Routes of Administration (Ocular)

Question 1

What does the outer layer of the eye consist of?

Answer 1

• Sclera
• Cornea

Question 2

What is the sclera?

Answer 2

• Around most of eye
• Tough, fibrous tissue
• Protects eye and maintains shape
• Front of sclera (white of the eye) covered by the conjunctiva (thin transparent mucous membrane) and lacrimal tears

Question 3

What is the Cornea?

Answer 3

• In front of iris and pupil
• Has extensive sensory nerves
• The surface is covered by tears from the lacrimal gland

Question 4

What are the chambers of the eye?

Answer 4

• 3 chambers: Anterior, posterior and vitreous

Question 5

What is the anterior and posterior chambers?

Answer 5

• Both in anterior segment (front of eye)
• Filled with aqueous humour: colourless, with electrolytes, growth factors
• If drainage from the eye is blocked, fluid and pressure accumulates leading to glaucoma

Question 6

What is the vitreous chamber?

Answer 6

• Contains vitreous humour (80% of the volume contains 98% hydrogel, 2% collagen fibrils and hyaluronic acid
• Proteins, inorganic salts are present pH 7.5

Question 7

What is the lacrimal gland?

Answer 7

• The pre corneal tear film lubricates and protects the eye surface
• It comprises 3 layers: Superficial lipid layer, Central aqueous layer (electrolytes, proteins), inner mucus layer

Question 8

What is the pH of the tear film?

Answer 8

• Normal tears : pH = 7.3-7.7
• pH = lowest on awakening
• Buffer capacity of the tears is determined by bicarbonate ions, proteins
• Tears are more acidic in contact lens wearers. Alkaline in diseases

Question 9

What is the blinking reflux?

Answer 9

• Eye drops are administered, tear volume increased - this causes rapid blinking reflex. Essential for periodic reforming of tear film
• Stop high speed foreign bodies approaching eye.
• Blinking also activates a pumping mechanism for the draining of tears through the lacrimal drainage

Question 10

What are the different drug delivery routes for ocular?

Answer 10

Delivery via
- Topical Cornea: main route –> reach aqueous humor (front0
- Periocular delivery –> By pass the conjunctival and corneal
- Intravitreal delivery –> Directly reach the back of the eye

Question 11

What are the barriers to ocular delivery?

Answer 11

• The lacrimal (tear) system continually washes eyes
• Blinking causes fluid clearance
• Maximum dose volume 20-30ul

Question 12

What are the elimination routes of the ocular drug delivery?

Answer 12

• Elimination from aqueous humor into systemic uveoscleral circulation
• Outflow through trabecular meshwork and schlemm’s canal
• Eliminate from vitreous humor via diffusion into anterior chamber

Question 13

What do topical preparations need to be?

Answer 13

• Isotonic
• Close to neutral pH
• Stable
• Sterile
• Particle free
• Contain preservatives

Question 14

What are some advantages of ocular route?

Answer 14

• Easy for patient to administer on their own
• Provides rapid onset of action
• Avoid hepatic metabolism

Question 15

Why does ocular preparations need to be sterile?

Answer 15

• Ocular infections can lead to vision less
• Preservatives must be included in multi dose containers (prevent going off) - inhibit microbial growth

Question 16

Why does ocular preparations need to be isotonic?

Answer 16

• Salt concentrations within the lacrimal fluid determines its osmolarity
• Dry eye = hypertonic lacrimal fluid (dehydration)
• Hypotonic causes oedema
• Both cause eye irritation

Question 17

Why does ocular preparations need to have suitable pH?

Answer 17

• pH of normal tears is close to neutral
• Buffer capacity of lacrimal fluid is low. Extreme pH could damage
• Can affect aqueous solubility and membrane permeability

Question 18

Why does ocular preparations need to consider surface tensions?

Answer 18

• Ophthalmic solution with a lower surface tension can destabilise the tear film and disperse the lipid layer into droplets - can lead to evaporation and lead to irritation

Question 19

Why does ocular preparations need to consider viscosity?

Answer 19

• Increasing the viscosity can prolong their residence time thus enhance drug absorption
• Water soluble polymers used include: methylcellulose, polyethene glycol
• Too high: higher force required for blinking

Question 20

What are the different types of opthalmic preparations?

Answer 20

• Solutions: Simple designs/ bottle. Better dose uniformity. More rapidly cleared by drainage
• Ointments: Reduce clearance from eyes. Used for poorly soluble drugs. Both hydrophilic and hydrophobic bases. Cause blurring
• Gels: More better for water soluble drugs than ointments. Uses polymers
• Ion exchange resins: Drug is ionically bound to an ion exchange resin –> forms an insoluble complex. Drug released from complex with exchange of drug ions with ions in tear fluids

Question 21

What are the different eye treatments?

Answer 21

• Ocular Implants: Made from biodegradable/non- biodegradable polymers
• Biodegradable intravitreal implant : treatment in posterior segment
• Intracameral Implant: Reduce pressure in eye
• Intravitreal Injections: Injecting into vitreous cavity