Drugs Used to Treat Glaucoma and Other Eye Disorders

Objectives

1 Describe the anatomy and physiology of the eye.

2 Describe the normal flow of aqueous humor in the eye.

3 Identify the changes in normal flow of aqueous humor caused by open-angle and closed-angle glaucoma.

4 Explain patient assessments needed for eye disorders.

5 Review the correct procedure for instilling eyedrops or eye ointments and discuss patient teaching needs for glaucoma medication use.

6 Compare the mechanisms of action of drugs used to lower intraocular pressure.

Key Terms

cornea () (p. 678)

sclera () (p. 678)

iris () (p. 678)

sphincter muscle () (p. 678)

miosis () (p. 678)

dilator muscle () (p. 678)

mydriasis () (p. 678)

lens () (p. 678)

near point () (p. 678)

zonular fibers () (p. 678)

cycloplegia () (p. 678)

lacrimal canaliculi () (p. 679)

intraocular pressure (IOP) () (p. 680)

closed-angle glaucoma () (p. 680)

open-angle glaucoma (p. 680)

Anatomy and Physiology of the Eye

http://evolve.elsevier.com/Clayton

The eyeball has three coats, or layers: the protective external, or corneoscleral coat; the nutritive middle vascular layer, called the choroid; and the light-sensitive inner layer, or retina (Figure 43-1).

The cornea, or outermost sheath of the anterior eyeball, is transparent so that light can enter the eye. The cornea has no blood vessels; it receives its nutrition from the aqueous humor and its oxygen supply by diffusion from the air and surrounding vascular structures. There is a thin layer of epithelial cells on the external surface of the cornea that is resistant to infection. An abraded cornea, however, is highly susceptible to infection. The cornea has sensory fibers, and any damage to the corneal epithelium will cause pain. Seriously injured corneal tissue is replaced by scar tissue that is usually not transparent. The sclera is the eye’s white portion that is continuous with the cornea and is not transparent. The pupil is the center black portion of the eye, which is actually a hole in the iris that allows light to reach the retina.

The iris is a diaphragm that surrounds the pupil and gives the eye its color—blue, green, hazel, brown, or gray. The sphincter muscle within the iris encircles the pupil and is innervated by the parasympathetic nervous system. Miosis is contraction of the iris sphincter muscle, which causes the pupil to narrow. The dilator muscle, which runs radially from the pupillary margin to the iris periphery, is sympathetically innervated. Mydriasis is contraction of the dilator muscle and relaxation of the sphincter muscle, which causes the pupil to dilate (Figure 43-2).

FIGURE 43-2 Effect of light or ophthalmic agents on the iris of the eye.

Constriction of the pupil normally occurs with light or when the eye is focusing on nearby objects. Dilation of the pupil normally occurs in dim light or when the eye is focusing on distant objects.

The lens is a transparent gelatinous mass of fibers encased in an elastic capsule situated behind the iris. Its function is to ensure that the image on the retina is in sharp focus. It does this by changing shape (accommodation). This occurs readily in youth, but with age the lens becomes more rigid and the ability to focus close objects is lost. The near point, the closest point that can be seen clearly, recedes. With age, the lens may lose its transparency and become opaque, forming a cataract. Blindness can occur unless the cataract can be treated or surgically removed.

The lens has ligaments around its edge, called zonular fibers, which connect with the ciliary body. Tension on the zonular fibers helps change the shape of the lens. In the unaccommodated eye, the ciliary muscle is relaxed and the zonular fibers are taut. For near vision, the ciliary muscle fibers contract, relaxing the pull on the ligaments and allowing the lens to become thick. Accommodation depends on two factors: (1) the ability of the lens to assume a more biconvex shape when tension on the ligaments is relaxed and (2) ciliary muscle contraction. Paralysis of the ciliary muscle is termed cycloplegia. The ciliary muscle is innervated by parasympathetic nerve fibers.

The ciliary body secretes aqueous humor, which bathes and feeds the lens, posterior surface of the cornea, and iris. After it is formed, the fluid flows forward between the lens and the iris into the anterior chamber. It drains out of the eye through drainage channels located near the junction of the cornea and sclera into a meshwork that leads into Schlemm’s canal and into the venous system of the eye.

Eyelids, eyelashes, tears, and blinking all protect the eye. There are about 200 eyelashes for each eye. The eyelashes cause a blink reflex whenever a foreign body touches them, closing the lids for a fraction of a second to prevent the foreign body from entering the eye. Blinking, which is bilateral, occurs every few seconds during waking hours. It keeps the corneal surface free from mucus and spreads the lacrimal fluid evenly over the cornea. Tears are secreted by lacrimal glands and contain lysozyme, a mucolytic lubrication for lid movements. They wash away foreign agents and form a thin film over the cornea, providing it with a good optical surface. Tear fluid is lost by drainage into two small ducts, the lacrimal canaliculi, at the inner corners of the eyelids and by evaporation.

