Contact Lenses and Ocular Prosthetics
Contact lens items test parameter selection, fit evaluation, and complication recognition, plus basic prosthetic eye care.
Lens selection and fit
Match base curve, diameter, power, oxygen permeability (Dk/t), water content, and modulus to the cornea and the patient's needs. Silicone hydrogels give high oxygen transmission and are preferred for hypoxic corneas. Evaluate the fit with fluorescein: centration, coverage, edge lift, and movement. A steep lens shows central pooling and tight edges; a flat lens shows central bearing and excessive edge lift.
Complications
CLARE is acute overnight corneal edema with photophobia after extended wear. Infiltrative keratitis shows focal infiltrates with intact epithelium; microbial keratitis shows an epithelial defect with stromal infiltrate and needs urgent culture and hourly antibiotics. Giant papillary conjunctivitis produces upper tarsal papillae and lens intolerance. Tight lens syndrome causes injection, pain, and reduced vision. Solution-related toxicity and case contamination are common and preventable.
Specialty fits
Orthokeratology flattens the central cornea for myopia control. Scleral lenses vault the cornea and are used in keratoconus, severe dry eye, and after penetrating keratoplasty; check apical clearance and limbal landing. Prosthetic eyes need daily cleaning, regular polishing, and replacement roughly every five years; watch for discharge, ptosis, and contracted socket.
Worked example
A keratoconus patient intolerant of corneal rigid lenses has K readings of 55 D. Reasoning: fit a scleral lens with apical clearance of about 200 to 300 microns, limbal clearance without impingement, and no bubbles; assess after 20 to 30 minutes of settling, then over-refract. A conventional flat rigid lens would bear on the cone and fail.
Traps
Ordering a lens without evaluating the fit; ignoring overnight-wear symptoms; missing giant papillary conjunctivitis; and fitting a scleral lens without checking limbal clearance.