George O. Waring IV, MD; R. Luke Rebenitsch, MD, PCEO; and Jason E. Stahl, MD
The advent of toric and presbyopia-correcting intraocular lenses (IOLs) has minimized the distinction between refractive and cataract surgeons. With refractive IOLs, however, it is no longer possible to choose a single go-to lens for all patients. Instead, the lens must be matched to the patient’s lifestyle. As no IOL is perfect, it is necessary to understand the patient’s comprehension and tolerance for the trade-offs involved with any IOL. Tracking patient outcomes can help identify important factors that determine level of satisfaction with a premium IOL.
The arena of premium IOLs continues to change rapidly. New concepts in presbyopia-correcting IOLs, such as chromatic aberration-reducing, extended depth-of-focus IOLs (Symfony, Abbott Medical Optics [AMO]), dual-optic accommodating IOLs (AMO), IOL optics that can change their curvature with accommodation (NuLens; FluidVision Lens, PowerVision Inc), and electroactive optics (Elenza, PixelOptics) are in clinical trials, currently available outside the United States, or in development. Even monofocal IOLs are seeing breakthroughs, such as the Calhoun Light Adjustable Lens (Calhoun Vision), which will allow for post-implantation changes in refraction. As the variety of premium IOLs and the understanding of how to match the patient to these lenses increase, patient groups that were once considered unsuitable for premium IOLs, such as post-LASIK patients or anisometropic patients,1 are now starting to achieve successful results with premium IOLs.2,3
The current choices in refractive IOLs include toric IOLs, multifocal IOLs (including refractive and diffractive IOLs), and accommodating IOLs. Each of the presbyopia-correcting IOLs has different strengths and weaknesses. As a result of light splitting with multifocal IOLs, eyes tend to have diminished contrast sensitivity in dim light and more reports of halos and glare than accommodating IOLs, which produce only a single image at the retina without splitting of light. The induction of higher-order aberrations and perception of halos is proportional to the separation of focal point with lower add powers having less-perceived halos and easier neuroadaptation; although this is being diminished with improved engineering.4 Multifocal IOLs are also sensitive to decentration, which can impact visual acuity and quality.5,6 Currently available accommodating IOLs are subject to variance in effective lens position and the resultant variance in postoperative refractive target.
Multifocal IOLs now have a much broader range of near points than in the past. In the United States, all Food and Drug Administration–approved multifocal lenses are bifocal. Trifocal IOLs with distance, intermediate, and near focal points are available elsewhere. For patients with the greatest near vision requirement, there is the Tecnis MF +4 (AMO). The trade-off is weaker intermediate visual acuity. For patients with more intermediate vision requirements, there are many more options. Currently available multifocal IOLs are the ReSTOR +3 (Alcon), ReSTOR +2.5 (Alcon), Tecnis MF +3.25 (AMO), Tecnis MF +2.75 (AMO), and ReZoom (AMO). Accommodating IOLs include the Crystalens AO IOL (Bausch & Lomb) and astigmatism-treating Trulign (Bausch & Lomb), which provide better intermediate visual acuity but less near acuity. These presbyopia-correcting IOLs, along with their spectacle plane, add powers, and method of presbyopia correction can be seen in Table 3-1. Presbyopia-correcting IOLs can also be combined, one in each eye, to increase a patient’s range of near-intermediate vision, although caution needs to be taken due to the difference in IOL design, optics, and neuroadaptation processes.
