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Ocuserts: A novel ocular-drug delivery method: An update
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DOI: 10.30574/wjbphs.2023.13.1.0025
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Ocuserts: A novel ocular-drug delivery method: An update
Navneet Nagpal 1, Sukhmanpreet Singh 2, Prince Ahad Mir 3, Mandeep Singh Chhina 2, Manisha Arora 3,
Deepinder Jeet Kaur 2, Rahul Kumar 4, Abhay Sharma 3, Priyanka 3 and Nishant Kumar 3, *
1 Lala Lajpat Rai College of Pharmacy, PS Sadar, Moga, Punjab 142001, India.
2 Amritsar Group of Colleges, Pharmacy department, 12 KM stone, Amritsar Jalandhar GT Road Amritsar 143001, India.
3 Khalsa College of Pharmacy GT road Amritsar, Punjab 143002, India.
4 Katyayani college of education meerut-Karnal Highway, Meerut, Uttar Pradesh 250241, India.
World Journal of Biology Pharmacy and Health Sciences, 2023, 13(01), 470–477
Publication history: Received on 03 December 2022; revised on 14 January 2023; accepted on 17 January 2023
Article DOI: https://doi.org/10.30574/wjbphs.2023.13.1.0025
Abstract
Ocuserts are sterile ocular preparations that may follow a controlled release technique to extend medication residence
duration and reduce nasolacrimal discharge. The goal of the ocuserts is to improve medication contact with conjunctiva
tissue to sustain consistent dosage release. Uniform ocular medication levels decrease systemic side effects, minimizes
dose, boosting patient compliance. Ocuserts are prepared by solvent casting, glass substrate, and melt extrusion
technique. Modified ocuserts may be used to obtain desired medication concentration for a given time at the site of
action. Extended corneal contact duration is the major success in ocular medication delivery. Non-conventional
approaches like liposome, microsphere, prodrug, etc. may improve ocular drug delivery systems and reduce side effects.
Diffusion, osmosis, or bioerosion are the various methods that govern drug release from ocusert.
Keywords: Ocuserts; Eye; Ophthalmic preparation; Conjunctiva; Corneal contact
1. Introduction
The eye poses unique challenges in drug delivery. Ophthalmic medication distribution is the most fascinating and
difficult task[1]. Eye is impervious to numerous foreign materials because to its anatomy, physiology, and biochemistry.
The key problem for pharmaceutical experts is to penetrate ocular defences without substantial tissue damage [2].
Ophthalmic preparation is employed for local therapy rather than systemic treatment owing to the high concentration
of medications in the eye's blood[3]. Formulating novel and enhanced ocular medication delivery systems is important
for developing breakthrough diagnostic and treatment procedures[4, 5]. Ocular disease treatment is tough for scientists
owing to the kind of disease and obstacles on the ocular surface, notably in the posterior area. In recent years,
researchers have tried to improve ocular medication absorption by varying viscosity and adding polymers [6]. Due to
limited ocular bioavailability and frequent eye drop instillation, medication persistence is crucial. A large and
inconsistent dose of medicine is given, creating local and systemic adverse effects. For current ocular medication
delivery methods to be improved, dosage formulations with an extended time period and controlled administration are
required[7].
2. Human eye
Human eye is a composite organ that exhibits anatomical wonders. Drug delivery to the eye is tricky owing to tissue
structure and corneal penetrability. The administered drug gets rapidly removed from the eye due to the defensive
function of the eyelids and lachrymal system.[8] To avoid this, the material should be tiny and compatible with the skin.
* Corresponding author: Nishant Kumar
Copyright © 2023 Author(s) retain the copyright of this article. This article is published under the terms of the Creative Commons Attribution Liscense 4.0.
World Journal of Biology Pharmacy and Health Sciences, 2023, 13(01), 470–477
The eye is a sphere with a spherical component within another encircled within the little front sphere[9]. Various ocular
barriers must be overcome to get a therapeutic medication concentration in the eye through local or systemic pathways.
The blood ocular barrier (BOB) controls the influx and outflow of aqueous humour, regulating its composition and eye
pressure. Physiological and anatomical barriers hinder ophthalmic drug administration.[10-13]
Physiological barriers, which include,
o Tear turn over
o Naso lachrymal drainage
o Blinking action of the eye
Anatomical barriers, which include static and dynamic barriers, are responsible for restricting drugs into the
anterior portion of the eye. Static barriers include,
o Corneal epithelium
o Stroma
o Blood aqueous barrier (BAB)
Dynamic barriers include,
o Conjunctival blood
o Lymph flow
o Tear drainage [14]
2.1. Absorption of drugs in the eye
Most ocular drugs are topically applied to the fornix. Corneal and non-corneal are the two pathways to absorb
medications from cul-de-sac. Most medication absorption occurs via the cornea and aqueous fluid. Non-corneal
absorption includes the sclera and conjunctiva, however this pathway limits medication entry into intraocular tissues.
