Refractive Lens Exchange: The Long and Short

As an increasing number of people are seeking spectacle independence, an ever-widening array of treatment options is becoming available. A significant proportion of refractive surgery is moving from the cornea into the eye, and more patients are undergoing refractive lens exchange (RLE). I believe RLE is a viable option for any presbyopic patient, one that should be presented as an option before undertaking any form of refractive surgery.

RLE should be considered as a viable treatment because it eliminates the need for future cataract surgery. More realistically, it is a highly predictable procedure with the option to use lenses of different designs that suit the individual needs of the patient. Should the need arise, we may fine-tune results with laser corneal refractive surgery or piggybacked IOLs.

Although RLE is suitable for a wide range of patients, this article focuses on RLE in highly myopic or hyperopic patients. These patients are usually outside the accepted norms for corneal laser refractive surgery. For presbyopic patients in this situation, RLE is probably the best—if not the only—option. The overall workup is the same as that for any patient considering RLE; however, specific issues must be considered during preoperative counselling, including the biometry, surgical technique, and patient expectations. I outline my working plan for such patients in this article.

Highly myopic or hyperopic patients are often the most rewarding patients to deal with. Because they are used to a high refractive error, they are often not overly optimistic about what to expect. The strategy of under-promise and over-deliver is viable in this setting. Patients with high refractive errors have lived their lives with the associated aberrations and the need for extreme optical aids. In most cases, they are delighted with the outcomes, even if results are not spot-on. These patients may have sought consultation for corneal laser refractive surgery, for which they were found unsuitable, before seeking an opinion for RLE.

COMMON FACTORS
Some common issues are shared by high myopes and high hyperopes that are best discussed together. We must convey to the patient that the predictability of biometry decreases as extreme refractive statuses are approached. Most modern biometric formulas are accurate around emmetropia (eg, -6.00 to +4.00 D sphere); however, the further away one's prescription is, the less predictable the formulas become. For most of my patients outside the -6.00 to +4.00 group, I emphasize that there is roughly a 10% to 15% chance that the sums will be inaccurate. If so, they will require spectacles for both distance and near tasks, although these are likely to be of a small power and their distance UCVA, even if not great, should be better that it has ever been. This is in a practice where the routine cataract patient achieves within 0.50 D of target approximately 95% of the time.

The surgical complication rates in these eyes may be higher than those in near-emmetropic eyes. This must be discussed with the patient candidly during the preoperative assessment.

The advent of biaxial microincision cataract surgery (B-MICS) has solved many of the fluidics problems encountered in these extreme eyes. The separation of irrigation from aspiration is a great advantage in these situations. An anteriorly directed irrigation serves to keep things stable. On the other hand, with coaxial phaco, the irrigation goes in behind the iris plane and increases instability.

THE HIGH MYOPE
Preoperative workup. A complete retinal examination to the ora serrata is mandatory. This is best achieved by indirect ophthalmoscopy with indentation, although some modern contact lenses with wide fields of view also allow a view up to the ora.

It is important to document that the entire retina has been evaluated. Any horseshoe (flap) tears should be treated prophylactically with laser retinopexy around the tears. About 60% to 70% of retinal breaks occur in areas of the retina that do not have any predisposing lesions.^1-3 Retinal tears develop in areas adjacent to prophylactic laser treatment.3 Without entering into the debate of whether prophylactic retinopexy (except for horseshoe tears) is worthwhile,⁴ it is prudent to warn the patient he has have a risk of developing a retinal tear or detachment following surgery. I generally state that they have a 6% to 8% chance of developing a tear or detachment, but I also highlight that should this unfortunate event occur, the results of vitreoretinal surgery in reattaching the retina and restoring vision are good.

Watch out for posterior pole staphylomas, as they may greatly influence axial lens measurement, thereby influencing IOL power selection. Slit-lamp examination can be deceptive, and indirect ophthalmoscopy as well as B-scan ultrasonography are advisable to exclude or document a posterior pole staphyloma.

Surgery. The deep anterior chamber can present problems. It can be difficult to work in the depths of the bag, as things go out of focus and the increased angle of the phaco probe causes corneal striae, obscuring vision. This is a great problem in cataract surgery; however, it is easily overcome in RLE. The surgeon can move the lens matter into the anterior chamber and perform aspiration from there. Because the lens is soft, ultrasonic energy need not be used (or can be used only sparingly). With the large anterior chamber depth, this can still be done at a safe distance from the endothelium.

In eyes with deep anterior chambers, and probably lax zonules, reverse pupillary block may occur. This is akin to the sudden, extreme deepening of the anterior chamber during phaco in vitrectomized eyes. The pupil is plastered to the peripheral anterior capsule, forming a complete diaphragm that brings the force of the infusion fluid to bear on it. The effect is an extremely deep anterior chamber that may be broken by lifting the iris from the lens capsule—often easily with the second instrument—which rapidly returns the anterior chamber to a more normal configuration. If this recurs, it is sometimes worth placing a single iris retractor (even with a well-dilated pupil) to keep the iris elevated off the anterior lens capsule, thus allowing normal fluid circulation.

IOLs. Negative-power IOLs are now available, some with ranges extending to -10.00 D. When using these IOLs, be aware that they are thin. Once implanted, the IOL may be slow to unfold; especially acrylic high-negative–power lenses may have to be actively unfolded within the eye (Figure 1). In high myopes, avoid silicone IOLs, in case retinal surgery with silicone oil becomes necessary in the future.

THE HIGH HYPEROPE
Preoperative work-up. Beware the enopthalmic eye: Any eye measuring less than 20 mm axial length should have a an ultrasound B-scan to assess scleral thickness. For biometric calculations, I use the Holladay Consultant or Hoffer Q formulas.

Surgery. Everything is crowded into the patient's small anterior chamber, which predisposes to shallowing of the anterior chamber and iris prolapse. My preferred approach is B-MICS because it allows use of a relatively square incision, which is inherently more stable and thus reduces the risk of iris prolapse. I prefer a local anaesthesia block or even general anaesthesia because it allows the iris to be handled with impunity, should the need arise.

IOLs. Most manufacturers today extend IOL designs up to 30.00 or 34.00 D. In the past, piggybacking was successfully deployed to address the need for higher-power IOLs (Figure 2). Although this strategy was successful, there were problems with postoperative interface opacification and variability of refractive outcomes.⁵ Also, the two convex lenses pushed up against each other in the visual axis to create unusual hot-spot problems.⁶ I avoid piggybacking implants as a primary procedure. Custom-ordered IOLs are now available well beyond 60.00 D, and it is therefore now possible to get a single lens suitable for any hyperopic eye (Figure 3).

In my personal experience (and this remains controversial), I have had good results when using accommodating IOLs in high hyperopes; although, not in emmetropes or myopes. If a patient wants to be spectacle independent for most tasks and is over 6.00 to start with, I will offer them an accommodating lens, generally the Eyeonics Crystalens (Bausch & Lomb, Rochester, New York) or the 1CU (HumanOptics AG, Erlangen, Germany).

Som Prasad, MS, FRCS(Ed), FRCOphth, FACS, is a Consultant Opthalmologist and Clinical Director of the Eye Department at Wirral University Teaching Hospital NHS Foundation Trust, Wirral, United Kingdom. Dr. Prasad states that he has received travel reimbursements from Bausch & Lomb, Novartis, and Alcon Laboratories, Inc; however, he has no direct financial interests in the products mentioned. He may be reached at tel: +44 1516047193; e-mail: sprasad@rcsed.ac.uk.

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