Pharmacology and Microbiology
Ocular Medications
Mydriatics dilate: phenylephrine stimulates alpha receptors and does not paralyze accommodation, while tropicamide and cyclopentolate are anticholinergics that also cause cycloplegia. Cycloplegia is needed for reliable refraction in children. Topical anesthetics such as proparacaine act quickly and briefly; repeated use delays epithelial healing and masks injury, so they are for examination only, never for at-home pain control.
Common therapeutic classes include antibiotic drops for infection, corticosteroids for inflammation, beta blockers and alpha agonists and carbonic anhydrase inhibitors and prostaglandin analogs for glaucoma. Prostaglandins increase outflow and can darken iris and lashes. Beta blockers are avoided in reactive airway disease.
Administration and Infection Control
Instill drops into the lower cul-de-sac, avoid touching the bottle tip to the eye, and use punctal occlusion to reduce systemic absorption and nasolacrimal drainage. Wait several minutes between different drops. Hand hygiene is the single most important infection-control measure. Distinguish cleaning, disinfection, and sterilization; tonometer tips require approved disinfection between patients, and contact lens trial sets require documented hygiene protocols.
Traps: assuming phenylephrine paralyzes accommodation (it does not), confusing steroid risks with antibiotic risks, and forgetting that punctal occlusion reduces systemic side effects.
Rule of thumb: if a question mentions bronchospasm or asthma, avoid topical beta blockers.
Worked example: a child needs refraction; tropicamide alone may be insufficient, so a cycloplegic such as cyclopentolate is chosen to relax accommodation and reveal true hyperopia.