The femtosecond laser is a powerful tool for ophthalmic surgery. While its use in creating corneal refractive surgery is widely accepted as groundbreaking, its reception for cataract surgery has been mixed, spanning the spectrum from enthusiastic to skeptical. These lasers are expensive to purchase, with each costing about half-a-million US dollars, and also expensive to run with maintenance contracts and per-use costs.
When we use a femtosecond laser to create incisions for cataract surgery: Are the results good? Is it worth the high cost? What are the pitfalls? How does it compare to diamond keratomes or steel blades? What are the tricks to getting great results?
The two main incisions that we make in cataract surgery are the main phaco incision and the smaller paracentesis incision. The paracentesis incision is the less critical of the two, though it still needs to be constructed appropriately so it seals well. We will focus very little on this incision since it makes little difference if it is made with a 15 degree blade, an MVR blade, a diamond, or a laser.
The main incision is more important because it can alter the astigmatic profile of the cornea, induce irregularities, and cause issues with intra-ocular movement of instruments. A poorly constructed main incision can be committed with any number of instruments including a femtosecond laser. Beginning surgeons may make an incision that is too long, too short, or misplaced.
The femto laser works best on tissue that is relatively transparent, so placing the incision in the sclera or limbus is typically avoided. While the default setting of the laser may be to create a completely avascular incision in the clear cornea, these types of incisions are problematic. Avascular incisions never quite fully heal with a sufficient strength and they can be opened with blunt instruments years later. They also induce more astigmatism and may cause more foreign body sensation to the patients.
Even in cases where I use a femtosecond laser to assist with cataract surgery, I prefer using a diamond keratome to make the main phaco incision. I have learned to program the femtosecond laser to produce the type of incision that I like: peripheral, nicking limbal vessels, appropriate width and tunnel length, astigmatically neutral, and balanced architecture.
There is a third incision that we sometimes do during cataract surgery in order to address astigmatism: relaxing incisions placed on the steep axis.
These incisions are of two main types:
- Limbal Relaxing Incisions (LRI)
- at the far-peripheral cornea near the limbus
- Astigmatic Keratotomy (AK)
- at the mid-peripheral cornea
Note that patients with 1.25 diopters or more of corneal astigmatism would be best served with a toric lens to address the astigmatism. LRIs and AKs are better suited to about 1 diopter or less of corneal astigmatism. The range from 1.0 to 1.25 diopters can go either way depending on the clinical situation and consistency of the biometry.
The femtosecond lasers can be programmed to perform AK treatments with the advantage being a very predictable architecture including depth to a specific value such as 80% of the measured pachymetry.
Today, femtosecond lasers are useful for cataract surgery with the utility dependent on the surgeon and the patient’s condition. For routine cases, I do not find a definitive benefit in using a femtosecond laser. But for cases such as shown in the video below with a white cataract, the femotsecond laser can be helpful.
In this video, even though I used the femtosecond laser to create the capsulorhexis and an astigmatic keratotomy incision, I still prefer using the diamond keratome for creation of the primary phaco incision. In the future, femtosecond lasers could evolve further to produce results that rival diamond keratomes — time will tell.