Mydriatics And Cycloplegics Flashcards
Autonomic: parasympathetic pathway to the iris
Pretectal n. -> EW n. -> ciliary ganglion -> sphincter
Autonomic, sympathetic pathway to the iris
Hypothalamus -> ciliospinal center of Budge -> superior cervical ganglion -> dilator muscle
Direct agonist
A substance that binds to and fully activates its neuronal receptor
(Drug acts as a NT)
Indirect agonist
Potentials the action of the neurotransmitter
Causing NT to bind
Antagonist
Any substance that inhibits the activity of the neurotransmitter
An antagonist may bind to __ but not activate it.
Bond to a receptor
Affinity but no efficacy
An antagonist may bind to ___ , thereby deactivating it.
Neurotransmitter
Cholinergic agents mimic
Acetylcholine
Acetylcholinerase
Degrades ACh and halts transmission
Muscarinic
ACh receptors present in the ciliary body’s and iris
Nicotinic
ACh receptors are present in somatic muscle
Muscarinic agonists bind to and activates
Cholinergic receptors
Muscarinic agonist drugs cause iris
Sphincter contraction leading to pupillary miosis
Muscarinic agonist causes ciliary body
Contraction leading to accommodation
Example of a muscarinic agonist
Pilocarpine, green cap
Muscarinic antagonist binds to and inhibits
Cholinergic receptors (antimuscarinic)
Muscarinic antagonist causes pupil
Sphincter inhibition leading to mydryasis
Muscarinic antagonist causes ciliary body
Inhibition leading to Cycloplegia
Examples of muscarinic antagonist:
STopACH
Scopolamine Tropicamide Atropine Cyclopentolate Homatropine (Red cap)
All Mydriatics/ cycloplegic drugs are classified by the FDA as pregnancy category___ meaning….
Category C
Potential benefits may warrant use of the drug in pregnant women despite potential risks
CNS side effects caused by antimuscarinic agents vary depending on
The ability of the drug to penetrate the blood- brain barrier
Potential CNS side effects of antimuscarinic drugs include
Drowsiness, hallucinations, cognitive impairment, and coma
Atropine is the most
Potent and longest acting anti cholinergic available for clinical use
Atropine is only used when
Total cycloplegia is required
Residual accommodation is
The amount the patient is able to accommodate at the time of maximal cycloplegia
Residual accommodation of atropine
Zero diopters
What are the clinical uses of atropine?
Refraction, myopia control, amblyopia, uveitis
How is atropine used for refraction
Evaluation of esotropia in children less than 6 yrs ole
Duration of action too long for routine refraction
Atropine in myopia control
Long term low dose therapy inhibit progression
Atropine used in amblyopia
Penalization of better seeing eye as alternative to occlusion
Atropine used in uveitis
Long term relaxation of ciliary body in severe anterior uveitis
Contraindications and precautions of atropine
Allergy
Down’s syndrome
small children
Spastic paralysis or brain damage
What happens if atropine is given to spastic paralysis or brain damage
Increased risk of CNS effects and death in pts
Systemic overdose symptoms of atropine
Hot as a hare, blind as a bat, dry as a bone, red as a beet, mad as a hatter
Fever, blurred vision,, dry skin, flushing, delirium (hallucinations and psychosis)
Adverse effects of atropine
Effects from systemic overdose, and IOP elevation
Atropine causes open glaucoma pts to experience a transient increase in IOP because
Decreased tension on the scleral spur by the ciliary body will tend to shrink the aqueous drainage passages through the trabecular mesh work
The elevation of IOP is NOT due to angle closure
Relaxation of the ciliary muscle
Increases IOP
Contraction of the ciliary muscle
Decreases IOP
IOP effect of cycloplegic agents in normal patients
Minimal and variable
Iop might increase slightly
IOP effect of cycloplegic agents in subjects with POAG
IOP will increase following cycloplegia
Cyclopentolate is the drug of choice for
Routine cycloplegic refraction
Mostly used in 1%
Typical residual accommodation of cyclopentolate is
1.25 D
Using cyclopentolate, you will see faster cycloplegia with less residual accommodation in
Lightly pigmented eyes
Pigment sequestration
Some drugs when instilled into the eye will reversible bind to melanin
What happens if pigment sequestration occurs when a drug is instilled
While bound to melanin the drug is not available to induce any pharmacological effects
The drug will have a normal effect after being released fro melanin
The net effect of pigment sequestration is
Delayed onset, prolonged duration of action and smaller peak pharmacological effect
Pigment sequestration is most pronounced in
Heavily pigmented eyes
Side effects of cyclopentolate
Stinging
Toxic keratitis with prolonged use
Transient elevation in IOP in POAG patients
DOSE RELATED CNS EFFECTS: TRANSIENT PSYCHOTIC REACTIONS MAY OCCUR BC IT READILY CROSSES BLODD BRAIN BARRIER
Contraindications of cyclopentolate
Increased risk of CNS effects in infants, young children and children with spastic paralysis and brain damage
Drug of choice for routine mydriasis
Tropicamide 0.5% and 1% sol.
