Eye and Ear Sensory Pathophysiology — Quick Reference

Glaucoma

  • Definition: group of eye diseases due to intraocular hypertension that damages the optic nerve; leads to progressive peripheral visual field loss; leading cause of irreversible blindness; can be asymptomatic until severe.
  • Pathophysiology: aqueous humor drainage blocked → fluid accumulation in the anterior chamber → elevated intraocular pressure (IOP) → optic nerve atrophy and peripheral vision loss.
  • Types
    • Open-angle glaucoma (OAUG): most common; open angle between iris and cornea; gradual (lifelong) progression; often asymptomatic until advanced; may involve impaired aqueous humor outflow through trabecular meshwork.
    • Closed-angle glaucoma (CAG): narrow/closed anterior chamber angle; rapid rise in IOP; medical emergency; acute symptoms when pupil dilates (darkness/stress).
    • Primary vs Secondary: primary with no identifiable cause; secondary due to trauma, steroids, tumors, inflammation, etc.
  • Open-angle glaucoma details
    • Most common form (~90% of cases).
    • Screening: regular monitoring of IOP is key.
  • Closed-angle glaucoma details
    • Can cause sudden vision loss within 24 hours; immediate treatment required.
  • Signs & Symptoms
    • OAUG: gradual peripheral vision loss; tunnel vision in advanced stages; usually no early symptoms.
    • CAG: severe eye pain, headaches, sudden vision changes (halos), red eye, blurred vision, corneal edema, mid-dilated pupil.
  • Risk factors
    • Elevation of IOP is the major risk factor; age >60; family history; ethnicity (higher in African Americans, Hispanics, Asians); thin corneas; diabetes/hypertension; long-term corticosteroid use; previous eye surgery; high myopia.
  • Additional notes
    • Regular screening for IOP is essential to detect progression before symptoms appear.

Cataracts

  • Definition: clouding of the eye lens due to sedimentation/aggregation of lens proteins; lens becomes harder with age; reduced light transmission and blurred vision.
  • Pathophysiology: aging proteins in the lens clump and the lens stiffens; decreased transparency and refractive accuracy lead to blurred vision and decreased color discrimination.
  • Causes/Risk factors
    • Aging (primary cause).
    • Genetic predisposition.
    • Medical conditions (diabetes, hypertension, obesity).
    • Trauma; long-term corticosteroid use; UV exposure; smoking; alcohol; previous eye conditions; radiation exposure; poor nutrition.
  • Signs & Symptoms
    • Blurry vision; difficulty with night vision; glare and halos around lights; yellowing or fading of colors; double vision; frequent prescription changes.
  • Notes
    • Cataracts progress gradually; treatment is typically surgical removal with lens replacement when vision impairment affects daily activities.

Macular Degeneration

  • Definition: age-related macular degeneration (AMD); leading cause of vision loss in older adults; central vision deterioration due to macular damage.
  • Prevalence: ~1:71:7 Australians over 50 show evidence of AMD; global impact substantial.
  • Pathophysiology: multifactorial; genetic, environmental, and biochemical factors affect the retinal pigment epithelium (RPE), photoreceptors, and retina; degeneration of the macula reduces central vision.
  • Macula basics
    • Macula is central retina enabling fine, color vision; cones support central/color vision; rods support night/low-light vision.
    • RPE maintains nutrient/waste exchange between retina and choroid; failure disrupts nutrient delivery and waste removal.
  • Causes/Risk factors
    • Age (>50).
    • Genetic factors (e.g., CFH variants).
    • Environmental/dietary: smoking, UV exposure, low antioxidant intake, high saturated fat, obesity.
    • Vascular and inflammatory factors; maternal hormones may influence risk; ethnicity (Caucasians higher risk).
  • Signs & Symptoms
    • Blurry or distorted central vision; difficulty recognizing faces; central blind spot (scotoma).
    • Difficulty with night vision; colors appear faded; metamorphopsia (straight lines appear wavy); possible peripheral vision changes; glare sensitivity.

Otitis Media (OM)

  • Definition: inflammation or infection of the middle ear, often from Eustachian tube dysfunction with fluid accumulation; can lead to complications if untreated.
  • Epidemiology: ~80 ext{%} of children experience OM; up to 4.0imes1044.0 imes 10^4 Australians affected; ~10 ext{%} of pediatric primary care visits relate to OM.
  • Pathophysiology
    • Eustachian tube dysfunction → negative middle-ear pressure → fluid accumulation.
    • Microbial infection (AOM) typically after URI: Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis.
    • Otitis media with effusion (OME): fluid without active infection, often following AOM or due to persistent Eustachian tube dysfunction.
    • Immune/inflammatory responses amplify mucosal swelling and may worsen Eustachian tube obstruction.
  • Complications / Chronic changes
    • Mastoiditis, meningitis (rare, severe).
    • Chronic OM with persistent effusion → hearing loss or speech delay in children.
    • Tympanic membrane perforation; cholesteatoma formation.
  • Signs & Symptoms
    • Severe ear pain; fever; irritability; sleep disturbance; tugging at the ear (children).
    • Fluid drainage from the ear (if perforated tympanic membrane).
    • Hearing loss (temporary); balance disturbances; reduced sleep.
  • Risk factors
    • Age <2 years; Eustachian tube dysfunction; recurrent URIs; allergies; exposure to tobacco smoke; daycare attendance; family history.
    • Anatomical abnormalities (e.g., cleft palate); immune deficiency; crowded living conditions.

Ménière's Disease

  • Definition: inner ear disorder causing vertigo, tinnitus, and sensorineural hearing loss; affects quality of life; no cure to date; symptoms managed.
  • Epidemiology: in Australia, ~4.0imes1044.0 imes 10^4 people affected; onset often in the 3rd decade; rare after age 60.
  • Pathophysiology
    • Abnormal accumulation of endolymph in the cochlea and vestibular apparatus (endolymphatic hydrops).
    • Excess endolymph increases pressure, damaging hair cells in the cochlea and vestibular system; progressive symptoms include tinnitus, fluctuating hearing loss, balance problems.
  • Causes (risk factors)
    • Swelling of the endolymphatic sac impairs fluid filtration/excretion.
    • Head injury; viral illness; middle ear infections; aspirin use (possible association).
  • Signs & Symptoms
    • Vertigo attacks (episodic, minutes to hours) with nausea/vomiting; nystagmus; sensory disturbance.
    • Hearing loss in one ear that fluctuates and tends to worsen over time.
    • Tinnitus and aural fullness; headaches or abdominal discomfort may occur.

Hearing Loss

  • Types
    • Conductive Hearing Loss: impaired transmission of sound through outer/middle ear; common causes include earwax impaction, Eustachian tube dysfunction, middle ear infections, ossicular chain disruption (e.g., otosclerosis), outer ear abnormalities.
    • Sensorineural Hearing Loss: damage to inner ear (cochlea) or auditory nerve pathways; causes include aging (presbycusis), noise-induced loss, ototoxic medications, infections, genetic factors.
    • Mixed Hearing Loss: combination of conductive and sensorineural components.
  • Key points
    • Conductive loss is mechanical in the outer/middle ear; sensorineural loss is due to inner ear or neural pathway damage; mixed includes both.
    • Prevention/management depends on the component and underlying cause (e.g., addressing wax, treating infections, protecting ears from noise, reviewing ototoxic exposures).