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Kelman’s IOL design concepts endure 30 years
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After 4 hours in the operating room, including 61 minutes of ultrasound time, Charles D. Kelman, MD, completed the first phacoemulsification procedure in 1967. Infection developed in that first patient, and the eye was ultimately removed. But Kelman tried again, and his second attempt was successful, changing the way cataract surgery was performed.
In 1982, 15 years after that first attempt, Kelman published his vision for IOL design in the inaugural issue of IOL Today, the precursor to Ocular Surgery News, which marks its 30th year with this issue. One of the intentions of Kelman’s 10 principles of IOL design was to help future ophthalmologists determine which IOL characteristics would be best for their patients.
Kelman described the purpose of his 10 principles of IOL design as ideas “to delineate some of the concepts of lens design so that a practicing physician can better evaluate the lenses he is currently using and any innovative new lenses which may appear over the next few years.”
“The principles … will also, in some cases, help an innovative surgeon to design a lens which may well turn out to be an improvement over current models,” he wrote.
In June 1992, Charles D. Kelman, MD, was awarded the National Medal of Technology and Innovation by President George H.W. Bush for his accomplishments in cataract surgery technology.
Image: Kelman CD
“Over the past several years, a tremendous proliferation of lens styles has taken place,” Kelman wrote in IOL Today.
Current OSN Board Members weighed in on how these concepts translate with respect to today’s technology and advancements.
Principle 1
The lens must not move against any ocular tissue, or the ocular tissue against the lens, when the eye is at rest or when the eye is deformed. For rigid lenses, a three-point fixation achieves maximum stability over a four-point lens.
“A lens which moves against intraocular tissue creates an inflammatory response with (in increasing severity) a cellular response, iritis, corneal decompensation, and finally macular edema. Of course the opposite is also true, that is to say, the ocular tissue must not move against the lens,” Kelman wrote.
Perspective
Charles D. Kelman’s 10 principles of IOL design are a well thought-out, in-depth perspective by a true innovator and offer surgical guidelines and shine cautionary light to avoid potential complications when a manmade prosthetic device such as an IOL comes to interact with human ocular tissues on a lifelong journey after IOL implantation. All of Kelman’s principles seem to stand the test of time, underscoring what a truly great surgeon he was.
Thomas John
The first principle, namely that the lens must not move against any ocular tissues within the eye, is extremely important. Because modern-day phaco surgery is all about vision restoration, improved quality of vision and a quick return to normal lifestyle activities, we should try to prevent any visual compromise postoperatively. When an IOL moves against ocular tissue, this repeated mechanical microtrauma can result in prosthetic-related anterior segment inflammation and lead to possible eye pain, photophobia and tearing. With time, secondary macular edema can significantly reduce vision. Such an occurrence with ongoing uncontrolled chronic inflammation can lead to the need for an IOL exchange and additional ocular risk.
Hence, thou shall not violate Kelman’s first principle if you want a happy patient and a happy surgeon.
Thomas John, MD
But technology has advanced, according to Jeffrey Whitman, MD, OSN Cataract Surgery Board Member.
“With new technology lenses, such as accommodative lenses, movement with and against tissues is now needed and desirable. We now have found that four-point fixation, such as in multiflex anterior chamber lenses, are even better tolerated than the old tripod models,” Whitman said.
Perspective
How wonderful it is to look back on the IOL design principles Dr. Kelman laid out for our profession and to gain insight on the state of the art 30 years ago. And how wonderful it is to see how far our IOL designs have progressed.
The early IOL pioneers gave the world the gift of freedom from aphakia. A later generation, using more precise biometry and more predictable implants, gave us deliverance from spherical refractive error. Astigmatism soon followed, and today we are conquering even presbyopia with truly physiologic IOL designs that don’t just mimic nature but, in many ways, improve on it.
John A. Hovanesian
While many of Dr. Kelman’s principles are still valid today, we’ve moved well beyond the idea that an IOL must remain inert and motionless. Moving, accommodating lenses are now a standard offering, and IOLs that elute drugs or allow noninvasive IOP measurement may soon be a reality.
Sadly, Charlie Kelman didn’t live to see today’s IOL designs and concepts. Still, knowing his childlike creativity and constantly active mind, I’ll bet in his later years, well after he wrote the 10 principles, he probably imagined them.
John A. Hovanesian, MD, FACS
Principle 2
The lens must not create pressure against any ocular tissue when the eye is at rest or when the eye is deformed. When pressure is applied to the globe at the outer perimeter of an inelastic structure in the eye, it will be transmitted to the internal inelastic structure and will be felt as pain. If a rigid triangle is used, external force is divided between two points, and internal pressure is cut in half.
