Fig. 13.1
The inner diameter of a 23G trocar is 23G but the outer diameter is 22G. A 23G trocar has therefore a 22G sclerotomy. The outer diameter of a 27G trocar is 25G. It is obvious that a 25G sclerotomy is water-tighter than a 22G sclerotomy
27G has therefore no leakage, the globe is watertight without sutures and the tiny instruments cause less intraoperative trauma.
We are convinced that size does matter. Size was the major motivator to switch from ECCE to phacoemulsification. The small incisions of phacoemulsification are better in almost all aspects than the gaping wound of ECCE: faster postoperative recovery, improved visual results, less astigmatism and a closed and safe globe.
The same principle applies for vitrectomy. Small sclerotomies and small instruments induce less intraoperative trauma, less leakage, prolonged postoperative gas-filling and faster postoperative recovery. The principle “the smaller the gauge, the better” is evident.
The Dilemma of the Law of Hagen–Poiseuille
Physics are against small-gauge vitrectomy. The Hagen–Poiseuille equation states that the flow is proportional to the fourth power of the internal diameter of a lumen. See Fig. 13.2. If for example the diameter of the lumen is reduced by half then the flow resistance will increase 16-fold. This is the case if you switch from 23G to 27G.
Fig. 13.2
Hagen–Poiseuille equation (Flow ≈ diameter 4 ) and its relevance for vitrectomy
This striking difference in flow between 23, 25 and 27G can be shown in performance measurements of the vitreous cutter. Continue with the next chapter.
A 27G TDC Cutter Is as Powerful as a Regular 25G Cutter
If you measure the required time for a vitreous cutter to aspirate artificial vitreous then you will find that a 27G cutter is 30 % slower than a 25G cutter. And the latter is 30 % slower than a 25G cutter (Fig. 13.3).
Fig. 13.3
Performance comparison of a cutter in relation to the Gauge. Measured is the aspiration time of artificial vitreous (Courtesy DORC)
This physical obstacle can only be overcome with more powerful vitrectomy machines and especially a new design of vitreous cutters (Videos 13.1 and 13.2 ). A novel 27G TDC cutter (for details see below) is as fast as a 25G regular cutter (Video 13.5).
Double Cut Vitreous Cutter
History of 27G
27G vitrectomy was developed in 2010 from Oshima and colleagues in Japan. The old 27G cutter had lower fluid dynamics and less cutting efficiency than a 25G cutter. The same applied also for aspiration and infusion rates. These obvious disadvantages of 27G became obsolete after a novel type of vitreous cutter was introduced. The companies DORC (Netherlands) and Geuder (Germany) developed this novel double-cut citreous cutter (Fig. 13.4).
Fig. 13.4
The novel Twin duty cycle (TDC) cutter. The cutter has 2 open cutting ports and a second cutting blade
History of Double-Cut Vitrector (Videos 13.1, 13.2, 13.3, and 13.4)
The initial idea for the novel vitreous cutter came from Hayafuji and colleagues from Japan in 1992 (see Fig. 13.5). After a journey of trial and errors the final vitrector was developed in 2013 from DORC. This new vitreous cutter has two open cutting ports and a second cutting blade. It is named Twin Duty cycle (TDC) cutter. This new invention comprises two new features: 1) a permanent flow and 2) two cutting blades.
Fig. 13.5
Historical development of TDC cutter (Photo courtesy DORC)
The New TDC Cutter Is Much faster than the Regular Cutter
Video 13.5: Left regular cutter Right TDC cutter 6000 cpm/450 mmHg
Video 13.6: 6 27G-asteroid hyalosis_TDC cutter
The two cutting blades have the result that the cutter cuts two times during one movement, effectively doubling the cutting speed. The vitreous cutter has a cutting rate of 8000 cuts/min. But the actual cutting rate with two cutting blades is 8000 × 2 =16,000 cuts/min, which reaches new dimensions. The second novelty is a continuous and even flow due to the two open cutting ports. This novel technology reduces vitreous traction, decreases the surgical time and increases the safety of surgery (Figs. 13.6 and 13.7).
Fig. 13.6
Illustration of a TDC cutter in action. One movement (forwards and backwards) results in two cuts. In old cutters one movement (forwards and backwards) results in one cut. The novel two blade cutters have therefore the same movement frequency like old cutters but a double cutting frequency: 5000 × 2 = 10,000 cuts/min
Fig. 13.7
Comparison of an old 23G cutter versus a new TDC 27G cutter. The new cutter has a stable flow in the complete cutting range from 0 to 8000 cuts/min. The old cutter has a high aspiration at 1000 cuts/min and a low aspiration at 8000 cuts/min
The New TDC Cutter Has a 1.5–1.75 More Power Than a Regular Cutter
Video 13.5: Left regular cutter Right TDC cutter 6000 cpm/450 mmHg
Figure 13.8 shows that the TDC cutter has 1,5× higher performance than a regular cutter. This results in a fast core vitrectomy.
Fig. 13.8
Performance comparison of TDC cutter vs. regular cutter (Courtesy DORC)
The small 27G sclerotomies and instruments enable intraoperatively a minimal surgical trauma and postoperatively a watertight globe; postoperative hypotony does not occur with 27G. All surgical indications which require these features make them to excellent candidates for 27G:
- 1.
