OCCULAR DRUG DELIVERY SYSTEM: A REVIEW

1. OCCULAR DRUG DELIVERY SYSTEM: AN OVERVIEW
By,
Souvik Chattopadhyay, M.Pharm, 1st Year
Department of Pharmaceutics
Himalayan Pharmacy Institute
Majhitar, East Sikkim, India-737136

2. This presentation will give you an idea about several
methods of delivery system of drug in those
unhappy eyes.
Eye is one of the most complex organ with very
challenging anatomy for the Healthcare
Professionals. Like any other organ, eye also suffers
from several diseases or injury. As a pharmaceutics
person our duty to design and discuss about various
approaches to send the drugs in targeted eye-site.

3. Anatomy of
an eye
1. Choroid: A thin membrane that consists largely of blood vessels that nourishes the outer part of
the retina.
2. Iris: A thin circular disc that gives our eyes their “color” and acts like the diaphragm of a camera.
3. Pupil: The center opening or circular aperture of the iris that appears black when viewing one’s
eyes. The pupil enlarges when a person is in dim light and constricts (gets smaller) in bright light.
4. Conjunctiva: it serves as a protective layer against allergens and infective agents.
5. Cornea: The anterior clear part of the eye. It is the first clear “window” through which the light
enters the eye.
6. Lens: This is a biconvex structure located between the pupil and vitreous.
7. Retina: A thin multi-layered sensory tissue that lines the back of the eye. The retina contains two
types of photoreceptors (neurons) called rods and cones.

4. MECHANISM OF
OCULAR ABSORPTION

5. Non- corneal absorption:
Penetration across sclera &
conjunctiva into intra ocular
tissues.
Non-productive: because
penetrated drug is absorbed by
general circulation.
Corneal absorption: Outer
epithelium: rate limiting barrier,
with pore size 60a, only access
to small ionic and lipophilic
molecules.
Trans cellular transport:
transport between corneal
epithelium and stroma.

6. ROUTES OF OCULAR DRUG DELIVERY
There are several possible routes of drug delivery into the ocular tissues.
The selection of the route of administration depends primarily on the
target tissue.
• Topical route: Typically topical ocular drug administration is
accomplished by eye drops, but they have only a short contact time on the
eye surface. The contact, and thereby duration of drug action, can be
prolonged by formulation design (e.g.m gels, gelifying formulations,
ointments, and inserts).
• Subconjunctival administration: Traditionally subconjunctival injections
have been used to deliver drugs at increased levels to the uvea. Currently
this mode of drug delivery has gained new momentum for various reasons.
The progress in materials sciences and pharmaceutical formulation have
provided new exciting possibilities to develop controlled release
formulations to deliver drugs to the posterior segment and to guide the
healing process after surgery.
• Intravitreal administration: Direct drug administration into the vitreous
offers distinct advantage of more straightforward access to the vitreous
and retina. It should be noted; however that delivery from the vitreous to
the choroid is more complicated due to the hindrance by the RPE (Retinal
Pigment Epithelium) barrier. Small molecules are able to diffuse rapidly in
the vitreous but the mobility of large molecules, particularly positively
charged, is restricted.

7. What is Drug
Delivery System?

8. Drug delivery refers to approaches, formulations, technologies, and systems for transporting a
pharmaceutical compound in the body as needed to safely achieve its desired therapeutic
effect. It may involve scientific site-targeting within the body, or it might involve facilitating
systemic pharmacokinetics; in any case, it is typically concerned with both quantity and
duration of drug presence.
What is Ocular Drug Delivery System?
Ocular administration of drug is primarily associated with the need to treat ophthalmic diseases. The eye is a complex
organ with an unique anatomy and physiology. The drug delivery system which is associated with the drug delivery
towards the ophthalmic route are specified by this drug delivery system.

9. Challenges

10. Drug loss from the ocular surface After instillation,
the flow of lacrimal fluid removes instilled
compounds from the surface of eye. Even though the
lacrimal turnover rate is only about 1 µl/min the
excess volume of the instilled fluid is flown to the
nasolacrimal duct rapidly in a couple of minutes.
Lacrimal fluid-eye barriers Corneal epithelium limits drug
absorption from the lacrimal fluid into the eye. The
corneal epithelial cells form tight junctions that limit the
paracellular drug permeation. Therefore, lipophilic drugs
have typically at least an order of magnitude higher
permeability in the cornea than the hydrophilic drugs. In
general, the conjunctiva is leakier
Blood-ocular barriers The eye is protected
from the xenobiotics in the blood stream
by blood-ocular barriers. These barriers
have two parts: blood-aqueous barrier and
blood-retina barrier.

