L4 Mydriatics, Cycloplegics and Miotics Flashcards
how is mydriasis achieved?
stimulation of the dilator muscle (mainly alpha receptors)
paralysis of the sphincter muscle
How is dilation achieved through the SYMPATHETIC AND
PARASYMPATHETIC division?
SYMPATHETIC: ACTIVATED
PARASYMPATHETIC: DEACTIVATED
what is an example of a Adrenergic agonist / Sympathomimetic drug? what are 3 ocular side effects?
Phenylephrine (1 gtt 2.5% sol)
* Takes longer to reach max action: ~20-60 mins, does not affect accom
side effects:
*widening of palpebral aperture
– alpha receptors are present in the Muller muscle
- blanching of the conjunctival blood vessels,BV constricts
– alpha receptors are present in conj bv. - Accom effect??
what are 2 other clinical uses of phenylephrine? 4 precautions?
Other clinical uses:
* Breaking posterior synechiae
* Diagnostic test for Horner’s syndrome
precautions:
* Cardiac disease
* Hypertension
* Arteriosclerosis
* Hyperthyroidism (hypersensitivity)
Sympathomimetic Drugs
what is an example of a Cholinergic Antagonists/ Parasympatholytic /Anti muscarinic drug? what is the onset, recovery and how can it be reversed?
Tropicamide (1 gtt 0.5% or 1.0 % sol)
(NOTE: 1% solution can be used for highly pigmented iris.)
- Rapid in action: 15 mins
- Recovery ~ 2hrs
- Can be reversed c/2% pilocarpine (M agonist)
what are 2 precautions of tropicamide?
- Down’s syndrome (hypersensitivity)
- Brain Disorders
what are the 4 steps we must take prior to dilation?
- Estimate angle of anterior chamber
- Shadow test
- Van Herick technique
- Gonioscopy - Perform IOP check (tonometry) before & after dilation
- Have an appropriate miotic available
- History
* Episode of angle closure
– Must be taken to ensure that patient has NOT had
angle closure before.
* Known allergy to drug
* Presence of glaucoma (treated with miotics)
* Systemic drugs
* Systemic diseases, health condition
7 Signs & Sxs of AACG
- Blurry vision
- Nausea + vomiting
- Pain
- Ciliary flush
- Elevated IOP
- Fixed semi-dilated pupil
- Corneal edema
4 contraindications for mydriatics?
- A narrow angle or closed angle
- iris supported IOL
- subluxated crystalline lens or IOL
- Hx suggesting angle closure glaucoma
NOTE:
Each mydriatic would have individual contraindications
what is a common combination of dilating drugs?
Common combination:
* Tropicamide (0.5%) + Phenylephrine (2.5%)
May be indicated in:
– elderly pxs
– diabetic pxs
what are cycloplegics? why are not all cycloplegics mydriatics even though they cause pupil dilation?
All cycloplegics are antimuscarinic agents.
* Therefore, all cycloplegics cause
mydriasis….but not all mydriatics are
cycloplegics. because *Cycloplegics block postsynaptic muscarinic
receptors in the iris & ciliary body.
3 common cycloplegics, their max action and they recovery
- cyclopentolate (0.5-1.0%)
Repeat 5 mins between drops
– Max action: 20-30 mins
– Recovery: 12-24 hrs - Atropine (0.5-1.0%)
– Max action: 1 day
– Recovery: 7-10 days - Tropicamide (1.0%)
– Max action: 20-30 mins
– Recovery: 6 hrs
4 traits of atropine poisoning?
- Blind as a Bat
– Effect on accommodation - Dry as a Bone
– Inhibition of sweat gland - Red as a Beetroot
– Dilation of blood vessel(??) - Mad as a Hatter
– CNS effects : hallucinations, confusion
4 uses of cycloplegics?
- For when a px cannot relax the accommodation sufficiently.
