Sclera: a tough white layer of Sclera: a tough white layer of connective tissue that covers connective tissue that covers all of the eyeball except the all of the eyeball except the cornea.cornea.Conjunctiva: external cover Conjunctiva: external cover of the sclera — keeps the of the sclera — keeps the eye moist.eye moist.

Cornea: transparent covering Cornea: transparent covering of the front of the eye.of the front of the eye.Allows for the passage of Allows for the passage of light into the eye and light into the eye and functions as a fixed lens.functions as a fixed lens.

Choroid: thin, pigmented layer Choroid: thin, pigmented layer lining the interior surface of the lining the interior surface of the sclera.sclera.Prevents light rays from Prevents light rays from

scattering and distorting the scattering and distorting the image.image.

o Interiorly it forms the iris.Interiorly it forms the iris.The iris regulates the size The iris regulates the size of the pupil.of the pupil.

Retina: lines the interior surface of Retina: lines the interior surface of the choroid.the choroid.Contains photo receptors.Contains photo receptors.

Except at the optic disk (where Except at the optic disk (where the optic nerve attaches).the optic nerve attaches).

The lens and ciliary body divide the The lens and ciliary body divide the eye into two cavities.eye into two cavities.

The anterior cavity is filled with The anterior cavity is filled with aqueous humor produced by the aqueous humor produced by the ciliary body.ciliary body.

The posterior cavity is filled with The posterior cavity is filled with vitreous humor.vitreous humor.

The lens, the aqueous humor, and The lens, the aqueous humor, and the vitreous humor all play a role the vitreous humor all play a role in focusing light onto the retina.in focusing light onto the retina.

Accommodation is Accommodation is the focusing of the focusing of light in the retina.light in the retina.

Mammals focus by Mammals focus by changing the changing the shape of the lens.shape of the lens.

The lens is The lens is flattened for flattened for distant objects.distant objects.

The lens is The lens is rounded for rounded for near objects.near objects.

Photoreceptors of the retina.rod cells - light sensitive but do not distinguish colors.

cone cells - not as light sensitive as rods but provide color vision

Most highly concentrated on the fovea – an area of the retina that lacks rods.

Vision is your ability to see.Vision is your ability to see. Vision involves the eye and the Vision involves the eye and the brainbrain.

The eye is one of your The eye is one of your sense organs.sense organs.The eye is made of the iris The eye is made of the iris

and the pupil.and the pupil.

The eye gathers pictures The eye gathers pictures and sends them to the and sends them to the

brain.brain.

The colored part of the eye The colored part of the eye is the iris.is the iris.

The black part of the eye is The black part of the eye is the pupil.the pupil.The pupil becomes The pupil becomes larger and smaller larger and smaller as it controls the as it controls the light coming into light coming into

the eyethe eye..

IrisIrisPupilPupil

From the moment you wake up in the morning From the moment you wake up in the morning to the time you go to sleep at night, your to the time you go to sleep at night, your eyes are acting like a video camera. eyes are acting like a video camera. Everything you look at is then sent to your Everything you look at is then sent to your brain for processing and storage much like a brain for processing and storage much like a video cassette. This is a very simplified video cassette. This is a very simplified explanation, but as you read on, you will explanation, but as you read on, you will discover why the sense of sight is actually discover why the sense of sight is actually considered the most complex of the five considered the most complex of the five senses. senses.

Take a moment to locate an object Take a moment to locate an object around you. Do you know how you are around you. Do you know how you are able to see it? Would you believe that able to see it? Would you believe that what you are actually seeing are what you are actually seeing are beams of light bouncing off of the beams of light bouncing off of the object and into your eyes? It is hard to object and into your eyes? It is hard to believe, but it is true. believe, but it is true.

The light rays enter the eye through The light rays enter the eye through the cornea, which is a thick, the cornea, which is a thick, transparent protective layer on the transparent protective layer on the surface of your eye. Then the light surface of your eye. Then the light rays pass through the pupil (the dark rays pass through the pupil (the dark circle in the centre of your eye) and circle in the centre of your eye) and into the lens.into the lens.

