Do the Advantages of 25-Gauge
Vitrectomy Outweigh the Disadvantages?
Our answer varies depending on the case because limitations remain.
RAJAT N. AGRAWAL, MD, EUGENE DE JUAN JR., MD
The introduction of pars plana vitrectomy more than 30 years ago changed the way we managed vitreoretinal problems. Since then, there has been a constant evolution of vitrectomy instruments, specifically moving toward smaller instrumentation and greater functionality.1
Machemer's original 17-gauge (1.5 mm diameter) multifunctional instrument was replaced by a 20-gauge system (0.9 mm) designed by O'Malley and Heintz that is still in use. The desire for less invasive approaches that achieve the same or better results has spurred the development and refinement of this surgical approach. 25-gauge transconjunctival sutureless vitrectomy is a major advance in the field of minimally invasive vitreoretinal surgery. It allows surgeons to perform minimally invasive surgical procedures, resulting in better outcomes and easier patient recuperation. The recent article by Carl Awh, MD, in Retinal Physician2 highlighted several advantages of this 25-gauge system:
► Operating time is significantly decreased because there is no need for a conjunctival peritomy or closure of the sclerotomies.
► The smaller scleral wound heals faster; a 25-gauge wound in a rabbit eye is imperceptible after only a few days, even though rabbit sclera is thinner than human sclera.3 In eyes with normal pressure, investigators found no unusual vitreous adhesions at the wound site, suggesting that suturing is indeed unnecessary.
► The instruments are interchangeable.
► The 25-gauge trocar-cannula system allows surgeons to approach the eye from another direction when necessary.
► The cannula system protects the entry site from damage caused by repeated insertion of instruments and the corresponding traction on the vitreous base.
Fujii et al. wrote4,5 that 25-gauge vitrectomy "... shows great potential usefulness," and has "several possible advantages over conventional vitrectomy in select cases." They noted, too, that it does have limitations. The areas where improvement is needed, and what can be done about them:
Size is the obvious constraint of this technology. The 25-gauge opening in the sclera limits the size, and possibly the shape, of the instruments that can be used. Situations that require the use of larger instruments, such as the removal of an intraocular foreign body, might not be treatable using this system. Modifying the procedure by enlarging the sclerotomy to allow the use of a larger instrument negates the advantages of using the 25-gauge system.
The smaller gauge vitreous surgery system requires special instruments. One example of this is the development of a "flexible-extendable" pick with a relatively blunt tip to be used for blunt dissection in surgical procedures, such as a sheathotomy for branch venous occlusion. The development of multifunctional instruments may be more difficult because the small entry port limits the available space. However, we foresee the development of better miniaturized light sources that will allow integration of the illumination source with the functional instrument.
Lack of instrument rigidity. The technology is currently limited by the instruments' lack of rigidity, which can affect how we bimanually move the operative field, using two superior ports of entry. The small caliber of these 25-gauge instruments makes it more difficult to use them in this way. However, the problem is more of an adjustment. The wide-field viewing systems most surgeons use provide an adequate view of the vitreous cavity. And it is likely that future instruments will be made more rigid, providing surgeons with nearly the same capabilities as the 20-gauge instruments. Also, the instruments that are currently used with 25-gauge systems are more delicate than the 20-gauge instruments; extra care is needed in handling them.
Endoillumination. This was an initial problem with 25-gauge surgery. Because the diameter of the light source was smaller, approximately 40% less light was available during surgery than with the current standard 20-gauge probe. But recent modifications and new light sources have improved the situation. Diffuse illumination is now available with the Chandelier system, and new light sources, such as the Xenon system, provide effective intraocular illumination.6,7
There is a significant learning curve for surgeons using a 25-gauge vitrectomy system. Surgeons must become familiar with the instruments and their capabilities before they become proficient with the system. Using the 25-gauge system and its special instruments can be challenging. Adequate time should be provided for the surgeon to develop a feel for the set-up before it becomes a regular feature in the operating room. The smaller port diameter and lower infusion and aspiration rates make it essential to change the machine settings. We recommend an aspiration rate of 450 to 550 mmHg, with a bottle height of 50 to 70 cm (30 to 50 mmHg), and a cut rate of 1500 cuts per minute.
