Thoughts on cataract & refractive surgery
Dr Kermani: Quality and safety in cataract and refractive surgery is better today than ever before. Femtosecond laser-assisted cataract surgery (FLACS) and premium IOLs are my gold standard now. Usually, I can perform what I have promised to my patients and this is a real game changer. However, the number of patients is significantly increasing and so the main challenge ahead, beside consolidation of results, is improving the perioperative set-up at all levels.
With challenges come opportunities and some of the new therapeutic technologies that have recently been introduced promise to revolutionise surgery. For example, the company Avedro, which develops corneal crosslinking (CXL) products, has developed the ‘Mosaic’ technology, which offers both customised remodeled vision (CuRV) and photorefractive intrastromal crosslinking (PiXL).
CuRV is a procedure that allows advanced cross-linking options to be offered to keratoconus patients. This treatment is customised to a patient’s specific corneal topography. Clinical studies have demonstrated that the CuRV procedure can result in greater flattening of K-max, improved corneal regularisation and reduced epithelial healing responses, compared with standard CXL.
The PiXL procedure applies cross linking to a selective part of the cornea to flatten the cornea. It results in the cornea being reshaped, thus having the potential to provide non-invasive vision improvement.
Dr Fazio: In my practice, I have only had two ectasia cases: one after LASIK and the other after photorefractive keratectomy (PRK). Each patient was around 30-years-old and neither was showing an abnormal topography; the amount of refractive error was in the mid-range. In my eyes, it is evident that the Randlemann rule is largely inadequate to protect patient and surgeons from late complications after refractive excimer treatments.
Tomography software claims to give useful clues. Lately, the Corvis instrument (Oculus) has been proposed as a means to analyse corneal biomechanics in order to rule out patients at risk of ectasia. We are in need of strongly validated ways to decide if a patient is truly a good candidate for LASIK or PRK.
There are also challenges with toric IOLs. Since the advent of toric IOLs, astigmatic correction of the refractive error after lens replacement has seemed possible. However, even though they are a very powerful means of correcting astigmatism, a certain degree of disappointment still weighs on the procedure.
Despite the eventual acknowledgement of the role of the posterior corneal curvature on the amount of corneal astigmatism, the goal of a consistent precise astigmatism correction remains elusive.
There are three reasons for this: firstly, unlike optical or laser correction of refractive error, which relies on a subjective test or precise wavefront analysis, astigmatic correction via toric IOLs rely on shape analysis of the cornea and effective lens position in terms of antero-posterior shift as well as centration. Believe it or not, shape analysis of the central anterior and posterior cornea is still an art to refine.
Secondly, even if the surgeon has determined axis and amount of toric correction, perfect alignment of the lens is a far from easy. And techniques using automated surface recognition or even intraoperative wavefront analysis seem to offer no more precision than manual techniques.
Finally, toric IOLs occasionally exhibit a tendency to rotate. I personally believe that anterior capsule fixation, instead of capsular fornix fixation, is worth exploring in order to ensure better IOL stability and centration.
Another challenge in 2018 and in the years to come is achieving emmetropia in 100% of postoperative cases. Both with laser vision correction and refractive or cataract lens exchange, this is often achieved. However, something is missing in our anatomical analysis of the eye.
Moreover, effective lens position, that is to say, where exactly your artificial lens will decide to sit into the eye of your patient, is still guess work. The impact strategy of our excimer laser has yet to be improved.
In a setting of premium surgery, 0.50D of emmetropia is considered a failure. The challenge is to reduce such a small error to zero, every time.
Dr Alio: Multifocal trifocal IOLs have shown excellent results, becoming the gold standard for the majority of patients receiving a multifocal lens after refractive lens exchange (RLE) or cataract surgery, due to its better defocus curve for intermediate vision (nowadays critical) and greater tolerance.
It is now a common treatment option for all hyperopic patients of >45-years-old who ask for refractive surgery. Knowing this, is it coherent to perform LASIK in a 40-year-old patient with +6D of sphere considering that this option will preclude him from receiving multifocal lenses in the future? Many surgeons decide to wait until presbyopia appears in those patients before performing an RLE, but does it make sense to wait?
On the other hand, where should we place the cut-off age limit? With the current performance of new multifocal lenses, this age limit will probably change, although we still do not know what adverse events might appear with such lenses in the very long term (for example, 30 years’ time). We might see glistening and opacification, for example.
Age limits for multifocal lenses probably need to be redefined today, although not forgetting the expected long survival of these lenses in such young patients.
Meanwhile, many extended depth-of-focus (EDOF) lenses are currently being launched. These lenses offer the theoretical advantage of reduced adverse visual symptoms compared with the usual diffractive lenses. However, we will have to define where such EDOF lenses fit in our clinical practice and be sure on their supposed advantages (it has been reported with some models that they can still induce significant halos and equivalent visual symptoms). Their safety and efficacy for post-refractive surgery patients (either myopic or hyperopic) still needs to be properly defined.