Orbit and Eye Anatomy Flashcards
What are the three layers of the eye?
Fibrous outer layer, uvea (middle layer), retina (inner layer)
What makes up the fibrous layer of the eye?
Sclera = muscle attachment Cornea = 2/3 of refractive power
What layer of the eye is the vascular layer?
The uvea
What are the parts of the uvea?
Iris = pupil diameter
Choroid = nutrition and gas exchange
Ciliary body = controls iris, shape of lens and secretion of aqueous humour
What layer of the eye is photosensitive?
The retina
What are the main three parts of the retina?
The macula, retina and optic disc
Where is the anterior segment of the eye located?
In front of the lens
What is the anterior segment of the eye divided into?
Anterior chamber = between cornea and iris
Posterior chamber = between iris and suspensory ligaments
Where is the posterior segment of the eye located?
Behind the lens = makes up 2/3 of the eye
What does the posterior segment contain?
Vitreous body = this contains the vitreous humour
Where is a common site for floaters?
The vitreous body of the posterior segment
What can raised intra-cranial pressure cause in the eye?
Ischaemia of the retina and glaucoma
What makes up the ciliary body?
Smooth muscles and blood vessels
What do ciliary processes secrete?
Secretes aqueous
Where does aqueous circulate in the eye?
Circulates within posterior chamber = nourishes lens
Then passes through pupil into anterior chamber = nourishes cornea
Where is aqueous reabsorbed?
Reabsorbed into scleral venous sinus (canal of Schlemm) at iridocorneal angle
What is the iridocorneal angle often associated with?
It is the angle referred to in open or closed angle glaucoma
What is an end artery?
An artery with insufficient anastomoses to maintain viability of the tissue supplied if arterial occlusion occurs
What is the end artery of the retina?
The central artery of the retina
What are the branches of the ophthalmic artery that supply the eye?
Ciliary artery and central artery of retina
What branches does the ciliary artery give rise to?
Anterior and posterior ethmoidal arteries = supply nasal cavity and contribute to Kiesselbach’s plexus
What is the only vein that drains the retina?
The central vein of the retina
What is the fundus of the retina?
Posterior area where light is focused
What structures are present within the fundus of the retina?
Optic disc, macula and fovea
Where is the point of CN II formation?
The optic disc = only point of exit/entry for blood vessels and axons of CN II
Why is the optic disc a blind spot in the eye?
It has no photoreceptors
Which area of the retina has the greatest density of cones?
The macula
Where is the fovea located within the retina?
In the centre of the macula = depression with 1.5mm diameter
What is the area of the retina with the most acute vision?
The fovea
Where do retinal veins and arteries lie?
Anterior to the retina
What does complete interruption of retinal artery branches or the retinal vein cause?
Loss of an area of the visual field that corresponds to the area of ischaemia
What does complete interruption to the central artery or vein of the retina cause?
Monocular blindness
What is the relationship between axons of the visual pathway?
They maintain a specific spatial relationship from each other
Where is light from objects in the right visual field processed?
By the left primary visual cortex
Where is light from objects in the lower visual field processed?
By the upper part of the primary visual cortex
What axes of the eye relate to the direction of gaze?
The vertical axis and the horizontal axis
What area of the eye does the anteroposterior axis relate to?
The superior pole of the eyeball
What are the movements related to each of the axes of the eye?
Vertical axis = abduction/adduction
Horizontal axis = elevation/depression
Anteroposterior axis = intorsion/extorsion (medial/lateral)
What does each extra-ocular muscle have?
Each muscle will have a primary movement = most also have secondary movement (except medial and lateral rectus)
Where do the movements of the extra-ocular muscles occur from?
The primary position (i.e gaze directed forwards)
What angle of gaze is related to the superior and inferior rectus muscles?
23 degrees
What angle of gaze is associated with the superior and inferior oblique muscles?
51 degrees
What movement does the lateral rectus muscle perform?
Can only abduct eyeball = brings line of gaze into same plane as superior and inferior rectus muscles
What nerve innervates the lateral rectus muscle?
CN VI
What movement does the superior rectus muscles perform?
Elevation = only muscle that can elevate when eyeball is in abduction
What movement does the inferior rectus muscle perform?
Depression = only muscle that can depress when eyeball is abducted
What is the action of the medial rectus muscle?
Can only adduct eyeball = brings line of gaze into same plane as superior and inferior oblique muscles
What extra-ocular muscles are innervated by CN III?
Superior and inferior rectus muscles, medial rectus muscle, inferior oblique muscle
What is the action of the inferior oblique muscle?
Elevation = only muscle that can elevate when eyeball is adducted
What movement does the superior oblique muscle perform?
Depression = only muscle that can depress when they eyeball is adducted
What nerve innervates the superior oblique muscle?
CN IV
What does movement of the eye normally require?
Action of more than one muscle = synergists, antagonists or both
What muscles act together to perform pure elevation?
Superior rectus and inferior oblique synergistically work together (antagonists as rotators)
What muscles act together to perform pure depression?
Superior oblique and inferior rectus synergistically work together (antagonists as abductors/adductors)
