Eyelids - two purposes: 1. Mechanical protection of globe 2. Creation of an optimum milieu for the cornea the techniques of keeping the formulation behind the lower eye lid 1. Kaufman et al have developed a new drug delivery system - collasomes.They combined collagen pieces or particles and a viscous vehicle that could be instilled beneath the eyelid, thereby simplifying application and reducing the blurring of vision. Collasomes were well tolerated; and because the collagen particles are suspended in carrier vehicles, they could be instilled safely and effecttively by patients in much the same fashion as drops or ointments. Kaufman HE, Steinemann TL, Lehman E, Thompson HW, Varnell ED, Jacob-Labarre T, et al. J Ocul Pharma 1994;10:17-27. 2.White Petrolatum and Mineral oil Lubricating Eye Ointment ADLUBE Eye ointment DOSAGE AND ADMINISTRATION For external use only. For topical Ocular administration. Wash your hands before use. Pull down the lower lid of the affected eye and apply a small amount (one fourth inch) of ointment to the inside of the eyelid. (Ideal for use at bedtime). There is no variation in dosage for age. To avoid contamination, do not touch tip of the container to any surface. Replace cap after using. 3. New treatment of dry eye: the effect of calcium ointment through eyelid skin delivery Kazuo Tsubota, Yu Monden, Yukiko Yagi, Eiki Goto, Shigeto Shimmura Br J Ophthalmol 1999;83:767-770 http://bjo.bmj.com/content/83/7/767.full.html#related-urls Article cited in: http://bjo.bmj.com/content/83/7/767.full.html#ref-list-1 4. The treatment for eye pads revealed, Aleksy Dobradin, MD www. Mesotherapyjournal.com 5. for ocular iontophoresis to lower eyelid see http://www.drugdeliverytech.com/ME2/dirmod.asp?sid=&nm=&type=Publishing&... http://www.faqs.org/patents/app/20090136598 6. Kimura C, Tojo K.Development of a stick-type transdermal eyelid delivery system of ketotifen fumarate for ophthalmic diseases.Performing your original search, drug delivery to eye lid, in PubMed will retrieve 19 records. Chem Pharm Bull (Tokyo). 2007 Jul;55(7):1002-5. 7. for implants and eyelid ssee http://www.drkaram.com/pdf/c23.pdf images of eyelid 8. The ophthalmic rod (OR) is a new drug delivery system, intended as an alternative to conventional therapy in ophthalmology. The rod is made of a nontoxic plastic. It is dipped into a drug solution which after drying forms a thin homogeneous coating. The OR is then packed and sterilized by gamma radiation. Pure drugs were used; no preservatives were included. To deliver the drug, the tip of the rod is introduced into the conjunctival sac and rubbed against the palpebral conjunctiva of the lower lid. ORs with tropicamide, oxybuprocaine HCl, pilocarpine HCl, and fluorescein sodium were used. ref Clinical Investigations The ophthalmic rod: A new ophthalmic drug delivery system I Safwat David Alani Graefe's Archive for Clinical and Experimental Ophthalmology Volume 228, Number 4, 297-301, DOI: 10.1007/BF00920050 achieving the sustained drug release for localized action To overcome these ( non Sustained release from solutions) problems various ophthalmic vehicles, such as suspensions, ointments, inserts, and aqueous gels, have been investigated to extend the ocular residence time of medications for topical application to the eye (Swarbrick and Boylan 1995; Ranade and Hollinger 1996). These ocular drug delivery systems offer some improvement over conventional liquid dosage forms but because of blurred vision (e.g., ointments) or lack of patient compliance (e.g., inserts), they have not been universally accepted. As a result, good ocular bioavailability following topical delivery of a drug to the eye remains a challenge yet to be resolved satisfactorily (Felt and Baeyens 1999; Chiou and Watanabe 1986). From the point of viewof patient acceptability, a liquid dosage form that can sustain drug release and remain in contact with the cornea of the eye for extended periods of time is ideal. thank you note : if you want more details pls send your mail id i will sent u the pdf files full as these open on subscription bases

general evaluation parameters of ocular drug delivery systems: relates to formulation clarity----free from foreign particles ---achieved by filtration. stability--in ophthalmic drug delivery stability refers to total product stability not just the chemical stability of a single component. estimation of PH, method of preparation, used additives, accelerated stability testing parameter. effect of buffer PH studies are required. tonicity-- iso osmotic pressure maintenance with lachrymal fluids viscosity--this will alter the residence time for a preparation hence studies are required relates to eye 1. ocular irritation test 2.trans corneal permeation study. other tests are depends on the type of formulation designed for extra matter pls refer Gerald hecht, chapter 89, opthalmic prepartions,Remington: The science and practice of pharmacy, 19 th edition 1995 page no 1570 print. thank you

