When counseling patients for refractive lens exchange (RLE), two basic scenarios are distinguishable—both of which require different approaches for extra considerations. First, there are patients who have low ametropia and are already presbyopic. In addition to the general considerations of surgical and postoperative risks, the main considerations for this group include the choice of IOL and the target refraction. Alternatively, the second group includes patients who seek treatment for high refractive errors that are not easily corrected by corneal procedures or phakic IOLs. For these patients, RLE may additionally signify loss of accommodation and introduce surgical and postoperative risks caused by the extreme architecture of the eye.

CHOICE OF IOL
Today, a variety of IOLs for the correction of aphakia are available. Beside classic monofocal IOLs, lens choices include multifocal/bifocal and toric IOLs, or a combination of these. Additionally, accommodating IOLs and the Light Adjustable Lens (LAL; Calhoun Vision, Inc., Pasadena, California) are finding increasing popularity. Another alternative is the yellow lens, which may be an appropriate choice for younger patients.

Multifocal/bifocal IOLs. Even though the visual quality of multifocal/bifocal IOLs has improved, careful patient selection and education is still mandatory.^1-4 When counseling patients about multifocal/bifocal IOLs, we must consider the following:

• Most available IOLs are bifocal because only two foci have useful contrast sensitivity—expressed as modulation transfer function. However, most patients also want good intermediate vision, which is not satisfactory with the bifocal IOLs. Therefore, patients must be informed accordingly.
• Mix and match (ie, combining different IOL types, such as monofocal plus bifocal IOL, multifocal plus bifocal, or two bifocal IOLs with different near foci), can be discussed with the patient.
• Patients must be willing to have compromised visual quality if they want to achieve spectacle independence. If patients are not willing to compromise or are dependent on nighttime driving, we do not advise implantation of multifocal/bifocal IOLs.
• Reaching the target of emmetropia is particularly crucial for patient satisfaction with multifocal/bifocal IOLs; patients must be willing to undergo fine-tuning, performed via a corneal refractive procedure, if the target refraction is unsatisfactory.⁵ Recent studies on RLE with these IOLs, however, show favorable results in achieving the target refraction. This may be attributed to better measuring technologies, such as the IOLMaster (Carl Zeiss Meditec, Jena, Germany) and IOL calculation formulas.²

 

Toric IOLs. Many companies now offer toric IOLs that feature standard correction between 1.50 and 12.00 D of astigmatism (nominal value). Additionally, some companies offer customized IOLs of any desired power.⁶

When in doubt, the surgeon should target undercorrection at the same axis rather than risking overcorrection with variation in cylinder axis because this is usually poorly tolerated. The main problem with toric IOLs is rotational stability, which may require a secondary surgical intervention to correct the axis.

Although this technology is a major advance, we do not consider correcting astigmatism in all patients, as it may offer some pseudoaccommodation. This can be discussed accordingly with the patient before surgery.

Patients with astigmatism higher than 1.50 to 2.00 D at the spectacle plane will likely benefit from a toric IOL: The higher the astigmatism, the more they will benefit. Around and below this range, patients have to choose between optimizing UCVA at a single distance and enhancing depth of focus. In the former case, an astigmatic reduction can be achieved by incisional methods. In the latter, astigmatism may be left unchanged through appropriate choice of incision technique to enable pseudoaccommodation between the main meridians. This may be particularly desirable for patients who have been—consciously or not—using this preoperatively. Careful evaluation of the patient's history will reveal such habit and help avoid unexpected disappointments by attempting to correct every amount of astigmatism.

Light-adjustable IOL. The power on this photosensitive silicone IOL can be adjusted noninvasively and cured after implantation using a low-power light source. Its use has been proposed after corneal refractive surgery—where refractive surprises may often be found.

Low cylinder correction may also be performed; however, the main disadvantages of the IOL are that it does not yet feature an aspheric or multifocal design and that the correction of refractive error is limited. Although this technology is promising, more thorough investigation in the form of clinical trials is needed to prove its superiority in achieving the desired target refraction without compromising quality of vision. To date, active marketing of the LAL in countries where the Conformité Europeéne (CE) mark is sufficient for commercial distribution is somewhat disproportionate to the peer-reviewed data available.⁷

Accommodating IOLs. Several accommodating IOLs have been promoted to date. The mechanism of action is based on either the Helmholtz theory, which refers to relaxation of zonular fibers with contraction of the ciliary body, leading to relaxation of the capsular bag; or rearrangement of the volume of the ciliary body on accommodative effort, which both then lead to movement of the IOL or its parts. Even though these IOLs perform reliable correction of aphakia, their true accommodative effect remains to be proven.