Drugs enter the cornea through transcellular and paracellular pathways. Paracellular transit is a pathway for lipophobic
drugs across intercellular gaps. The transcellular route includes a channel for lipophilic drugs. Passive diffusion along
the concentration gradient permeates both pathways.[15]
2.2. Ophthalmic preparations
Ophthalmic preparations are sterile liquid, semi-solid, or solid treatments for the conjunctiva or eyelids [16].
Ophthalmic medications cure corneal ulcers, conjunctivitis, bacterial keratitis, and other eye diseases. Eyedrops, suspe
nsions, ointments, etc. are common ocular medication delivery systems. These standard dose forms are extensively us
ed but have drawbacks include shorter duration of action, lower corneal contact time, poor absorption, frequent dosin
g, and patient noncompliance. Ophthalmic medication therapy like gels, gelforming solutions, ocuserts, intravitreal inj
ections, and implants are controlled dosage forms[17].
Easy-to-administer eye drops are most often given. The primary disadvantage is the rapid and widespread removal of
the medication from the eye, requiring more frequent administration. Very little medication penetrates the cornea and
reaches ocular tissue[18, 19].
Modern medication delivery technologies like ocuserts manage drug release to alleviate these drawbacks with better
corneal penetration and improved drug contact time[20]. Reservoir-based systems consist of micro-structured and have
several benefits. These technologies may be utilized outside or within the body to manage dosage form. It improve
dosage form stability and distribution time. It can aid with zero-order medication delivery vs sustained-release.
Progress in reservoir medication delivery assisted pinpoint delivery [21].
3. Ocuserts
Ocuserts are sterile controlled-release formulations that extend medication residence duration and prevent
nasolacrimal leakage[22]. They are sterile, solid or semisolid formulations designed for ocular delivery. They're drug-
filled polymers. Ocuserts are put in the eye's lower cul-de-sac. Ocuserts enhance medication contact time with
conjunctival tissue to sustain continuous dosage release[23]. Ocusert is a drug reservoir sandwiched between two
microporous membrane sheets. Lachrymal fluid penetrates the membrane, controlling medication release. Internal
pressure is high enough to force medication from the reservoir. Diffusion controls medication delivery rate [24]. Ocusert
is a drug reservoir sandwiched between two microporous membrane sheets. Lachrymal fluid penetrates the membrane,
controlling medication release. Internal pressure is high enough to force medication from the reservoir. Diffusion
controls medication delivery rate[25].
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World Journal of Biology Pharmacy and Health Sciences, 2023, 13(01), 470–477
Ocuserts extend medication duration, improve bioavailability, and decrease dosage frequency, improving patient
compliance. The regulated release of the medication allows for ocular administration. Ocuserts save time for doctors
and patients.[26]
3.1. Advantages of ocuserts
Various advantages of ocuserts are as follows -
Increased contact time with the ocular surface can be obtained and hence bioavailability is also increased
Sustained and controlled drug delivery can be achieved
Due to extended drug release, better efficacy is obtained
Accurate dosing can be done
Less systemic side effects
Less frequent dosing is required unlike conventional dosage form
Overcoming the effects of repeated administration of a conventional dosage form is possible
Increased comfort and patient compliance
Handling is easy
Vision and oxygen permeability are not interfered
Reproducible release kinetics
Sterile preparation
A stable drug delivery system and better therapeutic performance of the formulation can be obtained
Due to the lack of water in the formulation, shelf life is improved when compared to aqueous solutions.
Barriers like drainage, lacrimation, conjunctival absorption, etc. can be avoided. [3, 27]
3.2. Disadvantages of ocuserts
Various disadvantages of ocuserts are as follows -
Accidental loss of ocusert can occur while sleeping or rubbing the eyes
For a while, the patient feels like there is some foreign body in their eye
Removal of ocusert can get difficult due to unnecessary relocation of the ocusert to the upper fornix of the eye
Not as easy to administer the ocuserts in the eye and also difficult removal in case of insoluble ocuserts
Dislocation of the ocusert in front of the pupil can occur
Ocusert can twist in the eye which can decrease the rate of drug delivery
Leakage can happen[4, 28, 29]
3.3. Classification of ocuserts
According to the solubility, ocuserts can be classified into different types. [6]
Figure 1 Classification of ocuserts
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World Journal of Biology Pharmacy and Health Sciences, 2023, 13(01), 470–477
3.3.1. Insoluble ocuserts
This type of delivery system gives drugs at a controlled rate and in different ways, but the delivery system needs to be
removed once it’s empty.
