Presbyopia / SPO - 3.2.6.1. Complications of multifocal lenses

3.2.6.1. Complications of multifocal lenses

Maria do Céu Pinto e João Coelho

Centro Hospitalar Universitário do Porto, Portugal

INTRODUCTION

Over the past few decades, cataract surgery has been continuously evolving from simple lens removal to refractive surgery, with the implantation of a multifocal intraocular lens (IOL). In this way, a vision independent of glasses is possible, while at the same time correcting ametropia and presbyopia, and increasing the quality of life for patients. This evolution has led to a progressive increase in patients' expectations, as well as the degree of dissatisfaction, when this goal is not fully achieved.

Crystalline surgery with implantation of multifocal IOLs has been increasingly used in the treatment of presbyopia because it offers the possibility of refractive correction at all distances1,2. It also provides functional vision at various distances at the expense of the so-called simultaneous view of two or more retinal images resulting from the division of light by two or more foci with consequent reduction of contrast2. Overall, multifocal IOL patients are satisfied, with significantly higher quality of life and vision scores, when compared to patients with monofocal IOLs2. Despite the great evolution of cataract surgery in recent decades, as well as the improvement of IOL materials and geometry, along with more reliable biometers and new generations of formulas, this procedure is still not without risks and complications.

In this chapter we will evaluate and discuss some of the negative aspects of multifocal IOLs, that may affect the patient's quality of life and level of satisfaction, as well as the strategies that should be used to prevent, detect and treat these unwanted outcomes.

PREVENTION

The first step in avoiding complications with multifocal IOLs, is the careful selection of patients to whom these lenses are implanted.

A thorough and rigorous ophthalmologic examination is mandatory for the selection of candidates who are considering implanting multifocal IOLs. It should include an ophthalmological and family history, to exclude glaucoma or retinal pathology, such as age-related macular degeneration (AMD), dystrophies, and diabetes among others. Careful biomicroscopy is essential to eliminate corneal pathology, and to verify the existence of zonule integrity, as well as the absence of pseudo-exfoliative material, which can condition decentration or even IOL dislocation3.

Fundoscopy is equally essential for assessing the optic nerve and macula. Multifocal IOL implantation should not be performed in patients with conditions that decrease contrast sensitivity such as glaucoma, optic neuropathies or macular diseases. Therefore, all patients who are candidates for refractive lens surgery should have a macular and optic nerve optical coherence tomography (OCT), to exclude pathology that limits the outcome, or even contraindicates any surgery3,4.

A detailed study of the cornea with topography, aberrometry and pachymetry should also be performed in all patients with the double objective of detecting irregular astigmatism and large aberrations, as well as evaluating the possibility of subsequent keratorefractive treatments with LASER, to correct residual refractive errors after implantation of the multifocal lens5. The calculation of the lens to be implanted must be done by biometers and last generation formulas, that are more reliable, so as to avoid residual refractive errors. The type of lens to be implanted should be the one best suited to the needs and preferences of the patient.

Multifocal IOLs in order to achieve good performance require both eyes to have their full vision potential intact, so, except in exceptional cases, their implantation should not be recommended in a single-eyed or amblyopic eye6,7. Visual acuity and oculomotor balance should also be carefully evaluated, as these types of IOLs are not suitable in patients with strabismus or high phorias, because these may decompensate after surgery3.

The human visual system is not prepared for simultaneous vision of two or more images, requiring a period of neuroadaptation, and the way to accelerate and make this process easier is to implant multifocal IOLs with a short time interval between the two eyes1,3.

In fact, many of these complications can be prevented by proper patient selection to exclude all contraindications to this procedure. In addition to conditions that interfere with the normal functioning of the visual system, it is also important to exclude all patients who, according to their psychological profile, show unrealistic expectations. It is up to the surgeon not to feed these expectations and demystify them with the detailed explanation of the procedure, its limitations and possible complications. Reflection time should be given, as well as a detailed information note on the procedure, for the decision to be properly considered. This way, the degree of satisfaction is significantly increased and consequently the number of clinical, and legal, complications is decreased.

