Essentials of Pathophysiology Chapter 38 Disorders of Special Sensory Function: Vision, Hearing, and Vestibular Function

Pre lecture quiz (true/false) Conjunctivitis, or inflammation of the conjunctiva, can be caused only by viral organisms. The eustachian tube is lined with a mucous membrane that is continuous with the nasopharynx, and provides a passageway for pathogens to enter the middle ear. Ringing of the ears is known as tinnitus. Many drugs are labeled as ototoxic, or damaging to inner ear structures. Hearing impairment may have a detrimental effect on language development in children. F T

Pre lecture quiz _____________, a group of conditions that feature an optic neuropathy, is usually associated with an increase in intraocular pressure. ______________ is a disorder of refraction that allows an individual to see objects at close distances without problems, but distant objects are blurred. A lens opacity that interferes with the transmission of light to the retina is known as _______________. ______________ media refers to inflammation of the middle ear, usually associated with an acute infection or an accumulation of fluid. An illusion of motion, often described as a sensation of spinning or tumbling, is a disorder of vestibular function known as ________________. Cataracts Glaucoma Myopia Otitis vertigo

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?

Disorders Affecting the Anterior Chamber Conjunctivitis Corneal abrasion Corneal edema Keratitis Glaucoma Open-angle Angle-closure

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?

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

The area where the iris meets the cornea It contains the: Iridocorneal Angle The area where the iris meets the cornea It contains the: Trabecular meshwork Canal of Schlemm

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

Open-angle Glaucoma The iridocorneal angle remains open Trabecular meshwork abnormality decreases the rate of aqueous humor reabsorption Gradual buildup of aqueous humor

Question Tell whether the following statement is true or false. Angle-closure glaucoma results in gradual buildup of aqueous humor in the anterior chamber.

Answer False Rationale: Open-angle glaucoma results in gradual buildup 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.

Lens Disorders Disorders of refraction Hyperopia Myopia Astigmatism Disorders of accommodation Presbyopia Cataracts

Retinal Blood Supply 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

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

Question What vessel(s) supply blood to the retina? Retinal artery Choroid vessels Optic artery All of the above a and b

Answer a and b Rationale: The retina receives blood from the retinal artery (mainly), and secondarily from the choroid vessels that are posterior/dorsal to it.

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

Damage to small retinal blood vessels Retinopathy Damage to small retinal blood vessels Microhemorrhages “Cotton-wool” exudate Microaneurysms

Retinopathy (cont.) Neovascularization New vessels are more fragile New vessels attach too tightly to the vitreous, fusing it to the retina

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

Macular Degeneration Dry Degeneration of retinal cells Wet Neovascularization of the choroid Blood vessels leak Fluid buildup pushes retina away from choroid

Question Which retinal disorder is caused by ischemia of the retina? Papilledema Retinopathy Retinal detachment Macular degeneration

Answer Retinal detachment Rationale: 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.

What are the possible explanations for this client’s visual problems? 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?

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?

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 2 5 6 3 1 4 7

Discussion Eye Optic nerve Optic chiasm Optic tract Lateral geniculate nucleus Optic radiation Visual cortex

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?

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

Middle Ear infection If the Eustachian tube becomes blocked, fluid builds up in the middle ear. This creates a haven for bacteria and viruses, which can cause infection. Doctors can detect fluid in the middle ear with a pneumatic otoscope. This device blows a small amount of air at the eardrum, making the eardrum vibrate. If fluid is present, the eardrum will not move as much as it should.

Ear tubes, or tympanostomy tubes If your child has recurrent ear infections or fluid that just won’t go away, hearing loss and a delay in speech may be a real concern. One solution is for your doctor to insert small tubes through the eardrum. Ear tubes let fluid drain out of the middle ear and prevent fluid from building back up. This can decrease pressure and pain, while restoring hearing. The tubes are usually left in for 8 to 18 months until they fall out on their own.

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

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

Inner Ear: Cochlea and Labyrinth

Disorders of the Inner Ear and Auditory Pathways Increased nerve firing Tinnitus Focal seizures Decreased nerve firing Sensorineural deafness Presbycusis

Question Which auditory disorder is characterized by increased firing of the otic nerve, causing “ringing” in the ears? Otosclerosis Conductive hearing loss Tinnitus Sensorineural deafness

Answer Tinnitus Rationale: 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.

Vertigo Motion sickness Meniere disease Benign paroxysmal positional vertigo Central vestibular disorders Sudden dizziness when positioning head to certain position