Eye drop is made up of solute and solvent and it is referred
to as a solution when the solute (drug) dissolves properly in the solvent but
when the drug does not dissolve in the solvent it is called suspension. The
solvent of an eye drop is usually saline water or purified water mixed with
preservatives such as benzalkonium chloride or ecozalkonium chloride.
Solutions and suspensions remain the most common route of
administration for ophthalmic drugs. They are easily instilled, cause less
interference with vision and have fewer potential complications. However, the
disadvantage they have includes: short contact time, imprecise and inconsistent
delivery of drug, frequent contamination and the possibility of ocular injury
with dropper tip. In addition, topical aqueous suspensions have the problem of
precipitation.
Ointments on the other hand are prepared by mixing the drug
with soft paraffin (Vaseline), liquid paraffin or wool fats. Preservatives are
also added to strengthen the shelf life of the ointments. Ointments are second
to solutions and suspensions in frequency of topical applications.
When applied to the inferior conjunctival sac, ophthalmic
ointments melt quickly and the excess spread out into the lid margin, lashes
and skin of the lids. The ointment at the lid margins act as a reservoir and
enhances the drug contact time. However, the disadvantages include: prolonged
ocular contact time, contact dermatitis of the lids, hypersensitivity reaction
may occur, blurred vision.
How eye drops and ointments work
- Antibiotics either kill bacterial organisms (bactericidal) or inhibit their multiplication (bacteriostatic).
- Antivirals disrupt the viral DNA synthesis without unduly harming the host cells.
- Antifungals kill fungi by disrupting their cell wall and membrane.
- Antiglaucoma drugs inhibit or reduce aqueous production and/ or increase their outflow (drainage).
- NSAIDs prevent the body from producing prostaglandins; a chemical released during allergic reaction.
- Corticosterids mimic the behavior of a hormone in the body (Cortisol) that aids proper body function during stressful situations.
- Decongestants shrink the eyes blood vessels that are swollen when exposed to an allergen.
- Antihistamines act on histamine receptors, preventing them from releasing histamine which triggers symptoms of an allergic reaction.
- Mast cell stabilizers strengthen the mast cells and inhibit them from releasing histamine and other chemicals that triggers symptoms of an allergic reaction.
Conditions of concern
Eye drops and ointments have been
of great benefit to patients suffering from eye diseases. However, some patient
may have conditions that must be considered before a decision is made on
treatment. The optometrist should be aware of the following:
- Glaucoma, Hypertension and Heart diseases- these conditions worsen with antihistamines and decongestants. In addition, Timolol aggravates bronchial asthmatic attack and heart diseases.
- Ocular tuberculosis, Viral and Fungal eye diseases- topical steroids worsen these conditions.
- Diabetes- decongestants aggravates this condition.
- Overactive thyroid- naphazoline aggravates this condition.
- Difficulty urinating due to an enlarged prostate- antihistamine can worsen this condition.
- Pregnancy or intention to become pregnant and breastfeeding mothers.
- Contact lens wearers.
- Drugs currently taken by the patient.
- Past allergic reactions to any drug.
- Present infection of the eye.
Common side effects
Most side effects of eye drops
and ointments are minor and resolves after few minutes. They include: temporary
blurry of vision, mild stinging sensation, irritation, dermatitis, itching,
redness, watering eye, runny nose, foreign body sensation, dry eye, dizziness,
headache, unusual bitter taste, dry nose, crusting eyelids, dilated pupils,
puff eyes, crusting eyelashes, etc.
To learn how to apply eye drops
and ointments click here.
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