Wednesday, April 8, 2009

Aberrations provide important cues for accommodation

Natural accommodation is a dynamic process that is aided by aberrations that give the eye cues as to which direction to focus, Ioannis G Pallikaris MD, PhD told attendees of the innovator session at the 2009 ASCRS annual meeting held at the Moscone Centre (pictured above) in San Francisco, US.

“Aberrations are necessary to guide accommodation,” Dr Pallikaris said. The defocus images of lenses without aberrations are identical whether they are over or under corrected, where as they are different in a lens with aberrations, he explained. Astigmatic, higher order, spherical and chromatic aberrations all play a role.

In patients with presbyopia, accommodation is slower and less stable than in younger patients. This leads to fatigue in older patients and the image on the retina is rapidly and constantly changing, particularly in near vision. This constantly changes the refractive qualities and aberrations in the lens.

Presbyopic correction with multifocal or accommodative lenses is a static compromise that cannot duplicate this process, Dr Pallikaris noted. It results in acceptable distance and near visual acuity at the expense of vision quality. “Achieving super vision is not a goal,” he said. Ophthalmologists must use their understanding and judgement to make the lens choice that best meets patient needs.

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