Opthalmology - Eye Anatomy Flashcards
Contents of the orbit.
- the eye
- extraocular muscles
- cranial nerve II-VI
- arterial supply and venous drainage
Layers of the eye.
Fibrous layer of the eye.
Cornea - located in the centre of the anterior aspect of the eye, and is transparent.
Sclera - covers the rest of the eye (white).
Vascular layer of the eye - contents.
- ciliary body
- choroid
- iris
Function of the ciliary body.
Attached to the lens via the suspensory ligaments, controlling the shape of the lens.
Forms the aqueous humour.
Function of the choroid.
Layer of connective tissue containing blood supply to the retina.
Function of the iris.
Structure containing the pupil, which contains smooth muscle to control its diameter.
Pupillary light reflex.
Accommodation reflex.
Inner layer of the eye.
Neural layer - composed of photoreceptors.
Pigmented layer - supports the neural layer and is continuous throughout the eye.
Photoreceptor concentration at the
a) fovea
b) optic disc
a) highest concentration
b) no photoreceptors
Sections of the eye.
Anterior and posterior chambers - aqueous humour.
Vitreous body - vitreous humour.
Extraocular muscles of the eye - innervation.
CNIII: superior rectus; medial rectus; inferior rectus; inferior oblique
CN IV: superior oblique
CN VI: lateral rectus
CN VI palsy.
CN IV palsy.
Lateral and inferior rectus muscles can compensate, meaning there is often no obvious eye displacement.
The patient may complain of diplopia, and develop a head tilt.
CN III palsy.
Depressed and abducted eyeball.
Arterial supply to the eye.
a) retina
b) choroid
c) lacrimal gland
a) central retinal artery
b) ciliary arteries
c) lacrimal artery
Venous drainage of the eye.
Central retinal and vortex veins - drain into opthalmic vein.
Pathways into the orbit.
- optic canal
- superior orbital fissure
- inferior orbital fissure
Function of the optic canal.
Transmits the opthalmic artery and optic nerve.
Function of the superior orbital fissure.
Transmits the common tendinous ring, containing:
- oculomotor nerve
- abducens nerve
- nasociliary nerve
Transmits outside the common tendinous ring:
- superior opthalmic vein
- trochlear nerve
- CN V1
- lacrimal nerve
- frontal nerve
Function of the inferior orbital fissure.
Transmits the inferior opthalmic vein and zygomatic nerve.
What is the visual field?
The entire area that can be seen by a patient without movement of their head, and with their eyes fixed on one point.
How is the image of an object in the visual field translated onto the retina?
- inverted upside-down
- flipped left-to-right
How does the retina transmit signals to the optic nerve?
Photoreceptors are stimulated by photos of light entering the eye, transmitting action potentials along the optic nerve.
What occurs at the optic chiasm?
a) nasal retinal fibres
b) temporal retinal fibres
a) nasal fibres decussate to the contralateral optic tract.
b) temporal fibres remain on their respective sides.
Optic tracts are formed.
What occurs at the lateral geniculate nucleus?
Optic tract splits into:
- superior optic radiation (lower retinal field)
- inferior optic radiation (upper retinal field)
What structure do the
a) superior optic radiations
b) inferior optic radiations
travel via?
a) parietal lobe
b) temporal lobe (Meyer’s loop)
What is the function of the calcarine sulcus?
Optic radiations terminate here, in the primary visual cortex.
This is where images from both eyes are collated and the final image is formed.
NB: the brain has to re-invert the image to the information is correctly orientated.
Blood supply to the optic nerve.
- opthalmic artery (branch of internal carotid)
Blood supply to the optic chiasm.
Branches from:
- internal carotid
- PcA
- ACA
- AcA
Blood supply to the optic tract.
MCA
Blood supply to the lateral geniculate nucleus.
Branches of MCA / PCA.
Blood supply to the optic radiations.
MCA
Blood supply to the calcarine sulcus.
Main: PCA
Backup: MCA (macula)
Lesion of optic nerve.
Field defect.
Ipsilateral monocular blindness.
Lesion of optic chiasm (central).
Field defect.
Bitemporal hemianopia.
Lesion of optic chiasm (lateral).
Field defect.
Ipsilateral monocular nasal hemianopia.
Lesion of optic tract.
Field defect.
Contralateral homonymous hemianopia (no macula sparing).
Lesion of superior optic radiation.
Field defect.
Contralateral inferior homonymous quadrantanopia
Lesion of inferior optic radiation.
Field defect.
Contralateral superior homonymous quadrantanopia.
Lesion of superior and inferior optic radiation.
Field defect.
Contralateral homonymous hemianopia (macula sparing)
Lesion of occipital cortex.
Field defect.
Contralateral homonymous hemianopia with macula sparing.
Assessment of visual acuity (distance).
Stand patient 6 meters from Snellen chart, cover one eye and ask to read the lowest line they are able to.
A patients visual acuity improves when they read through a pinhole. What does this suggest?
There is a refractive component to the patient’s poor vision.
If a patient is unable to read the top line of the Snellen chart at 6 meters, what should you do?