Your lens in your eyes change size all Your lens in your eyes change size all the time. When you look at objects real the time. When you look at objects real close up, the lens gets thicker. If you close up, the lens gets thicker. If you look at objects far away, it gets thinner. look at objects far away, it gets thinner. It does this to help you focus the It does this to help you focus the correct image on the retina. correct image on the retina.

After light passes through the lens it After light passes through the lens it shines through the vitreous humor to shines through the vitreous humor to the back of the eye where it hits the the back of the eye where it hits the retina. The retina takes the light and retina. The retina takes the light and changes it into nerve impulse so the changes it into nerve impulse so the brain can understand what the eye brain can understand what the eye sees. It sends the message to the brain sees. It sends the message to the brain by way of the optic nerve.by way of the optic nerve.

Rods and cones are special cells that process light. Rods and cones are special cells that process light. Rods and cones are extremely small. In fact, there are Rods and cones are extremely small. In fact, there are

about 120 million rods and 7 million cones in each about 120 million rods and 7 million cones in each eye! eye!

Rods help us see black and white and shades of grey. Rods help us see black and white and shades of grey. Cones help us see color. You have three kinds of cones Cones help us see color. You have three kinds of cones

are - red, green, and blue. These cones work together are - red, green, and blue. These cones work together to help us see millions of colors.to help us see millions of colors.

When you see images, they turn upside When you see images, they turn upside down when they hit the retina. So your down when they hit the retina. So your brain sees everything in the world upside brain sees everything in the world upside down. Your brain basically flips everything down. Your brain basically flips everything around so it is right side up again.around so it is right side up again.

There are the six small muscles that move each eye from side There are the six small muscles that move each eye from side to side, up and down and on the slant. When these muscles to side, up and down and on the slant. When these muscles don't work together, it can affect vision. One condition that don't work together, it can affect vision. One condition that can arise when these muscles don't work together is “lazy can arise when these muscles don't work together is “lazy eye”, a condition that affects about 5% of children and arises eye”, a condition that affects about 5% of children and arises when the eye muscles don't work together properly. This when the eye muscles don't work together properly. This leads to "lazy eye," in which one eye takes over all the vision leads to "lazy eye," in which one eye takes over all the vision duties. A defining characteristic of these tiny muscles is that duties. A defining characteristic of these tiny muscles is that they are nearly always moving, even during sleep. In fact, they are nearly always moving, even during sleep. In fact, even when "staring" at a fixed object, the eyes keep moving even when "staring" at a fixed object, the eyes keep moving over the image. Although these muscles are very small, they over the image. Although these muscles are very small, they use a lot of energy because they are always on the go. use a lot of energy because they are always on the go.

Because the eye is such an important and Because the eye is such an important and complex part of our body, we have many complex part of our body, we have many features which protect the eye. features which protect the eye.

The eyebrows The eyebrows are the strips of hair are the strips of hair above your eyes which prevent sweat from above your eyes which prevent sweat from running into them. running into them.

EyelashesEyelashes help keep the eye clean by help keep the eye clean by collecting small dirt and dust particles collecting small dirt and dust particles floating through the air. The eyelashes floating through the air. The eyelashes also protect the eye from the sun's and also protect the eye from the sun's and other light's glare. The eyelids sweep dirt other light's glare. The eyelids sweep dirt from the surface of the eye. The eyelid from the surface of the eye. The eyelid also protects the eye from injury. also protects the eye from injury.

Tears Tears are sterile drops of clean water are sterile drops of clean water which constantly bathe the front of the which constantly bathe the front of the eye, keeping it clean and moist.eye, keeping it clean and moist.

NearsightedNearsightedNot all people have perfect vision. Not all people have perfect vision.

People who can see things up close, but not far People who can see things up close, but not far away are considered to be nearsighted. This away are considered to be nearsighted. This happens when the light entering the eye happens when the light entering the eye focuses on a point in front of the retina. focuses on a point in front of the retina.

Whether a person is nearsighted or farsighted, glasses or Whether a person is nearsighted or farsighted, glasses or contacts help that person to see things much more clearly!contacts help that person to see things much more clearly!

