Presbyopia / SPO - 3.2.3.2. Monovision and mini-monovision

3.2.3.2. Monovision and mini-monovision

Fernando Llovet Osuna (1) y Julio Baviera Sabater (2)

1. Clínica Baviera, España

2. Clínica Baviera-CareVision, España

INTRODUCTION

Presbyopia is the most frequent refractive error in people over 40 years of age; it is estimated that more than one billion people suffer from it worldwide1. Today, this is a challenge of enormous magnitude, both for refractive surgeon ophthalmologists and for the millions of patients who suffer from it. Numerous surgical procedures have been described to treat presbyopia. Each one has its advantages and disadvantages and usually involves a certain compromise between the near and distant vision of the patient. Currently presbyopia can be corrected in different ways, among which are the glasses (for near vision, bifocal or progressive), contact lenses (multifocal), corneal surgery (conductive keratoplasty, photoablation with excimer laser, intracorneal implants), scleral surgery and lens surgery with accommodative or multifocal intraocular lens implantation, among others2,3.

The term “monovision”, also called “blended vision” defines a visual situation in which one eye focuses for distant vision and the other for near vision, so that the patient is able to clearly perceive distant, intermediate and nearby images, without the need for corrective aid and in various daily activities1. Refractively, to reach the monovision situation, one eye must be emmetropic (the one focused for far vision), and the other eye should be slightly myopic (the one focused for near vision). The mechanism that allows the success of monovision is called "interocular blur suppression"4.

This situation may be present in patients with mild anisometropia or it may be induced optically or surgically. Monovision was initially used in optometry, in the 1960s, through the adaptation of contact lenses for the treatment of presbyopia (originally "single vision")5-7. In the 1980s, with advances in lens surgery and monofocal intraocular lens implants, monovision was introduced in patients operated on for cataracts or with refractive lensectomy (pseudophakic eye, which has obligatorily lost accommodation) with the objective of improving not only the distant vision, but also the near and the intermediate ones. Since then, and up to the present time, it is considered that the "pseudophakic monovision" is a useful technique in patients who are going to schedule a lens surgery, with a monofocal intraocular lens implant.

The incorporation of excimer laser (1990s) in refractive surgery made it possible to correct various refractive errors (myopia, hyperopia and astigmatism) and achieve independence from the daily use of optical correction, although there was a limitation of presbyopic age, which prompted the use of monovision (e.g. LASIK monovision).

Less importance, in terms of its use, have other techniques that support its effect on monovision, such as conductive keratoplasty (CK) or some intracorneal implants.

Some studies have reported success and satisfaction rates between 80-98%, performing monovision after excimer laser correction8-10, 91% after cataract surgery and 95% after crystalline refractive interchange (CRI)7. It is striking that post-surgical monovision with excimer laser has a success rate higher than that achieved with contact lenses (around 70-75%).

Monovision works in the majority of patients, except in those with a significant anisometropia or with a clear ocular dominance or a poor stereopsis, all of them factors that hinder ocular suppression. Women tend to adapt better than men and satisfaction will be greater at early ages of presbyopia, due to the greater accommodative remnant of the lens11. Monovision can also be performed by inducing myopia in the dominant eye (cross monovision), and similar results have been reported with both alternatives2.

Monovision has some limitations due to certain alterations that it causes in some visual functions, such as the reduction of visual acuity in low contrast conditions, contrast sensitivity and stereopsis10. In addition, it requires reaching emmetropia in the eye for far vision, a thorough preoperative examination and the postoperative adaptation is sometimes long. Reviewing that, when the technique is not performed on the lens, its effect will be limited in time, due to the progressive deterioration of the crystalline function and transparency. However, it is a very simple, satisfactory, safe, effective and predictable technique that, since it does not induce significant corneal aberrations, will not lead to great limitations in the choice of the intraocular lens (IOL) in a future lens surgery in cases where it is performed with corneal surgery3.

Although several studies show high levels of satisfaction after surgically induced monovision (86%, Wrigt6; 95.6%, Goldberg12; 88%, Jain13; 97%, Reilly8), the incorporation of multifocal intraocular lenses into surgery for presbyopia has relegated that to certain situations, as we will mention later.

