Presbyopic Lens Exchange

With new developments in laser vision correction, people have been lining up to reduce their need for glasses. However, for many patients, this will only mean a decreased dependency on glasses for distance vision. Prepresbyopic patients undergoing refractive surgery generally ignore the fact that their loss of near vision in the years ahead will necessitate a return to glasses. With the rapid expansion of electronic communication and the increase in the amount of time spent at the computer, satisfactory near vision will become even more valuable. Consequently, surgical methods to improve uncorrected near vision will receive much greater attention in the years ahead.

OPTIONS FOR CORRECTING PRESBYOPIA
Aside from various bifocal contact lenses, monovision has been the most widely accepted method for restoring multifocality. Despite its popularity, little is known about maximizing the potential of the procedure, and even with contact lens trials, predicting success is complicated. Although the long-term benefits are significant, prepresbyopes have an especially difficult time adjusting to monovision after refractive surgery. Multifocal IOLs have now emerged as the first true alternative to monovision for the cataract patient interested in better near vision. Like monovision, multifocal IOLs can provide near acuity in all fields of gaze, not just inferior gaze, as is the case with bifocals or readers. Patient satisfaction with multifocal IOLs is optimized if (1) surgeons and their clinical staff carefully follow proven inclusion and exclusion criteria for patient selection, (2) office systems are in place to improve IOL calculation accuracy, (3) surgeons take advantage of the latest technology and techniques in cataract extraction, (4) surgeons learn to reduce unwanted astigmatism, (5) surgeons and their patients regard poor uncorrected near vision after surgery as an undesirable result, and (6) patients understand that, as with any new visual system, the process of visual cortical adaptation is necessary before optimal results are achieved.

Presbyopic lens exchange, or PRELEX, is a procedure that encompasses both lens surgery for purely refractive purposes and the use of the ARRAY lens (Allergan Inc., Irvine, CA) for cataract patients (Figure 1). In the US, using the ARRAY IOL in patients who have not been diagnosed with cataracts is considered an off-label use of an FDA-approved device. PRELEX has been approved for use as a purely refractive procedure in Europe. Precataract PRELEX is especially beneficial in hyperopic presbyopes who are poor LASIK candidates. These patients include those who desire near vision without glasses, have marginal corneal thicknesses, and show early cataract changes. Poor LASIK candidates may be better suited for a lens surgical procedure rather than a corneal surgical procedure to reduce their dependency on eyeglasses.

VISUAL CORTICAL ADAPTATION
Almost all PRELEX patients have the capability to neuroadapt to their new visual systems, which is an important process in achieving the best quality of vision after surgery. These patients experience simultaneous near and distance vision, and their brains need to learn how to ignore one when focusing on the other. For instance, PRELEX patients learn how to disregard the overlying near image they see when looking at distant objects, such as halos around lights at night. They also learn to ignore their distance vision when focusing at near (at first, they may see some “fuzz” around letters when they read). Younger patients have the potential to neuroadapt faster than older patients. Almost all patients will see a significant improvement in their ability to drive and in their comfort in driving at night, as well as in their ability to read, 2 to 3 months after having the PRELEX procedure performed on their second eye. PRELEX raises the bar for refractive lens surgery. Its success depends on accurate IOL calculations, precise lens surgical techniques, and effective astigmatic control.

SURGICAL TECHNIQUE
I recommend using topical anesthesia and clear corneal temporal incisions, which enable rapid visual improvement and a more cosmetically acceptable result in the immediate postoperative period. The latest in phacofluidics, available through such machines as the Sovereign (AMO, Santa Ana, CA), the Legacy (Alcon Surgical, Fort Worth, TX), the STAAR Wave (STAAR Surgical, Monrovia, CA) and the Millennium (Bausch & Lomb Surgical, San Dimas, CA), reduces the amount of phacoemulsification turbulence that might impede quality of vision, particularly in the first few days following surgery. Some surgeons may find it advantageous to perform flipping techniques for nuclei that might be difficult to chop or crack. This can be especially beneficial with precataractous PRELEX. One method I have incorporated is the burst hemiflip method, which I execute in the following manner.

First, I create a deep trough from the central nucleus out to the periphery and rotate the nucleus 180º. Next, I separate the nucleus using a sideport instrument, such as a Conner Wand (Rhein Medical, Tampa, FL), and the phaco tip. After a complete separation of the nuclear halves, I embed the 30º-phaco tip into the top one-third of a distal heminucleus, and with gentle pressure on the phaco foot pedal, I engage burst mode with either the Sovereign or the Legacy. I carefully flip the first heminucleus into the iris plane and remove it with the help of the sideport instrument. In the same manner, I flip the remaining heminucleus into the iris plane and continue to phacoemulsify.

Along with a careful phacoemulsification technique, astigmatic control is important to PRELEX success. When we anticipate that a patient may be left with a residual cylinder of 0.75 D or greater after lens surgery, we will perform limbal relaxing incisions. These incisions are actually peripheral corneal incisions and are generally performed 1.0 to 1.5 mm from the limbus in the clear cornea.

PRELEX ENHANCEMENT
Limbal relaxing incisions can also be offered postoperatively for problem astigmatism, and we now perform them in an office setting in a dedicated surgical suite. If spherical errors lead to unhappy patients, the surgeon must consider other forms of refractive enhancements, like mini-RK for low-level myopia, as well as new procedures in development, such as CK for low-level hyperopia, and laser vision correction for sphere and cylinder. Punctal occlusion may be necessary for patients with severe dry eye, which may affect the quality of their vision, particularly at near.

POSTSURGICAL MANAGEMENT
After the surgical procedure is complete, we remind our patients that they should expect to experience some confusion postoperatively in the first eye, which should improve after their visual system balances. We continue to personalize the lens constant, and encourage patients to use readers when they feel it is necessary. We will use topical steroids longer, usually in younger patients, and may sometimes use nonsteroidal anti-inflammatory topical medications. In addition, we continue to encourage visual cortical adaptation, and investigate methods of enhancing tear function, which is a common cause of poor near vision in the first few weeks and months following PRELEX.

SUMMARY
PRELEX represents a new concept in the treatment of presbyopia, one that is likely to gain popularity. Using the name PRELEX reemphasizes the fact that this is actually an interdependent system of procedures, including careful biometry, astigmatic control, predictable lens surgery, and constant outcomes analysis to improve results. In the long run, PRELEX will most likely make us better overall lens surgeons and will lead to a higher level of patient satisfaction.

R. Bruce Wallace III, MD, FACS, is Director of Wallace Eye Surgery in Alexandria, Louisiana, and also serves as Clinical Professor of Ophthalmology at the LSU School of Medicine in New Orleans. Dr. Wallace is a paid consultant for AMO. He may be reached at (318) 448-4488; rbw123@aol.com.
Portions extracted with permission from Wallace RB: Presbyopic Lens Exchange. Cataract & Refractive Surgery Today. 2002;4(suppl):13-14.