Pharmacology, part 25: Nervous System Medications - Antiglaucoma Agents
by Cathy Parkes March 11, 2021 Updated: December 29, 2021 9 min read
In this article, we cover the important medications you need to know for glaucoma, beginning with a brief overview of open angle vs closed angle glaucoma. The Nursing Pharmacology video series follows along with our Pharmacology Flashcards, which are intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI, and NCLEX.
When you see this Cool Chicken, that indicates one of Cathy's silly mnemonics to help you remember. The Cool Chicken hints in these articles are just a taste of what's available across our Level Up RN Flashcards for nursing students!
What is glaucoma?
Glaucoma is an eye disorder that results in increased intraocular pressure.
Intraocular pressure (IOP) is a measure of fluid pressure in the eye and is measured using tonometry, a test that measures the cornea's resistance to indentation. mmHg, which stands for millimeters (mm) of mercury (Hg), is a unit used to measure pressure. You might recognize mmHg because it's also used for blood pressure!
A normal level of intraocular pressure is between 10 and 21 mmHg. An intraocular pressure above 21 mmHg can be a sign of glaucoma.
Want an easy way to remember the expected range for intraocular pressure that has to do with IHOP? Check out our Lab Values flashcards for nursing students!
Open angle glaucoma
Open angle glaucoma is the most common type of glaucoma marked by gradually increasing intraocular pressure. This can cause loss of peripheral vision, mild aching in the eyes, and headache.
Closed angle glaucoma
Closed angle glaucoma is less common. It occurs when forward displacement of the iris closes the angle between the iris and sclera completely, resulting in a sudden increase of intraocular pressure. This can cause severe eye pain, severe headache, nausea/vomiting, and reddened sclera.
Glaucoma is one of many important disorders covered in our Medical-Surgical flashcards for nursing students!
Topical Beta Blocker - timolol (Timoptic)
Timolol is used to treat primarily open-angle glaucoma. It is applied topically
How to remember timolol is for the eye: Tim stuck his finger in my eye and laughed out loud (lol).
Mode of action
Because Timolol is a nonselective beta-blocker, it decreases the aqueous humor production in the eye which helps to lower intraocular pressure.
Timolol has some mild side effects, including temporary stinging in the eye.
If you have a patient using timolol, advise them not to touch the applicator to their eye.
After your patient puts the drops in, teach them to hold gentle pressure to the nasolacrimal duct (also called the puncta) for about one minute to help the medication absorb and act locally on their eye.
Throughout your normal life, your nasolacrimal duct drains away old lubricating eye fluid via the nasal cavity, so new eye fluid can be replenished. When medicated eye drops are added to the eye, we don't want them to be drained right away. The medication needs to be on the eye (and absorbed into the eye) to help the eye!
Think of a fluoride treatment at the dentist. You use a tray so that the fluoride can sit against (and act on) your teeth. If you didn't use a tray, you would salivate and swallow like normal, and the fluoride would disappear very quickly, and it would not be able to act effectively on your teeth. Blocking the nasolacrimal duct so the medication doesn't immediately drain is the same idea.
Importantly, nasolacrimal occlusion also helps prevent systemic absorption.
Timolol is only meant to act locally on the eye. If correct application procedures are not used with timolol, it can drain into the nasal cavity and be absorbed systemically (like an intranasal drug) and cause the same side effects normally seen with nonselective beta blockers, including hypotension, bronchoconstriction, and bradycardia.
Carbonic anhydrase inhibitor - acetazolamide (Diamox)
Acetazolamide can be used to treat glaucoma as well as heart failure and altitude sickness. Unlike the other antiglaucoma agents covered here, acetazolamide is an oral medication.
I can see a zoo because acetazolamide fixed my glaucoma.
Mode of action
Acetazolamide inhibits carbonic anhydrase in the eye (which indirectly reduces fluid transport), which decreases aqueous humor production and helps to lower intraocular pressure.
It inhibits carbonic anhydrase in the kidneys which causes increased excretion of sodium, potassium, bicarbonate, and water. So acetazolamide acts as a diuretic as well, which is why it's used for heart failure.