TYPES OF MONOVISION

Monovision can be classified according to:

a ) The surgical technique:

Monovision with pseudophakia (lensectomy with monofocal intraocular lens implant)
Monovision with corneal techniques (corneal photoablation with laser excimer/LASIK, or surface ablation/PRK/LASEK, conductive keratoplasty or intracorneal implant).

b) The visual and refractive target:

Standard monovision (inducing between 1.5 and 2.5 diopters (D) of myopia in the eye for near vision)
- Mini-monovision (in which the resulting myopia will not exceed 1 D)
- Monovision with improvement in the depth of focus:
  - Micro-monovision (a corneal ablation with laser excimer and optimized profile that will increase the corneal spherical aberration and increase the depth of field, adding to a monovision between -1 and -1.5 D in the reading eye)14.
  - Advanced monovision (whose foundation is to create an aspherical profile in both eyes and inducing a moderate myopia in the non-dominant eye of -1 D)15,16.

FUNDAMENTALS OF MONOVISION

OCULAR DOMINANCE

As mentioned above, the mechanism by which the monovision functional situation is achieved is the "suppression of the blurred image", for which, regardless of the surgical technique, it is necessary to determine which eye has to focus for near vision and the one that will do it for vision far away, which necessarily involves studying ocular dominance.

Ocular dominance is defined as the predominance of the visual function of one eye over the other. Under conditions of anomalous binocular vision, the image perceived by one of the eyes is that selected by the brain, there being a clear dominance (in a strabismus the "suppression" can occur, sensory mechanism by which the brain eliminates the retinal impression of the eye diverted to avoid diplopia). However, under physiological conditions the existence of a dominant eye under conditions of binocularity has also been postulated17.

The magnitude of ocular dominance can influence the success of monovision, with a better prognosis for patients with lower ocular dominance18,19. Patients with greater ocular dominance have lower capacity to suppress the blurred image, and lower binocular depth of focus2.

Patients with successful monovision should be able to suppress the blurred image of the contralateral eye, and patients with less marked ocular dominance seem to be better able to achieve this with both eyes4.

In addition, as described in the medical literature, the ability to suppress the blurred image is less in high contrast conditions, such as night driving. In monovision, the suppression of the blurred image is not absolute, always maintaining a certain depth perception, since part of the information of the blurred image is used at the same time as the clear contralateral image4.

Several authors have studied ocular dominance in healthy patients, and it has even been classified into two types:

Motor ocular dominance: choice between both eyes in situations that allow only a monocular vision (an example will be the choice of an eye to look through the lens of a camera).
Sensory ocular dominance (ocular prevalence): in conditions of binocular vision, the images perceived by each of the eyes compete with each other, predominating one over the other.

MAGNITUDE OF ACCOMMODATION

The ability to accommodate is another factor that we should keep in mind when planning for monovision. The lens modifies its morphology with age. A young crystalline lens achieves a complete accommodation at 30 years and over the years the accommodation range progressively decreases and is around 55 years when the accommodation tends to disappear (Figure 1).

Figure 1. Accommodation path according to age.

Since presbyopia is the progressive loss of the focusing power of the lens (accommodation), directly related to age (from 40-45 years) and that causes difficulty in seeing distant objects, it will be necessary to understand how the patient focuses according to his age. A child can see clearly at a distance as short as 10 centimeters. As the age of the individual increases, the capacity for near vision decreases. The eye of a 45-year-old subject can accommodate one diopter, which implies that his or her accommodation is between 1 meter and infinity, one of 50 years will accommodate half a diopter, so his/her range of accommodation will be between 2 meters and infinity. However, the 55-year-old eye (or the one who has undergone a lensectomy) has lost the accommodation and his vision will exclusively focus on infinity.

CONCEPT OF "EYE OF FAR AND EYE OF NEAR"

In the medical literature conventional monovision is defined, when the dominant eye focuses for distance, and cross monovision when the dominant eye focuses for close11. However, Jain13 demonstrated that cross monovision obtains satisfaction results similar to those of conventional monovision (88% satisfaction). In the medical literature, mention is made of the "dominant eye" (sometimes without defining the chosen test) and this eye is assigned for far vision. In our group, when we perform the preoperative exploration for monovision, we usually decide what the eye for near vision will be, which we call "reading eye"22, by means of the +1 D test in far vision (described below), because it reproduces a real situation similar to that induced with monovision.

Some studies propose that, in order to decide which eye is to be programmed as the eye for distance, the following factors can be assessed (in addition to ocular dominance):

Focusing for far the eye that the patient uses most frequently for distant activities, such as looking through the lens of the camera, or a shotgun.
Focusing for close the eye that has the closest near convergence point.
Focusing the eye for distance the eye that the patient uses more frequently in his daily life.
Focusing the eye for far the eye with less ametropia, as it has a greater chance of becoming emmetropic with only one surgery.

