the special senses: the eye

The Special Senses:The Special Senses:

The EyeThe Eye

22

FunctionsFunctions

Receptor organs for the sense of sightReceptor organs for the sense of sight

Ocul/o, ophthalm/oOcul/o, ophthalm/o mean eye mean eye– Extraocular means outside the eyeExtraocular means outside the eye– Intraocular means within the eyeIntraocular means within the eye

Opt/i, opt/oOpt/i, opt/o mean vision or sight mean vision or sight

33

StructureStructure

AdnexaAdnexa– AKA Adnexa oculiAKA Adnexa oculi– Extraocular structures of the eyeExtraocular structures of the eye

Include the orbit, eye muscles, eyelids, eyelashes, Include the orbit, eye muscles, eyelids, eyelashes, conjunctiva, and lacrimal apparatusconjunctiva, and lacrimal apparatus

AdnexaAdnexa means accessory structures means accessory structures

44

StructureStructure

OrbitOrbit– AKA eye socketAKA eye socket– Bony cavity of the skull that contains and Bony cavity of the skull that contains and

protects the eyeball and the adnexaprotects the eyeball and the adnexa

55

StructuresStructures

Eye MusclesEye Muscles– Three pairs of muscles are attached to each eyeThree pairs of muscles are attached to each eye

Superior and Inferior Rectus, Medial and Lateral Superior and Inferior Rectus, Medial and Lateral Rectus, Superior and Inferior ObliqueRectus, Superior and Inferior Oblique

– The muscles of both eyes work together in The muscles of both eyes work together in coordinated movementcoordinated movement

66


EyelidEyelid– Upper and lower eyelids protect the eye from foreign Upper and lower eyelids protect the eye from foreign

matter, excessive light, and impactmatter, excessive light, and impact– Spread tears around the eyes to cleanseSpread tears around the eyes to cleanse– Canthus – angle where the upper and lower lids meetCanthus – angle where the upper and lower lids meet

Inner canthus is closer to the noseInner canthus is closer to the noseOuter canthus is towards the side Outer canthus is towards the side of the faceof the face

– Tarsus – stiffening plate within the Tarsus – stiffening plate within the eyelids that provides stiffness and eyelids that provides stiffness and shapeshape

77


Eyebrows and EyelashesEyebrows and Eyelashes– Prevent foreign matter from reaching the eyesPrevent foreign matter from reaching the eyes– Eyelashes are actually cilia on the edges of Eyelashes are actually cilia on the edges of

the eyelid the eyelid help to detect proximity of objects - eyelid then help to detect proximity of objects - eyelid then closes reflexivelycloses reflexively

88


ConjunctivaConjunctiva– Transparent mucous Transparent mucous

membrane that lines membrane that lines the underside of the the underside of the eyelideyelid

Also continues on Also continues on to cover the to cover the exposed surface of exposed surface of the eyeballthe eyeball

99


Lacrimal ApparatusLacrimal Apparatus– AKA Tear ApparatusAKA Tear Apparatus– Lacrimal glands secrete lacrimal fluid (tears)Lacrimal glands secrete lacrimal fluid (tears)

Located above the outer corner of the eyeLocated above the outer corner of the eye– Lacrimal canals collect tears and direct them into the Lacrimal canals collect tears and direct them into the

lacrimal sacslacrimal sacsTwo ducts in the inner corner of the eyeTwo ducts in the inner corner of the eye

– Lacrimal sac (tear sac)Lacrimal sac (tear sac)Enlargement of the upper portion of the lacrimal ductEnlargement of the upper portion of the lacrimal duct

– Nasolacrimal DuctNasolacrimal DuctDrains excess tears into the nasal cavityDrains excess tears into the nasal cavity

– Lacrim/o Lacrim/o mean tearsmean tears

1111


EyeballEyeball– AKA globeAKA globe– Walls are made of three Walls are made of three

layerslayersSclera Sclera

ChoroidChoroid

RetinaRetina

– The interior of the eye is The interior of the eye is divided into anterior and divided into anterior and posterior segmentsposterior segments

