Ophthalmic Drugs and Ocular ( eye drugs + eye medication)

Ocular Anatomy and Physiology

• External Eye Structures:

  • Eyebrows, eyelids, and eyelashes serve as the outermost protective features.

  • The palpebral fissure is defined as the space existing between the upper and lower eyelids when the eyes are open and in a relaxed state.

  • The medial canthus and lateral canthus refer to the corners where the upper and lower lids meet.

  • The lacrimal caruncle and lacrimal glands are essential for fluid production and tear drainage.

• Ocular Layers:

  • Protective External Layer: Composed of the cornea and the sclera.

  • Vascular Middle Layer (Uvea): Includes the choroid, iris, and ciliary body.

  • Internal Layer: Consists of the retina, which houses photoreceptors.

• Extrinsic Eye Muscles:

  • Each eye is secured and mobilized by six distinct muscles: four rectus muscles and two oblique muscles.

  • Specifically, these include the Levator palpebrae superioris, the Superior rectus, the Superior oblique (assisted by the Trochlea), the Medial rectus, the Inferior rectus, the Lateral rectus, and the Inferior oblique.

• Internal Eye Components and Fluids:

  • The eye contains an anterior chamber and a posterior chamber.

  • The Canal of Schlemm is the primary drainage site for eye fluids.

  • Aqueous humour is the clear fluid found in the anterior segment, while vitreous humour resides in the posterior segment.

  • The retina contains rods (responsible for vision in low light and color) and cones (responsible for detailed color vision).

  • The lens is responsible for accommodation; opacity of the lens is known as cataracts.

Nervous System Control of Pupil Size

• Parasympathetic Nervous System (PSNS):

  • Controls the circular smooth muscle and the sphincter muscle.

  • Stimulation results in miosis, which is the decrease of pupil size.

• Sympathetic Nervous System (SNS):

  • Controls the radial smooth muscle and the dilator muscle.

  • Stimulation results in mydriasis, which is the increase of pupil size.

Classifications of Ophthalmic Drugs

• Mydriatics: These agents dilate the pupil. An example is apraclonidine.

• Miotics: These agents constrict the pupil. Examples include acetylcholine and pilocarpine.

• Cycloplegics: These agents paralyze the ciliary body and possess mydriatic properties. Examples include atropine sulphate and cyclopentolate.

Glaucoma Pathophysiology and Treatment

• Mechanism of Disease:

  • Glaucoma involves the inhibition of the normal flow and drainage of aqueous humour.

  • This lead to an increase in intraocular pressure (IOP).

  • Elevated IOP exerts pressure against the retina, destroying neurons and leading to impaired vision or total blindness.

  • The progression follows a sequence: $\uparrow$ Aqueous humor $\rightarrow$ $\uparrow$ IOP $\rightarrow$ $\uparrow$ Pressure on retina $\rightarrow$ Impaired vision.

• General Classifications of Antiglaucoma Drugs:

  • Cholinergic Drugs (Miotics).

  • Sympathomimetics.

  • $\beta$-adrenergic blockers.

  • Carbonic anhydrase inhibitors.

  • Osmotic diuretics.

  • Prostaglandin agonists.

Pharmacotherapy for Glaucoma

• Cholinergic Drugs (Miotics):

  • These mimic the neurotransmitter acetylcholine (parasympathomimetics).

  • Mechanism: Cause pupillary constriction (miosis), which increases the outflow of aqueous humour, thereby reducing IOP.

  • Direct-acting miotics: Utilize acetylcholine or similar substances to increase cholinergic activity (e.g., pilocarpine, used in gel and solution forms).

  • Indirect-acting miotics: Act as acetylcholinesterase inhibitors to increase cholinergic activity.

• Sympathomimetics:

  • These mimic epinephrine and norepinephrine.

  • Mechanism: Stimulate the dilator muscle to cause mydriasis and enhance aqueous humour outflow through the canal of Schlemm.

  • Specific Drugs:

    • apraclonidine hydrochloride (Iopidine): Structurally related to the $\alpha_2$ stimulant clonidine. It stimulates $\alpha_2$- and $\beta_2$- receptors to reduce IOP by $23$ to $39 \%$. It prevents ocular vasoconstriction and reduces aqueous humour formation. It is primarily used to inhibit perioperative IOP increases.

    • brimonidine (Alphagan, Alphagan P, Alphagen): Similar to apraclonidine but used primarily for glaucoma maintenance.

    • dipivefrin hydrochloride: A prodrug of epinephrine that is hydrolyzed to its active form, allowing for better tissue penetration.

