Ocular pharmacology of glaucoma week 1 Flashcards
What is glaucoma?
First aid: Optic disc atrophy with characteristic cupping usually with elevated intraocular pressure (IOP) and progressive peripheral visual field loss.
Notes:
- Usually associated with increased intraocular pressure
- The pressure results in direct and vascular damage to the optic nerve
- The result is loss of vision
- The process can be acute or chronic
- The outflow tract can be “closed” or “open”
Where is aqueous humor produced?
What is the normal flow of aqueous humor?
Aqueous Flow
Aqueous humor is produced in the ciliary body
Aqueous movement:
- from the posterior chamber through the pupil to the anterior chamber
- into the trabecular meshwork
- into the Canal of Schlemm
- then into the episcleral veins
Alternatively, some aqueous moves in a “uveo-scleral outflow” or “non-conventional pathway”, and is mysteriously absorbed
For normal flow:
- There must be free movement through the pupil (obstructed in closed angle glaucoma due to movemnt of lens against iris)
- The “angle” (the route to the trabecular meshwork) must be open (obstructed in closed angle glaucoma)
- The trabecular meshwork must be porous enough for aqueous to flow through it
Which ANS system (SANS or PANS) has greater influence on the control of the pupil?
What SANS and PANS receptors are present in the pupil?
PANS >>> SANS
alpha-1 (SANS) and M3 PANS)
What is the result of M3 agonists acting on the pupil? What is the best example of this? (drug)
What is the result of M3 antagonists acting on the pupil?
What is the result of an alpha-1 agonist acting on the pupil? Alpha-1 antagonist?
M3 agonists induce miosis
(pilocarpine is best example)
• M3 antagonists promote mydriasis or dilation
PANS >> SANS
- Alpha-1 agonists induce mydriasis
- Alpha-1 antagonists induce miosis, but are very weak
Name 3 drugs commonly used to dilate the pupil.
What are their mechanisms of action?
What is their relative length of action?
Dilating the eye is a common practice during eye exams.
Short-acting atropine-like drugs are generally used (common drugs are tropicamide and cyclopentolate).
Short-acting adrenergic drugs (phenylephrine) are often added to enhance the effect.
These drugs pucker the iris at the pupil! Can cause further pinching off of angle in closed angle glaucoma
tropicamide (muscarinic anagonist): mydriasis, cycloplegia (ciliary muscle paralysis)
cyclopentolate (muscarinic anagonist): mydriasis, cycloplegia
phenylephrine: direct competitive alpha 1 agonist. mydriasis. also used to increase BP (vasoconstriction), decongestant, enhance alertness in CNS
Explain what occurs in acute angle closure glaucoma.
Acute Glaucoma
- Dilation, and then slow reversal of dilation results in the pupil being caught in the “mid-position”
- Impeding of aqueous flow results in “pupillary block”
- Pressure builds behind the iris, pushes it forward, closes the angle, and rapidly increases intraocular pressure: Acute angle closure glaucoma
What is pupillary block?
What are the physical exam findings and symptoms?
Pupillary block
Exam/symptoms
- Pupil fixed in mid-position
- Cloudy view of the iris from corneal edema
- Very high intraocular pressure
- No view of normal angle structures
- Very red eye
- PAIN!
How is angle closure treated?
Angle closure treatment
- Constrict the pupil! (pilocarpine)
- Reduce production of aqueous humor (b-blocker and carbonic anhydrase inhibitor)
- Peripheral laser iridotomy (prevents pupillary block from forward movement of the iris)
- djo.harvard.edu: During the LPI, a laser is used to make a small opening in the peripheral iris (the colored part of the eye). This changes the fluid dynamics in the eye and “opens” the angle. If a patient already has acute angle closure glaucoma, the small opening that is made in the peripheral iris allows fluid to drain more normally and also lowers the eye pressure.
What is open angle glaucoma? What is the cause?
What does examination of the angle reveal?
What is the intraocular pressure like?
Open angle Glaucoma (identify site of abnormalilty)
- The trabecular meshwork becomes resistant to flow with age (increase in production of glycosaminoglycans)
- Examination of the angle reveals normal-appearing trabecular meshwork (“open angle”)
- Intraocular pressure can range from 20 to 50 without pain or redness (no pain bc is a chronic issue)
How is open angle glaucoma treated? (classes of drugs used and what they do)
Open angle treatment
- b-blockers (reduce aqueous humor production)
- Prostaglandins: PGF2-a analogues (increase “uveal-scleral” outflow
- alpha-2 agonists (reduce production of aqueous humor and increase uveo-scleral outflow—very weak)
- CA inhibitors, either oral or topical (reduce production of aqeuous humor)
Name common medications used for open angle glaucoma tx and their effects.
Common medications
- B-Blockers timolol maleate was the first
- PGF2a analogs: latanoprost was the first
- alpha-2 agonists are weak (neuroprotection?) brimonidine
- carbonic anhydrase inhibitors: acetazolamide orally or IV dorzolamide topical
