Sunday, June 29, 2008

WOC debates the future of refractive surgery

The World Ophthalmology Congress (WOC) got rolling in earnest with a number of sub-specialty sessions. We report from the Cataract and Refractive Surgery programme.

Seven well-known researchers offered their prognostications for what refractive surgery might look like in 2020.

Luis Ruiz MD, a true LASIK pioneer, described a new procedure he has developed which promised to dramatically alter the treatment of presbyopia. The technique, which he calls intraCOR, provides flapless intrastromal ablation using the Femtec femtosecond laser (20/10 Perfect Vision) to achieve reshaping of the cornea without touching epithelium, endothelium, Bowman’s membrane, or Descemet’s membrane.

Compared with existing refractive surgery techniques, intraCOR has multiple advantages that include simplicity, speed and safety. The procedure would avoid complications related to flap ablation and surface ablation, can be performed in thin corneas, does not weaken corneal biomechanics nor induce dry eye, and has a reduced risk of infection.

Dr Ruiz has experience with intraCOR in more than 700 patients who have been treated for presbyopia, myopia, hyperopia and astigmatism using customised patterns. Although this new procedure is still being refined, he presented results from a study of presbyopia treatment that included 45 eyes treated with an identical ablation protocol. All had at least one month of follow-up with a range up to six months. Simultaneous UCVA distance and near results showed 100 per cent of eyes achieved 20/25 or better and J2 or better. At three months no patient had lost even one line of distance best corrected visual acuity. Contrast sensitivity was improved in both photopic and mesopic conditions.

Safety data are encouraging – hysteresis was increased, the corneal resistance factor was unchanged, and there were no changes in endothelial cell density or corneal thickness.

“It would be difficult to find an easier or more effective procedure, and in my experience with refractive surgery for presbyopia, I have never seen such amazing safety and quality of vision,” said Dr Ruiz.

The wavefront data provide an explanation for the outstanding results and reveal the treatment results in a true multifocal corneal with a decrease of defocus that results in a myopic shift and an increase in spherical aberration yielding increased depth of field.

Dr Ruiz concluded his talk by acknowledging the need for further studies, but Jorge Alio MD, PhD, chairman of the session commented that if the promising outcomes being achieved with this important innovation are confirmed in subsequent research, it will completely change the way refractive surgeons approach the treatment of presbyopia.

Myopia prevention

Donald Tan MD, Singapore, discussed prevention of myopia progression in schoolchildren using a treatment called Neurovision. This approach is particularly relevant in Singapore where myopia progression in children occurs at a rate of about 100 degrees per year so that by age 18, about 80 per cent of Singaporeans are myopic.

“As myopia progresses in young children, their spectacles fail to keep up with the progression rate and visual acuity is suboptimal. Neurovision aims to enhance visual acuity without changing the refraction so that theoretically, visual acuity can be shifted toward a more normal level. And, maybe if we are successful in preventing myopia evolution, we will not need to perform so much refractive surgery in the future,” he said.

The approach involves a computerised, Internet-based program that uses visual stimuli to optimise image processing by the visual cortex, enhancing contrast sensitivity by neural adaptation and repetitive visual memory exercise to result in enhanced visual acuity. The exercises use a visual psychophysics tool and are performed every other day for a total of 30 sessions.

More than 1,300 patients have been treated with the Neurovision approach to date both in clinical trials and commercially. Patients have included mild myopes, children and adults with amblyopia, presbyopes, post-refractive surgery patients, and people with high functional visual demands aiming for sharper vision. Results have been published in the literature showing consistently that patients gain more than two lines of ETDRS visual acuity and maintain a majority of the benefit after 12to 18 months.

Its efficacy in reducing myopia progression in schoolchildren was evaluated in a pilot study that had a prospective non-comparative design. Thirty children ages seven to nine years performed the sessions using a treatment adapted to a computer game and were followed for 18 months after completing the program.

The results were consistent with other studies in showing a mean improvement of logMAR visual acuity of about 2.2 lines along with improvement in contrast sensitivity that enabled the children to wear spectacle undercorrection and still get good vision.

“This may be the first effective treatment modality to reduce myopia progression in children without medical or surgical treatment. The results of this pilot study provide the basis for a large-scale, placebo-controlled randomised clinical trial that will be launched in four schools this year,” said Dr Tan.

Ultra-thin corneal inlays

Placement of a corneal inlay represents another approach under investigation for the treatment of presbyopia. Relative to some other techniques, it has a major advantage of being reversible and exchangeable, said Perry Binder MD, US.

Dr Binder discussed the ACI 7000 (AcuFocus) corneal inlay, a small, ultra-thin device placed within a pocket that works via a pinhole effect to increase depth of focus. The goal of this procedure is to create less of a blurred image on the retina up close without interfering with distance vision. The surgery takes just five minutes and cosmesis is excellent.