Insoluble ocuserts are divided into 2 categories:
Reservoir system
In this system, diffusion or osmosis release drugs. It may be colloid, gel, semisolid, liquid, solid matrix, or carrier.
Diffusional inserts - In this form, drug release is diffusional. The ocular insert is a permeable membrane medication
delivery method.
Osmotic inserts - These consist of a centre component surrounded by a part and may be classed into two groups:
Type 1 - The innermost section is a drug reservoir surrounded by polymer, which may contain osmotic solute.
Semi-permeable, insoluble polymeric membrane forms the periphery. Due to osmotic pressure, matrix
apertures leak drugs.
Type 2 – This kind has a two-compartment centre. One compartment contains medicine, the other osmotic
solute. A semipermeable membrane surrounds the solute compartment. The medication compartment is
impermeable.
Matrix systems
This system includes contacts and insoluble ophthalmic equipment. A 3-D matrix holds water, aqueous preparations, or
solids. This system contains hydrophilic or hydrophobic cross-linked polymers e.g. vision correction contact lenses. This
mechanism corrects eyesight while releasing medicines..[3]
3.3.2. Soluble ocuserts
Soluble inserts are homogenous polymeric ocuserts that gradually dissolve and release the medicine in the eye.
Hydrolysis of enzymes or chemicals causes dissolution and erosion. Owing to tear fluid penetration, ocusert's drug
content is released due to swelling and chain relaxation, resulting in drug diffusion. It's not necessary to remove it after
administration.[4, 30]
According to the type of polymer source, they can be further divided into two groups:
Natural polymers
Collagen is utilised to manufacture soluble ophthalmic inserts. Ocusert is soaked, dried, then rehydrated before
application. The amount of medicine in ocusert depends on the preparation's concentration, soaking time, and binding
agent concentration. The medication is released when the collagen dissolves. [6]
Synthetic and semi-synthetic polymers
Ophthalmic inserts are made from synthetic and semisynthetic materials. Cellulose derivatives and synthetic polymers
like polyvinyl alcohol may be used to make it. Coating the ocusert with eudragit might slow release. [6]
3.3.3. Bio-erodible ocuserts
Bio-erodible ocuserts employ cross-linked gelatin and polyester derivatives. These polymers' key benefit is that their
final structure may be changed during manufacture or by adding anionic or cationic surfactants to limit erosion.[30]They
include :
Soluble ophthalmic drug insert (SODI)
SODI is a small oval wafer, which is made to use in weightless conditions as eye drops cannot be used in these
conditions.[31]
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World Journal of Biology Pharmacy and Health Sciences, 2023, 13(01), 470–477
Collagen shields
Collagen is found bone, tendons, ligaments, and skin. It makes about 25% of mammalian body proteins. This intestine
collagen protein has several biological uses, including catgut suturing. This insertion must be applied with anaesthetized
cornea and blunt forceps..[32]
4. Mechanism of drug release
Drug from the ocuserts can be released by one of the following methods depending upon the type of ocusert:
Diffusion [33]
Osmosis [34]
Bioerosion[33]
5. Formulation methods of ocuserts
5.1. Solvent casting method
Due of its cost-effectiveness and simplicity, solvent casting is utilised to make ocuserts. In this procedure, rheological
properties of polymer are examined since they impact ocusert thickness, drying rate, homogeneity, etc. De-aeration is
needed because polymer mixing might create air bubbles. Polymers are casted onto the correct substrate after adequate
mixing. After the mixture dries, the solvent evaporates, leaving the ocusert film. Then, ocusert films are trimmed to
size.[35]
5.2. Glass substrate technique
Glass substrate technology is utilised to produce thin films. A transparent polymer solution is utilised to form a drug
reservoir film. The polymer solution is vortexed to mix in the medication. Drug dissolution is followed by plasticizer
addition. To make films, solution is added to a glass mould and dried. Drying at room temperature takes 24 hours. Dried
films are then trimmed to size and then stored[34].
5.3. Melt extrusion technique
Melt extrusion is an alternative for solvent casting. It's utilised for non-organic solvents. In this process, polymers and
other components are melted and then passed through a die to prepare films. The films are then trimmed. This approach
isn't for thermolabile substances.[35]
6. Evaluation parameters for ocuserts
6.1. Organoleptic characteristics
Ocuserts are evaluated for the organoleptic characterization i.e. color, appearance, texture, and odor.
