased pressure is increased pressure

within the anterior chamber of the within the anterior chamber of the eye. It leads to blindness.eye. It leads to blindness.

This form of blindness is more common in This form of blindness is more common in third-world countries because we have third-world countries because we have tests to detect it and treat it. tests to detect it and treat it.

The test measures how much pressure The test measures how much pressure there is here by seeing how easily the there is here by seeing how easily the cornea is deformed, either with air or cornea is deformed, either with air or direct pressure. How many of you have direct pressure. How many of you have had this test?had this test?

Glaucoma

2. POSTERIOR CAVITY2. POSTERIOR CAVITY is filled with is filled with VITREOUS HUMORVITREOUS HUMOR, which is jelly-like, , which is jelly-like, and helps give shape to the eyeball.and helps give shape to the eyeball. It It leaks out from a cut, you’ll go blind leaks out from a cut, you’ll go blind because the body can’t replace it.because the body can’t replace it.

The four main things that cause The four main things that cause blindness are macular blindness are macular degeneration, cataracts, glaucoma, degeneration, cataracts, glaucoma, and diabetic retinopathy.and diabetic retinopathy.

AMBLYOPIAAMBLYOPIA

AMBLYOPIAAMBLYOPIA = Lazy Eye. In a child, one = Lazy Eye. In a child, one eye will track and focus, the other won’t. eye will track and focus, the other won’t.

If untreated in children, eventual blindness If untreated in children, eventual blindness in weak eye because the brain will shut in weak eye because the brain will shut down in the occipital lobe. down in the occipital lobe.

Treatment is to patch the good eye to force Treatment is to patch the good eye to force the bad eye to make the connections, or a the bad eye to make the connections, or a surgery to weaken the muscle to make the surgery to weaken the muscle to make the strong side just as weak.strong side just as weak.

Other Eye Problems

Cancer of the Eye:Choroidal Melanoma

Live worm in the eye

NOTENOTE

If a child is blind until age 4-5, and If a child is blind until age 4-5, and then you restore the sight, he will still then you restore the sight, he will still be blind because the brain doesn’t be blind because the brain doesn’t form properly.form properly.

With kids who have astigmatism or With kids who have astigmatism or weak eye muscles, one eye stops weak eye muscles, one eye stops seeing (or sees double). seeing (or sees double).

The thalamus in the brain will shut The thalamus in the brain will shut off all the signals from the bad eye. off all the signals from the bad eye.

NOTENOTE

To protect your eyesight To protect your eyesight throughout your life, use the 20-20-throughout your life, use the 20-20-20 rule:20 rule:

Every 20 minutes look up for 20 Every 20 minutes look up for 20 seconds at something 20 feet away.seconds at something 20 feet away.

The rest of this lecture is not on the The rest of this lecture is not on the exam!exam!

The red lines are straight!

Look at the dot

and move your head

forward and back

Stare at the + for 30 seconds and the pink dots will disappear!

FUN FACTS ABOUT FUN FACTS ABOUT VISIONVISION

Why do you cry when you cut onions?Why do you cry when you cut onions? It releases an enzyme that reacts with the It releases an enzyme that reacts with the

amino acids in the onion that create an acid amino acids in the onion that create an acid that diffuses into the air and irritates your that diffuses into the air and irritates your eyes. Scientists have tried to make a eyes. Scientists have tried to make a non=crying onion, but it turns out that non=crying onion, but it turns out that enzyme is needed for the onion flavor. You can enzyme is needed for the onion flavor. You can heat the onion before chopping or chop under heat the onion before chopping or chop under running water. Or order take-out.running water. Or order take-out.

Do cucumbers relieve puffy eyes?Do cucumbers relieve puffy eyes? No, they are just cool and filled with water, so No, they are just cool and filled with water, so

the cooling effect reduces the swelling.the cooling effect reduces the swelling.


Can carrots help improve your vision? Can carrots help improve your vision? This myth dates back to WWII when the British Royal This myth dates back to WWII when the British Royal

Air Force was attempting to hide the fact that they Air Force was attempting to hide the fact that they developed a new radar system to shoot down German developed a new radar system to shoot down German bombers. They bragged that the great accuracy of bombers. They bragged that the great accuracy of thie British fighter pilots at night was a result was a thie British fighter pilots at night was a result was a result of them being fed an enormous amount of result of them being fed an enormous amount of carrots. It is true that carrots contain beta carotene carrots. It is true that carrots contain beta carotene which converts to vitamin A which is needed to which converts to vitamin A which is needed to prevent night blindness, but we only need a small prevent night blindness, but we only need a small amount, and having more than that will not improve amount, and having more than that will not improve vision. In fact, too many carrots can cause your skin vision. In fact, too many carrots can cause your skin to turn orange.to turn orange.