Despite however taking all these precautions, sometimes difficult-to-resolve complications arise, which cause great dissatisfaction to the patient and concern for the surgeon.

There are numerous studies in the literature that characterize, quantify and suggest proposals for resolution of these potential complications. Fortunately, most of them are transient and have little impact on patients' quality of life, but there is a residual percentage that is difficult to resolve and sometimes ends up in IOL explant.

In the case of patients not satisfied with the procedure, it is necessary to study the nature of their complaints and try to adapt the currently available treatments.

REASONS FOR PATIENT DISATISFACTION

The objective of multifocal IOL implantation is to allow the patient to be independent from glasses at all distances. Most studies indicate that patients achieve high levels of satisfaction with multifocal IOLs, with no differences in visual acuity and performance, or levels of satisfaction and complications, even among patients from different age groups8-11.

However, complications sometimes occur, that significantly influence a patients' level of satisfaction and quality of life.

A correlation between complaints of positive dysphotopsies and personality type was recently published. In this study, despite complaints, 82.2% of patients would opt for a multifocal IOL again, and only 3.7% responded negatively. Satisfaction with surgery was positively correlated with low postoperative astigmatism, good visual performance, poor perception of halos or glare, and high independence from glasses. Patients with obsessive-compulsive or perfectionist personalities, had significantly more complaints of glare and halos, and therefore had worse levels of satisfaction. The authors concluded that multifocal IOL implantation should be carefully considered in patients with these personalities12.

Blurred or foggy vision is the main cause of dissatisfaction among patients undergoing surgery with multifocal IOLs, and series are described in which approximately 93% of patients have these complaints13. Several etiologies have been pointed out, in most cases being justified by the presence of postoperative ametropia, posterior capsule opacification, and dry eye.

According to Gibbons et al, complaints of blurred vision were the most frequently found, and in 57% of cases they were justified by the existence of residual postoperative refractive error, while in 35% by lachrymal film instability14. In a recent study by Kim et al these complaints were the main reason for proceeding with the explant of multifocal lenses (60%), the second reason being the photopic phenomena (57%)15.

In another study, complaints of foggy or blurred vision (with or without photopic phenomena) were reported in 72 eyes (94.7%) and photopic phenomena (with or without foggy or blurred vision) in 29 eyes (38.2%), with both symptoms being present in 32.9% of the eyes. Residual ametropias and astigmatism, posterior capsule opacification, and big pupillary sizes, were the etiologies most frequently associated with patients' complaints16.

A systematic review of the published literature on multifocal IOLs describes that complaints of photopic phenomena are 3.5 times more frequent with multifocal lenses than with monofocal ones, however most of the time, there is no identifiable cause2.

COMPLICATIONS AFTER CATARACT SURGERY WITH MULTIFOCAL LENS

Decentration of multifocal IOLs

Several studies have been conducted to assess the degree and clinical impact of multifocal IOL decentration17,19. Overall, the average decentration (after uneventful cataract surgery) presented in the studies is 0.30 ± 0.16 mm (ranging from 0 to 1.09 mm) depending on the method used for the measurement. When a multifocal IOL is decentered, it may lose its optical properties, even more so if it is a toric lens, which significantly decreases its intended visual function1 (Figure 1).

Figure 1 - Offset ocular multifocal IOL

There are essentially three factors that determine how the vision is affected by the decentration of a multifocal IOL: amount of decentration, type of IOL and pupillary size. For a better understanding of the impact of these factors, 4 different multifocal (2 diffractive and 2 refractive) IOL models, with increasing degrees of decentering in a model eye with a pupillary size of 3 mm, were studied by Soda et al. For the AcrySof® diffractive/refractive IQ ReSTOR® SA60D3 lens (Alcon), visual results for near, deteriorate with increasing degrees of decentration, while in the distant vision they tend to improve. This feature is explained by the design of this lens because its periphery is similar to a monofocal IOL. In other models of multifocal IOL, such as the Tecnis® ZM900 (AMO), the entire optical surface has a diffractive structure, thus, decentrations greater than 0.75mm in this type of IOLs compromises its performance, in both near and far vision. For the ReZoom® (AMO) and SFX-MV1® (Hoya) refractive models, even with 1-mm offsets, no changes in near vision were observed, however, a reduction in the far-sight vision results from 0.75- and 1-mm respectively, were observed20.