According to Thomas F. Neuhann, MD, OSN Refractive Surgery Board Member, this principle holds true, and yet tripod lenses have virtually disappeared from practice.
Thomas F. Neuhann
R. Bruce Wallace III, MD, OSN Cataract Surgery Board Member, recalled his personal account of Kelman’s principles: “Dr. Kelman’s 10 IOL principles date back to the early era of implantation of anterior chamber IOLs after intracapsular cataract extraction. I attended a course Dr. Kelman gave in New Orleans in the early 1980s where these principles were advocated. Dr. Kelman had modified the Ridley anterior chamber IOL to a tripod PMMA AC IOL simply known as ‘the Kelman lens.’ Conversion to extracapsular and phacoemulsification cataract extraction was not universal at this time, and the need for AC IOLs, especially for secondary implantation, was still frequently encountered.”
R. Bruce Wallace III
Principle 3
The lens must not increase, decrease or change the area of contact when the eye is deformed. A change in area of contact in size or position would be equivalent to intermittent touch, which would cause inflammation. Furthermore, flexion of a flexible implant must take place away from the areas where the lens is in contact with the tissue; that is, flexion should take place close to the optic of the lens, and the flexion must take place in the same plane as the optic and not brought forward toward the cornea.
“The basic principle holds, but flexible two-piece accommodating IOLs are on the horizon,” William J. Fishkind, MD, FACS, OSN Cataract Surgery Board Member, said.
William J. Fishkind
“Again, with posterior chamber lenses and accommodative lenses, the idea of contact is now redefined,” Whitman said. “We are no longer near the cornea, so fear of corneal touch is pretty much a thing of the past. We even sew lenses behind the iris now to avoid anterior chamber lenses.”
Principle 4
The lens must not be a physical or chemical irritant. PMMA is inert in the anterior chamber, and lenses made of it would not be a chemical irritant. With careful attention to the edge of the lens and to design, physical irritation to the iris and other structures can be minimized.
This principle is still true, Fishkind said, “But with different types of biocompatibility now, the search is on for new materials of greater or different biocompatibility.”
“Although we still use PMMA anterior chamber lenses, these have been supplanted by foldable lenses made of silicone, acrylate and Collamer, which can be inserted through smaller incisions that were never even thought of ‘back in the day’ and laid to rest in the very same capsular bag from which the cataract was removed,” Whitman said.
Principle 5
The lens should not increase the incidence of reoperation due to dislocation or improper size.
“When evaluating a new lens style, it is important to try to visualize what could go wrong and what circumstances could require reintervention,” Kelman wrote, adding that reintervention would likely lead to an increased rate of complications.
“As the IOL design and manufacturing have improved, safety and function have improved so that complications that were foreseen by Dr. Kelman have been eliminated,” Eduardo C. Alfonso, MD, OSN Cornea/External Disease Board Member, said.
“Safety concerns have been surpassed with current-generation IOLs,” Alfonso said. “The function has been improved beyond what Dr. Kelman wrote but probably thought possible. For example, the improvement in the measurement of the eye’s refractive error and the use of the IOL to correct this is more precise than what was possible at the time.”
With respect to patient safety, Alfonso regards Kelman’s principles as important today as they were when they were first written.
“[Kelman’s principles] embody the concepts of patient safety above all others,” he said. “Kudos to Dr. Kelman and our professional standards.”
Principle 6
The lens should be easy to insert. Complications increase as the complexity of the insertion increases. Lenses that must be dialed in or that have several planes require more expertise than simpler implants.
Perspective
William B. Trattler
Charles Kelman was clearly a visionary, and many of his principles of IOL design clearly hold true today. Perhaps the one principle that has clearly come to fruition is principle 6: The lens should be easy to insert. Surgeons have gravitated toward one-piece IOL designs that can easily be inserted through smaller and smaller incisions and typically unfold in a very controlled fashion. Manufacturers have made further innovations since Dr. Kelman published his principles, including improved insertion systems for lenses that provide easy loading of IOLs and safe delivery of these lenses into the eye and, more recently, pre-loaded IOL systems that help avoid even the rare loading issue. Future innovations are sure to continue to expand on Dr. Kelman’s vision on IOL design.
William B. Trattler, MD
Injectable lenses are an advance in technology that was not even considered 30 years ago, Whitman said, thus increasing the safety and simplicity of implanting lenses.
