(PM3A) Ocular Therapeutics Flashcards
What is the orbit?
Boney socket containing the eye
Formed from a number of fused bones
Mounting point for 6 striatal muscles
Protection of delicate eye
What are the internal eye structures?
(1) Sclera
(2) Lens
(3) Cilliary body
(4) Iris
(5) Choroid
(6) Retina
(7) Optic nerve
What is the sclera?
Internal eye structure
Tough
Outer protective coat
What is the lens?
Transparent biconvex structure
Suspended by lens zones
What is the cilliary body?
Internal eye structure
Provides attachment for lens zonules
Changes the focusing power of the lens
What is the iris?
Internal eye structure
Regulates light entering the eye
Attached by cilliary body
What is the choroid?
Internal eye structure
Maintains the eye’s blood supply
What is the retina?
Internal eye structure
Inner layer containing visual photoreceptors
What is the optic nerve?
Internal eye structure
Transmits images from photoreceptors to brain
What is the lachrymal gland?
Tear production
What is responsible in the eye for tear production?
Lachrymal gland
What are the different types of tear?
(1) Basic tears
(2) Reflex tears
(3) Emotional
What are basic tears?
To maintain tear film on the corneal surface
For optical, metabolic and lubricant purposes
What are reflex tears?
Response to chemical or mechanical irritation
e.g. cold/ light
What is the ‘three layers theory’?
Comprises the precorneal tear film
(1) Superficial lipid layer
(2) Central aqueous layer
(3) Inner mucous layer
What is the lipid layer in the eye?
Consists mainly of sterol esters, triacylglycerols and phospholipids, free sterols and free fatty acids
Spreads over the aqueous layer during eye opening
Reduce the evaporation rate
Maintain normal tear osmolarity
What components comprise the aqueous layer in the eye?
Inorganic salts Glucose Urea Retinol Ascorbic acid Various proteins Lipocalins (tear-specific pre-albumins) Immunoglobulins Lysozyme Lactoferrin Glycoproteins
What is the function of the tear film?
(1) Prevent cornea drying
(2) Transport of oxygen and nutrients to cornea
(3) Maintain clean + smooth cornea
(4) Protects against infection
What is the pH of the tear film?
7.3 – 7.7 (mean value 7.4)
Can also vary between 5.2 and 9.3 depending on age + diseases
How does the tear film buffer its pH?
Bicarbonate ions, proteins + mucins
How does the pH of the tear film vary in contact lens wearers?
Tears are more acidic
Less efflux of carbon dioxide
How does the pH vary in patients with dry eye?
More alkaline
What is the normal human tear volume?
7-9mcL
What is the maximum volume of fluid that can be held in the lower eyelid sack?
25-30mcL
What volume of tears comprises the precorneal film?
3mcL
Why do eye drops cause rapid reflex blinking?
Sudden increase in tear volume
What is blinking?
Important defence mechanism of the eye
Reflex fast enough to prevent high speed foreign bodies entering the eye
Periodic reformation of the tear film
Activates a pumping mechanism for the drainage of tears
Describe the lipophilicity of the epithelium of the cornea.
Lipophilic
What is the function of the cornea?
(1) Passage of light
(2) Refraction of light
(3) Protection of the eye
What is the aqueous humour?
Transparent viscous fluid
Located in the anterior chamber of the eye
98% water
What is the function of aqueous humour?
(1) Maintains intraocular pressure + inflates globe of the eye
(2) Provides nutrition for the avascular ocular tissues
(3) Light refraction
(4) Potential immune response
Describe the structure of the lens?
Elastic - can change shape
Thicker - close focus
Thinner - long sight
(1) Lens capsule
(2) Lens epithelium
(3) Lens fibres
What is the vitreous humour?
Clear gel that fills the space between the lens + retina
What is the function of vitreous humour?
(1) Maintain normal anatomic expansion of the globe
(2) Impedes the diffusion of substances between the retina and the anterior segment of the eye
(3) Reservoir of substances such as oxygen, glucose and ascorbic acid, which support the metabolism of adjacent structures
Describe the composition of the vitreous humour.
99% water
Network of collagen fibrils
Large molecules of hyaluronic acid
What are photoreceptors?
Located on retinal surface
Rods act in low light levels, no colour + poor spatial resolution
Cones operate at higher light levels, colour + good spatial resolution
How is an action potential generated in the optic nerve?
(1) Rods/ cones (photoreceptors) activated
(2) Action potential generated
How do action potentials enter the skull?
Via optic canal
Meet at optic chiasma
What are stages in perception of sight?
(1) Light enters eye and activates photoreceptors (rods/ cones)
(2) Activation of photoreceptors generates an action potential in the optic nerve
(3) Action potential travels from optic nerve to optic canal to optic chiasma
(4) Nerves project to visual cortex in occipital lobes
