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The Special Senses: The Eye. Functions. Receptor organs for the sense of sight Ocul/o, ophthalm/o mean eye Extraocular means outside the eye Intraocular means within the eye Opt/i, opt/o mean vision or sight. Structure. Adnexa AKA Adnexa oculi Extraocular structures of the eye

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  • Receptor organs for the sense of sight
  • Ocul/o, ophthalm/o mean eye
    • Extraocular means outside the eye
    • Intraocular means within the eye
  • Opt/i, opt/o mean vision or sight
  • Adnexa
    • AKA Adnexa oculi
    • Extraocular structures of the eye
      • Include the orbit, eye muscles, eyelids, eyelashes, conjunctiva, and lacrimal apparatus
      • Adnexa means accessory structures
  • Orbit
    • AKA eye socket
    • Bony cavity of the skull that contains and protects the eyeball and the adnexa
  • Eye Muscles
    • Three pairs of muscles are attached to each eye
      • Superior and Inferior Rectus, Medial and Lateral Rectus, Superior and Inferior Oblique
    • The muscles of both eyes work together in coordinated movement
  • Eyelid
    • Upper and lower eyelids protect the eye from foreign matter, excessive light, and impact
    • Spread tears around the eyes to cleanse
    • Canthus – angle where the upper and lower lids meet
      • Inner canthus is closer to the nose
      • Outer canthus is towards the side of the face
    • Tarsus – stiffening plate within the eyelids that provides stiffness and shape
  • Eyebrows and Eyelashes
    • Prevent foreign matter from reaching the eyes
    • Eyelashes are actually cilia on the edges of the eyelid
      • help to detect proximity of objects - eyelid then closes reflexively
  • Conjunctiva
    • Transparent mucous membrane that lines the underside of the eyelid
      • Also continues on to cover the exposed surface of the eyeball
  • Lacrimal Apparatus
    • AKA Tear Apparatus
    • Lacrimal glands secrete lacrimal fluid (tears)
      • Located above the outer corner of the eye
    • Lacrimal canals collect tears and direct them into the lacrimal sacs
      • Two ducts in the inner corner of the eye
    • Lacrimal sac (tear sac)
      • Enlargement of the upper portion of the lacrimal duct
    • Nasolacrimal Duct
      • Drains excess tears into the nasal cavity
    • Lacrim/o mean tears
  • Eyeball
    • AKA globe
    • Walls are made of three layers
      • Sclera
      • Choroid
      • Retina
    • The interior of the eye is divided into anterior and posterior segments
  • Sclera
    • AKA white of the eye
    • Tough, fibrous tissue that forms the outer layer of the eye (except for the cornea)
    • Protects and maintains the shape of the eye
  • Cornea
    • Transparent anterior surface of the eye that covers the iris and pupil
    • Focuses light rays entering the eye
  • Uveal Tract
    • AKA Uvea
    • Vascular layer of the eye
    • Iris
      • Pigmented, muscular layer that surrounds the pupil
        • Muscles contract to restrict the size of the pupil
      • Colour is determined by the amount of melanin
    • Pupil
      • Circular opening in the center of the iris
      • Permits light to enter the eye
  • Lens
    • Clear, flexible, curved structure that focuses images on the retina
  • Choroid
    • AKA choroid coat
    • Opaque middle layer of the eyeball
    • Provides blood supply for the eye
  • Ciliary Body
    • Located within the choroid
    • Set of muscles and ligaments that adjust the thickness of the lens to refine the focus
  • Retina
    • Innermost layer of the eye wall – lines the posterior segment
    • Contains light sensitive cells called rods and cones
      • Rods are black and white receptors
      • Cones are colour receptors
      • Both receive images and convert them to nerve impulses to be sent to the brain
  • Macula
    • AKA macula lutea
    • Yellow area in the center of the retina
    • Area of sharpest central vision
  • Fovea Centralis
    • Pit in the middle of the macula containing a lot of cones and no rods
    • Best spot for colour vision
  • Optic Disk
    • AKA Blind Spot
      • Small region where the nerve endings enter the optic nerve
      • Contains no rods or cones
  • Optic nerve
    • Second cranial nerve
    • Transmits nerve impulses from the retina to the brain
  • Segments of the Eye
    • Anterior Segment– front 1/3 of the eyeball
      • Divided into anterior and posterior chambers
      • Anterior chamber is between the cornea and the iris
      • Posterior chamber is between the iris and the ciliary body
      • Both chambers are filled with aqueous humor, which maintains the eye’s shape and nourishes the intraocular structures
