(PM3A) Ocular Therapeutics Flashcards by David Vincent-Waterson

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

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What are the internal eye structures?

(1) Sclera
(2) Lens
(3) Cilliary body
(4) Iris
(5) Choroid
(6) Retina
(7) Optic nerve

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What is the sclera?

Internal eye structure

Tough

Outer protective coat

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What is the lens?

Transparent biconvex structure

Suspended by lens zones

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What is the cilliary body?

Internal eye structure

Provides attachment for lens zonules

Changes the focusing power of the lens

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What is the iris?

Internal eye structure

Regulates light entering the eye

Attached by cilliary body

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What is the choroid?

Internal eye structure

Maintains the eye’s blood supply

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What is the retina?

Internal eye structure

Inner layer containing visual photoreceptors

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What is the optic nerve?

Internal eye structure

Transmits images from photoreceptors to brain

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What is the lachrymal gland?

Tear production

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What is responsible in the eye for tear production?

Lachrymal gland

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What are the different types of tear?

(1) Basic tears
(2) Reflex tears
(3) Emotional

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What are basic tears?

To maintain tear film on the corneal surface

For optical, metabolic and lubricant purposes

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What are reflex tears?

Response to chemical or mechanical irritation

e.g. cold/ light

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What is the ‘three layers theory’?

Comprises the precorneal tear film

(1) Superficial lipid layer
(2) Central aqueous layer
(3) Inner mucous layer

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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