L16 - Diseases of the eye Flashcards
Describe the role of the Iris ?
- Regulates amount of light that enters eye.
- Forms coloured, visible part of eye in front of lens.
- Light enters through central opening called the pupil.
What layers can the eyeball be divided into? (3)
- Fibrous
- Vascular
- Inner layers
Describe fibrous layer of the eye?
Outermost.
Consists of Sclera and cornea (continuous with each other)
Describe the Sclera? (4)
- Comprises majority of the fibrous layer.
- Provides attachment to extraoccular muscles.
- Not transparent.
- White part of eye.
Describe cornea?
- Transparent
- positioned centrally at front of eye.
- No BV.
What does the vascular layer of the eye consist of? (3)
- Choroid
- Ciliary body
- Iris
Describe the Choroid?
- Layer of connective tissue and BV.
- Provides nourishment to outer layers of retina.
Describe the Ciliary body?
2 parts:
- ciliary muscle
- ciliary processes
a. Attached to lens of eye.
b. Controls shape of lens.
c. Contributes to formation of aqueous humor.
Describe the Iris?
Circular structure with aperture in the centre (the pupil).
Describe the inner layer of the eye?
- Retina (light detecting part)
- Neural layer - Inner most, photoreceptors.
- Pigmented layer
Attached to choroid layer.
Where is the lens located?
located anteriorly between vitreous humor and pupil.
Describe the anterior and posterior chambers of eye?
Filled with aqueous humor.
Describe the production of aqueous humor? (4)
- Produced at Ciliary processes
- Flows from post. chamber —> pupil —> ant. chamber
- Flows out through trabecular meshwork into Schlemm’s canal.
- Subsequently absorbed into episceral veins via collector channels.
Where is aqueous humor secreted from?
Ciliary epithelium lining ciliary processes.
Enters the post. chamber.
What are zonules?
- Fibrous strands
- connect ciliary body with crystalline lens of eye.
Briefly state a cause of glaucoma?
- If drainage of aqueous humor obstructed
- can result in glaucoma.
What is intraocular pressure?
Fluid pressure inside eye.
What determines intraocular pressure?
- Production and drainage of aqueous humour
- by the ciliary body
- and its drainage via the trabecular meshwork and uveoscleral outflow.
How would you measure intraocular pressure?
Tonometer.
What are the seven extraocular muscles?
- levator palpebrae superioris
- superior rectus
- inferior rectus
- medial rectus
- lateral rectus
- inferior oblique
- superior oblique
Which muscles are responsible for eye movement?
- Recti
sup, inf, medial, lateral - Oblique
inf
Which is the only muscle involved in raising the superior eyelid?
Levator palpebrae superioris
What is the attachment, action and innervation of levator palpebrae superioris?
- Originates from lesser wing of sphenoid bone.
- Attaches to superior tarsal plate of upper eyelid.
- Elevates upper eyelid.
- CN III, oculomotor.
Describe the superior tarsal muscle?
- Collection of smooth muscle fibres, small portion of Levator Palpabrae Superioris.
- Innervated by sympathetic nervous system.
Where do the four recti muscles originate from?
- Common tendinous ring.
- Fibrous ring of tissue surrounding optic canal at back of orbit.
Superior rectus
- attachment
- actions
- innervation
- Originates from sup part of common tendinous ring.
Attached to sup. ant. aspect of sclera.
- ELEVATION.
contributes to adduction and medial rotation of eye. - CN III
Inf. Rectus
- attachment
- actions
- innervation
- Orig from inf. part of common tendinous ring.
attached to inf. ant. aspect of sclera. - DEPRESSION.
also has role in adduction and lateral rotation of eye. - Innervation via CN III
Medial Rectus
- attachments
- actions
- innervation
- Orig from medial part of common tendinous ring.
- attaches to anteromedial aspect of sclera.
- ADDUCTS eyeball
- Innervation via CN III
Lateral rectus
- attachment
- actions
- innervation
- Origin: lateral part of common tendinous ring.
- attaches to anterolateral aspect of sclera
- ABDUCTS eyeball
- Innervation via Abducens nerve CN VI.