WHEN IT WORKS WELL AND WHEN IT DOESN'T
In these particular situations, use of 25-gauge technology in its present form is limited:
Intraocular foreign bodies. The foreign bodies are usually much larger than the 25-gauge sclerotomy port. Also, currently available instruments cannot manipulate the intraocular foreign body.
Ocular trauma. Organized vitreous bands cannot be managed with a 25-gauge system.
Thick scars. The scissors tips do not generate sufficient force to cut through scar tissue.
Extensive membranes. Current instruments are ineffective for conditions such as complicated diabetic retinopathy.
Currently, a 25-gauge system works well for procedures that do not require extensive vitreous dissection, such as the management of simple vitreous hemorrhage, removal of epiretinal membranes, repair of macular holes, and repair of uncomplicated retinal detachment.
Indications for the use of a 25-gauge system have increased exponentially since it was first devised. Some surgeons have found the system to be useful but time-consuming in difficult cases. Potentially, this system would be beneficial in cases such as proliferative vitreoretinopathy because it would save time during the opening and closing procedures.4
LOOKING TOWARD THE FUTURE
Interest in and experience with 25-gauge vitrectomy is increasing, as evidenced by the number of presentations on this topic in meetings and other venues. As noted above, this relatively new technology is already being refined. As it develops over time, we will see modifications in the instrumentation and in its surgical use.
Future modifications in vitrectomy instrumentation must achieve a balance between incision size and maximum functionality: making the instruments ever smaller may not make them better.4 While not fully replacing the 20 gauge system, the 25-gauge approach appears to be a new surgical tool. As of today, the 20-gauge vitrectomy system maintains its place in the toolbox of the vitreoretinal surgeon. But its full functionality may not always be required. In such situations, the 25-gauge system allows the surgeon to perform a less invasive procedure that provides patient with a shorter and easier recuperation.
We believe that the 25-gauge vitrectomy system, even with its current limitations, is superior to the 20-gauge system in many cases. Case selection remains important with the present system, although future technology might allow us to use this system for most of the cases we encounter in our practices.
Address correspondence to Rajat Agrawal, MD, Doheny Retina Institute, 1450 San Pablo Street, Los Angeles, Calif. 90033. Telephone: (323) 442-6776. E-mail: firstname.lastname@example.org.
From Doheny Retina Institute, University of Southern California, Los Angeles, Calif. Dr. Agrawal has no financial interest in the products discussed in this article. Dr. de Juan is a consultant for Bausch & Lomb.
For a different perspective on this question, see page 51 of the previous issue of Retinal Physician, which was published in August.
1. Machemer R, Buettner H, Norton EW, Parel JM. Vitrectomy: a pars plana approach. Trans Am Acad Ophthalmol Otolaryngol. 1971;75:813-20.
2. Awh CC. Do the advantages of 25-gauge vitrectomy outweigh the disadvantages? Retinal Physician. 2004;1:51-3.
3. Trese M. Discussion. Ophthalmol. 2002;109:1813.
4. Fujii GY, de Juan E Jr, Humayun MS, et al. A new 25-gauge instrument system for transconjunctival sutureless vitrectomy surgery. Ophthalmol. 2002;109:1807-12.
5. Fujii GY, de Juan E Jr, Humayun MS, et al. Initial experience using the transconjunctival sutureless vitrectomy system for vitreoretinal surgery. Ophthalmol. 2002;109:1814-20.
6. Awh CC. New illumination devices for vitreo-retinal surgery. ASRS presentation 2004, San Diego.
7. Chow DR. Shedding some light on current endoillumination. ASRS presentation 2004, San Diego.