Femtosecond laser technology

Femtosecond laser technology is giving a new lease of life to incisional techniques for correcting postoperative astigmatism, according to a study presented here. “There has certainly been something of a rebirth of these techniques in recent years thanks to advances in laser technology,†Eric D Donnenfeld MD told delegates attending the XXIX Congress of the ESCRS.

“The advantages of laser femtosecond incisions are that they are customisable and adjustable, meaning that refractive incisions are no longer an art form as they were in the past – they are now a science with the ability to place incisions of the exact size and exact depth and in the exact place you want them every single time,†he said.

Dr Donnenfeld, in private practice at Ophthalmic Consultants of Long Island, New York and clinical professor of ophthalmology at New York University, noted that limbal relaxing incisions (LRIs), the traditional mainstay of surgical astigmatism correction, offer many advantages to surgeons.

“They are inexpensive, easy to perform, and use minimal instrumentation. They can be done at the same time as cataract surgery, they have no impact on the cataract healing process and they can be repeated postoperatively if necessary,†he said.

The downside of LRIs includes the fact that the surgeon must have a topographer and be able to interpret topography. They may also induce irregular astigmatism when greater than 2.0 D, they carry the risk of perforation, and they are less precise than laser vision correction, he said.

In using LRIs, one of the major challenges facing an ophthalmologist is where to place them during cataract surgery, said Dr Donnenfeld.

“Do we place them on the refractive axis, the keratometric axis or the topographic axis? And the answer is ‘none of the above’,†he said.

A critical step in obtaining accurate astigmatic correction is being able to calculate the surgically induced cylinder from the incision, said Dr Donnenfeld. While there are several ways to achieve this, the problem is that the measurements are all based on an assumed incisional induced astigmatism, which in reality can be very variable.

“Therefore the only true way to measure postoperative astigmatism accurately is to do it intraoperatively and I think this is the future of cylinder correction,†he said.

Dr Donnenfeld said that preoperative planning for LRI procedures has been greatly facilitated thanks to online calculators such as AMO’s LRIcalculator.com which allow surgeons to input the preoperative information in order to obtain better postoperative results.

“It uses the Donnenfeld and the Nichamin nomograms, you insert the preoperative Ks, the incision location, and it gives you a prediction of where to place your incision which is very useful to bring to the operating room with you,†he said.

Dr Donnenfeld said that he typically uses LRIs for small amounts of cylinder, between 0.50 and 0.75 D, and he also uses the phoropter to locate and centre incisions on the steep axis and further refine the postoperative astigmatism.

To take LRIs to an even higher level of precision and accuracy, however, the femtosecond laser represents a major advance for incisional techniques, said Dr Donnenfeld.

“The true rebirth of incisional technology is the advent of arcuate incisions with the femtosecond laser. The early results with the LenSx femtosecond laser (Alcon) have really been quite interesting and I think represents the future direction for astigmatic correction,†he said.

The incisions are essentially dragged and dropped onto the eye using on-screen technology and surgeons can measure pachymetry intraoperatively using the onboard OCT. More reproducible cataract incisions create more predictable postoperative astigmatism, he explained.

“I usually preset the depth of my incisions to 85 per cent and then these incisions can be opened and adjusted on the table as required. One of the nice aspects of these incisions is that they have very minimal effect until the incisions are open, which allows you as a surgeon to manipulate these incisions postoperatively or intraoperatively to predict better astigmatic results,†he said.

Dr Donnenfeld said that using intraoperative aberrometry (Wavetec ORange) can also be used to titrate results in the operating room.

“The patients can also be examined the next day with topography and refraction and the incisions can then be opened, if needed, to increase the effect of the incision and adjust the refraction,†he said.

The results of the first case series of 14 patients treated with arcuate incisions showed that 86 per cent of eyes had postoperative astigmatism of 0.50 D or less and 71 per cent of 0.25 D or less, said Dr Donnenfeld.

Summing up, Dr Donnenfeld said that image-guided femtosecond laser cataract surgery looks set to regenerate interest in corneal incisional techniques.

“I believe this will bring the 80 per cent of ophthalmologists who do not perform LRIs at the present time into the ability to perform incisional surgery. It is computer controlled and it is faster, safer, easier, customisable, adjustable and repeatable. I think that this approach will remove many of the inconsistencies of the procedure and will improve understanding and accuracy of not only LRIs, but of all our corneal incisions,†he said.