1212


ScleraSclera– AKA white of the eyeAKA white of the eye– Tough, fibrous tissue that Tough, fibrous tissue that

forms the outer layer of the forms the outer layer of the eye (except for the cornea)eye (except for the cornea)

– Protects and maintains the Protects and maintains the shape of the eyeshape of the eye

CorneaCornea– Transparent anterior Transparent anterior

surface of the eye that surface of the eye that covers the iris and pupilcovers the iris and pupil

– Focuses light rays entering Focuses light rays entering the eyethe eye

1313


Uveal TractUveal Tract– AKA UveaAKA Uvea– Vascular layer of the eyeVascular layer of the eye– IrisIris

Pigmented, muscular layer that surrounds the pupilPigmented, muscular layer that surrounds the pupil– Muscles contract to restrict the size of the pupilMuscles contract to restrict the size of the pupil

Colour is determined by the amount of melaninColour is determined by the amount of melanin

– PupilPupilCircular opening in the center of the irisCircular opening in the center of the iris

Permits light to enter the eyePermits light to enter the eye

1414

StructuresStructures– LensLens

Clear, flexible, curved structure Clear, flexible, curved structure that focuses images on the retinathat focuses images on the retina

– ChoroidChoroid

AKA choroid coatAKA choroid coat

Opaque middle layer of the eyeballOpaque middle layer of the eyeball

Provides blood supply for the eyeProvides blood supply for the eye– Ciliary BodyCiliary Body

Located within the choroidLocated within the choroid

Set of muscles and ligaments that Set of muscles and ligaments that adjust the thickness of the lens to adjust the thickness of the lens to refine the focusrefine the focus

1515


RetinaRetina– Innermost layer of the eye wall – Innermost layer of the eye wall –

lines the posterior segmentlines the posterior segment– Contains light sensitive cells called Contains light sensitive cells called

rods and conesrods and cones

Rods are black and white Rods are black and white receptorsreceptors

Cones are colour receptorsCones are colour receptors

Both receive images and Both receive images and convert them to nerve impulses convert them to nerve impulses to be sent to the brainto be sent to the brain

1616


– MaculaMacula

AKA macula luteaAKA macula lutea

Yellow area in the center Yellow area in the center of the retinaof the retina

Area of sharpest central Area of sharpest central visionvision

– Fovea CentralisFovea Centralis

Pit in the middle of the Pit in the middle of the macula containing a lot of macula containing a lot of cones and no rodscones and no rods

Best spot for colour Best spot for colour visionvision

1717


– Optic DiskOptic DiskAKA Blind SpotAKA Blind Spot

– Small region where the nerve endings enter the Small region where the nerve endings enter the optic nerveoptic nerve

– Contains no rods or conesContains no rods or cones

– Optic nerveOptic nerveSecond cranial nerveSecond cranial nerve

Transmits nerve impulses from the retina to the Transmits nerve impulses from the retina to the brainbrain

1818


Segments of the EyeSegments of the Eye– Anterior Segment– front 1/3 of the eyeballAnterior Segment– front 1/3 of the eyeball

Divided into anterior and posterior chambersDivided into anterior and posterior chambersAnterior chamber is between the cornea and the Anterior chamber is between the cornea and the irisirisPosterior chamber is between the iris and the Posterior chamber is between the iris and the ciliary bodyciliary bodyBoth chambers are filled with Both chambers are filled with aqueous humoraqueous humor, , which maintains the eye’s shape and nourishes the which maintains the eye’s shape and nourishes the intraocular structuresintraocular structuresConstantly drained to regulate the intraocular Constantly drained to regulate the intraocular pressurepressure

1919

StructureStructure

– Posterior SegmentPosterior SegmentFilled with vitreous humor (or gel)Filled with vitreous humor (or gel)

