Contact Lenses
Lens types and materials, insertion, removal, and care, and recognizing common complications.
Lenses, Care, and Complications
Lens families — soft (hydrogel and silicone hydrogel: comfort, easy adaptation) vs rigid gas-permeable (crisper optics, corrects corneal astigmatism through the tear lens, masks irregular corneas). Torics correct astigmatism; multifocals address presbyopia.
Fit vocabulary — base curve (larger radius number = flatter = looser fit), diameter (larger = tighter), and power (converted from the spectacle Rx for vertex distance above ±4.00 D).
Care rules that prevent disasters — fresh disinfecting solution every night, never top off, never tap water (Acanthamoeba), no sleeping or swimming in lenses unless specifically prescribed, replace cases quarterly.
Red flags — pain, redness, light sensitivity, or discharge in a lens wearer is a keratitis until proven otherwise: lenses out, same-day exam, bring the lenses and case for culture.