Regarding pupillary size, and the impact that this factor may have on the performance of a decentered multifocal lens, patients with small pupils have been shown to have worse visual outcomes at near vision, with decentering having more of an impact on far and intermediate vision. On the other hand, when evaluating monofocal lenses, both the pupil size and IOL offset did not impact visual acuity. Thus, many authors have pointed out that the more sophisticated the technology and design of a multifocal lens is, the more sensitive it is to any decentering21.

Decentration of multifocal lenses is also associated with a greater prevalence of photopic symptoms such as halos and glare, as well as decreased contrast sensitivity and consequent worse performance of night vision22. Another factor to consider, that should be investigated in patients with complaints of poor vision, despite a perfect IOL positioning, is the existence of a high K angle23. Recent studies suggest that the elevated K angle can contribute to the existence of photopic phenomena after the implantation of multifocal IOLs, so this parameter should be evaluated in the preoperative period and investigated postoperatively in patients with these complaints that cannot be attributed to other causes22,24.

Decentration of a multifocal lens does not necessarily imply its explant. In most cases requiring treatment, performing an Argon laser iridoplasty is the recommended treatment1.

Tilting of multifocal IOLs

The material and the biocompatibility of haptics play a key role in the positioning of IOL25. Acrylic IOLs, due to their flexible nature and risk resistance, allow implantation through small corneal incisions. However, the combination of acrylic material with C-loop haptics can facilitate IOL decentering and tilt when the capsular bag contracts26,27. Capsular tension rings have shown that in addition to inhibiting posterior capsule opacification, they may play a role in the stability and positioning of some IOL subtypes, such as in asymmetric or diffractive refractive multifocal lenses, preventing any movement caused by capsular bag contraction28,29.

Mastropasqua et al30 compared the aberrometry and visual performance of AcrySof® IQ ReSTOR® SA60D3 diffractive multifocal IOL, with and without capsular tension ring, demonstrating that high-order aberrations were significantly lower in the tension ring group, due to the better positioning and centering of the lens, without however observing differences in uncorrected far and near visual acuity nor in contrast sensitivity studies30.

Compared to asymmetric refractive multifocal lenses such as LentisMplus® LS-312 (Oculentis), studies on experimental models have proven that tilting and decentration have more impact on the visual performance of this multifocal lens subtype than diffractive multifocal lenses, in this case AcrySof® IQ ReSTOR® SN6AD1 (Alcon)31.

Thus, plate-shaped lenses, unlike C-loop lenses, exhibit greater stability and more predictable behavior even after capsular bag contraction.

Pupillary Size

Pupil size after surgery is an important parameter that determines IOL performance. One of the main challenges regarding pupillary size is to predict its size after surgery, which often changes compared to preoperative measurements. Thus, a very small postoperative pupil will limit near-vision performance on most multifocal lenses. On the other hand, large postoperative pupillary diameters are associated with an increase in photopic phenomena1.

In general, visual acuity correlates with pupil size32,33. Larger pupils allow greater use of the optic zone in refractive lenses as well as greater contrast sensitivity in IOLs with diffractive designs, but this subtype is less dependent on pupil size21. Carson et al evaluated the influence of pupillary size on lenses of the same subtype, diffractive trifocals, FineVision® MicroF and AT LISA Tri® 839MP (Zeiss). The authors describe that for a pupillary size of 3.0 mm no differences are observed in the performance of these lenses at the various distances evaluated34. However, with larger pupil diameters (4.5 mm) Ruiz-Alcocer et al report that FineVision® MicroF achieved better results in far vision and AT LISA Tri® 839MP (Zeiss) in the intermediate and near vision35. Although both IOLs are aspherical diffractive trifocals and composed of hydrophilic acrylic materials, they have different optical zone designs and, therefore, different light distribution, and AT LISA Tri® 839MP has an additional hydrophobic surface36.

In this way it is understood that even within the same subgroup of multifocal lenses, there are significant differences in the performance of the lens, induced by the size of the pupil, which depends on the unique characteristics of each model.