Eye Fun FactsEye Fun Facts

• A chameleon's eyes can look in A chameleon's eyes can look in opposite directions at the same opposite directions at the same time.time.

• A newborn baby sees the world A newborn baby sees the world upside down because it takes upside down because it takes some time for the baby's brain to some time for the baby's brain to learn to turn the picture right-learn to turn the picture right-side up.side up.

• One in every twelve males is One in every twelve males is colour blindcolour blind

A male human can see over 1 A male human can see over 1 million coloursmillion colours

Whereas a female human can see Whereas a female human can see over 100 billion colours over 100 billion colours

By the end of this presentation By the end of this presentation you will be able to:you will be able to:Recognize major components of Recognize major components of the eyethe eye

Have a basic understanding of Have a basic understanding of how the eye workshow the eye works

Understand how eye disease Understand how eye disease affects the components of the affects the components of the eyeeye

The eye allows us to see and interpret the The eye allows us to see and interpret the shapes, colors and dimensions of objects in shapes, colors and dimensions of objects in the world by processing the light they reflect the world by processing the light they reflect or emit or emit

The eye is able to see in bright or dim light, The eye is able to see in bright or dim light, but it cannot see objects when light is absentbut it cannot see objects when light is absent

When you look at any object When you look at any object Light waves from that object Light waves from that object

enter the eye first through the enter the eye first through the cornea, which is the clear dome cornea, which is the clear dome at the front of the eye at the front of the eye

Light waves progress through Light waves progress through the pupil, the circular opening in the pupil, the circular opening in the center of the colored iristhe center of the colored iris

Immediately behind the iris (and Immediately behind the iris (and pupil) is the crystalline lens, and pupil) is the crystalline lens, and light passes through that also.light passes through that also.

Light waves are bent (converged) first by the Light waves are bent (converged) first by the cornea, then even more so by the crystalline cornea, then even more so by the crystalline lens, to a nodal point which is immediately lens, to a nodal point which is immediately behind the lensbehind the lens

At the nodal point, the light waves (image) At the nodal point, the light waves (image) become reversed (turned backwards) and become reversed (turned backwards) and inverted (turned upside down)inverted (turned upside down)

Light waves continue through the vitreous Light waves continue through the vitreous humor, the clear gel that makes up about humor, the clear gel that makes up about 80% of the eye’s volume, and then back to a 80% of the eye’s volume, and then back to a clear focus on the retina behind the vitreousclear focus on the retina behind the vitreous

The small, central area of the retina is the The small, central area of the retina is the macula; it provides the best vision of any macula; it provides the best vision of any location in the retinalocation in the retina

The light impulses are changed into The light impulses are changed into electrical signals, then sent through electrical signals, then sent through the optic nerve along the visual the optic nerve along the visual pathway to the occipital cortex, or pathway to the occipital cortex, or posterior (back), of the brainposterior (back), of the brain

This is where the electrical signals This is where the electrical signals are seen by the brain as a visual are seen by the brain as a visual imageimage

When light entering the eye is bright When light entering the eye is bright enough, the pupils will get smaller enough, the pupils will get smaller (constrict) due to pupillary light (constrict) due to pupillary light responseresponse

Extra ocular MusclesExtra ocular Muscles

All of the extra ocular muscles, with the All of the extra ocular muscles, with the exception of the inferior oblique, form a exception of the inferior oblique, form a “cone” within the bony orbit“cone” within the bony orbit

The apex of the cone is in the posterior The apex of the cone is in the posterior aspect (back) of the orbit, while the base aspect (back) of the orbit, while the base of the cone is the attachment of the of the cone is the attachment of the muscles around the midline of the eye. muscles around the midline of the eye. This conic structure is referred to as the This conic structure is referred to as the “annulus of Zinn,” and within this cone “annulus of Zinn,” and within this cone runs the Optic nerve (cranial nerve H)runs the Optic nerve (cranial nerve H)

Within the optic nerve are the ophthalmic Within the optic nerve are the ophthalmic artery and the ophthalmic veinartery and the ophthalmic vein