General Considerations for Topical Ophthalmic Drug Therapy

The most common route of administration for ophthalmic drugs is topical application. Advantages include convenience, simplicity, noninvasive nature, and the ability of the patient to self-administer. Topically administered medications do not penetrate adequately for use with posterior eye diseases, so topical administration is not used for such diseases as with the optic nerve or retina.

Proper administration is essential to optimal therapeutic response. The administration technique used often determines drug safety and efficacy (see pp. 113-114).

• Based on the volume that the eye can retain, use of more than one drop per administration is questionable.

• If more than one drug is to be administered at about the same time, separate the administration of the different medications by at least 5 minutes. This ensures that the first medication is not washed away by the second, or that the second medication is not diluted by the first.

• Minimize systemic absorption of ophthalmic drops by compressing the tear duct at the inner canthus of the eye for 3 to 5 minutes after instillation. This reduces the passage of medication via the nasolacrimal duct into areas of absorption, such as the nasal and pharyngeal mucosa.

• Eyecup use is discouraged because of the risk of contamination.

• Ophthalmic ointments may impede delivery of other ophthalmic drugs to the affected site by serving as a barrier to contact. Administer drops before applying ointments. Try not to administer drops for a few hours after the use of ointment. The ointment should be administered beginning at the inner canthus to the outer aspect of the eye.

• Ointments may blur vision during the waking hours. Use with caution in conditions in which visual clarity is critical (e.g., operating motor equipment, reading).

• Observe expiration dates closely. Do not use outdated medication.

• Solutions and ointments are frequently misused. Do not assume that patients know how to effectively use these agents.

• In an effort to enhance safety of ophthalmic medications, the ophthalmic medicine industry recommends the use of standard colors for drug labels and bottle caps (see chart below). Ophthalmic drug labels include “For Ophthalmic Use.” Nurse should become familiar with these colors and types of ophthalmic medications to help prevent inadvertently picking up and administering the wrong solution.

Therapeutic Class	Cap and Label Color
Anti-infectives	Brown or tan
Beta-adrenergic blocking agents	Yellow, blue, or both
Miotics	Green
Mydriatics and cycloplegics	Red
Nonsteroidal anti-inflammatory agents	Gray

Glaucoma

Glaucoma is an eye disease characterized by abnormally elevated intraocular pressure (IOP), which may result from excessive production of the aqueous humor or from diminished ocular fluid outflow. Increased pressure, if persistent and sufficiently elevated, may lead to permanent blindness. There are three major types of glaucoma, primary, secondary, and congenital. Primary includes closed-angle glaucoma and open-angle glaucoma. These are diagnosed by determination of the iridocorneal angle of the anterior chamber, where aqueous humor reabsorption takes place. Secondary glaucoma may result from previous eye disease or may occur after a cataract extraction and may require drug therapy for an indefinite period. Congenital glaucoma requires surgical treatment.

Open-angle glaucoma develops insidiously over the years as pathologic changes at the iridocorneal angle prevent the outflow of aqueous humor through the trabecular network to Schlemm’s canal and into the veins of the eye (Figure 43-3). In cases of open-angle glaucoma, there is reduced outflow of aqueous humor through the trabecular network and Schlemm’s canal because of resistance of the aqueous humor outflow; the iridocorneal angle is open (Figure 43-4).

FIGURE 43-3 Anterior and posterior chambers of the eye. Arrows indicate the pathway of aqueous flow.

Intraocular pressure builds up and, if not treated, will damage the optic disc. Initially, the patient has no symptoms, but over the years there is a gradual loss of peripheral vision. If untreated, total blindness may result.

Acute closed-angle glaucoma occurs when there is a sudden increase in IOP caused by a mechanical obstruction of the trabecular network in the iridocorneal angle (Figure 43-5). This occurs in patients who have narrow anterior chamber angles. Symptoms develop gradually and appear intermittently for short periods, especially when the pupil is dilated. (Dilation of the pupil pushes the iris against the trabecular meshwork, causing the obstruction.) Symptoms often reported are blurred vision, halos around white lights, frontal headache, and eye pain. Patients often associate the symptoms with stress or fatigue. An attack can also be precipitated by administration of a mydriatic agent, such as atropine or scopolamine, for eye examination.