Soft, clear, jelly-likeSoft, clear, jelly-like

Helps the eye maintain its shapeHelps the eye maintain its shape

2020

Normal Action of the EyesNormal Action of the Eyes

AccomodationAccomodation– Adjustments the eye makes to see objects at Adjustments the eye makes to see objects at

various distances various distances

ConvergenceConvergence– Simultaneous inward movement of the eyes Simultaneous inward movement of the eyes

as objects come nearer (to preserve binocular as objects come nearer (to preserve binocular vision)vision)

2121

Normal Action of the EyeNormal Action of the Eye

EmmetropiaEmmetropia– Normal relationship between the refractive Normal relationship between the refractive

power of the eye and the shape of the eye power of the eye and the shape of the eye that allow light rays to focus properly on the that allow light rays to focus properly on the retinaretina

RefractionRefraction– Ability of the lens to bend light raysAbility of the lens to bend light rays

2222

Normal Action of the EyesNormal Action of the Eyes

Visual AcuityVisual Acuity– Ability to distinguish object Ability to distinguish object

details at a distancedetails at a distance– Measured using a Snellen Measured using a Snellen

ChartChart– Recorded as a fraction of Recorded as a fraction of

distance from the chart over distance from the chart over the maximum distance from the maximum distance from which someone with which someone with “normal” vision could read “normal” vision could read the same linethe same line

– Ex 20/20, 20/25, 20/40Ex 20/20, 20/25, 20/40

2323

Medical SpecialtiesMedical Specialties

OphthalmologistOphthalmologist– Physician who specializes in diagnosing and Physician who specializes in diagnosing and

treating disorders of the eyetreating disorders of the eye

OptometristOptometrist– Specializes in measuring the accuracy of Specializes in measuring the accuracy of

vision and prescribing corrective lensesvision and prescribing corrective lenses– Holds a Doctor of Optometry degreeHolds a Doctor of Optometry degree

2424

PathologyPathology

EyelidsEyelids– BlepharoptosisBlepharoptosis

Drooping of the upper eyelid – usually due to Drooping of the upper eyelid – usually due to paralysisparalysisBlephar/o means eyelidBlephar/o means eyelid

– EctropionEctropionEversion of the edge of an eyelidEversion of the edge of an eyelidExposes the inner surface to irritation and prevents Exposes the inner surface to irritation and prevents tears from drainingtears from draining

– EntropionEntropionInversion of the edge of an eyelid, which causes Inversion of the edge of an eyelid, which causes the eyelashes to rub against the corneathe eyelashes to rub against the cornea

2626

PathologyPathology

– HordeolumHordeolum

AKA StyeAKA Stye

Pus-filled lesion on the eyelidPus-filled lesion on the eyelid

Results from the infection of a sebaceous glandResults from the infection of a sebaceous gland– ChalazionChalazion

AKA internal styeAKA internal stye

Localized swelling inside the Localized swelling inside the eyelid resulting from eyelid resulting from obstruction of one of the obstruction of one of the sebaceous glandssebaceous glands

2727

PathologyPathology

AdnexaAdnexa– ConjunctivitisConjunctivitis

AKA pinkeyeAKA pinkeyeInflammation of the Inflammation of the

conjunctivaconjunctivaUsually caused by infection Usually caused by infection

or allergyor allergy

– XerophthalmiaXerophthalmiaAKA Dry eyeAKA Dry eyeMay be due to disease or a lack of Vitamin AMay be due to disease or a lack of Vitamin A

2828

PathologyPathology

Sclera, Cornea, IrisSclera, Cornea, Iris– ScleritisScleritis

Inflammation of the scleraInflammation of the sclera

– KeratitisKeratitisInflammation of the corneaInflammation of the cornea

Kerat/oKerat/o means cornea or hard means cornea or hard

– Corneal AbrasionCorneal AbrasionInjury, such as a scratch to the outer layers of the Injury, such as a scratch to the outer layers of the corneacornea

