Incorrect IOL power is one of the most frequent reasons for IOL exchange following cataract surgery. Different options for the correction of residual refractive errors are being developed, including piggyback IOLs, light-adjustable lenses and multicomponent IOLs.
By: Dr Dimitra M. Portaliou, PhD, FEBOphth; Reviewed by Alessandro Franchini
Take-home: IOL exchange following cataract surgery can be difficult and lead to complications. Piggyback IOLs, light-adjustable lenses and multicomponent IOLs offer different options for the correction of residual refractive errors.
Cataract surgery is considered very effective for the restoration of precise visual acuity. The refinement of current surgical techniques, paired with technological advancements in IOL design and biometry methodology, has increased the accuracy of IOL power calculations, minimising refractive surprises following cataract surgery.
Nevertheless, it has been established that no cataract or refractive surgery will ever be 100% accurate due to errors in biometry, pre-existing or induced astigmatism, previous corneal refractive surgery, effective lens position and variables associated with wound healing.1 Most clinical studies report mean errors in IOL power calculation of approximately 0.50 D, with a standard deviation of 0.50 D or higher. Errors higher than 3 D are extremely rare but do occur,1–5 especially post refractive surgery.
In this latter subgroup of patients, despite the use of special formulas for the IOL calculation,6 residual refractive errors are a frequent occurrence. In general, refractive surprises after cataract surgery can compromise an otherwise successful result by creating unsatisfactory visual acuity outcomes and can create situations that are difficult to handle for both patient and physician.
Corneal-based procedures (laser refractive surgery) and lens-based procedures are commonly used in order to resolve the issue of poor refractive results following cataract surgery. However, corneal refractive surgery has several limitations: it is not suitable for high refractive errors and requires access to an Excimer laser, which may not always be available.
Additionally, patient acceptance of new IOLs (e.g., multifocal) may require lens exchange where laser procedures would not be helpful. Finally, dry eye symptoms can be created/exacerbated with corneal laser surgery, creating yet another challenge for both patient and physician. These problems are easily solved with multicomponent or piggyback IOLs.
Lens-based procedures include IOL exchange, piggyback IOLs, light-adjustable lenses and multicomponent IOLs.
Lens-based procedures have significant advantages in certain situations.7 In particular, lens-based procedures are more suitable for the correction of high ametropias: 1) they are tissue-saving techniques, and 2) no corneal aberrations are induced; the corneal surface remains intact and the original cataract wounds can be used, avoiding additional unpredictable wound-induced astigmatism.
In IOL exchange, the incorrect lens is removed and replaced by a new lens inserted through the same incision. IOL exchange can be difficult (e.g., removing the primary lens from the capsular bag) due to progressive capsular bag shrinkage. Complications such as capsular tear, vitreous loss, retinal tears and macular oedema can occur,8 which can permanently compromise the final refractive result. Lens exchange becomes an even bigger challenge once posterior laser capsulotomy has been performed.
In 1993, Gayton and Sanders9 first described the piggyback IOL technique to provide adequate power in highly hyperopic patients. The technique involves the implantation of two IOLs in the posterior chamber of the same eye. The technique has been successfully expanded to address pseudophakic refractive error in normal eyes and eyes that have undergone penetrating keratoplasty. Piggyback implantation has been combined with the use of newly available minus-power lenses to provide appropriate power for cataract patients with keratoconus, as well as to correct pseudophakic myopia.10,11 Different designs with very promising results have been reported.11
Interlenticular fibrosis (ILF) with resultant hyperopic shift, opacification and loss of vision has become a concern linked with piggyback IOL implantation.11 There are some additional limitations; for example, if both lenses are placed in the bag, lens exchange is difficult. If one lens is in the bag and one in the sulcus, exchange of the sulcus lens is easier, but rotational stability and optical alignment are ongoing concerns.
Light-adjustable IOLs can correct the remaining refractive errors after cataract surgery. Appropriate spatial light intensity patterns are used to irradiate the IOLs and modify their shape after implantation, allowing the correction of spherical errors as well as astigmatism.12,13 Clinical studies have demonstrated that, after cataract surgery, light-adjustable IOLs irradiated with the appropriate spatial patterns can successfully correct residual myopia, hyperopia and astigmatism.12,13
However, the behaviour of light-adjustable IOLs in the human eye and the accuracy of the corrections are still under investigation. There are several problems with the concept, which is still evolving. Firstly, the lens has to be sheltered from UV light prior to the final adjustment, which means that the patient must be protected from UV light for an indeterminate time. The refractive results of the IOL implant can change over a period of several weeks, perhaps months, depending on the nature of capsular contraction. Therefore, these lenses may have to be light adjusted then frozen prior to the final refractive stability in the eye.
