Contact Lens Fitting and Evaluation
Fitting and evaluation
Start with keratometry, horizontal visible iris diameter, palpebral aperture, and tear film. Soft lenses typically have base curves of 8.0 to 9.5 mm and diameters of 13.8 to 14.5 mm; a good fit shows centration, full corneal coverage, 0.2 to 0.5 mm of movement on blink, and resistance on the push-up test. Rigid gas permeable lenses are judged by fluorescein pattern: alignment with gentle apical clearance, mid-peripheral bearing, and adequate edge lift. Over-refract over the lens before ordering.
Care and complications
Teach hand washing, rubbing and rinsing with the correct solution, never tap water, and adherence to the replacement schedule. Recognize contact lens acute red eye after overnight wear, microbial keratitis (pain, photophobia, infiltrate; Pseudomonas is the classic overnight-wear organism), giant papillary conjunctivitis, neovascularization, and dryness.
Worked example
A rigid lens shows central pooling, a broad mid-peripheral band of bearing, and excessive edge lift. That is a steep fit: flatten the base curve by 0.05 to 0.10 mm or slightly reduce the diameter, then re-evaluate after 20 minutes of wear.
Traps
Handling lenses without washing hands. Using tap water. Not inspecting the lens for defects before insertion. Skipping over-refraction. Failing to ask about overnight wear, the single biggest risk factor for microbial keratitis.