Since the advent of pars plana vitrectomy in the 1970s, technological advances in instrument design and surgical techniques have resulted in better outcomes for patients and streamlined operating procedures. One need only talk to operating room personnel who vividly remember the six- to eight-hour vitrectomy procedures of the '70s or '80s to realize that things have certainly changed for the better.

Improvements in procedure have broadened the indications for vitreous surgery. Today surgeons routinely treat posterior segment pathology such as vitreomacular traction, choroidal neovascularization, vitreous opacities and more mild epiretinal membranes that once might have been considered foolhardy.

What can be done to make an excellent procedure even better? To answer this, we look to our colleagues performing cataract surgery. Small incision cataract surgery has revolutionized lens removal, permitting less traumatic surgery resulting in rapid visual rehabilitation. The same should be true for vitreoretinal surgery; less surgical trauma permitting more rapid recovery, while at the same time eliminating the more tedious aspects of the surgery.

The 25-ga. transconjunctival vitrectomy system (Bausch & Lomb, 25-TVS) appears to be the next evolutionary step in vitreoretinal surgery. This system was designed through a coordinated effort between the Microsurgical Advanced Design Lab (MADLAB, now located at the Doheny Retina Institute) and Bausch & Lomb. A 25-ga. transconjunctival cannula system permits rapid entry into the eye without extensive conjunctival dissection. The sclerotomies are reduced in diameter from 1.0 mm to 0.5 mm, creating self-sealing incisions and eliminating the need for scleral suturing at the completion of surgery.

Two critical developments were necessary for the initiation of self-sealing transconjunctival standard vitreoretinal surgery: The first was the development of an effective system to enter the eye directly through the conjunctival/scleral, and the second was the development of a vitreous cutter that could produce adequate flow rates through a 25-ga. opening.

Figure 1. Site-alignment cannulas are made of rigid polyamide tubing.

The 25-ga. entry site-alignment cannulas (See Figure 1) are made of rigid polyamide tubing with an inner/outer diameter of 0.57/ 0.62mm. Through the central lumen, a 25-ga. stainless steel stylet (trocar) is placed and used to penetrate the eyewall, its removal opens the flow to the posterior segment. The cannulas can be placed atraumatically in less than one minute and removed in even less time. The infusion line fits through one of the cannulas and does not require suturing to the sclera for stability (See Figure 2).

Figure 2. The infusion line fits through one of the cannulas and does not require suturing to the sclera for stability.

The design of the 25-ga. vitreous cutter is identical to the 20 ga. Lightning Cutter, and permits cutting rates up to 1500 cpm (See Figure 3). The Lightning Cutter is an electrically driven instrument requiring a larger hand piece but delivers smooth high-speed cutting even with the smaller-caliber 25-ga. vitrector. Since the lumen of the 25-ga. vitreous cutter is significantly smaller (0.6 x 0.4 mm for the 25 ga. vs. 0.7 x 0.6 for the standard cutter), higher rates of aspiration are required. In fact, an aspiration setting of 500 mmHg is necessary to efficiently de-bulk vitreous and vitreoretinal membranes. The high rates of aspiration are well- matched with infusion pressure set to 35 mmHg. In general, the infusion and aspiration rates are approximately seven times less at 25-ga. than at 19 ga., but remain balanced, minimizing the chance of globe collapse. As a result of lower flow rates, much less infusate is necessary for these cases, a potential boost for overhead expenses.

Figure 3. The design of the 25-ga. vitreous cutter is identical to the 20-ga. Lightning Cutter and permits cutting rates up to 1500 cpm.

A variety of vitreoretinal instruments have been designed and are currently available for use through the microcannula system including: light pipe, vertical scissors, micro-pic forceps, rigid intraocular picks, tissue manipulator-pic, aspirator, and an extendable curved pick.

The extendable curved pick is designed to remain retracted into the shaft of the 25-ga. instrument for insertion. Inside the eye the retractable pick is extended permitting a curved configuration that is parallel to the retinal surface (See Figure 5). This pick is effective for epiretinal and internal limiting membrane removal and aids in vascular sheathotomy in cases of branch retinal vein occlusion. The ergonomic hand piece facilitates fine intraocular manipulations.
The smaller caliber of these instruments has one notable drawback, reduced stiffness of the instrument shaft. As a result, the shafts are more flexible making rotating the eye during the surgery more difficult. However, the instruments are resilient and can tolerate significant stress without permanent bending or breaking.

Figure 5. Inside the eye the retractable pick extends, permitting a curved configuration parallel to the retinal surface.

