comanagement
Hitting the Jackpot
How patients and your practice win with presbyopic IOLs.
BY JUSTIN HOLT, O.D. AND DANE DANSIE, O.D.

With more and more Baby Boomers approaching cataract age, annual cataract surgery volumes are expected to increase dramatically within the coming years. This is relevant for optometrists as well as surgeons, of course, as we will comanage many of these cases. What's good news for these patients is the development of new multifocal or "presbyopia-correcting" IOLs that give patients both near and distance vision. Our patients now have three very different IOLs to choose from, depending on their visual needs and lifestyle. Presently, the FDA has approved these for use in the United States: the ReZoom (Advanced Medical Optics), the ReSTOR (Alcon) and the crystalens (eyeonics). Here's what you should know about them.

The crystalens provides accommodation up to 3.33D.

The crystalens

Because a phakic lens is about 5mm thick and an IOL is about 1mm thick, early researchers hypothesized that there may be space within which an IOL could move, thus providing a level of accommodation. The crystalens is designed to provide accommodation up to 3.33D by dynamic retinoscopy. The FDA approved the IOL in November 2003, and it's currently the only truly accommodating (rather than pseudo-accommodating) IOL available on the market.

The lens features a hinged plate-haptic with a relatively small 4.5mm silicone optic. When the patient attempts to accommodate, the ciliary body contracts and the tension on the capsular bag diminishes. The increased pressure within the vitreous body then allows the lens to vault forward at the hinges, resulting in near focus.

One of the advantages of the crystalens is that the optic is monofocal. Research measuring contrast sensitivity indicates that multifocal design intraocular implants can slightly decrease the level of contrast sensitivity that a patient experiences after cataract surgery. With the monofocal single optic design of the crystalens, patients can maintain levels of contrast sensitivity and gain a slightly better quality of vision. The limited excursion of the lens optic during accommodation provides an average amplitude of 1.00D to 1.50D.

The ReZoom

The ReZoom IOL is a second-generation, acrylic, three-piece lens with a 6mm optic. The FDA approved it in March 2005. The lens is built on the platform of the company's first-generation multifocal IOL, the Array. Due to a high volume of patient complaints of dysphotopsia, the Array never gained wide popularity. The ReZoom addresses the Array's shortcomings with the incorporation of the company's "balanced view optics" technology.

It utilizes five optical zones proportioned to provide good visual function across a range of distances in varying light conditions. The center of the optic is distance-dominant; the second zone provides near-dominant vision.

The other four concentric refractive zones of the lens create true multifocal vision. Zones 1, 3, and 5 are distance-dominant, while zones 2 and 4 are near dominant.

AMO created an aspheric transition between each zone, which it says is designed to provide the balanced intermediate vision critical for many patients' everyday activities. This is particularly useful to patients spending a great deal of time at the computer. In addition to this, AMO has altered the size of the rings in proportion to those used in the design of the Array lens.

These modifications have greatly decreased the degree of dysphotopsia, though they have not eliminated it completely. The ReZoom typically provides very good distance and intermediate vision, but patients will have to use reading glasses occasionally for very small print. Typical near vision tends to be around 20/30. Though the add measures 3.50D, the effective add at the corneal plane ends up at about 2.25D.

The ReSTOR

The AcrySof ReSTOR received FDA approval in March 2005. The lens is an apodized diffractive optic IOL that uses a mathematically derived image enhancement algorithm called apodization. Apodization gradually blends the diffractive step heights, effectively managing the light that's delivered to the retina. Thus it improves vision quality while minimizing visual disturbances. The factors that afford enhanced contrast and image quality improvement are balanced use of optical power, number of diffractive rings, step height and ring width. 

The ReSTOR features 12 zones and gradually blends diffractive step heights.

This IOL has 12 diffractive steps, with the first step height equaling 1.3microns. It tapers to a 0.2micron 12th step, effectively delivering slightly over 3.00D at the spectacle plane. In fact, clinical studies indicate that 80% of the individuals in FDA trials did not need to wear eyeglasses at all after they received the ReSTOR lens.

