PURPOSES AND ACTIONS OF OPHTHALMIC DRUGS
Ophthalmic drugs may be used as a part of tests to diagnose eye disorders, as a principal treatment of eye conditions, or as an adjunct to surgical eye treatment. In addition to their desired action for each use, drugs of all kinds have certain side effects, some of which can be harmful. Because ophthalmic medical assistants often apply topical drugs or assist in ordering or setting up medications for the doctor to administer, they need to be familiar with the most common types of drugs used in ophthalmic practice and their general uses and actions.
DIAGNOSTIC MEDICATIONS:
Medications used to diagnose eye conditions include mydriatics, cycloplegics, dyes and anaesthetics. Most of these are available as topical solutions or suspensions, and some are prepared as oinments. Some of these drugs also produce effects that make them additionally useful in treating certain eye disorders.
1. MYDRIATICS:
The act of dilating the pupil is called mydriasis. Thus, mydriatic drugs cause the pupil to dilate, usually by stimulating the iris dilator muscle. Mydriatic drops are used mainly to facilitate examination of the fundus. During this examination, the more fully dilated pupil allows a greater area of the fundus to be seen with the ophthalmoscope. Occasionally, mydriatics may be used to improve the vision of patients with cataracts or other media opacities, but they are usually used to diagnose eye conditions.
Side effects associated with mydriatics include slight stinging on administration, headache, increased blood pressure, photophobia, and (very rarely) death. Because these agents open the pupil, mydriatics may stimulate an attack of angle-closure glaucoma in patients with a narrow anterior chamber angle. The ophthalmologist should check the patient's anterior chamber angle before ordering the use of a mydriatic drug. The most commonly used mydriatic is phenyllephrine 2.5% (Neosynephrine, Mydfrin).
2. CYCLOPLEGICS:
The term applied to the ability of a drug to paralyze the ciliary muscle temporarily is cycloplegia. Cycloplegic drugs essentially paralyze the iris sphincter muscle, causing dilation of the the pupil. These agents also limit or prevent accommodation by paralyzing the ciliary muscle, which controls the ability of the lens to expand and contract. Cycloplegic agents differ from mydriatics in that cycloplegics both dilate the pupil and paralyze accommodation, whereas mydriatics only dilate the pupil.
The principal uses of cycloplegics include:
1. Performing a refraction that requires an absence of accommodation (Cycloplegic refraction is especially important in children, who have a strong accommodation mechanism that frequently interferes with accurate refraction without cycloplegia).
2. Conducting a fundus examination.
3. Treating uveitis (inflammation of the uveal tract) in some patients.
4. Treating intraocular inflammation that occurs after surgery.
All cycloplegic drugs may sting slightly when administered to the eye. Another important reaction to cycloplegic medication is blurred vision or difficulty seeing at near due to paralysis of accommodation. This altered vision may last from a few hours to days, depending on the type and strength of the drug used. Other major side effects associated with cycloplegics include sensitivity of light, dry mouth, fever, rapid pulse, hallucinations, disorientation, bizarre behavior, and angle-closure glaucoma in patients with a narrow anterior chamber angle.
Cycloplegic drugs may be categorized by the duration of their action. Short-acting compounds are chosen for refraction and retinal examination because their side effects of blurred vision and paralyzed accommodation decrease soon after application. The most common short-acting cycloplegic compounds used in ophthalmology are
1. tropicamide 0.5% and 1.0% (Mydriacyl)
2. cyclopentolate 1.0% and 2.0% (Cyclogyl)
In children, cyclopentolate is used to obtain an accurate, objective measurement of the eye's refractive error.
Long-acting compounds, which are used for refraction and treatment of uveitis, include
1. homatropine 2.0% and 5.0%
2. atropine 0.5% and 1.0% (to refract children)
3. scopolamine 0.25% (Hyoscine)
Because the bottles of most cycloplegic agents looks alike (that is, many have red tops), it is crucial that the assistant check the label of the bottle before using, to be sure the correct agent will be instilled.
