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Some doctors do try to customize the post operative spherical aberration by matching the corneal spherical aberration to the IOL spherical aberration. However note that this is not something that can be done with the same precision as targeting spherocylindrical power. Neither is it as crucial to the final visual outcome. With aspheric lenses the negative spherical aberration is constant for a particular lens platform. With the Acysof IQ range it is of the order of -0.2 microns at 6mm with the Tecnis range it is -0.27 microns. With the Bausch and Lomb lenses (Sofport AO Akreos AO Envista) it is 0 microns. In order to customise the spherical aberration the doctor would have to choose a different lens platform altogether. How did the companies decide on the amount of SA to put in? With the Tecnis that was based on the average in a group of people. There will inevitably be people with more or less than this amount of SA. I do not know how Alcon chose the number for their lens and for B+L the zero number is a reflection of the fact that if SA correcting lenses like the Tecnis are decentered or tilted the negative SA in the lens can give rise to other aberrations. ie the zero SA lenses are very forgiving of any small imperfections in lens position. Cutting SA down to a bare minimum eg putting a Tecnis in an eye with +0.27 microns of corneal SA means getting really good contrast and clarity at the focal point of the lens. This comes at the expense of depth of focus. ie there are pros and cons of nottle SA and of having some SA. In any case for may people the effects of customizing vs not customizing are not noticeable. Where customizing the lens is more relevant may be in post LASIK eyes. ie post myopic LASIK corneas tend to have a lot of +SA and do well with the Tecnis range of lenses. Post hyperopic LASIK corneas tend to have a lot of -SA and do well with the normal spherical lenses like the AR40e. But choosing lenses like this does not really require customization either it is based on knowledge of what was done before. The IOLmaster does not capture this information. In order to get this information corneal topography needs to be done. The topographer machine could be separate from the biometer or in some cases like the Aladdin from Topcon the topographer is integrated with the biometer. If your doctor is just using the IOLmaster then he/she is not making any attempt at customizing the SA but as I mentioned before this is not usually a very crucial thing to do.

2014-12-26 02:40:21

David