Implantation of multifocal IOLs and planned monovision offer freedom from glasses after cataract surgery that is a highly desirable outcome and important characteristic of the quality of life today
Natalia Y Makhotkina MD
Noël JC Bauer MD PhD
Rudy MMA Nuijts MD PhD
University Eye Clinic,
Maastricht University Medical Center,
Maastricht, The Netherlands
Email: [email protected]
Young eyes, when corrected for refractive error, provide a continuous range of sharp vision from near up to infinity. According to the Helmholtz theory of accommodation, the crystalline lens is able to adapt the optical power by changing its shape and position as a result of relaxation or contraction of the ciliary muscle (Figure 1).
After the age of 40, the elasticity of the crystalline lens and the strength of the ciliary muscle continuously decay. This results in a gradual loss of accommodation, also known as presbyopia. Therefore, visual tasks at the near (for example, 35–40cm) or intermediate (for example, 60–70cm) distance become increasingly difficult and require the use of reading spectacles.
Along with a loss of accommodation, ageing also leads to changes in the crystalline lens proteins and clouding of the crystalline lens, a process called cataract formation. Cataracts can lead to an impairment of overall quality of life as a result of the decrease in visual acuity and quality of vision. Various light sensations such as glare and halos may be disturbing symptoms in cataract patients.
Fig. 1: Accommodative response. When the eye views a near object, the ciliary muscles contract and the lens becomes thicker. The optical power of the eye increases and the image is focused on the retina.
In cataract surgery, the cloudy crystalline lens is removed from the capsular bag and replaced by an artificial intraocular lens (IOL). With sophisticated intraocular lens power calculations and small-incision cataract surgery, spectacle independence for distance or emmetropia can be achieved in the majority of patients. A traditional IOL is monofocal and this single focal point provides a sharp vision only at one fixed distance.
Thus, despite spectacle independence for distance being achieved, glasses are usually needed for reading and also for computer work. Nowadays, an increasing number of patients that undergo cataract extraction demand for complete spectacle independence after surgery. Hence, an IOL that could restore the ability to accommodate would be highly desirable.
In theory, a monofocal IOL that could change its axial position in the eye would allow patients to regain accommodation. Accommodative IOLs were designed for this purpose. However, in clinical practice the movement of these accommodative IOLs has been shown to be insufficient to improve near visual acuity and clinical results are disappointing.1
Another attractive option is to refill the capsular bag with a clear and elastic substance in order to recreate a lens that can function as a natural one. However, despite ongoing experimental research, the effectiveness of this method has not yet been proven.2,3
Although it is still impossible to fully restore the ability to accommodate, there are widely acknowledged options that aim to provide freedom from spectacles after cataract surgery. These options are implantation of multifocal IOLs and planned monovision where one eye is corrected for seeing in the distance and the other eye for seeing near.
Fig. 2a: PanOptix multifocal IOL.
Fig. 2b: PanOptix multifocal IOL in situ.
Multifocal IOLs
Multifocal IOLs (Figure 2) aim to increase depth of focus, that is, the range of distances where visual acuity is sufficient to perform visual tasks. These IOLs have multiple optical zones that divide the incoming light between either two (bifocal) or three (trifocal) foci. Hence, images of objects that are located at different distances from the eye can be focused on the retina using different optical zones.
Therefore, multifocal IOLs always present patients with two or more retinal images at the same time, while only one image is sharp. For example, when a patient views a near object, a sharp image of this object is projected onto the retina while the out of focus image(s) that are also projected onto the retina are being suppressed by the brain. This concept is known as ‘simultaneous vision’.4
The first multifocal IOLs were introduced in the late 1980s5 and nowadays several types are available on the market. Multifocal IOLs can have refractive (for example, ReZoom, Abbott Medical Optics, Santa Clara, California and MPlus, Oculentis, GmbH, Berlin, Germany), diffractive (for example, Tecnis ZM900, Abbott Medical Optics, Santa Clara, California) or combined refractive–diffractive (for example, ReSTOR, Alcon Laboratories, Fort Worth, Texas) optic design. Either diffractive or refractive multifocal IOLs can provide excellent unaided near and distance visual acuity and offer a high rate of spectacle independence.6
Multifocal IOLs are originally designed as bifocal, that is, they can provide sharp vision at two working distances: far and near. This means that some patients will still require glasses for the intermediate distance, for example for computer work. New trifocal IOLs (for example, FineVision Micro F trifocal IOL Physiol, Liege, Belgium and AT LISA tri 839MP, Carl Zeiss, Meditec AG, Jena, Germany) deal with this problem by providing good intermediate visual acuity without compromising vision at near and far, in other words by improving depth of focus.7,8
In 2015, a novel trifocal IOL (Acrysof IQ PanOptix, Alcon Laboratories, Fort Worth, Texas), designed to further improve the range of sharp vision, was introduced in Europe. The first clinical results are encouraging: the new IOL provides very good visual acuity at near, intermediate and far distance and seems to be associated with fewer patient complaints compared to the other multifocal IOLs.9
Despite clear benefits with respect to spectacle independence, multifocal IOLs still have some caveats. Unrealistic patient expectations and side effects can lead to significant patient dissatisfaction. Thorough preoperative counselling and ophthalmological examination is therefore crucial in order to reach high satisfaction in patient undergoing cataract surgery with implantation of multifocal IOLs.
