Flashcards in Anatomy and Physiology of vision I Deck (57):
What are the main functions of the eye?
To transmit light to the retina
To refract light so that it is focused on the retina
To transduce light into an electrical signal
To process the electrical signal before it is transmitted to the CNS
What are the two eye segments? What are they composed of?
Anterior segment (Anterior and posterior chambers)
Posterior Segment (vitreous, retina, choroid and optic nerve)
What is the part of sclera covering the optic nerve?
What are the 3 components of the conjunctiva ?
What is episclera and what are its two layers?
Vascular plexus between the conjunctiva and the sclera
Superficial episcleral vessels
Deep episcleral vessels
What are the relative refractive powers of the cornea and the lens?
Cornea: 2/3 refractive power (fixed)
Lens ~1/3 refractive power (variable)
Why is the cornea transparent?
what are the 5 layers of the cornea?
Epithelium, bowman's membrane, stroma, Descemet's membrane, endothelium
What is the function of corneal epithelium?
Acts as a barrier to trauma and infection (5-8 cells thickness)
What are two important characteristics of the stroma?
1- comprises 90% of the corneal thickness
2- does not regenerate
What is the function of the endothelium?
maintains corneal hydration
What is the structural difference between the sclera and the cornea?
Same structure, but the collagen in the sclera is coarse and irregularly distributed
What are the components of a lens?
capsule, cortex, nucleus, epithelium
What are the major classes of cataracts?
Nuclear sclerosis (aging)
Posterior subcapsular (Steroids, diabetes)
Where can the intra ocular lens be inserted?
Posterior chamber (inside the capsule)
What are the components of the Uvea?
What is the significance of the stroma in the iris?
Contains the following:
1- Muscles: a) shincter constricting muscles (CNIII) b) dialator muscles
3- Blood vessels
What is a common finding associated with congenital horner's syndrome?
What are the main parts of the ciliary body?
What are the functions of the ciliary body?
1- Production of aqueous humour
Where is the aqueous humour produced?
Produced by the two layered epithelium in the ciliary body to nourish avascular structures (cornea and lens)
How is the aqueous humour drained from the anterior chamber?
Drained by tubercular meshwork to canal of schlem and via uveascleral outflow to episcleral venous vessels
What two structures form the angle?
The cornea and the iris
What causes glaucoma?
Obstruction of the aqueous drainage which leads to increased intraocular pressure (IOP)
What effect does increased IOP have on the optic nerve?
Could result in glaucomatous damage to the optic nerve
Appears as a reduced rim in fundoscopy
How is glaucomatous increased IOP treated?
Either by decreasing aqueous production by the ciliary body or by increasing aqueous outflow through the trabecular meshwork and uveouscleral outflow pathways
What is the accommodation process for near sight? (near Triad)
1- Ciliary body contracts and moves anteriorly which leads to relaxation of the zonules which allows the lens to round up in shape
2- Convergence of the eyes
3- Pupillary constriction to decrease spherical aberration
What makes up the vitreous?
99% water, 1% collagen, HCL
What changes to the vitreous occur with age?
The vitreous liquifies and condenses
What is the centre of the retina? What is the centre of that centre? (yes for real)
Macula and fovea
What constitutes the retinal blood barrier? What is its function?
The retinal pigment epithelium (RPE) that supports the metabolism of photoreceptors
What is the function of the choroid?
Highly vascular part of the Uvea that provides the retina with much of its metabolic requirements
What makes the choroid essential to the fovea?
The fovea is avascular and its support is dependent on the choroid
What is the pathway of the optic nerve?
Intraocular (1mm), intraorbital (25mm), intracannalicular (9mm), intracraneal (16 mm)
What constitute the adnexal structures?
Bony orbits, lacrimal ducts, eyelids, and extraocular muscles
What makes up the roof of the orbit?
Frontal bone and lesser wing of the sphenoid
What makes up the floor of the orbit?
Zygomatic bone, maxillary bone, palantine bone
What makes up the medial wall of the orbit?
Ethmoid bone, maxillary bone, lacrimal,` and sphenoid
What makes up the lateral wall of the orbit?
Greater wing of the sphenoid, and zygomatic bone
What is the first bone to break following an orbital trauma (ex punch to the eye)?
What passes through optic foramen?
Optic nerve and artery (through sphenoid bone)
What passes through SOF?
CNIII, IV, V1, VI, and vessels (between greater and lesser wings of sphenoid)
What passes through IOF?
Sympathetics and vessels
What muscles originate at the orbital apex?
All but Inferior oblique
What muscles are responsible for lid opening?
Levator palpebrae superioris (CNIII) and Mullers muscles (Sympathetics )
What muscles are responsible for lid closing?
Obircularis oculi (CNVII)
What is contained within the eyelid?
Muscles, glands, tarsal plate, site of attachment of orbital plate
What is the tear film composed of?
1- Mucin layer
2- Aqueous layer
3- Lipid layer
Where is the mucin layer produced and what is its function?
Produced by conjunctival goblet cells
Aids tear adherence to the cornea
Where is the aqueous layer produced and what is its function?
Produced by the accessory lacrimal glands (glands of Krau and Wolfring)
Forms bulk of tear film
Where is the lipid layer produced and what is its function?
Produced by meibomian gland in lid margin
Reduced tear evaporation
What is the function of the tear film?
Maintains refractive function
What could cause dry eye?
Loss of lipid layer (tear evaporation) loss of aqueous layer, loss of mucin layer (tear slides off)
Where is the lacrimal gland located?
Lateral superior orbit
What causes the lacrimal gland to secrete?
In reflex to bright light, emotion, and irritation (CN II, V)
What glands provide basal secretions? Where are the located?
Kraus and Wolfring
Located in conjunctival fornix