Acetazolamide, and other medications that inhibit carbonic anhydrase, can result in flu-like symptoms and GI upset, an electrolyte imbalance (because of the sodium and potassium excretion), and hyperchloremic acidosis (because of the bicarbonate excretion).
Nursing Care and Administration
If you have a patient taking acetazolamide, make sure to monitor their electrolyte levels, acid-base balance, and intraocular pressure.
Acetazolamide should be administered with food to help prevent the common side effect of GI upset.
Cholinergic (direct acting) - Pilocarpine (Diocarpine), acetylcholine (Miochol-E)
Pilocarpine and acetylcholine are direct-acting cholinergic medications used to treat open angle glaucoma. They are applied topically.
Now that pilocarpine fixed my glaucoma, I can see your big pile ‘o crap by the door.
Mode of action
Pilocarpine and acetylcholine work to decrease intraocular pressure by improving aqueous humor outflow.
Side effects of pilocarpine and acetylcholine may include blurred vision, some stinging, as well as eye pain.
If you have a patient using pilocarpine or acetylcholine for glaucoma, instruct them not to touch the applicator to their eye, and hold pressure to the nacrolasimal duct for one minute to prevent systemic absorption.
Prostaglandin agonists - travoprost (Travatan), latanoprost (Xalatan)
Travoprost and latanoprost are prostaglandin agonists used to treat open angle glaucoma.
Mode of action
Travoprost and latanoprost work to reduce intraocular pressure by improving the outflow of aqueous humor. They are applied topically.
Travoprost and latanoprost can include side effects like eye stinging, which is common across most topical anti-glaucoma agents. In addition, this class of medication can also cause eyelash growth! Another medication in this class is bimatoprost (which also ends in -prost) which is sold under the brand name Latisse, for eyelash growth!
These medications can also result in eye color change due to an increase in iris pigmentation. For some users, this may be a less desirable side effect than the eyelash growth.
Let’s raise our glasses and say “Prost!” (cheers in German) now that my glaucoma is fixed AND I have longer/thicker eyelashes.
If a patient is using travoprost or latanoprost, they should be given the same teaching we covered in the other topical antiglaucoma agents, which is to not touch the eye with the applicator.
If you have a patient using travoprost or latanoprost, make sure to monitor their intraocular eye pressure which should be in the desired range of 10-21 mmHg.
Sympathomimetic - Brimonidine (Alphagan P, Lumify)
Brimonidine is a sympathomimetic (mimics stimulation of the sympathetic nervous system) used for open angle glaucoma. It is applied topically.
Mode of action
Brimonidine helps to reduce intraocular pressure by decreasing production of aqueous humor and improving aqueous humor outflow.
Brimonidine can cause the common side effect of eye pain and stinging, as well as drowsiness.
If you have a patient using brimonidine, advise them not to touch the applicator to their eye. After they put the drops in, teach them to hold gentle pressure to the nasolacrimal duct for about one minute to help prevent system absorption.
If you have a patient using brimonidine, make sure to monitor their intraocular eye pressure which should be in the desired range of 10-21 mmHg.
Okay, in this video we are going to talk about medications that are used for glaucoma, starting with a topical beta-blocker which is timolol.
So timolol is used to treat primarily open-angle glaucoma.
It is a nonselective beta-blocker, so basically it decreases the aqueous humor production in the eye which helps to lower intraocular pressure.
In terms of side effects, they're usually pretty mild. It can cause some temporary stinging in the eye.
When your patient is getting this medication, you want to advise them not to touch the applicator to the eye. And then after they put the drops in, they want to hold gentle pressure to the nasolacrimal duct or puncta for about one minute to help prevent systemic absorption.
So with systemic absorption, you would expect some of the side effects that we see with nonselective beta-blockers, so this can include hypotension, bronchoconstriction as well as bradycardia. As long as they kind of hold pressure there and don't overdo it on the drops, they should not get those systemic side effects.
Also, keep in mind that the normal intraocular pressure that we want to see in patients is between 10 and 21 mmHg, so that is the goal.