The superior oblique muscle is The superior oblique muscle is different from the others, because different from the others, because before it attaches to the eye, it before it attaches to the eye, it passes through a ring-like tendon, passes through a ring-like tendon, the trochlea, which acts like a pulley the trochlea, which acts like a pulley in the nasal portion of the orbitin the nasal portion of the orbit

The inferior oblique muscle (not a The inferior oblique muscle (not a member of the annulus of Zinn) arises member of the annulus of Zinn) arises from the lacrimal fossa in the nasal from the lacrimal fossa in the nasal portion of the bony orbit and attaches portion of the bony orbit and attaches to the inferior portion of the eyeto the inferior portion of the eye

The primary muscle that moves The primary muscle that moves an eye in a given direction is an eye in a given direction is known as the agonistknown as the agonist

A muscle in the same eye that A muscle in the same eye that moves the eye in the same moves the eye in the same direction as the agonist is known direction as the agonist is known as a synergistas a synergist

A muscle in the same eye that A muscle in the same eye that moves the eye in the opposite moves the eye in the opposite direction of the agonist is the direction of the agonist is the antagonistantagonist

Cardinal positions of gazeCardinal positions of gazeUp/rightUp/rightUp/leftUp/leftRightRightLeftLeftDown/rightDown/rightDown/leftDown/left

In each position of gaze, one muscle In each position of gaze, one muscle of each eye is the primary mover of of each eye is the primary mover of that eye, and is “yoked” to the that eye, and is “yoked” to the primary mover of the other eyeprimary mover of the other eye

A “vergence” or A “vergence” or “disconjugate” movement “disconjugate” movement involves involves simultaneous simultaneous movement of both eyes in the movement of both eyes in the opposite opposite directionsdirections

There are two principal There are two principal vergence movementsvergence movementsConvergence – both eyes Convergence – both eyes moving nasally or inwardmoving nasally or inward

Divergence – both eyes Divergence – both eyes moving temporally or upwardmoving temporally or upward

StrabismusStrabismusUsually when we see an object, the lines Usually when we see an object, the lines of sight are both eyes intersecting at of sight are both eyes intersecting at the object, or both eyes are pointing at the object, or both eyes are pointing at the object being viewed. An image of the object being viewed. An image of the object is focused upon the macula of the object is focused upon the macula of each eye and the brain merges the two each eye and the brain merges the two retinal images into one retinal images into one When there is an extra ocular muscle When there is an extra ocular muscle imbalance, one eye is not aligned with imbalance, one eye is not aligned with the other eye, which results in a the other eye, which results in a strabismusstrabismus

Strabismus, (cont’d)Strabismus, (cont’d)With strabismus, while one eye is With strabismus, while one eye is fixating on a particular object, the fixating on a particular object, the other eye is turned in another other eye is turned in another direction, either inward (cross-eyed), direction, either inward (cross-eyed), outward (wall-eyed), upward, or outward (wall-eyed), upward, or downwarddownwardAs a result, the person either As a result, the person either experiences “diplopia” (double vision) experiences “diplopia” (double vision) or the brain learns to turn off or the brain learns to turn off (suppress) the image of the strabismic (suppress) the image of the strabismic eye to maintain single visioneye to maintain single visionThe angle of deviation of the The angle of deviation of the strabismus is measured in prism strabismus is measured in prism dioptersdiopters

Diabetic RetinopathyDiabetic RetinopathyThis is a complication of diabetes This is a complication of diabetes mellitus in which long-term exposure mellitus in which long-term exposure to high glucose levels in the blood to high glucose levels in the blood has damaged retinal blood vessels. has damaged retinal blood vessels. This results in new growth of This results in new growth of abnormal blood vessels, fluid buildup abnormal blood vessels, fluid buildup in the macula (macular edema), in the macula (macular edema), inadequate blood supply to the retina inadequate blood supply to the retina and possibly blood and fluid leakage and possibly blood and fluid leakage into the retina and the vitreous bodyinto the retina and the vitreous body

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A cataract is a clouding of the eye's A cataract is a clouding of the eye's natural lens, which lies behind the iris natural lens, which lies behind the iris and the pupil and the pupil

