Mydriatics

Mydriatics are dilating eye drops that are used to enlarge the pupil for eye examinations, with the ability to visualize the optic nerve and retina as well as the whole lens

• Dilating drops work either by temporarily paralyzing the muscle that makes the pupil smaller (the iris sphincter muscle) or by stimulating the iris dilator muscle.
  • Patients with lighter eye color (blue, hazel) are more sensitive and dilate faster than patients with darker eye color (brown)
  • Keeping the pupil big is essential after surgery to prevent scar tissue formation (synechia)
• Making the pupil big before cataract surgery makes it easier for the surgeon to remove the lens of the eye (the cataract is in the lens)
• If the cataract is small, enlarging the pupil can allow the patient to see ‘around the cataract’ and perhaps avoid surgery  
• After glaucoma surgery, mydriatics help the eye to stay well formed and recover when the eye pressure gets too low
• Some forms of glaucoma are due to the iris and pupil coming too far forward. Dilating drops help to restore the normal anatomy of the eye and treat/prevent this kind of glaucoma (closed-angle glaucoma)
• Dilating drops can temporarily blur vision, so in children can blur the good eye to force the brain to use the bad eye to treat amblyopia (lazy eye)
• All dilating drops make the pupils large and may make the eyes more sensitive to bright lights

Mode of Action

Parasympathetic antagonists (parasympatholytics)

Act by paralyzing the iris sphincter muscle. This category of medicines will make the pupil larger and paralyze the muscle in focusing the lens (accommodation). As a result, they will cause the eye to be blurry, especially for up close (reading, near play)

Tropicamide

(Tropicamide, Mydriacyl, Tropicacyl)

Drops are available at 0.5% (used in premature infants) and 1%

Duration of action: up to 6 hours

Cyclopentolate

(Ak-Pentolate, Diopentolate, Cyclogyl)

Drops available are 0.5% (used in premature infants), 1%, and 2% (rarely used)

Duration of action: up to 24 hours

Homatropine

(Isopto Homatropine)

Drops are available at 2% and 5%

The lower strength is usually preferred in children

Duration of action: 2-3 days

Atropine

(Atropisol, Isopto Atropine)

Drops are available at 0.5% or 1% and ointment at 1%

Duration of action: 1-2 weeks

Sympathetic agonists (sympathomimetics)

Act by stimulating the iris dilator muscle

Phenylephrine

(Ak-Dilate, Dionephrine, Mydfrin, Prefrin Liquifilm, Spersaphrine)

Drops are available at 2.5% and 10% (should never be used in children)

Duration of action: 3-6 hours

Although the advantage of phenylephrine is that it does not cause blurring of vision like the parasympatholytic, it tends not to dilate the pupil well enough unless used in combination with parasympatholytics. Some doctors chose to use both types of drops mixed in the same bottle: eg, 0.8% tropicamide + 5% phenylephrine

Side Effects

Whitening of the eyelids and skin around the eyes

• This is completely harmless and will resolve spontaneously
• It is due to the constriction of small skin blood vessels 

Atropine can cause redness/flushing of the face, a warm sensation of the skin to touch, irritability, or sweating

All mydriatics sting for a few seconds after they are instilled in the eye