CATARACTS & THE FUTURE OF INTRAOCULAR LENS TECHNOLOGY | BY DR. PHILLIPS KIRK LABOR

 3 years ago


Cataract surgery, the replacement of the eye’s natural crystalline lens with an intraocular lens implant, has become one of the most common and safest outpatient surgeries performed in the United States today. 2009 statistics from the U.S. Department of Health and Human Services National Health Statistics Reports revealed the leading diagnosis at ambulatory surgery visits was for cataract surgery – 3.0 million. Cataract surgery is performed for people who have demonstrated some form of visual impairment when it comes to limitations of his or her activities of daily living (ADL) and while the majority of these patients are elderly, cataracts may also occur in younger patients. Furthermore, more and more patients are requesting lens replacement surgery to reduce their dependence on glasses both for distance and near vision. This has led to the development of specialized intraocular lens implants (IOLs) to help satisfy this demand.

In performing cataract surgery, the eye’s natural lens is removed because it has become the cataract. As we go through life the lens of the eye accumulates protein, which is deposited within the substance of the lens in any manner of configurations. It is this conglomeration of protein that leads to the symptoms associated with cataracts such as loss of sharpness of vision, need for brighter light when reading and glare and star bursting around lights at night among others. When these proteins are visible to an eye care specialist on exam, a patient is given the diagnosis of cataract; when the symptoms one experiences begin to affect his or her ADL’s then cataract surgery may be warranted. Significantly, the lens of the eye provides about one third of the natural focusing ability of the eye with the remaining two thirds coming from the cornea, which is the clear dome over the iris and pupil. If the lens and cornea do not provide enough, or provide too much focusing power for the eye, the vision must be augmented with glasses, contact lenses or for some, refractive surgery such as LASIK or lens replacement surgery. Furthermore, in an effort to more fully understand cataracts and cataract surgery, it should be noted that loss of near vision due to age is known as Presbyopia and is due the same proteins that accumulated to create the cataract.  Because of the significant contribution of the lens to the overall focusing power of the eye and because this focusing power has been removed through the removal of the lens at the time of cataract surgery, it must be replaced. It is for this reason that an IOL must be placed in the eye at the time of cataract surgery, to restore the focusing power of the eye. Importantly, it should be noted that each implant will have a power ground into it that will be specific for a patients’ right and left eye, respectively. This may be thought of as being similar to a pair of glasses or contact lenses that have a lens with power specific to the right and left eye.

Currently, the predominant type of IOL implanted at the time of cataract surgery is known as a monofocal intraocular lens and generally requires a patient to wear glasses or, less frequently, contact lenses to eliminate residual blurred vision and obtain his/her sharpest vision post-operatively; this is true for both distance and near vision. Furthermore, this isn’t always limited to monofocal IOLs and may be the case for some of the more advanced IOLs described below. This residual blurriness, as well as all blurriness correctable with glasses or contact lenses, is known as the refractive error of the eye. There are a myriad of reasons for residual blurred vision due to uncorrected refractive error after cataract surgery but two of the predominant ones have to do with how the eye heals around the implant and, significantly, whether the eye has any corneal astigmatism. Astigmatism has two primary sources in the eye: the cornea and the lens. Since lenticular astigmatism is addressed by removal of the cataractous natural lens, the remaining corneal astigmatism is what may, in part, contribute to blurred vision after cataract surgery. While astigmatism can be a difficult concept, it may be simply described through the following analogy: if an eye has no corneal astigmatism it is shaped like a hemisphere, like a basketball cut in half; on the other hand, if the eye does have some corneal astigmatism, it is shaped like an ellipse, like an American football cut length-wise. This astigmatism will bring images to a focal line instead of a focal point, which will in turn lead to blurred vision. Additionally, the unpredictable healing around the IOL may not only leave the patient with uncorrected astigmatism but uncorrected near-sightedness (myopia) or far-sightedness (hyperopia…more than a very small amount of which will create blurred vision). Thankfully, as mentioned previously, corrective lenses will eliminate this blurriness. In a tribute to research and technology, over the course of the past decade, IOL’s have been developed and refined to reduce which is more common or, in some cases eliminate, the post-operative need for glasses or contact lenses. These lenses include such lenses as the Bausch & Lomb Crystalens and Trulign, Alcon ReStor and Toric, AMO Tecnis MF and Toric as well as the Staar Nanoflex and Toric. The Crystalens, ReStor and Tecnis MF were created to help correct the need for glasses at both distance and near and the Trulign, to correct distance, near and astigmatism at the same time. A Toric IOL is one that has been manufactured to correct astigmatism and while all of these IOLs have proved to be extremely effective in providing some relief from the use of glasses post-operatively, they all have a common drawback: the power of the IOL is determined preoperatively and is therefore fixed and cannot be changed. This may invariably lead to residual uncorrected refractive error and its associated blurred vision. Changing the power of the IOL was impossible, until now.

Throughout the modern period of cataract surgery, surgeons have been looking for ways to provide patients with the best possible outcomes and this desire, to provide patients a better quality of life after cataract surgery, has included the desire to create independence from corrective lenses (glasses or contact lenses) post-operatively. While advances in surgical techniques and IOL technology have gotten us closer to this goal, in some rare cases actually achieving it, we still have not been able to uniformly achieve it in the United States. I believe this is about to change with the addition of a new (to the U.S.) IOL technologyThis “new” IOL technology, currently in clinical trials, will allow surgeons to customize an intraocular lens power for a particular eye. And while this technology is currently under investigation in the U.S., it has been successfully utilized worldwide for the past decade.

This new IOL allows a surgeon to adjust the power of the implant in a very specific and very safe way to account for any residual refractive error AFTER the initial implantation of the lens. Using proprietary technology, a U.S. company has created an IOL that will respond predictably to treatment with a specific wavelength of light AFTER it has been implanted to eliminate any residual refractive error therefore providing a patient sharper vision than ever before. In fact, most of the patients treated have uncorrected vision (no glasses or contacts) equal to or better than 20/20 for distance. This may be compared with routine cataract surgery or cataract surgery with astigmatism correction where less than 50% of patients are able to achieve uncorrected vision this sharp. This technology represents a true breakthrough in the advancement of cataract surgery and IOL technology in that, for the first time, surgeons may actually customize the IOL correction to each eye. This in turn, may lead to further developments for customized near vision applications as well. In fact, research is ongoing, outside the United States, which addresses this very issue.

In summary, cataract surgery remains one of the most common and safest surgical procedures in the United States today. It is one of the few surgical procedures available to patients with the ability to restore function to pre-dysfunctional levels and indeed, improve that functionality to something better than the patient had prior to the onset of his or her ocular morbidity whether through the development of a cataract or because of a significant refractive error such as myopia, hyperopia, astigmatism or presbyopia. The development of an intraocular lens implant that has the capability of having its power changed through post-operative manipulation, in-situ, affords cataract surgeons the ability to customize visual treatment for each eye in ways that may render some current IOL technology obsolete. The light at the end of tunnel may be a train, but the light is in focus and is clearly at the head of a powerful locomotive leading a train pulling cars full of immense promise when it comes not just to visual restoration, but of improvement in visual potential as exemplified by this new technology.

Learn more at Dr. Phillips Kirk Labor

 

 

Posted in: Ophthalmology

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