The way I remember this medication is that Tim, some little kid named Tim, little bully, stuck his finger in my eye and he laughed out loud, so timolol. And that's how I remember that timolol is for my eye and it is used to treat open-angle glaucoma.
Alright, now we're going to talk about a carbonic anhydrase inhibitor which is acetazolamide.
Acetazolamide can be used to treat glaucoma as well as heart failure and altitude sickness.
So my somewhat lame tip for remembering what this medication is for if you look at the word acetazolamide, it looks like "I can see a zoo." And I can see that zoo because my glaucoma is fixed thanks to acetazolamide. So that's all I've got here. If you have another tip then definitely leave it here in the comments.
So acetazolamide inhibits carbonic anhydrase in the eye which decreases aqueous humor production and helps to lower the intraocular pressure. It also inhibits carbonic anhydrase in the kidneys which causes increased excretion of sodium, potassium, bicarb, and water. So it acts as a diuretic as well, which is why it's used for heart failure.
In terms of side effects, flu-like symptoms are very common with this class of medication in addition to GI upset.
And then electrolyte imbalances are also a risk because we're causing that excretion of sodium and potassium that can really mess with those electrolyte levels.
Another side effect is hyperchloremic acidosis because we're getting rid of bicarb as well, so that can cause acidosis.
So when we are giving a patient acetazolamide, we're definitely going to want to monitor their electrolyte levels and their acid-base balance. Keep in mind that our goal for intraocular pressure is between 10 and 21 mmHg.
And we should administer this medication with food to help prevent GI upset, which is a common side effect with this medication.
Alright. Let's now talk about a direct-acting cholinergic medication used for glaucoma. Medications that fall within this class include pilocarpine as well as acetylcholine.
These medications are used for open-angle glaucoma.
They work to decrease intraocular pressure by improving aqueous humor outflow.
Side effects may include blurred vision, some stinging, as well as eye pain.
The way I remember pilocarpine is that it kind of looks like pile o' crap. So I can see your big ole pile o' crap because my glaucoma's been fixed, thanks to this medication! So that's my little weirdo hint for remembering this medication.
Again, you want to teach your patient not to touch the applicator to their eye, and they should hold pressure to that nasolacrimal duct for a minute to help prevent systemic absorption.
Alright. Now let's talk about prostaglandin agonists, which include medications such as travoprost and latanoprost. Both of these end in that -prost at the end.
They're used for open angle glaucoma.
They help to reduce intraocular pressure by improving the outflow of aqueous humor.
Side effects can include stinging, which is really common across all of these topical anti-glaucoma agents, but in addition, this particular medication can cause eyelash growth, which is kind of awesome, right? I think this is the only med I can think of that has a really great side effect that you can look forward to.
But it can also cause eye color change due to an increase in iris pigmentation, which may not be something you want.
So my tip for this class of medication, because they end in -prost, prost means cheers in German, so let's raise our glasses and say "prost" because our glaucoma is fixed, and we have longer eyelashes because of this little awesome side effect that this class of medication carries.
Keep in mind, we want to do our same teaching that we did with our other anti-glaucoma agents in terms of not touching the eye with the applicator, monitoring the IOP, which should be between 10 and 21 mmHg.
Okay. The last anti-glaucoma agent that I want to go over here is a sympathomimetic named brimonidine.
Brimonidine is used for open angle glaucoma.
It helps to reduce intraocular pressure by decreasing production of aqueous humor and also improving aqueous humor outflow.
Side effects include stinging, which is the same thing we've seen with all of these topical anti-glaucoma agents. In addition, eye pain and drowsiness are possible side effects.
And again, you're going to want to do the same teaching for your patient in terms of not touching the applicator to the eye, holding pressure at the lacrimal duct after installation of the eyedrops for about a minute, and then you'll want to keep an eye on intraocular pressure. It should be somewhere between 10 and 21 mmHg.
So that is it for our anti-glaucoma agents. In my next video, we will get into other nervous system medications for disorders such as Alzheimer's and Parkinson's disease, so hang in there with me!
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