      • Constantly drained to regulate the intraocular pressure
  • Posterior Segment
    • Filled with vitreous humor (or gel)
    • Soft, clear, jelly-like
    • Helps the eye maintain its shape
normal action of the eyes
Normal Action of the Eyes
  • Accomodation
    • Adjustments the eye makes to see objects at various distances
  • Convergence
    • Simultaneous inward movement of the eyes as objects come nearer (to preserve binocular vision)
normal action of the eye
Normal Action of the Eye
  • Emmetropia
    • Normal relationship between the refractive power of the eye and the shape of the eye that allow light rays to focus properly on the retina
  • Refraction
    • Ability of the lens to bend light rays
normal action of the eyes1
Normal Action of the Eyes
  • Visual Acuity
    • Ability to distinguish object details at a distance
    • Measured using a Snellen Chart
    • Recorded as a fraction of distance from the chart over the maximum distance from which someone with “normal” vision could read the same line
    • Ex 20/20, 20/25, 20/40
medical specialties
Medical Specialties
  • Ophthalmologist
    • Physician who specializes in diagnosing and treating disorders of the eye
  • Optometrist
    • Specializes in measuring the accuracy of vision and prescribing corrective lenses
    • Holds a Doctor of Optometry degree
  • Eyelids
    • Blepharoptosis
      • Drooping of the upper eyelid – usually due to paralysis
      • Blephar/o means eyelid
    • Ectropion
      • Eversion of the edge of an eyelid
      • Exposes the inner surface to irritation and prevents tears from draining
    • Entropion
      • Inversion of the edge of an eyelid, which causes the eyelashes to rub against the cornea
  • Hordeolum
    • AKA Stye
    • Pus-filled lesion on the eyelid
    • Results from the infection of a sebaceous gland
  • Chalazion
    • AKA internal stye
    • Localized swelling inside the eyelid resulting from obstruction of one of the sebaceous glands
  • Adnexa
    • Conjunctivitis
      • AKA pinkeye
      • Inflammation of the


      • Usually caused by infection

or allergy

    • Xerophthalmia
      • AKA Dry eye
      • May be due to disease or a lack of Vitamin A
  • Sclera, Cornea, Iris
    • Scleritis
      • Inflammation of the sclera
    • Keratitis
      • Inflammation of the cornea
      • Kerat/o means cornea or hard
    • Corneal Abrasion
      • Injury, such as a scratch to the outer layers of the cornea
  • Corneal Ulcer
    • Pitting of the cornea caused by infection or injury
    • Will heal, but may leave a cloudy scar
  • Pterygium
    • Noncancerous growth that develops on the cornea and can grow large enough to distort vision
  • Synechia
    • An adhesion that binds the iris to an adjacent structure
  • Eye
    • Anisocoria
      • Condition in which the pupils are unequal in size
      • May be congenital or caused by injury or disease (aneurysm, etc)
    • Loss of transparency of the lens
    • Usually due to aging, although they may also be disease related or congenital
  • Floaters
    • AKA Vitreous floaters
      • Particles of cellular debris that cast shadows on the retina
      • Occur normally with aging
      • May be associated with detachments, tears, or intraocular inflammation
  • Nystagmus
    • Involuntary, constant movement of the eyeball
    • Congenital, or caused by neurological injury or drug use
  • Detached Retina
    • Retina pulls away from the choroid
    • Retina may tear when it detaches
    • Can be spontaneous, ordue to trauma, agingdiabetes, etc
  • Uveitis
    • Inflammation anywhere in the uveal tract
    • Can damage the eye and produce cataracts, swelling, and/or glaucoma
  • Glaucoma
    • Group of diseases characterized by increased intraocular pressure (IOP)
    • Results in damage to the retinal nerve fibers and the optic nerve
    • Caused by a blockage of fluid out of the eye
    • Results in loss of peripheral vision and eventual blindness
  • Open-angle glaucoma (chronic glaucoma) occurs when the drainage system for the anterior segment becomes blocked
    • Can be detected during an eye exam (symptoms do not usually occur until the optic nerve is damaged
  • Closed-angle glaucoma (acute glaucoma) occurs suddenly when the opening between the cornea and the iris narrows, and fluid cannot reach the drain
    • Produces severe pain, nausea, redness of the eye, blurred vision
    • Blindness may occur in as little as two days
  • Macular Degeneration
    • Gradually progressive condition in which the macula is damaged
    • Results in the loss of central vision, but not total blindness
    • Frequently age-related (most common cause of legal blindness in people over 60)
