In early March 2010, Glaucoma Today's second annual Innovative Glaucoma Surgery Symposium was held in Naples, Florida. Attendance at this meeting was by invitation only, and the audience and presenters included clinicians, scientists, and members of industry. The goal was to create an open environment in which both the attendees and the panelists could freely discuss cutting-edge topics in glaucoma. Richard Lewis, MD, and Iqbal Ike K. Ahmed, MD, served as the course directors.
The 1-day symposium focused primarily on ways of restoring outflow in glaucoma surgery without using a subconjunctival reservoir. Presenters and attendees also discussed new instrumentation, enhancing visualization of the target tissue, clinical matters, and device development. This article provides an overview of the day's offerings.
HEALING RESPONSE AFTER INTERVENTION
IN SCHLEMM'S CANAL AND THE
SUPRACHOROIDAL SPACE
Returning to the meeting this year were Carol Toris, PhD,
and Haiyan Gong, MD, PhD, each of whom presented basic
science concerning Schlemm's canal. Dr. Toris gave an excellent
review of electron microscopy of the canal and the surrounding
structures.1 Dr. Gong led a discussion of the
histopathology of Schlemm's canal and the collector channel
system.2 Topics of interest included how, in primary
open-angle glaucoma, there is a collapse of Schlemm's canal
and a shorter scleral spur.
Diamond Tam, MD, presented a case of a patient who underwent surgery with the Solx Gold Shunt (Solx, Inc., Waltham, MA). His video showed that a membrane had covered the device, causing its failure.3 Attendees debated whether the membrane was endothelial downgrowth or fibrovascular material from the choroid. An overwhelming majority felt that a typical wound healing response had caused a fibrovascular encapsulation of the implant, as occurs with conventional glaucoma drainage devices.
CURRENT RESEARCH IN CONVENTIONAL
AND UNCONVENTIONAL OUTFLOW
John Samples, MD, provided an update on conventional
suprachoroidal flow. He speculated that a proteoglycan
called versican is likely a central aspect of
damage to the trabecular meshwork, and Q-dot
nanoparticles can be used to mark the anterior segment
outflow to determine the location of the versican.
Moreover, Dr. Samples stated that, in the future,
surgeons may need to assess new surgical devices relative
to blood pressure and postoperative flow. He concluded
by noting that glaucoma has many phenotypes,
so one surgery will not suit all patients. Each phenotype
will vary by diurnal fluctuation, corneal thickness,
and ganglion cell loss. Interventions to treat glaucoma
should stop the vicious circle of pressure-sensitive ganglion
cell loss and optic nerve damage.4
Drawing on his extensive research on the structure of Schlemm's canal, Dr. Johnstone explained that, with age, anterior placement of the uveal tract in combination with vector forces on the ciliary body and scleral spur caused Schlemm's canal to close.5 This concept may help to explain why cataract extraction sometimes opens Schlemm's canal.
