Presbyopia Correction On The Cornea; Are We Really Able To Induce Depth Of Focus Or Is It Just Fancy Monovision?

PresbyLasik is growing in popularity. Much is presented talking about the induction of depth of focus through induced spherical aberration on the cornea but results are varied and at times look like simple monovision.  We compare 2 excimer laser presbylasik profiles. The induction of negative spherical aberration  to give a central near effect  is found to be more effective for enhacing close vision.  Significant differences are demonstrated between the 2 laser systems in their ability to achieve a targeted spherical aberration result.

Presbylasik is shown to be an effective treatment option for presbyopic patients but it is better to be able to achive a real shift in spherical aberration giving significant extension of the depth of focus. 

Private refractive surgey practice over several years using both Zeiss and Schwind Excimer laser platforms. A single highly experiened refractive surgeon performed all the procedures and followed up all patients at post operative visits.  Diagnostic equipment used includes Pentacam, Atlas, MS39, WASCA, iTrace and Combi Wavefront analyser.

Patients having laser vision correction for refractive error who also seek correction for presbyopia are studied. The first cohort were operated on the Zeiss Mel 80 laser using the Presbyond treatment profile.  This data was analysed and published.  The second cohort of patients were operated using the Schwind Amaris Excimer laser with the Presbymax treatment profile.

Refractive results, visual outcomes, functional vision and final values for spherical aberration are analysed, presented and interpreted.

 Zeiss:  Myopes had  average of 0.032 um (6mm pupil) extra +ve SA compared with  non-presby treatment.  As positive SA this gives a peripheral near effect and would account for just 0.09D extra Depth of focus (DOF) when the pupil dilates.  Hyperopes showed 0.059um more negative SA giving a central near effect that would give an extra 0.12D DOF.

 Schwind Presbymax  targets a specific value of post operative SA.  The average  postoperative SA was -0.26um @ 6mm  which would account for  0.6D extra DOF.  Negative SA was induced for  myopes and hyperopes. A weak association was found between the final value for SA and patient satisfaction with near vision.  Patients with higher pre-operative SA had less predictable values for final SA.

The Zeiss Presbyond profile controls the range of final SA.   The inability to target a predictable value for SA and the induction of positive spherical SA in all myopes limits its ability to give a useful elongation of the depth of focus above monovision. 

Schwind Presbymax induces  negative spherical aberration for all refractive corrections and the ability of the system to truly compensate for the potential induced SA intrinsic in the underlying refractive correction make this a versatile platform.  Presbylasik treatments work and newer treatment algorithms such as Presbymax  give the surgeon more control over the balance between monovision and induced depth of focus.