- Reduce the distance to 3 meters from the Snellen chart.
- Reduce the distance to 1 meter from the Snellen chart.
- Ask to count fingers you’re holding up.
- Assess if they can see gross hand movements.
- Assess if they can detect light from a pen torch shone into each eye.
Assessment of near vision.
Ask the patient to cover one eye and read fine print text.
Causes of reduced visual acuity.
- refractive errors
- amblyopia
- ocular media opacities (e.g. cataracts, corneal scarring)
- retinal disease (age-related macular degeneration)
- optic nerve pathology (e.g. optic neuritis)
- lesions in visual pathway
What can be used to assess colour vision?
Ishihara plates
General inspection of the eye.
Note any abnormalities such as:
- swelling
- redness
- discharge
- eyelid position
- pupil shape, size and symmetry
Causes of painless red eye.
- conjunctivitis
- subconjunctival haemorrhage
- episcleritis
- dry eye
Causes of painful red eye.
- scleritis
- uveitis
- corneal abrasion
- corneal ulcer
- acute angle-closure glaucoma
- foreign bodies
What is a relative afferent pupillary defect?
When the afferent limb in one of the optic nerves is damaged, both pupils will constrict less when light is shone into the affected eye compared to the normal eye.
What is a unilateral efferent pupillary defect?
Extrinsic compression of the oculomotor nerve results in loss of the efferent limb of the ipsilateral pupillary reflex.
This means the ipsilateral pupil is dilated and non-responsive to light entering the eye.
As the afferent limb is unaffected, the contralateral pupil will constrict (ie. consensual light reflex affected).
Causes of an absent fundal reflex in adults.
- cataracts
- vitreous haemorrhage
- retinal detachment
Causes of an absent fundal reflex in children.
- congenital cataracts
- retinal detachment
- vitreous detachment
- retinoblastoma
Fundoscopy - assessment of the optic disc.
Contour: borders of the optic disc should be clear and well defined.
Colour: orange-pink doughnut with a pale centre (cup).
Cup: verticle size of the cup should occupy one third of the height of the optic disc.
Fundoscopy - optic disc pathology.
Papilloedema.
Optic disc swelling secondary to raised intracranial pressure.
Results in borders of the optic disc appearing blurred.
Fundoscopy - optic disc pathology.
Pale disc.
Suggests presence of optic atrophy:
- optic neuritis
- advanced glaucoma
- ischaemic vascular events
Fundoscopy - optic disc pathology.
Increased cup-to-disc ratio.
Reduced volume of healthy neuro-retinal tissue.
Occurs in glaucoma.
Fundoscopy - assessment of the retina.
Assess each quadrant of the retina:
- super
- temporal
- inferior
- nasal
Fundoscopy - retinal pathology.
Arteriolar narrowing.
Subtle, with generalised arteriolar narrowing with typical copper or silver wire appearance.
Commonly associated with early stages of hypertensive retinopathy.
Fundoscopy - retinal pathology.
Arteriovenous nipping.
Areas of focal narrowing at arteriovenous crossing, with bulging retinal veins either side of the crossing.
Commonly associated with grade 2 hypertensive retinopathy.
Fundoscopy - retinal pathology.
Dot and blot haemorrhages.
Bleeding capillaries in the middle layers of the retina; may look like microaneurysms.
Commonly associated with diabetic retinopathy.
Fundoscopy - retinal pathology.
Hard exudates.
Waxy yellow lesions, often surrounding leaking microaneurysms.
Commonly associated with diabetic retinopathy and grade 3 hypertensive retinopathy.
Fundoscopy - retinal pathology.
Flame haemorrhages.
Large haemorrhages with flame-like appearance, caused by rupture of arterioles or small veins.
Commonly associated with hypertensive retinopathy, thrombocytopenia, retinal vein occlusion and trauma.
Fundoscopy - retinal pathology.
Cotton wool spots.
Small, fluffy, whitish lesions and represent infarcts of the neuro-retinal layer.
Commonly associated with diabetic retinopathy and grade 3 hypertensive retinopathy.
Fundoscopy - retinal pathology.
Neovascularisation.
Formation of new blood vessels that appear as a net of small curly vessels, with or without haemorrhages.
Commonly associated with advanced proliferative diabetic retinopathy.
Fundoscopy - assessment of the macula.
Ask the patient to look directly into the light of the opthalmoscope - the macula is lateral to the optic nerve head.
Fundoscopy - macula pathology.
Drusen
Yellow-white flecks scattered around the macular region, representing remnants of dead retinal pigment epithelium.
Fundoscopy - macula pathology.
Cherry-red spot.
Associated with central retinal artery occlusion, which typically presents with sudden profound visual loss.
What advise should be given to patients if mydriatic drops were instilled?
Cannot drive for the next 3-4 hours until their vision has returned to normal.
Further assessment and investigations following examination of the eyes.
- Amsler chart (?central visual loss)
- Cranial nerve examination
- blood pressure (?hypertensive retinopathy)
- capillary blood glucose (?diabetic retinopathy)
- retinal photography