TORIC INTRAOCULAR LENSES
Until recently there has only been one toric presbyopia-correcting IOL available in the United States: the accommodating Trulign; although toric, multifocal, and accommodating IOLs have been available outside the United States and in US clinical trials. The Symfony Toric IOL, which works through extending depth of focus, is the newest astigmatism correcting premium IOL. These IOLS are an excellent lens choice for patients desiring astigmatism correction and a presbyopia correction IOL. In refractive cataract or refractive lens exchange patients with astigmatism, a decision must be made whether to use one of these toric presbyopia-correcting IOLs, to use a multifocal IOL with corneal astigmatic correction, or to correct just the astigmatism with a monofocal toric IOL. First, toric IOLs may not be appropriate for patients with high degrees of irregular astigmatism. For patients not desiring presbyopia correction, we usually recommend a toric IOL for those patients with significant astigmatism (> 2.0 diopters [D]) over limbal relaxing incisions (LRI). Toric IOLs with monovision are also a reasonable choice for people with high astigmatism who wish to reduce dependency on spectacles. For high astigmatism patients who are committed to having a presbyopia-correcting IOL, we make sure they understand that a second corneal procedure (LASIK, photorefractive keratectomy [PRK], or LRIs) will be necessary to correct the astigmatism and allow them to receive the full benefit of the IOL.
Toric IOLs are an excellent introduction to implementing a refractive style approach in a cataract practice. They require a little more chair time and some education on how a toric IOL can improve vision, but not as much as for the presbyopia-correction patient. When using the Trulign, patients are also usually less demanding, as they expect some spectacle wear after surgery.
PRESBYOPIA-CORRECTING INTRAOCULAR LENSES
Greater than 0.50 D of astigmatism should be surgically addressed when implanting any presbyopia-correcting IOL. A database survey by Kezirian7 demonstrated the decrease in uncorrected distance visual acuity with residual cylinder of greater than 0.75 D (Figure 3-1).
LASIK or other corneal procedures can be combined with implantation of a presbyopia-correcting IOL. Low levels of astigmatism (≤ 1.75 D) can be managed with LRIs.8
Refractive Cataract Patient Assessment
The preoperative examination for refractive cataract surgery should include, but may not be limited to, determination of eye dominance, visual acuity, refraction, and keratometry. Corneal topography is necessary for all patients to detect highly aberrated eyes that do not do well with multifocal IOLs, or any other corneal abnormality, to check ocular surface quality, and to plan for astigmatism management. There should be agreement between topographic and keratometric cylinder magnitude. If not, carefully repeat measurements and plan for lenticular astigmatism that may be additive or subtractive depending on the relative meridians. Pupil size should be measured in bright and dim light. A careful dilated fundus examination and macular optical coherence tomography can help identify retinal pathology that may affect outcomes.
The popularity of corneal refractive surgical procedures such as PRK and LASIK has raised patient expectations for excellent vision without spectacles or contact lenses. In our practice, we have found a significant increase of patients in their 50s and 60s coming in for LASIK because of a decrease in quality of their vision. They have good Snellen acuity, although they have decreased contrast sensitivity and are losing accommodative amplitude. We find that the crystalline lens in these patients frequently has lenticular opacities that increase forward light scatter, decrease contrast sensitivity, and increase spherical aberration (Figure 3-2). We term this dysfunctional lens syndrome (DLS).
The Dysfunctional Lens Syndrome and Refractive Lens Exchange Patient Assessment
Not all patients have a loss of Snellen visual acuity sufficient to meet the medical diagnostic criteria of cataract. However, the increase in light scatter, loss of contrast sensitivity, and sensitivity to glare can impact a patient’s quality of life. DLS can be measured with advanced diagnostics such as Scheimpflug imaging and Hartmann-Shack aberrometry as well as double pass aberrometry, ray tracing, and contrast sensitivity measures. The double pass AcuTarget HD (Visiometrics) displays point spread function and a simulated loss of clarity of the retinal image. The ray tracing, iTrace (Tracey Technologies), separates corneal aberrations from crystalline lens aberrations, allowing the surgeon to locate the cause of the visual disturbances along the visual axis as well as objectively determine whether the cornea is too aberrated to allow for good vision with a multifocal IOL. Both the double pass and ray tracing system help patients understand that a refractive procedure such as LASIK may not address these changes due to degradation of the crystalline lens. Patients with DLS may also be good candidates for lens extraction followed by implantation of a presbyopia-correcting IOL. The clinical assessment and approach to these patients is the same as for a cataract patient interested in a presbyopia-correcting IOL.