“Preloaded lenses, better inserters and newer lens materials have made it easier for all surgeons to become ‘experts’ at lens insertion and have made it safer for the patient as well,” Whitman said.
“Insertion devices have taken the complexity from the act of insertion, to the surgeon or the assistant who loads them, away from the surgical field. Thus, loading is complex, but insertion is simple,” Fishkind said.
Perspective
Uday Devgan
Dr. Kelman was truly a sage in the ophthalmology world, and his ideas, designs and principles have influenced thousands of surgeons and helped millions of patients. With regard to IOL design, the principle of simpler is better has held true for decades and will continue to do so in the future. Just a decade ago, our primary foldable IOLs were three-piece designs with haptics individually staked into the optic. These delicate haptics could bend, break or even detach from the optic, and delivering the three-piece IOLs into the eye often required complex movements with folding forceps and then with injectors. That changed when single-piece acrylic IOLs were introduced. Here was a design that was simpler, stronger and easier to implant in the eye. Insertion was simplified with smaller incisions and easy delivery, and the single-piece acrylic IOLs soon became the market leader. I think we will see Dr. Kelman’s words continue to ring true with future IOL designs, which will continue to become easier to insert while delivering excellent vision for our patients.
Uday Devgan, MD
Principle 7
No part of the lens should be adherent in an area that cannot be visualized. Later removal may be complicated, with danger of hemorrhage, vitreous loss, macular edema and retinal detachment being greatly increased. Lenses in the posterior chamber against the ciliary body are not as safe in the long run as lenses that are readily removable.
OSN Board Members tend to agree that, even though this principle remains true, advantages of modern technology outweigh disadvantages.
“This [principle] is true, but modern technology allows for placement of haptics in the equatorial bag where they might not be visualized,” Fishkind said, giving examples of Hoffman pockets, cow hitch knots and Agarwal glued IOLs, which are all placed in contradistinction to the rule but remain necessary problem solvers.
“Modern implantation in the bag has so many advantages that this ‘disadvantage’ is negligible,” Neuhann said.
“All lenses left in the eye long enough are more difficult to remove and can cause complications within the eye. However, instrumentation and techniques have improved to lessen the chance of vision-threatening outcomes,” Whitman said.
Principle 8
The lens should be suited to all types of surgery, that is, intracapsular, extracapsular, phacoemulsification and secondary implantation. If a lens is suitable to all types of surgery, the surgeon will become proficient in a minimum amount of time.
OSN Board Members again agree that this principle is no longer true.
“Progress has taken us along a different path,” Whitman said. “We have excellent lenses that are only intended to go in the capsular bag, three-piece lenses that can go in the bag or sulcus, and PMMA lenses that can go in the anterior chamber angle — but really none that can be used for all types of surgery.”
Jeffrey Whitman
Perspective
Of Kelman’s original 10 principles of IOL design, three simple principles and one significant anatomical positioning point sum up the main requirements for modern-day IOL implantation: 1) The lens material must be inert, 2) the implant must fit well within the eye (meaning that it must be stable without undue pressure at any point on delicate intraocular structures), and 3) the implant must be flexible, both the optic and haptics, so that it will fit through a minimal incision due to its foldable nature and the haptics will gently spread the pressure of fixation over a large surface area.
The most important advancement in IOL implantation in my practice career has been the continuous curvilinear capsulorrhexis, which assures almost perfect anatomical positioning of the lens implant in the natural crystalline lens bag. Here the IOL is well separated from delicate vascularized intraocular structures even though that position is hidden from view behind the iris. This location allows for significant extraocular deformation with minimal intraocular effect on the IOL or haptics, due to the floating, suspended zonular support of the lens capsule.
Richard J. Duffey
Kelman’s goal of one single implant design suitable for intracapsular and extracapsular cataract surgery, phacoemulsification, small-incision surgery and secondary lens implantation is clearly no longer possible or even desirable today.
Richard J. Duffey, MD
Perspective
This impressive listing of Dr. Charles Kelman’s principles of IOL design confirms once again that he was a man of genius. Of particular importance, several of the statements deal with the critical necessity that an IOL should not cause physical trauma or incite inflammatory response. Most of the 10 principles he specified continue to strongly inform lens design today.
Priscilla E. Perry Arnold
One of the statements seems to be an exception to this case — that an implant should be appropriate for use with every surgical technique or situation. This would seem to be unrealistic for any single lens design. For example, while fixation of an implant within the capsule is the most physiologic choice, in some cases this is not possible. Dr. Kelman significantly designed an IOL still widely used today in absence of capsule support. But this is not the end of the story. Patients benefit from new enhancements available in lens design and function, and we honor the vision of Charles Kelman by continuing to offer new, safer and more functional lens designs to our patients.
