American Academy of Ophthalmology Web Site: www.aao.org
News in Review
A Look at Today's Ideas and Trends
As the Joint Meeting of the Academy and the Pan- American Association of Ophthalmology (PAAO) approaches, EyeNet brings you a preview of some of the papers to be presented there. Several chairmen and chairwomen in charge of paper sessions each selected one abstract that constitutes important news in the field or is illustrative of a trend. Although only five subspecialties are represented below, there also will be paper sessions in intraocular inflammation/uveitis, oculoplastics, oncology, neuro-ophthalmology and pediatrics. Look for a complete list of papers in the Final Program or Pocket Guide or at www.aao.org/onlineprogram09.
Robot for Eye Surgery
Robotic surgery has the potential to eliminate tremor and enhance dexterity, significantly improving upon the precision of unassisted human hands. Although it has revolutionized many surgical specialties, robot-assisted surgery has yet to make clinical inroads in ophthalmology. Demands for greater precision from robots, as well as smaller size and better maneuverability inside the eye, have all raised the bar for designers of robotics systems in the ophthalmic OR, said Howard F. Fine, MD, an ophthalmologist in private practice at the Retina- Vitreous Center in New Brunswick, N.J.
Dr. Fine and Nabil Simaan, PhD, head of Advanced Robotics and Mechanism Applications in the department of mechanical engineering at Columbia University, are cofounders of Auris Surgical Robotics, the maker of a novel dualarm microsurgical system designed specifically for ophthalmic surgery.
Compatible with operating microscopes and vitreoretinal lens systems, Dr. Fine and Simaan’s robotic system has a total of 16 degrees of freedom (DoF), with a modular 2-DoF robotic tool for intraocular manipulation using interchangeable surgical instruments.
Dr. Fine and colleagues recently tested a prototype in animal models of retinal vasculature, successfully demonstrating cannulation of retinal veins followed by stent deployment. “To my knowledge, these are the smallest stents deployed in blood vessels,” said Dr. Fine.
This shows promise, said Jennifer I. Lim, MD, professor of ophthalmology and visual sciences and director of the retina service at the University of Illinois Eye and Ear Infirmary. “It has the ability to allow for very fine manipulations that could not otherwise be done manually with safety. Cannulation of retinal vessels is difficult and dangerous unless one can allow for no error in movement.” Dr. Lim is chairwoman of the Retina papers committee.
Although the prototype exhibits 4.5 ± 0.9 µm translational precision, other features are undergoing further development or testing. For example, the Auris team has devised an approach to temporarily stabilize the head, offering an option for procedures that require precise registration. “Our idea is to make a stiff mold of the patient’s upper teeth that we can affix to the rigid steel halo, so wherever the upper teeth move, the skull and robot stay in precise registration,” said Dr. Fine.
Dr. Fine added that enhancements to the interface are under way.
“Currently, the robot is steered with joysticks, which is not the most intuitive way to operate,” Dr. Lim said. “I would prefer a system that is similar to what I hold for today’s pars plana vitrectomy surgery.”
Dr. Fine’s hope is that further testing in animals and humans will prove the system’s applicability not only for microvascular stenting but also for other anterior segment and posterior segment procedures where increased precision is at a premium.
Dr. Fine is cofounder of Auris Surgical Robotics. Dr. Lim has no financial interests related to this story.
Patients, Especially Older Ones, May Have Bugs
Cataract surgeons should assume that the eyes of at least half of their patients harbor methicillin-resistant bacteria and that the risk increases substantially with advancing age, according to a study of 399 cataract patients.
The study at 10 sites across the nation found that the probability of a patient carrying resistant lid or conjunctival bacteria grew by 24.7 percent per decade between ages 50 and 90, doubling by age 80.
The researchers hypothesize two reasons for the increase in risk with advancing age. “It may be that these patients have had longer exposure to antibiotics and to resistant organisms in the community, and that they may have greater susceptibility because their immune systems are less active as they age,” said study coauthor Eric D. Donnenfeld, MD, in private practice on Long Island and a clinical professor of ophthalmology at New York University.
Approximately half of the study subjects who were culture-positive had a preoperative presence of methicillin-resistant Staphylococcus epidermidis (MRSE) or S. aureus (MRSA). The former is the most common cause of endophthalmitis, and the latter is the most common cause of infection after refractive surgery.
“This study documents the highest rate of MRSA and MRSE in normal cataract patients to date, and suggests that the risks are increasing,” Dr. Donnenfeld said.
In contrast to previous studies by other investigators, the research by Dr. Donnenfeld’s group did not support a finding that health care workers and their close contacts had the highest risk of carrying resistant bacteria. “We saw a trend toward health care workers having greater risk, but it was not statistically or clinically significant,” Dr. Donnenfeld said. “So, while health care workers continue to have a risk, the general population is catching up.”
The results of this study suggest that ophthalmologists should take extra steps to prevent endogenous MRSE or MRSA from causing postoperative infections in patients, even if there are no obvious risk factors, Dr. Donnenfeld said. His infection prevention protocols include:
1 Moshirfar, M. et al. Ophthalmology 2007;114(4):686–691.
Dr. Donnenfeld is a consultant to Allergan, which funded the research.
Investigation Into DSAEK Failure Rates
One of the most notable recent advances in the treatment of Fuchs’ dystrophy and other forms of endothelial dysfunction is Descemet’s stripping automated endothelial keratoplasty (DSAEK), an increasingly accepted alternative to full-thickness corneal transplantation in these patients. Yet despite the successes with this approach, DSAEK grafts do fail.