3.DYES:
Dyes temporarily stain cells or systems within the eye to outline or highlight defects in their structure or function. Ophthalmologists employ topical dyes in clinical practice chiefly to evaluate the ocular surface. Topical dyes are also used in applanation tonometry and contact lens fitting. Dyes administered by injection may be used to evaluate retinal conditions.
The most common dyes used in ophthalmology are fluorescein, which has fluorescent properties, and rose bengal, a red dye. Both are available for topical use as solutions or as paper strips impregnated with the dye, and both are available under numerous brand names. Fluorescein additionally is available as a solution for injection. Rose bengal stains and highlights degenerating corneal and conjunctival cells, and so is used to test for and diagnose this condition. Fluorescein similarly stain cells, but has other, more complex uses.
For topical testing and diagnostic use, the examiner applies fluorescein drops or a fluorescein- impregnated strip to the eye and exposes the eye to a special cobalt-blue light. Under this lighting condition, the dye fluoresces a bright yellow-green color. In the normal eye, only the tear layer fluoresces, a characteristic that makes the dye useful for applanation tonometry and contact lens fitting. In an abnormal eye, fluorescein and highlights defects in the tear film. It also stains defective or abscent corneal epithelium, allowing the doctor to observe and identify corneal epithelium abrasions, infections and other defects.
When administered intravenously by a doctor or registered nurse, fluorescein courses through the bloodstream to reach the eye. Once there and exposed to cobalt-blue light, the dye highlights retinal structures, especially blood vessels. The doctor may use an ophthalmoscope to observe highlighted defects in the retinal vessels. Used in this way, fluorescein injection is an important adjunct to diagnosing conditions affecting the retinal vessles, such as diabetic retinopathy. Fluorescein given by injection may cause some patients to experience nausea or, rarely, an allergic reaction, although topically applied fluorescein and rose bengal rarely do.
4.ANESTHETICS:
An anesthetic drug causes a temporary deadening of a nerve, which results in loss of feeling in the surrounding tissue and, in some circumstances, paralysis of the affected muscles. Anesthetics used in ophthalmology may be applied as a topical solution or injected. These drugs commonly affect only the eye receiving the medication. Most ophthalmic anesthetics act within a minute or so and have an effect lasting from 10 to 20 minutes for topical anesthetics and hours for some injected types.
Topical anesthetics are most often used to prevent discomfort during diagnostic procedures such as tonometry, gonioscopy, ultrasonography, and other examinations that involve touching the surface of the eye. These agents are also used in therapeutic procedures, such as removal of foreign bodies from the eye and sutures from the cornea. On extremely rare occasions, a topical anesthetic may be used to alleviate pain for the few minutes required to diagnose or treat a painful condition. Injectable anesthetics, however, are used more often to perform minor surgery, such as an eyelid procedure and major eye surgery. Although these ophthalmic anesthetics are injected, they still produce only local anesthetic effects; nevertheless, systemic toxicity can occur.
Anesthetics can produce an allergic reaction in a sensitive individual. Topical anesthetics become toxic to the cornea if in contact with the eye for long periods or if used often. They delay the resurfacing of the cornea by the corneal epithelium, which inhibits healing, and they can disrupt the normal stromal architecture, which can cause permanent clouding of the cornea. For these reasons, anesthetics are not used as a treatment except to alleviate pain for a few minutes until definitive therapy can be started.
The ophthalmic medical assistant should caution the patient receiving an ophthalmic anesthetic not to rub the eye, because the numbed eye could be easily scratched without the patient being aware of it until the anesthesia wears off. Never give a patient a topical anesthetic for home use or use one yourself; blindness could result.
