The special senses the eye
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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)

  • Cataract

    • 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