PROGRAMMING THE MYOPIA IN THE READING EYE

Once the ocular dominance is known, the path of accommodation, we will program as the reading eye the one that better tolerates the distant defocus and the one that tolerates worst the +1 D lens in far vision (that is, the one that tolerates the defocus worst) will be the one we will choose for far.

There is an upper limit of anisometropia tolerated in patients who undergo monovision, which Goldberg12 established at -2.5 D. However, Greenbaum, in a study on pseudophakia monovision, programmed -2.75 D in the eye chosen for near vision7. The Goldberg nomogram, based on age12, establishes the following myopic spherical equivalents for the reading eye: 40 years: -1.25 D; 45 years: -1.50 D; 50 years: -1.75 D; 55 years old: -2.00 D; 60 years: -2.25 D; ≥ 65 years: -2.50 D.

Another study showed that the average binocular visual acuity in patients with monovision was independent of the magnitude of the defocus of the reading eye (anisometropia between 1 D and 3 D), of the selected eye as a the reading one (dominant or non-dominant) and the pupillary size23. Other studies agree that the suppression capacity of the blurred image is independent of the pupillary size2,19. Some authors limit the anisometropia to 1.5 or 2 D3,6. Wright6, recommends not to induce anisometropia greater than 2 D in the reading eye, as this could alter the binocular fusion and further decrease the distant stereopsis.

In our group, we usually program a refractive target between -1 and -1.5 D of myopic sphere in the reading eye. In our experience, in monovision patients this myopic defect is sufficient to provide good near vision (J3 on the Jaeger scale, in near binocular vision, without correction), and an excellent intermediate vision (J6), without significantly affecting far vision. As we commented before, the binocular sum starts to disappear when the anisometropia is greater than 1.5 D, so in our opinion this is the most recommended number when it comes to programming monovision. Despite this, the amount of myopia that we program in the reading eye may vary slightly, depending on the age and the usual activities performed by the patient. In general, if the spherical equivalent obtained is between -1 and -2 D, the patient will consider that the result is good (Figure 2).

Figure 2. Situation of monovision in the emmetropic patient, according to age and degree of accommodation.

PREOPERATIVE STUDY

Taking into account that when talking about surgically induced monovision we do it from a refractive technique, preoperative tests should include all those that are considered "standard for refractive surgery":

visual acuity without and with correction, mono and binocular, in far, intermediate and near vision
subjective and cycloplegic refraction, far and near
keratometry
corneal topography
corneal pachymetry
anterior segment examination (biomicroscopy)
posterior segment examination (including OCT if necessary, in case of crystalline surgery)
extrinsic ocular motility
intrinsic ocular motility
pupillometry
lacrimal function (especially TBUT and Schirmer)
biometry
endothelial cell count (if lensectomy)

But, in the case at hand, it will be necessary to submit the candidates to a series of “special” examination tests, that will offer us some data related to the prognosis of the monovision. Among these, we include the following:

Ocular dominance
Binocular summation
Help test
Determination of the reading eye
Stereopsis
Contrast sensitivity

Advanced orthoptic exploration is recommended in patients who meet the following criteria: previous history of strabismus, inadaptation to contact lenses and patients who wear hypo or overcorrected glasses.

OCULAR DOMINANCE

There are several types of tests, to determine ocular dominance24:

Ocular motor dominance tests (also called "sighting eye dominance"). The subject must choose between one eye and the other.
- Test with the hole between the hands or on a cardboard ("Hole-in-card test"): the patient, with the arms outstretched, leaves a hole between the palms of the hands or holding a cardboard with a hole in the center with both hands, and he/she is asked to look through the hole at an object located 6 meters away. The patient is asked to alternately close one eye and the other, so that the eye that holds the object aligned, will be the dominant one (Figures 3, 4). This is the test that we use routinely.

