When the first intraocular lens (IOL) was inserted over 50 years ago it offered ophthalmologists no options. Its size forced a relatively large incision, there was no choice of materials, and no talk of meeting the eye’s natural accommodation.
While still a fair distance from truly duplicating the human eye, today’s IOLs offer significant advances towards replicating natural vision and minimizing surgical risks.
Constantly shrinking IOL size, for example, means surgeons can perform less invasive procedures. Not only are the IOLs ever-smaller, but since 1989 there have been foldable implants. Both changes have played a major role in reducing incision size from 10 mm to as small as 2.5 mm.
One of the strongest debates among ophthalmologists concerns lens material: acrylic or silicone, specifically second-generation silicone. The latter is seen as comparable to acrylic, thanks to a slightly higher refractive index and thinner lenses than the first-generation offered. Some experts also feel that silicone is easier to work with.
For some patients acrylics are specifically indicated; i.e., those who run a higher risk of post-op inflammation due to chronic conditions such as diabetes or uveitis. Other acrylic advocates are even more specific: they opt for hydrophobic vs. hydrophilic acrylic IOLs, to avoid the calcification and opaqueness the latter have been found to cause after several years.
Another debate concerns whether acrylic or silicone better prevents posterior capsule opacification (PCO). Studies show mixed results and many experts say the relative ease of correcting PCOs with YAG surgery makes the question moot.
In some cases the lens offers no choice of material. The only presbyopic lens so far is silicone ; a new lens with ultraviolet and blue light-filtering capabilities is acrylic.
There are several debates concerning haptics, the lens anchor. Some surgeons argue that the soft haptics of some implants causes the device to decenter too easily. Another argument concerns the pros and cons of loading the lens using an injector. Some doctors find this avoids haptic capture outside of the capsular bag.
Another material advance concerns collamer-coated haptics. Strongly gaining popularity, collamer’s excellent biocompatibility also reduces inflammation and protects the implant against the body’s immune system.
One of the greatest challenges still facing IOL designers is creating an implant with the eye’s natural ability for accommodation. IOLs labeled as truly accommodative are available overseas, but not in the U.S. Instead, today’s IOLs can generally provide the patient with an ability to see within a short range of distances; for anything outside that distance corrective lenses are still needed.
One solution is the use of multifocal IOLs. Today’s multifocals offer numerous advances, including preventing PCOs and correcting higher-order aberrations. More importantly, they can provide patients with complete independence from spectacles. Their major disadvantage is the development of night vision halos, a side effect that still makes many ophthalmologists reluctant to use them.
Wavefront-adjusted IOLs are among the most-discussed technological advances in IOL development: Wavefront analysis provides doctors with better capability for quantifying all the aberrations of the eye, thus creating the optimal lens. The IOL currently designed via this technology mimics the negative spherical aberration (SA) of the eye and contrasts it to the positive SA of the cornea, with the aim of ultimately duplicating the eye’s original neutral SA. Wavefront-adjusted IOLs offer less spherical aberration and their use is recommended for jewelers, pilots and others who do precise work.
Thanks to all these options (and many others) leaders in cataract surgery are urging their colleagues to go outside their comfort zone when choosing a patient’s IOL. Too many surgeons, they say, get used to relying on one IOL for all their patients. Experts urge physicians to evaluate the unique ophthalmic needs and optical characteristics of each patient (e.g., tear film and pupil size) and customize their lens selection to meet an individual’s specific needs.