The lens is mostly made of water and The lens is mostly made of water and protein. The protein is arranged in a protein. The protein is arranged in a precise way that keeps the lens clear and precise way that keeps the lens clear and lets light pass through it. But as we age, lets light pass through it. But as we age, some of the protein may clump together some of the protein may clump together and start to cloud a small area of the and start to cloud a small area of the lens. This is a cataract, and over time, it lens. This is a cataract, and over time, it may grow larger and cloud more of the may grow larger and cloud more of the lens, making it harder to seelens, making it harder to see

Researchers are identifying factors Researchers are identifying factors that may cause cataracts such as:that may cause cataracts such as:People with diabetesPeople with diabetesUsers of steroids, diuretics, and Users of steroids, diuretics, and major tranquilizersmajor tranquilizers

Users of a lot of saltUsers of a lot of saltCigarette smokeCigarette smokeAir pollutionAir pollutionHeavy alcohol consumptionHeavy alcohol consumption

Glaucoma Glaucoma Glaucoma represents injury to the optic nerve Glaucoma represents injury to the optic nerve

secondary to elevated pressure inside the eye. secondary to elevated pressure inside the eye. However, there are exceptions to this definitionHowever, there are exceptions to this definition

Some patients with sustained high intra-ocular Some patients with sustained high intra-ocular pressure never develop any of the signs of optic pressure never develop any of the signs of optic nerve damage and therefore, do not truly have nerve damage and therefore, do not truly have glaucoma. These patients are said to have glaucoma. These patients are said to have ocular hypertensionocular hypertension

Other patients may progressively lose vision Other patients may progressively lose vision and become blind, even though they never and become blind, even though they never exhibit "high" eye pressures. These patients exhibit "high" eye pressures. These patients have low tension glaucoma (also called normal have low tension glaucoma (also called normal tension glaucoma)tension glaucoma)

Glaucoma (cont’d)Glaucoma (cont’d) Most patients with glaucoma do have Most patients with glaucoma do have

elevated intraocular pressure. Along with elevated intraocular pressure. Along with the eye pressure, other parameters are the eye pressure, other parameters are evaluated in the search for glaucoma, evaluated in the search for glaucoma, such as peripheral vision, visual contrast such as peripheral vision, visual contrast sensitivity, optic nerve cupping (a sensitivity, optic nerve cupping (a hollowing out of the center of the optic hollowing out of the center of the optic nerve head in the back of the eye), and nerve head in the back of the eye), and gonioscopy (visualizing the anatomy of gonioscopy (visualizing the anatomy of the filtering angle of the eye, where the the filtering angle of the eye, where the cornea and the iris join)cornea and the iris join)

Miscellaneous tidbits about the eyesMiscellaneous tidbits about the eyesAnterior chamber – refers to the fluid filled Anterior chamber – refers to the fluid filled

(aqueous humor) space between the cornea (aqueous humor) space between the cornea and the iris/pupiland the iris/pupil

Posterior chamber – refers to the fluid filled Posterior chamber – refers to the fluid filled (aqueous humor) ring-shaped space between (aqueous humor) ring-shaped space between the iris/pupil and the lens and ciliary bodythe iris/pupil and the lens and ciliary body

Anterior segment – refers to the intraocular Anterior segment – refers to the intraocular portion of the eyeball and holds the anterior portion of the eyeball and holds the anterior and posterior chambers of the eyeand posterior chambers of the eye

Posterior segment – refers to the large Posterior segment – refers to the large vitreous-filled space between the retina and vitreous-filled space between the retina and the lens and where the optic nerve comes into the lens and where the optic nerve comes into the eyethe eye

Miscellaneous tidbits about the eyes Miscellaneous tidbits about the eyes (cont’d)(cont’d)

A newborn’s eyeball is about 18 A newborn’s eyeball is about 18 millimeters in diameter, from front to millimeters in diameter, from front to back. It grows gradually to a length of back. It grows gradually to a length of approximately 24-25 millimeters (about approximately 24-25 millimeters (about 1”), or just smaller than a 1 1/2” ping 1”), or just smaller than a 1 1/2” ping pong ball!pong ball!