In patients with complaints of near visual acuity due to a small pupil diameter the use of cyclopentolate for dilatation may be of interest and indication. If a good visual acuity is achieved with this method, its chronic use may be indicated13. Argon laser iridoplasty may also be used3.

If, on the contrary, the patient has a large pupillary diameter and therefore complains of photopic phenomena, the use of 0.2% brimonidine to decrease nocturnal mydriasis may be of interest, as it is currently an option with good results and frequently used in refractive surgery13,33.

Residual refractive error

Despite the recent advances in cataract surgery and in all that is associated with it, we still sometimes observe unsatisfactory visual results, due to the existence of a significant postoperative refractive error that compromises the visual outcome. Multifocal IOLs are more sensitive to residual refractive errors, however small, which are one of the most frequent causes of patient complaints and dissatisfaction.

Studies analyzing refractive results of more than 17,000 eyes after cataract surgery, report that only the target refractive error, emmetropia, was achieved in 55% of the eyes37. The existence of postoperative refractive errors may be justified by multiple causes, namely, errors in biometrics, inadequate IOL power selection, limitations of IOL calculation formulas, especially in cases of extreme ametropias, or errors in IOL positioning38. The therapeutic approach should be made according to available means, surgeon experience, anatomical conditions and magnitude of residual error. When the residual error is high, the patient does not meet the conditions for keratorefractive procedures, or there is no available technology, IOL exchange is necessary.

Different studies have demonstrated efficacy, predictability and safety in myopic and hyperopic corrections with Excimer laser (LASIK or PRK) after cataract surgery39. On the other hand, in some centers these techniques are not available, and it is sometimes necessary to resort to IOL replacement or to the implantation of a piggy-back IOL in sulcus. Gundersen et al in a sample of 416 eyes with multifocal lenses showed a retreatment rate of 10.8% (45 eyes), with no difference in relation to the type of multifocal IOL previously implanted, and in 89% of the eyes opted for the placement of a lens in the sulcus with a high success rate40.

Regarding the correction of residual errors after multifocal lens implantation, studies have reported significant improvements in visual acuity for distance, with limited however results in photopic phenomena41. Santhiago et al as well as Schallhorn et al describe significant improvements in both uncorrected visual acuity and spherical equivalent, with high safety and predictability rates, in eyes with both diffractive and refractive lenses41,42. When comparing the efficacy, predictability, and safety of LASIK in the correction of residual refractive errors after cataract surgery, in patients implanted with either multifocal or monofocal IOLs, it is observed that the results are more accurate and predictable in patients with monofocal IOLs. Predictability and results are even more limited in hyperopic eyes subject to implantation of multifocal IOLs43,44.

The correction of the refractive error after implantation of multifocal IOLs should not be performed taking into account only the near and far vision, because this way the results may be quite unsatisfactory. It is rather recommended that a complete defocus curve be previously performed, for better planning and predictability of the keratorefractive intervention2.

Posterior capsule opacification

The most common long-term complication of the multifocal lenses is the posterior capsule opacification3 – Figures 2 and 3.

Figures 2 and 3 - Toric multifocal IOL with posterior capsule opacification

A systematic review, showed significantly higher posterior capsule opacification rates in hydrophilic lenses versus hydrophobic, in sulcus lenses versus in-the-bag lenses, and in eyes with large capsulorhexis^13,16. Lower opacification rates were also observed in the IOLs with the posterior surface angled, compared to the round ones, with no differences between the 3-piece IOLs and the others⁴⁵.

When comparing the frequency of posterior capsulotomies in patients with multifocal and monofocal lenses, it was found that the need for this procedure is significantly more frequent in patients with multifocal IOLs because of their requirements and needs. A study with an average postoperative follow-up of 22 months with multifocal Acrysof^® and monofocal IOLs reports posterior YAG laser capsulotomy rates of 15.49% and 5.82%, respectively⁴⁶.