Dr. Toris described the physiology of the suprachoroidal space,6 and Dr. Gong discussed preferential aqueous outflow.7
At the 2009 symposium, attendees voiced a need for an angiogram of the canal outflow system. This year, Joel Schuman, MD, described his work imaging porcine outflow and how it one day might help with presurgical planning and basic glaucoma diagnostics. In preparation for imaging this outflow, he described a spectral domain OCT in a pig's eye. If surgeons had the ability to identify obstructed areas of the canal, they could target which areas to avoid and which ones to treat with new surgical devices or technologies. In cases of severe obstruction, surgeons might decide to avoid accessing the canal altogether and opt instead for a more traditional glaucoma filtering procedure.8
INSTRUMENTATION AND ENHANCED
VISUALIZATION OF THE TARGET TISSUE
Dr. Johnstone and Dr. Ahmed stated that postoperative
flow can show a reflux of blood through the collector
channels if the eye is in a homeostatic position. Like
other such circulatory loops, the aqueous circulatory
loop returns aqueous to the heart. Moreover, the rate
of flow in the collector channels changes—as does the
IOP—with the pulse, ocular motion, and blinking. As
the IOP increases, the pulsatile flow or stroke volume
rises to decrease the IOP and restore homeostasis. More
aqueous in the aqueous veins and less reflux of the
blood can be observed. In glaucoma, however, pulsatile
flow is reduced.9
Dr. Lewis delivered a video presentation of TrueVision (TrueVision Systems, Inc., Santa Barbara, CA). Rather than operate while looking through a microscope, the surgeon wears 3-dimensional glasses and looks at a television screen displaying the surgery in three dimensions. Dr. Lewis showed footage of both canaloplasty and surgery using a gonioprism.10
The RetCam 3 (Clarity Medical Systems, Inc., Pleasanton, CA) is frequently used for pediatric retinal imaging for retinopathy of prematurity, in-office gonioscopy, and the documentation of shaken baby syndrome. Robert Chang, MD, made the case for the RetCam's use for goniography. He noted that the unit could assist with visualization of the angle as well as, perhaps, tube shunts and the Ex-Press mini glaucoma shunt (Alcon Laboratories, Inc., Fort Worth, TX). Unlike endoscopic viewing, no corneal incision would be required. 11 Attendees noted the limitations of this technique such as the need to hold the device with one hand, which means that both hands are not free for surgery. Some suggested that a mechanical arm might free the surgeon's second hand. Other attendees noted that the incorporation of a zoom feature could be of benefit for ab interno procedures.
DEVICE DEVELOPMENT:
GAINING CLINICAL ACCEPTANCE
Sean Ianchulev, MD, stated that there are currently
548 ongoing glaucoma studies compared with 532 on
age-related macular degeneration and 361 on cataract.
Of the glaucoma studies, he said that 283 are sponsored
by industry, 24 are device studies, and 198 are in the
phase of active recruitment.12 Attendees discussed how
each new technology changes the treatment paradigm.
The group noted that the difficulty with clinical trial
design is a frequent lack of clearly defined IOP outcomes
and the existence of multiple definitions of success.
Moreover, attendees mentioned the problems of
variability in IOP, the confounding effects of medications,
and the confusion raised by single IOP outcomes
versus composite end points. Certainly, the focus on
innovation for earlier surgical treatment in glaucoma
has increased. The future will doubtless bring greater
regulatory scrutiny of devices and a more robust 510(k)
process with more specific guidelines from the
American National Standards Institute for clinical trials
using evidenced-based medicine.
Closing out the symposium, Dr. Ahmed presented the results of a large clinical trial and discussed how to implement them in practice. Specifically, he reviewed the clinical data for the iStent (Glaukos Corp., Laguna Hills, CA), with the majority of information on combining phacoemulsification and implantation of the device with typical targets for mild-to-moderate glaucoma.13 A spirited question-and-answer session followed. Most of the controversy centered on the near equivalence of the IOP in the reported data among the patients who underwent phacoemulsification alone and those who underwent phacoemulsification combined with placement of the iStent, while the number of medications used in the latter group was lower. Many in the audience felt that this was an appropriate indicator of success, but others argued that the study was not sufficiently vigorous to permit conclusions. A criticism was that the target IOP was not standardized, but other attendees stated that the overall percentage of decrease in IOP is important. With only a few dissenters, the group concurred that it would be worth incorporating into practice a procedure that achieved an IOP similar to the preoperative pressure but with one fewer medication.
CONCLUSION
The Innovative Glaucoma Surgery Symposium
proved to be a useful exchange of information and
ideas by surgeons and representatives from industry.
The physicians present were all committed to surgical
innovation and drew on extensive personal experience
with techniques that are untraditional and avoid a
dependence on filtering blebs. This meeting should
become a model for gathering people together with
the goal of creating real and expedient solutions for
individuals with glaucoma.
Steven R. Sarkisian Jr, MD, is a clinical assistant professor at The Dean A. McGee Eye Institute of the University of Oklahoma in Oklahoma City. He acknowledged no financial interest in the products or companies mentioned herein. Dr. Sarkisian may be reached at (405) 271- 1093; steven-sarkisian@dmei.org.