Priscilla E. Perry Arnold, MD
Principle 9
Late complications that occur 10 years or more after surgery must be predictable and curable.
“A lens in the anterior chamber might conceivably have some irritating effect on the cornea,” Kelman wrote. “This is predictable, of course, if the patient has annual endothelial cell counts and if, before the cornea decompensates, the lens is removed. Lenses in the posterior chamber, which create more posterior-type complications, are less likely to have predictable and curable complications.”
OSN Board Members believe that, with advances in surgical techniques and IOL design, complications resulting from lenses in the posterior chamber are fewer and less severe since Kelman wrote his guidelines.
“Complications such as cystoid macular edema are now more rare with posterior lenses than with intracapsular and anterior lenses,” Whitman said. “Otherwise, late complications are mostly a thing of the past — not gone, but dwindling. Also, retinal surgical techniques have also improved so that most late complications can be dealt with successfully.”
Perspective
David R. Hardten
It is amazing to me to read how much insight Dr. Kelman had from 30 years ago. As I read the principles of IOL design, I feel that almost all of these are just as true today as they were 30 years ago. Many of these principles over the years have been violated, and then we relearned the original principles. The one point that may have been a little early in its prediction is principle 9, as we have become very convinced that the posterior chamber is really the right place for IOLs for most circumstances.
David R. Hardten, MD
Principle 10
One size lens should fit all eyes. Even if the surgeon were able to measure accurately the internal size of the eye, lens sizes are approximate fits. Even if the surgeon were able to measure the internal diameter of sclera spur to sclera spur to within a tenth of a millimeter, which is highly unlikely, the manufacturer would not be able to supply lenses in tenths of a millimeter. It is therefore important to have a lens that can adapt to all eyes.
Fishkind called this principle a “work in progress” in today’s practices.
Perspective
The last of Charlie’s principles is certainly not the least: One size lens should fit all eyes. In the past 30 years, it has become increasingly obvious, with the increased sophistication of imaging and OCT techniques, how much variation there is between individual eyes that is not readily visible to the operating surgeon. How insightful he was to anticipate this phenomenon and demand that all lenses be compatible, fundamentally just because they are placed in the center of the pupil, visual axis or limbal margins.
Noel A. Alpins
This is how we fundamentally practice surgical implantology today, just as Charlie did in his own time. In most cases, one lens diameter works fine in the bag, unless a special situation exists. Surgical advancements have demanded more precision in physical placement, for example, continuous curvilinear capsulorrhexis and in-the-bag placement; consequently, the refractive outcome is dependent on predictable biological anterior/posterior alignment of the new elements of the visual axis with calculation of the effective lens position. There have been many changes in a relatively short time — few have outpaced Charlie’s foresight.
Noel A. Alpins, MD
Relevance of Kelman’s ideas
Sir Harold Ridley, an ophthalmologist at St. Thomas’ Hospital and Moorfields Eye Hospital in London, invented the IOL and implanted the first lens in 1949. But the impact of the IOL on cataract surgery was not fully appreciated until improvements were made in IOL designs and Kelman’s phacoemulsification procedure became more prevalent.
Before phacoemulsification, the surgical removal of cataracts required a hospital stay of 10 days, as long as no complications occurred, with a recovery period of several months. Today, the procedure is an outpatient surgery under topical or intraocular anesthesia.
“Dr. Kelman’s ideas were forward thinking. Concerns were many at the time that safety of IOLs was not researched in a non-human model,” Alfonso said. “This led to prospective clinical human studies that proved the safety and efficacy of IOLs.”
Eduardo C. Alfonso
Between 1967 and 1973, 3,500 cataracts in the United States were removed by Kelman’s procedure, 500 of them performed by Kelman. Millions of phacoemulsification procedures are now performed each year.
“It still amazes me to this day that Kelman was so forward thinking and had advanced cataract surgery and IOLs to a place that it had never been before,” Whitman said.
Many ophthalmologists remember Kelman both inside and outside of the operating room.
“Dr. Kelman had many interests,” Wallace said. “He played the saxophone at Carnegie Hall, piloted a helicopter in busy New York City, and invented cataract cryoprobe extraction and Kelman phacoemulsification. I remember a well-attended meeting at Gleneagles golf resort in Scotland in 1985 where most surgeons also took part in the meeting’s golf tournament. Charlie Kelman was the keynote speaker and also won the golf tournament.”
Kelman passed away in 2004 at age 74. – by Cheryl DiPietro