The following characteristics are required to optimize ocular drug delivery systems. ? A good corneal penetration. ? A prolonged contact time with corneal tissue. ? Simplicity of installation for the patient. ? A non-irritative and comfortable form (the viscous solution should not provoke lachrymation and reflex blinking). ? Appropriate rheological properties and concentration of viscolyzer. 1. Keister JC, Cooper ER, Missel PJ, Lang JC and Hager DF. Limits on optimizing ocular drug delivery. J. Pharm. Sci. 1991; 80:50-53. 2. Masatoshi Tomi & Ken-ichi Hosoya; The role of blood--ocular barrier transporters in retinal drug disposition: an overview; Expert Opin. Drug Metab. Toxicol. (2010) 6(9):1111-1124

bioavailability of suspensions is high than solutions in ocular delivery: reason suspensions are dispersions of finely divided relatively insoluble drug substances in an aq. vehicle containing suitable suspending agents, Because of a tendency for the particles to be retained in the cul-de-sac, the contact time and duration of action of a suspension exceed those of a solution. Solutions * Convenience * Rapid pre-corneal elimination, * Loss of drug by drainage, * No sustained action. Suspensions * Patient compliance * Best for drugs with slow dissolution. * Drug properties decide performance * prolonged contact time. of all above considerations it is concluded that "bioavailability of suspensions is high than solutions in ocular delivery" 1. sheetu wadhwa, et al, nanocarriers in ocular drug delivery; An updated review, current pharmaceutical drug design, 2009,15,2724-2750. 2. Indu pal kaur,et al, ocular preparations:the formulation approach, drug development and industrial pharmacy, 28(5),473-493(2002). thank you

Effect of particle size in ocular drug delivery system 1. Tight junctions serve as a selective barrier for small molecules Example; glycerol, m.wt 92, 0.6nm and PEG200, 400 are able to penetrate via corneal route. 2. corneal stroma is a highly hydrophilic tissue contains water with open structure and allows drugs of up to 500000 size can diffuse in normal stroma 3. Drugs of about 20nm can diffuse across normal epithelium. 4. The limiting particle size for conjunctival penetration is between 20000 to 40000. Literature reported data for the effect of particle size in ocular drug delivery system 1. A study in Dr Kompella's lab showed that 200 nm and 2 mm particles were retained at the eriocular site of injection, 20 nm particles were rapidly cleared. AMRITE AC, KOMPELLA UB: Size-dependent disposition of nanoparticles and microparticles following subconjunctival administration. J. Pharm. Pharmacol. (2005) 57(12):1555-1563. 2. Kompella et al. 2006 determined whether topical ocular delivery of

1. specifications for this ODDS >General specifications includes (1)The formulation must be well tolerated, or non-irritating to the eye, (2) The formulation must be easy to administer, (3) The formulation ideally has an increased CsA residence time in the eye, (4) Systemic absorption of the formulation should be avoided because the toxic CsA concentration in blood is above 300 ng/ml, (5) The formulation should have a long shelf life and (6) The formulation should be easily manufactured. >Specifications for drug to be considered while dosing of ODDS Physico chemical nature Chemical category Activity profile ADR reports Stability profile >Specifications for formulation Buffer and PH Isotonicity Viscosity optimization >Specifications for application Type of dosage form site specification required Type of disease Read more: http://www.faqs.org/patents/app/20080299206#ixzz3ic2MPcKi Physician's desk reference for ophthalmology 2. role of polymers in this drug delivery system Role of polymers in ocular drug delivery, simply Drug related Physical * Improves the viscosity to the solution, * Slow drug drainage from site of application, * Solubility is of desire ness increasing or decreasing. * Accurate dosing Chemical * Improve drug stability Biological * High margin of safety * Reduced side effects * Reduced systemic absorption Patient * Better patient compliance resulting from reduced frequency of administration * Lower incidence of systemic side effects * Eliminating the potential for both under- and overdosing. * Patient compliance Formulation * Effective drug delivery, * Enhanced contact time of drug in cul-de-sac, * Sustained drug action Polymers simply * Affects release rate, mechanism and pharmacotherapy Ritu M GIlhotra, Polymeric Systems for Ocular Inserts, Latest Reviews, controlled drug delivery Ocular drug delivery system, 2009 Vol. 7 Issue 2 http://www.pharmainfo.net/reviews/polymeric-systems-ocular-inserts By Ritu M GIlhotra - 04/05/2009 in controlled drug delivery Ocular drug delivery system 3. polymers of certain show adr on eye and eye muscles example hayalouronic acid By Ritu M GIlhotra - 04/05/2009 in controlled drug delivery Ocular drug delivery system thank you

