The Special Senses: The Eye

1. The Special Senses: The Eye

2. 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

3. Structure • Adnexa • AKA Adnexa oculi • Extraocular structures of the eye • Include the orbit, eye muscles, eyelids, eyelashes, conjunctiva, and lacrimal apparatus • Adnexa means accessory structures

4. Structure • Orbit • AKA eye socket • Bony cavity of the skull that contains and protects the eyeball and the adnexa

5. Structures • 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

6. Structures • 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

7. Structures • 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

8. Structures • Conjunctiva • Transparent mucous membrane that lines the underside of the eyelid • Also continues on to cover the exposed surface of the eyeball

9. Structures • 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

11. Structures • Eyeball • AKA globe • Walls are made of three layers • Sclera • Choroid • Retina • The interior of the eye is divided into anterior and posterior segments

12. Structures • 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

13. Structures • 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

14. Structures • 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

15. Structures • 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

16. Structures • 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

17. Structures • 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

18. Structures • 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

19. Structure • Posterior Segment • Filled with vitreous humor (or gel) • Soft, clear, jelly-like • Helps the eye maintain its shape

20. 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)

21. 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

22. 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

23. 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

24. Pathology • 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

26. Pathology • 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

27. Pathology • Adnexa • Conjunctivitis • AKA pinkeye • Inflammation of the conjunctiva • Usually caused by infection or allergy • Xerophthalmia • AKA Dry eye • May be due to disease or a lack of Vitamin A

28. Pathology • 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

29. Pathology • 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

30. Pathology • Eye • Anisocoria • Condition in which the pupils are unequal in size • May be congenital or caused by injury or disease (aneurysm, etc)

31. Cataract • Loss of transparency of the lens • Usually due to aging, although they may also be disease related or congenital

32. Pathology • 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

33. Pathology • 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

34. Pathology • 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

35. Pathology • 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

36. Pathology • 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

37. Pathology • 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

38. Pathology • 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

39. Pathology • 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

40. Pathology • 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)

41. Pathology • 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

42. Pathology • 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

43. Pathology • 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

44. Pathology • 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

45. 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

46. Treatment • 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)

47. Treatment • 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

48. Treatment • 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

49. Treatment • 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

50. Treatment • 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