INTRODUCTION

The phacoemulsification of the lens with multifocal intraocular lens implantation has become, in recent years, the procedure of choice for the surgical treatment of presbyopia. This is thanks to the development of techniques and equipment used in cataract surgery, making this surgery extremely safe and predictable, and to the development and evolution of multifocal intraocular lenses allowing the surgeon to choose the lens most suited to the needs of the patient with a minimum commitment of visual quality^1,2.

The multifocal intraocular lenses evolved from bifocality to trifocality² with the aim of improving the intermediate vision, and more recently to the extended depth of focus lenses^3,4 (Extended Depth Of Focus – EDOF), which are an alternative for patients who are less tolerant to photic phenomena, more demanding with intermediate vision, and less demanding with near vision. The multifocal lens designation used in this chapter encompasses bifocal, tri-focal lenses and lenses for extended depth of focus.

Other therapeutic options in the lens plane are the implantation of accommodating intraocular lenses or the implantation of monofocal intraocular lenses using monovision. The former have the advantage, relative to multifocal lenses, of lower reduction of contrast sensitivity, less glare and fewer halos. However, their real accommodation capacity is quite limited^5,6, being therefore little used, and therefore will not be considered in this chapter in the decision process.

The second option, monovision, may lead to excellent results⁷, having however the disadvantage of loss of stereopsis. Tolerance to anisometropia⁸ must be explored beforehand and the patient informed about its implications. It is unanimously accepted that bilateral implantation of a multifocal lens is necessary to obtain maximum functional benefit⁹.

Not all lenses are indicated for all patients and, regardless of the lens chosen, there is always a compromise between its advantages and its drawbacks^9,10.

It is very important that the advantages and disadvantages are explained, and the patient understands them. The decision to implant a multifocal intraocular lens for treatment of presbyopia involves the evaluation of various subjective and objective parameters¹¹ which will be analyzed in more detail below. The patient's motivation, personality, expectation, visual needs, profession and lifestyle are factors of the utmost importance to be taken into account, as well as the absence of ocular pathology.

DECISION ON THE BASIS OF PSYCHOLOGICAL PROFILE, LIFESTYLE AND VISUAL NEEDS

Table I summarizes the characteristics of patients regarding motivation, personality, expectations, visual needs and lifestyle, which are favorable or unfavorable to satisfaction after implantation of a lens intraocular.

Motivation

It is fundamental that the patient is motivated and wants independence in the use of glasses for a large part of the tasks at different distances. Poorly motivated patients tend not to value the benefits of surgery and to value the less positive aspects of multifocal lenses.

Personality

Individuals with type A personality, ambitious and perfectionist, with the demand of perfect vision are generally bad candidates. Individuals with type B personality, optimistic and relaxed tend to be satisfied with the results obtained with implantation of a multifocal lens.

Expectations

The assessment of expectations allows us to gauge if what the patient expects can be given with the surgery. Expectations should be realistic, and the patient should be able to understand the limitations of a multifocal lens. It should be explained to the patient that when choosing a multifocal lens, the independence of the glasses is not completely guaranteed, and that their choice entails a compromise namely in reducing contrast sensitivity and in the existence of photic phenomena such as halos and glare.

Lifestyle / Visual Needs

Lifestyle, profession and visual needs are important factors to consider when deciding to implant a multifocal lens. Aviation pilots and professional drivers, particularly if they drive at night, are not good candidates because of the possibility of photic phenomena.

Depending on whether the patient occupies a large portion of the time in reading, or on the computer, the lens chosen may be a multifocal, trifocal or an EDOF. However, if the visual demands are high, the patient may experience difficulties in adverse conditions, regardless of the type of lens chosen.

REFRATIVE ERROR AND AGE

The best candidates for implantation of a multifocal intraocular lens are high or moderate hyperopes. Significant dependence on spectacles for near and also for distance usually results in a high satisfaction with the result obtained.

Low myopic and emmetropic patients are usually poor candidates for implantation of a multifocal intraocular lens. The former are often dissatisfied with near vision, while emmetropes often refer to poor visual quality at different distances. The implantation of a multifocal intraocular lens is generally used to treat presbyopia from the age of 50. However, age is not a strict limit. In the presence of elevated ametropias, multifocal intraocular lenses can be used successfully in earlier stages of presbyopia.

