The advancement of vitreous surgery from the 20-gauge (20G) era to the present day Transconjunctival Sutureless Vitrectomy (TVS) has favorably transformed patient outcomes in the surgical management of retinal diseases. The 20G system (O’Malley and Heintz, 1974) has been the gold standard technique in modern vitreous surgery for nearly three decades, beginning from the earliest 17G vitrectomy as introduced by Machemer in 1971. The 20G systems were associated with sutured port closure, longer and irregular wound healing, higher vitreous turbulence, greater incidence of port-related complications like retinal breaks, and a longer surgical time. On the other hand, the trochar and cannula based micro incision vitrectomy surgery (MIVS) are associated with early post-operative recovery, better and uniform wound healing, lesser port related complications, lesser vitreous turbulence and increased patient comfort with earlier visual recovery.
As with any surgical procedure, the decision and planning of vitreous surgery starts with proper and well-planned initial steps, and placement of sclerotomy ports is an integral part of this process. Evolution of the surgical instrumentation over the years has witnessed the modification in the techniques and approaches of construction of the sclerotomy ports. Whether it is a 20 G or a TVS system, complications can occur, even during port placement which can jeopardize the ultimate outcomes of a well accomplished vitreous surgery. Let me discuss the issues with sclerotomy port placement and the tips that one should follow, especially as a beginner.
Choosing the correct gauge
The option of a correct port size was limited when 20G system was into vogue, and the only additional decision to be made was the use of a 4 mm or a 6 mm cannula. With the advent of smaller gauge systems, it becomes imperative to choose the right gauge size of the port, along with the right cutting speed and the mechanics. Among the TVS, while a hypotonic or traumatized globe or extensive proliferative retinal disease may necessitate a 23 G system, a simple vitreous hemorrhage or a macular hole surgery may be easily managed by a 25 G or even a 27 G system. Of course, surgeon’s expertise and comfort are also determinants in choosing the correct gauge size of the ports being used. Maneuvering the smaller gauge instruments may be difficult in an eye requiring extensive membrane dissection.
Choosing the correct location
The most common location of the infusion port placement is chosen to be the inferotemporal quadrant, as the cannula is least obstructed by the lids when the eyeball is maneuvered during the surgery. Similarly, the active and the inactive ports are made in the supero-temporal and superonasal quadrants, depending upon the eye. The port location may be modified, based on the disease (an extensive proliferation may necessitate the placement of infusion port in another location), the ocular surface condition (adhesions/ scars/ scleral ectasia may guide the port placement in a healthier location), a recent surgery (a port placement is usually avoided in a recently operated port location), or a deep-set eye/ comfort of holding instruments for a particular eye. This is also important when an unforeseen vitreous surgery in case of a lens drop is planned during cataract surgery, wherein the intraocular lens placement may need a scleral fixation/ glued IOL technique and the port location is chosen in such a way so as not to obstruct the location of scleral flap/ haptic placement depending upon the surgery.
The surgical sequence
Not all surgical steps are the same, even though the clinical diagnosis may be similar. During the era of the 20G system, the effective decision of initiation of the surgery entailed the amount and exact approach of conjunctival opening, including complete peritomy, partial peritomy, localized conjunctival opening, a possible encirclage placement after the completion of the surgery, and so on. Also, there are situations that demand the placement of a 6mm infusion cannula and the superior ports followed by additional surgical steps like IOL removal/ endophthalmitis vitrectomy/ adequate media clearing through the anterior approach. The infusion is switched on after visualization of the cannula and the surgery is proceeded with. A surgical decision to exchange a 4mm cannula with a 6 mm cannula, or a change of the gauge of the cannula during the surgery may be required, and the surgeon should be prepared for port closure/ conjunctival opening and replacement of the trochar. In that case, the location of the port may need to be modified depending upon the exact cause of switching over to another gauge, like a suprachoroidal or a subretinal location of the initially placed cannula. The sequence of correct assessment, sclerotomy infusion port placement, visualization of the port in the vitreous cavity, securing the infusion cannula, and starting the infusion, followed by superior port construction should always be followed. Extreme caution is advised while making the ports in an extremely hypotonic globe, when a saline injection in the anterior chamber or with a 30G needle through pars plana may be necessary prior to port placement. Also, in an eye with a large choroidal detachment, it may be obligatory to drain the choroidals and form the globe with saline injection prior to the placement of the infusion sclerotomy port.
Examination in the pre-operative period
A sincere word of advice to all the beginners and fellows under training to examine the case record, and the fundus in the pre-operative period, before anesthesia, and after administration of local anesthesia, as well as examine the eye carefully before painting and draping, and finally while sitting on the surgical chair. Apart from focal sources of infection, the surgical decision can change based on the clinical condition at any stage. These include the new appearance or resolution of a pre-existing vitreous hemorrhage, changed configuration of a retinal detachment, resolution of subretinal fluid under a detached retina, or occurrence of a new onset of retinal detachment and so on, which can modify the surgical decision altogether. A possible globe perforation during the administration of local anesthesia is also picked up early, avoiding any surgical surprises at a later stage.
