Surgical options for the treatment of presbyopia.
Dispensing opticians **
1 CET POINT
Presbyopia is an inevitability of age. It occurs due to the loss of accommodative power that is usually first noticed between 40 and 50 years of age. In 2005, it was estimated that 1.04 billion people worldwide suffer with presbyopia, 67% of whom live in the developing world. (1) In the US, a multicentre study reported an association between presbyopia and substantial negative effects on quality of life. (2) Worldwide, it is estimated that the presbyopia population will increase to over 2 billion people by 2020.
Although single vision, progressive or bifocal lenses provide a good solution, many patients either struggle to adapt to wearing them or else seek to be independent of glasses for sport and outdoor activities. Contact lenses provide another option either in the form of monovision or multifocal correction but presbyopes tend to have a worse and declining ocular surface compared to their younger counterparts which may make contact lens tolerance more challenging. For these reasons, some patients will seek out surgical options to address their presbyopia and may source guidance on the options available from their eye care practitioner. It is, therefore, critical for practitioners to be up to date with the surgical options available with modern technology and to know and understand what the various advantages and limitations of such options might be for their patients.
The surgical management of patients with presbyopia presents both diagnostic and surgical challenges. The visual world has become significantly more orientated to close activities which makes presbyopia symptoms more problematic and manifest at an earlier age. For example, the viewing distance for mobile phones is often closer than the traditional 30-40cm for print reading. Computer technology now governs almost every aspect of life which also necessitates more time spent reading and engaging in close vision. Our requirement for excellent distance vision in order to be able to hunt for food has evolved I with the necessity to see, for instance, a mobile phone app and order shopping online. Whereas in the past we used to talk of 'fighter pilot vision' nowadays the ability to see a screen and control a drone remotely may be more helpful. Likewise, distance vision requirements for driving may change when computer operated driverless cars are implemented. For these reasons it is uniquely rewarding as well as visually advantageous for refractive surgeons to be able to accurately assess and address presbyopia in our treatment approach.
Diagnosis and assessment
There are several different tables that give an estimate of the degree of presbyopia that might be expected with a patient's age, for instance, as detailed in Table 1. (3) However, relying on these alone for diagnosis and planning is inadvisable for several reasons. Firstly, the degree of presbyopia for a given age varies widely even if patients are perfectly emmetropic. Some of this variability can be accounted for by differences in an individual patient's lens but also pseudoaccommodation due to pupil size and non-refractive aberrations can also increase the depth of focus. For these reasons, as well as the likelihood that there is some accompanying ametropia, it is essential to measure the patient's uncorrected and distance corrected near vision binocularly and monocularly. Following this, measuring the amount of near add that a patient requires in each eye is important.
In patients where laser or intraocular lens (IOL) blended vision (mini or full monovision) is considered after confirming and establishing good binocular fusion, it is helpful to carry out a trial lens test where +1.00D is briefly presented over the non-dominant eye to assess how likely a patient may be to accept and adapt to this kind of vision.
Despite advances in technology, a poor tear film can still interfere significantly with the accuracy of measurements as well as the safety of treatment--it is, therefore, essential that this is diagnosed, taken into account and ideally optimised with medical dry eye therapy prior to surgical planning.
General surgical principles
Many of the surgical principles set out in previous articles by the author, (4-6) still apply in the context of presbyopia surgery; however, additional considerations apply to address the presbyopia in the context of the particular kind of refractive error and these will be outlined here. In general, there are either dynamic or static surgical options for treating presbyopia. Dynamic options include: scleral expansion techniques; accommodating IOLs; and refilling and disruption of the crystalline lens. These methods show inconsistent results and have, therefore, attracted less clinical interest. (7) This review will focus on static surgical options, which can be broadly divided into corneal-based surgery, including laser vision correction, and lens-based surgery, including specific IOLs.