The choice of lens type should also take into account that older patients tend to value near vision more at the expense of mid-distance, while younger patients generally prefer a good intermediate vision.

OCULAR PATHOLOGY

Cornea and ocular surface

The success of a phacoemulsification with implantation of a multifocal intraocular lens usually involves a healthy eye.

A healthy, non-dysfunctional ocular surface of the Meibomian glands is an important factor for the success of the surgery. The pathology of the ocular surface alters the optical quality of the human eye¹², reducing contrast sensitivity and compromising the visual performance of multifocal lenses. It also reduces the accuracy of preoperative measurements, increasing the likelihood of residual ametropias, which also compromise a good functional outcome.

The evaluation of the ocular surface should be made by clinical evaluation, Shirmer’s tests and rupture time of the tear film. In dystrophies and corneal scarring, aberrations resulting from an irregular corneal surface constitute a contraindication for multifocal lenses.

Keratoconus, even its form fruste, usually results in poor visual function given the reduction in better visual acuity and the high likelihood of unpredictable residual ametropia that cannot be corrected with subsequent corneal surgery. Multifocal intraocular lenses are also not indicated in Fuchs' dystrophy because there is a reduction in the contrast sensitivity and poor visual quality, as well as for the progressive nature of the disease.

Anterior Segment

Decentration or tilting of the lens leads to decreased contrast sensitivity, aberrations and decreased visual acuity¹³, which occurs because of the zonular fragility associated with pseudo-exfoliation.

Alterations of the pupil, such as iris atrophy, corectopia, or coloboma, are also a contraindication for the implantation of a multifocal lens.

Retinal Pathology

In general, retinal diseases associated with poor macular function, and especially if they are progressive, are a contraindication to implanting multifocal intraocular lenses. Common examples include diabetic retinopathy, age-related macular degeneration (AMD), and vitreoretinal interface syndromes. In these diseases there is a reduction of the contrast sensitivity, which will add to the reduction of the contrast sensitivity resulting from the multifocal lens, leading in most cases to a poor functional result.

Optic Nerve Pathology

Optic nerve diseases reduce visual acuity, contrast sensitivity, chromatic perception, and visual field. Depending on the degree of functional repercussion or probability of progression, they may constitute an absolute or relative contraindication.

In the most common pathology of the optic nerve, glaucoma, it is generally agreed that if it is at an advanced stage and at risk of progression, this is an absolute contraindication.

PRIOR ABLATIVE CORNEAL SURGERY

Previous ablative corneal surgery is not an absolute but relative contraindication, depending on the magnitude and type of high order aberrations present in the cornea¹⁴. The biometric calculation after corneal ablative surgery is also more complex¹⁵, involving a higher risk of residual ametropias.

In the cases of coma, the poor visual quality and the resulting decreased contrast sensitivity, adds up to the reduced contrast sensitivity associated with multifocal lens implantation.

Regarding the positive spherical aberration, good results have been described after surgery for myopia, although with a high percentage of residual ametropias requiring correction¹⁶. The greatest limitations are after photoablative hyperopia surgery, which results in a hyperprolate cornea with negative spherical aberration. In this case, the multifocal intraocular lenses to be implanted present negative asphericity, which will increase even more the negative spherical aberration, leading to poor quality visual.

UNILATERAL IMPLANTATION OF MULTIFOCAL INTRAOCULAR LENSES

Due to the decrease in contrast sensitivity associated with the implantation of a multifocal intraocular lens, bilateral implantation is usually necessary for a better visual performance. However, in selected cases there may be benefit and satisfaction of the patient in the implantation of a multifocal intraocular lens in only one eye¹⁰.

In the presence of a unilateral cataract, with the patient's expectation of independence of glasses, a multifocal intraocular lens can be implanted until the decision to perform surgery to the other eye is made.

Also, in a unilateral cataract in a young patient, the multifocal intraocular lens may be an option to ensure good visual binocular function at different distances.

Patient satisfaction in these cases is largely dependent on the understanding of the limitations and compromise of multifocal intraocular lenses.

ANATOMICAL AND INTRA-OPERATIVE CONDITIONING FACTORS

Functional success after implantation of a multifocal intraocular lens depends on a perfect centering of the lens¹³. Thus, implantation in patients with a very high K angle can result in poor functional outcome due to poor lens centering.