Hearing loss and eye disorders
Hearing loss, eye and orbit disorders, pain, fever and hypothermia: mechanisms
Hearing loss, eye and orbit disease, pain, fever and hypothermia for FCPS Part 1, explained by mechanism. It covers deafness types, orbital imaging, referred pain, febrile infections and cold injury.
One of the most tested topics in past papers
Hearing loss: where the fault lies
| Type | Site | Tuning forks | Typical causes |
|---|---|---|---|
| Conductive | External canal, drum, ossicles, oval window | Rinne negative; Weber to the bad ear | Wax, otitis media, otosclerosis, ossicular erosion |
| Sensorineural | Cochlea, cochlear nerve | Rinne positive; Weber to the good ear | Noise, ageing, aminoglycosides, meningitis, congenital infection |
- The inner ear comes from the otic placode (surface ectoderm); middle and external ear from pharyngeal arches, pouch and cleft, so aural atresia spares the inner ear.
- The cochlea has two and a half turns; an apex fused into a cyst (about one and a half turns) is the Mondini (incomplete partition) anomaly. Cochlear implants enter the scala tympani through the round window.
- Noise: outer hair cells at the 4 kHz region fail first (audiogram notch).
- Aminoglycosides: gentamicin and streptomycin are mainly vestibulotoxic: they destroy the hair cells of the vestibular end organs on both sides symmetrically, so the patient has imbalance in the dark and on uneven ground and oscillopsia, without spinning vertigo, and audiometry may be normal. Amikacin and neomycin are more cochleotoxic. A maternally inherited mitochondrial 12S rRNA variant causes deafness after a single dose.
- Meningitis: bacteria reach the cochlea through the cochlear aqueduct, causing labyrinthitis ossificans; implant early.
- Otosclerosis: new bone at the anterior oval window fixes the stapes; worsens in pregnancy. Chronic otitis media erodes the long process of the incus first.
- Temporal bone fracture: facial nerve injured most often at the perigeniculate segment. Ramsay Hunt syndrome: varicella-zoster in the geniculate ganglion.
- Aberrant internal carotid artery: pulsatile red mass behind the drum; never biopsy.
Eye and orbit
- Glaucoma: loss of retinal ganglion cell axons: cupping and arcuate field defects. Angle closure in small hypermetropic eyes when the pupil mid-dilates.
- Myopia: high myopia is mostly axial: the globe is too long (normal axial length about 23–24 mm; 29 mm gives about −9 dioptres), with a posterior staphyloma; high myopes are at risk of retinal detachment.
- Diabetic retinopathy: pericyte loss gives microaneurysms; ischaemia drives VEGF and new vessels.
| Ultrasound membrane | Shape | Attachment |
|---|---|---|
| Retinal detachment | Folded, funnel shape | Anchored at the optic disc and ora serrata |
| Choroidal detachment | Smooth thick domes | Not at the disc |
| Posterior vitreous detachment | Thin, very mobile | Separate from the disc |
- Retinal detachment surgery may leave intraocular silicone oil, which makes the vitreous uniformly dense on CT; intraocular gas bubbles expand with altitude or nitrous oxide.
- Choroidal melanoma: collar-stud shape through Bruch's membrane; melanin makes it T1 bright, T2 dark.
- Leukocoria: retinoblastoma (calcified mass), Coats disease, persistent fetal vasculature.
- Orbital muscle enlargement:
| Condition | Muscle pattern |
|---|---|
| Thyroid eye disease | Bellies enlarged, tendons spared; inferior and medial recti first; painless, bilateral |
| Idiopathic orbital inflammation | One muscle, belly and tendon involved, with fat stranding; acutely painful red proptosis; dramatic response to steroids (biopsy if it relapses, as lymphoma can respond partly) |
- Congenital dacryocystocele: bluish swelling at the medial canthus in a newborn with a dilated sac and duct ending in an intranasal cyst: obstruction at the valve of Hasner at the lower end of the nasolacrimal duct in the inferior meatus. A large cyst can block the nose of an obligate nasal breather.
- Metal fragments: a grinder or metalworker needs orbital radiographs before MRI, even if a fragment was removed before; a moving ferromagnetic fragment can blind.
- Cortical blindness: bilateral occipital infarcts (posterior cerebral arteries, often embolic from AF); pupils react and fundi are normal, and patients may deny blindness (Anton syndrome).