While this lens clearly provides better near vision than other presbyopia-correcting lenses, there may be some trade-offs. Because the effective add is about 3.00D, patients may need to hold things closer, approximately 31cm, to read them than they were accustomed to with their bifocals prior to the surgery. Also, patients may find that their intermediate vision is not as clear due to the closer working distance.

Glare issues

The ReZoom and the ReSTOR are very different from the crystalens. While they do not move axially within the eye, they provide pseudo-accommodative vision. These lenses are based on refractive and apodized diffractive optics, respectively. Light from multiple focal planes is simultaneously focused on the retina. These multiple planes will cause light scatter and often create halos at night.

This will require some neuroadaptation on the patient's part. Similar to the way patients adapt to monovision, this can take anywhere from a few minutes to six months. The glare and halos can alarm patients if you don't educate them about the possibility before surgery.

The ReZoom utilizes five zones to provide good visual function across a range of distances.

Even if you do educate them, patients can occasionally be so concerned with glare and halos at night that they may wonder if they should have elected to receive a monofocal implant. In these cases, I use a -2.50D loose lens over each eye to show them what their vision would be at near if they had chosen a monofocal lens. This often reassures them that they made the right choice and that the small amount of glare at night isn't as bothersome as their near vision would be with a monofocal lens. Again, I tell these patients that any glare they see initially will get better with time. I explain that it's analogous to putting on a new watch: Initially you will feel it all the time; then, eventually, you don't notice it at all.

What to expect post-op

Postoperatively, the management of these patients remains largely unchanged from that of a traditional monofocal implant patient. However, there are a few exceptions. Despite preoperative discussion of the likelihood of initial halos and glare, some patients are very conscious of them during the neuroadaptation period. Some doctors have found Alphagan P (brimonidine tartrate ophthalmic solution 0.15%, Allergan) helpful in decreasing patient symptoms of dysphotopsia, due to its mild miotic effect. Antireflective plano glasses for night driving have also proven beneficial.

These patients can also be very symptomatic to small degrees of dry eye and associated superficial punctate keratopathy (SPK). You should treat even minor degrees of surface disease aggressively prior to surgery. In these cases, preoperative Restasis (cyclosporine, Allergan) has been used successfully and the surgeon and comanaging O.D. should consider it for any patient with even minuscule amounts of SPK.

Mild posterior capsule opacification also has a much greater impact on vision for these patients vs. a traditional monofocal IOL patient. Surgeons subsequently may have a much lower threshold for performing a capsulotomy. Residual cylinder beyond 0.50D is also very poorly tolerated. Often one or more limbal relaxing incisions (LRI), subsequent LASIK, mini-radial keratotomy or a couple of conductive keratoplasty spots can alleviate what seems to be very little correction.

Get the best result

There are subtle trade-offs for each design and no single lens can guarantee perfect vision at distance, intermediate and near. Many surgeons have developed a process of IOL "staging" to find the best results for their patients. The surgeon will implant one eye, and then based on the outcome, decide what changes need to be made, if any, for the fellow eye.

There is now a trend among cataract surgeons to use these three multifocal IOLs in a complementary fashion. For instance, a patient may have a ReZoom implanted in the first eye and be happy with his or her vision at near, far and intermediate. The surgeon may then implant another ReZoom lens in the second eye.

However, if that patient complains a few weeks postoperatively that his or her near vision isn't as good as necessary, but distance is great, the surgeon may consider a ReSTOR for the second eye. If the patient does a lot of night driving, the surgeon might consider bilateral crystalens implants, knowing that the patient may still require reading glasses after surgery. (Editor's note: Alcon has cautioned against mixing and matching IOLs because the ReSTOR lens received FDA approval as a binocular implant.)

They'll only get better

The best candidates for multifocal IOLs are well motivated with a realistic understanding of expectations. Preoperative discussion of possible postoperative glare and halos is imperative. Fortunately, these symptoms usually fade with time. Although some patients may still need to wear a weak near correction for tasks such as reading the phone book, etc., the vast majority of their needs at near can be addressed through the lens designs we've discussed.

With the next generation of presbyopia-correction IOLs on the horizon, we can minimize side effects even further, while improving patients' visual quality at all distances.

References available upon request.