Using this system we have successfully performed vitreous surgery for a wide variety of indications (See Table 1). In general, the system works extremely well for more routine surgical indications such as macular diseases and nonclearing vitreous hemorrhage. In cases requiring more extensive dissection, such as severe proliferative diabetic retinopathy, retinal detachment with proliferative vitreoretinopathy, and severe open globe injury, this system is probably not appropriate, in part because of the lack of currently available instrumentation, but also because reduction in effective levels of aspiration and smaller port size limits removal of dense membranes.

Table 1

Indications for 25 ga. vitrectomy

Nonclearing Vitreous Hemorrhage

Epiretinal Membrane

Macular Hole

Vitreous Biopsy

Rhegmatogenous Retinal Detachment without PVR

Vascular Sheathotomy

Removal of Retained Cortical Material

Vitreomacular Traction Syndrome

Traction Retinal Detachment

The system does not have a companion 25-ga. fragmatome, so that in cases of retained nucleus at least one larger sclerotomy is necessary. The 25-ga. cutter can remove retained cortical material without clogging the system, although the time necessary to remove the cortex will be increased over the larger vitrectors.

Use of the 25-ga. system does entail a learning curve to maximum efficiency, but the curve is short for the adaptable surgeon, and most appreciate the potential benefits of the system after only one use. The ideal first cases for trial of this system are eyes requiring epiretinal membrane removal, as most have a preoperative posterior vitreous separation.

There are a number of potential drawbacks of a 25-ga. sutureless system, the most obvious being hypotony and increased risks of endophthalmitis. Since the sclerotomies are not sutured after the procedure, a 24- to 25-ga. opening in the sclera remains (cannula slightly larger than 25-ga.). The opening is often plugged internally with vitreous or may be sealed with overlying tenons. Despite this there are times when the scleral opening may remain leaky.

To eliminate the chance of a direct conduit between the sclera and the environment, the conjunctiva should be displaced prior to inserting the cannula so that after removal of the cannula the conjunctival opening will not match in location the scleral opening. A leaky sclerotomy will thus create only a conjunctival bleb. In most cases the intraocular pressure on the first postoperative day is between 10 and 15 mmHg. A few patients will have pressure < 5 and some may even have elevated intraocular pressure (>30). Having performed nearly 50 cases with the 25-ga. system, I have experienced no complications related to hypotony in the postoperative period (i.e. hypotony maculopathy or large choroidal detachment) and in all patients the intraocular pressure was >10 mmHg at the one week postoperative exam.

With the advent of sutureless cataract surgery there was initial concern that the approach might lead to an increased incidence of endophthalmitis. Despite case reports of endophthalmitis following clear cornea sutureless cataract surgery, a significant increased risk of infection is unlikely. Endophthalmitis is extremely uncommon following vitreous surgery but we are concerned that 25-ga. sutureless surgery may result in an increased risk of endophthalmitis, though I know of no case of endophthalmitis associated with the use of this system. In theory, leaving the sclerotomies open in a hypontous state might result in the influx of bacteria. Also, the reduced amount of fluid flowing through the eye might be a second mechanism of infection. A possible explanation for why endophthalmitis is far less common following vitrectomy than cataract surgery is that the infusate flowing through the eye dilutes or flushes out organisms that might enter the eye during the procedure. By reducing the amount of infusion with the 25-ga. system, we may also lose this potential benefit.

The principle of surgical evolution has always been to make procedures less invasive. In general, less invasive means quicker and better recovery following surgery. The 25-ga. system should offer many of our patients a chance at a less invasive but safe approach to their eye disease, resulting in an overall better experience during and following the procedure. 

Dr. Pieramici is co-director of the California Research Foundation, 515 E. Micheltorena, Santa Barbara, CA.  Contact him at dpieramici@ yahoo. com. Dr. Fujii is an instructor at Doheny Retina Institute.

Suggested reading
1. Au Eong KG, Fujii GY, et al. A new three-port cannular system for closed pars plana vitrectomy. Retina 2002;22(1):130-2.
2. Fujii GY, Au Eong KG, et al. A new extendable flexible pick for subretinal dissection. Retina. 2000; 20(5):570-2.
3. Fujii GY, De Juan E Jr, et al. Initial experience using the transconjunctival sutureless vitrectomy system for vitreoretinal surgery. Ophthalmology 2002;109(10): 1814-20.
4. Fujii GY, De Juan E Jr, et al. A new 25-gauge instrument system for transconjunctival sutureless vitrectomy surgery. Ophthalmology 2002;109(10): 1807-12.