Commonly used topical ophthalmic anesthetics include:
1. proparacaine 0.5% (Ophthaine, Ophthetic, Alcaine)
2. tetracaine 0.5% (Anacel, Pontocaine)
3. lidocaine 1.0% to 5.0% (Xylocaine)
4. benoxinate plus fluorescein (Fluress)
5. proparacaine plus fluorescein (Fluoracaine)
Ophthalmic drugs may be used as a part of tests to diagnose eye disorders, as a principal treatment of eye conditions, or as an adjunct to surgical eye treatment. In addition to their desired action for each use, drugs of all kinds have certain side effects, some of which can be harmful. Because ophthalmic medical assistants often apply topical drugs or assist in ordering or setting up medications for the doctor to administer, they need to be familiar with the most common types of drugs used in ophthalmic practice and their general uses and actions.
DIAGNOSTIC MEDICATIONS:
Medications used to diagnose eye conditions include mydriatics, cycloplegics, dyes and anaesthetics. Most of these are available as topical solutions or suspensions, and some are prepared as oinments. Some of these drugs also produce effects that make them additionally useful in treating certain eye disorders.
1. MYDRIATICS:
The act of dilating the pupil is called mydriasis. Thus, mydriatic drugs cause the pupil to dilate, usually by stimulating the iris dilator muscle. Mydriatic drops are used mainly to facilitate examination of the fundus. During this examination, the more fully dilated pupil allows a greater area of the fundus to be seen with the ophthalmoscope. Occasionally, mydriatics may be used to improve the vision of patients with cataracts or other media opacities, but they are usually used to diagnose eye conditions.
Side effects associated with mydriatics include slight stinging on administration, headache, increased blood pressure, photophobia, and (very rarely) death. Because these agents open the pupil, mydriatics may stimulate an attack of angle-closure glaucoma in patients with a narrow anterior chamber angle. The ophthalmologist should check the patient's anterior chamber angle before ordering the use of a mydriatic drug. The most commonly used mydriatic is phenyllephrine 2.5% (Neosynephrine, Mydfrin).
2. CYCLOPLEGICS:
The term applied to the ability of a drug to paralyze the ciliary muscle temporarily is cycloplegia. Cycloplegic drugs essentially paralyze the iris sphincter muscle, causing dilation of the the pupil. These agents also limit or prevent accommodation by paralyzing the ciliary muscle, which controls the ability of the lens to expand and contract. Cycloplegic agents differ from mydriatics in that cycloplegics both dilate the pupil and paralyze accommodation, whereas mydriatics only dilate the pupil.
The principal uses of cycloplegics include:
1. Performing a refraction that requires an absence of accommodation (Cycloplegic refraction is especially important in children, who have a strong accommodation mechanism that frequently interferes with accurate refraction without cycloplegia).
2. Conducting a fundus examination.
3. Treating uveitis (inflammation of the uveal tract) in some patients.
4. Treating intraocular inflammation that occurs after surgery.
All cycloplegic drugs may sting slightly when administered to the eye. Another important reaction to cycloplegic medication is blurred vision or difficulty seeing at near due to paralysis of accommodation. This altered vision may last from a few hours to days, depending on the type and strength of the drug used. Other major side effects associated with cycloplegics include sensitivity of light, dry mouth, fever, rapid pulse, hallucinations, disorientation, bizarre behavior, and angle-closure glaucoma in patients with a narrow anterior chamber angle.
Cycloplegic drugs may be categorized by the duration of their action. Short-acting compounds are chosen for refraction and retinal examination because their side effects of blurred vision and paralyzed accommodation decrease soon after application. The most common short-acting cycloplegic compounds used in ophthalmology are
1. tropicamide 0.5% and 1.0% (Mydriacyl)
2. cyclopentolate 1.0% and 2.0% (Cyclogyl)
In children, cyclopentolate is used to obtain an accurate, objective measurement of the eye's refractive error.
Long-acting compounds, which are used for refraction and treatment of uveitis, include
1. homatropine 2.0% and 5.0%
2. atropine 0.5% and 1.0% (to refract children)
3. scopolamine 0.25% (Hyoscine)
Because the bottles of most cycloplegic agents looks alike (that is, many have red tops), it is crucial that the assistant check the label of the bottle before using, to be sure the correct agent will be instilled.
