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Thesis

Optical Centration in Multifocal Lens Design and its Effect on Vision

4 December 2015

Abstract

Multifocal contact lenses rely on a complex optical delivery system to provide the needed optics to the eye. Proper centration of these optics is vital to success. Conventionally these lenses are fitted over the center of the cornea (pupillary axis). This method of fitting contact lenses does not necessarily ensure proper alignment of the multifocal optics over the visual axis. Our purpose is to investigate the effect of multifocal optical centration on objective (distance acuity) and subjective (clarity, visual ghosting, and visual fluctuation) vision.

Five clinical emmetropes (with no existing ocular or systemic diseases) was recruited for our study. Medmont Corneal Topography was used to identify the optical location of the multifocal contact lenses and their distances from the visual axis. Visual acuity and subjective vision was compared to identify the effect multifocal contact lens centration had on vision.

Findings show consistent correlation between optical centration to both objective and subjective vision. Lenses appear to consistently decenter superiorly and temporally despite a manufactured 1.00mm nasal offset of optical centration. There appears to be an association between increasing ADD power and decreasing subjective vision. This association was not evident on objective distance vision.

With this study we hope to identify a variable clinician can consider when fitting multifocal contact lenses. The corneal topographer is an instrument that is capable of detecting the location of the multifocal optics on the eyes. We hope to improve the success of multifocal contact lenses in the management of presbyopia and other accommodative disorders. In addition, the use of high add multifocal soft contact lenses have proven successful in myopia control. We hope to apply what we learned to further the success of these lenses with children and ensure a good visual outcome.


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