Whats the difference for 0.5% and 1% tropicamide
Equivalent mydriatic effect of 0.5% and 1%, greater cycloplegia with 1% solution
Tropicamide is a clinically effective cycloplegia because
It lasts about 30 min
Duration of action of tropicamide
Max mydriasis 20-30 min duration 6 hrs
Max cycloplegia 20-45 min duration 6 hrs
Contraindications of tropicamide
No reported adverse systemic effects
Extremely safe systemically
Side effects of tropicamide
Stinging upon instillation
Transient increase IOP in POAG patients
Clinical considerations of homatropine
Weak but prolonged cycloplegic effect and strong mydriatic effect make it suitable for uveitis therapy
Duration of action of homatropine
Max mydriasis 40-60 min duration 1-3 days
Max cycloplegia 30-60 min duration 1-3 days
Contraindications of homatropine
Same as atropine :
Hypersensitivity, Down’s syndrome
Clinical considerations of scopolamine
Not routinely used
Reserved for pts allergic to the others
Duration of scopolamine
Very long
Max mydriasis 20-30 min duration 3-7 days
Max cycloplegia 30-60 min duration 3-7 days
Contraindications of scopolamine
CNS effects are more common than other agents because it more easily crosses the blood brain barrier
Cycloplegic refraction advantages (3)
More accurate refraction in kids and pts who are unable to cooperate
Diagnosis of accommodative esotropia and evaluating strabismus in kids
Necessary to diagnose latent hyperopia and pseudomyopia (acc spasm)
Cycloplegic refraction disadvantages (4)
Decrease VAs because if spherical aberration
Loss of normal ciliary tonus lead as to refraction thats too hyperopic
Blurry vision and photophobia
Risk of adverse drug effects
Cycloplegic refraction can lead to a refraction that is too hyperopic so you will need to
Cut plus from the refraction prior to prescription
Tropicamide during cycloplegic refraction
Effectiveness decreases after____. Useful for ____patients.
Effectiveness decreases after 35 min
Useful for non amblyopia, non strabismus, myopic, or low hyperopic kids and adults
Cyclopentolate for cycloplegic refraction
Drug of choice for cycloplegic refraction
Atropine during cycloplegic refraction is used for ____.
Use in esotropia children < 6 years
Can reveal additional hyperopia in these children compares to cyclopentolate
When will cycloplegic refraction be unreliable
If residual accommodation is >2.00D
Using pupillary reactions to asses redisual accommodation
NOT RELIABLE
Assessment of residual accommodation during cycloplegic refraction
Subjective push up of accommodative target ‘
Stability of Retinoscopy reflex
Adrenergic neurotransmitter
Norepinephrine
Transmitter uptake stops
Transmission
What type of agonist/anti agonist is phenylephrine
Direct acting agonist
Substance that increases the activity of the neurotransmitter
Indirect acting agonist
Indirect acting agonist have 2 methods (and examples)
- Inhibit reputable of norepinephrine (cocaine)
2. Release of stored presypnaptic norepinephrine (hydroxyamphetamine)
Direct alpha-Adrenergic agonist bind to
And activate alpha Adrenergic receptors
Direct alpha Adrenergic agonist effect on eye (iris and ciliary body)
Causes stimulation of iris dilator muscle -> mydriasis
But no effect on ciliary body or accommodation -> no cycloplegia
An example of a direct alpha Adrenergic agonist (mydriasis but no cycloplegia)
Phenylephrine (red cap)
Mode of action of indirect alpha - Adrenergic agonist
Causes release of stored norepinephrine from the presypnaptic neuron
Mydriatic effect of indirect alpha Adrenergic agonist
Same as direct
Stimulation of iris dilator - mydriasis
An example of a indirect alpha Adrenergic agonist
Hydroxyamphetamine (red cap)
Phenylephrine cardiovascular effects
Risk of adverse cardiovascular event have been more frequently reported with the 10% strength
Therefore 2.5% is recommended for routine use
10% phenylephrine solution increases
10% strength produces an increase in rate but not magnitude of mydriasis
10% strength of phenylephrine useful for
Breaking posterior Synechia
% of phenylephrine used in clinic
2.5%
Drug contraindications of phenylephrine
MAO inhibitors
Tricyclics antidepressants
Reserpine, guanthidine or methyldopa
Avoid phenylephrine in patients who
Patients taking systemic antropine
Orthostatic hypotension
Malignant hypertension
Thyrotoxicosis
Limit 10% strength phenylephrine to _________ when attempting to break synechia
Limit 10% strength to 1gtt per hour per eye when attempting to break synechia
Do not give multiple doses of 2.5% sol for _____
routine dilation
Only recommended in infants and the elderly
Phenylephrine systemic side effects
Acute systemic hypertension ventricular arrhythmia, tachycardia, subarachnoid hemorrhage
Deaths following phenylephrine
Following use of 10% topical phenylephrine have been reported
Ocular side effects of phenylephrine
Mild stinging, pigmented aqueous floaters, little or no effect on IOP
Use of 10% phenylephrine for routine dilation
NEVER
Only used for breaking posterior synechia
When to use multiple doses of phenylephrine
NEVER for routine pupil dilation
If patient isn’t dilating , instill additional drops of tropicamide, not phenylephrine
Hydroxyamphetamine clinical considerations
Mydriatic effectiveness equivalent to phenylephrine
Role in localizing lesions in Horner syndrome
Only commercially available as 1% solution combine with 0.25% tropicamide
Localizing lesion in Horner syndrome
Hydroxyamphetamine
Duration of action hydroxyamphetamine
Max mydriasis 60 min
Duration 6 hrs
Side effects of hydroxyamphetamine
Little to no elevation of IOP in POAG pts
Less stinging than phenylephrine
Safety difference between hydroxyamphetamine and phenylephrine
May be safer than phenylephrine in high risk pts. However, cardiovascular events have occurred shortly following paremyd instillation
Hydroxyamphetamine can be used in the differential diagnosis of
Horner syndrome
Indirect alpha Adrenergic agonist
Hydroxyamphetamine causes
Release of norepinephrine from the presypnaptic neuron
If presypnaptic neuron is dead -> no dilation in response to hydroxyamphetamine
