Letters

To the Editor:

In the July/August issue of Retina Today, an article titled “The Next Generation of Machines for Modern Vitrectomy,” by John Kitchens, MD, and his co-authors of the Vit/Buckle Society presented a review of currently available vitrectomy units. Considering recent advances, in particular the move to microincisional vitreous surgery, this review is particularly important for both beginning and seasoned retinal surgeons. The review of the equipment was presented in a “pro vs con” fashion and provided good (although sometimes subjective) information regarding the pluses and minuses of each platform. The review was adequate, but it would have been easier for the reader to compare the units if they had reviewed the same performance aspects of the different units. For example, a comparison of the lighting of one unit to another, one cutter to another, or one entry system to another, as well as highlighting the best feature of each unit, would have been helpful to enable the reader to quickly and easily assess each unit's strengths.

Although the platforms of the vitrectomy systems were mentioned, no detailed explanation was provided as to the difference between a venturi and a peristaltic vitrectomy unit. With the recent shift to microincisional vitrectomy, control of flow at the cutter tip is an important feature for the modern vitrectomy unit. Venturibased systems are vacuum-driven, requiring connection to a vacuum at the wall. Because vacuum is the only parameter that can be controlled, control of flow in a vacuum-based unit is accomplished by control of the cut rate or duty cycle of the handpiece. Since the early 1980s, vitrectomy in the United States has been predominated by venturi systems. Therefore, when smaller incisions required attention to flow, manufacturers responded by altering the cut rate and duty cycles of the hand cutters. It should be noted that flow can only be measured in the cassette once it has left the eye or by estimation in a vacuum-based or venturi system.

Peristaltic-based systems are flow-based and operate by displacement of fluid over time or by actual flow (mL/sec.) Therefore, the cut rate and duty cycle can be varied without an effect on flow. This allows full utility of the cutter handpiece and potentially could increase the versatility of the unit. In a peristaltic system, the cutter can be used to engage tissue of varying density without concern regarding flow. Additionally, because it does not require a vacuum, a peristaltic unit does not have to be tethered to the wall. Therefore, flow-based vitrectomy is very useful for vitreous base shaving with a mobile detached retina and/or membrane peeling over the retinal surface.

Finally, no fair comparison of equipment should be done without some reference to patient safety. Thankfully, the Department of Health and Human Services has a Manufacturer and User Device Experience (MAUDE) database that logs and documents complaints about surgical equipment. In fairness, it should be noted that a search of the MAUDE database of these units revealed that several complaints were logged against the Constellation (Alcon Laboratories Inc.), and none were logged against either the Stellaris (Bausch + Lomb) or the Associate (Dutch Ophthalmic USA), as of October 2011.

In closing, it is clear that all these systems provide a significant advance in vitreoretinal surgical techniques and efficiency. The authors presented a good discussion of the benefits and pitfalls of each unit but could have been more complete in providing accurate information for your subscribers to consider in their evaluation of this new technology.

SINCERELY,
KEITH A. WARREN, MD

Keith A. Warren, MD, is President and Chief Executive Officer of Warren Retina Associates in Overland Park, KS. He states that he is an advisor to and on the speaker's bureau for Alcon Laboratories Inc., Dutch Ophthalmic USA, and Genentech.

AUTHOR REPLY

To the Editor:

Dr. Warren correctly points out some critical shortcomings of our article. Because of the manner in which the machines were evaluated (each in an isolated manner by different surgeons in diverse OR environments on decidedly nonuniform patient populations) and the fact that each of the authors' opinions was formulated independently, it was difficult to directly compare parameters of each machine. Our attempt was more of a subjective description of hands-on experience with each machine. This approach precludes quantitative comparisons of lighting systems, cutter performance, and other features in a head-to-head fashion, but it is certainly a first step in the right direction.

Dr. Warren's reference to patient safety is both critical and educational. Reference was certainly made to the recall of the Constellation machine in the article. At the time of the article's creation, the presence of the MAUDE searchable database of complaints logged against medical devices and the absence of any such complaints about the Stellaris PC and the Associate were unknown to the authors. We greatly appreciate Dr. Warren bringing this helpful database to our attention and applaud his valuable and relevant commentary on our article.

SINCERELY,
CHRISTOPHER D. RIEMANN, MD FOR THE VIT-BUCKLE SOCIETY RESEARCH GROUP

Christopher D. Riemann, MD, specializes in medical and surgical vitreoretinal diseases at the Cincinnati Eye Institute in Ohio. He states that he receives lecture fees from Iridex, is a paid consultant and receives royalties from MedOne, and holds intellectual properties and equity ownership in MaCor Industries.