Where do oblique muscles attach too?
Posterior surface of the sclera.
Superior oblique
- attachment
- actions
- innervation
- origin: body of sphenoid bone.
- tendon passes through trochlear and then attaches to sclera of eye. posterior to surface of sclera.
- DEPRESS, ABDUCT, MEDIALLY ROTATES
- Innervation via Trochlear CN IV
Inferior oblique
- attachment
- actions
- innervation
- Originates from ant aspect of orbital floor. attaches to sclera of eye, posterior to lateral rectus.
- ELEVATES, ABDUCTS AND LATERALLY ROTATES EYEBALL
- Innervation via oculomotor nerve CN III
Lesion in Oculomotor nerve may result in?
- Most of extraocular muscles affected.
- Eye displaced laterally by lateral rectus and inferiorly by sup oblique.
- Eye adopts ‘down and out’ position
Lesion in Trochlear nerve may result in?
- Paralyse superior oblqiue muscles.
- Patient will complain of diplopia (double vision)
- May develop a head tilt away from site of lesion.
Lesion is Abducens nerve may result in?
Paralyse lateral rectus.
Affected eye will adduct by resting tone of the medial rectus.
What are the triad of symptoms involved in Horner’s syndrome where there is damage to the neck?
- Partial ptosis
- Miosis
- Anhydrosis
Describe partial ptosis
Drooping of upper eyelid
- Result of denervation of superior tarsal muscle
Describe Miosis
Pupillary constriction
- due to denervation of dilator pupillae muscle
Describe anhydrosis
Absence of sweating
Ipsilateral side of face
- due to denervation of sweat glands
Clinical revelance of Glaucoma
Group of eye diseases that result in damage to optic nerve
- Open angle
- outflow of aqu.hum. through tracbecular meshwork is reduced.
- gradual reduction in peripheral vision. - Closed angle
- iris forced against trabecular meshwork, prevents drainage of aqu.hum.
- can rapidly lead to blindess
What is a refractive error?
Occurs when shape of eye prevents light from focusing directly on retina.
What is myopia?
Nearsightedness
- objects near are clear
- objects further away are blurry
What is hyperopia?
Farsightedness
- distant objects clearer
What is astigmatism?
Type of refractive error caused by irregularities in patients cornea shape.
- cornea rugby ball shaped instead of football
What is presbyopia?
Long-sightedness caused by loss of elasticity of the lens of the eye, occurring typically in middle and long age.
What is keratoconus?
Non-inflammatory eye condition
Cornea progressively thins causing a cone-like bulge to appear.
- impairs ability of eye to focus light properly.
Describe a normal cornea?
Round dome-shaped clear window of eye.
What is cataracts?
Clouding of lens inside eye.
How may cataracts form?
As we age:
- lens in eyes becomes less flexible
- less transparent
- thicker.
- tissues within lens break down and clump together
- which clouds small areas within lens
What is Age-related macular degeneration?
- Occurs when macula (central bit of retina) deteriorates
- Affects middle part of vision but not edges.
How may diabetes lead to loss of vision?
Diabetes can lead to swelling in the Macula
- diabetic macular edema.
Overtime this disease can destroy the sharp vision in that part of the eye.
Describe retinal vascular disorders?
Range of eye diseases that affect the BV in eye.
Describe retinal detachment?
Retina separates from back of inside of eye.
- preceded by posterior vitreous detachment
- gives rise to —> brief flashes of light (photopsia) in extreme peripheral vision.
Describe refractive errors in children?
examples: myopia, hyperopia and astigmatism
- caused blurred vision due to inability to focus images on retina.
Describe strabismus?
Cross-eyed
Children with strabismus initially have double vision - occurs due to the misalignment of two eyes in relation to one another.
What is leucoma?
White opacity in the cornea of the eye.
What is retinitis pigmentosa?
Genetic disorder of eyes causing loss of vision.
Symptoms: trouble seeing at night and decreased peripheral vision.
What is the underlying mechanism of retinitis pigmentosa?
Progressive loss of rod photoreceptor cells in the back of the eye.
- followed by loss of cone photoreceptor cells.