FIGURE 43-5 **Closed-angle glaucoma.** Obstruction to the flow of aqueous fluid, causing closed-angle glaucoma.

Drug Therapy for Glaucoma

The treatment of open-angle glaucoma is maintenance of IOP at normal levels to prevent further blindness. Treatment options include surgery, laser surgery, and drug therapy. A beta-adrenergic blocking agent (e.g., timolol maleate) has become the initial drug of choice. Other agents that may also be used are prostaglandins (e.g., latanoprost, sympathomimetic agents (e.g., brimonidine), carbonic anhydrase inhibitors (e.g., acetazolamide), and cholinesterase inhibitors (e.g., echothiophate iodide). The selection of the drug is determined to a great extent by the requirements of the individual patient and response to therapy.

Acute angle-closure glaucoma requires immediate treatment to reduce IOP. Intravenous mannitol, an osmotic diuretic, may be administered to draw aqueous humor from the eye. Topical corticosteroids may be used to reduce ocular inflammation. Other medications used to reduce formation of aqueous humor include beta blockers, prostaglandins, a sympathomimetic agent, or a carbonic anhydrase inhibitor. After IOP has been reduced, pilocarpine may be used to induce miosis, relieving the pressure of the iris against the trabecular network and allowing drainage of the aqueous humor. Analgesics and antiemetics may be administered if pain and vomiting persist. Surgery is then required to correct the abnormality.

Nursing Implications for Glaucoma and Other Eye Disorders

The nurse has an important role in educating the public and promoting safety measures to protect the eye from potential sources of injury. Health professionals can participate in this role during their daily contacts with people in the community. The use of safety glasses in potentially hazardous situations, prevention of chemical burns from common household cleansing items or other agents at home or work, proper cleaning and wearing of contact lenses or glasses, and selection of safe toys and play activities for children are some areas about which the nurse can teach the public. These safety measures can significantly reduce the number of injuries that occur annually.

Nurses play an important role in detecting eye disorders and implementing treatment plans. An example of this is in patients with diabetes mellitus. Encourage annual, or more frequent, eye examinations to detect and prevent complications associated with the disease.

The primary delivery of eye care is through self-administration of drugs. One of the greatest challenges in the care of chronic eye disorders such as glaucoma is convincing the patient of the need for long-term treatment and adherence to the therapeutic regimen.

Assessment

Eye Examination

• When an eye injury has occurred, document visual acuity by screening vision with the Snellen chart. Comparison screenings should be performed at each subsequent visit.

• Observe for eyelid edema. It may be an indication of a systemic disease process or tumor. Report if present.

• Assess pupils for equality of size, roundness, and response to light. Report irregular contour, unequal size, or decreased response to light.

• Observe for and report nystagmus.

• Observe for any redness or drainage in the eyes.

• Observe for complete closure of the eyelid. This is essential for protection of the cornea. Patients who have received corneal anesthesia, have had fifth cranial nerve surgery, have exophthalmos, or are unconscious must have the cornea protected to prevent damage.

• Ask whether glasses or contact lenses are worn.

• Inspect the eye dressings and report immediately for evaluation if any drainage is observed. Never remove the surgical dressing after surgery to inspect the eye.

History of Symptoms

• Ask the patient to describe the symptoms for which treatment is being sought. How do symptoms affect daily life? Do visual problems affect ability to read?

• Is there a family history of cataracts, glaucoma, or macular degeneration?

• Are activities limited in any way by any vision problem?

• Do any leisure activities have the potential for eye injury?

• Has the person had any noticeable pain, burning, foreign body sensation, blurred or halo vision, or loss of vision?

• Ask whether there is any difficulty in adjusting vision when going from a dark to a brightly lighted area or vice versa.

• Are colors clear and crisp, or do they lack clarity?

• Has there been an increase in tearing or discharge from the eye? If so, ask for details of appearance and amount of drainage.

• Has there been any recent nausea or vomiting?

Psychological.

What type of response is the patient exhibiting to the disturbance in visual acuity? Is the patient withdrawing socially? Identify a support system available for at-home care and assistance. Plan a specific time to meet with the patient and significant others to discuss at-home care and community resources available if assistance is indicated.

Life Span Considerations

Diminished Visual Acuity

Diminished visual acuity affects most aspects of a person’s life, so it is imperative to evaluate an individual’s ability to perform the usual activities of daily living when visual impairment develops. Many medications used to treat other disorders can reduce visual acuity; this adverse effect should be anticipated and its consequences monitored. Every attempt must be made to help the patient adapt to the visual impairment and provide for personal safety.