2929

PathologyPathology

– Corneal UlcerCorneal UlcerPitting of the cornea caused by infection or injuryPitting of the cornea caused by infection or injury

Will heal, but may leave a cloudy scarWill heal, but may leave a cloudy scar

– PterygiumPterygiumNoncancerous growth that develops on the cornea Noncancerous growth that develops on the cornea and can grow large enough to distort visionand can grow large enough to distort vision

– SynechiaSynechiaAn adhesion that binds the iris to an adjacent An adhesion that binds the iris to an adjacent structure structure

3030

PathologyPathology

EyeEye– AnisocoriaAnisocoria

Condition in which the pupils are unequal in sizeCondition in which the pupils are unequal in sizeMay be congenital or caused by injury or disease May be congenital or caused by injury or disease (aneurysm, etc)(aneurysm, etc)

3131

– CataractCataractLoss of transparency of the lensLoss of transparency of the lens

Usually due to aging, although they may also be disease Usually due to aging, although they may also be disease related or congenitalrelated or congenital

3232

PathologyPathology

– FloatersFloatersAKA Vitreous floatersAKA Vitreous floaters

– Particles of cellular debris that cast shadows on Particles of cellular debris that cast shadows on the retinathe retina

– Occur normally with agingOccur normally with aging– May be associated with detachments, tears, or May be associated with detachments, tears, or

intraocular inflammationintraocular inflammation

– NystagmusNystagmusInvoluntary, constant movement of the eyeballInvoluntary, constant movement of the eyeball

Congenital, or caused by neurological injury or Congenital, or caused by neurological injury or drug usedrug use

3333

PathologyPathology

– Detached RetinaDetached Retina

Retina pulls away from Retina pulls away from the choroidthe choroid

Retina may tear when it Retina may tear when it detachesdetaches

Can be spontaneous, orCan be spontaneous, ordue to trauma, agingdue to trauma, agingdiabetes, etcdiabetes, etc

– UveitisUveitis

Inflammation anywhere in the uveal tractInflammation anywhere in the uveal tract

Can damage the eye and produce cataracts, Can damage the eye and produce cataracts, swelling, and/or glaucomaswelling, and/or glaucoma

3434

PathologyPathology

– GlaucomaGlaucomaGroup of diseases characterized by increased Group of diseases characterized by increased intraocular pressure (IOP)intraocular pressure (IOP)

Results in damage to the retinal nerve fibers and Results in damage to the retinal nerve fibers and the optic nervethe optic nerve

Caused by a blockage of fluid out of the eyeCaused by a blockage of fluid out of the eye

Results in loss of peripheral vision and eventual Results in loss of peripheral vision and eventual blindnessblindness

3535

PathologyPathology

– Open-angle glaucoma (chronic glaucoma) Open-angle glaucoma (chronic glaucoma) occurs when the drainage system for the occurs when the drainage system for the anterior segment becomes blockedanterior segment becomes blocked

Can be detected during an eye exam (symptoms Can be detected during an eye exam (symptoms do not usually occur until the optic nerve is do not usually occur until the optic nerve is damageddamaged

3636

PathologyPathology

– Closed-angle glaucoma (acute glaucoma) Closed-angle glaucoma (acute glaucoma) occurs suddenly when the opening between occurs suddenly when the opening between the cornea and the iris narrows, and fluid the cornea and the iris narrows, and fluid cannot reach the draincannot reach the drain

Produces severe pain, nausea, redness of the eye, Produces severe pain, nausea, redness of the eye, blurred visionblurred vision

Blindness may occur in as little as two daysBlindness may occur in as little as two days

3737

PathologyPathology

– Macular DegenerationMacular DegenerationGradually progressive condition in which the Gradually progressive condition in which the macula is damagedmacula is damagedResults in the loss of central vision, but not total Results in the loss of central vision, but not total blindnessblindnessFrequently age-related (most common cause of Frequently age-related (most common cause of legal blindness in people over 60)legal blindness in people over 60)

