Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 38 Disorders of Special Sensory Function: Vision, Hearing, and Vestibular Function

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Eye Anatomy Discussion List the structures light must pass through on its way from the outside to the retina. What part does each structure play in vision?

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Disorders Affecting the Anterior Chamber Conjunctivitis Corneal abrasion Corneal edema Keratitis Glaucoma –Open-angle –Angle-closure

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Scenario B. is a 13-year-old girl who is involved in youth recreation programs at the Community Center where you volunteer… She complains of eye irritation The left eye is reddened and watery, with some crusting on the eyelashes Question What possible disorders will you consider?

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Aqueous Humor Aqueous humor is formed by the ciliary body It then flows between the iris and the lens to enter the anterior chamber In the anterior chamber, it delivers food and oxygen to the lens and cornea Then it drains into tubules of the trabecular meshwork They empty into the Canal of Schlemm

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Iridocorneal Angle The area where the iris meets the cornea It contains the: –Trabecular meshwork –Canal of Schlemm

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Angle-Closure Glaucoma The iris is displaced forward –Usually due to iris thickening caused by pupil dilation The angle is closed so aqueous humor cannot flow in to the trabecular meshwork Rapid buildup of aqueous humor in the anterior chamber

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Open-Angle Glaucoma The iridocorneal angle remains open Trabecular meshwork abnormality decreases the rate of aqueous humor reabsorption Gradual buildup of aqueous humor

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false: Angle-closure glaucoma results in gradual build-up of aqueous humor in the anterior chamber.

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer False Open-angle glaucoma results in gradual build-up of aqueous humor in the anterior chamber (because the iridocorneal angle stays open). In angle-closure glaucoma, the iridocorneal angle is closed, so the aqueous humor accumulates quickly.

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Lens Disorders Disorders of refraction –Hyperopia –Myopia –Astigmatism Disorders of accommodation –Presbyopia Cataracts

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Retinal artery enters the eye through the center of the optic nerve Retinal vein leaves the eye through the same nerve The retina has a second blood supply from the choroid blood vessels directly behind it Retinal Blood Supply

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Normal Appearance of the Retina Optic nerve enters at the optic disk Retinal arteries and veins can be seen at the center of the optic disk Retinal blood vessels are smooth with relatively straight paths

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question What vessel(s) supply blood to the retina? a.Retinal artery b.Choroid vessels c.Optic artery d.All of the above e.a and b

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer e.a and b The retina receives blood from the retinal artery (mainly), and secondarily from the choroid vessels that are posterior/dorsal to it.

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Papilledema or Choked Disk Increased intracranial pressure affects the optic nerve Optic disk protrudes into eye, with blurred margins Blood vessels in its center are not distinct; the pressure has made them collapse

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Retinopathy Damage to small retinal blood vessels –Microhemorrhages –“Cotton-wool” exudate –Microaneurysms

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Retinopathy Neovascularization –New vessels are more fragile –New vessels attach too tightly to the vitreous, fusing it to the retina

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Retinal Detachment Retina is separated from the choroid blood vessels behind it –Retinal cells lack oxygen –Cannot make enough ATP –Stop functioning –Painless loss of vision in the part of the retina that is detached

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Macular Degeneration Dry –Degeneration of retinal cells Wet –Neovascularization of the choroid –Blood vessels leak –Fluid buildup pushes retina away from choroid

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which retinal disorder is caused by ischemia of the retina? a.Papilledema b.Retinopathy c.Retinal detachment d.Macular degeneration

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer c.Retinal detachment In this disorder, the retina becomes detached/removed from the blood vessels behind it (choroid vessels). Because the blood supply is diminished, less oxygen travels to retinal cells. Oxygen and glucose are needed to make ATP (energy). Without oxygen, ATP can’t be produced and the cells die.

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Scenario Mrs. X is 47 years old and has been having trouble with her eyes. She says that she has trouble focusing and has had to get reading glasses A few weeks ago, she had an episode of “sparkling” in her left eye, and now there seems to be a shadow in her vision from that eye. Question What are the possible explanations for this client's visual problems?

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Scenario (cont.) She did not have a detached retina but has returned to her doctor because the episode recurred and this time has not gone away When the doctor tests her vision, she has identical defects in the right superior visual field of both eyes Question What might be going wrong?

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion Arrange the structures of the optic neural pathways in the correct order: Optic nerve Lateral geniculate nucleus Optic radiation Optic chiasm Eye Optic tract Visual cortex

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion List the structures a sound wave goes through as it enters the ear. Which structures: –Direct the sound wave? –Transmit the sound wave? –Create a nerve impulse in response to the sound wave?

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Middle Ear Conducts sound from eardrum to inner ear Eustachian tube lets air in and out to maintain equal pressure on both sides of eardrum

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Middle Ear Disorders Problems with pressure in the middle ear –Patent eustachian tube, eustachian tube obstruction, acute otitis media Problems with adhesions between the ossicles –Adhesive otitis media, otosclerosis Problems with erosion of the tissues –Cholesteatoma, mastoiditis

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Conductive Hearing Loss Ossicles do not conduct sound from eardrum to inner ear –Sounds that enter through the ear sound faint Sounds that are conducted through other bones of the head sound louder –Chewing –Own voice

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Inner Ear: Cochlea and Labyrinth

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Disorders of the Inner Ear and Auditory Pathways Increased nerve firing –Tinnitus –Focal seizures Decreased nerve firing –Sensorineural deafness –Presbycusis

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which auditory disorder is characterized by increased firing of the optic nerve, causing “ringing” of the ears? a.Otosclerosis b.Conductive hearing loss c.Tinnitus d.Sensorineural deafness

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer c.Tinnitus Increased firing of neurons of the inner ear results in the classic symptom of “ringing” in the ears. Sensorineural deafness is caused by less frequent firing of neurons in the inner ear; otosclerosis is caused by adhesions between the ossicles in the middle ear; conductive hearing loss is the result of the ossicles’ inability to conduct sound from the eardrum to the inner ear.

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Vertigo Motion sickness Meniere disease Benign paroxysmal positional vertigo Central vestibular disorders