Diagnostics.

Ask the patient to describe what eye diagnostic procedures have been completed before admission (e.g., visual acuity measurement, tonometry, slit-lamp examination, visual fields). Normal IOP using an applanation tonometer is 10 to 21 mm Hg.

Medications.

Ask for a list of all prescribed, over-the-counter medications and herbal products being taken. Ask for details on medications, dosage, schedule, and degree of compliance. List all ordered medications on the medication administration record (MAR). If beta blockers are being taken, list the pulse and blood pressure on the MAR as a preassessment to administration of the ophthalmic drops. Mark the Kardex or enter data into the computer with parameters relating to the prevention of injury, the activity and exercise level permitted, and diet orders.

Implementation

• Perform assessments every shift consistent with the patient’s status and diagnosis.

• Prepare the patient for eye examinations, diagnostics, or eye surgery.

• Administer cycloplegic and mydriatic medications prescribed for dilation of the eye before an eye examination or ophthalmic surgery.

• Administer miotic medication to produce constriction of the eye after eye examination or diagnostic procedures, as prescribed.

• Administer all ophthalmic medications prescribed while maintaining aseptic technique to prevent the transfer of infection from one eye to the other.

• Protect the cornea from damage during anesthesia or in an unconscious patient through the use of ophthalmic ointment or artificial tears to prevent corneal drying.

• Assist with diagnostic procedures (e.g., visual fields, tonometry, visual acuity).

• Take baseline vital signs.

• Institute appropriate comfort measures.

• If eye surgery has been performed (e.g., trabeculectomy), institute routine postoperative care measures. Position the patient as ordered, usually on the back or on the unoperated side. With the scleral buckling procedure, positioning orders may be extremely specific.

• Ensure that an eye patch and shield are applied properly to protect the eye from further injury.

• Explain and enforce activity and exercise restrictions. To prevent an increase in IOP, instruct the patient to avoid heavy lifting, straining on defecation, coughing, or bending and placing the head in a dependent position.

• A blind or disoriented patient, or a patient with both eyes patched may experience effects of sensory deprivation.

• Always speak before touching a person with impaired vision.

• Check on the patient at frequent intervals; initiate conversations and regularly orient the patient to date, time, and place.

• If the patient is agitated, contact the prescriber; it may be necessary to obtain an order to remove one eye patch or sedate the patient.

• Provide emotional support.

Health Promotion

• Perform hand hygiene thoroughly each time the area is touched (before or after eye treatments or instillation of medications).

• Use only sterile medications or dressings on the eye.

• Wipe the eye from the inner canthus outward; discard the tissue used; perform hand hygiene before proceeding to the second eye.

• When an infection is present, prevent cross-contamination; always use a separate source of medication and dropper for each eye.

• Never touch the eyeball or face with the tip of the dropper or opening of the ointment container. Demonstrate the proper way to set the lid down so that the inside is not contaminated.

• When inserting or removing contact lens, perform hand hygiene first and then follow the manufacturer’s instructions regarding the cleansing and care of the lenses.

• Report any persistent redness or drainage from the eyes.

Patient Teaching and Health Promotion

After Eye Surgery

• Teach the patient and family proper hygiene and eye care techniques to ensure that medications, dressings, and/or surgical wounds are not contaminated during necessary eye care.

• Teach the patient and family about signs and symptoms of infections, and when and how to report them to allow early recognition and treatment of possible infection.

• Instruct the patient to comply with postoperative restrictions on head positioning, bending, coughing, and the Valsalva maneuver to optimize visual outcomes and prevent increased IOP.

• Instruct the patient to instill the eye medications using aseptic techniques and to comply with prescribed eye medication routine to prevent infection (see Figures 8-6 and 8-7). In general, using more than one drop per dose of medication does not improve response but increases the frequency of adverse effects and the cost of therapy. Instruct the patient on how to block the nasolacrimal duct during instillation to minimize systemic effects.

• When using more than one medication, separate drop instillation of each agent by at least 5 to 10 minutes to provide optimal ocular contact for each medication.

• Instruct the patient to monitor pain and take prescribed pain medication as directed; report pain not relieved by prescribed medications.

• Instruct the patient about the importance of continued follow-up as recommended to maximize potential visual outcomes.

Written Record.

Enlist the patient’s aid in developing and maintaining a written record (see Patient Self-Assessment Form for Eye Medications on the Evolve Web site at http://evolve.elsevier.com/Clayton) of monitoring parameters (e.g., blood pressure and pulse with adrenergic and beta-adrenergic blocking agents, degree of visual disturbance, progression of impairment) and response to prescribed therapies for discussion with the physician. Encourage the patient to take this record to all follow-up visits.

