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Up Front | Jan 2008

Reasons for Choosing Monofocal IOLs

In modern cataract and clear lens extraction surgery, we have a couple of options for aphakia correction, of which multifocal IOL implantation has attracted much attention. In the ideal case, multifocal IOLs can offer total spectacle independence, and thus they are certainly an excellent option.

Noticeably, however, with the best efforts, only one-fourth of patients achieve total spectacle independence,1 and the overall perceived quality of vision with multifocal IOLs may indeed not match that of traditional monofocal IOLs.2 At present, most surgeons and authors agree that multifocal IOL implantation is not suited for all patients, which makes patient selection an important matter when considering multifocal IOLs. Additionally, certain multifocal IOLs may be better suited for certain types of visual requirements.3 This makes the selection even more sensitive, especially since the patient's visual requirements may change over time, a common example being the shift from extensive computer work to other activities (eg, reading books, distance work) after retirement. In this context, I feel we must not forget the possibilities offered by monofocal IOL implantation.

Experience with monofocal IOLs dates back many decades, and we know that these IOLs will continue to perform well—even in an aging retina with macular degeneration or diabetic retinopathy, which may not always hold true for a multifocal IOL. A multifocal optic always means a compromise, because what is gained in near vision is lost in other aspects of visual quality (eg, reduced contrast sensitivity,2,4 increased higher-order aberrations,4,5 glare and halos,1,2,6 phenomena that may affect the overall quality of vision seriously in patients developing retinal diseases).

Another concern is the risk for reoperation, especially in younger myopes who are at risk for retinal detachment and other serious complications after any intraocular procedure.7

When we look at IOLs that do not perform well and have to be explanted, dislocation/decentration and incorrect IOL power are the main reasons for explantation in all types of monofocal IOLs.8 The former can be partially prevented by improved techniques in the primary surgery and less extensive reposition/fixation methods, the latter by improved devices and biometry formulas. Glare and optical aberrations, on the other hand, which remain the main causes for explantation of a multifocal IOL,8 may not be as predictable or preventable.

Naturally, economy also has to be taken into account when implanting multifocal IOLs. Not only is a multifocal IOL more expensive, but considering multifocal IOL implantation also means considering bilateral surgery, at least in presbyopes. Although a unilateral multifocal IOL implantation may be an option in a nonpresbyopic, emmetropic patient,9 presbyopes make up a major part of the cataract population10-12 and are less likely to be satisfied with such a solution. A large-scale increase in bilateral surgery with more expensive IOLs is likely to have significant effects on health care economics in many countries.7,10,11/p>

In my experience, the ordinary elderly cataract patient rarely asks for total spectacle independence, at least not actively. In case of such a request, however, monovision may be an alternative, with a high reported level of patient satisfaction.13 Often, myopia of approximately -1.50 D in the nondominant eye, together with some pseudoaccommodation,14 will suffice for reading price tags and shorter texts.15 Also, this low level of anisometropia will have little negative effect on binocular function.16 Thus, for longer reading or near work, reading glasses are likely to give acceptable binocularity. The monovision approach means no compromise in optical quality in the individual eye, and if the patient is not satisfied, a piggyback implantation in the myopic eye is undoubtedly less extensive than a bilateral IOL exchange.

The ultimate goal we all dream of is an aphakia correction offering the visual quality of a young, healthy, emmetropic eye with intact accommodation. With all solutions herein discussed, we are still far from that goal. Although multifocal IOLs are certainly a good option with the right patient selection, a multifocal IOL will always mean a compromise—and a larger degradation of the eye's optical quality than seen with a monofocal IOL. Therefore, even when making the complex decisions of mixing and matching, to aim for spectacle independence, I feel that unilateral surgery with implantation of a conventional monofocal IOL and bilateral surgery with monovision must still be kept in mind as viable options.

Anders Behndig, MD, PhD, practices in the Department of Clinical Science/Ophthalmology, Ume University Hospital, Sweden. Dr. Behndig states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +46 90 785 37 31; fax +46 90 13 34 99; anders.behndig@ophthal.umu.se.