First of all, it is very important to inform patients about the imperfections of multifocal IOLs and possible side effects. Dividing the light in two foci may reduce contrast sensitivity, while simultaneous presentation of two retinal images may lead to blurred vision, halos and glare. These side effects are inherently related to the special design of the multifocal IOL. It is our experience that only a small number of patients will actually complain about them.
Furthermore, not all patients are good candidates for multifocal IOL implantation per se. For example, very critical patients or those with high visual demands and patients with low myopia, a large pupil diameter or dependency on intermediate vision (computer work) may not necessarily benefit from multifocal IOL implantation.
Lastly, ocular pathology such as a severe ocular surface disease, substantial irregular astigmatism, age-related macular degeneration and extensive glaucoma are conditions, which could lead to unsatisfactory outcomes and are relative contraindications for implantation of multifocal IOLs.
In clinical practice, the most common causes of patient dissatisfaction after implantation of a multifocal IOL are residual refractive error, posterior capsule opacification or secondary cataract, a large pupil diameter, decentration of the IOL and coexisting ocular pathology.10 More than 80% of the symptoms can be treated successfully10 and an IOL exchange is only rarely required in severe cases.11
Planned monovision
Planned monovision can be a good alternative for those patients in whom possible side effects of multifocal IOLs, such as insufficient intermediate visual acuity, blurred vision and halos, are unacceptable. For example, middle-aged patients with low myopia may be very unhappy with multifocal IOLs as they are used to having excellent distance visual acuity with their myopic correction and have yet not had to deal with loss of near and intermediate vision, since they can read perfectly without glasses. These patients will likely not accept a minimal loss of visual acuity and contrast sensitivity with multifocal IOLs and planned monovision may be a good choice.
The conception of monovision is based on the induction of anisometropia (each eye a different refraction) with monofocal IOLs. The dominant eye is usually fully corrected for distance vision, that is, made emmetropic, while the non-dominant eye is left slightly myopic in order to see sharp at a near distance (book reading, computer work). Hence, spectacle independence is achieved while maintaining sufficient quality of vision without the side effects of multifocal IOLs.
The current opinion on the amount of anisometropia to be induced is not yet unequivocal. A large difference in refraction between two eyes might be beneficial for near visual acuity but would compromise stereopsis and distance visual acuity.12 In general, 1.5 diopters of myopia has been shown to give acceptable outcomes and sufficient patient satisfaction. This concept is known as modest monovision. The amount of anisometropia can of course be customised based on individual requirements of the patient. Simulation of the postoperative situation using contact lenses preoperatively can be helpful.
Clinical practice shows that patients with monovision are more dependent on reading glasses than those with multifocal IOLs. A recent randomised clinical trial has shown that only 25% of patients with monovision achieved complete spectacle freedom, compared to 85% patients with multifocal IOLs.13 Interestingly, despite this difference the overall satisfaction with the quality of vision was similarly high in both groups. The possible explanation is that patients with monovision usually experience fewer problems with visual tasks at intermediate distances and fewer halos and glare.
Conclusion
Spectacle independency after cataract surgery becomes an increasingly popular and desirable outcome. Currently, implantation of a multifocal IOL and planned monovision are options that can offer freedom from spectacles after surgery. However, both methods have some limitations and will not fully restore the natural accommodation.
Patients should be aware of this and be prepared to make a compromise between the spectacle independence and possible side effects, for example, loss of contrast sensitivity and halos with multifocal IOLs or a decrease in distance visual acuity of the non-dominant eye and loss of stereopsis when choosing monovision. Careful selection of patients, extensive counselling and examination help to find a customised solution for each individual case in order to achieve high postoperative patient satisfaction.
References
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- Nishi Y et al. Lens refilling to restore accommodation. Journal of cataract and refractive surgery 2009;35(2):374–82.
- Charman WN. Developments in the correction of presbyopia II: surgical approaches. Ophthalmic & physiological optics: the journal of the British College of Ophthalmic Opticians 2014;34(4):397–426.
- Davison JA, Simpson MJ. History and development of the apodized diffractive intraocular lens. J Cataract Refract Surg 2006;32(5):849–58.
- Keates RH, Pearce JL, Schneider RT. Clinical results of the multifocal lens. J Cataract Refract Surg 1987;13(5):557–60.
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- Nuijts RMMA. A new approach in trifocality: the AcrySof® IQ PanOptix® presbyopia correcting IOL. XXXIII Congress of ESCRS, Barcelona, 2015.
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- Wilkins MR et al. Randomized trial of multifocal intraocular lenses versus monovision after bilateral cataract surgery. Ophthalmology 2013;120(12):2449–55 e2441.