3.DYES:
Dyes temporarily stain cells or systems within the eye to outline or highlight defects in their structure or function. Ophthalmologists employ topical dyes in clinical practice chiefly to evaluate the ocular surface. Topical dyes are also used in applanation tonometry and contact lens fitting. Dyes administered by injection may be used to evaluate retinal conditions.
The most common dyes used in ophthalmology are fluorescein, which has fluorescent properties, and rose bengal, a red dye. Both are available for topical use as solutions or as paper strips impregnated with the dye, and both are available under numerous brand names. Fluorescein additionally is available as a solution for injection. Rose bengal stains and highlights degenerating corneal and conjunctival cells, and so is used to test for and diagnose this condition. Fluorescein similarly stain cells, but has other, more complex uses.
For topical testing and diagnostic use, the examiner applies fluorescein drops or a fluorescein- impregnated strip to the eye and exposes the eye to a special cobalt-blue light. Under this lighting condition, the dye fluoresces a bright yellow-green color. In the normal eye, only the tear layer fluoresces, a characteristic that makes the dye useful for applanation tonometry and contact lens fitting. In an abnormal eye, fluorescein and highlights defects in the tear film. It also stains defective or abscent corneal epithelium, allowing the doctor to observe and identify corneal epithelium abrasions, infections and other defects.
When administered intravenously by a doctor or registered nurse, fluorescein courses through the bloodstream to reach the eye. Once there and exposed to cobalt-blue light, the dye highlights retinal structures, especially blood vessels. The doctor may use an ophthalmoscope to observe highlighted defects in the retinal vessels. Used in this way, fluorescein injection is an important adjunct to diagnosing conditions affecting the retinal vessles, such as diabetic retinopathy. Fluorescein given by injection may cause some patients to experience nausea or, rarely, an allergic reaction, although topically applied fluorescein and rose bengal rarely do.
4.ANESTHETICS:
An anesthetic drug causes a temporary deadening of a nerve, which results in loss of feeling in the surrounding tissue and, in some circumstances, paralysis of the affected muscles. Anesthetics used in ophthalmology may be applied as a topical solution or injected. These drugs commonly affect only the eye receiving the medication. Most ophthalmic anesthetics act within a minute or so and have an effect lasting from 10 to 20 minutes for topical anesthetics and hours for some injected types.
Topical anesthetics are most often used to prevent discomfort during diagnostic procedures such as tonometry, gonioscopy, ultrasonography, and other examinations that involve touching the surface of the eye. These agents are also used in therapeutic procedures, such as removal of foreign bodies from the eye and sutures from the cornea. On extremely rare occasions, a topical anesthetic may be used to alleviate pain for the few minutes required to diagnose or treat a painful condition. Injectable anesthetics, however, are used more often to perform minor surgery, such as an eyelid procedure and major eye surgery. Although these ophthalmic anesthetics are injected, they still produce only local anesthetic effects; nevertheless, systemic toxicity can occur.
Anesthetics can produce an allergic reaction in a sensitive individual. Topical anesthetics become toxic to the cornea if in contact with the eye for long periods or if used often. They delay the resurfacing of the cornea by the corneal epithelium, which inhibits healing, and they can disrupt the normal stromal architecture, which can cause permanent clouding of the cornea. For these reasons, anesthetics are not used as a treatment except to alleviate pain for a few minutes until definitive therapy can be started.
The ophthalmic medical assistant should caution the patient receiving an ophthalmic anesthetic not to rub the eye, because the numbed eye could be easily scratched without the patient being aware of it until the anesthesia wears off. Never give a patient a topical anesthetic for home use or use one yourself; blindness could result.
Commonly used topical ophthalmic anesthetics include:
1. proparacaine 0.5% (Ophthaine, Ophthetic, Alcaine)
2. tetracaine 0.5% (Anacel, Pontocaine)
3. lidocaine 1.0% to 5.0% (Xylocaine)
4. benoxinate plus fluorescein (Fluress)
5. proparacaine plus fluorescein (Fluoracaine)
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