CPT codes in the 60,000 series are divided CPT codes in the 60,000 series are divided by the anatomical location of eitherby the anatomical location of either

Anterior segmentAnterior segmentPosterior segmentPosterior segmentOcular adenexaOcular adenexa

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1.1. How do you see?How do you see?Rays of light pass through the pupil Rays of light pass through the pupil in your eye , which is like a small in your eye , which is like a small hole. Behind each pupil is a lens hole. Behind each pupil is a lens which bends light so that it shines on which bends light so that it shines on an area at the back of your eye called an area at the back of your eye called the retina. This makes an upside the retina. This makes an upside down picture on the retina of what down picture on the retina of what you are seeing The optic nerves in you are seeing The optic nerves in your eyes send this information to your eyes send this information to your brain which lets you see it the your brain which lets you see it the right way up. right way up.

Your pupil is the black circle in the Your pupil is the black circle in the middle of the coloured part of your middle of the coloured part of your eye. It is actually a hole in your eye eye. It is actually a hole in your eye that lets light in. Your eyes work just that lets light in. Your eyes work just like a camera, when it is bright your like a camera, when it is bright your eyes don't need to let so much light eyes don't need to let so much light in for you to see so the muscles of in for you to see so the muscles of the iris {the coloured part of your the iris {the coloured part of your eye} contract making the pupil hole eye} contract making the pupil hole smaller. In light the iris expands to smaller. In light the iris expands to make the pupil as large as possible make the pupil as large as possible to allow all the available light to to allow all the available light to enter your eye.enter your eye.

Your eyes constantly make tears, Your eyes constantly make tears, which stop your eyes drying out. which stop your eyes drying out. Tears contain proteins that kill Tears contain proteins that kill germs, helping prevent infections in germs, helping prevent infections in your eyes. You blink about fifteen your eyes. You blink about fifteen times every minute, spreading the times every minute, spreading the tears across your eyes. Extra tears tears across your eyes. Extra tears fluid drains through a small tube fluid drains through a small tube into your nose, which is why your into your nose, which is why your nose also runs when your water or nose also runs when your water or you are crying.you are crying.

The colour of your eyes depends The colour of your eyes depends on the amount of pigment that is on the amount of pigment that is in the iris. Brown eyes have a lot in the iris. Brown eyes have a lot of pigment, while blue eyes have a of pigment, while blue eyes have a little. You inherited your eye little. You inherited your eye colour from your parents. The colour from your parents. The most common eye colour is brown. most common eye colour is brown. If one of your parents has brown If one of your parents has brown eyes and the other has blue eyes, eyes and the other has blue eyes, your eyes will most likely be your eyes will most likely be brown. brown.

A blind person who is colour cannot tell the A blind person who is colour cannot tell the difference between certain colours, most difference between certain colours, most often red and green. This is a condition often red and green. This is a condition which is inherited and about ten percent of which is inherited and about ten percent of males have it. It is very rare in females. males have it. It is very rare in females.

6.6. How do my eyes help me see?How do my eyes help me see? Each of your eyes is a ball. At the front, Each of your eyes is a ball. At the front, there’s a black whole called the pupil, there’s a black whole called the pupil, which lets in light. Behind the pupil is a which lets in light. Behind the pupil is a lens that help you to see things close to or lens that help you to see things close to or far away. The optic nerve carries messages far away. The optic nerve carries messages about what you see to your brain.about what you see to your brain.

Have you noticed that animals eye shine in the dark? This is because their eyes reflect Have you noticed that animals eye shine in the dark? This is because their eyes reflect light back, so if you shine a light on them, the reflection can be seen in the dark. A light back, so if you shine a light on them, the reflection can be seen in the dark. A man called Edwin Shaw, from England, noticed this and made “cat’s eyes”man called Edwin Shaw, from England, noticed this and made “cat’s eyes”From glass which were set in rubber and placed in the middle of roads helping driver’s From glass which were set in rubber and placed in the middle of roads helping driver’s stay on the road in the dark.stay on the road in the dark.

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Now it’s time for Now it’s time for some eyesome eye MAGICMAGIC