The main goal of ocular medication delivery is to maximize the amount of medication that reaches the ocular site of action in sufficient concentration to produce a beneficial therapeutic effect, demonstrated by the dynamics of pharmacokinetics.
- Absorption into the aqueous humor through the different routes of administration is determined by the characteristics of the medication. Natural barriers include: limited size of conjunctival sac (~50 mcL), worth ~2 drops of commercial topical ocular solutions (20 to 35 mcL); corneal membrane barriers; blood-ocular barriers; and tearing, blinking, drainage that dilute, wash out, or expel instilled eye drops.
- Distribution vary by tissue type. Hydrophilic medications diffuse via intracellular diffusion, and lipophilic medications diffuse via intercellular diffusion. Topical administration usually does not reach the retina in adequate concentrations. If required, an intraocular injection is often chosen to bypass the natural barriers.
- Aqueous solutions are the most affordable but have short corneal contact time as they become diluted from tears. Ophthalmic ointments improve concentration and retention, but blur vision. These are the best treatments used for the eyelids and their margins. Treatment for conjunctiva, limbus, cornea, and anterior chamber (this may also use subconjunctival injection) are effectively treated with instilled solutions or suspensions. High concentrations within the posterior chamber are delivered with intravitreal injections or systemically absorbed medications.
- Contact lenses and collagen shields soaked in antibiotics may also be used for corneal infections.
Common Ocular Medications
These include topical anesthetics, mydriatic, and cycloplegic agents that reduce IOP; anti-infective medications; corticosteroids; NSAIDs; antiallergy medications; eye irrigants; and lubricants.
- Topical Anesthetic Agents: one or two drops of proparacaine hydrochloride and tetracaine hydrochloride are used prior to diagnostic procedures such as tonometry and minor ocular procedures such as removal of sutures or conjunctival or corneal scrapings. These may also be used for severe eye pain to allow the patient to open their eyes for examination or treatment (e.g. eye irrigation for chemical burns).
- Onset occurs within 20 to 60 seconds, and lasts for 10 to 20 minutes.
- Instruct the patient to not rub the eye while anesthetized, as this may result in damage to the cornea.
- Mydriatic and Cycloplegic Agents: “Mydriasis” or pupil dilation is the main objective of these medications. The two types function differently, and are used in combination to achieve maximal mydriasis that is needed during surgery and fundus examinations to give the ophthalmologist a better view of the internal eye structures.
- Mydriatics potentiate alpha-adrenergic sympathetic effects that result in the relaxation of the ciliary muscle, causing dilation. This process, however, does not last long. The resultant light exposure stimulates miosis (pupillary constriction). Cycloplegic medications are given to paralyze the iris sphincter.
- Effects of these drugs can last from 3 hours to several days. Difficulty reading, glare, and inability to focus the eyesight are common side effects. The patient is advised to wear sunglasses.
- Other CNS manifestations may occur with patients, such as increased blood pressure, tachycardia, dizziness, ataxia, confusion, disorientation, incoherent speech, and hallucination.
- Contraindications: patients with narrow angles or shallow anterior chambers, patients taking MAOIs, or patients taking TCAs.
- Glaucoma-Treating Medications are drugs that lower IOP either by decreasing aqueous production or increasing aqueous outflow. As these therapies are life-long, the patient must be educated with both ocular and systemic side effects of the medication.
- Anti-Infective Medications: antibiotic (penicillin, cephalosporins, aminoglycosides, fluoroquinolones), antifungal (mainly amphotericin B), and antiviral agents (acyclovir, ganciclovir). Most are available as drops, ointments, or subconjunctival or intravitreal injections.
- Side effects of Amphotericin, an antifungal, are serious. It includes severe pain, conjunctival necrosis, iritis, and retinal toxicity.
- Antivirals are used for ocular infections associated with herpes virus or cytomegalovirus (CMV).
- Corticosteroids and NSAIDs are commonly used in inflammatory conditions of the eyelids, conjunctiva, cornea, anterior chamber, lens, and uvea. Other parts may be better treated with parenteral and oral routes.
- Suspensions, when prescribed, require the patient to shake the bottle to promote mixture and maximize its therapeutic effect.
- Common ocular side effects of long-term topical corticosteroid use are glaucoma, cataracts, susceptibility to infection, impaired wound healing, mydriasis, and ptosis. High IOP is reversible after discontinuation. NSAIDs are used as an alternative to avoid the side effects of corticosteroids.
- Antiallergy Medications: allergies (e.g. allergic conjunctivitis) are extremely common, primarily from environmental allergens. Corticosteroids are commonly used as anti-inflammatory and immunosuppressive agents to control ocular hypersensitivity reactions.
- Ocular Irrigants are mostly used to maintain lid hygiene, normalize pH (e.g. in chemical burns), eliminate debris, or to inflate the globe intraoperatively. Lubricants, like artificial tears, help alleviate corneal irritation, such as dry eye syndrome. These are preparations of carboxymethylcellulose or hydroxypropyl methylcellulose eye drop solutions, ointments, or ocular inserts (inserted at the lower conjunctival cul-de-sac once each day). Depending on the severity, eye drops can be instilled as often as every hour.
- The corneal surface should not be irrigated in cases of threatened corneal perforation.
- When chemical burns occur, NSS is commonly used to irrigate the corneal surface.
Instilling Eye Medications
- Patient Instructions:
- Never use eye solutions that have changed colors.
- Perform hand hygiene before and after instillation. Avoid touching the bottle to your eye or face, as this may contaminate it with bacteria.
- Ensure adequate lighting.
- Read the label of the eye medication to verify correct medication.
- Remove contact lenses as needed.
- Assume a comfortable position. Lying down is an easy method to ensure the drop enters the eye.
- Hold the lower eyelid down, applying gentle pressure on the cheekbone (not the eye!) to anchor it down.
- Instillation:
- Eye drops come before ointments.
- Apply a 0.25 to 0.5 inch ribbon of ointment to the lower conjunctival sac.
- Absorption:
- Keep the eyelids closed, applying gentle pressure on the inner canthus (for punctal occlusion) near the bridge on the nose for 1 to 2 minutes immediately after instillation.
- Use a clean tissue to gently pat skin to absorb excess eye drops that run onto the cheeks.
- Wait 5 minutes before another eye drop, and 10 minutes before another ointment.
- Reinsert contact lenses (if applicable)
Nursing Management
- Ensure proper administration and maximize the therapeutic effects.
- Inform the patient of the temporary side effects of instillation: blurred vision, stinging, and a burning sensation.
- The patient may refrigerate their eye drops if they are unable to feel the drop when instilled. A cold drop is easier to detect.
- Ensure safety by monitoring for side effects (local and systemic).
- Make sure to occlude the puncta to avoid systemic nasolacrimal duct absorption, especially for patients most vulnerable to medication overdose (older adults, pregnant or lactating women, and patients with cardiac/pulmonary/hepatic/kidney disease).
- A five-minute interval between different types of ocular drops is recommended.
- Prevent infection: maintain meticulous hand hygiene before and after instillation. Never touch any part of the eye with the tip of the eye drop bottle or ointment tube. Recap them immediately after use.