Article
Pushing the envelope for the sake of ophthalmology
In his latest blog, Mark Packer, MD, reflects on ophthalmic pioneers of the past, and writes why controversy and challenging the norm is what drives the future of advancements.
Editor’s Note: Welcome to “Eye Catching: Let's Chat,” a blog series featuring contributions from members of the ophthalmic community. These blogs are an opportunity for ophthalmic bloggers to engage with readers with about a topic that is top of mind, whether it is practice management, experiences with patients, the industry, medicine in general, or healthcare reform. The series continues with this blog by Mark Packer, MD, FACS, CPI. The views expressed in these blogs are those of their respective contributors and do not represent the views of Ophthalmology Times or UBM Advanstar.
With the passing of Robert Sinskey, MD, I was reminded of an epiphany I had during my residency training. As I sat one night in the Boston City Hospital emergency room after repairing an eyelid laceration, I was watching the infamous O.J. Simpson “slow-speed chase” on TV.[1] I guess it was the Brentwood connection that triggered the memory of my father.
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As a young boy growing up in Brentwood, I watched one morning as my father stood in front of his bathroom mirror wearing eyeglasses that had one lens removed. He washed his hands and, leaning forward for more magnification, put a contact lens on his left eye. I was vaguely aware at the time of some conversation among my parents and their friends about “the implant.” Were you going to have “the implant?” It was always said in a slightly hushed, heavily freighted voice, as if it were contraband, or at least highly questionable. The name "Sinskey" was associated in my mind with “the implant.”
It suddenly dawned on me that (of course!) my father had cataract surgery without “the implant!” That was why he had to put in a contact lens every morning. The idea that my father had been aphakic suddenly made him seem ancient.
Office-based survery coming sooner than you think
In the early 1970s, implants remained controversial, and for good reason: pseudophakic bullous keratopathy. Improvements came, but Ralph Nader, the consumer advocate who had become famous for his 1965 expose of the automobile industry, “Unsafe at Any Speed,”[2] remained skeptical of medical device corporations. The Ophthalmic Devices Panel of the FDA was convened, and hearings were held on the safety and effectiveness of “the implant,” more correctly called the intraocular lens, or IOL.
“The Health Research Group (HRG) of Ralph Nader’s Consumer Organization, Public Citizen, waged a relentless campaign against IOLs. This activity forced the FDA into action . . . In 1980, a meeting was held in a large room at the FDA headquarters and was packed with surgeons, reporters, and legislators. Several of us presented data demonstrating the virtues of IOLs. It was the testimony of a single patient, however, that ensured victory for U.S. implant surgeons. His name was Robert Young, the actor who played the role of Marcus Welby, MD, on a popular television show by the same name. He also starred in Father Knows Best. With great eloquence, he described how lens implants placed in his eyes by Richard Kratz, MD, in 1976 had saved his career. His stunning speech made a tremendous impact. The FDA decided that, if IOLs were good enough for Dr. Welby, they were good enough for the country.”[3]
By the time I began practice in 1995, IOLs had become a routine part of cataract surgery. The key question for patients rapidly changed from, “Should I get an implant?” to, “Which implant should I get?” Toric, multifocal, accommodative, aspheric . . . today, we have an exciting list of options, with a variety of risks and benefits.
(Photo courtesy of ©Dmitry Kalinovsky/Shutterstock.com)
Controversy continues
The ancient history of IOL development-the FDA hearing was 35 years ago, after all-might seem irrelevant today. A bit less ancient, the history of aspheric IOL development occurred less than 15 years ago. Today, it makes perfect sense that implanting an IOL more like the natural youthful lens, with zero or less spherical aberration, leads to overall better quality of vision. However, this concept remained controversial at first.
Dysfunctional lens syndrome paradox
The first aspheric IOL, the Tecnis (originally marketed by Pharmacia, Groningen, the Netherlands; now produced by Abbott Medical Optics, Santa Ana, CA), was developed and tested in the first few years of this century.[4]
The Tecnis optical design incorporated a modified prolate anterior surface to create negative spherical aberration, like the youthful crystalline lens. Not only did the IOL improve contrast sensitivity, it also significantly improved night-driving performance when compared with a spherical IOL. In an analysis conducted by the Potomac Institute, the impact of this IOL on highway safety was found to be greater than that of the center high-mounted brake light mandated on cars when Elizabeth Dole was the U.S. Secretary of Transportation.[5]
The clinical outcomes demonstrated with the Tecnis IOL led to the designation of aspheric IOLs as a new category of New Technology IOLs (NTIOLs) by Medicare on Jan. 26, 2006:[6] “Today’s announcement of coverage with additional payment for an innovative type of intraocular lens reflects Medicare’s attention to improved clinical benefits,” said CMS Administrator Mark McClellan, MD, PhD. “For these lenses, there is clear evidence of improved functional vision and contrast acuity.”[7]
The concept of the aspheric IOLs rapidly developed traction among surgeons, so that today the vast majority of IOLs implanted in the United States are aspheric. In addition to aspheric monofocal IOLs, the toric, multifocal, and accommodative IOLs have also been designed and built on aspheric platforms. Nevertheless, several key issues require thorough understanding in order to optimize the performance of these lens implants:
Pupil Size
Spherical aberration depends on aperture size. With a 3-mm pupil, little difference can be found in ocular wavefront between eyes with aspheric or spherical IOLs implanted; however, with a 5-mm pupil the differences are pronounced.[8] For this reason, greater differences may also be found when measuring mesopic contrast sensitivity or night-driving performance, when the pupil is naturally larger in dim light.