Effect of cubosomes on occular drug delivery system; cubosomes generally, Cubosomes are discrete, sub-micron, nanostructured particles of bicontinuous cubic liquid crystalline phase. Cubosomes possess the same microstructure as the parent cubic phase but have much larger specific surface area and their dispersions have much lower viscosity than the bulk cubic phase. The relative insolubility of cubic phase-forming lipid in water allows cubosomes to exist at almost any dilution level, as opposed to most liquid crystalline systems that transform into micelles at higher levels of dilution. As a result, cubosomes can be easily incorporated into product formulations. Effects on ocular delivery ? To reduce ocular irritancy and improve bio availability ? To improve its preocular retention and ocular bio availability. ? Solubility-bio availability and Slow release with Bio compatibility ? Liquid crystals as delivery systems should be able to improve the dissolution of poorly water-soluble drugs ? Thermodynamically stable Articles related 1. Novel vehicle based on cubosomes for ophthalmic delivery of flurbiprofen with low irritancy and high bio availability. Confirms low-irritant vehicle based on cubosomes might be a promising system for effective ocular drug delivery. Acta pharmacologica Sinica 1745-7254 990-998. http://www.bioportfolio.com/resources/pmarticle/35738/Novel-Vehicle-Base... 2. Li Gan, et al. self-assembled liquid crystalline nanoparticles (cubosomes) as an ophthalmic delivery system for dexamethasone (DEX) to improve its preocular retention and ocular bioavailability. Confirms, self-assembled liquid crystalline nanoparticles might represent a promising vehicle for effective ocular drug delivery. thank you

in consideration to the last part of my ppt i.e conclusion i have shown the triangle picture includes 1. principles----selectivity i.e for the selection of drug delivery techniques to eye we should follow theoretical aspects of eye including from anatomy to formulation ingredient part. 2. practices-----specificity i.e for the delivery of a drug to a specific part of eye we should do a lot of practices as compare to parenteral delivery techniques. 3. precautions---sensitivity i.e for the protection from various responses we should take precautions as the eye part is most sensitive. your question includes all the three parts upon my search according to the above it is concluding that biodegradable polymers can only used if use other it may lead to be fatal. thank you

first of all i would like to thank you for ur comment the eyes which i used are having connectivity for a particular slide if u found and mainly my aim is to provide good attention towards ocular drug delivery see the conclusion slide once for the same here the answer for the question "drug formulation to treat damaged macular area" When the macula is damaged, many daily activities such as driving, reading and recognizing faces become increasingly difficult as Sharp, clear, 'straight ahead' vision is processed by the macula, which is the central part of the retina. the damage also called Age related macular diseases AMD There are two forms of AMD: dry and wet The wet form of AMD can be treated with Lucentis(r) , Lucentis (ranibizumab injection), Macugen(r), * Macugen (pegaptanib sodium injection), Avastin (Bevacizumab), photodynamic therapy and laser photocoagulation. There is no specific treatment for dry macular degeneration; however, taking a specific high dose formula of vitamins and mineral supplements (AREDS formula) can significantly reduce the risk of progressing from intermediate dry macular degeneration to advanced or wet macular degeneration. for reference pls go through 1.http://www.ahaf.org/macular/questions/index.jsp?page=4 2.http://www.pharmainfo.net/reviews/age-related-macular-degeneration-amd 3.http://www.ahaf.org/macular/treatment/common/ 4.http://www.nei.nih.gov/health/maculardegen/armd_facts.asp thank you