Decreased visual acuity and an increase in photopic phenomena, such as halos and glare, are the main complaints of multifocal IOL patients with posterior capsule opacification, which is the reason for complaints in 54% and 66% of cases, respectively^13,16. The rate of capsulotomies after the implantation of different multifocal IOL models has also been compared. A hydrophobic lens (AcrySof^® IQ ReSTOR^®) had a 2-year capsulotomy rate of 8.8% while a hydrophilic multifocal IOL (Acri.LISA^® Zeiss) had a rate of 37.2% (P<0.0001). Thus, it is understood that there is currently a clear preference for implanting hydrophobic over hydrophilic multifocal IOLs⁴⁷.

Bilbao-Calabuig et al evaluated the posterior capsule opacification rate and the need for YAG laser capsulotomy on two types of multifocal diffractive lenses, FineVision^® MicroF and AT LISA Tri^® 839MP (Zeiss), reporting capsulotomy rates in 9% and 23% respectively, with no differences until the 9^th postoperative month⁹.

The best treatment to resolve an opacification of the posterior capsule is the Nd:YAG laser capsulotomy. However, before proceeding with this treatment, all other causes that may justify the patient's complaints should be excluded and possibly treated. Although it is a simple and effective procedure, it is not free of risks and complications, such as the development of cystoid macular edema, ocular hypertension, vitreous opacities and retinal detachment^1,3. Although IOL exchange is rarely required, this procedure is significantly more difficult and associated with an increased risk of complications when the posterior capsule is previously open. Thus, this should be taken into account whenever one is in the presence of a dissatisfied patient and in whom the explant of the multifocal IOL may become a possibility².

Dysphotopic phenomena (positive/negative) and contrast sensitivity

In several literature reviews, dysphotopic phenomena and loss of contrast sensitivity are the disadvantages most often associated with multifocal lenses^2,48-50. As mentioned earlier, these complaints are among the most frequent reasons for patient dissatisfaction, as well as for explanting multifocal lenses^13,16. Halos and glare are significantly more frequent complaints in patients with multifocal IOLs than in monofocal IOLs^1-3,16,49. Among multifocal IOLs, refractive ones are more associated with photopic phenomena than diffractive ones⁵¹, with no difference between trifocal (PanOptix^®, Alcon) and extended-depth-of-focus (Symfony^®, AMO) lenses⁵².

Negative dysphotopsia has been clinically reported after posterior chamber IOL implantation, as a dark crescent in the peripheral temporal visual field, that is accentuated with contraction and reduces with pupillary dilation, and is thought to be associated with high IOL borders and refractive index. Coverage of the 360º optics by the anterior capsule has a preventive effect on the development of this symptom. According to Holladay et al, the factors that determine the presence of these phenomena are: small pupils, space between iris and IOL greater than 0.06 mm, high refractive index of IOLs, high K angle, degree of nasal deviation of pupil, and transparency of anterior capsule⁵³. In a study by Henderson et al, the implantation of an acrylic IOL with the inferotemporal haptic-optic junction decreased the incidence of negative dysphotopsia 2-3 times⁵⁴. These usually tend to decrease in intensity with the opacity of the anterior capsule. In another study, Osher et al report that negative dysphotopsia is present in 15.2% on the first postoperative day, 3.2% in the first year and 2.4% between 2 and 3 years⁵⁵.

Multifocal IOLs are also associated with lower contrast sensitivity than monofocal IOLs, especially in mesopic conditions⁵⁶. Patients with diffractive multifocal IOLs have been shown to have a significant reduction in contrast sensitivity, especially in the lower mesopic ranges, compared with monofocal IOL patients⁵⁷. Comparing multifocal IOLs, diffractive lenses appear to have results similar to or slightly higher than refractive multifocal IOLs in contrast sensitivity^58,59. Although patients with trifocal diffractive lenses generally have fewer complaints of halos and glare, as well as decreased contrast sensitivity, Marques et al, as well as Bilbao-Calabuig et al with a study of more than 10,000 eyes implanted with FineVision^® MicroF and AT LISA Tri^®839MP lenses, describe that 42% of patients report a loss of contrast sensitivity when evaluated 3 months after surgery, describing greater difficulty in night driving, with no differences between the two types of lenses evaluated^9,36. Although there is currently no recommended multifocal lens to be implanted in sulcus, and regardless of the model, they are associated with an increased risk of halos and glare⁶⁰.