– Dry-type macular degeneration is caused by Dry-type macular degeneration is caused by deterioration of cells in the maculadeterioration of cells in the macula

– Wet-type macular degeneration is caused by Wet-type macular degeneration is caused by formation of new blood vessels that produce formation of new blood vessels that produce small hemorrhages and damage the maculasmall hemorrhages and damage the macula

3838

PathologyPathology

Functional DefectsFunctional Defects– DiplopiaDiplopia

AKA Double VisionAKA Double Vision

Perception of two images of a single objectPerception of two images of a single object

Often a symptom of another condition (such as Often a symptom of another condition (such as MS)MS)

-opia-opia means vision means vision

– HemianopiaHemianopiaBlindness in one half of the visual fieldBlindness in one half of the visual field

3939

PathologyPathology

– MonochromatismMonochromatismAKA colour blindnessAKA colour blindness

Inability to distinguish certain coloursInability to distinguish certain colours

Caused by defects in the cone cellsCaused by defects in the cone cells

Usually inheritedUsually inherited

– NyctalopiaNyctalopiaAKA night blindnessAKA night blindness

Individual with normal day vision has trouble Individual with normal day vision has trouble seeing at nightseeing at night

May be congenital, or due to a lack of vitamin AMay be congenital, or due to a lack of vitamin A

4040

PathologyPathology

– PresbyopiaPresbyopiaCommon changes that occur with agingCommon changes that occur with aging

Near vision suffers as the lens becomes less Near vision suffers as the lens becomes less flexible and the muscles of the ciliary body flexible and the muscles of the ciliary body weaken (the image is focused poorly on the weaken (the image is focused poorly on the retina)retina)

4141

PathologyPathology

– StrabismusStrabismusAKA squintAKA squint

Disorder in which the eyes point in different Disorder in which the eyes point in different directions (or are not aligned) because the directions (or are not aligned) because the muscles are unable to work togethermuscles are unable to work together

– Esotropia – AKA cross-eyesEsotropia – AKA cross-eyes– Exotropia – AKA walleyeExotropia – AKA walleye

Often treated by placing a patch over the Often treated by placing a patch over the stronger eye so the weaker muscles will stronger eye so the weaker muscles will strengthenstrengthen

4242

PathologyPathology

Refractive DisordersRefractive Disorders– Occurs when the lens and cornea do not Occurs when the lens and cornea do not

refract the light properly so it focuses on the refract the light properly so it focuses on the retinaretina

– AmetropiaAmetropiaAny error of refractionAny error of refraction

– AstigmatismAstigmatismEye does not focus because of uneven curvatures Eye does not focus because of uneven curvatures of the corneaof the cornea

4343

PathologyPathology

– HyperopiaHyperopiaAKA farsightednessAKA farsightednessThe eyeball is too short for the The eyeball is too short for the curvature of the cornea, so the curvature of the cornea, so the light rays focus beyond the light rays focus beyond the retinaretinaMost common after 40Most common after 40

– MyopiaMyopiaAKA nearsightednessAKA nearsightednessThe eyeball is too long, so the light rays focus in The eyeball is too long, so the light rays focus in front of the retinafront of the retinaMost common around pubertyMost common around puberty

4444

PathologyPathology

BlindnessBlindness– Inability to seeInability to see– Legal blindness is the point at which the law Legal blindness is the point at which the law

considers an individual to be blindconsiders an individual to be blindEx when the individual’s best corrected vision is Ex when the individual’s best corrected vision is 20/200 or less20/200 or less

– AmblyopiaAmblyopiaDimness of vision or partial loss of sight without Dimness of vision or partial loss of sight without detectable disease in the eyedetectable disease in the eye

– ScotomaScotomaAKA blind spotAKA blind spotAbnormal area of depressed vision surrounded by Abnormal area of depressed vision surrounded by an area of normal visionan area of normal vision

