The controversy with monovision lies in the disparity that patients may experience when fitted for a different visual range in each eye. Traditionally, monovision has been associated with adverse effects involving near vision, including a general lack of visual clarity, blurriness, and reduced stereopsis.^1,2 Monovision has often been considered a compromise; although vision is afforded at all ranges, it has less clarity than visual results achieved with multifocality or accommodative implants. Monovision treatment also requires neural adaptation, which is not possible in every case.^3,4

Recent multifocal and accommodative IOL technologies are designed to improve vision at multiple ranges in both eyes, which may be the preferred choice for many eye care professionals and their patients.⁵

Despite these issues, monovision cannot completely be replaced by multifocal or accommodative implants. Monovision offers a unique treatment option with distinct advantages that may be ideal for some patients, such as presbyopes. It is particularly important to consider monovision in light of the emerging novel technologies that now aim to reduce the adverse effects traditionally associated with monovision. In this cover series, surgeons disclose the importance of monofocality in their specific area of interest—contact lenses, cataract surgery, and refractive surgery. This introduction to the topic attempts to review the benefits of monovision and decipher its place in the ophthalmic market.

WHY SHOULD MONOVISION BE RECONSIDERED?
Monovision is facing competition from multifocal and pseudoaccommodating technologies; however, it remains a successful treatment option. The monovision debate has been reopened because it is now recognized that multifocal and pseudoaccommodating lenses do not always satisfy the demands of presbyopic patients. With technological and surgical developments, monovision treatments have improved significantly. For instance, better stability and superior lens composition of monofocal IOLs enables less sensitivity to decentration, high refractive predictability, and the possibility to achieve a deeper visual field.

Monovision avoids the high rates of glare and halos and low contrast sensitivity associated with multifocal treatments. It also decreases sensitivity to lens decentration.^6-8 Monovision is an established presbyopia treatment, with a high success rate and patient satisfaction levels.^4,9 For patients with active lifestyles, monovision equips them with the visual abilities necessary to perform daily tasks requiring good vision at multiple ranges.

In our clinic, we have been working with new foldable IOL technology for cataract surgery or refractive lens exchange using monovision. The neutral aspheric design of the Miniflex (Mediphacos, Belo Horizonte, Brazil; Figure 1) has shown promising results for monovision cataract treatment, particularly for presbyopia correction, at 1 year. Recently we conducted a clinical study to evaluate the safety and efficacy of this treatment (see Presbyopia Treatment With Miniflex and Monovision). Our results with this IOL demonstrate that monofocal implants are an effective treatment method. Visual results are favorable, and refractive target predictability is high. It is with the emergence of new technologies such as the Miniflex that monovision treatment should be reconsidered.

CONCLUSION
Among the ophthalmic and optical treatments for presbyopia available today, monovision has distinct benefits that must be considered. With contact lenses, fitting patients with monovision lenses is easier—not to mention less expensive—than multifocal lens fitting. In refractive surgery, current multifocal laser ablation profiles do not always deliver the expected results, so it is important to reconsider less aggressive spherical profiles that can offer monovision with achievable results. In cataract surgery, monofocal IOLs for presbyopia seem a promising treatment that has produced good visual results.¹⁰

Included in this cover focus is a series of articles written from the viewpoints of Bruce J. W. Evans, BSc (Hons), PhD, FCOptom, DipCLP, DipOrth, FAAO, FBCLA, a contact lens specialist; Ronald R. Krueger, MD, MSE, a refractive surgeon; and Graham D. Barrett, MD, FRACO, a cataract surgeon, on the topic of monovision. As our techniques and technlogies continue to develop, the possibilities of visual and refractive correction continue to expand. Consequently, monovision must be reconsidered.

Carlos Vergés MD, PhD, is Head of the Department of Ophthalmology, CIMA, Universitat Politecnica de Catalunya, Spain. Dr. Verges is a member of the CRST Europe Editorial Board. He states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +34 93 551 33 14; fax: +34 93 551 33 14; e-mail: verges@attglobal.net.

1. Richdale K, Mitchell GL, Zadnik K. Comparison of multifocal and monovision soft contact lens corrections in patients with low-astigmatic presbyopia. Optom Vis Sci. 2006;83(5):266-273.
2. Leyland M, Zinicola E. Multifocal versus monofocal intraocular lenses in cataract surgery: a systematic review. Ophthalmology. 2003;110(9):1789-1798.
3. Josephson JE, Caffery B. Monovision vs. aspheric bifocal contact lenses: A crossover study. J Am Optom Assoc. 1987;58:652-654.
4. Jain S, Arora I, Azar DT. Success of monovision in presbyopes: Review of the literature and potential applications to refractive surgery. Surv Ophthalmol. 1996;40(6):491-499.
5. Cillino S, Casuccio A, Di Pace F, Morreale R, Pillitteri F, Cillino G, Lodato G. One-year outcomes with new-generation multifocal intraocular lenses. Ophthalmology. 2008;115(9):1508-1516.
6. Javitt JC, Steinert RF. Cataract extraction with multifocal intraocular lens implantation: a multinational clinical trial evaluation clinical, functional, and quality-of-life outcomes. Ophthalmology. 2000;107:2040-2048.
7. Rocha KM, Chalita MR, Souza CE, et al. Postoperative wavefront analysis and contrast sensitivity of a multifocal apodized diffractive IOL (ReSTOR) and three monofocal IOLs. J Refract Surg. 2005;21:S808-S812.
8. Hayashi K, Hayashi H, Nakao F, Hayashi F. Correlation between pupillary size and intraocular lens decentration and visual acuity of a zonal-progressive multifocal lens and a monofocal lens. Ophthalmology. 2001;108:2011-2017.
9. Goldberg DB. Laser in situ keratomileusis monovision. J Cataract Refract Surg. 2001 Sep;27(9):1449-1455.
10. Greenbaum S. Monovision pseudophakia. J Cataract Refract Surg. 2002;28:1439-1443.