Introduction to ophthalmology

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  • Created by: z
  • Created on: 13-03-16 13:49

Visual system

  • NB: ophthalmology involves whole visual system back to visual cortex
    • commonest cause of registered partially sighted and blindness cases for <65 yro is DM
  • visual system consists of:
    • coordinated pair of eyes
    • appropriate protective mechanisms
    • neural apparatues to interpret visual info
  • eyes:
    • form focused image on the retina, dep on:
      • ocular shape
      • transparency of ocular media
      • ability of transparent structures to refract light
    • transduction of image into electrical signal
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Anatomy of the eye


  • retina - light sensitive layer
  • cornea - clear window
  • iris - colored part
  • pupil - hole to lens
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Anatomy of the eye: cornea

  • cornea:
    • transparent
      • stroma is relatively dehydrated - maintained by impermiable epithelium (ant.) and active pumping by endothelium (post.)
      • b/w regularly spaced stormla collagen fibrils
    • refraction
      • major refractive component of the eye (not the lens!) - 48/58 dioptre (unit of measurement of optical power of a curved lens)
    • barrier to infection and trauma
      • layers:
        • epithelial cels
        • Bowman's membrane
        • stroma
        • Descemet's membrane
        • endothelial cells
    • NB innerv by CNV1 via short and long ciliary- corneal reflex
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Anatomy of the eye: sclera

  • forms posterior 5/6 of outer coat of eye
    • opaque
    • mechanically tough
    • consists of irregularly arragend collagen fibres
  • maintains eye shape
  • maintains IOP
  • barrier to infection and trauma
  • continuous w/ cornea
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Anatomy of the eye: aqueous humour

  • transparent gelatinous fluid, low protein conc
  • actively secreted by epithelium of ciliary body
  • drained via 2 routes:
    • "conventional" (85%) - through trabecular meshwork into canal of Schlemm in anterior chamber angle
    • "uvoscleral" (15%) - through ciliary body into ciliary circulation
  • balance b/w secretion and drainage determines the IOP
    • normal is 10-21 mmHg
    • high IOP = glaucoma
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Anatomy of the eye: crystalline lens

  • transparent:
    • orderly arranged lens fibred
    • small difference in refractive index b/w various components
    • no blood vessels
  • fine focusing
    • shape changes due to action of ciliary muscles
      • close vision: rounder lens as more refraction (accomodation): ciliary muscles contract (parasympathetic) which decr tension in ciliary fibres- allows lens to curve more
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Ciliary ganglion

  • parasymp > ciliary muscles, sphincter pupillae
  • symp > dillator pupillae, superior tarsal m. (raises upper eyelid, thus dysfunc=partial ptosis)
  • sensory > from cornea (corneal reflex)
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Anatomy of the eye: vitreous humour

  • transparent, firm gel
    • collagen type II, arranged as fibrils
    • hyalocytes (only a few) secreting glycosaminoglycan
  • protects ocular structures
    • is 80% of globe volume
  • passive transport and removal of metabolites
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Anatomy of the eye: retina

  • retina
    • transparent
    • transduces light energy into nervous impulses
    • 11 layers
    • photoreceptors - 120 mil rods, 6 mil cones (colour vision)
  • macula
    • central vision area of the retina, area of highest visual acuity
    • lateral to optic disc, visible as slightly darker due to yellow luteal pigment
    • fovea lies at centre (cones only)
  • optic nerve
    • fibres only myelinated after exitting eye
    • nasal fibre decussation at optic chiasm
  • optic disc
    • entry point of nerve into eye
    • corresponds to blind spot as no overlying photoRs
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Ophthalmic Hx taking

  • HPC
    • general symtpoms: uni/bilat, onset/duration, any pain/photophobia/redness/discharge etc
    • visual symptoms:
      • visual loss (sudden/gradual/distortion)
      • field defect (uni/bilat. central/peripheral)
      • flashes/floaters
      • diplopia (horizontal/vertical bino/monocular)
  • past ocular Hx (incl refractive Hx e.g. glasses, contacts)
  • FHx (esp of ocular disease)
  • PMH
  • DH/allergies
  • general health
  • social (ADLs, hobbies able to do?)
  • if a child- obstetric/birth details/neonatal complications, milestones, imm Hx
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Common ophthalmic symptoms

  • "red eye" (pain, redness, photophobia, discharge) > issue at front of eye
  • painless loss of vision > back of eye
  • distortion of vision/central scotoma > macula
  • flashes and floaters > vitreous or retina
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Refractive error and accommodation

  • emmetropia = no refractive error
  • ametropia = error
    • myopia: short sighted, light ray scome to focus in front of retine
      • either eye is too long (=axial myopia) or lens is to strong (index myopia- due to nuclear sclerotic cataract)
    • hypermetropia: long sighted, light ray comes to focus behind the retina
      • either the eye is too short or the convergng power of the cornea or lens is too weak
    • astigmatism
      • cornea is not spherical (instead rugby ball shape)
  • accomodation
    • allows close objects to be focused on the retina
    • ciliayr muscle contracts, suspensory ligaments become lax, naturally elastic lens assumes more globular shape
    • with age (>45yrs) lens gradually hardens and becomes unable to accommodate: presbyopia
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Ophthalmic examination

  • vision
    • acuity, fields, colour
  • pupils
    • light reaction
  • front of eye
    • pen torch, ophthalmoscope or slit-lamp biomicroscope
  • back of eye
    • direct or indirect ophthalmoscope
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  • 3 components: lenses, light and diaphragm
  • high magnification approx 15x
  • small field of view approx 6.5-10 degrees
    • thus will not see macula w/ undilated pupil b/c disc will take up whole foeld of view, NB don't get pt to look into light as they will accommodate and make pupil smaller
  • lens setting
    • keep your glasses on
    • remove pt glasses and set according to their refractive error
      • ask if they wear glasses
        • only for reading? > set to 0
        • for distances > long or short sighted?
          • if pt doesn't know - look through glasses, if appear smaller they are myopic (red numbers), if larger they are hypermetropic (black numbers). NB if big diff then dial to bigger number
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Direct ophthalmoscopy

  • don't put hand on pts head
  • hold ophthalmoscope w/ index finger of lens dial
  • angle of approach
    • from 15 degrees temproal from pt
    • same height as pt
    • aim 15 degrees nasal to see optic disc- macula is lateral
  • start w/ dominant eye and close the other
  • small beam for undilated pupil/lg for dilated (e.g. w/ tropicamide, muscarainic antagonist)
  • red reflex
  • look at:
    • "3 Cs" - cup:disc ratio, colour, contour (margins)
    • vessels - arterioles and veins, new/collateral vessels
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Diabetic retinopathy

  • background retinopaty
    • scattered haemorrhages and hard exudates not affecting the macula
    • not sight threatening
  • diabetic maculopathy
    • haemorrhages and hard exudate w/in the macula
    • macular oedema
    • treated w/ focal laser
  • pre-proliferative retinopathy
    • > 5 Cotton Wool Spots
    • venous changes- thickened, tortuous, beading
    • indicates retinal ischaemia
    • sight threatening
  • proliferative retinopathy
    • new vessels to disc (NVD) or elsewhere (NVE) which bleed causing vitreous haemorrhage
    • requires extensive laser Rx (panretinal photocoagulation)
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