4545

Diagnostic ProceduresDiagnostic Procedures

RefractionRefraction– Examination to determine an eye’s refractive error so Examination to determine an eye’s refractive error so

corrective lenses can be prescribedcorrective lenses can be prescribedTonometryTonometry– Measurement of intraocular pressureMeasurement of intraocular pressure

OphthalmoscopyOphthalmoscopy– Visual examination of the back part of the eye (retina, Visual examination of the back part of the eye (retina,

choroid, optic disk)choroid, optic disk)– May require the pupil to be dilated through the use of May require the pupil to be dilated through the use of

mydriatic drops (produce temporary paralysis of the mydriatic drops (produce temporary paralysis of the iris)iris)

Visual Field TestingVisual Field Testing– AKA perimetryAKA perimetry– Determines loss of peripheral visionDetermines loss of peripheral vision

4646

TreatmentTreatment

Orbit and EyelidsOrbit and Eyelids– OrbitotomyOrbitotomy

Surgical incision into the orbitSurgical incision into the orbit

For biopsy, abscess drainage, removal of a tumour For biopsy, abscess drainage, removal of a tumour or foreign objector foreign object

– TarsorrhaphyTarsorrhaphyPartial or complete suturing together of the eyelidsPartial or complete suturing together of the eyelids

Performed to protect the eye when the eyelids Performed to protect the eye when the eyelids cannot close properly (due to paralysis)cannot close properly (due to paralysis)

4747

TreatmentTreatment

Conjunctiva and EyeballConjunctiva and Eyeball– ConjuctivoplastyConjuctivoplasty

Surgical repair of the conjunctivaSurgical repair of the conjunctiva

– KeratoplastyKeratoplastyCorneal transplantCorneal transplant

Replacement of scarred or diseased cornea with a Replacement of scarred or diseased cornea with a cornea from a donorcornea from a donor

– IridectomyIridectomySurgical removal of a portion of the irisSurgical removal of a portion of the iris

4848

TreatmentTreatment

– Radial KeratotomyRadial KeratotomySurgical procedure to correct myopiaSurgical procedure to correct myopia

Incisions are made partially through the cornea to Incisions are made partially through the cornea to cause it to flattencause it to flatten

– LensectomyLensectomyRemoval of a cataract-clouded lensRemoval of a cataract-clouded lens

Replaced with an artificial lensReplaced with an artificial lens

Pseudophakia is an eye in which the natural lens Pseudophakia is an eye in which the natural lens has been replacedhas been replaced

4949

TreatmentTreatment

Corrective LensesCorrective Lenses– Alter the angle of the light rays before the Alter the angle of the light rays before the

enter the corneaenter the corneaConcave lenses are used for myopiaConcave lenses are used for myopia

Convex lenses are used for hyperopiaConvex lenses are used for hyperopia

– Lenses can have different areas with different Lenses can have different areas with different refractive powersrefractive powers

Ex bifocals, trifocalsEx bifocals, trifocals

5050

TreatmentTreatment

Laser TreatmentsLaser Treatments– Laser iridotomyLaser iridotomy

Used to treat acute glaucoma by creating an Used to treat acute glaucoma by creating an opening in the iris to allow drainageopening in the iris to allow drainage

– Laser trabeculoplastyLaser trabeculoplastyUsed to treat chronic glaucoma by creating an Used to treat chronic glaucoma by creating an opening in the meshwork that drains the eyeopening in the meshwork that drains the eye

– LASIKLASIKLaser-Assisted in Situ KeratomileusisLaser-Assisted in Situ KeratomileusisA flap is opened in the surface of the cornea, A flap is opened in the surface of the cornea, then a laser is used to change the shape of the then a laser is used to change the shape of the deep corneal layerdeep corneal layer

5151

TreatmentTreatment

– RetinopexyRetinopexyReattachment of the retinaReattachment of the retina

– PhotocoagulationPhotocoagulationUse of lasers to treat some forms of macular Use of lasers to treat some forms of macular degeneration by sealing leaking blood vesselsdegeneration by sealing leaking blood vessels

the special senses: the eye

Documents