Contact Lenses and Ocular Prosthetics
What this domain tests
Contact lens questions test material science, fitting logic, complication recognition and prosthetic eye care. You must connect oxygen transmission, fit and hygiene to corneal health.
Materials and fitting
- Dk is oxygen permeability; Dk/t is transmissibility and depends on thickness.
- Silicone hydrogels achieve high Dk/t; conventional hydrogels rely on water content.
- Rigid gas-permeable lenses use tear exchange; assess fluorescein pattern: central pooling with mid-peripheral bearing indicates a steep fit.
- Base curve, diameter and sagittal depth determine the fit; keratoconus needs steeper, larger RGP designs or scleral lenses.
Complications
- CLARE, microbial keratitis, giant papillary conjunctivitis, neovascularisation and solution hypersensitivity.
- Red eye with pain, photophobia or decreased vision means remove the lens and refer the same day.
Prosthetics
- A conformer maintains the socket after enucleation or evisceration; a custom ocular prosthesis is fitted later.
- Clean the prosthesis with the prescribed solution, avoid alcohol, and check socket health regularly.
Worked example
An RGP wearer has 3+ central staining and a steep fluorescein pattern with central pooling. Reasoning: mechanical and hypoxic insult from a steep fit. Withhold lens wear, treat the epithelium, refit with a flatter base curve or higher Dk/t material, and review after epithelial healing.
Traps
Confusing Dk with Dk/t; refitting a keratoconic eye with a flat lens; advising tap-water rinsing; missing microbial keratitis in a painful red eye.