IMPROVING IOLS

With high-quality central optics, square edges that retard posterior capsular opacification (PCO), reasonable pseudoaccommodative designs and toric optics, today’s intraocular lenses (IOLs) meet most patient needs. But there is still plenty of room for improvement in IOL design, Douglas D Koch MD, Baylor College of Medicine, Houston, told the 2015 ASCRS•ASOA Symposium & Congress in San Diego, USA.

Lenses of silicone or hydrophobic acrylic with square edges inhibit lens growth on the posterior capsule (PC) better than other materials and designs, Dr Koch noted. But studies still find PCO in three to four per cent of square-edged lenses within three years of implantation, and rates go up with time.

Dr Koch has seen PCO in seven per cent of patients within 40 months with one square-edge design, and four per cent at 15 months with another. “You see these rates rise to 75 per cent or higher if you follow patients long enough… I think this is a much bigger problem than we appreciate,” he said.

Square-edge lenses also produce dysphotopsias in many patients. Early designs with polished edges produced light reflections, or positive dysphotopsias. Frosting lens edges have greatly reduced reflections, but shadows, or negative dysphotopsias, remain common.

Studies suggest dysphotopsias occur in 1.6 to 7.8 per cent of patients at three weeks, Dr Koch said. But when asked, many more patients may acknowledge them. “As often as I see it in my practice, it feels to me like a bit of an epidemic,” said Dr Koch.

Subtle IOL movement, which can be detected at the slit lamp by observing the fourth Purkinje image, complicates the problem by preventing neuroadaptation to a stationary shadow. “When I see that I know that dysphotopsia will not go away until the lens stabilises,” said Dr Koch.

Samuel Masket MD has designed an IOL intended to eliminate dysphotopsias (Morcher). It features a groove around the optic into which the anterior capsulotomy edge fits like a tyre on a rim. “Hopefully these kinds of advances will reduce dysphotopsias. Their greater stability might also improve lens power predictability and further reduce PCO,” said Dr Koch.

SAFETY AND DURABILITY

To date, only one accommodating lens is available in the USA, though several are marketed in Europe and elsewhere, and more are in development. But some don’t appear to work at all and others are untested over the long haul, Dr Koch noted.

“Do we need to look at completely new approaches and think entirely out of the box? Ultimately this is where we are probably going to go for the best solutions,” said Dr Koch.

Drug-eluting lenses are also desirable for controlling postoperative inflammation and infection, Dr Koch noted. “Why are we still either prescribing eye drops or injecting drugs through the zonules or even the pars plana? There must be better ways to do that,” he said. Overall, though, the quality of current IOLs is excellent, Dr Koch said. Barriers to further improvement include technology, cost of development and regulatory requirements, he concluded.

Douglas D Koch: dkoch@bcm.edu