The authors of one study document the incidence and risk factors associated with DSAEK graft failure, reviewing the first 500 consecutive DSAEK surgeries performed at Duke Eye Center from December 2005 to December 2008.
They designed a comparative case-control study. It included eyes with a failed DSAEK graft that required repeat surgery, and controls were defined as eyes in which the DSAEK successfully improved corneal edema.
The authors found that graft failure occurred in 24 (4.8 percent) eyes, “a figure on par with the literature,” according to Derek W. Del- Monte, MD, a third-year ophthalmology resident at Duke University.
Interestingly, while there does exist a learning curve when performing DSAEK, there were not an excessive number of failures early in the study. In fact, the failure rate remained steady throughout. “We are constantly trying newer techniques with more complex patients, which could explain this finding,” Dr. DelMonte said. This is in contrast to the graft dislocation rate, which is more likely to improve with more surgical experience, he said.
The statistically significant risk factors for graft failure included a prior history of glaucoma, a tube shunt in the anterior chamber and prior failed penetrating keratoplasty (PK).
In addition, pachymetry measurements on the failed grafts (cases) were an average of 705 µm preoperatively, while those that did not fail (controls) averaged 667 µm preoperatively. And prior to surgery, best-corrected visual acuity was 20/400 in patients whose grafts failed and 20/125 in the patients whose grafts did not fail.
“The take-home message is that DSAEK represents a viable alternative to full-thickness PK in most patients with endothelial dysfunction, with a relatively low graft failure rate,” Dr. DelMonte said. “It also gives clinicians an early clue as to who may be at higher risk for graft failure, including patients with glaucoma, those with a tube shunt and those patients who have failed PK surgery.”
Study coauthor Natalie A. Afshari, MD, associate professor of ophthalmology at Duke University, noted that while DSAEK grafts may fail in certain high-risk patients, “full thickness corneal transplants can also fail. This should not dissuade us from performing the DSAEK procedure. In my mind, DSAEK is probably the more advantageous procedure compared to fullthickness corneal transplantation in most patients, with fewer complications.”
—Lori Baker Schena
Phakic ACIOL Holds Up
An anterior chamber phakic IOL designed to correct stable high myopia appeared to be welltolerated four years after insertion, according to a report by Michael C. Knorz, MD, professor of ophthalmology at the University of Heidelberg in Mannheim, Germany.
The phase 3 study of 513 eyes was designed to evaluate endothelial cell density (ECD) and morphology, following implantation of the AcrySof angle-supported phakic IOL (Alcon).
Evaluation of central and peripheral images of the cornea, obtained during prospective global clinical trials, revealed that the average surgery-induced central ECD percentage loss was 2.94 percent (n = 488) at six months, compared with preoperative values. Between six months and four years, the mean annualized loss was 0.64 percent centrally and 1.11 percent peripherally (n = 65).
Dr. Knorz said that—within the range of normal cell loss—2 percent of corneal endothelial cells is considered the upper limit.
The single-piece IOL was designed to correct moderate to high levels of myopia, with refractive powers ranging from –6 D to –16.5 D. Because it is foldable, the lens can be implanted through a 2.4-mm to 2.6-mm incision, Dr. Knorz said.
Parag A. Majmudar, MD, associate professor of ophthalmology at Rush University Medical Center, Chicago, and chairman of the Refractive Surgery papers committee, said that as the limitations of LASIK have become evident, the desire for noncorneal surgical alternatives to treating myopia has intensified. Surgeons would welcome an anterior chamber lens that can be introduced through a small incision, he said, noting that currently, only two phakic IOLs are FDA-approved. One requires a large incision; the other is designed for the posterior segment.
An Alcon spokesperson said FDA approval is expected in early 2011.
Dr. Knorz is a paid consultant for Alcon. Dr. Majmudar is a consultant/ speaker for AMO, Alcon, Allergan, B&L, Inspire, IOP and Ista, but he has no financial interest in the subject matter herein.
Improper Drop Instillation
Patients may claim to administer their glaucoma drops correctly, but one study found that approximately two-thirds of them were unable to do so. Lead investigator Alan L. Robin, MD, of Johns Hopkins University, referred to the Early Manifest Glaucoma Treatment Study, which revealed that more than 50 percent of treated patients experienced a progression in glaucoma: “We wanted to know why and found that the medicines never reached the targeted locations in many cases.
“Our research showed that patients were instilling a mean of 1.8 drops per administration,” said Dr. Robin. “This is a major issue because, at almost double the prescribed dose, patients will run out of their medication early and have to pay an additional cost to make up the difference, take it at inadequate levels or not use it at all.
“Ninety-five percent of study patients had been instilling their drops for more than one year—these were people who were experienced and should have been experts,” said Dr. Robin.
The potential for infection was also significant. In addition to dispensing more than the prescribed dose, the vast majority of patients—more than 98 percent—did not wash their hands prior to administration. Furthermore, 40 percent of patients had difficulty instilling the drop without touching their eye.
“We routinely ask patients if they are having trouble instilling drops, and they typically respond that they are not. Asking the question is obviously not enough. There is a disconnect between what patients say and what actually happens. Do not assume anything, and watch patients who instill their own drops to make sure they are doing it correctly,” said Dr. Robin.