Can you lose a contact lens in the back Can you lose a contact lens in the back of your head? of your head?

No; the underside of the eyelid is connected No; the underside of the eyelid is connected to the sclera (white part of the eye).to the sclera (white part of the eye).

Why do you get bags under your eyes Why do you get bags under your eyes when you are tired? when you are tired?

The skin under the eyes is the thinnest in The skin under the eyes is the thinnest in the body, and it allows the dark, venous the body, and it allows the dark, venous blood to show through. Dark rings tend to blood to show through. Dark rings tend to be genetic and get worse as you age. Good be genetic and get worse as you age. Good rest and nutrition minimizes the rings.rest and nutrition minimizes the rings.


Should you put a steak on a black eye? Should you put a steak on a black eye? It doesn’t do any more good than an ice packIt doesn’t do any more good than an ice pack Does hysterical blindness really exist? Does hysterical blindness really exist? Yes. There is a device that can check for Yes. There is a device that can check for

someone faking blindness; they put a black someone faking blindness; they put a black and white spinning pinwheel in front of the and white spinning pinwheel in front of the eyes, and if you can see, your eyes will eyes, and if you can see, your eyes will automatically move a little back and forth.automatically move a little back and forth.


Why do you see stars when you are hit in Why do you see stars when you are hit in the head?the head?

It happens to Wile E. Coyote every time he gets It happens to Wile E. Coyote every time he gets hit on the head with an anvil by the Road hit on the head with an anvil by the Road Runner. Yes, it can happen, and it indicates Runner. Yes, it can happen, and it indicates there is a concussion. The visual area of the there is a concussion. The visual area of the brain has hit against the inside of the skull.brain has hit against the inside of the skull.

Will staring at an eclipse make you go Will staring at an eclipse make you go blind?blind?

The intense light burns some of the cells in the The intense light burns some of the cells in the retina, but it doesn’t cause complete blindness.retina, but it doesn’t cause complete blindness.


Why is it impossible to sneeze with your eyes Why is it impossible to sneeze with your eyes open?open?

Sneeze impulse affects a variety of body parts, Sneeze impulse affects a variety of body parts, including the abdomen, chest, neck, and face. During including the abdomen, chest, neck, and face. During a sneeze, the impulses that travels through your face a sneeze, the impulses that travels through your face causes your eyelids to blink. This response is entirely causes your eyelids to blink. This response is entirely automatic. There's nothing you can do about it. automatic. There's nothing you can do about it. Sneezing puts a lot of pressure on your head and Sneezing puts a lot of pressure on your head and respiratory system, so blinking is probably a respiratory system, so blinking is probably a protective mechanism. protective mechanism.

The point is that all of these responses (the abdominal The point is that all of these responses (the abdominal contraction, the sharp burst of air out of your lungs, contraction, the sharp burst of air out of your lungs, the general lunging movement) are intertwined.the general lunging movement) are intertwined.


Can a person who is blind from birth Can a person who is blind from birth "see images" in their dreams?"see images" in their dreams?

People who are visually impaired from People who are visually impaired from birth appear to lack visual imagery in birth appear to lack visual imagery in their dreams but have a “very high their dreams but have a “very high percentage of gustatory, olfactory, and percentage of gustatory, olfactory, and tactual sensory references," something tactual sensory references," something very unusual for sighted dreamers to very unusual for sighted dreamers to experience.experience.

FUN FACT OR FICTION?FUN FACT OR FICTION?

Extensive computer usage can cause dry eyes.Extensive computer usage can cause dry eyes. FactFact. Extensive computer use can lead to dry . Extensive computer use can lead to dry

eyes. A person experiencing minor amount of eyes. A person experiencing minor amount of dryness will feel much worse after prolonged dryness will feel much worse after prolonged computer use. Studies have shown that computer use. Studies have shown that computer users tend to stare at the screen computer users tend to stare at the screen without blinking for a long time, which may without blinking for a long time, which may cause dry eyes. Dry eyes are one of the factors cause dry eyes. Dry eyes are one of the factors leading to Computer Vision Syndrome. Thus leading to Computer Vision Syndrome. Thus frequent blinking is essential to lubricate the frequent blinking is essential to lubricate the eyes and prevent them from drying.eyes and prevent them from drying.