Corneal-based treatment of presbyopia
Laser refractive surgery
Induction of monovision using laser vision correction is the simplest approach to laser presbyopia correction. It is also significantly less interventional than IOL techniques. Broadly speaking, the dominant eye is targeted for emmetropia with the non-dominant eye being targeted for varying levels of myopia depending on the accommodative capacity and needs of the individual patient. The maximum amount of disparity that patients generally tolerate is 2D, that is to say, the non-dominant eye is deliberately made -2.00DS, but often lower amounts of myopia are targeted to ensure that patients maintain comfortable and good binocular quality of vision. Pre-operative planning and discussion with patients are essential so that they know what to expect from their new vision. Laser vision correction tends to induce positive spherical aberration. While this is a higher order aberration that tends to be imperceptible to patients it does have the advantage of increasing depth of focus which allows the intermediate range of vision to function well between both the distance eye and near vision eye. There are several laser platform specific adjustments that can be used to manipulate and increase the effect of this; PresbyLASIK, or multifocality achieved using an excimer laser, uses an ablation profile after flap creation to induce corneal multifocality at the expense of induced higher order aberrations. The algorithms are generally classified as central (centre near), peripheral (peripheral near), or laser-blended vision. In peripheral presbyopic laser vision correction, software provided by NIDEK lasers (NIDEK Co Ltd., Gamagori, Japan) alters the mid-peripheral cornea for near vision by inducing spherical aberration and leaves the central cornea for far vision. In central presbyopic laser vision correction, provided by Supracor lasers (Technolas Perfect Vision GmbH, Munchen, Germany), laser ablation is used to treat the central cornea to improve near vision. A PresbyMAX software profile introduced by SCHWIND (SCHWIND eye-tech-solutions GmbH, Kleinostheim, Germany) ablates a bi-aspheric cornea, which is more positive in the centre than other profiles. Laser blended vision, or Presbyond, is a profile that creates improved monovision in the non-dominant eye at approximately 1.50D (Carl Zeiss Meditec, Inc., Jena, Germany) and simultaneously creates a gradual power slope to the periphery using wavefront-assisted ablation. (8)
All of the rigorous safety criteria must still apply to allow for safe presbyopic laser. The main considerations are: normal regular corneal thickness and shape; good tear production (in the absence of contact lens overwear and / or meibomian gland dysfunction both of which can and should be treated first); clear natural lenses; healthy maculae; no significant amblyopia; and refractive error within the safe range for surgery--normally between -10D to +4D and less than 6D of astigmatism. For patients well into the presbyopic age/accommodative range, the cutoff for hyperopia in the non-dominant eye is normally +2.50D as significantly more laser is required to induce myopia in this eye. Furthermore, as patients approach cataract age range (more than 60 years of age) the threshold for laser changes as most surgeons become less comfortable with treating at the full limit of safe laser in these cases given that refractive lens exchange remains a more permanent option. Additional considerations for presbyopic laser vision correction are that patients must be binocular and able to fuse well. Furthermore, this age group of patients, especially females, tend to have a poor ocular surface so it is important to have a low threshold for diagnosing and treating this first.
Patients need to understand that it can take six to 12 weeks and sometimes more to fully adapt to presbyopic laser vision correction. During this time, patients may complain of reduced visual acuity in darkness, loss of contrast sensitivity, reduction of stereopsis, and intermediate vision reduction. There is also a higher enhancement rate as each eye must accurately achieve its target and will not be able to 'rely' on that same vision from the fellow eye.
Due to increased depth of focus, as explained above, presbyopic laser eye surgery tends to be better tolerated than contact lens monovision. On account of this, as well as the three-month neuroadaptation requirement, the author does not normally want or need patients to undergo a trial with contact lenses. Exceptions to this are in some emmetropes / low myopes who are particularly fussy/ attentive to detail and /or have jobs with high functioning visual requirements such as pilots and surgeons.
Corneal inlays work by increasing depth of focus in the non-dominant eye; this is achieved by either using small aperture optics (the pinhole effect) and /or by increasing corneal curvature allowing more near focus (see Table 2). (8) Many of these inlays over longer term follow up eventually result in foreign body reaction which results in haze and regression of effect requiring explantation of the device. (9) For this reason, they have not found widespread use as yet.
Refractive lens exchange/cataract surgery
For presbyopic patients seeking a permanent option to achieve complete independence of glasses, refractive lens exchange or cataract surgery with premium IOLs remains the procedure of choice.
Toric IOLs represent an excellent option for presbyopic patients undergoing refractive lens exchange or cataract surgery. In a randomised controlled trial, Holland et al reported less than ID postoperative residual refractive astigmatism in 88% of toric IOL eyes versus 48% in the monofocal group; 60% of the toric IOL group reported spectacle independence compared with 36% in the monofocal group. Toric IOLs can be used to achieve emmetropia or myopia (normally in targeted monovision or mini-mono vision) for patients who have 0.75D or more of corneal astigmatism. Most modern toric IOLs are very rotationally stable and rotational instability (more than 5[degrees]) is uncommon. The author prefers this option for any patient who has more than 2.50D of corneal astigmatism or for any patient already tolerating contact lens or natural ametropic monovision.
