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Cataract Surgery | Oct 2009

Monovision From the Contact Lens Practitioner’s Perspective

Good monocular visual acuities are important for monovision.

A recent literature review1 found that typical success rates of monovision for contact lens wearers are between 59% and 67%.2-4 Although the review also showed a lack of double-masked, randomized, placebo-controlled trials, this research design is inappropriate because participants are likely to know when they are wearing monovision. In studies comparing different methods of presbyopic correction (eg, monovision vs multifocal contact lenses), it should be possible for the researcher to be masked; however, few studies in this review stated whether this was the case. How successful is monovision compared with other contact lens options for correcting presbyopia? This article attempts to answer this question from the viewpoint of a contact lens practitioner.

Rigid gas permeable (RGP) contact lenses can be fitted so that the lens and eye movements are decoupled, thus facilitating their use as translating multifocals. Optically, this can provide normal distance, near, and stereo vision.5 But this type of contact lens is challenging to fit, and not all patients adapt to RGP lenses.

There is now a wide range of simultaneous-vision multifocal contact lenses—typically soft contact lenses—that have the distance correction at the edge or, less commonly, at the center of the lens. Pupil dependence can be problematic with these lenses, although some designs minimize its occurrence. The problem with the simultaneous-vision multifocal contact lens approach is that in addition to the clear (ie, desired) image of the object of regard, there will also always be an out-of-focus image present. Many patients adapt; however, it is likely to have a detrimental effect on visual performance.6

This seems to be an inevitable limitation of simultaneous-vision multifocal contact lenses: If a lens simultaneously provides two foci, one is always likely to be defocused. A physiological mechanism exists for interocular blur suppression,7 and so monovision may be less of a compromise for many patients than simultaneous-vision multifocal contacts.

VISUAL ACUITY, STEREOACUITY
Most studies comparing monovision with simultaneous-vision multifocal contact lenses find that monovision provides slightly better visual acuity but worse stereoacuity.1 One advantage of simultaneous-vision multifocal contact lenses (and multifocal IOLs) is that they are typically marketed as a novel, high-tech approach, which, if communicated to the patient, is likely to create a greater placebo effect than monovision. It is therefore desirable for research comparing monovision with simultaneous-vision multifocal contact lenses to control for the placebo effect by providing an equally convincing explanation for each mode of correction. It is unclear whether much of the available research has taken this precaution, which may account for some of the contradictions in the literature as illustrated by the following summary of three recent studies.

Situ and colleagues8 refitted successful monovision wearers with simultaneous-vision multifocal contact lenses and found that 68% preferred the latter. However, 1 year later, only 53% were still wearing their multifocal lenses. One crossover study found that 76% of participants preferred simultaneous-vision multifocal contact lenses to monovision;9 another found that only 40% preferred simultaneous-vision multifocal contact lenses, with 50% preferring monovision and 10% undecided.10

INDICATIONS AND CONTRAINDICATIONS
Monovision impairs stereoacuity, and the effect increases as the degree of induced anisometropia increases.11 However, monocular cues to depth perception are still operative and can be powerful.12 The effect of monovision on binocular coordination is slight,1 but monovision should not be prescribed to patients with long-standing unilateral strabismus, amblyopia, incomitant deviations, or intermittent strabismus/decompensated heterophoria.13 However, some cases of alternating strabismus14 or acquired incomitant strabismus15 are well suited to monovision.1 Binocular status should be carefully assessed16 in potential and existing monovision patients.1

FITTING MONOVISION CONTACT LENSES
In most people, the dominant eye varies with testing method, position of gaze,1 and monocular blur.17 Blur suppression18 is a more meaningful test than sighting dominance to detect the proper eye to fit with the distance lens.1 A simple test of blur suppression is as follows: correct both eyes for distance vision and, while the patient binocularly fixates on a distance target, introduce a plus lens of the near addition power first over one eye and then the other. Ask the patient to state which option gives the best distance vision. The limiting case for monovision is often night driving, so the test can be repeated while the patient views a spotlight in the dark.

Good monocular visual acuities are important for monovision. The correction of low degrees of astigmatism can therefore be helpful.19

Is age a limiter to successful monovision? In some patients, higher reading additions can prove too much for their interocular blur suppression; others can cope with the maximum add without experiencing blur. Depending on pupil size and reading distance, some older patients may have problems with intermediate vision. In patients over the age of 70 years, monocular blur may increase the risk of falls.20

PATIENT MANAGEMENT
As with any mode of presbyopic correction, the patient should be carefully quizzed about his vocational requirements. Monovision is generally considered unsuitable for pilots21 or those with other vocations requiring precise stereoacuity. Patients must understand the limitations of monovision; informed consent is required. Typically, patients are advised not to drive until they are adapted to monovision.1 Not all patients adapt to monovision, and therefore a monovision contact lens trial before surgical monovision is strongly advocated.22

Many patients can drive safely with monovision during the day23 and at night.24 Indeed, monovision causes fewer symptoms of glare during night driving than simultaneous-vision multifocal contact lenses.24 Patients who have difficulties under specific conditions (eg, night driving, computer use) may need spectacles to correct the induced anisometropia during problematic tasks, although this is uncommon.

