Anatomy and Physiology SC2 2012-13

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A REVIEW OF THE ANATOMYAND PHYSIOLOGY OF THE

EYE

Senior Cycle 22012-13


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Learning Outcomes

At this end of this tutorial, you will be able to:

Describe the anatomy and physiology of the orbit,its contents, and adnexa

Understand and describe the components of thevisual pathway

Understand and describe the optical elements ofthe eye

Explain the principles of refractive error and itsrelated terminology


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Orbit

Thin walled; medial and floor Transmission of cranial nerves

via fissures and foramen

Close proximity to paranasalair sinuses (Sinusitis)

Susceptibility to trauma (Blow-out Fractures)

Orbital fat swells in thyroiddisease

Image credit: http://frca.mikrocom.co.uk/Anaesthetics/FRCA/headNeckAnatomy.php


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Eyelids

Protect Ocular surface Facilitate spread of pre-

corneal tear film

Comprises skin andorbicularis muscle (anteriorlamella) & tarsus andconjuctiva (posterior lamella)

Meibomian glands located intarsus

http://health-7.com/Atlas%20of%20Pediatric%20Physical%20Diagnosis/Eyelids%20%26amp%3B%20Adnexae-Anatomy%20of%20the%20Eyelid


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Eye lids


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Tears: Protect and maintain clarity

Important for maintenanceof corneal clarity andrefraction

Contains important defencemechanisms against infection

Requires integrity of lids andin correct position to spreadtears and drain

(dryness vs. epiphora)


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Conjunctiva

Important to recogniseextent of conjunctival

covering

Areas of redness importantin differentiating causes ofred eyes (conjunctivitis,

iritis, etc)


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Conjunctiva: Clinical appearance


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Cornea

Transparency dependentupon hydration maintainedby endothelial pump

Devoid of blood vessels

Highly innovated fromTrigeminal nerve


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Cornea: The effect of Overhydration


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Sagittal View of the Eye


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Aqueous maintains intraocular pressure

Aqueous humour formed byciliary body

Constantly produced anddrained via canal of

Schlemm

Maintains intraocularpressure (10-21 mm Hg)


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Lens

Normally transparent

Refractive

Reduced elasticity with age(Presbyopia)

Loss of transparency withage (Cataract)


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Uveal Tissue

Consists of Iris, Ciliarybody and choroid

Highly vascularised

Immune competent

Susceptible toinflammation

Image credit: http://www.vision-and-eye-health.com/uveitis.html


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The optic nerve


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The pupil and autonomic control

Constrictor and dilatormuscles control pupil

aperture

Sympathetic control fordilation via sympatheticchain (Horners)

Parasympathetic control forconstriction via IIIn


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Retina

Transparent inner mostlayer of globe

Underlying melaninrich Retinal pigment

epithelium for

maintenance ofphotoreceptor health


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Retina: Organised Neurosensory arrangement and end

artery blood supply

Cones are colour-sensitiveand centrally distributed

Rods are for peripheral andnight vision

Blood supply of inner 2/3via central retinal artery(Internal Carotid) andcentral retinal vein


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Macula: the area of greatest resolvingpower

Highest concentration ofcones

More than one layer ofganglion cells

Fovea is central and lacksblood vessels (nourished bychoroid)


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Synchronous movements of eyes in ninepositions of gaze

Must recognise muscleactions and their nervesupply

Underactive muscles causesquints and symptoms ofdiplopia

MR, IR and SR: III nerve LR: VI nerve SO: IV nerve


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Visual Pathway

Made up of Retina Optic nerve Optic chiasm Optic tracts Lateral Geniculate Body Optic radiations Visual cortex


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Visual Pathway

Image credit: http://www.vision-and-eye-health.com/uveitis.html


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Optics of the eye

Terms to know: Emmetropia Myopia Hypermetropia Astigmatism Presbyopia


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Emmetropia

Eye without refractive error Distant objects are focussed on retina with lens in

a relaxed state

Close-up objects are focussed by accommodation- the intraocular lens becomes thicker andstronger

Presbyopia is the natural loss of accommodationpower after age 40, resulting in need forreading glasses


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Refractive Error- myopia

Short-sightedness Poor distance vision, good near

vision

Eye is too long, or cornea is toocurved

Myopia very uncommon in youngchildren, tends to develop inteenage years and beyond

4% in 11-13 year olds 25% in adults >20 years


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Refractive Error - hypermetropia

Long-sightedness Poor near vision, good

distance vision

Eye is too short orcornea is too flat

Very common in infantsand reduces

significantly in earlylife


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Refractive Error - astigmatism

Eye is short sighted inone plane and long

sighted at 90 to this

Images are distorteddue to irregular cornea


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Optics of the eye

PresbyopiaThe ability of the lens to accommodate gradually

declines with age and by middle age reading

glasses (convex lenses) are usually necessary

AnisometropiaRefraction of the two eyes is different


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Learning Outcomes

Describe the anatomy and physiology of the orbit,its contents, and adnexa

Understand and describe the components of thevisual pathway

Understand and describe the optical elements ofthe eye

Explain the principles of refractive error and itsrelated terminology

Anatomy and Physiology SC2 2012-13

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