thank you

answer Glaucoma is a progressive optic neuropathy with characteristic optic nerve head changes and decreases in retinal sensitivity that lead to visual loss. It has been said that there are about 14 million glaucoma patients in India, 67 million people worldwide and the disease ranks second as the basis for adventitious blindness. v- Adrenergic antagonists like Timolol maleate is mostly used. other agents like adrenergic agonists and parasympatheticomimetic agents were used as second line drugs. new drugs have been introduced for glaucoma treatment, like selective a- agonists (Brimonidine tartrate), carbonic anhydrase inhibitors CAI's (acetazolamide, dorzolamide) and prostaglandins broadening the therapeutic choices5-6. Pilocarpine preparations have been used. In the 1980s, beta-blockers were developed, reducing the administration frequency to twice a day. In 1999, prostaglandin-type ophthalmic preparations that require once-a-day administration. During the process of the development of these new ophthalmic agents, Ocusert(r), a sustained-release pilocarpine preparation that is inserted intra-ocularly only once a week, was designed and applied clinically. To treat pigmentary glaucoma with eyedrops such as Betagan, Timoptic, Optipranlol and Xalatan. These eyedrops have a relatively low incidence of side effects and are generally well-tolerated in younger patients. Doctors may also use medications such as Pilocar, and Ocusert, which are from a class of drugs called miotics. These medications cause the pupil to constrict (become smaller) and inhibit the iris from rubbing against the supporting fibers of the eye's lens, helping to prevent further release of pigment. However, miotics have side effects such as blurred vision which can limit their use. A number of ocular delivery systems lengthen the extent of drug action by enhancement of corneal absorption; these include suspension, soluble gels and emulsions, hydrophilic ocular inserts, ion-pair associations, liposomes, niosomes, nanosuspension, nanoparticles and prodrugs. Other delivery systems endow with a controlled release of drugs, thus avoiding the pulse-entry with which side-effects are associated. These systems can be based on any of several different mechanisms, and include both erodible and nonerodible matrices, wafers are used as treatmet for glaucoma literature reviews 1. Jain, S.P. et al., (2007), formulated and evaluated twice a day ocular inserts of acyclovir by melt extrusion method used for treatment of various ocular infections to improve patient compliance, using HPC as a thermoplastic polymer.the developed formulation overcome greasy nature of eye ointment, stable, non-irritant and provided release of the drug over a period of 10 hrs in vitro18. 2. Abhilash, A.S. et al., (2005), formulated ocular inserts of timolol maleate using different polymers at various concentrations. The polymers used were HPMC, EC, Eudragit RL 100 and RS 100. The ocuserts were evaluated for moisture absorption studies, moisture loss studies, thickness, weight uniformity, folding endurance, drug content, in vitro drug release studies and in vivo release studies19. 3. Horwath-Winter et al., (2005) treated human subjects suffering from dry eye syndrome with an antioxidant, iodide, using iontophoresis and demonstrated it to be a safe and well tolerated method of improving subjective and objective dry eye factors in patients with ocular surface disease20. 4. Eljarrat-Binstock et al., (2004) prepared solid hydrogels of hydroxyethyl methacrylate hydrogels (HEMA), crosslinked with ethylene glycol dimethacrylate, (EGDMA), and cross-linked arabinogalactan or dextrin to deliver gentamicin sulphate transscleraly. Transscleral iontophoretic treatment resulted in high concentrations of drugs in the posterior segments of the eye21. 5. Hayden et al., (2004) examined pharmacological logical distribution of carboplatin in New Zealand rabbits after its iontophoretic focal application (5.0 mA/cm2, 20 minutes). They found iontophoretc delivery of carboplatin did not produce any toxicity in eye over sub-conjunctival injection22. 6. Dandagi, P.M. et al., (2004), developed Ocular films of cromolyn sodium by solvent casting technique using PVA and sodium alginate with glycerin and PEG 400 as plasticizers. The prepared films were evaluated for thickness, percent elongation at break, tensile strength and drug content uniformity, in vitro release studies and in vivo release studies23. 7. Rao, V. and Shyale, S. (2004), formulated several ocular patches/inserts of norfloxacin-v-cyclodextrin in HPMC matrix. They studied the influence of rate controlling membranes made of ethyl cellulose (EC) alone and in combination with PVP K30 in different proportions on drug release kinetics. The films were evaluated for various physical characteristics. In vitro release studies were carried out in a fabricated flow through cell24. 8. Charoo, N.A. et al., (2003), developed reservoir type ocular inserts using sodium alginate containing ciprofloxacin hydrochloride as the core that was sandwiched between the Eudragit and/or polyvinyl acetate films. Ocular inserts were evaluated for in vitro release rate studies, microbial efficacy, in vivo release studies, efficacy against induced bacterial conjunctivitis in rabbit's eyes and stability studies. International Journal of Pharmaceutical Sciences Review and Research Page 25 Available online at www.globalresearchonline.net

