Anatomy of the Eye Flashcards
Retina. State the dimensions of:
- Posterior pole
- Macula
- Fovea
- Optic disc
Posterior pole: 5-6mm
Macula: 1.5mm
Fovea: 0.35mm
OD: 1.8mm
Ora serrata - is it closer to the limbus nasally or temporally?
The ora serrata is 1mm closer to the limbus nasally.
State the 2 attachment points of the neural retina.
- Ora serrata (anterior termination)
2. Margins of optic nerve head
State the 4 attachment points of the vitreous.
- Vitreous base: 3-4mm wide band covering the ora serrata and pars plana
- Posterior lens capsule: Ring-shaped attachment at site of hyaloid canal, ligamentum hyaloide capsulare
- Margins of optic disk
- Inner limiting membrane of retina esp around retinal vessels (variable)
State the volume of the vitreous cavity and its borders.
4-5mL (2/3 total vol. of globe)
Borders:
Anteriorly - ciliary body, posterior lens zonules & lens
Posteriorly: retinal cup
Primary collagen types in different ocular tissues:
- Corneal stroma
- Descemet’s membrane
- Sclera
- Lens
- Vitreous
- Bruch’s membrane
Corneal stroma: Type 1, 3, 5, 6 in stroma (structure stabilised by 6)
Descemet’s membrane: Type 4 (since it is a BM)
Sclera: Type 1, 3, 5, 6 (same as cornea)
Lens capsule: 1, 3, 4 (Ocular BM - type 4 as well as type 3. Type 3 confers elasticity which aids in lens rounding in accommodation)
Vitreous: Type 2, 9
Bruch’s: 1, 3, 4, 5
Cone and rod density in the retina.
Ganglion cell body layers in the retina.
Peripheral retina: Rod-dominant (30 000/mm3), single layer of ganglion cell bodies
Posterior pole / central retina: Cone-dominant, >1 layer of GC bodies
Fovea: Cones only (150 000/mm3), GC bodies displaced peripherally
Number of: - Rods - Cones - Bipolar cells - Ganglion cells in the retina
Rods: 120 million
Cones: 6 million
Bipolar: 36 million
GC: 1 million
State the 10 layers of the retina from outermost to innermost.
- Retinal pigment epithelium
- Photoreceptor layer
- Outer limiting membrane
- Outer nuclear layer
- Outer plexiform layer
- Inner nuclear layer
- Inner plexiform layer
- Ganglion cell layer
- Nerve fibre layer
- Inner limiting membrane
What forms the inner and outer limiting membranes of the retina?
Müller cells which have their cell bodies in the inner nuclear layer and span the width of the retina.
Inner limiting membrane: Formed by astrocytes and foot processes of Müller cells
Outer limiting membrane: Formed by tight junctions of Müller cells to each other and to the photoreceptor cells just deep to the inner segments.
Total area of retina
1.1 cm2
Thickness of retina at:
- Temporal edge of optic disc
- Fovea
- Ora serrata
- Temporal edge of OD: 250 um
- Fovea: 150 um
- Ora serrata: 80um
Give an overview of the 9 types of bipolar cells.
Rod bipolar cells - synapse with 10-20 / 30-50 rods (central/peripheral)
Cone bipolar cells:
- Diffuse - 5 types (usually 5-7 cones / up to 20 cones)
- Midget - 3 types (single cones)
What are the choroid and sclera homologous to in the CNS?
Choroid: Pia-arachnoid layer
Sclera: Dura mater
Thickness of the choroid?
220um posteriorly, 100um anteriorly
What are the 3 attachments of the choroid?
Scleral spur, vortex veins and optic nerve
What are the two retinal attchnents?
Ora serrata and optic nerve
What is the arterial and venous supply of the lacrimal gland?
Lacrimal artery - branch of ophthalmic
Drains to superior ophthalmic vein
What is the nervous supply of the lacrimal gland?
Parasymp: lacrimal nucleus in superior salivary nucleus of CNVII —> greater superficial petrosal nerve —> joins symp from deep petrosal nerve —> Vidian’s nerve —> pterygopalatine ganglion —> lacrimal nerve
How many Meibomian glands are there in the top and bottom eyelid?
50 in top eyelid, 25 in bottom
What are the 3 components of the tear film and what secretes each part?