Figures 3 and 4. Test of the hole between the hands (motor dominance)

Other tests:
- Test of the alignment of the pencil ("pointing a finger"): similar to the test of the hole in the cardboard, but in this case the patient holds a pencil with both hands, being asked to align it with a target located 6 m away.
- Kaleidoscope test: the patient holds a kaleidoscope with both hands (a camera can also be used, or any other monocular instrument), being asked to look through it. To do this, the patient must choose an eye, which will be considered the dominant one.
- Close convergence point test: when close convergence is being explored, the eye that diverges in the first place is the non-dominant eye.
Sensory ocular dominance tests (prevalence test): the balance of both eyes is measured before a sensory stimulus.
- +1 D Test ("Plus 1 D test" or "swinging-plus test"): with the patient looking at an optotype at 6 meters distance, with its corrected distant refraction, a lens of +1 or +1.5 spherical diopters is alternated between both eyes. The patient must decide which of the two situations is most comfortable for him. If it is more comfortable to have the positive lens in front of the right eye, then the dominant eye will be the left one, and vice versa. This test can also be performed at close distances, in which case if the patient finds it more comfortable to have the positive lens in front of the right eye, that eye (right) will be the dominant eye, and vice versa (Figure 5). This one is used by us on a regular basis.

Figure 5. “+1” or “plus 1” test (sensory dominance).

Other tests:

Worth’s 4-point test.
Polarized test (dissociative polarized glasses).
Far stereopsis test (polarized glasses).
Haidinger’s test (synophore). This test allows quantifying the magnitude of ocular dominance. According to the studies of Seijas et al16, analyzing each of these types of tests separately, they found that the tests that obtained the highest proportion of dominance were those of the hole in the hand, the +1 D, and that of Haidinger.

In most of the published studies on monovision, only one test is mentioned to determine the ocular dominance (usually a motor test: the “hole-in-card test”)1,9. Sometimes, some studies do not even describe the type of test used to determine which is the reading eye10. In spite of this, and since the satisfaction results are very similar between different studies (the majority of patients with successful monovision are those who do not have a frank ocular dominance), we think that patients who do not adapt to monovision would be those who have a strong dominance (and therefore less able to perform the alternation and the suppression of the blurred image).

The ocular motor dominance in emmetropic presbyopes presents a constant alternation; in myopic presbyopes with anisometropia less than 1.75 D the dominance was 50% in the most myopic eye and 50% in the least myopic one. However, when the anisometropia was higher, in 100% of the cases dominated the more myopic eye (fact that questions the adjustment for far vision of the "motor" dominant eye, in monovision). Hyperopic presbyopes are usually less tolerant of the monovision situation19.

The examination of ocular dominance should allow us to rule out those patients with marked ocular dominance (e.g. strabismus), since they will tolerate the monovision worse, since there is no correct binocular coordination, which prevents the adequate suppression of the blurred image.

BINOCULAR SUMMATION

The binocular summation allows the contrast sensitivity to be greater than the monocular, even though both eyes have different sensitivities. When the anisometropia is greater than 1.5 D, the binocular sum begins to disappear. If the anisometropia becomes greater than 2.5 D, the binocular sum may then completely disappear and the binocular contrast sensitivity equals the average monocular contrast sensitivity16.

The so-called by us "help test" makes it possible to simulate how the patient's binocularity will be, in case it is submitted to monovision24. In the clinic, the patient looking at the optotypes from afar, with its far refractive correction in the phoropter, is placed a spherical + 1 D lens in front of the eye for reading. Then, the reading eye is alternately occluded and de-occluded, keeping the eye for far always uncovered. When the patient reports being more comfortable with the reading eye uncovered, we will consider that the help test is positive. However, if the patient is more comfortable with the reading eye occluded, we will consider that the help test is negative. This test can serve as a prognostic test. When the help test is positive, it indicates that the reading eye, even if it is out of focus, helps in distant vision (the patient is able to enjoy the binocular sum, and suitably suppresses the blurred image). On the contrary, if the help test is negative, the patient is not able to suppress the blurred image (in this case, the distant blurred image of the reading eye), and does not enjoy the binocular sum, indicating a worse prognosis in the adaptation to monovision.

For monovision to work, the patient must have a normal binocular coordination, and present good visual acuity in both eyes9. If the binocular coordination is abnormal (strabismus), the patient will have a marked ocular dominance, and it will be difficult to achieve the interocular alternation necessary to suppress the blurred image. If the patient has a moderate or deep amblyopia in one eye, or a situation of low visual acuity in both eyes, it will be difficult for the monovision to be successful (despite having normal binocular coordination), since the image offered by each eye will not have enough quality to allow a useful near and far vision.