Tilt and Decentration
The performance of aspheric IOLs is degraded when they are tilted or decentered relative to the optical axis.[9] Although the limits of tolerance are fairly forgiving,[10] some caution is advised in patient selection. Eyes with severe zonulopathy or intraoperative capsular complications impacting IOL stability may not be the best candidates for negatively aspheric IOLs. The purely aspheric enVista IOL (Z[4,0]=0; Bausch + Lomb, Irvine, CA) avoids the decline in optical quality that occurs with tilt and decentration of negatively aspheric IOLs.
Depth of Field
Better optical quality without spherical aberration sacrifices some depth of field.[11] One approach to this dilemma has been to take a compromise position in IOL optical design, simultaneously maximizing both optical quality and depth of field with a purely aspheric IOL. The enVista follows this paradigm.
OD-performed surgery unacceptable, dangerous
An interesting innovation involving depth of field and spherical aberration is the programmed induction of negative spherical aberration to increase depth of field following implantation of the Light Adjustable Lens (Calhoun Vision, Pasadena, CA).[12] The near vision obtained with this method is superior in those eyes with the larger magnitude of spherical aberration.
Customizing Asphericity
In their review of aspheric IOLs, Montes-Mico et al. conclude by noting that surgeons should “try to customize the asphericity depending on the patient’s corneal spherical aberration to obtain the optimum visual performance.”[13] Historically, the Tecnis IOL was developed based on the mean corneal spherical aberration measured at the 6-mm optical zone in a cohort of European cataract patients, + 0.27 μm. The Tecnis was designed to complement the average cornea, leaving the eye with zero residual spherical aberration. However, the distribution of corneal spherical aberration in those populations that have been studied is Gaussian. In the North American Caucasian population, Z[4,0] measures +0.274 ± 0.089 μm .[14] In the Japanese population, corneal spherical aberration has been measured at +0.203 ± 0.100 μm.[15]
Given the range of aspheric IOLs available today, one might select a specific IOL to best achieve a given target total spherical aberration in any given eye.[16] This approach may be recommended particularly in eyes with a history of keratorefractive surgery. For example, myopic LASIK generally results in a larger magnitude of positive spherical aberration.
Defocus and Astigmatism
Blur from residual uncorrected refractive error in pseudophakic patients can easily render moot the benefits of aspheric IOLs. To truly reap the benefits of increased contrast sensitivity from aspheric optics, sphere and cylinder should be reduced as much as possible and practical. Biometry and IOL calculations, as well as intraoperative aberrometry, continue to play a crucial role in obtaining optimal outcomes, particularly in those desiring postoperative spectacle independence.
Dr. Packer's med school regrets
The development and adoption of aspheric IOLs has driven forward the field of optical quality for pseudophakic patients and enhanced the concept of refractive cataract surgery. Providing youthful vision-in terms of both image quality and freedom from presbyopia-has become the goal of every refractive lens surgeon.
We’ve been able to see this far because we have stood on the shoulders of giants.
[1] Wells J. 20 years ago today: O.J. Simpson's slow-speed chase stopped L.A. http://www.latimes.com/local/lanow/la-me-ln-20-years-ago-oj-simpson-chase-20140617-story.html
[2]https://en.wikipedia.org/wiki/Unsafe_at_Any_Speed
[3] Jaffe NS. The Introduction of IOLs. Cataract & Refractive Surgery Today. October 2005: 32-5. http://crstoday.com/PDF%20Articles/1005/CRST1005_cs_History350.pdf.
[4] Artal P. History of IOLs that correct spherical aberration. J Cataract Refract Surg. 2009;35:962-963; author reply 963-964.
[5] McBride DK, Matson W. Assessing the significance of optically produced reduction in braking response time: possible impacts on automotive safety among the elderly. Potomac Institute for Policy Studies. April 1, 2003.
[8] Kohnen T, Klaproth OK, Bühren J. Effect of intraocular lens asphericity on quality of vision after cataract removal: an intraindividual comparison. Ophthalmology. 2009;116:1697-1706.
[9] Fujikado T, Saika M. Evaluation of actual retinal images produced by misaligned aspheric intraocular lenses in a model eye. Clin Ophthalmol. 2014;8:2415-2423. doi: 10.2147/OPTH.S72053. eCollection 2014.
[10] Packer M. Tilt and decentration: Toward a new definition of tolerance, in Fine IH, ed., Perspectives in Lens and IOL Surgery. EyeWorld May, 2005. http://www.eyeworld.org/article.php?sid=2558&strict=&morphologic=&query=ophthalmology
[11] Marcos S, Barbero S, Jiménez-Alfaro I. Optical quality and depth-of-field of eyes implanted with spherical and aspheric intraocular lenses. J Refract Surg. 2005 May-Jun;21(3):223-35.
[12] Villegas EA, Alcón E, Mirabet S, Yago I, Marín JM, Artal P. Extended depth of focus with induced spherical aberration in light-adjustable intraocular lenses. Am J Ophthalmol. 2014 Jan;157(1):142-9.
[13] Montés-Micó R, Ferrer-Blasco T, Cerviño A. Analysis of the possible benefits of aspheric intraocular lenses: review of the literature. J Cataract Refract Surg. 2009;35:172-181.
[14] Beiko GH, Haigis W, Steinmueller A. Distribution of corneal spherical aberration in a comprehensive ophthalmology practice and whether keratometry can predict aberration values. J Cataract Refract Surg. 2007;33:848-858.
[15] Shimozono M, Uemura A, Hirami Y, Ishida K, Kurimoto Y.Corneal spherical aberration of eyes with cataract in a Japanese population. J Refract Surg. 2010;26:457-459.
[16] Packer M, Fine IH, Hoffman RS. Aspheric intraocular lens selection based on corneal wavefront. J Refract Surg. 2009;25:12-20.
