Glaucoma experts please help?

Question

there are many types and subtypes of glaucoma the open angle and the one which is narrowed or blocked angle glaucoma. There are many drugs used to manage these types of glaucoma. I have found out that adrenergic agonists(sympathomimetic) /alpha agonists are used to treat OPEN ANGLE glaucoma. My question is 1. why are these adrenergic agonists used in glaucoma when in fact they mimic the sympathetic response they cause pupillary dilation which increases intraocular pressure which is contraindicated in glaucoma, please explain how it can help in glaucoma if it causes pupil dilation? I have also found out that beta blockers(sympatholytic) suppress the sympathetic response causing pupil constriction decreasing intraocular pressure which helps in glaucoma. Cholinergic drugs/parasympatholytic mimic parasympathe response also helps by pupil constriction. and for open +narrow glaucoma 2. is my understanding correct? which drugs are used for which type? 3.why are benzodizepines not for glaucoma

Answer 1

There goes the answers to your questions:


Adrenergic agonists are effective in reducing intra ocular pressure.. (IOP).. this is a well established fact... hteir mechanism of action is by increasing conventional trabecular uveoscleral outflow of aquoes from the anterior chamber of the eye so reducing the IOP.

There are two types of adrenergic agonist... which are

a) non selective: as epinephrin (eyedrops preparation called epifirin)... but although these agents decrease IOP they are no longer used in treating glaucoma due to multiple side effects... as irritation and mydriasis and CME and rapid tolerance..
you will hardly find any physician really treating glaucoma using epinephric nowadays..

b) selective adrenergic agonists:.. these agents selectively stimualte alpha 2 adrenergic receptors.. teh best known highly selective alpha 2 adrenergic agonist is brimonidine.. known in the market as Alphagan eyedrops.. very popular... that drug by selectively stimulating the alpha 2 receptors only will decrease IOP while avoiding the side effects that were caused by nonselective agents that stimulated all receptor types... so it doesn't cause pupil dilatation like the nonselective agents.. the drug Alphagan is used in markets widely nowadays and is a good effective drug and is a selective alpha 2 agonist..




As for Beta blockers.. .: they are effetive agents in reducion of IOP.. and they are still used in the market .. as Timolol.. or in the famous combination eyedrops Cosopt which is a combination of beta blocker and acetazolamide.. beta blockers do NOT cause pupilary constriction.. they just have systemic side effects that can be serious sometims and are contraindicated in some cases as asthma and heart block.. their mechanism of IOP reduction is by inhibiting cAMP production so reduce aquoes secretion..

you should not really try to explain the mechanism of action of every anti-glaucoma medicaiton by its effect on the pupil..



All of the antiglaucoma medications can be used in open angle and angle closure glaucoma.. with some prefernces of course..

however the important MIOTIC to use in termination of angle closrue glaucoma attack is Pilocarpine which is a parasympathomimetic agent.. directly acting on cholinergic receptors.. it does cause miosis.. but other than miosis it is a potent antiglaucoma medication that decreases IOP and can be used in treating open angle glaucoma but is no more in fashion due to side effects and the availbility of better medications nowadays..



one thing in your question: cholinergic drugs are parasympathomimetics not lytics.. that is they mimic parasypmathetic... like pilocarpine that act on end organ cholinergic receptors.. the betablocker eye drops doesn't act on the autonomic nervous system at all.. although it is a parasympatholyitic in theory... but it acts on teh beta receptors present on ciliary epithiliuem decreasing aqous producion.. i hope this is clear..



As for benzodiazepines .. it is a group of tranquilizer drugs.. why would it be used in glaucoma??!! ..

you might have meant brinzolamide.. or acetazolamide.. and both belong to the group of carbonic anhydraze inhibitor.. .. both of these drugs are used in glaucoma treatment.. avaiable in teh market as eyedrops preparation Azopt (Alcon), and Trusopt (MSD).. and in combination as Cosopt (MSD)
and acetazolamide can be takes orally as cidamex tabs or injections (Diamox) for management of acute glaucoma attacks..

hope that answers you..


you can contact me in case you need further elaboration..

Answer 2

Adrenergic agents like adrenalin are SYMPATHOMIMETIC and dilate pupil and are NEVER used in glaucoma..Parasympatholytics like atropine hyoscine also are NEVER used. Pilocarpine Acetyl choline Neostigmine and Physostigmine are parasympathomimetic and so can be used in glaucoma to constrict pupils. Diamox is a diuretic works by inhibiting the enzyme carbonic anhydrase and used specifically for glaucoma.