The gradual tapering of the diffractive steps from the center to the outside edge of a lens to create a smooth transition of light between the distance, intermediate, and near vision focal points.
Various light-related vision disturbances encountered by pseudophakic (and phakic) patients. Positive dysphotopsias are characterized by brightness, streaks, and rays emanating from a central point source of light, sometimes with a diffuse, hazy glare. Negative dysphotopsias are characterized by subjective darkness or shadowing.
Estimated lens position
An estimation of the distance at which the principal plane of the IOL will be situated behind the cornea. Derived from biometric measurement of the eye used in IOL power calculation.
Modulation transfer function
A measure of optical performance that describes contrast degradation of a sinusoidal pattern as it passes through the optical system as well as the cutoff special frequency beyond which fine detail will not be resolved. Often used when discussion wavefront aberrations.
A refractive strategy for the selection of contact lens or IOL powers such that one eye has better distance vision and the other eye has better near vision.
Piggyback intraocuar lens
A second IOL inserted in an eye that already has an IOL in place. A piggyback lens may be used when the postoperative IOL power is incorrect or when the needed IOL power is higher than what is commercially available.