Keynotes on Ophthalmic Preparations

The human eye plays an important role. It includes various parts such as the cornea, iris, ciliary body, conjunctiva, lens, aqueous humour (anterior parts of the eye), retina, vitreous humour, choroid, and sclera. 

• Aqueous humour is a type of fluid found in the anterior segments of the eye. It provides nourishment to the cornea and lens
• Iris is the pigmented portion of the eye
• The pupil is the central opening of the eye
• The shape of the eye is controlled by the contraction and relaxation of the ciliary muscles
• The sclera is the white portion of the eye
• The retina is a sensitive tissue to light that is multilayered

Cornea

The cornea is the outermost part of the human eye. It is multilayered and lacks blood supply. It gets nourishment from the aqueous humour. Layers of the human cornea include corneal epithelial, Bowman’s membranes, stroma, Descemet’s membrane, and endothelium.

Characteristics of Ophthalmic Preparations

Ophthalmic preparations can be easily applied to patients by themselves or by nurses.

Route of Administration of Ophthalmic Preparations

• Eye Drops
• The eye drops route of administration is used to treat diseases of the anterior segment.
• The eye drop route is a topical administration route of drug delivery to the eyes
• It is the most preferred method of drug delivery
• Eye drops administration acts on the iris and anterior parts of the eye
• Examples of eye drops include Zinc sulfate, pilocarpine, atropine, etc
• Systematic Route
• It is limited to blood aqueous-retinal areas of the anterior and posterior sides of the eye
• It is a type of parenteral route of drug administration that targets the retina for the delivery of a drug
• Oral Route
• The oral route of drug administration to the targeted site can be done alone or combined with a topical route of administration. Topical administration has failed in the posterior segment as it was unable to produce sufficient therapeutic concentrations
• It is a highly preferred route of administration by patients
• It is helpful for the treatment of chronic retinal diseases

Miscellaneous routes of administration are periocular and intravitreal. Patients less prefer these routes of administration.

Characteristics of Solutions

• Sterile.
• Prepared in solid form.
• Need extra care for installation.
• Polyethylene glycol and polyvinyl alcohol are used to enhance viscosity.

Characteristics of Suspensions

• Suspensions are used to increase the contact time of the drug.
• Suspensions are solid forms of drugs.
• Steroids are highly accepted for the drug delivery systems.
• Surfactants are used in the dispersion of drugs efficiently.
• They are suitable for the eyes and non-irritating.
• They can be easily degraded on sterilisation. 
• They use anti-inflammatory agents.
• Some examples of eye suspension include fluorometholone, blephamide, prednisolone, etc.

Characteristics of Ointments

• Like suspensions, ointments are difficult to produce with sterility but can be terminally sterilised.
• This does not cause any irritation to the eyes.
• They can be melted or softened at normal body temperature, which causes blurred vision.

Characteristics of Gels

• Gels are polymers and mucoadhesive.
• They can be attached to a biological tissue hence called bioadhesive.
• Sodium alginate is a common example.

Contact lenses are the most widely used form of ophthalmic preparations.

Evaluation of Ophthalmic Preparations

• Test for sterility
• By direct inoculation and by filtering the membrane. 
• Direct injection involves the direct administration of test samples into the media culture. 
• Method of membrane filtration can be done by membrane filter to remove the inhibition property of the drug. 
• Test for clarity checking

A clarity checking test is done to check whether the solution contains foreign particles or undissolved ingredients. If found in the solution, they are removed using various treatment methods. 

Advantages of Ophthalmic Preparations

• Ophthalmic preparations are easy to administer.
• The eyes can easily absorb them.
• They have an increased shelf life.
• They possess minimal side effects.

Disadvantages of Ophthalmic Preparations

• These need high preservation and careful handling.
• Dissolved drugs are unstable.
• Their bioavailability is low.

Limitations of Ophthalmic Preparations

• Eye solution can be drained out. Suspension can irritate the human eye.
• Ointments can cause blurred vision.
• Sometimes ocular inserts are hard to remove and insert into the patient’s eye.
• Triggering of hydrogels can take place at high temperatures.

Conclusion

Ophthalmic preparations include eye drops, contact lenses and ointments. However, a lot of active substances that are used to treat ocular disorders have limitations. These limitations pose a challenge in administering the drug, and ocular drug delivery is the only route that can treat local diseases of the human eye.