CONTACT LENS TEST

We agree with other authors not to routinely include in the preoperative period the “simulation” of the monovision through contact lenses4,5, among other reasons because the tolerance to surgical monovision is greater than with contact lenses, since a better binocular adaptation is achieved, with constant refractive correction, less aniseikonia, and elimination of intolerance and/or complications secondary to the use of contact lenses1. In our protocol, it is a useful test in some specific cases. However, in our protocol, we consider it a test of utility in the postoperative period, as we will see later on.

SELECTION OF THE PATIENT. INCLUSION AND EXCLUSION CRITERIA

Patient selection is important in refractive surgery and becomes relevant in monovision. Patients whose life style requires excellent vision in extreme distances, especially in low light conditions, are not good candidates for monovision. Certain professions, such as pilots, professional drivers, sports requiring very good visual acuity (golf, tennis, hunting ...), are described in some studies as contraindications5,7. A correct anamnesis is essential to know the way of life of the patient, its occupation, sports that he/she practices, hobbies (photographer, hunter) or some activity that requires monocular approach, driving (type, nocturnal/diurnal, routes, etc.).

The age of the patient and his refractive defect are decisive when making the decision to induce monovision. Some authors offer monovision to patients from 35-45 years of age, others recommend it from 40 years of age and others with age equal to or greater than 45 years3,5,6. We value the option of monovision in patients who already suffer from presbyopia, that is to say, patients who, with their distance correction, are not able to read adequately (usually from 45 years of age, with variations). As a rule, we do not perform monovision in pre-presbyopic patients, although we value this option in certain cases (in particular the myopic presbyopes). The lens surgery with an intraocular lens implant must now be considered to improve the patient's visual acuity and to eliminate or reduce the previous refractive defect, if any, minimizing the dependence on glasses and improving the quality of life of patients. After refractive lens replacement with lensectomy and monofocal intraocular lens implant, we consider that monovision should be applied, in general, in all cases of bilateral lensectomy (as long as there are no exclusion criteria), since this way we will be able to minimize the use of the near and intermediate glasses, providing greater patient satisfaction.

The importance of applying a selection protocol leads us to propose the following inclusion and exclusion criteria for monovision3,9.

Inclusion criteria:

Emmetropic presbyopic patients, or ametropic (myopia, hyperopia, and/or astigmatism).
Post-surgical refractive state "target" possible.
Patients who do not demand excellent visual acuity for extreme distances (very far, very close), especially in low light conditions.
Motivated patients who wish to improve their near vision without glasses, due to their profession or usual activities.

Exclusion criteria:

Patients who require excellent visual acuity in low light conditions (professional or nocturnal drivers, hunters).
Demanding personalities, with high expectations on the outcome of the surgery.
Ophthalmological exclusion criteria: amblyopia, low vision, strabismus, strong ocular dominance, macular diseases, and all those eye diseases that can cause an important loss of vision in the short or medium term.

As we have already mentioned, in the preoperative visit, it is necessary to assess certain aspects of the patient's daily life before inducing monovision. But, in addition, the patient should receive a wide explanation about his or her case: diagnosis (presbyopia), cause (failure in the accommodation or loss of the lens), alternatives (glasses, contact lenses, other techniques), technique (monovision with laser excimer or pseudophakia), prognosis (visual and refractive), advantages and disadvantages, and complications. Another important aspect is the personalization of the Informed Consent. In our group, we added a document attached to the standard document of the main surgical technique, in which the most relevant peculiarities of monovision are mentioned.

The correct selection of the patient, after an exhaustive anamnesis and exploration, is important, but also the patient's education, so that their expectations are similar to the results obtained, which will imply that they are satisfied with the results. We make special emphasis on the concept of "useful vision" (one that covers daily activities and that can be obtained with surgery) and the "extreme visions" for far/near (for which he/she could require the use of glasses). It is necessary to make the patient understand that he should not expect to have a vision like that of a person of twenty years, who does not have any visual defect and does not need glasses.

In general, most patients with monovision do not request glasses. We agree with other authors, in that patients with monovision requested more frequently the spectacle for close than the spectacle for afar10,24.

SIDE EFFECTS. INABILITY FOR ADAPTATION AND REVERSIBILITY

Side effects, described in the medical literature, that may occur in patients with monovision are decreased contrast sensitivity, and decrease in stereopsis, distant binocular visual acuity, and depth of focus7. In addition, monovision can decompensate a latent strabismus25.