Traditional multifocal IOLs nowadays use diffractive optics with two focal points: distance and near. Asymmetric bifocals are lenses where there are two different zones normally with a superior portion of the IOL for distance and the inferior portion of the IOL for near. Trifocal lens technology gives three focal points for distance, intermediate and near and represent the latest presbyopic lens technology. These IOLs are an option for patients who are motivated to be completely independent of glasses and the latest trifocal lenses achieve complete spectacle independence in 97% of patients. (10) However, patients being considered for this kind of lens technology need to be counselled about the neuroadaptation process which means that many patients need to allow several weeks following the surgery until they feel completely comfortable with their new vision.
In order for patients with this lens technology to be satisfied with their vision the following should apply:
* The lenses need to completely eliminate residual refractive error. Patients with multifocal vision are exquisitely sensitive to even low amounts of astigmatism and any surgeons using multifocal or trifocal IOL technology must be willing and able to address this either pre- or post-operatively. Although combined multifocal tories represent a modality to correct both presbyopia and astigmatism caution does need to be applied for high astigmatism, that is to say, more than 2.50D of corneal astigmatism. The reason being is that some small degree of toric misalignment is relatively common and whereas monofocal toric IOL patients will be unlikely to be bothered by small amounts of residual or consecutive astigmatism--multifocal IOL patients most likely will be
* Patients need to have a good tear film to tolerate any kind of multifocal vision so if necessary this must be treated prior to and following lens implantation
* The corneal shape needs to be regular
* Patients with these lenses are very sensitive to even small amounts of posterior capsular opacification so the threshold for needing a YAG laser posterior capsulotomy is lower in this group
* Patients with macular problems such as diabetic macular oedema, epiretinal membranes and macular degeneration are not good candidates for these lenses
* Normally, binocular implantation is required as patients with these lens technologies in just one eye are less satisfied.
Extended depth of focus
The considerations here are very similar to those above (multifocal/ trifocal/toric); however, these lenses tend to be produce slightly less significant haloes at night and are, therefore, a good option for patients who need to do more night-time driving.
These lenses do not actually correct presbyopia; however, they do increase the depth of focus (similar to a pinhole effect). They are an excellent option in patients with irregular astigmatism such as previous radial keratotomy.
For patients who are only very early presbyopes (normally under the age of 55) and who do not fulfill the criteria for safe laser eye surgery, phakic IOLs represent another alternative.
There are several excellent surgical options for presbyopia correction with the optimal choice of I procedure being dependent on the prescription being treated, the age of the patient and the unique anatomical factors of the individual.
Under the enhanced CET rules of the GOC, MCQs for this exam appear online at www.optometry.co.uk. Please complete online by midnight on 7 December 2018. You will be unable to submit exams after this date. Please note that when taking an exam, the MCQs may require practitioners to apply additional knowledge that has not been covered in the related CET article.
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Course code: C-60003 Deadline: 7 December 2018
* Be able to explain to presbyopic patients about the surgical options available (Group 1.2.4)
* Understand the surgical management of presbyopia (Group 6.1.11)
* Be able to explain to presbyopic patients about the surgical options available (Group 1.2.4)
* Understand the surgical management of presbyopia (Group 8.1.3)
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Alton Barsam is a consultant ophthalmic surgeon and director of corneal and refractive surgery at the LS.D University Hospital NHS Trust, UCL partners and director/founding partner at Ophthalmic Consultants of London. His NHS practice is a tertiary centre of excellence in the treatment of complex cornea and anterior segment disease and his private practice is almost exclusively laser eye surgery and lens based refractive surgery including cataract surgery with premium lenses.
Table 1 Expected quantitative reduction in accommodative amplitude with age Age (years) Amplitude of accommodation (D) 10 13.40 15 12.30 20 11.10 25 9.90 30 8.70 35 7.30 40 5.80 45 3.60 50 1.90 55 1.30 60 1.20 Table 2 Key features of different corneal inlays Flexivue microlens Raindrop inlay Material Copolymer of hydroxyethyl Hydrogel methacrylate and methyl methacrylate with UV blocker Design and size Piano central 1.8mm Positive diameter zone; peripheral meniscus- annular zone with added shaped, power diameter of 2mm and centre thickness of 32pm Underlying principle Changes the refractive Alters the power of the central cornea refractive to enhance near vision power by increasing the central radius of curvature of the cornea overlying the implant Implantation depth 280-300pm 150pm Kamra inlay Material Polyvinylidene fluoride Design and size 5pm thin microperforated artificial aperture with a total diameter of 3.8mm and a central aperture of 1.6mm Underlying principle Increases depth of focus through the pinhole aperture Implantation depth 170-200pm
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|Title Annotation:||Refractive surgery|
|Date:||Nov 1, 2018|
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