3.2.4.1. Unilateral implantation of multifocal intraocular lenses after cataract extraction and presbyopia correction
3.2.4.1. Unilateral implantation of multifocal intraocular lenses after cataract extraction and presbyopia correction
Clínica Oftalmológica Joaquim Mira, Coimbra, Portugal
Presbyopia is a decrease in accommodative capacity. It usually begins around the age of 40 and worsens with age, causing total loss of accommodation by the age of 601-3. There are different methods to correct presbyopia, including scleral expansion surgery4, corneal inlays5, LASIK or PRK by zones, and accommodative or multifocal lenses6. Monovision7 in phakic or pseudophakic eyes may impair visual binocular function in near and far vision. The use of multifocal intraocular lenses (IOLs) is currently the preferred method because it widens the depth of focus in near and intermediate vision and maintains a good binocular visual function.
The implementation of a multifocal lens requires preoperatively:
After cataract surgery, especially with multifocal IOLs, some people may notice bright rings around the lights at night. After three months, this sensation diminishes and they almost stop seeing them, but if they look and try to see them it is possible to perceive them. As Farrell explains8, brain adaptation to multifocal IOLs is like getting a new ring of vision. At first the patient realizes its existence, looking through it and dealing with its existence. Over time this sensation is attenuated, but it will still be possible to observe the ring.
The correction of refractive errors of residual ametropies in eyes with diffractive multifocal IOLs is generally made from the refractive point of view, as if they were monofocal lenses or as if the eyes were phakic. People with diffractive multifocal IOL implants in both eyes or in one eye (whether the other eye is phakic or with monofocal IOL) may need to wear glasses temporarily or permanently for residual ametropia in near or far vision, or, sometimes, to read small characters in low light environments. In these people the refraction should be adjusted as if a monofocal IOL had been implanted or as if the eyes were phakic, i.e. in far vision both eyes are corrected with the best correction to obtain the best vision and, at close range, the addition is made depending on the working distance.
In cases of unilateral cataract, the implant of accommodative or pseudo-accommodative multifocal IOLs to restore binocular vision is controversial. Likewise, it is debatable whether in individuals already operated on the first eye with a monofocal IOL, a multifocal IOL may be implanted in the second eye. In these cases there is some fear that when implanting an IOL with a multifocal optic in one eye, if there is previously a monofocal IOL or the presence of the crystalline lens in the eye, the individual can perceive the difference of optics in each eye and cause some unpleasant visual disturbance, making neuro-adaptation difficult.
Some presbyopes with unilateral cataracts and emmetropia in the other eye, or with a small refractive error, only want to be operated on the eye with the cataract. If the patient meets the selection criteria for a multifocal IOL and does not want or need surgery for the fellow eye within a short time, there is no contraindication to having multifocal IOL implanted in the first eye, leaving the fellow eye phakic. Later, when the patient decides or needs surgery on the second eye, a multifocal IOL can then be implanted. Other people who have previously had cataract surgery with a monofocal IOL but who have nonetheless developed cataract in the second eye show interest in having a multifocal IOL implant.
In presbyopia, it is generally recommended that the multifocal IOLs be implanted in both eyes.
Bilateral multifocal IOL implantation in well-selected people benefits from brain addition, improving distance and near binocular vision by at least 1.5 lines of visual acuity. Patients should be advised that the brain only achieves the best visual quality, masking any eventual eye deficiency, after both eyes have been operated on with multifocal IOLs.
The implantation of multifocal IOLs in both eyes can achieve higher rates of independence of glasses (76 to 92% of patients) than those implanted with monofocal IOLs (8 to 12% of patients)9,11, although at the expense of some decrease in contrast vision, as well as the more frequent appearance of dysphotopic phenomena at night, since multifocal IOLs present simultaneous images for near and distant vision9,12-14,16,17.
Young people, or pre-presbyopes, have an accommodative capacity. If they see well in the distance without glasses, they do not need glasses to see at close range. If they have unilateral cataract and are operated on with monofocal IOL and are made emmetrope for distance, they will have a good binocular function in distant vision, but monofocal IOL-induced presbyopia means that this eye needs near vision glasses and this difference in prescription between both eyes can lead to different degrees of anisometropia and aniseikonia, and may compromise binocular near vision. Multifocal IOLs provide good long-range visual acuity by increasing the depth of focus in near vision, do not compromise binocular vision in young or pre-presbyopic patients with unilateral cataract, often allowing independence of glasses11,18-20. In young people with accommodative capacity and cataract only in one eye, if possible, a multifocal IOL should be implanted, seeking in general to obtain emmetropia and should not be operated on to the other eye10. Studies have shown the restoration of binocular vision for far and near vision with unilateral multifocal IOL implantation in young and presbyopic eyes10 and a reduced or insufficient binocular function for near and intermediate vision has been found with monofocal IOL implantation10,21.
