mydriatics

Introduction

mydriatics are agents used to dilate the pupil of the eye, primarily to allow fundoscopy, but can also be used to treat uveitis

known or suspected narrow-angle glaucoma
iris-clip intraocular lenses as mydriasis may cause the lens to dislocate
phenylephrine and cyclopentolate are used with extreme caution (or avoided) in premature infants or those with feeding intolerance or necrotising enterocolitis
plus specifically for antimuscarinics:
- use with extreme caution in infants, young children, and individuals with severe neurological impairment due to risks of central nervous system (CNS) toxicity (seizures, psychosis)
- atropine is heavily restricted or avoided in very young children due to high absorption and risk of systemic anticholinergic poisoning
plus specifically for sympathomimetics:
- high-dose (10%) phenylephrine is absolutely contraindicated in infants and the elderly due to severe toxicity risks
- severe hypertension, tachycardia, or a history of recent myocardial infarction
- uncontrolled hyperthyroidism
- patients taking monoamine oxidase inhibitors (MAOIs) or tricyclic antidepressants
in general, patients should not drive a car or operate machinery while these are active due to impaired vision

dilate the pupil by blocking the iris sphincter muscle from constricting
Homatropine hydrobromide:
- mainly use as mydriatic: 1% → peak 40-60min; return normal 1-3 days;
  - 5% → full mydriasis but still not full cycloplegia;
Cyclopentolate HCl:
- mainly as mydriatic: 0.5-1% → peak 30-60min, return normal 1 day;
Tropicamide:
- mainly as mydriatic: 0.5-1% → peak 20-40min, return normal 6hrs;
Dicyclomine:
- Used in peptic disease & hypermotility states;

dilate the pupil by stimulating the alpha-1 adrenergic receptors on the iris dilator muscle
they do not paralyze the focusing muscles (cycloplegia) and typically leave pupil light reflexes intact
phenylephrine