Applied to eye surface the produce modified release dosage form.
Advantages:
· Prolong use:They provide durability as well as clear, crisp vision for the patient.
· They provide strength as well as relatively easy care regimen.
· They are easy to has well asle during insertion as well as removal.
· Rigid hydrophobic lenses are impermeable to oxygen as well as water. So these are relatively resistant the absorption of disinfectants, surfactants, cleaners as well as environmental contaminant.
· They are particularly well suited for the patient who has an irregularly shaped cornea.
· Versatility of dosage forms enables them to be suitable for the function of the preparation.
Disadvantages:
· They require a more adaptation time as long as week for wearing comfort as well as tolerate.
· Difficult wear as well as tolerate because of their rigidity.
· They may become easily dislodged nor fall out from the eye.
· The direct contact between hard lens and surface of the cornea cause physical damage to the epithelial tissue of the eye.
· They practically impermeable to oxygen as well as moisture. Thus it is complicated for patient comfort as well as corneal epithelial respiration.
Example
Some of the solid preparations include-
Ocular inserts-which gradually dissolves as well as release
Eye pac-cotton plug dissolves in the drug solutions or eye preparations as well as than applied to the eye.
Iontophor-electrical current that influence the drug to ionize as well as polar media absorb this ion usually occurs in aqueous humour region which has two chamber anterior chamber (water in nature) as well as posterior chamber (non-aqueous in nature) as well as process is called ionophorosis as well as the drug that are used is called ionophor.
Contact lens- it is composed of methacrylate polymers. There are two classes of methacrylate polymers. They are-
· HEMA-hydroxy ethyl methacrylate polymer
· PMMA-poly methyl methacrylate polymer
CONTACT LENSES
Advantages:
· Less magnification (5%) of the image,
· elimination of aberrations as well as prismatic effect of thick glasses,
· wider as well as better field of vision,
· cosmetically better accepted by young persons.
Disadvantages:
· more cost,
· cumbersome to wear,especially in old age as well as in childhood,
· corneal complications may occur.
What are the types of contact lenses you know of?
a. Hard contact lenses
b. Soft contact lenses
c. Rigid gas-permeable (RGP) contact lenses
What are advantages as well as disadvantages of hard contact lenses?
Hard contact lenses are made up of PMMA (polymethylmethacrylate) which is a light weight, nontoxic but of hydrophobic material.
Advantages:
· Cheap,durable as well as have high optical quality.
Disadvantages
· Difficult to wear as well as tolerate because of their rigidity.
· Contact lenses made from PMMA materials are virtually impermeable to gases.
· Can cause corneal hypoxia as well as corneal abrasions.
· Being hydrophobic in nature,resists wetting but a stable tear film can be formed over it.
PMMA contact lenses are sparingly used clinical practice because of poor patient acceptance.
What are advantages as well as disadvantages of soft contact lenses?
Soft contact lenses made up of HEMA (hydroxyethylmethacrylate) which is hydrophilic,to small amount of cross linking agents this provide hydrogen network.
They are contain between 30 to 80 % water which enables enhanced permeability to oxygen.Due to presence of water it is more susceptible to growth of microorganism.
Advantages
· Being soft as well as oxygen permeable, they are most comfortable as well as so well tolerated.
Disadvantages
· Problems of proteinaceous deposits, getting cracked,limited life, inferior optical quality, more chances ofcorneal infections, as well as inability to correct astigmatism of more than one dioptre.
RIGID GAS PERMEABLE(RGP) CONTACT LENS
Lenses are made up of materials which are permeable to oxygen.Basically these are also hard, but somehow due to their O2 permeability they have become popular by the name of semisoft lenses.
Advantages:
· Can be used in both extended as well as once daily.
· Can be used at the time of coronial respiration
· They can found in both hydrophilic and hydrophobic forms.
Disadvantages:
· This is quite expensive.
OINTMENT
It is a sterile semi-solid preparation of homogenous appearance intended for application to the conjunctiva.
The principle semisolid dosage form used in ophthalmology is an anhydrous ointment to a petrolatum base.The ointment vehicle is usually a mixture of mineral oil as well as white petrolatum.Mineral oil is added reduce the melting point as well as modify consistency.
Advantage:
· Ointments do offer the advantage of longer contact time as well as greater total drug bioavailability,albeit to slower onset.
· Complete absorption of the drug.It takes a longer time to reach peak absorption.
· The principle advantages of the petrolatum-based ointments are their blas well asness as well as their anhydrous and inert nature, which enables them as suitable carrier for moisture-sensitive drugs.
· Ointments are used almost exclusively as vehicles for antibiotics,sulfonamides,antifungals, as well as anti-inflammatories.The petrolatum vehicle is also used as an ocular lubricant following surgery or to treat various dry eye syndromes.Anesthesiologists may prescribe the ointment vehicle for the non-ophthalmic surgical patients to prevent severe as well as painful dry eye conditions that could develop during prolonged surgeries.
Disadvantage:
· Dosage variability probably is greater than to solutions(although probably not to suspensions).
· The chief disadvantages of the use of ophthalmic ointments are their greasy nature as well as the blurring of vision produced,due to the melting of ointment base as well as spreading across the lens.So their use is usually limited to bedtime instillation.