answer Hurdles to ODDS can be divided in to 1. Anatomy of the eye 2. physico chemical properties of drug 3. Types of drugs deliver to site of eye 4. Abnormal conditions that is disease status 5. selectivity and sensitivity see the conclusion slide. 1. principles----selectivity i.e for the selection of drug delivery techniques to eye we should follow theoretical aspects of eye including from anatomy to formulation ingredient part. 2. practices-----specificity i.e for the delivery of a drug to a specific part of eye we should do a lot of practices as compare to parenteral delivery techniques. 3. precautions---sensitivity i.e for the protection from various responses we should take precautions as the eye part is most sensitive.

answer ocular implants -- modern advanced technique in ODDS (controlled release) used to deliver drug to vitreoretinal tissue Diseases treated by this systems 1. cytomegalovirus retinitis CMV 2. AIDS 3. Macular oedema 4. Diabetic retinopathy 5. branch retinovirus occlusion. etc. avilabilty in the shapes of 1. rods 2. plugs 3. discs 4. Sheets types 1. Non biodegradable 2. Biodegradable designed for 1. increase in selectivity of drug action by zero order 2. decrease in frequency of administration drug nature for design 1. hydrophilic 2. Hydrophobic general categories of drugs 1. anti viral 2. anti biotics 3. anti glaucoma agents 4. anti cancer etc. implantable drugs 1. Doxirubicin 2. Adriamycin 3. ganciclovir 4. piolcarpin etc. 1. Yasuhiko Tabata, Drug delivery from ocular implants,Expert Opin. Drug Deliv. (2006) 3(2) 2. Karthikeyan, et al.: An overview on ocular inserts, Asian Journal of Pharmaceutics - October-December 2008

there are somany drug formulations to full fill your question example include New drug delivery systems (NDDS), for the anterior segment of the eye includes (a) Ocular inserts , corneal shields and contact lenses , which provides controlled delivery of drug to the eye, (b) In situ gelling systems , which provides ease of administration as drops and gets converted to gel form in the eye, thereby providing some sustained effect of drug in the eye, (c) Vesicular systems , offers advantages of targeted delivery, bio-compatibility and freedom from blurring of vision, (d) Mucoadhesive systems provides better retention in the eye, (e) Prodrugs (f) Penetration enhancers , (g) Lyophilized carrier systems , (h) Particulates , (i) Submicron Emulsions , (j) Iontophoresis , (k) Dendrimers for exampls eye ointments Onset of action of ADLUBE (petrolatum) begins within 10 minutes of application, peak at 30 minutes, while concentrations at 6 hours were still at levels near 20% of peak concentration.Therefore ADLUBE (petrolatum) remains in the eye for a longer time. New treatment of dry eye: the effect of calcium ointment through eyelid skin delivery thank you

no drug is released into the market if it causes blurring the formulations corresponds to your question mentioned in 16,17,45 slides ok thank you

explanation: Lacrimal glands contain a large amount of glands which express secretory proteins as well as phase I and phase II biotransformation enzymes. In this review the metabolic activation, covalent binding and toxicity of chemicals will occur. The activity of the enzymes: lactate dehydrogenase (LDH), pyruvate kinase (PK), malate dehydrogenase (MDH), amylase (AM) and lysozyme (LZM) was studied during lacrimation in healthy persons. The activity of the enzymes of energy-producing metabolism: LDH, PK and MDH fluctuated in parallel with each other. Fluctuations in AM activity showed no correlation with other enzymes and LZM concentrations remained rather constant. The origin of these enzymes in the process of lacrimal secretion is discussed. for example Ascorbic acid is thought to contribute to protection against the potentially damaging effects of radiation, oxygen toxicity, and abrasion in the eye. The anterior surface of the cornea is particularly subject to insult from each threat. We considered the possibility that the lacrimal gland of pigs has transport and/or metabolic capability to sequester the reduced or oxidized form of ascorbic acid and prepare it for secretion in the tears. for further details pls go through ref:- 1. N. J. van Haeringen, Enzymatic studies in lacrimal secretion, Experimental Eye Research Volume 19, Issue 2, August 1974, Pages 135-139. 2. Dreyer R, Rose RC, Lacrimal gland uptake and metabolism of ascorbic acid, Proc Soc Exp Biol Med. 1993 Feb;202(2):212-6

yes retinal drug delivery is useful you can refer the slides of retinal drug delivery

