Change in Efficiency of Aspheric Intraocular Lenses Based on Pupil Diameter

We read with interest the article by Eom and associates on aspheric intraocular lens performance. The authors stated that “aberrations of the cornea increase with age.” Although according to recent studies this is true for all corneal higher-order aberrations, it is very important to highlight that the amount of change of those aberrations with age has been found to be far less (approximately half) than the change in total ocular higher-order aberrations. Furthermore, specifically with regard to corneal spherical aberration, it has been shown to be stable with age.

The authors performed measurements under high mesopic conditions (8 lux). We carried out some light measurement using a luxometer (HD450 Digital Light Meter; Extech, Nashua, New Hampshire, USA) and found that in the street in front of the clinic at night (with some street lights on), the value ranged between 13 and 15 lux. So, a level of 8 lux is rather uncommon in normal life. Thus, we believe that in less strict mesopic conditions, a much higher percentage of eyes than 10% in their group would have shown smaller pupil size than the minimum calculated for having any positive effect of asphericity.

According to our experience (unpublished data, 2010), eyes with a similar amount of corneal spherical aberrations (Keratron Scout; Optikon 2000 S.p.a., Rome, Italy) implanted with an aspheric intraocular lens, the AcrySof SN60WF (Alcon, Inc, Fort Worth, Texas, USA), had significantly lower ocular total spherical aberration (0.05 μm) than eyes with a spheric intraocular lens, the AcrySof SA60AT (Alcon, Inc; 0.17 μm), measured with a Shack-Hartman wavefront sensor (WASCA; Carl Zeiss Meditec AG, Jena, Germany). However, the 2 groups did not show differences in contrast sensitivity (Optec 6500; Stereo Optical Co, Chicago, Illinois, USA) either in photopic (85 cd/m 2 ) or scotopic (3 cd/m 2 ) conditions, and with or without glare.

We believe that we did not find differences in contrast sensitivity since our typical cataract patient in Colombia is older than 60 years and has dark irises and small pupils, which cancels out any positive effect of the asphericity. To reach a 5-mm pupil we had to dilate their pupils pharmacologically.

A rational approach to the selection of best lens in a cataract patient certainly should include assessment of corneal spherical aberration before surgery in a diameter equivalent to the mesopic natural pupil and comparison of this value with that determined for the same diameter for the various aspheric lenses available on the market (data that manufacturers have not supplied). In this way, the surgeon could offer patients real information on the beneficial effect or not of that particular lens on postoperative visual quality. Furthermore, optimal remnant spherical aberration after cataract surgery is an unsettled issue.

Undoubtedly, we have a long way to go in this topic.

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Jan 9, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Change in Efficiency of Aspheric Intraocular Lenses Based on Pupil Diameter

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