Control and treatment of these photopic phenomena begins before surgery, with careful patient selection and education, preparing them for this possibility and the loss of contrast sensitivity they may notice after surgery. The candidate for multifocal IOL implantation should also be informed that he or she may notice the presence of some degree of halos and glare after surgery^3,13,16. Although in most cases these phenomena are only mild or moderate, and most patients eventually become accustomed to it through neuroadaptation processes, they should be reported before surgery and investigated postoperatively^61,62.

In general, it is not recommended to implant multifocal IOLs in patients whose activity is predominantly nocturnal (e.g. professional drivers), and even less recommended if the patient has a large pupillary size under scotopic conditions that will invariably increase the perception of halos and glare at night^2,9.

When photopic phenomena are disabling and affect patients' quality of life, surgical intervention is required. This approach can be done by IOL exchange, piggyback IOL implantation, reverse optic capture, and iris suture to the bag-lens complex⁵³. Any of these surgical treatments have limited efficacy because the mechanism is multifactorial and not yet fully understood.

Multifocal IOL explant

IOL explant is the worst-case scenario after cataract surgery with multifocal IOL, because in addition to being associated with new complications, it usually leads to the loss of the purpose of the surgery. Fortunately, only a small percentage of patients require it, and then it should be done at around 6 months, to allow time for the neuroadaptation process to take place and to avoid difficulties and complications¹. In a study by Venter et al with 9,633 eyes implanted with Lentis Mplus^® (Oculentis), only 80 lenses were explanted (0.85%), 55 for dysphotopic phenomena and 25 for decentration⁶³. Other studies show explant percentages for dissatisfaction ranging from 4% to 7%, the most frequent causes being photopic phenomena and decreased contrast sensitivity^13,16. In another study, where the main causes of explant in Spain are analyzed, neuroadaptation failure appears as the 4^th cause, the first being decentration, the second refractive error, and the third opacification of the lens⁶⁴.

Dry eye

Dry eye is a multifactorial disease of the tear film and ocular surface, that often results in symptoms of eye discomfort and visual disturbances, justified by tear film instability. It is now recognized that cataract surgery can induce complaints and signs of dry eye, or exacerbate a pre-existing disease. Corneal incisions created during surgery may impair corneal neuroarchitecture, reducing its sensitivity⁶⁵. Thus, in refractive surgery, the use of corneal micro incisions is always recommended, because in addition to inducing less astigmatism, they are less likely to cause dry eye. Considering the importance of the ocular surface and tear film in the quality of vision, dry eye can significantly alter visual outcomes in patients undergoing surgery, having even more impact when multifocal IOLs are implanted, due to the complexity of all optical phenomena involved, and the higher patient demands^13,16. According to Diaz-Valle et al the poor quality of vision in mild to moderate dry eye, results from the instability of the tear film that induces light scattering, and the use of a drop of lubricant, decreases scattering for 60 minutes⁶⁶.

In general, dry eye treatment should be initiated by educating the patient to use preferably preservative-free artificial tears, accompanied by improved eyelid hygiene. Whenever infections, eyelid inflammation and dysfunction of the Meibomian glands exist, they should be treated using antibiotics and/or anti-inflammatory drugs. The use of topical corticosteroids for short periods of time has been shown to be effective in reducing signs and symptoms. In more resistant cases, topical cyclosporine has already been shown to be a useful treatment, with improvement of symptoms and break-up tear film time⁶⁵. An alternative to consider is the implantation of plugs in the tear ducts, especially in patients with water tear deficiency and without associated inflammation. Still another hypothesis to consider, for the most severe cases, is the use of platelet-rich plasma⁶⁷.

CONCLUSION

Most complaints that lead to dissatisfaction of patients with multifocal IOLs are transient, or successfully treated with mildly invasive measures, and multifocal IOL explant should rarely be necessary. Crystalline surgery with multifocal IOL implantation is currently the best option available to simultaneously treat refractive errors and presbyopia, in properly selected, informed and motivated patients.

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