• $\beta$-Adrenergic Blockers:

  • Drugs: betaxolol hydrochloride (Betoptic), levobunolol hydrochloride (Betagan), timolol maleate (Betimol, Timoptic).

  • Mechanism: Reduce IOP by both reducing aqueous humour formation and increasing its outflow.

  • Unique Feature: They do not affect pupil size, night vision, or accommodation.

• Carbonic Anhydrase Inhibitors:

  • Drugs: brinzolamide (Azarga, Azopt), dorzolamide (Cosopt, Trusopt).

  • Mechanism: Inhibit the enzyme carbonic anhydrase, resulting in decreased formation of aqueous humour and lower IOP.

• Osmotic Diuretics:

  • Mechanism: Produce ocular hypotension by creating an osmotic gradient that forces water from the aqueous and vitreous humours into the bloodstream.

  • Administration: Glycerin is usually the first choice and can be given orally (though it may cause hyperglycemia). Mannitol is utilized via intravenous administration if glycerin is unsuccessful.

• Prostaglandin Agonists:

  • Drugs: latanoprost (Xalacom, Xalatan), travoprost (Travatan Z), bimatoprost (Lumigan).

  • Mechanism: Increase the outflow of aqueous fluid.

  • Dosing: Most allow for single daily dosing due to effects lasting $20$ to $24$ hours.

Ocular Antimicrobials and Anti-inflammatories

• Antimicrobials:

  • Available as antibacterial, antiviral, and antifungal agents for topical administration.

  • Side effects include transient inflammation, burning, and stinging.

  • Combining these with corticosteroids can hinder the eradication of the infection.

• Anti-inflammatory Drugs:

  • NSAIDs: ketorolac tromethamine (Acular), flurbiprofen sodium (Ocufen), diclofenac sodium (Voltaren, Ophtha).

  • Corticosteroids: dexamethasone (AK Dex, Doidex, Dioptrol, Maxidex), fluorometholone (Flarex, FML), loteprednol etabonate (Alrex, Lotemax), prednisolone acetate (Diopred), rimexolone (Vexol).

  • Corticosteroids are used during the acute phase of an injury to prevent fibrosis and scarring that leads to visual impairment.

Diagnostic and Specialized Ophthalmic Drugs

• Topical Anaesthetics:

  • Drugs: tetracaine hydrochloride (Minims) and benoxinate hydrochloride.

  • Used for procedures, examinations, and foreign body/suture removal. They are for short-term use and not for self-administration.

• Diagnostic Dyes:

  • fluorescein sodium (AK-Fluor): Used to identify corneal defects and locate foreign objects. Defects appear bright green or yellow-orange; foreign bodies exhibit a green halo.

• Antiallergic Drugs:

  • Antihistamines: olopatadine hydrochloride (Patanol), ketotifen (Zaditor).

  • Mast cell stabilizers: cromolyn sodium (Opticrom), nedocromil sodium (Alocril), lodoxamide (Alomide).

  • Decongestants: tetrahydrozoline hydrochloride (Visine), phenylephrine hydrochloride, oxymetazoline hydrochloride (Visine Workplace), naphazoline (Clear Eyes). These work by promoting vasoconstriction of blood vessels around the eye.

• Lubricants and Moisturizers:

  • Artificial tears are over-the-counter products available as drops or ointments (e.g., GenTeal, Isopto Tears, Murine, Akwa Tears, Refresh, Tears Plus).

Nursing Implications and Administration

• Assessment:

  • Obtain a complete medication and medical history.

  • Establish baseline vital signs and visual acuity.

  • Perform a physical assessment of the eye and surrounding structures.

• Administration Guidelines:

  • Eye drops should be placed into the lower conjunctival sac, never directly onto the cornea.

  • The patient should look up at the ceiling during administration.

  • The tip of the dropper must never touch the eye or any other surface.

  • Apply eye ointments in a thin layer within the conjunctival sac.

  • Apply pressure to the inner canthus for at least $1$ minute following drop administration to reduce systemic absorption.

  • If a patient wears contact lenses, determine if they must be removed prior to drug application.

Questions & Discussion

• Question: When administering eyedrops for glaucoma, what is the desired drug effect?

• Answer: Decreased intraocular pressure (IOP).

• Question: Which statement regarding the use of corticosteroids for ocular inflammation is true?

• Answer: They are used during the acute phase of the injury process to prevent fibrosis and scarring, which result in visual impairment.

• Question: A patient receiving tetrahydrozoline asks how the medication works. What is the best response?

• Answer: The drug works by promoting vasoconstriction of blood vessels in and around the eye.

• Question: When administering eye drops to a patient, where does the nurse place the drop?

• Answer: Into the lower conjunctival sac.