The cataract lies within a clear bag called the capsular bag. In conventional cataract surgery, the surgeon makes a continuous circular opening (5 to 6mm in diameter) into the front part of the capsular bag. This is required to gain access to the cataract in order to remove it. The remainder of the bag is left intact in the eye so it can hold the new intra-ocular lens that the surgeon implants.
In conventional cataract surgery, the surgeon opens the front of the bag manually using a fine needle and forceps. The aim is get to a near perfect circular opening in the front of the bag to ensure that your new intra-ocular lens sits centred within your eye. If the capsular bag is torn, then the new intra-ocular lens may well not sit in the centre of your eye and your vision may not as good as we had hoped for.
In laser cataract surgery, the femtosecond laser automatically makes the circular opening in the front of the capsular bag by producing high pulses of energy to cut the bag. The idea is that the laser can do this more accurately than the human hand.
The evidence suggests that the laser is indeed more accurate than the human hand as expected. However this step of cataract surgery is often deemed relatively straightforward by most experienced surgeons and some think that automating it with a laser may not improve vision results.
It seems that the actual characteristics of each person’s bag such as its flexibility and the way it is held in the eye has more to do with the risk of abnormal centering than the way we open the front of the bag.
Some surgeons believe that a more precise circular opening with the femtosecond laser is important in patients who are receiving multifocal orpremium intra-ocular lenses. We are still awaiting study data to see if this is the case.