In the past, rejuvenating the eye meant the need for invasive surgical options. Although these may be necessary in advanced cases, invasive surgical procedures have become second-line treatment options since the advent of topical therapies and minimally invasive procedures including botulinum toxin, dermal filler injections, laser, chemical peels, laser skin resurfacing, microdermabration and intense pulsed light photorejuvenation. Studies indicate that patients prefer minimally invasive procedures over traditional surgical options, likely related to their efficacy in achieving good outcomes while minimizing recovery times and having lower side effect profiles. With the continued seemingly exponential growth and ever increasing experience in minimally invasive procedures to enhance the eyes, a well-versed dermatologic surgeon has an exciting future in enhancing the beauty of eyes. http://www.thefreelibrary.com/Enhancing+the+eyes%3A+use+of+minimally+inv...

every drug delivery systems have the kinetics drug in tear fluid-----> -------> ocular absorption ---1. corneal route 2.aqueous humor 3.ocular tissues-- -------> systemic absorption 1. conjunctiva 2. lacrimal --------------------------- elimination thank you s.p vyas,controlled drug delivery: concepts and advances, ocular drug delivery, page no. 389

Here is the explanation for your questions: Tonicity Role 1. pH Values for Tissue Fluids Fluid PH Aqueous humor 7.2 Blood, arterial 7.4 Blood, ... 5.3 Lacrimal fluid (tears) 7.4 the role of isotonicity: tonicity refers to the osmotic pressure exerted by salts in aq. solutions if not means the problems such as irritation to Blindness will occur as the eye is the most sensitive part towards the change in PH Isotonicity explanation 2. isotonic means that the solution is neither hypotonic, nor hypertonic. Thus, it won't make water inside your cells go out, and the water from the solution won't go to inside of your cells. This means that the solution contains about the same amount of dissolved substances as cytoplasm of your cells. Is lacrimal fluid is isotonic with blood 3. Lacrimal fluid is isotonic with blood,having an isotonicity value corresponding to that of a 0.9%sodium chloride solution. Tolerable tonicity for eye 4.Ideally,an ophthalmic solution should have this isotonicity value;but the eye can tolerate isotonicity values as low as that of a 0.6%sodium chloride solution and as high as that of a 2.0%sodium chloride solution without marked discomfort. ref: Gerald Hecht,PhD, opthalmic prepartions, Remington: The science and practice of pharmacy,Vol II,chapter 36, page no. 1569-1571, 19th edition,Mack publishing company, 1995, print. thank you

your question is related to slide no. 38 cross linker in Hybrid nano particles and it is related to Hybrid nano particles --- chitosan purpose of usage of cross linker in Hybrid nano particles 1. deliver drugs in continuation fashion 2. minimize drug degradation 3. prevent harmful effects 4. increase drug bioavilability 5. increase the fraction of the drug accumulated in the site of action. 6. enhanced drug permeation recent works Hybrid chitosan nanoparticles s.no. ---type------biomolecule-----relevant features 1.-----Liposomes----FITC-BSA-------Demonstrated interaction with the ocular mucosa, showing a pattern that is ---------------------------------dependent on the lipidic composition, and a good ocular tolerance. 2.-----Carbopol-----Pilocarpine----Sustained release and prolonged therapeutic effect of drug-loaded NP when ---------------------------------compared with eye drops or pilocarpine-loaded into gels and liposomes 3.-Poly(acrylic acid)-Pilocarpine--Sustained release and prolonged therapeutic effect versus pilocarpine eye drops. 4.--Hyaluronan------pDNA-----------Important interaction of the NP with the ocular epithelia, leading to the ---------------------------------transfection of the tissues and expression of the reporter protein for up to 1 ---------------------------------week, without causing any damage or inflammation to the ocular structures Chitosan is a cationic polysaccharide able to gel when in contact with specific multivalent polyanions, such as sodium tripolyphosphate (TPP)generally used as cross linker for further details see ref:- 1.Paolicelli, de la Fuente, Sanchez, Seijo & Alonso, Chitosan nanoparticles for drug delivery to the eye, Expert Opin. Drug Deliv. (2009) 6(3) 2.Nicolas Duceppe et al, Advances in using Chitosan-based nanoparticles for invitro and in vivo drug and gene delivery, Expert Opin. Drug Deliv. (2010) 7(10): 1191-1207. thank you