Interface vitrectomy describes the use of vitreous cutters, scissors, forceps, and other instruments at the interface between silicone oil, air, or liquid perfluorocarbon (PFO) and residual vitreous, epiretinal membrane, and retina. Vacuum should not be applied to the vitreous cutter or soft tip cannula within the air, oil, or PFO bubble to avoid plugging with oil or air lock, and to reduce the risk of loss of oil or PFO.
For 30 years I have performed removal of residual vitreous traction and performed retinectomy, epiretinal membrane peeling/segmentation/delamination, subretinal surgery, and bipolar diathermy under air and oil. Air stabilizes the retina because of the inherent springlike properties of a compressible gas. Air also reduces unwanted retinal motion, confines bleeding to the airretinal interface, and prevents infusion fluid from flowing into the subretinal space.
THE TECHNIQUE
I developed internal drainage of subretinal fluid and
fluid-air exchange; used simultaneously, these techniques
can be used for the reattachment experiment. If
subretinal air appears, vacuum should be released as
quickly as possible and inspection of the retinal surface
initiated to determine the cause of residual traction.
Residual vitreous can be removed using interface vitrectomy
technique, and the epiretinal membrane, typically
in proliferative vitreoretinopathy (PVR) cases, can be
managed with forceps membrane peeling (Figure 1)
using end-grasping forceps such as the Grieshaber DSP
25-gauge internal limiting membrane (ILM) forceps
(Alcon Laboratories, Inc., Fort Worth, TX). If the epiretinal
membrane is highly adherent, typically in diabetic
traction retinal detachment cases, access segmentation
should be followed by inside-out delamination (Figure
2) with Grieshaber DSP 25-gauge curved scissors (Alcon
Laboratories, Inc.). If residual vitreous or epiretinal
membrane cannot be identified, incremental retinectomy,
not “relaxing retinotomy,” which leaves tissue anterior to the cut, should be used until the retina becomes
attached.
Silicone oil produces viscous dampening, which reduces retinal motion during epiretinal membrane peeling, removal of residual vitreous traction, retinectomy, epiretinal membrane peeling/segmentation/delamination, and subretinal surgery. All of these techniques are easily performed just outside the silicone oil bubble, at or near the retinal surface.
Perfluorocarbon liquids, such as n-perfluorooctane (PFO), can be used for interface vitrectomy in addition to being essential for giant break management, as reported by Chang et al.1 The high specific gravity of PFO (approximately 2X mass) produces both inertial stabilization (2X mass, F=MA) and gravitational stabilization (approximately 2X gravitational force) on the retina. Quiroz-Mercado et al2 developed perfluorocarbon perfused vitrectomy initially to provide oxygenation to the retina during periods of nonperfusion for tumor resection; it was noted, however, that retinal detachments often disappeared during vitrectomy under PFO. The concept behind intraoperative use of PFO is retinal stabilization to offset dissection forces. After traction forces are removed from the retina, PFO causes retinal reattachment because PFO is immiscible in balanced salt solution and subretinal fluid is less dense than PFO and is displaced anteriorly exiting the subretinal space through retinal breaks, drainage retinotomies, or retinectomies. Laser energy settings must be reduced when treating under PFO because the subretinal fluid is completely gone. This is usually not the case with simultaneous fluid-air exchange and internal drainage of subretinal fluid except anteriorly.
REOPERATION WITHOUT
REMOVING SILICONE OIL
Many surgeons unnecessarily remove silicone oil
when reoperating for epimacular membrane or recurrent
retinal detachment. For more than 25 years I have
operated “under” silicone oil when reoperating these
eyes.
Key advantages to this approach include decreased surgical trauma (especially to the lens and cornea), realistic assessment of traction removal, and significantly reduced operating times, cost, and trauma. Reducing damage to conjunctiva, Tenon's capsule, and episclera is especially important if the patient has glaucoma and may require filtration surgery.
Silicone oil produces approximately 50% less interfacial surface tension than air or gas interface with infusion fluid or aqueous humor; therefore, reoperation with oil in place gives a realistic assessment of the relative force due to interfacial tension and retinal surface contraction.
Many surgeons have performed fluid-air exchange, endophotocoagulation, and air-silicone exchange for a PVR case only to find the retina was partially detached the next day because of the surface tension disparity.
Typical operating times are 20 minutes or less for epimacular membrane cases and 30 to 45 minutes for PVR or diabetic traction retinal detachment reoperation. Time savings are significant because it is easier on the patient and OR staffing costs (70%) are reduced.
I have used two-port 25-gauge vitrectomy for reoperation in eyes with silicone oil for the past 5 years and a 20/25 technique during the prior 2 years since 25- gauge technology became available. The 20/25 technique is performed by connecting the Viscous Fluid Control (VFC; Alcon Laboratories, Inc.) containing 1000-centistoke silicone oil to a short piece of tubing connected to the infusion cannula for surgeons who prefer 20-gauge surgery. The preferred 25-gauge twoport method (Figure 3) is performed using the Viscous Fluid Injector (VFI; MedOne, Sarasota, FL) 25-gauge cannula to sequentially inject oil after internal drainage of subretinal fluid reduces the intraocular pressure (IOP). The two-port method is effective because the viscosity of the oil prevents reflux out the 25-gauge cannulas and resultant decreased IOP during instrument exchange.
Forceps membrane peeling, scissors segmentation/ delamination, cutter delamination, retinectomy, internal drainage of subretinal fluid, removal or resection of subretinal traction elements, retinectomy, and endophotocoagulation all work well with silicone oil in place. It is often necessary to remove a preretinal fluid layer and add silicone oil before initiating epiretinal membrane dissection. A vacuum setting of 600 mm Hg to 650 mm Hg is required for cutter removal of residual vitreous or cutter delamination. A maximum linear vacuum setting of 600 mm Hg to 650 mm Hg is required for internal drainage of subretinal fluid unless extreme care is taken to keep silicone oil out of the soft tip cannula. PVR and diabetic traction retinal cases often require retinectomy; this is accomplished by removing contracted, stiff retina, epiretinal membrane, and subretinal fluid or oil together with the cutter. Large vessels should be coagulated first with bipolar diathermy with the tip in contact with the vessel because, unlike infusion fluid, silicone oil is not conductive.
SUMMARY
In summary, understanding the physical properties of
oil, gas, and PFO, and learning the techniques described
above will result in effective, efficient vitreoretinal surgery
in complex cases.
Steve Charles, MD, is Founder of the Charles Retina Institute in Memphis, TN, and is a Clinical Professor in the Department of Ophthalmology at the University of Tennessee College of Medicine. He is a Retina Today Editorial Board member and states that he is a consultant for Alcon Laboratories, Inc. Dr. Charles can be reached via e-mail: scharles@att.com.
_1773249222.png?auto=compress,format&w=75)