      • Dry-type macular degeneration is caused by deterioration of cells in the macula
      • Wet-type macular degeneration is caused by formation of new blood vessels that produce small hemorrhages and damage the macula
  • Functional Defects
    • Diplopia
      • AKA Double Vision
      • Perception of two images of a single object
      • Often a symptom of another condition (such as MS)
      • -opia means vision
    • Hemianopia
      • Blindness in one half of the visual field
  • Monochromatism
    • AKA colour blindness
    • Inability to distinguish certain colours
    • Caused by defects in the cone cells
    • Usually inherited
  • Nyctalopia
    • AKA night blindness
    • Individual with normal day vision has trouble seeing at night
    • May be congenital, or due to a lack of vitamin A
  • Presbyopia
    • Common changes that occur with aging
    • Near vision suffers as the lens becomes less flexible and the muscles of the ciliary body weaken (the image is focused poorly on the retina)
  • Strabismus
    • AKA squint
    • Disorder in which the eyes point in different directions (or are not aligned) because the muscles are unable to work together
      • Esotropia – AKA cross-eyes
      • Exotropia – AKA walleye
    • Often treated by placing a patch over the stronger eye so the weaker muscles will strengthen
  • Refractive Disorders
    • Occurs when the lens and cornea do not refract the light properly so it focuses on the retina
    • Ametropia
      • Any error of refraction
    • Astigmatism
      • Eye does not focus because of uneven curvatures of the cornea
  • Hyperopia
    • AKA farsightedness
    • The eyeball is too short for the curvature of the cornea, so the light rays focus beyond the retina
    • Most common after 40
  • Myopia
    • AKA nearsightedness
    • The eyeball is too long, so the light rays focus in front of the retina
    • Most common around puberty
  • Blindness
    • Inability to see
    • Legal blindness is the point at which the law considers an individual to be blind
      • Ex when the individual’s best corrected vision is 20/200 or less
    • Amblyopia
      • Dimness of vision or partial loss of sight without detectable disease in the eye
    • Scotoma
      • AKA blind spot
      • Abnormal area of depressed vision surrounded by an area of normal vision
diagnostic procedures
Diagnostic Procedures
  • Refraction
    • Examination to determine an eye’s refractive error so corrective lenses can be prescribed
  • Tonometry
    • Measurement of intraocular pressure
  • Ophthalmoscopy
    • Visual examination of the back part of the eye (retina, choroid, optic disk)
    • May require the pupil to be dilated through the use of mydriatic drops (produce temporary paralysis of the iris)
  • Visual Field Testing
    • AKA perimetry
    • Determines loss of peripheral vision
  • Orbit and Eyelids
    • Orbitotomy
      • Surgical incision into the orbit
      • For biopsy, abscess drainage, removal of a tumour or foreign object
    • Tarsorrhaphy
      • Partial or complete suturing together of the eyelids
      • Performed to protect the eye when the eyelids cannot close properly (due to paralysis)
  • Conjunctiva and Eyeball
    • Conjuctivoplasty
      • Surgical repair of the conjunctiva
    • Keratoplasty
      • Corneal transplant
      • Replacement of scarred or diseased cornea with a cornea from a donor
    • Iridectomy
      • Surgical removal of a portion of the iris
  • Radial Keratotomy
    • Surgical procedure to correct myopia
    • Incisions are made partially through the cornea to cause it to flatten
  • Lensectomy
    • Removal of a cataract-clouded lens
    • Replaced with an artificial lens
    • Pseudophakia is an eye in which the natural lens has been replaced
  • Corrective Lenses
    • Alter the angle of the light rays before the enter the cornea
      • Concave lenses are used for myopia
      • Convex lenses are used for hyperopia
    • Lenses can have different areas with different refractive powers
      • Ex bifocals, trifocals
  • Laser Treatments
    • Laser iridotomy
      • Used to treat acute glaucoma by creating an opening in the iris to allow drainage
    • Laser trabeculoplasty
      • Used to treat chronic glaucoma by creating an opening in the meshwork that drains the eye
    • LASIK
      • Laser-Assisted in Situ Keratomileusis
      • A flap is opened in the surface of the cornea, then a laser is used to change the shape of the deep corneal layer
  • Retinopexy
    • Reattachment of the retina
  • Photocoagulation
    • Use of lasers to treat some forms of macular degeneration by sealing leaking blood vessels