Contact lenses
lens tightness
REFRACTIVE ERRORS, LENS, CORNEA
Three types of multifocal contact lenses were used to compare the dependency variances between different optical or different material designs (Table Contact lens design and specification parameters.The process of fitting begins with an initial assessment, which includes evaluating eye health, visual acuity, and specific refractive errors, as well as patient's medical history. Subsequently, a trial lens fitting assessment are performed, which involve checking for signs of decentration, excessive movement, or lens tightness. The central cornea and limbus should not experience compression, and a certain tear thickness should be ensured. Initially, the central area generally needs to maintain a tear thickness of about 300 µm. The initial position of the landing zone should be located at approximately halfway between the corneal edge and the lens edge, and it should not exert excessive pressure on the cornea. After wearing the trial lenses for 30 min, the central tear thickness should still be around 150–200 µm. Only after determining the appropriate trial lenses should a refraction check be performed. Subsequent follow-up appointments, training, education, and regular monitoring were required.