Fig 22. Patients wearing bifocals of +1.75 D or more may experience difficulty seeing at intermediate distances. The uncertainties of patient acceptance of trifocals may be reduced by using Fresnel lenses. A patient"s existing bifocals can be convened into trilocals by applying a lens strip above the bifocal as illustrated on the left. On the right a large-field trifocal has been created by applying to a single vision carrier lens a Fresnel lens for the reading segment and a second Fresnel lens to create the intermediate area.