--- module: 055-01 language: en chapter: 55 title: "The Eye: Visual Physiology, Examination, and Common Disease" module_title: "Foundations" source_sha256: 34c1d79c3e5f71d0a9c458a0a7927c8c909b5790e03b255ecf82a1cafe711727 --- # The eye: foundations ## Orientation ### Vision needs optics, retina, pathways, movement, cortex ### Symptoms reveal local, neurological, systemic disease ### Immediate action #### Sudden loss or painful red eye with poor vision #### Chemical injury and penetrating trauma #### Angle closure, occlusion, endophthalmitis, arteritis ## Optics and retinal signalling ### Cornea gives most power, lens fine-tunes #### Ciliary contraction lets the lens thicken for near ### Refractive errors #### Myopia focuses in front of retina, hyperopia behind #### Refraction cannot restore retinal or neural loss ### Rods for dim light, cones for colour and acuity ### Light hyperpolarises photoreceptors #### Alters glutamate release to bipolar networks ### Nasal fibres cross, giving characteristic field defects ### Pupil reflex tests afferent and parasympathetic paths #### Relative afferent defect: asymmetric retina or nerve ### Aqueous outflow resistance sets pressure ## History ### Monocular or binocular, onset, progression ### Flashes, floaters, curtains, halos, colour loss ### Diplopia with either eye covered #### Monocular usually optical #### Binocular reflects misalignment ### Drug history #### Steroids: cataract, glaucoma, infection #### Anticholinergic dilation may cause angle closure ## Examination ### Acuity in each eye first, habitual correction #### Pinhole improvement suggests refractive blur ### Fluorescein reveals epithelial defects ### Pupils, fields, movements, cover test ### Fundoscopy: red reflex, disc, vessels, macula #### Dilation aids view, not specialist review ### Suspected open globe #### Avoid pressure, shield rather than patch #### No tonometry, cautious ultrasound ## Red eye ### Conjunctivitis: discharge, vision preserved ### Corneal ulcer: pain, opacity, fluorescein uptake #### Urgent cultures and antimicrobials ### Anterior uveitis: ciliary injection, chamber cells #### Steroid drops can worsen herpetic keratitis ### Scleritis deep pain, episcleritis self-limited ### Angle closure: pain, halos, mid-dilated pupil #### Rapid pressure lowering protects the nerve ### Chemical injury: irrigate before history #### Alkali penetrates deeply ## Sudden visual loss ### Arterial occlusion: painless retinal ischaemia #### Assess arteritis, emboli, stroke risk ### Venous occlusion: haemorrhage and oedema ### Detachment: flashes, floaters, curtain #### Vitreous separation may tear retina #### Macula-on detachment is time-sensitive ### Optic neuritis: subacute, painful, colour loss ### Ischaemic optic neuropathy: sudden, disc swelling ### Giant-cell arteritis in older patients #### Immediate steroids protect the other eye ### Occipital injury: homonymous loss, pupils spared ### Never dismiss new loss as migraine ## Glaucoma ### Progressive optic neuropathy, not always high pressure ### Open-angle loss painless and peripheral ### Risks: age, family, pressure, thin cornea ### Treatment lowers pressure #### Prostaglandin analogues increase outflow #### Beta blockers cut production, worsen asthma #### Adherence and drop technique matter ### Angle closure needs anatomical management ## Cataract, macula, and diabetes ### Cataract: painless blur, glare, poor contrast ### Macular degeneration damages central vision #### Geographic atrophy: gradual loss #### Neovascularisation: distortion, rapid loss ##### Anti-vascular endothelial growth factor injections ### Diabetic retinopathy: leakage to new vessels #### Macular oedema threatens vision at any stage #### Rapid glucose improvement can transiently worsen it ## Paediatric and neuro-ophthalmic principles ### Amblyopia: sensitive period, less reversible with age ### Leukocoria, strabismus, poor fixing need urgency #### Retinoblastoma causes leukocoria ### Diplopia: nerve palsy, junction, thyroid, orbit ### Painful ophthalmoplegia, proptosis, fever #### Orbital cellulitis, cavernous sinus, aneurysm ### Papilloedema: raised intracranial pressure