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Pharmaceutics > Routes of Administration - Ocular > Flashcards

Routes of Administration - Ocular Flashcards

1
Q

What does the outer layer of the eyes consists of?

A

Sclera - posterior 5/6ths of the eye
Cornea - anterior 1/6th of the eye

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2
Q

Describe the structure of the sclera?

A
  • Tough, fibrous tissue
  • Protects eye and maintains shape
  • Front of the sclera is the ‘white of the eye’ covered by the conjunctiva and lacrimal tears
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3
Q

Describe the cornea.

A
  • Positioned in front of iris and pupil
  • Has extensive sensory nerves
  • Avascular perfused by anterior ciliary arteries
  • The surface is covered by tears from the lacrimal gland
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4
Q

State the 3 chambers the eyes consist of?

A
  • Anterior chamber
  • Posterior chamber
  • Vitreous chamber
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5
Q

What does the anterior chamber and posterior chamber contain?

A
  • Filled with aqueous humour: colourless with electrolytes, growth factors, proteins
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6
Q

What happens if drainage from the eyes is blocked in the anterior and posterior chamber?

A

Fluid and pressure accumulate leading to glaucoma

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7
Q

What does the vitreous chamber contain?

A

Vitreous humour: hydrogel, collagen fibrils and hyaluronic acid
- Proteins
- Inorganic salts
- Glucose
- Ascorbate

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8
Q

What is the function of the pre-corneal tear film?

A
  • Lubricates and protects the eye surface
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9
Q

State the three layers which make up the pre-corneal tear film.

A
  • A superficial lipid layer
  • A central aqueous layer
  • An inner mucus layer
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10
Q

What is the superficial lipid layer composed of and what is its function?

A
  • Composed of sterol esters, wax, esters and fatty acid s
  • Reduce evaporation rate of tears
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11
Q

What does the central aqueous layer consist of?

A
  • Electrolytes
  • Proteins
  • Glycoproteins
  • Biopolymers
  • Glucose
  • Urea
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12
Q

State the function of the inner mucus layer.

A

Allows spread of tear film over the eye surface on blinking

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13
Q

What is the buffer capacity of the tears determined by?

A
  • bicarbonate ions, proteins and mucins
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14
Q

Why are tears more acidic for contact-lens wearers?

A

Due to impediment of the efflux of carbon dioxide

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15
Q

In which cases are tears more alkaline?

A
  • In the case of diseases such as dry eye, sever ocular rosacea and lacrimal stenosis
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16
Q

Why is blinking important for humans?

A
  • It is an important defence mechanism of the eye
  • brisk blinking reflex is fast enough to precede high-speed foreign bodies approaching the eye
  • Essential for the periodic reforming of the tear film
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17
Q

What does blinking activate?

A
  • A pumping mechanism for the drainage of tears through the lacrimal drainage apparatus
18
Q

State the ocular drug delivery routes.

A
  1. Cornea - main route for topical to reach aqueous humour
  2. Periocular delivery - bypass the conjunctival and corneal epithelium
  3. Intravitreal delivery - directly reach the back of the eye
19
Q

What challenges does the eye present for effective drug delivery?

A
  • The lachrymal (tear) system continually washes the eye.
  • Blinking also promotes fluid clearance.
20
Q

Which routes is ocular drug delivery eliminated?

A
  • Elimination from aqueous humour into systemic
    uveoscleral circulation.
  • Outflow through the trabecular meshwork and
    Schlemm’s canal.
  • Eliminate from the vitreous humour via diffusion into
    the anterior chamber.
  • Clearance via posterior route across blood retinal
    barrier.
21
Q

What must eye solutions be?

A
  • Isotonic
  • Close to neutral pH
  • Stable
  • Sterile
  • Particle free
  • Contain preservatives if multi-dose container
  • Easy for patient to administer on their own
  • Can provide rapid onset of action
  • Avoid hepatic metabolism
22
Q

Why must ophthalmic preparation be sterile?

A
  • Ocular infections can rapidly lead to vision loss
23
Q

Why are preservatives included in multi-dose containers?

A
  • Inhibit microbial growth
  • Cannot be used in intraocular products
  • Benzalkonium chloride is often used
24
Q

What determines osmolality?

A

Salt conc. within the lacrimal fluid - dry eye patients have hypertonic lacrimal fluid

25
Q

What do both hypotonic and hypertonic solutions cause?

A
  • both cause irritation and induce tear production - clears any applied solution
26
Q

What is the acceptable pH range for ocular solution?

A

3.5 to 9 - at extreme pH could damage ocular tissue

27
Q

What does pH control of ionisation also affect?

A

Aqueous solubility and membrane permeability

28
Q

What happens if an ophthalmic solution has a lower surface tension?

A

Can destabilise the tear film and disperse the liquid layer into droplets - this can affect evaporation and lead to irritation

29
Q

What happens if we increase the viscosity of solutions?

A
  • Can prolong their residence time thus enhance drug absorption
30
Q

What happens to the eye as a result of exceeding the viscosity limit?

A
  • Over the viscosity limit, i.e. a higher force (over 0.9N) is required for blinking, would cause pain.
  • Very viscous solution can cause blurring and may block the puncti and lacrimal canals.
31
Q

What are the advantages of solutions?

A
  • Simple designs: cheap to manufacture
  • Solutions are homogenous - better dose uniformity
32
Q

What are the disadvantages of solutions?

A
  • Are rapidly cleared by drainage: can add viscosity modifiers
33
Q

What are ointments used for?

A
  • Reduce clearance from the eyes
  • Can be used for poorly soluble drugs
  • Used for antibiotics, antifungals and steroids
34
Q

What may ointments cause?

A

Blurring

35
Q

In what case would gels be more suitable than ointments?

A

As semi-solid, water-soluble bases so more suitable for water-soluble drugs

36
Q

Describe ion-exchange resins.

A
  • The drug is ionically bound to an ion-exchange resin to form an insoluble complex.
  • Drug is released from the complex through exchange of the drug ions with ions in tear fluids.
  • The resin particle size is one of the factors that controls the rate of drug release.
37
Q

What are intraocular implants?

A
  • Controlled drug delivery systems prepared from biodegradable or non-biodegradable polymers
38
Q

How are ocular implants introduced?

A
  • Introduced into the vitreous through an incision in the ocular pars plane, which is located posterior to the lens and anterior to the retina
39
Q

What is biodegradable intravitreal impkant used to treat?

A
  • Treatment of macular oedema and noninfectious uveitis affecting the posterior segment of the eye
40
Q

How are intravitreal injections administered?

A
  • By injecting a drug solution, suspension or intraocular implants into the vitreous cavity
  • Main route to deliver macromolecules to the posterior segment into the eye
  • Has become the gold standard treatment for many retinal diseases

Pharmaceutics (20 decks)

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