11. OPTHALMIC DOSAGE FORM FOR OVERCOMING BARRIERS

13. NOVEL
APPROACHES

15. • Nanomicelles: Nanomicelles are the most commonly used carrier systems to formulate therapeutic agents in to clear aqueous
solutions. In general, these nanomicelles are made with amphiphilic molecules. These molecules may be surfactant or polymeric in
nature.The have high drug encapsulation capability, ease of preparation, small size, and hydrophilic nanomicellar corona generating
aqueous solution. In addition, micellar formulation can enhance the bioavailability of the therapeutic drugs in ocular tissues,
suggesting better therapeutic outcomes.
• Nanoparticles: Nanoparticles are colloidal carriers with a size range of 10 to 1000 nm. For ophthalmic delivery, nanoparticles are
generally composed of lipids, proteins, natural or synthetic polymers such as albumin, sodium alginate, chitosan, poly (lactide-co-
glycolide) (PLGA), polylactic acid (PLA) and polycaprolactone. Nanoparticles represents a promising candidate for ocular drug delivery
because of small size leading to low irritation and sustained release property avoiding frequent administration.
• Nanosuspensions: Nanosuspensions are colloidal dispersion of submicron drug particles stabilized by polymer(s) or surfactant(s). It is
emerged as promising strategy for delivery of hydrophobic drugs. For ocular delivery, it provides several advantages such as
sterilization, ease of eye drop formulation, less irritation, increase precorneal residence time and enhancement in ocular bioavailability
of drugs which are insoluble in tear fluid.
• Liposomes: Liposomes are lipid vesicles with one or more phospholipid bilayers enclosing an aqueous core . The size of liposomes
usually range from 0.08 to 10.00 μm.
• Dendrimers: Dendrimers are characterized as nanosized, highly branched, star shaped polymeric systems. These branched polymeric
systems are available in different molecular weights with terminal end amine, hydroxyl or carboxyl functional group. The terminal
functional group may be utilized to conjugate targeting moieties. Dendrimers are being employed as carrier systems in drug delivery.

16. • Contact lens: Contact lenses are thin, and curved shape plastic disks which are designed to cover the cornea. After
application, contact lens adheres to the film of tears over the cornea due to the surface tension. Drug loaded contact lens
have been developed for ocular delivery of numerous drugs such as β-blockers, antihistamines and antimicrobials.
• Intraocular implants : They are specifically designed to provide localized controlled drug release over a extended period.
These devices help in circumventing multiple intraocular injections and associated complications. Usually for drug delivery
to posterior ocular tissues, implants are placed intravitreally by making incision through minor surgery at pars plana which
is located posterior to the lens and anterior to the retina. Though implantation is invasive procedure, these devices are
gaining interest due to their associated advantages such as sustained drug release, local drug release to diseased ocular
tissues in therapeutic levels, reduced side effects and ability to circumvent blood retina barrier. Several implantable
devices have been developed for ocular drug delivery especially for the treatment of chronic vitreoretinal diseases.
• Microneedles:Microneedle based technique is an emerging and minimally invasive mode of drug delivery to posterior
ocular tissues. This technique may provide efficient treatment strategy for vision threatening posterior ocular diseases
such as age-related macular degeneration, diabetic retinopathy and posterior uveitis. This new microneedle-based
administration strategy may reduce the risk and complications associated with intravitreal injections such as retinal
detachment, hemorrhage, cataract, endophthalmitis and pseudoendophthalmitis. Moreover, this strategy may help to
circumvent blood retinal barrier and deliver therapeutic drug levels to retina/choroid. Microneedles are custom designed
to penetrate only hundreds of microns into sclera, so that damage to deeper ocular tissues may be avoided

17. • CONCLUSION
• Drug delivery to targeted ocular tissues has
been a major challenge to ocular scientist, for
decades. Administration of drug solutions as
topical drop with conventional formulations was
associated with certain drawbacks which initiated
the introduction of different carrier systems for
ocular delivery. Tremendous efforts are being put
into ocular research toward the development of
safe and patient compliant novel drug delivery
strategies. Currently, researchers are thriving
hard to improve in vivo performance of
conventional formulations. On the other hand,
advent of nanotechnology, new techniques,
devices and their applications in drug delivery is
developing immense interest to ocular scientists.

18. REFERENCES
1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4289909/
2. https://www.researchgate.net/publication/225897418_OCULAR_DRUG_DELIVERY_SYSTEM_-_A_REVIEW
3. http://ijpsr.com/bft-article/ocular-drug-delivery-system-an-overview/?view=fulltext
4. https://www.liebertpub.com/doi/abs/10.1089/jop.1986.2.67
5. https://www.sciencedirect.com/science/article/pii/S0378517303005179
6. https://www.sciencedirect.com/science/article/pii/0169409X9500012V
7. https://en.wikipedia.org/wiki/Drug_delivery
8. https://www.researchgate.net/publication/233422329_Recent_advances_in_ocular_drug_delivery

20. Q & A SESSION