Almost 400 eyes have been implanted with this inlay and up to three years of follow-up is available. Results show no change in distance uncorrected visual acuity but a significant improvement in near vision with most eyes achieving J1 or better. Similarly positive results are being achieved in a smaller series of patients who have received a thinner model inlay (5 vs 10 microns thick).

“Lots of questions need to be answered, including what is the best material to use, what is the best method to centre the device, and should it be placed through a flap or pocket. However, we have found patients are happy and achieve the benefit of a +1.5 D lens without handicapping their distance visual acuity,” Dr Binder said.

Considering that it takes 10 to 12 years between the time an investigational IOL is first implanted in human eyes and then achieves approval by the US FDA, David F Chang, MD, US, reviewed four accommodating IOLs that have the potential to be available in 2020 because they have already entered clinical trials.

Accommodative IOLs

The Synchrony dual optic accommodating IOL (Visiogen) combines a +32 D moving front optic with a posterior optic of variable minus power based on the individual patient’s needs. It is a silicone, bag-filling IOL that comes pre-loaded in an injector system for delivery through a small incision. The implant is designed to work according to the Helmholtz theory and delivers +2 to +2.5 D of accommodation.

A Phase III US FDA trial including 475 eyes was completed in November 2007. While data are not available from that study, Ivan Ossma, MD, has reported a randomised clinical trial comparing the dual optic accommodating IOL with the ReSTOR multifocal IOL (Alcon Laboratories) in 100 patients. Its results favoured the dual optic IOL for better intermediate vision, contrast sensitivity, reading speed, and problems with haloes. High-definition UBM studies confirm movement of the anterior optic, said Dr David Chang.

Two shape-changing lenses (NuLens, Power Vision) have the potential to provide +8 to +10 D of accommodation. The NuLens features a deformable substance between two rigid plates that is pushed forward through a small aperture by ciliary muscle contraction to create a change in lens curvature. The anticipated commercial design will consist of a haptic unit and a base unit assembled inside the eye.

Jorge Alio MD, PhD, has conducted a pilot trial in 10 blind eyes with BSCVA of 20/200or worse and showed attainment of up to +10 D of accommodation that provided enough magnification so patients could read large print.

The Power Vision accommodating IOL is based on movement of fluid from a reservoir and has been evaluated in five blind eyes. Proof of concept has been demonstrated by anterior segment OCT imaging after pharmacological stimulation of accommodation.

Based on the unexpected finding that a patient implanted with the Light Adjustable Lens (Calhoun Vision) achieved J1 reading vision after treatment for residual myopia, this platform is also being considered as a presbyopia-correcting lens. The algorithm would involve creation of an aspheric design that is gradually sloping off into the periphery with a blend, like a Varilux lens, to create a multifocal lens without discrete rings.

“This approach would reduce problems with glare or haloes and would simultaneously allow guaranteed treatment of residual sphere and cylinder,” Dr Chang said.

Future directions in science, and marketing

Ioannis Pallikaris MD, PhD, Crete, discussed the emerging field of “Presby-optics”. He described evolving knowledge of the underlying physiology of presbyopia that has developed as a result of improved technology for studying the dynamic accommodative process.

“Understanding Presby-optics is about merging this basic knowledge and clinical experience and then applying it to identify the best overall solution for each patient,” he said.

Richard Lindstrom MD, US, concluded the session by providing his thoughts on the future directions for market growth in IOLs for presbyopia correction. Currently, monofocal implants account for 95 per cent of the pseudophakic market with multifocal IOLs accounting for four per cent and the remaining one per cent represented by accommodating IOLs. Looking ahead, Dr Lindstrom expects to see a significant market share shift as monofocal IOLs undergo a steady decline, multifocoal IOLs enjoy an initial surge but then disappear completely, and accommodating IOLs enjoy increasing growth to account for 20 per cent of implants by the year 2020.

“While revenue growth in the cataract IOL market has been occurring at a rate of about three per cent a year, 59 per cent of the growth in IOL revenue in 2006 came from presbyopia-correcting lenses. I expect we will continue to be seeing these new growth patterns into the future. However, surgeons should also remember that monovision with monofocal IOLs remains a popular option that should be offered to patients,” Dr Lindstrom said.

Dr Lindstrom is not alone in his belief that multifocal IOLs are the future of presbyopia-correcting implants. In the 2007 survey of ASCRS members, 76 per cent of respondents said they would favour an accommodating IOL for themselves if they had a presbyopia-correcting lens.

There is also clinical trial evidence that accommodating IOLs can generate satisfactory objective and subjective patient outcomes when used symmetrically or asymmetrically with other types of implants. His outlook for an advance in accommodating IOL market share is also based on the promise of IOLs in development that can provide a greater range of accommodative amplitude.

1 comment:

Anonymous said...

Cool blog!