The distinction between monovision and simultaneous-vision multifocal contact lenses is becoming increasingly ill defined, and modified monovision or enhanced monovision are common options.1

In summary, monovision is a simple solution to presbyopia that is effective in most cases. With modern disposable contact lenses, it is relatively straightforward for patients to undertake a trial with contact lens monovision.

Bruce J. W. Evans, BSc (Hons), PhD, FCOptom, DipCLP, DipOrth, FAAO, FBCLA, is the Director of Research, Institute of Optometry; Visiting Professor, City University; and Visiting Professor, London South Bank University, all located in London. Professor Evans also is a practicing optometrist and contact lens practitioner in Brentwood, Essex. He may be reached at e-mail: bruce.evans@virgin.net.

  1. Evans BJW. Monovision: a review. Ophthal Physiol Opt. 2007;27:417-439.
  2. Erickson DB, Erickson P. Psychological factors and sex differences in acceptance of monovision. Percept Mot Skills. 2000;91:1113-1119.
  3. Back AP, Holden BA, Hine NA. Correction of presbyopia with contact lenses: comparative success rates with three systems. Optom Vis Sci. 1989;66(8):518-525.
  4. Du Toit R, Ferreira JT, Nel ZJ. Visual and nonvisual variables implicated in monovision wear. Optom Vis Sci. 1998;75(2):119-125.
  5. Evans BJW, Thompson DA. An overview of bifocal contact lenses. J Brit Contact Lens Assoc. 1991;14(2):71-74.
  6. Plakitsi A, Charman WN. Ocular spherical aberration and theoretical through-focus modulation transfer functions calculated for eyes fitted with two types of varifocal presbyopic contact lens. Cont Lens Anterior Eye. 1997;20(3):97-106.
  7. Simpson T. The suppression effect of simulated anisometropia. Ophthal Physiol Opt. 1991;11:350-358.
  8. Situ P, Du TR, Fonn D, Simpson T. Successful monovision contact lens wearers refitted with bifocal contact lenses. Eye Contact Lens. 2003;29(3):181-184.
  9. 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.
  10. Gupta N, Naroo SA, Wolffsohn JS. Visualcomparison of multifocal contact lens to monovision. Optom Vis Sci. 2009;86(2):98-105.
  11. Durrie DS. The effect of different monovision contact lens powers on the visual function of emmetropic presbyopic patients (an American Ophthalmological Society thesis). Trans Am Ophthalmol Soc. 2006;104:366-401.
  12. Harwerth RS, Moeller MC, Wensveen JM. Effect of cue context on the perception of depth from combined disparity and perspective cues. Optom Vis Sci. 1998;75(6):433-444.
  13. Kushner BJ, Kowal L. Diplopia after refractive surgery: occurrence and prevention. Arch Ophthalmol. 2003;121:315-321.
  14. McMonnies CW. Monocular fogging in contact lens practice. Austral J Optom. 1974;57:28-32.
  15. London R. Monovision correction for diplopia. J Am Optom Assoc. 1987;58(7):568-570.
  16. Evans BJW. Pickwell's Binocular Vision Anomalies. 5th ed. Oxford: Elsevier, 2007.
  17. Charnwood L. Observations on ocular dominance. The Optician. 1949;19:85-96.
  18. Schor C, Landsman L, Erickson P. Ocular dominance and the interocular suppression of blur in monovision. Am J Optom Physiol Opt. 1987;64(10):723-730.
  19. Collins M, Goode A, Brown B. Distance visual acuity and monovision. Optom Vis Sci. 1993;70(9):723-728.
  20. Vale A, Buckley JG, Elliott DB. Gait alterations negotiating a raised surface induced by monocular blur. Optom Vis Sci. 2008;85(12):1128-1134.
  21. Nakagawara VB, Veronneau SJH. Monovision contact lens use in the aviation environment: a report of a contact lens-related aircraft accident. Optometry. 2000;71(6):390-395.
  22. Vogt U. Kersley lecture: eye believe in contact lenses: contact lenses and/or refractive surgery. Eye Contact Lens. 2003;29(4):201-206.
  23. Wood JM, Wick K, Shuley V, Pearce B, Evans D. The effect of monovision contact lens wear on driving performance. Clin Exp Optom. 1998;81(3):100-103.
  24. Chu BS, Wood JM, Collins MJ. Effect of presbyopic vision corrections on perceptions of driving difficulty. Eye Contact Lens. 2009;35(3):133-143.

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