The advantage of this lens system is that the adjustment or correction can be done without additional intraocular surgery and requires only exposure to UV light. Once the adjustment has been made, no further adjustments are possible. If longer term adjustments are required, for example in cases of intolerance to multifocal optics or development of macular pathology, IOL exchange remains the only option.
The multicomponent intraocular lens (MC-IOL, PrecisightTM IOL, Infinite Vision Optics) is a lens system (two lenses, one front lens, one base lens) that enables customised correction of all degrees of sphere, cylinder and multifocality in the primary surgery, as well as giving the surgeon the possibility to fine tune and/or reverse the optical properties of the lens at any postoperative time point.14
Besides accuracy and adjustability, the MC-IOL concept has several additional advantages. The front and base lens haptics are angled in different directions, such that the capsulorrhexis is captured during the primary surgery between the two haptics, preventing lens rotation. This is critical for toric correcting. Because of the capture of the capsulorrhexis between the front and base lens haptics, the front lens remains in front of the rhexis, outside the capsule, facilitating front lens exchange.
This adjustable IOL allows the initial refractive result to be fine tuned by exchanging one of the two optical elements of the lens implant, the front lens. Postoperative surgical adjustments can be performed in the short term in order to correct residual refractive errors. Additionally, because vision is dynamic, the MC-IOL allows for long-term adjustments for the management of refractive changes such as progressive against-the-rule astigmatism (wound healing, age factors) and capsule contraction. Undesirable optics can easily be exchanged, for instance in cases of multifocal intolerance. Optical adjustments are often desirable years after the primary surgery, perhaps on development of age-related macular degeneration. Finally, the multicomponent lens can be used for paediatric patients, in whom the eye’s growth causes progressive refractive change over time.15 All such lens-exchange surgical procedures are performed in a fraction of the time required for full lens exchange.
From a surgeon's perspective
From a surgeon’s perspective, such a multicomponent IOL offers a customised prescription to patients at the time of the primary surgery; utilising a small inventory of lens components minimises the need for secondary touchups as well as offering adjustability at any postoperative time point.
A feasibility study conducted with the MC-IOL, previously reported, described the two-year follow up after implantation in six patients.14 Previous studies of piggyback lens systems have demonstrated problems related to ILF, fibrotic membranes that develop between the two piggybacked lenses.11 Unlike these previous lens implantations, which placed both lenses in the capsular bag, the MC-IOL optically integrated dual lens system places the base lens in the bag while the front, piggyback, lens sits in front of the anterior capsule, outside the bag, thus avoiding ILF.14 Safe lens exchange can be performed even after posterior laser capsulotomy. The main disadvantage to this system is that a second intraocular surgery is required in some cases, if refractive adjustments are necessary.
A new multicomponent IOL recently has entered the European market–the Harmoni Modular IOL from ClarVista, United States. The ClarVista system, with its unique modular design, offers visual correction of aphakia in patients following cataract surgery. The lens has one component that serves as a haptic-holding device to secure a second element, the optic.
The design of the IOL is intended to enable safe and easy exchange of the optic component to reduce residual postoperative refractive error at the time of surgery or at 3 months postoperatively, which is similar to the MC-IOL concept. The Harmoni received CE mark in September 2015.
Despite advances in cataract surgery and biometry, incorrect IOL power remains one of the most frequent reasons for IOL exchange. In the near future, there might be an increase in the frequency of incorrect power calculations as the percentage of patients who have undergone previous corneal refractive surgery grows; these patients are particularly desirable of spectacle independence. Different surgical options for the correction of residual refractive errors are currently or soon to be available, including piggyback IOLs, light-adjustable lenses and multicomponent IOLs.
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Dimitra M. Portaliou, MD, practices at the School of Health Sciences, Institute of Vision and Optics, in the University of Crete, Greece. She has no financial or proprietary interest in any materials or methods described herein.
Dimitra M. Portaliou, MD