Applied anatomy & physiology of the eyes Flashcards
Staring at the green box, identify each part of the eye
Note the ‘Fovea’ is part of the Macula (but the names are used interchangeably)
What are the 3 coats (Tunics) of the eye?
What parts of the eye make up each layer
Fibrous coat:
- Cornea, sclera
Vascular coat
- Iris, Ciliary body, choroid
Sensory coat
- Retina
What is the cornea?
The transparent front part of the eye that covers the iris, pupil, and anterior chamber.
The cornea, with the anterior chamber and lens, refracts light, with the cornea accounting for approximately two-thirds of the eye’s total optical power.
What is the sclera?
The opaque, fibrous, protective, outer layer of the human eye containing mainly collagen and some elastic fibres
Briefly describe each of the layers that make up the vascular coat of the eye
Iris:
- Thin contractile diaphragm which regulates the amount of light reaching the retina
Ciliary body:
- Part of the eye that includes the ciliary muscle, which controls the shape of the lens, and the ciliary epithelium, which produces the aqueous humor
Choroid:
- Dark red/brown layer between the sclera and retina
- Basically just where all the blood vessels are
- Continous anteriorly with Ciliary body
What is aqueous humor?
A transparent, watery fluid similar to plasma, but containing low protein concentrations.
It is secreted from the ciliary processes
Contained in both anterior and posterior chambers of the eye (but not the vitreous humour bit)
What is vitreous humor?
Clear gel that fills the space between the lens and the retina
Shown below is the histology of the cornea
Identify and describe the layers numbered
1) - Non-keratinised stratified squamous epithelium
2) - Bowman’s membrane (basement membrane)
3) - Stroma
- Regularly arranged collagen
- No blood vessels
4) - Descemet’s layer
5) - Endothelium (single layer) - 2500 cells mm-2
What is this method of investigation shown below
Identify the labels if you please
Slit lamp
How does the cornea maintain its transparency?
Stroma (3):
- Regularly arranged collagen = more transparent than irregular
- No blood vessels to get in the way of light
Endothelium cell layer (5):
- Has pumps to actively keep aqueous humor out
- Damage to epithelium = AH gets in and cornea becomes swollen & opaque
Why is the cornea described as ‘immune-privileged’ and how does this benefit corneal transplant surgery?
Cornea is avascularised (nae blood vessels)
As blood is such an important transport route for WBCs n stuff = lesser chance of foreign antigens from a corneal graft being recognised by the recipient, so lesser chance of a graft rejection
What is Schlemm’s canal?
Circular lymphatic-like vessel in the eye that collects aqueous humor from the anterior chamber and delivers it into the episcleral blood vessels via aqueous veins
Found where the cornea & sclera join
(remember the eye doesn’t have lymph)
What is trabecular meshwork?
Area of tissue at the base of the cornea (beside Schlemm’s canal)
Responsible for draining the aqueous humor from the eye (via the anterior chamber) by yeeting it to Schlemm’s canal
Identify le stuff
Describe the innervation of the cornea
Innervated through the Ophthalmic nerve (CN V1)
Incredibly sensitive to touch
Responses to foreign bodies (dust etc) will elicit blinking, tears, pain
Shown below is the Retina
Identify the boxes and identify the section of the eye below the retina in the diagram
Layer below is the Choroid
What is the purpose of the pigmented epithelial layer?
Reinforces the light-absorbing function of the Choroid by reducing the scattering of light
It is a single layer of cells
Shown below are a rod and cone
1 - Describe their functional difference.
2 - Identify which one is which.
3 - Identify the labels.
Rods:
- provide vision during dim light or night also known as scotopic vision
- much more sensitive to photons
Cones:
- provide vision during day time or at bright light also known as photopic vision
Describe the vasculature of the Choroid and the retina
Choroid is made up of fenestrated blood vessels of varying diameter.
These supply the outer layers of the retina with blood by diffusion.
(The inner layers of the retina get blood from branches of the central retinal artery.)
This photo was taken through an ophthalmoscope
Which eye is this?
What is the arrow pointing at?
Left eye (optic disc is on left)
Fovea centralis
How is the Fovea Centralis different from the rest of the retina?
Its packed with Cones so has maximum visual acuity
What is the Lens of the eye?
Transparent, crystalline biconvex structure
Suspended by zonules from the ciliary body.
It can change shape (i.e. become less or more convex.)
As we know, for many structures in the eye, they are avascular in order to be as transparent as possible
The lens is an example of this.
What problems are linked to the lens being like this?
avascularity is one of the factors that predispose it to become opaque later in life
(Cataracts)
What thingy is this?
Lacrimal sac
the upper dilated end of the nasolacrimal duct, and is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla
Describe how tears are formed and drained from the eye
Identify the labels for extra points
Lacrimal gland produces tears
Tears drained into the puncta and move through canaliculi into lacrimal sac
What is the tear film?
Thin fluid layer that covers the outer mucosal surfaces of the eye
What is the structure of the tear film?
Composed of 3 layers
- Outer, Oily layer (smallest <1%)
- Middle, aqueous layer (largest 69% hehe)
- Inner, mucinous layer that overlies the corneal epithelium (30%)
What are the functions of the tear film?
- Keep cornea MOIST
- Wash away particulate foreign bodies
- Contain antibodies and lysozymes to kill microbes
- Smooths outer surface of cornea providing smooth surface for refraction
How is secretion of tears into conjunctival sac controlled?
Parasympathetic control via CN VII (facial nerve)
Describe how the state of the tear film will stimulate blinking?
Eyes open:
- Middle watery layer of tear film evaporates
- Oily layer gets close to mucinous layer
- When they touch, the film breaks
- This stimulates blinking
- When they touch, the film breaks
- Oily layer gets close to mucinous layer
