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Femtosecond laser capsulotomy fixation lens design
The development of femtosecond laser cataract and lens surgery has changed the surgical paradigm. There is a dramatic increase in surgical precision with exact capsulotomy sizing, shape and position. In addition corneal cylinder is treated with intrastromal astigmatic keratotomies, so there is the potential for excellent post-op optics.
A decentred or tilted lens implant, which induces unintended spherical change as well as decentration aberrations is a limiting factor on visual outcome. It is important to ensure the lens implant is perfectly centred at the time of surgery and remains centred for the long term.
X-Y coronal placement of the capsulotomy
The ability of the femtosecond laser to create precise capsulotomies facilitates a radical change in lens implant design. The femtosecond laser capsulotomy can be placed at any given coronal or x-y location and this can be used to hold a lens implant optic. A groove is placed at the periphery of the optic, so the optic is captured by the capsulotomy, which is placed into this groove.
Then the lens optic is centred and there is avoidance of excess tilt, so long as the bag is stable. Instead of the lens optic moving inside the capsular bag, it is held stable by the capsulotomy. The lens haptics can be redundant, but can remain useful as stabilisers and also as a backup if a capsulotomy is not intact.
Having just a groove is sufficient for capsular capture, but can be fiddly. It is much easier to have some lugs as well as a groove and then the lens implant can be easily held by the capsulotomy. Following design and development by Oculentis in the Netherlands this lens is now European Union CE marked.
Since the lens sits further forward then if the optic was sited within the capsular bag then the lens constant for biometry is less than for the equivalent lens optic held within the capsular bag. For the Oculentis 313 lens the lens constant within the capsular bag is 118.2 and for the capsulotomy fixated lens is 117.8
Another lens developed by Dr Samuel Masket and manufactured by Morcher Gmbh has a groove on the anterior edge near around the optic periphery and this may reduce dysphotopsia. This lens has been researched by Dr Hans Burkhard-Dick in Germany, who is using a Catalys femtosecond laser to create the capsulotomy.
Nishi in the 1980s in Japan first realised the value of capsular fixation and more recently Professor Marie Tassignon developed the “bag-in-the-lens”, which is CE marked. Professor Tassignon realised that capturing an anterior and posterior capsulotomy eliminated PCO and resulted in a stable optic captured by the anterior and posterior capsule. The issue then was that manual capsulorrhexis performed by the most accomplished surgeon, is variable in size, shape and position. Even with corneal marking and guide instruments this is technically exacting to be consistent. Primary posterior capsulorrhexis also has issues and is even more exacting to perform consistently than anterior capsulorrhexis. The femtosecond laser then is ideal to create these precise capsulotomies, which will allow reliable and stress-free implantation of the "bag-in-the-lens".
These advanced lens designs employ the unique precision of the femtosecond laser to deliver a reliable, centred lens implant optic.