- Optic neuritis hurts on eye movement (recti arise from the tendinous ring fused to the nerve sheath). Giant cell arteritis blinds through the posterior ciliary arteries.
Pain
- Aδ fibres carry fast, sharp, well-localised pain; C fibres slow, burning pain. Loss of Nav1.7 causes congenital insensitivity to pain.
- Mediators at a cut: damaged cells release K⁺ and H⁺; bradykinin is the most potent pain-producing mediator; prostaglandins (PGE2) sensitise nociceptors (hyperalgesia); substance P from C fibres spreads the reaction.
- Referred pain: visceral and somatic afferents converge on the same spinal neurons.
| Source | Nerve or referral |
|---|---|
| Cornea (welder's flash) | Long ciliary nerves (V1) |
| Disc annulus | Sinuvertebral nerve |
| Facet joint | Medial branches of dorsal rami |
| Sphenoid sinus | Deep retro-orbital and vertex headache, worse on bending, no facial tenderness; easily missed |
| Pancoast tumour | C8 and T1 roots, Horner syndrome |
- Traumatic (amputation) neuroma: a painful nodule at a scar from disorganised regenerating axons in fibrous tissue.
- Kernig sign (pain and resistance on extending the knee with the hip flexed) and Brudzinski sign indicate meningeal irritation; their absence does not exclude meningitis.
Fever
- Bacterial products and tissue injury make macrophages release IL-1 (the classic endogenous pyrogen), IL-6 and TNF, which induce PGE2 in the preoptic hypothalamus, raising the set point. Fever after a blow with a swollen hand is IL-1 driven. Antipyretics block COX.
- Febrile non-haemolytic transfusion reaction: recipient antibodies against donor leucocytes and cytokines in stored blood; leucodepletion prevents it.
- Brown fat (supraclavicular, paravertebral) is activated by cold through UCP1 (thermogenin) and takes up FDG on PET: symmetrical uptake in fat-attenuation tissue on a cold day; warm the patient and repeat if in doubt.
| Fever picture | Cause |
|---|---|
| Sore throat, lymphadenopathy, atypical lymphocytes, Monospot positive | EBV (infectious mononucleosis); atypical cells are activated CD8 T cells reacting to infected B cells |
| Monsoon, retro-orbital pain, day 5 platelets falling, haematocrit rising 20% | Dengue with plasma leakage (critical phase) |
| Butcher at Eid, tick bite, bleeding gums | Crimean–Congo haemorrhagic fever: strict barrier nursing |
| Unpasteurised milk, undulant fever, back pain, hepatosplenomegaly | Brucella |
| Lambing, atypical pneumonia, raised liver enzymes, culture negative | Q fever (Coxiella burnetii): confirm by serology; chronic form causes culture-negative endocarditis |
| Rat bite, migratory arthritis, rash | Streptobacillus moniliformis (rat-bite fever) |
| Vesicles on palms and soles, mouth ulcers | Coxsackie A (hand, foot and mouth) |
| Falciparum treated irregularly, haemolysis, cola urine, AKI | Blackwater fever |
| Fever every 48 hours | P. vivax or ovale (tertian) |
| Step-ladder fever, relative bradycardia | Typhoid |
- Congenital rubella (infection in the first trimester, e.g. 5 weeks): cataracts, sensorineural deafness and PDA; confirm with rubella-specific IgM in the baby (only IgG crosses the placenta). Congenital CMV causes progressive deafness.
- Normal lymphocytes: about 70–80% T cells and 10–15% B cells.
Hypothermia and pressure
- Core below 35 °C; J (Osborn) waves, bradycardia, then ventricular fibrillation with rough handling.
- Afterdrop on rewarming; cold diuresis (raised central volume suppresses ADH); K⁺ moves into cells on cooling and out on rewarming; enzymes and platelets slow (coagulopathy with normal laboratory tests run at 37 °C).
- Therapeutic cooling for neonatal hypoxic–ischaemic encephalopathy must start within 6 hours.
- Decompression sickness: a diver who ascends rapidly releases dissolved nitrogen as bubbles in joints (bends), lungs (chokes) and spinal cord. Barotrauma on descent: the Eustachian tube opens only actively.
Remember The disc anchors the retina: a membrane tethered to the optic disc on ultrasound is a retinal detachment.
Exam trap Rinne negative means conductive loss; do not read a "negative" test as normal.
