Introduction to ophthalmology

?
  • 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
1 of 16

Anatomy of the eye

(http://www.eyesightresearch.org/images/American_Academy_of_Ophthalmology.gif)

  • retina - light sensitive layer
  • cornea - clear window
  • iris - colored part
  • pupil - hole to lens
2 of 16

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
3 of 16

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
4 of 16

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
5 of 16

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
6 of 16

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)
7 of 16

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
8 of 16

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
9 of 16

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
10 of 16

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
11 of 16

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
12 of 16

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
13 of 16

Ophthalmoscopy

  • 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
14 of 16

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
15 of 16

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)
16 of 16

Comments

teacup23

Report

good.

Similar Medicine resources:

See all Medicine resources »See all Ophthalmology resources »