Eating carrots will Eating carrots will improve your visionimprove your vision

FallacyFallacy. It is true that carrots are . It is true that carrots are rich in Vitamin A, which is an rich in Vitamin A, which is an essential vitamin for our eyes. essential vitamin for our eyes. However, we require only a small However, we require only a small amount of this vitamin for good amount of this vitamin for good vision. A well- balanced diet, with or vision. A well- balanced diet, with or without carrots, provides all the without carrots, provides all the Vitamin A necessary for good vision.Vitamin A necessary for good vision.


Sitting close to a television set, Sitting close to a television set, movie or computer screen can harm movie or computer screen can harm your eyes.your eyes.

FallacyFallacy. Our eyes are not harmed by . Our eyes are not harmed by viewing these at a short distance. viewing these at a short distance. There is, however, a greater There is, however, a greater likelihood of experiencing eye fatigue likelihood of experiencing eye fatigue or a headache.or a headache.


Reading in dim light is harmful to your Reading in dim light is harmful to your eyes.eyes.

FallacyFallacy. For centuries, all night time . For centuries, all night time reading and sewing was done by reading and sewing was done by candlelight or with gas or kerosene candlelight or with gas or kerosene lamps. Reading in dim light does not lamps. Reading in dim light does not damage the eyes. However, good damage the eyes. However, good lighting does make reading easier and lighting does make reading easier and prevents eye fatigue, especially for prevents eye fatigue, especially for people who wear bifocals.people who wear bifocals.

Computers and eyestrainComputers and eyestrain Computers can put stress on the eyes causing headaches, Computers can put stress on the eyes causing headaches,

blurred vision and eye fatigue. The following steps can be blurred vision and eye fatigue. The following steps can be taken to reduce eyestrain:taken to reduce eyestrain:

Computer screen is at least 18 to 26 inches away from your Computer screen is at least 18 to 26 inches away from your eyes. eyes.

Arrange the monitor so that the top line of on-screen text is Arrange the monitor so that the top line of on-screen text is at eye level. Placing a monitor too high exposes more of the at eye level. Placing a monitor too high exposes more of the eye, causing it to dry out. eye, causing it to dry out.

Arrange lighting to minimize glare and reflections. Arrange lighting to minimize glare and reflections. Keep the computer screen clean and dust-free to minimize Keep the computer screen clean and dust-free to minimize

glare. glare. Take frequent vision breaks to stretch your body and rest Take frequent vision breaks to stretch your body and rest

your eyes. your eyes. Remember to blink often to keep your eyes moist. Remember to blink often to keep your eyes moist. Place reference material alongside and as close to the Place reference material alongside and as close to the

computer screen as possible to avoid frequent head and computer screen as possible to avoid frequent head and eye movements and focusing changes. eye movements and focusing changes.

Television and your eyesTelevision and your eyes

Never watch TV in a completely darkened Never watch TV in a completely darkened room. The best lightning conditions consist of room. The best lightning conditions consist of a back light and dim general light in the room. a back light and dim general light in the room.

Place the set to avoid glare and reflections Place the set to avoid glare and reflections from lamps, windows and other bright sources. from lamps, windows and other bright sources.

View from a distance at least five times the View from a distance at least five times the width of the television screen. width of the television screen.

Have the set at approximately eye level. Have the set at approximately eye level. Wear lenses prescribed for vision correction. Wear lenses prescribed for vision correction. Avoid staring at the screen. Briefly look away Avoid staring at the screen. Briefly look away

from the picture, around the room. from the picture, around the room.

Avoid eye strain while Avoid eye strain while readingreading

Keep the reading material at the best Keep the reading material at the best distance: place knuckles under your chin and distance: place knuckles under your chin and book under the elbow. Try to avoid reading book under the elbow. Try to avoid reading while lying on your back, stomach, or side. while lying on your back, stomach, or side. Make sure that there is good light on close Make sure that there is good light on close work tasks and good room light as well. A work tasks and good room light as well. A light positioned behind and over one's light positioned behind and over one's shoulder works well for reading. Also, looking shoulder works well for reading. Also, looking up from time to time from your reading can up from time to time from your reading can help keep your eyes relaxed. help keep your eyes relaxed.

senses three types of senses: 1. somatic senses: light touch (being touched by a feather), heat,...

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