Exam trap Thyroid eye disease spares the tendon; orbital inflammation involves belly and tendon.
How FCPS asks about this
- Unsteady in the dark after streptomycin, normal audiogram: vestibular hair cell damage.
- Endogenous pyrogen in fever: IL-1 acting via hypothalamic PGE2.
- Atypical lymphocytes in glandular fever: activated CD8 T cells.
- Newborn with cataracts, deafness and PDA: congenital rubella; confirm with rubella IgM.
- Bilateral blindness with reacting pupils and normal fundi: bilateral occipital infarcts.
- Dense vitreous on CT after retinal surgery: silicone oil.
- Rapid ascent with joint pain and dyspnoea: decompression sickness from nitrogen bubbles.
Test yourself on this topic
5 of the 138 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
A 22-year-old woman with occasional headaches is found to have elevated optic discs in both eyes. The disc margins are lumpy, with glistening yellow bodies on the surface; there are no haemorrhages, the veins are not engorged and spontaneous venous pulsation is present. What is the most likely cause of the elevated discs?
Answer: Optic disc drusen
Optic disc drusen are deposits of calcified hyaline material within the nerve head, thought to come from abnormal axonal metabolism in a crowded disc. They make the disc look swollen (pseudopapilloedema), with lumpy margins and refractile bodies, but without the haemorrhages, venous engorgement and loss of venous pulsation of true papilloedema. Because they are calcified they can be confirmed by ultrasound or CT. Recognising drusen avoids unnecessary investigation for raised intracranial pressure.
Pseudopapilloedema
- Calcified hyaline bodies in the disc
- Lumpy margins, glistening bodies
- No haemorrhage, venous pulsation present
- Avoids a mistaken raised ICP work-up
Remember Lumpy disc with pulsating veins: drusen, not papilloedema.
Exam trap Drusen and true papilloedema can coexist, so a patient with drusen and new symptoms of raised pressure still needs investigation.
Why the other options are wrong
- Papilloedema from raised pressure Shows a swollen, hyperaemic disc with haemorrhages, engorged veins and lost venous pulsation.
- Optic nerve sheath meningioma Usually one-sided with slowly progressive visual loss and optociliary shunt vessels.
- Retinoblastoma A childhood tumour forming an intraocular mass, not elevated discs in an adult.
- Optic neuritis Usually one-sided with painful visual loss, and the disc is normal or mildly swollen.
A 3-week-old baby has had a watery left eye since birth, and pressing over the lacrimal sac makes mucus come back out of the puncta. At which site is the drainage most likely blocked?
Answer: Valve of Hasner
The nasolacrimal duct runs down from the lacrimal sac and opens into the inferior meatus of the nose, beneath the inferior turbinate. Its lower end is guarded by a mucosal fold, the valve of Hasner, which is the last part of the duct to canalise and is often still imperforate at birth. Tears and mucus then collect in the duct and sac and regurgitate through the puncta on pressure. Most open spontaneously in the first year, with massage; persistent cases need probing.
Congenital nasolacrimal obstruction
- Duct opens into the inferior meatus
- Lower valve of Hasner canalises last
- Watery eye, mucus on sac pressure
- Most open in the first year
Remember Watery eye in a newborn: the lower valve of the duct has not opened.
Exam trap A bluish swelling at the medial canthus in a newborn (dacryocystocele) can become infected or, with a nasal cyst, block the nose of an obligate nasal breather.
Why the other options are wrong
- Valve of Rosenmüller Guards the junction of the common canaliculus and the sac; mucus from the sac could not then reflux.
- Lacrimal punctum A blocked punctum would stop tears entering, so pressure on the sac would not return mucus.
- Common canaliculus Obstruction here prevents tears reaching the sac, so the sac would not fill with mucus.
- Middle meatus The nasolacrimal duct opens into the inferior meatus, not the middle meatus.
A 38-year-old man has deep central low back pain without leg symptoms, caused by a tear in the posterior part of the annulus fibrosus of the L4–L5 disc. Which nerve carries pain from this part of the disc?
Answer: Sinuvertebral (recurrent meningeal) nerve
The nucleus pulposus and inner annulus have no nerve supply, but the outer third of the annulus is innervated. Posteriorly, the outer annulus and the posterior longitudinal ligament are supplied by the sinuvertebral (recurrent meningeal) nerve, which arises from the ventral ramus and grey ramus and re-enters the canal through the intervertebral foramen. Tears in the posterior annulus allow nerve endings and granulation tissue to grow in, so they cause deep axial back pain. The anterior and lateral annulus is supplied by branches from the sympathetic trunk and grey rami.