Assessment of the health of conjunctiva
The efficacy of the TVS system depends a whole lot on the health of the conjunctiva, apart from the subconjunctival tissue which helps the port to be self-sealed at the conclusion of surgery. A properly mobilized conjunctiva is adequate enough to cover the sclerotomy site adequately after removal of the ports in most of cases. However, ballooning of conjunctiva after the anesthesia or after the removal of cannula might necessitate a localized peritomy and adequate port closure with suture. A traumatized conjunctiva or a previously operated eye with extensive fibrous scar may necessitate a suture for adequate port closure.
Direction of movement
The sclerotomy port during the era of the 20G system was made with direct entry of MVR blade in the direction of the center of the globe. This needed a thorough clearing of the vitreous at the port site as the chances of vitreous prolapse were always higher. The smaller gauge systems are usually made with an initial oblique direction, with a short intrascleral course, before finally dipping the trochar towards the center of the globe. The direction of the port tract, however, should remain parallel to the limbus at all times. This ensures a better chance of self-sealed wound as compared to a direct entry, as well as keeps the distance between the limbus and port entry site as desired. Even with a peritomy, this oblique direction of trochar entry ensures a stable cannula during the surgery, when a globe hypotony/ manipulation may expel the cannula out inadvertently intraoperatively.
A point to remember here is that the trochar system is sharp, and it exchanges hands between the assisting staff and the surgeon. It should always be passed on with a blunt end pointing towards the receiving hands. Once the active hand is placed close to the desired site, the movement of the hand with a sharp trochar should be avoided. A cotton tip applicator or a toothed forceps is used to hold and mobilize the conjunctiva, preferably from the fornix towards the limbus, and once the trochar enters the sclera, the conjunctival counter traction should be released. This prevents any tearing of the conjunctiva at that location. Also, checking for the bent tip of the trochar, and the presence of cannula on the trochar (it may slip while the trochar is being handed over to the surgeon), before an entry is made is advisable. The bent cannula should be avoided to make sclerotomy ports, as the wound site will be irregular causing improper wound healing, as well as causing undue traction at the vitreous base.
Keep track during the surgery
There are a few issues that need to be addressed here, especially because the trochar cannula systems are being re-used after adequate sterilization. The cannula may acquire an irregular caliber internally and may be pulled out along with the instrument being used during the surgery. This has a slightly higher chance when the trochar entry was directed towards the center of the globe without any intra-scleral course. Also, the infusion cannula system should be secured with sterile tape on the drape, with an adequate amount of mobile tubing so as to permit mobility of the tubing while maneuvering the eye during surgery. An additional cannula should be kept handy when LPFC-Silicone oil exchange is being performed as the cannula can become smudged with silicone oil and the tubing gets expelled during silicone oil injection. Furthermore, the infusion cannula gets blocked with silicone oil as the silicone oil gets pushed into the infusion port while making the superior entries in an oil-filled eye, so, adequate time should be given for the oil to get released from the tubing while silicone oil removal is being done to prevent hypotony of the globe when aspiration is initiated.
Removing the cannula
Pre-placed vicryl suture was an essential step to hold the cannula during a 20G system. I have seen fellows struggling to remove the temporary suture knots around the 20G infusion system at the conclusion of surgery. As the knot gets smudged by blood and fluids after the surgery, holding both the loose ends together and pulling them slightly usually exposes the knot, and the knot can be loosened. Similarly, it was highly advisable to preplace the sutures across the sclerotomy sites prior to removing the plugs to prevent excess turbulence intraocularly. Also, adequate vitreous clearing prior to taking the knot was an essential step for adequate wound healing. With TVS, removing cannula is less time-consuming, and considered an easier step. However, caution is advised to the beginners to give a counter pressure with a cotton-tipped applicator when removing the cannula from a hypotonous globe/gas-filled eye or a defective cannula with bent ends, to prevent a rare complication such as supra-choroidal hemorrhage. As the cannula is a hollow tube, with negative pressure inside, securing a plug over the tube prior to removal reduces the traction on the vitreous base. It is important for any gauge system to have a good vitrectomy done around the port sites before the ports are removed.
During the era of the 20G system, a sclerotomy port within 5-7 days of a previous surgery could be opened by removing the sutures and the same port could be used for the instruments. But during the MIVS system, a sclerotomy has much higher chances of leakage if a previous sclerotomy site is used. However, if the subconjunctival tissue is healthy, making another sclerotomy for repeat surgery within 2-3mm usually stays self-sealing.
As any surgery would entail, there is always a learning curve for every surgical step to be effective and safe. Even if the sclerotomy port construction is a seemingly simple and safe procedure for initiating a vitreous surgery, learning the right way and taking adequate precautions at each step is essential for excellent post-operative patient recovery and comfort, avoiding unwarranted complications.