Chapter 87: Eye Flashcards
glaucoma
Visual field loss secondary to optic nerve damage
Leading cause of preventable blindness in the United States
Of the 4 million Americans with glaucoma, only 50% are diagnosed
90% could have saved their sight with timely treatment
Forms
Primary open-angle glaucoma (POAG)
Acute angle-closure glaucoma
“silent eye disease”
Aqueous Humor
Produced in ciliary body
Secreted into posterior chamber of the eye
Circulates around the iris into the anterior chamber
Exits the anterior chamber via the trabecular meshwork and the canal of Schlemm
If outflow of AH is impeded, pressure will build in eye, IOP increase -> pressure on optic nerve -> blindness
Primary Open-Angle Glaucoma
Most common form of glaucoma in the United States
Progressive optic nerve damage, with eventual impairment of vision
Devoid of symptoms until significant and irreversible optic nerve injury has occurred
Risk factors
Elevation of intraocular pressure (IOP)
Family history of POAG
Advancing age
African and South American ancestry
Treatment
Directed at reducing elevated IOP (the only modifiable risk factor)
Principal method: Chronic therapy with drugs
Drug Therapy for Glaucoma
Drugs lower IOP by:
Facilitating aqueous humor outflow
Reducing aqueous humor production
Preferred route: Topical
Systemic effects relatively uncommon
Combined therapy more effective than monotherapy
If drugs are ineffective, surgical intervention is needed to promote outflow of aqueous humor
Laser trabeculoplasty
Trabeculectomy
first line drugs for glaucoma
Beta-adrenergic blocking agents
Timolol
Alpha2-adrenergic agonists
Brimonidine [Alphagan]
Prostaglandin analogs
Latanoprost [Xalatan]
2nd line drug therapy for glaucoma
Cholinergic agonists
Carbonic anhydrase inhibitors
Angle-Closure Glaucoma
Also known as narrow-angle glaucoma
Precipitated by displacement of the iris, which prevents the exit of aqueous humor
Develops suddenly and is extremely painful
No treatment; irreversible loss of vision in 1 to 2 days
Much less common than open-angle glaucoma
Treatment
Drug therapy
Corrective surgery -> Laser iridotomy, Iridectomy
Beta-Adrenergic Blocking Agents
Approved for use in glaucoma: Betaxolol, carteolol, levobunolol, metipranolol, and timolol
Lower IOP by reducing production of aqueous humor
Used primarily for open-angle glaucoma
Initial therapy and maintenance therapy
Considered first line – although prostaglandin analogs are becoming more favored
Adverse effects
Local: Usually minimal - stinging
Systemic: Heart and lungs if absorbed in sufficient amounts (bradycardia, bronchospasm)
Cardioselective agents (betaxolol (B1 selective) is recommended for asthma patients
Prostaglandin Analogs
Latanoprost
Lowers IOP by facilitating aqueous humor outflow
As effective as beta blockers, with fewer side effects
Can cause harmless brown pigmentation of the iris
Travoprost
Bimatoprost
Tafluprost
Alpha2-Adrenergic Agonists
Two agents approved for use:
Apraclnidine: Only for short-term therapy
Lowers IOP by reducing aqueous humor production and possibly by increasing outflow
Does not cross blood-brain barrier and therefore does not promote hypotension
Brimonidine [Alphagan]: First-line drug for long-term therapy
OTC as Lumify – ocular decongestant
Common side effects
Headache, dry mouth & nose
Alpha2 Agonist/Beta Blocker Combination
Combigan: 0.2% brimonidine and 0.5% timolol
Treatment: 1 drop applied to affected eye twice daily (about every 12 hr)
Benefits and adverse effects are about equal to those seen when the two drugs are applied separately
Use if pts pressure was not controlled with one drug only
Pilocarpine
Direct-acting cholinergic agonist that causes:
Miosis
Contraction of the ciliary muscle
Now considered a second-line drug for open-angle glaucoma
Emergency treatment of acute angle-closure glaucoma
Adverse effects
Retinal detachment
Decreased visual acuity
Local irritation, brow pain, and eye pain
Systemic effects
Cholinesterase Inhibitor:Echothiophate (phospholine iodide)
Long duration of action
Inhibits the breakdown of acetylcholine (ACh), promotes accumulation of ACh at muscarinic receptors
Effect on eye: Miosis, focusing of the lens for near vision, reduction of IOP
No longer a first-line drug
Adverse effects
Myopia; absorption into the system can cause parasympathomimetic responses
Cataracts
Carbonic Anhydrase Inhibitors (CAIs)
Dorzolamide [Trusopt] topical
Reduces IOP by decreasing production of aqueous humor
Generally well tolerated: Ocular stinging, bitter taste, allergic reaction in 10% to 15% of patients
Acetazolamide and methazolamide: Systemic CAIs
Adverse effects
Nervous system, teratogenic, acid-base disturbances, electrolyte imbalances
Cycloplegics and Mydriatics
Cycloplegics: Paralyze ciliary muscles
Mydriatics: Dilate the pupil
Uses
Adjunct to measurement of refraction
Intraocular examination
Intraocular surgery
Treatment of anterior uveitis
Adverse effects
Blurred vision and photophobia
Precipitation of angle-closure glaucoma
Systemic effects- not admin in enough amounts to have systemic effects
Phenylephrine: Adrenergic agonist
Mydriatic agent (pupil dilation)
Does not cause cycloplegia
