Either criterion may be applied in accordance with a proposed international standard for IOLs. The model eye method can be applied over a broader range of dioptric powers and is relevant for materials that interact with aqueous. Both tests appear to have a greater ability to detect unwanted surface aberrations than resolution testing of IOLs in a water cell using parallel light, a method described in the current American National Standards Institute standard.
We describe a methodology to predict the outcome of clinical tests caused by changes made to the optical elements of the human eye. This formalism, called the expected visual outcome model, is based on in vitro measurements of the optical transfer function and takes into account a simple model of human threshold performance. The clinical tests under consideration are high-contrast visual acuity and contrast sensitivity. Using the expected visual outcome, we describe a useful performance index called the predicted visual acuity graph, which can be measured clinically. The theoretical results are compared with visual function measured in patients with pseudophakic (multifocal and monofocal) implants.
The optical performance of new multifocal intraocular lens designs is frequently assessed using the modulation transfer function (MTF). We discuss the relationship between the MTF and clinical measures of human visual function, such as threshold visual acuity and contrast sensitivity. Using in vitro MTF measurements of a human eye model containing a multifocal or monofocal intraocular lens, we predict relative changes in acuity and contrast sensitivity and outline the techniques using a simple model of human retinal threshold detection. Specific concepts introduced include the visual acuity graph, predicted visual acuity graph, and predicted contrast sensitivity function.
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