Nerve supply of the disc
- Nucleus and inner annulus: no nerves
- Outer posterior annulus: sinuvertebral nerve
- Also supplies the PLL and anterior dura
- Annular tear: axial back pain
Remember Pain from the back of the disc travels in the sinuvertebral nerve.
Exam trap The nucleus pulposus itself has no nerves; pain needs involvement of the outer annulus.
Why the other options are wrong
- Medial branch of the dorsal ramus Supplies the facet joints and multifidus, not the posterior annulus.
- Lateral branch of the dorsal ramus Supplies skin and the erector spinae muscles, not the disc.
- Grey ramus communicans only Grey rami contribute to the sinuvertebral nerve and the lateral annulus but are not the main nerve to the posterior annulus.
- Ventral ramus of the L5 spinal nerve Forms the lumbosacral plexus to the limb; compression causes sciatica, not this axial pain.
A 52-year-old man with 15 years of poorly controlled diabetes suddenly loses vision in his left eye. The red reflex is dull and the fundus cannot be seen. What is the most likely source of the bleeding?
Answer: Fragile retinal new vessels
In proliferative diabetic retinopathy, retinal ischaemia drives release of VEGF, and new vessels grow from the retina and optic disc onto the posterior surface of the vitreous. These vessels are thin-walled and fragile, and traction from the contracting vitreous tears them, filling the gel with blood. The blood blocks the red reflex and the view of the fundus. Laser photocoagulation of the ischaemic retina, or anti-VEGF injection, makes the new vessels regress.
Diabetic vitreous haemorrhage
- Ischaemia drives VEGF
- New vessels grow onto the vitreous
- Vitreous traction tears them
- Treat ischaemia: laser, anti-VEGF
Remember Sudden visual loss in a diabetic: bleeding new vessels.
Exam trap Dense blood can hide a tractional retinal detachment, so ultrasound must be done when the fundus is not visible.
Why the other options are wrong
- Microaneurysms in the macula Microaneurysms leak and cause dot haemorrhages and oedema within the retina, not vitreous bleeding.
- A ruptured central retinal artery Arterial occlusion causes a pale retina, not haemorrhage into the vitreous.
- A torn choroidal melanoma Nothing suggests a tumour, and the history points to diabetes.
- Vessels of the ciliary body The ciliary body is not involved in diabetic proliferation.
A 50-year-old man has severe pain in the right ear, vesicles in the concha and ear canal, right facial weakness involving the forehead, vertigo and hearing loss. In which ganglion has the causative virus been lying dormant?
Answer: Geniculate ganglion
This is Ramsay Hunt syndrome (herpes zoster oticus). Varicella-zoster virus lies dormant in the geniculate ganglion of the facial nerve and, on reactivation, causes painful vesicles in the area of skin supplied by the facial nerve (concha and canal) and a lower motor neurone facial palsy. Spread to the nearby vestibulocochlear nerve in the internal acoustic meatus adds vertigo and sensorineural hearing loss. Bell palsy, often linked to herpes simplex, does not produce vesicles or eighth-nerve involvement.
Ramsay Hunt syndrome
- VZV latent in the geniculate ganglion
- Vesicles in concha and canal
- LMN facial palsy
- Vertigo and deafness from CN VIII spread
Remember Vesicles in the ear plus facial palsy: zoster at the geniculate ganglion.
Exam trap Vesicles may appear after the palsy, so a patient labelled as Bell palsy should have the ear re-examined.
Why the other options are wrong
- Trigeminal (Gasserian) ganglion The site of latency in ophthalmic zoster, which gives a forehead and eye rash, not ear vesicles with facial palsy.
- Spiral ganglion of the cochlea Contains cochlear neurons; it is involved secondarily, not the site of latency.
- Pterygopalatine ganglion A parasympathetic ganglion with no sensory cell bodies to harbour the virus.
- Otic ganglion A parasympathetic ganglion for the parotid; the virus does not lie dormant here.
Where this sits in the CPSP syllabus
- Diagnostic Radiology, Paper 2: Nervous system disorders, Hearing loss, eye disorders, pain, fever and hypothermia