– Binocular vision anomalies eg:squints
– Latent hyperopia
– Children < 6 yrs of age - Treatment of myopia
- Treatment of amblyopia
- Treatment of uveitis: relaxes ciliary muscle spasm & prevents posterior synechiae
2 Advantages of cycloplegics
- Associated mydriasis
– facilitates examination of fundus, DFE - Bruckner test, test red reflex
how do miotics cause pupil constriction?
- Stimulate the sphincter (agonist)
- Paralysis of the dilator (antagonist)
what is an example of a Parasympathomimetics /Cholinergic agonist / Cholinomimetic drug?
Eg: Pilocarpine (2%, 1 gtt)
* Direct agonist
what is an example of a cholinergic antagonist/ Anti AcetylCholinEsterase (Anti-Ache) drug?
Eg: Physostigmine (0.25%)
- Terminating acetylcholinesterase (which causes constriction to be reduces) effect will allow Ach to accumulate.
what is an example of a Adrenergic antagonist (miotic) drug?
Thymoxamine (0.5%, 1 gtt)
* beta blocker
3 uses of miotics?
- Reversal of mydriasis
- Anti-glaucoma medication
- Diagnostic agent in Adie’s pupil
what are the 3 Pupil Disorders characterized by anisocoria? 3 common characteristics these disorders?
- physiological anisocoria
- horner’s syndrome
- adies syndrome
common characteristics:
* Only one pupil is involved
* Affected pupil is either unable to dilate OR constrict.
* This would indicate whether the parasympathetic or sympathetic system is involved.
what are the 4 characteristics of physiological anisocoria?
- Good light reaction in both eyes
- ***Tends to be equal anisocoria in bright and
dim light or slightly greater anisocoria in the dark - Pupillary size difference usually less than 1 mm
- no dilation lag
what causes horner’s syndrome?
Damage at any point along the sympathetic pathway may result in Horner’s syndrome
Damage can occur in the form of trauma, tumour involvement, infarction (abnormal blood clot), middle ear infection, or diseases of
the eye itself.
what are the features of horner’s syndrome?
- ptosis
- Miosis
- Anhidrosis
– impaired sweating ipsilaterally - Heterochromia iridis
- dilation lag
Exact presentation varies from life-threatening to benign conditions.
practice horners syndrome drawings
ok
what drug is used to detect horner’s syndrome? what is the mechanism of action?
Cocaine (5-10%)
Mechanism:
– Prevents reuptake of NE that has been released into
the synaptic junction
– In Horner’s, sympathetic innervation is disrupted affecting flow of nerve impulse that causes release of NE
» hence NO MYDRIASIS
How to distinguish between pre & post ganglionic lesion? what is the mechanism of action?
– Paredrine test:
* Hydroxyamphetamine (1%)
» Indirect-acting sympathomimetic
* Mechanism: Hydroxyamphetamine stimulates norepinephrine
release from the presynaptic vesicles an of intact neuron.
If the lesion is preganglionic, there will be normal norepinephrine stores.
* If the postganglionic neuron is not intact, nonorepinephrine is released.
Intact neuron: Normal NE stores
hence:
Post-ganglionic lesion
NO MYDRIASIS
Pre-ganglionic lesion
* MYDRIASIS
alternative to Paredrine test?
Phenylephrine supersensitivity
* Post ganglionic Horner’s will show supersensitivity. This
is not apparent in normal or preganglionic problems
Alternative
what is the cause of Adie’s Tonic Pupil? what us it characterised by?
Caused by a postganglionic parasympathetic lesion (denervation of the postganglionic nerve supply to the sphincter and ciliary muscle
pupils and accommodation are affected).
- Characterized by sluggish and segmental constriction to light
what is the 1 pharmacologic evaluation for adie’s tonic pupil?
The sphincter shows cholinergic hypersensitivity.
Larger pupil is supersensitive to 0.125% pilocarpine (cholinergic agonist ).