In presbyopic individuals with unilateral cataract, monofocal IOL implantation is the most frequent option because there are no problems with binocular vision, since these eyes will not suffer from anisometropia and aniseikonia, since the fellow healthy eye also needs correction with glasses for near vision, similar to that of the operated eye1,20. Presbyopes with unilateral cataracts and emmetropia in the fellow eye can, however, benefit from the implant of a diffractive multifocal IOL, provided they are aware of the real expectations and the possibility of dysphotopic phenomena18,19.
In several studies with different types of multifocal IOLs, no differences in uncorrected visual acuity have been found in any of these types of lenses. However, the accommodation achieved with accommodative lenses was not as efficacious as that of multifocal IOLs10.
Previous studies in children, youngsters and presbyopes with unilateral cataract have shown that refractive or diffractive multifocal IOL implantation provides better binocular visual acuity for near than monofocal IOLs10,11,22-24. In a diffractive multifocal IOL study, it was concluded that patients were satisfied with unilateral multifocal IOL implantation in the dominant eye only, but bilateral multifocal IOL implantation provided better visual outcomes and stereopsis9,25.
In a survey on satisfaction post-implantation of diffractive multifocal IOL in one eye and a monofocal IOL in the other eye, 91% would reimplant this IOL again, 75% reported being satisfied with their vision and 57% achieved glasses independence, while in patients with monofocal IOLs in both eyes satisfaction was achieved in only 8%9. Although not benefiting from binocular addition, individuals with multifocal IOLs in one eye and monofocal IOLs in the other eye reported fewer halos than individuals with bilateral multifocal IOLs.
Another study in 40- to 60-year-old patients with unilateral cataract showed that the +3.0 D addition diffractive multifocal IOL implantation allowed a significant improvement in near and intermediate binocular visual acuity (VA) regardless of whether the other eye is myope, hyperope or emmetrope, enabling a lower need for glasses, unlike the unilateral monofocal IOL implant11. Distant binocular VA was the same for both lenses, although contrast sensitivity for far was slightly worse with multifocal IOLs. Halo complaints were higher in the refractive and diffractive multifocal IOL groups compared with the accommodative and monofocal IOL groups11. Satisfaction with near vision was higher in multifocal IOL patients than in monofocal IOLs, while in far vision it was comparable, suggesting that multifocal diffractive IOL implantation provides, in most patients, a sufficient binocular function and visual quality for near11. Stereopsis for near was better in individuals with multifocal IOLs than in monofocal IOLs, although stereopsis for far was comparable in both types of IOLs11. Jacobi et al found that Randot-Lang stereotests and the Titmus test were positive in 77% and 40%, respectively, of individuals with unilateral multifocal IOLs (Array SA40-N) and monofocal lenses10.
In the study by Mesci et al18 binocular near vision was better in patients between the ages of 40 and 60 with multifocal IOL implantation in one eye than in patients with monofocal IOL implantation.
A study of 20 cataract-operated patients who underwent a multifocal diffractive apodised IOL implant in one eye, while the other eye was phakic (because the opacity of the lens was not visually significant yet and the subject did not want to be operated on the second eye), reported that most people noticed that the vision of the operated eye was clearer, the colors were more vivid, and without any visual disturbance. Some time later they failed to notice any difference. Twenty-five per cent of these people reported never having worn glasses again, 40% wore glasses for some near activities and 35% used them permanently to correct some ametropia in either eye or near vision, but did not feel any visual disturbance in wearing glasses because one eye had a multifocal IOL and the other was phakic.
In another study, a group of 17 people who had had single-eye cataract surgery with a monofocal IOL implant intended to have a multifocal IOL implanted in their second eye. The advantages, disadvantages and limitations of this technology have been clarified. Most reported being able to dispense with glasses for most daily tasks. The fact that they had a different optics in each eye did not cause any visual difficulties or adaptation to the glasses. Only a small percentage reported (after being asked) that they sometimes noticed halos in night vision, but that did not bother them.
Implantation of a monofocal IOL in young and middle-aged individuals with cataract can induce impaired near and intermediate binocular vision. On the other hand, implantation of a diffractive multifocal IOL after extraction of a unilateral cataract is effective in providing a binocular visual function useful for distance, intermediate and near vision. In different studies, individuals' satisfaction was substantially higher in those with multifocal IOLs than with monofocal IOLs26.
It can be concluded from different studies, that the unilateral implantation of a multifocal IOL, especially in young or pre-presbyopic individuals, provides a wide range of functional vision from distance to near, high satisfaction rates, independence from glasses, and better stereoscopic vision at close view, even though there are some rare complaints of halos and glare, which justifies and does not preclude the use of multifocal IOLs in unilateral cataract.
Several types of multifocal IOLs with different designs and addition powers have recently been developed. Further studies are needed to know which multifocal IOL is best suited for implantation in individuals with unilateral cataract.