Children eyes: No sutures necessary
- 2.
Long eyes: No sutures necessary, excellent tamponade
- 3.
Uveitis eyes: 27G causes minimal postoperative inflammation
- 4.
Silicone oil removal: Less hypotony compared with 23G and 25G
- 5.
Retinal detachment: The small sclerotomies result in less leakage and prolonged gas tamponade
- 6.
Lens exchange: Less hypotony compared with 23G
Fig. 13.9
Intraoperative status of 3-port vitrectomy with 27G trocars from DORC, high infusion line, vitreous cutter and a light fiber
Fig. 13.10
A histological section of a sclera after removal of a 27G trocar. The sclerotomies are watertight, require no suture and no hypotony is present the day after. This is an excellent feature for long eyes and children eyes
27G Is Less Useful for Following Pathologies
These indications have a low risk of postoperative hypotony. There is not really a difference to 23G and 25G regarding this important feature:
- 1.
Macular pucker: No advantage to 23G except of faster postoperative recovery
- 2.
Macular hole: better tamponade with 27G but clinically no difference
If you, however, wish a white eye after 1 week follow-up like after phacoemulsification, then you should again choose 27G.
The following videos illustrate the novel features of 27G and the TCD cutter:
Video 13.6: 27G–asteroid hyalosis_TDC cutter
Video 13.7: Diabetes_27G_EVA
Video 13.6: Tractional detachment
Pediatric Vitrectomy
General Introduction
We operate all children eyes with 27G. The reason for this is that the sclera of young eyes is soft and leaks more easily than an adult eye. In addition, we perform a perpendicular and not a lamellar insertion of trocars due to the risk of damaging the lens. If you perform a perpendicular insertion with 23G or 25G trocars you need to suture the sclerotomies. In 27G a suture is not necessary and this is also valid for newborn eyes.
Physiology of a Neonate Eye
In the neonatal eye, the pars plana region is incompletely developed and almost not existent. The axial length of a newborn eye is 16 mm in the 34th gestational week and 17 mm in the 40th gestational week. The anterior retina lies just behind the pars plicata. The site of sclerotomy is therefore much closer to the limbus. The sclerotomy should be performed 1.0 mm behind the limbus. See Fig. 13.11. The newborn eye has a huge lens compared to the globe. A big lens and a short sclerotomy site allow only a small canal to insert and manoeuvre the instruments. Utmost care is needed in inserting a vitreoretinal instrument or in administering an injection, because it may cause inadvertent lens touching, traction on the vitreous base, and retinal damage.
Fig. 13.11
Site of sclerotomy in relation to the age
The vitreous body is completely intact; there is no degeneration of the vitreous body present. The vitreous body is very firmly attached to the retina; a PVD is virtually not possible. If you try to induce a PVD you risk creating a retinal tear.
Retinal Detachment Secondary to ROP
A retinal detachment for ROP is a tractive retinal detachment and not a rhegmatogenous retinal detachment. Due to the fact that a retinal break is not present, there is no need for a tamponade or even postoperative posture. The aim of surgery is to remove the vitreous body in order to relieve retinal traction. The retina will reattach in a few days after surgery. In addition an anti-VEGF injection is needed to reduce the vascular activity and remove the pathophysiologic stimulus of the tractive detachment. We use ranibizumab (Lucentis®) because the half-life in serum is lower compared to bevacizumab (Avastin ®). Regarding the dose, we use 50 % adult dose, i.e. 0.025 ml Lucentis.
In a 4 A and 4B detachment, we have an excellent experience with the sutureless 27G technique; to perform a lens sparing vitrectomy and inject intravitreal Lucentis.
Timing of Surgery
Timing of surgery is of utmost importance. We only operate ROP stage 4 A (retinal detachment and attached macula) and 4B (retinal detachment and detached macula). See Fig. 13.12. We do no operate stage 5 ROP. Do not operate too late. The risk that you will not succeed is high and the risk that you will have complications is even higher. Try to operate in stage 4 A.
Fig. 13.12
Our treatment algorithm for treatment of ROP
Surgery: Intravitreal Lucentis® Injection
We inject 0.025 ml Lucentis in non-vitrectomized eyes. If possible, we use the microscope in order to see the medication enter the eye. Both eyes are therefore dilated. Mark the sclera 1.0 to 1.5 mm behind the limbus, pierce the eye globe with the syringe and aim towards the optic nerve. The newborn lens is thick and can be easily damaged. Find the tip of the syringe under the microscope. Then inject the medication. Observe that the medication leaves the tip of the syringe.
Surgery: Lenssparing 27G Vitrectomy
Video 13.9: ROP_RE
The surgery is easy but you have to operate absolutely without complications: No lens touch, no retina touch and NO retinal tear. A lens touch will result in a lensectomy and amblyopia. A retinal touch with retinal tear will result in retinal detachment and blindness. Be careful when inserting the trocars and instruments. Aim towards the optic nerve. Perform a central and peripheral vitrectomy. Do not induce a PVD; it is almost impossible in newborn. Do not remove membranes; you may induce a retinal tear. A tamponade is not necessary.
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