Yellow IOLs. It has been suggested⁸ that the yellow discoloration of the aging crystalline lens may protect against macular damage induced by light at the blue end of the visible spectrum. Using this underlying theory, some manufacturers have developed yellow or orange IOLs with an integrated short-wavelength filter. Attempts to demonstrate disadvantages in color vision due to these additional filters have not showed clinically relevant dyschromatopsia.⁹ On the other hand, clinical superiority regarding macular protection has not been proven either, despite logical theoretical considerations and experimental evidence.^10,11 Additionally, the influence of blue light on circadian rhythm is under investigation.¹²

Most patients, we recommend conventional IOLs with the use of sunglasses for adequate macular protection outdoors. The yellow IOL produces a somewhat unnatural anticipation of vision perceived in later life due to natural aging of the lens. However, the potentially long life expectancy of younger patients may be an argument in favor of using a blue-blocking IOL. This discussion is still ongoing.

TARGET REFRACTION
The majority of patients seek to achieve good distance UCVA; however, a small subgroup may prefer a different target refraction. In our experience, hyperopes prefer exact emmetropia or slight residual hyperopia (eg, +0.25 D) over slight myopia. Alternatively, monovision, which can easily be simulated with contact lenses before surgery and then customized, is a popular option for many low myopes. It may also be a monocular option for a presbyopic emmetropic patient who seeks independence from near vision correction and who is willing to wear glasses while driving. In this case, the emmetropic eye undergoes RLE with a myopic target refraction.

Highly myopic patients who have been wearing contact lenses will generally also prefer distance correction. Patients who have not been wearing contact lenses, however, may prefer a slight distance correction (eg, -3.00 D) with spectacles and the ability to read without them.¹³

The more extreme the axial length, the more crucial it is to inform the patient about the possibility of a missed target refraction. We inform all our RLE patients that fine-tuning by a corneal refractive procedure or IOL exchange may be necessary to reach the desired refractive outcome.⁵ We do not favor piggyback IOL implantation or rotation of the IOL into the sulcus to change the functional power of the lens.⁴

For the correction of astigmatism, toric IOLs are available; however, limbal relaxing incisions or extra correction of astigmatism via a corneal refractive procedure can alternatively be performed.

IOL calculation formulas have improved since the introduction of the IOLMaster, which allows superior measurement of biometric parameters. This is especially true for long eyes with posterior staphylomas in which the axial length can now be measured according to fixation of the patient. We prefer the SRK-T formula for long eyes and the Hoffer-Q formula in short eyes. Additionally, if the Holladay 2 formula is unavailable, we recommend using the Haigis formula for either short or long eyes.⁴

GENERAL SURGICAl, POSTOPERATIVE RISKS
Just as with any surgical procedure, RLE has risks, which are similar to the risks of cataract surgery. The main complications include elevation of intraocular pressure, capsular bag rupture, cystoid macular edema, missed target refraction, endothelial damage, endophthalmitis, and retinal detachment (RD). The frequency of these complications depends on the (1) surgeon, (2) surgical difficulty, and (3) patients' predisposing factors.^14,15

LOSS OF ACCOMODATION
Loss of accommodation is an important factor to discuss with younger patients who undergo RLE for the correction of high ametropia. Preserving accommodation is one of the highest goals, and we believe that RLE should be performed in young patients only if no other option, such as a phakic IOL, is available.

If there is no other option and the patient is well informed and willing to undergo RLE, we consider loss of accommodation acceptable. Special guidance and counseling is needed if RLE is performed in only one eye because intermediate or near binocular problems may result.

ADDITIONAL RISKS in HIGHLY HYPEROPIC OR HIGHLY MYOPIC EYES
In highly hyperopic eyes, additional problems can be encountered intraoperatively. Short eyes have a generally higher risk of vitreous pressure with all possible ensuing complications. In cases of intraoperative ciliary block, we perform a deep vitreous puncture via the pars plana.

In highly myopic eyes, the main problems—namely retinal complications—are expected to occur postoperatively. The rate of RD is elevated after general cataract surgery,¹³ and in RLE the main retinal complication is postoperative vitreous detachment induced by mechanical or molecular changes in the vitreous. Whether the already high risk of RD in myopia is additionally altered by surgery is unclear; however, the literature does not indicate a dramatically increased rate of RD caused by lens exchange.

Risk factors for postoperative RD are identical to those for idiopathic RD, including genetic factors, male sex, myopia, and the presence of lattice degeneration. Prophylactic coagulation of asymptomatic lattice lesions or round holes has not been shown to be beneficial to date,16 but this discussion is ongoing. Preoperative screening of myopic patients for the presence of posterior vitreous detachment may lower the risk of RD. Patients with high myopia should be well informed and ieducated about warning symptoms and monitored regularly.¹⁷

Irmingard M. Neuhann, MD, FEBO, practices with the Tuebingen University Eye Hospital, Germany. Dr. Neuhann states that she has no financial interest in the products or companies mentioned. She may be reached at tel: +49 7071 29 84761; fax: +49 7071 29 3730; e-mail: irmingard.neuhann@med.uni-tuebingen.de.

Thomas F. Nehuann, MD, practices at the Praxis Professor Neuhann und Kollegen, Munich, Germany. Professor Neuhann states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: prof@neuhann.de.

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