6.2. Uniformity of thickness
The ocusert's uniform thickness facilitates the even dispersion of components. A micrometre screw gauge is utilised to
determine uniform thickness[35][36].
6.3. Uniformity of weight
The ocusert's weight homogeneity shows how constant its constituents are. Three ocuserts are weighed from each
batch. Mean weights are recorded.[37]
6.4. Drug content
Drug content measures active substances in each formulation. Ocusert is dissolved in 10 ml STF. UV visible
spectrophotometer is used to estimate absorbance value after proper dilutions.[37]
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World Journal of Biology Pharmacy and Health Sciences, 2023, 13(01), 470–477
6.5. Swelling index
Swelling index measures a formulation's swelling or water-absorption characteristics. Ocusert is weighed and added to
4 ml of STF. After 5 minutes, the ocusert is removed and excess simulated tear fluid is weighed. [38] The % swelling index
can be calculated by the formula given below –
(Weight of swollen ocusert after time t – initial weight of ocusert)
%Swelling index = 𝑋 100
initial weight of ocusert
6.6. % Moisture absorption
Moisture absorption test measures ocuserts' physical stability in wet environments. After weighing each batch, 3
ocuserts are inserted in aluminium chloride desiccators. After 3 days, the ocuserts are weighed again. [39]The % moisture
absorption is determined by the formula given below -
% Moisture absorption = Final weight - Initial weight / Initial weight x 100
6.7. Folding endurance
This test measures the ocusert's folding resistance. For this, the film is folded repeatedly until it breaks. Folding
endurance is the number of times a film can be folded without breaking.[40]
6.8. Surface pH
Ocusert is allowed to swell at room temperature for 30 minutes in 1ml of distilled water in a closed petri plate. A digital
pH metre measures the surface pH.[39]
6.9. In-vitro drug release study
Diffusion cell method was utilised to conduct this study. An open cylinder used as a donor compartment is lined with
pre-hydrated cellophane membrane. Simulated tear fluid touches the membrane's ocusert. Using a magnetic stirrer, the
simulated tear fluid is mixed and kept at 37 ± 0.5 ºC. After certain times, 1 ml of receptor compartment is
spectrophotometrically analysed. For each sample, artificial tear fluid is added.[41]
6.10. Ex-vivo permeation studies
This study utilizes diffusion cells. Goat cornea is taken from the eye and put on a diffusion cell so the corneum side
remains in touch with the donor ocusert. A magnetic stirrer is used to mix artificial tear fluid at 37 ± 0.5 ºC. 1 ml of
receptor compartment is spectrophotometrically analysed after particular times. Each sample is replaced with artificial
tear fluid[42].
6.11. Sterility test
This test uses Indian Pharmacopoeia. 2 ml of ocusert solution is aseptically transferred to fluid thioglycolate and
soyabean-casein digest media. During 14 days, fluid thioglycolate media must be kept at 30 °C to 35 °C, and soyabean-
casein digest medium at 20 °C to 25 °C.[43]
6.12. Stability study
Stability study is done following ICH guidelines. Increasing a product's temperature speeds up its breakdown,
determining its shelf life, variation in medication concentration, colour, folding endurance, etc. may be tracked during
stability experiments[44].
7. Conclusion
Ocuserts are sterile ophthalmic preparations that may follow a controlled release strategy to lengthen the drug's
residence time and minimise nasolacrimal discharge. This is performed by regulating medication release into the eye.
These are available in a number of forms, each characterised by the application to which it is put. The ocuserts extend
the duration of drug contact with the conjunctiva to keep the dose constant. Because of the stable drug level in the eye,
it has fewer detrimental effects on the body. It reduces dosage frequency, which increases patient compliance. Ocuserts
are manufactured via solvent casting, the glass substrate method, or melt extrusion. After being put through their paces,
optimised ocuserts may be used to achieve an effective medicine concentration at the suitable rate for a given duration.
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World Journal of Biology Pharmacy and Health Sciences, 2023, 13(01), 470–477
This technique of delivering medicine maintains therapeutically-relevant drug concentrations at the target site of action
for a particular duration. The most crucial step in success of ocular medicine delivery has been enhancing corneal
contact duration. Therefore, it makes sense to examine non-conventional techniques such as liposomes, microspheres,
prodrugs, and the like for efficient release, as well as to enhance ocular drug delivery systems and lessen after effects.
Compliance with ethical standards
Disclosure of conflict of interest
No conflict of interest.
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