ARCUATE INCISIONS

Arcuate keratotomy performed with a femtosecond laser at the time of cataract surgery can produce results approaching those achieved with toric intraocular lenses (IOLs), and the accuracy of the technique is likely to improve as experience increases with this steadily advancing new technology, said Roberto Bellucci MD, Hospital and University of Verona, Italy.

“I definitely think this is the future of our cataract surgery in our astigmatic patients in whom we decide not to implant a toric lens,” Dr Bellucci told the 19th ESCRS Winter Meeting in Istanbul, Turkey. Dr Bellucci noted that delegates responding to a survey conducted by the ESCRS at its meeting last year in London stated that they thought that, with modern cataract surgery, postoperative astigmatism should be no greater than 0.5D. He added that in his own experience, toric IOLs can achieve that result fairly reliably. For example, in a study he and his associates conducted, astigmatic patients implanted with toric IOLs had a mean residual astigmatism of only 0.42D.

However, toric IOLs have a few disadvantages. For example, they have to be ordered in advance, which in a few instances might mean that surgery needs to be delayed. In addition, they may not be available for extremes of high myopia or high hyperopia. The lenses also require precise alignment and can rotate in the postoperative period, and even a small rotation will lead to a great loss in anti-astigmatic effect.

“Incisional approaches also have problems. They are not perfectly centred and in the case of cataract surgery we don't exactly know if the existing refractive astigmatism is perfectly matching the topographic corneal astigmatism,” Dr Bellucci said.

Femto may improve precision

Dr Bellucci noted that the steady evolution of femtosecond laser technology and its increasing diffusion through ophthalmic practices appears likely to bring the efficacy and predictability of femtosecond laser incisional surgery into parity with that of toric IOLs before too long.

He presented the results of a study in which 23 eyes of 16 cataract patients with a mean age of 69 years underwent femtosecond laser arcuate incision procedures to correct 1.5D to 5.5D of congenital corneal astigmatism. Dr Bellucci performed the arcuate corneal incisions at the time of surgery prior to performing the phaco incisions. In all eyes he used the Victus femtosecond laser (Bausch & Lomb) and he calculated the length of the incisions using the Bascom Palmer protocol.

“That is quite an old protocol and useful for manual cuts, but so far there is no protocol for femtosecond laser incision. Hopefully the diffusion of femtosecond laser cataract surgery will lead us to a new protocol in a short time. However, this is the protocol that we decided to start with,” Dr Bellucci said.

After six months the mean astigmatism was reduced from almost three dioptres to 0.7D. However, that was still a little bit above 0.5D, which is the level of astigmatism that surgeons today consider acceptable after cataract surgery.

“We could be more precise with the cut angle and we could also take account of discrepancies between the corneal astigmatism and the refractive astigmatism in our treatment planning, by careful study of the cornea with the Scheimpflug camera in the preoperative assessment stage,” Dr Bellucci said.

One advantage femtosecond laser-created incisions have over manually created incisions is that they may be performed intrastromally, Dr Bellucci noted. He cited a study by Gunther Grabner’s group in Salzburg, Austria, in which 16 eyes of 16 patients underwent intrastromal incisions with a fixed protocol in which all eyes received incisions with the same arc length and the same 7.5mm optical zone. “On average, the results were very satisfactory, although there was a standard deviation of 0.7D, indicating that probably the different corneas responded in different ways to the same surgical treatment,” Dr Bellucci said.

Dr Bellucci noted that precision with the technique is likely to improve with the introduction of new nomograms based on empirical data and designed specifically for incisions created with the femtosecond laser. Other developments that may improve the predictability of outcomes are the use of curved interfaces that induce much less applanation, the incorporation of accurate posterior cornea measurements, and the preoperative planning and intraoperative visualisation of incision creation by optical coherence tomography (OCT) imaging.

“The latest generation of femtosecond laser allows us to design our laser incisions directly on the OCT image and it tells us the exact pachymetry so we can adjust the cut depth accordingly, and do it intrastromally. This is the most important advancement with the femtosecond laser,” Dr Bellucci added.

Roberto Bellucci: robbell@tin.it