Eye Disorders - Pharmacology

The eye has three layers. The first layer contains the cornea and sclera. The second layer contains the choroid, iris, and ancillary body.The third layer contains the retina that connects to the brain through the optic nerve.

There are three common disorders of the eye: glaucoma, conjunctivitis, and corneal abrasion.

GLAUCOMA

The eye is under constant intraocular pressure (IOP) that increases in patients who have glaucoma. This increased pressure damages the optic nerve resulting in decreased peripheral vision and eventually blindness.

About three million Americans have glaucoma, 120,000 of them have lost their eyesight. Glaucoma is the leading cause of blindness. There are two types of glaucoma: chronic (primary) open-angle glaucoma (POAG) and acute closed-angle glaucoma.

Chronic open-angle glaucoma

Chronic open-angle glaucoma is the most common form of glaucoma. The “open” drainage angle of the eye can become blocked leading to a gradual increase in eye pressure. If this increased pressure results in optic nerve damage, it is known as chronic open-angle glaucoma. The optic nerve damage and vision loss usually occurs so gradually and painlessly that you are not aware of trouble until the optic nerve is already badly damaged.

Angle-closure glaucoma

Angle-closure glaucoma results when the drainage angle of the eye narrows and becomes completely blocked. In the eye, the iris may close off the drainage angle and cause a dangerously high eye pressure. When the drainage angle of the eye suddenly becomes completely blocked, pressure builds up rapidly, and this is called acute angle-closure glaucoma. The symptoms include severe eye pain, blurred vision, headache, rainbow haloes around lights, nausea, and vomiting. Unless an ophthalmologist treats acute angle-closure glaucoma quickly, blindness can result. When the drainage angle of the eye gradually becomes completely blocked, pressure builds up gradually, and this is called chronic angle-closure glaucoma. This form of glaucoma occurs more frequently in people of African and Asian ancestry, and in certain eye conditions.

Acute angle-closure glaucoma is a medical emergency. If IOP is not reduced within hours of onset, the patient’s vision can be permanently damaged.

CONJUNCTIVITIS

Conjunctivitis, commonly known as pink eye, is an inflammation of the thin, clear membrane that covers the white part of the eye and the eyelids (the conjunctiva). This inflammation causes the white of the eye and the inside of eyelids to become pink or red. The patient’s eyes may be itchy or painful.

There are four types of conjunctivitis. These are:

  1. Viral conjunctivitis. Viral conjunctivitis affects only one eye causing excessive eye watering and a light discharge from the eye.
  2. Bacterial conjunctivitis. Bacterial conjunctivitis affects both eyes causing a heavy greenish discharge.
  3. Allergic conjunctivitis. Allergic conjunctivitis also affects both eyes causing itching and redness and excessive tearing. The patient may also experience an itchy and red nose.
  4. Giant papillary conjunctivitis. Giant papillary conjunctivitis (GPC) affects both eyes causing contact lens intolerance, itching, heavy discharge, and tearing and red bumps on the underside of the eyelids.

CORNEAL ABRASION

A corneal abrasion is a cut or scratch on the cornea, which is the clear, protective membrane covering the colored part of the eye (iris). Corneal abrasion can be caused by sand, dust, dirt, and shavings from materials such as metal. Fingernails, tree branches, rubbing your eyes, and even contact lenses can also scratch the cornea. Some patients have a weak outer layer of the cornea that can sustain an abrasion for no apparent reason.

Most corneal abrasions heal properly with the proper treatment. However, if the treatment isn’t successful, the abrasion can reappear months following the originally injury. Corneal abrasions are painful because of the sensitivity of the cornea. Patients may feel as if there is sand in their eye. Their eyes become teary and red. Their vision is blurry and light hurts their eyes (photophobia). Corneal abrasions have been known to cause headaches.

Fluorescein sodium and fluress (fluoresce in sodium and benoxinateHCl) are used to diagnose corneal abrasions and to locate lesions or foreign objects in the eye.

Fluorescein is a dye used to demonstrate defects in corneal epithelium and is excreted in nasal secretions if the lacrimal (tear) duct is patent.

When fluorescence strips are used to examine the eye:

  • Corneal scratches turn bright red.
  • Foreign bodies are surrounded by a green ring.
  • Loss of conjunctiva appears orange yellow.

Fluress is a dye and a local anesthetic and is used for short corneal and conjunctival procedures such as removing foreign bodies from the eye.

Eye Medication

Eye disorders are treated by using one of a variety of medications (Ophthalmic medications).

Topical Anesthetics

Topical anesthetics are used to anesthetize the eye for comprehensive eye examinations and for removal of foreign bodies from the eye. Onset occurs in about 1 minute and lasts for 15 minutes. During this time, the blink reflex is temporarily lost and the corneal epithelium is temporarily dried. The patient is required to wear a protective eye patch until the effects of the drug wear off.

Anti-infectives and Antimicrobials

Anti-infectives and antimicrobials are administered for eye infections such as conjunctivitis. These drugs can cause local skin and eye irritation. You learned about anti-infective and antimicrobial medication in(Inflammation)and(Antimicrobials Fighting Infection).

Lubricants

Lubricants are used to alleviate the discomfort that is associated with dry eyes and to moisten contact lenses and artificial eyes. Lubricants are also used to maintain the integrity of the epithelial surface and to moisten the eye during anesthesia and unconsciousness.

Miotics

Miotics lower intraocular pressure in open-angle glaucoma allowing increased blood flow to the retina. This results in less retinal damage and prevents the loss of vision. There are two types of miotics: direct-acting cholinergics and cholin-esterase inhibitors. Direct-acting cholinergics pupillary constrict and cholinesterase inhibitors pupillary constrict. Patients who take miotics might experience headache, eye pain, decreased vision, brow pain, and less frequently hyperemia of the conjunctivia (red eye). Miotics can be systemically absorbed resulting in the patient experiencing nausea, vomiting, diarrhea, frequent urination, precipitation of asthma attacks, increased salivation, diaphoresis, muscle weakness, and respiratory difficulty.

Carbonic Anhydrase Inhibitors

Carbonic anhydrase inhibitors are used as a long-term treatment for open-angle glaucoma by decreasing intraocular pressure by interfering with the production of aqueous humor. Patients who take carbonic anhydrase inhibitors can experience lethargy, anorexia, drowsiness, paresthesia, depression, polyuria, nausea, vomiting, hypokalemia, and renal calculi. It is because of these adverse side effects that patients frequently discontinue taking carbonic anhydrase inhibitors. Carbonic anhydrase inhibitors are contraindicated in the first trimester of pregnancy and for patients who are allergic to sulfonamides.

Osmotics

Osmotics are preoperative and postoperative medications used to reduce intraocular pressure by decreasing vitreous humor volume. They are also used in the emergency treatment of closed-angle glaucoma. Patients who are administered osmotics can experience headache, nausea, vomiting, and diarrhea. Elderly patients can become disoriented.

Anticholinergic mydriatics and cycloplegics

Anticholinergic mydriatics and cycloplegics are used in diagnostic procedures and ophthalmic surgery. Anticholinergic mydriatics dilate the pupils. Cycloplegicsparalyze eye muscles. Patients who are treated with these medications experience tachycardia, photophobia, dryness of the mouth, edema, conjunctivitis, and derematitis. You learned about anticholinergics in (Nervous System Drugs).


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