Week 1 - Overview of the eye Flashcards
The ocular adnexa are the structures that support and protect the eye and include…….. (4)
-The eyelids,
-The conjunctiva,
-The lacrimal gland,
-The lacrimal drainage system
What are the 3 main functions of the ocular adnexa?
-Defense against microbial colonization
-Smoothing the tear film for good optical clarity
-tear production
What are the 3 types of blinks?
1- Reflex
2 - Conscious
3 - Unconscious
Why do we reflex blink?
occurs in response to a tactile, visual, or auditory stimulus
What is conscious blinking?
a voluntarily controlled movement
What is unconscious blinking? 2
- also called spontaneous
-most common type occurs 10-15 times per minute
What 3 things happen when you blink while wearing contact lenses?
1 - distribution of tear film across the lens
2 - activities with reduced blink rate
3 - movement of the lens during blink
What are the 5 layers of the cornea (in order outer to inner)?
- Epithelium
- Bowman’s Membrane
- Stroma
- Descemet’s Membrane
- Endothelium
The cornea is a clear transparent structure with a brilliant, shiny surface that is responsible for 2/3 of the refractive power of the eye. T/F
True
What are characteristics of the cornea?4
-convex surface
- forms with the sclera
-tough fibrous outer coat that encloses ocular tissues
-protects the eye from injury.
The cornea is avascular meaning it does not have a blood supply. T/F
True
What does the cornea rely on to get oxygen, glucose, vitamins and amino acids? 3
1 - the atmosphere,
2- the perlimbal vasculature,
3 - the tear film or the
aqueous humour.
Can contact lenses cause metabolic stress and why?
Yes as contact lenses reduce the amount of oxygen the cornea gets from the atmosphere
What 3 oxygen states can the cornea be in after wearing cls?
- Anoxia - severe lack of oxygen
- Hypoxia - low levels of oxygen
- Hypercapnia - too much carbon dioxide in your blood
What is the crystalline lens?
transparent biconvex structure situated between the iris and the vitreous
What are the 3 parts of a crystalline lens (inner to outer)?
nucleus
cortex
capsule
What is the crystalline lens attached to and where?
Attached to the ciliary processes and to the posterior portion of the ciliary body by fine suspensory ligaments (zonular fibres)
If the crystalline lens is thin it is viewing the ………………… (1).
If the crystalline lens is thick it is viewing the …………….. (2) due to …………………..(3).
1 - distance
2 - near
3 - accommodation
The iris is the most anterior structure of the uveal tract. T/F
True
How does the iris dilate in bright light?
relaxation of the sphincter muscle
What are the 3 parts of the conjunctiva and where are they attached?
Bulbar conjunctiva - sclera
Palpebral conjunctiva - eyelid
Conjunctival fornix - where it folds
What is the function of the conjunctiva?
acts as a barrier against microbial infection, wounds and scratches
What is the function of the epithelium? 3
-regenerates quickly
-blocks foreign bodies
-distributes nutrients
What is the function of the Bowman’s Membrane? 3
- composed of collagen
-function unclear
-vision loss may occur during healing
What is the function of the Stroma? 4
- 90% of the cornea
-made of water and collagen
-crystalline proteins maintain clarity in cornea
-provides structural support/gives curved shape
What is the function of the Desment’s Membrane?3
-thin and strong
-regenerates slowly
-protective barrier against injury and infections
What is the function of the endothelium? 2
- delicate/does not regenerate
-endothelium pumps ecess water which help maintains transparency of cornea
What is the average dimension of the cornea? (vertically/horizontally)
Vertically - 10.6mm
Horizontally - 11.5mm
What is the purpose of keratocytes? 2
-deposition and maintenance of the transparency and clarity of the cornea. -located in the stroma
What is meant by corneal innervation?
-most densely innnervated tissue in the body - most amount of nerve endings
What are the two eyelid muscles ?
levator palpebrae
orbicularis oculi
