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NEW ERA OF OCULAR THERAPY


About Authors:
Richa Thakur*, Gaurav Swami, M.S. Rathore, A.K. Sharma
CT Institute of Pharmaceutical Sciences,
Jalandhar, Punjab, India

*thakur.richa89@gmail.com

ABSTRACT
The anatomy, physiology and biochemistry of the eye render this organ exquisitely impervious to foreign substances. The main challenge to the formulator is to circumvent the protective barriers of the eye without causing permanent tissue damage. The newly developed particulate and vesicular systems like liposomes, pharmacosomes and discosomes are useful in delivering the drug for a longer extent and helpful in reaching the systemic circulation. The most recent advancements of the ocular delivery systems provide the delivery of the genes and proteins to the internal structures which were once inaccessible and thus are of great importance in treating the diseases which are caused due to genetic mutation, failure in normal homeostasis, malignancy but also maintaining the physiological function of eye. The review focuses on the developments achieved in this mode of delivery of the drugs along with the pros and cons associated with greater focus on the advanced delivery systems.

Reference Id: PHARMATUTOR-ART-1309

INTRODUCTION
Ocular drug delivery is one of the most fascinating and challenging errands facing the Pharmaceutical researchers. One of the major barriers of ocular medication is to obtain and maintain a therapeutic level at the site of action for prolonged period of time. The anatomy, physiology and biochemistry of the eye render this organ exquisitely impervious to foreign substances. The challenging to the formulator is to circumvent the protective barriers of the eye without causing permanent tissue damage. The development of newer, more sensitive diagnostic techniques and therapeutic agents renders urgency to the development of maximum successful and advanced ocular drug delivery systems1.

In the earlier period, drug delivery to the eye has been limited to topical application, redistribution into the eye following systemic administration or directs intraocular/periocular injections. Conventional drug delivery systems; which include solutions, suspensions, gels, ointments and inserts, suffer with the problems such as poor drainage of instilled solutions, tear turnover, poor corneal permeability, nasolacrimal drainage, systemic absorption and blurred vision2.

Nanocarrier based approaches seem to be most attracting and are extensively investigated presently. it has been reported that particulate delivery system such as microspheres and nanoparticles; vesicular carriers like liposomes, niosomes, pharmacosomes and discomes improved the pharmacokinetic and pharmacodynamic properties of various types of drug molecules3.

Emerging new controlled drug delivery systems such as dendrimers, ocusert, micro emulsions, muco-adhesive polymers, hydro gels, iontophoresis, collagen shield, prodrug approaches have been developed for this purpose. These novel systems offer manifold advantages over conventional systems as they increase the efficiency of drug delivery by improving the release profile and also reduce drug toxicity.
The rapid progress of the biosciences opens new possibilities to meet the needs of the posterior segment treatments. The examples include the antisense and aptamer drugs for the treatment of cytomegalovirus (CMV) retinitis and age-related macular degeneration, respectively, and the monoclonal antibodies for the treatment of the age-related macular degeneration. Other new approaches for the treatment of macular degeneration include intravitreal small interfering RNA (siRNA) and inherited retinal degenerations involve gene therapy. This review article briefly covers general outline with examples of various conventional and recent past time formulations for ophthalmic drug delivery. It also provides the limitations of conventional delivery with a view to find modern approaches like vesicular systems, nanotechnology, stem cell therapy as well as gene therapy, oligonucleotide and aptamer therapy, protein and peptide delivery, ribozyme therapy for treatment of various ocular diseases.

DISORDERS OF EYE
Human eye, from anterior to posterior segment, consists of vitreous humor, ciliary body, lens, cornea, conjunctiva, aqueous humor, iris, choroid, retina and sclera. The shape of human eye is spherical with a diameter of nearly 23mm. It has complicated arrays of delicate mechanisms behind its visible portions which work in union to transmit an image of the seen object to the brain. The extent and quality of light entering into the eye is regulated and filtered by pupil, which dilates and contracts as per requirement. Functionally structural components of the eyeball can be divided into three layers: (i) outer most coat comprises of the clear, transparent cornea and white, opaque sclera; (ii) middle layer hold the iris anteriorly, choroid posteriorly, and ciliary body as intermediate part; (iii) inner layer possess retina, which is an extension of the central nervous system

The fluid systems viz the aqueous humor and vitreous humor plays an important and decisive role in maintenance of homeostasis of the eye. Cornea, an optically transparent tissue having diameter of 11.7 mm and thickness 0.5-0.7 mm, performs as the principal refractive element of the eye. The common eye disorders include age-related macular degeneration, diabetic macular edema, cataract, proliferative vitreoretinopathy, uveitis, cytomegalovirus and glaucoma4-6. The detailed discussion on ocular disorders is beyond the scope of this manuscript. However a brief overview has been presented in Fig. (1).


Figure 1Common ocular disorders associated with various tissues of eyes57

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