Drug Class: Osmotic Agents

Actions

Osmotic agents are administered intravenously, orally, or topically to reduce IOP. These agents elevate the osmotic pressure of the plasma, causing fluid from the extravascular spaces to be drawn into the blood. The effect on the eye is reduction of volume of intraocular fluid, which produces a decrease in IOP.

Uses

The osmotic agents are used to reduce IOP in patients with acute narrow-angle glaucoma; before iridectomy; preoperatively and postoperatively in conditions such as congenital glaucoma, retinal detachment, cataract extraction, and keratoplasty; and in some secondary glaucomas.

Therapeutic Outcome

The primary therapeutic outcome expected from osmotic agents is reduced IOP.

Nursing Implications for Osmotic Agents

Premedication Assessment

1 Initiate an intravenous (IV) line for administration of the osmotic agent. Be certain the IV site is functional and not infiltrated before hanging the osmotic agent for infusion.

2 If a Foley catheter is used, ensure that it is functional; initiate strict intake and output monitoring.

3 Assess and record baseline weight, hydration status, lung sounds, and vital signs.

4 Record premedication IOP readings and visual acuity data.

Availability

See Table 43-1.

Table 43-1

Osmotic Agents

GENERIC NAME	BRAND NAME	AVAILABILITY	DOSAGE	COMMENTS
mannitol	Osmitrol	5%, 10%, 15%, 20%, 25% solutions for infusions	IV: 1.5-2 g/kg as a 20% solution over 30 min	Used intravenously when oral methods are unacceptable
				When used preoperatively, administer 60-90 min before surgery
				Use an in-line filter because mannitol has a tendency to crystallize
urea	Ureaphil	40 g in 150 mL	IV: 1-5 g/kg	Administer as a 30% solution at an infusion rate not to exceed 4 mL/min
				Used when mannitol and oral methods are not available
				Do not exceed 120 g daily
				Use extreme caution against extravasation, or tissue necrosis may result
				Do not infuse in veins of lower extremities because of the possibility of thrombus formation

Dosage and Administration

See Table 43-1.

• Catheter: Be certain the patient has an indwelling catheter if these drugs are used during an operative procedure; check with the health care provider before scrubbing for the procedure.

• IV: Assess the IV site at regular intervals for any signs of infiltration. Tissue necrosis may occur from infiltration into the surrounding tissue. If it occurs, stop the IV, report, and then elevate the extremity and follow hospital protocol for extravasation.

• Mannitol crystals: Check the mannitol solution for crystals; DO NOT administer if present. Follow directions in the literature accompanying the medication for a warm bath to dissolve the crystals, and then cool the solution before administration.

Medication Safety Alert

Do not use veins in lower extremities for administration of osmotic agents because these may cause phlebitis or thrombosis.

Monitoring

Serious Adverse Effects

Hematologic

Thirst, Nausea, Dehydration, Electrolyte Imbalance.

The electrolytes most commonly altered are potassium (K⁺), sodium (Na⁺), and chloride (Cl⁻). Many symptoms associated with altered fluid and electrolyte balance are subtle and resemble general symptoms of drug toxicity or the disease process itself. Gather data about changes in the patient’s mental status (alertness, orientation, and confusion), muscle strength, muscle cramps, tremors, nausea, and general appearance (drowsy, anxious, lethargic). Always check the electrolyte reports for early indicators of electrolyte imbalance. Keep accurate records of intake and output, daily weights, and vital signs.

Neurologic

Headache.

This is an indication of cerebral dehydration. Keeping the patient in a supine position can minimize it.

Vascular

Circulatory Overload.

These medications act on the blood volume by pulling fluid from the tissue spaces into the general circulation (blood). Assess the patient at regularly scheduled intervals for signs and symptoms of fluid overload, pulmonary edema, or heart failure. Perform lung assessments; report the development of crackles and increasing dyspnea, frothy sputum, or cough.

Drug Interactions

Lithium.

Mannitol increases the excretion of lithium. Patients being treated with lithium should be monitored for low lithium levels if treated with mannitol.

Drug Class: Carbonic Anhydrase Inhibitors

Actions

These agents are inhibitors of the enzyme carbonic anhydrase. Inhibition of this enzyme results in a decrease in the production of aqueous humor, thus lowering IOP.

Uses

These agents are used in conjunction with other treatments to control IOP in cases of intraocular hypertension and closed-angle and open-angle glaucoma. Dorzolamide has the advantage of intraocular administration, with less potential for systemic adverse effects.