By: Priscilla Lynch in Southport
Modern LAsiK technologies and techniques and more advanced lens technologies are leading to increased options and better outcomes for patients with higher degrees of myopia. Experts debated the merits of each approach at the XXXV UKISCRs Congress. Advocating LAsiK as the best option for this cohort, Dan Reinstein MD, MA(Cantab) FRCsC, FRCOphth, DABO, FEBO, medical director of the London Vision Clinic, highlighted the risks and invasiveness of refractive lens exchange (RLE), particularly its effect on accommodation while demonstrating the relative increased safety and efficacy of LASIK.
He listed the potential serious complications of RLE, such as macular oedema, endophthalmitis, suprachoroidal haemorrhage and retinal detachment. The latter is much higher in high myopic clear lens exchange than it is in cataract surgery. In addition, when multifocal iOLs are not tolerated following RLE it often leads to IOL explantation and exchange procedures that are highly risky, and all this when a micromonovision extraocular procedure would have done the job, he said.
"So this is the scenario that we're talking about when going inside the eye to do an elective procedure for someone that can already see albeit with glasses. This level of risk needs to be explained to the patient in the context of the elective nature of the procedure," Prof Reinstein contended. He pointed out that the literature has plenty of studies for high myopic clear lens exchange in the early 1990s but less as time went on. This implied the reluctance in the ophthalmic community to continue to offer RLE and publish results, he suggested.
On the other hand, high myopic LASIK was curbed at the time because of induced night vision problems as well as the increased risk of ectasia, and a number of studies found better results with phakic iOLs than LAsiK. however, Prof Reinstein noted this was because the excimer machines used in the published comparison studies were older and less advanced - ie, were using only primitive ablation profiles without modern spherical aberration compensation compared to what is now currently available. "Further studies have come out since then but they are still comparing older technologies and not modern excimer lasers and modern laser excimer ablation profiles," he added.
The question of spherical aberration increasing after myopic ablations was described in detail by Prof Reinstein, who demonstrated his research using the Artemis VhF digital ultrasound scanner in which he shows that the majority (about 85 per cent) of spherical aberration actually comes from biomechanical corneal changes – primarily, the fact that the stroma actually thickens in the periphery outside the ablation zone. While spherical aberration pre-compensation can help, if it is excessive it can lead to central islands, he cautioned. Prof Reinstein believes there is a lot of confusion in the profession about the current capabilities of high myopia corneal surgery because people are made to think all technologies are the same by certain manufacturers.
"What we have developed as forefront technology in controlling the induction of night vision problems is way superior to what is currently called 'wavefront-guided' or 'wavefront-optimised' surgery – which by the way, are actually similar although certain manufacturers claim they are different. it is not going to be long now before the three superior excimer lasers are also doing this and further down the road before all excimer lasers will be copying it," he told EuroTimes. he also promoted the merits of two stage procedures and said it is known now that topography-guided treatments work far better than wavefront-guided treatments in reducing spherical aberration, increasing contrast sensitivity and reducing night vision disturbances.
Addressing the risk of ectasia, Prof Reinstein said keratoconus screening has improved significantly as have surgical techniques in the last decade. "Our ability to pick up sub-clinical keratoconus is much better than it used to be and our ability to not inadvertently go too deep within the cornea by creating very thin flaps – 80 microns with the Carl Zeiss Meditec VisuMax femtosecond laser – means our chances of producing ectasia have gone from very low to exceedingly low," he elaborated. Concluding his arguments, Prof Reinstein maintained that moderate to high myopia is best treated by thin flap LASIK and he also favoured partial correction for even higher myopia over the risks of refractive lens exchange.
RLE has its benefits
In contrast, Rajesh Aggarwal FRCs, FRCOphth, southend University hospital, Essex, promoted RLE as the better option for moderate to high myopia. he reminded delegates of the problems of glare and night vision in some LAsiK patients and the difficulties associated with LAsiK in patients with thin corneas. Both of these issues were more likely when treating patients with a higher degree of myopia. LAsiK also does not address the problem of presbyopia nor the potential for cataracts, he noted. "And the refractive error after LAsiK is not stable because although the corneal refraction may be stable, you still get lenticular changes as the patient gets older, and patients will also develop cataracts as they get older," Dr Aggarwal pointed out. Phakic iOLs with improved lens design have come back in favour and do have the advantage of being reversible, but still have risks. These include endothelial cell loss, resulting in bullous keratopathy, glaucoma, cataract formation, iritis and pupil ovalisation.
"So if we look at clear lens exchange as an alternative it has many advantages. With newer technology surgeons have lots of options including monovision, using refractive multifocals, diffractive multifocals and sectorial multifocal iOLs. You can also use a combination of these. We also have newer technologies in accommodative lenses which almost certainly is where the future lies," Dr Aggarwal commented. The advantages of clear lens exchange are obvious, he said. it is a very familiar procedure for surgeons; it is very rapid, predictable and gives a very stable outcome. The optics now are excellent and in future there will be customised aberration correction, he continued, adding that cornea thickness is not an issue with clear lens exchange.
Another advantage is that clear lens exchange addresses presbyopia and there is no regression due to age-related lenticular change. Hence a second procedure later in life is avoided. however, he did note that clear lens extraction was not without risk. This included the risk of retinal detachment which is between zero and eight per cent for clear lens exchange compared to two to four per cent following cataract surgery. Acknowledging that LASIK can be a better option for younger patients, Dr Aggarwal concluded that clear lens exchange remains the better option for older patients and those with higher myopia. Moreover, as designs for iOLs improve, younger patients are more likely to opt for clear lens exchange.