Lipid - Meibomian glands
Aqueous - Lacrimal gland / accessory lacrimal glands
Mucinous - goblet cells of conjunctiva
What is the most common causative organism in chronic dacryocystitis?
Actinomyces israelii
What is the most common cause of congenital dacryocystitis?
Imperforate valve of Hasner
What is Jones test (primary and secondary) for causes of epiphora?
Jones test is done AFTER complete obstruction is ruled out using probing and irrigation.
Primary: Distinguishes between hypersecretion and partial obstruction
- Instill fluoroscein –> retrieve from inf. meatus. If fluoroscein is retrieved well, no issue with drainage. Issue is hypersecretion
Secondary: Distinguishes site of partial obstruction
- After primary Jones test, insert cannula into nasolacrimal sac and irrigate with saline. If fluoroscein-stained saline is retrieved, then obstruction is below NL sac. If clear saline is retrieved, obstruction is proximal to NL sac.
What is the normal height of the palpebral fissure?
8-11mm
What is Riodan’s muscle?
It is the most superficial aspect of the orbicularis oculi and corresponds to the grey line at the eyelid margin.
What structures make up the anterior, posterior and middle lamellae of the eyelid?
Anterior: Skin, subcut tissue, protractor muscles (orbicularis oculi)
Middle: Orbital septum
Posterior: Retractor muscles (LPS and Müller), tarsus, conjunctiva
Describe the spiral of Tillaux.
Insertions of rectus muscles around the limbus.
MR: 5.5
IR: 6.5
LR: 6.9
SR: 7.7
Which is the only extraocular muscle not to be affected in a retrobulbar block? (Consider anatomy of orbital apex)
Lateral rectus (abducens nerve travels outside the annulus of Zinn)
Which ocular motor nuclei control their contralateral muscles?
Superior oblique and superior rectus
Think: superior muscles are contrarian
What is the order of appearance of the extraocular muscles during embryological development?
LR > SR > LPS (5wks) > SO > MR > IO > IR
Clockwise around the eye starting from lateral rectus
Where in the brain are the horizontal and vertical gaze centres located?
Horizontal: Dorsal pons
Vertical: Dorsal midbrain
What are the main components of the horizontal gaze centre?
- Abducens nucleus
- PPRF
Connects to contralat oculomotor nucleus via MLF
What are the main components of the vertical gaze centre?
- Rostral interstitial MLF
- Interstitial nucleus of Cajal
- Posterior commissure
Which of the vestibular nuclei controls the vestibulo-ocular reflex?
Medial vestibular nucleus
What is the difference between a saccade and a pursuit?
Saccade: Fast intentional movement to look at a target
Pursuit: Smooth eye movement tracking a moving target
Which supranuclear areas control saccades and pursuits respectively?
Saccades: Frontal eye field
Pursuits: Parieto-temporal-occipital region
What is the blood supply of the pretarsal and posttarsal eyelid?
Pretarsal: Branches of superficial temporal and facial arteries (ext carotid)
Post tarsal: Branches of ophthalmic artery (int carotid)
What is the main source of antioxidants in the anterior chamber?
The ciliary body (contains high levels of superoxide dismutate, glutathione peroxidase, catalase)
What is the main detoxifying mechanism in the anterior chamber?
CYP450 system
What percentage of the total ocular blood flow passes through the uveal layer?
98%
85% - choroid
7% - ciliary body
5% - iris
What is the major membrane protein of lens fibres?
AQP-0 (previously major intrinsic protein, MIP-26)
Lens fibres also have heterodimeric connexon gap junctions
What is the major phospholipid in the lens epithelium membrane?
Sphingomyelin (dihydrosphingomyelin to be precise)
What are the main collagen types in the vitreous?
Type 2/6 and Type 9
What size molecules can pass through the blood-retina barrier?
What about through the lens epithelium?
Blood-retina barrier: <20,000 Da
Lens epithelium: <50,000 Da
Describe the location and anatomical relations of the ciliary ganglion.
1cm anterior to the annulus of Zinn. Lies between optic nerve and lateral rectus.
Carries PNS and SNS fibres to the anterior chamber, and sensory fibres from. 3 roots: PNS, SNS and CNV1 sensory. Only PNS fibres synapse in the ganglion.