In most of the published studies, a reduction of distant steropsis and contrast sensitivity has been demonstrated in patients with monovision, compared with patients without monovision11. However, Wright did not find statistically significant differences in the stereoscopic acuity measured with the Worth’s 4-point test, and with the titmus stereotest6. In the study, Wright established that binocular distant visual acuity, stereopsis, contrast sensitivity, and amplitude of convergence and fusion were similar between a group of patients without monovision and another with monovision. Specifically, the distant stereopsis was somewhat lower in the group of patients subjected to monovision (compared to the control group, with both eyes focused for far), but the difference was not statistically significant. In this study, contrast sensitivity was very similar in both groups. Logically, the group with monovision presented a better near visual acuity without correction6. On the other hand, patients with successful monovision have a lower reduction in distant stereopsis, when compared with patients with unsatisfactory monovision19.

The dissatisfaction of the patient (or inadaptation) to the combined vision (monovision) is a fact to be taken into account and that may involve the reversal of the monovision situation and adjust the two eyes for far vision. Goldberg asked the reasons for their decision to the patients who chose to reverse their monovision, and focus their reading eye for far, finding that most of them reported that they were not comfortable with the situation of having two different eyes, while one of them made the decision because he had difficulty in sports. The patients described the freedom of glasses for far and near as a monovision advantage, and as disadvantages the possibility of needing glasses for night driving, the lack of perfection in distant visual acuity, the situation of having both eyes focused different, and the period of adjustment to monovision. Miranda found in a study that most of the patients who chose to reverse their monovision could not specify a specific reason, while other possible reasons are the excess of myopia in the reading eye, or the lack of emmetropia in the far-focused eye20.

Monovision reversal rates published in the literature vary between 2.4%7, 4.4%5, 5%10 and 7.5%20. Let us summarize the causes of dissatisfaction:

Poor vision for distance (the common cause is usually the existence of a residual defect in the eye for far)
Poor near vision (due to insufficient myopia in the eye for near)
Torpid neuro adaptation. We will resort to the "help test" to assess whether the cause is due to some of the above or other assumptions (a normal help test will imply a poor refractive result; an abnormal help test confirms the poor neuroadaptation). At this time the utility of the "contact lens test" is recognized, when being able to find two assumptions for its adaptation and subsequent assessment by the patient:
1. When a correct refractive result is observed, but the patient does not obtain any benefit (he will be shown what the visual situation will be after reversing the monovision)
2. When induced myopia in the reading eye is excessive for the desired purpose (he will be offered a partial reversal of induced myopia)

MINI-MONOVISION AND MICRO-MONOVISION

The mini-monovision is a relatively new term, which defines that situation of monovision in which a slight myopia (between -0.75 and -1 D) is induced in the reading eye. Obviously, this low degree of myopia will only make possible the focus at a moderate distance, not close, of the objects (computer), depending on the age and the situation of the lens (pseudophakia). It is used in incipient presbyopic patients and even pre-presbyopic myopia, in lens surgery with a bifocal multifocal intraocular lens (MIOL) implant and even in those with extended depth of focus lenses.

Monovision with increased depth of focus (micro-monovision or advanced monovision) is based on the induction of moderate myopia in the non-dominant eye combined with an aspherical treatment with excimer laser (micro-monovision or “laser blended vision” with CRS Master and MEL excimer laser; advanced monovision with Custom Q excimer laser Allegretto Eye Q). Although their results have been published, they are not techniques that have obtained wide dissemination15,16.

ALTERNATIVES TO MONOVISION

As an epilogue to this chapter, in our opinion, monovision induced with surgery, either corneal or intraocular, is a useful technique for the treatment of presbyopia. Its indication and execution require a detailed study of the patient, like the rest of refractive surgery, and the knowledge of a series of concepts, such as ocular dominance, the reading eye or the inclusion and exclusion criteria, in addition to its limitations. But more than talking about alternatives to monovision, we must look into “when is monovision an alternative” to other surgical techniques used today in presbyopia surgery.

There is no doubt that, during these years of the 21st century, refractive lens replacement with multifocal intraocular lens implants has gained ground to other techniques, including monovision, to restore near vision26. However, we consider that laser monovision is an appropriate technique in cases of myopic presbytes without crystalline alteration (lens or cataract dysfunction syndrome) who wish to minimize the use of glasses27,28, as is monovision with pseudophakia in those cases in which patients are not good candidates for MIOL implantation (high refractive defects, such as large myopic or hyperopic)29-31.

We advocate to maintain the knowledge and use of this technique, since its visual and refractive results and patient satisfaction allow us to consider it useful in the “armamentarium” of any refractive surgeon.

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