Micro Incision Vitrectomy Surgery (MIVS)

Micro Incision Vitrectomy Surgery or more commonly known as MIVS systems have evolved significantly in the past decade, leading to the creation of 23- and 25-gauge platforms, which in large part have replaced traditional 20-gauge pars plana vitrectomy (PPV). 

Pars plana vitrectomy (PPV) is a surgical procedure that involves removal of vitreous gel from the eye. The procedure derives its name from the fact that vitreous is removed (i.e. vitreous + ectomy = removal of vitreous) and the instruments are introduced into the eye through the pars plana.

Vitrectomy is a surgical procedure undertaken by a specialist where the vitreous humor gel that fills the eye cavity is removed to provide better access to the retina. This allows for a variety of repairs, including the removal of scar tissue, laser repair of retinal detachments and treatment of macular holes.

 In today’s world of Nano-technology where bigger no longer means better, everything from smartphones to surgical incisions are getting smaller and more refined. The advantages of smaller surgical incision have resulted in faster postoperative recovery. Vitreoretinal surgery is no exception. We have come a long way since the time of open sky vitrectomy and Machemer’s first 17-gauge closed pars plana vitrectomy (PPV) in 1971. In 1974, O’Malley and Heintz introduced a smaller 20-gauge (G) vitrector (0.9 mm diameter) for use with the three-port sclerotomy system that became the gold standard for modern PPV and has been the standard of care for almost three decades. However, in current times, just attaching the retina is not enough. Variables like patient comfort (both intra and post-operative), surgical time and precision, post-operative recovery time, surgically induced refractive error, cosmesis, etc. are becoming increasingly important. To take these factors into account, ‘Transconjunctival sutureless vitrectomy’ (TSV), subsequently renamed and popularly known as microincision vitrectomy system (MIVS) has come about. The 25-gauge vitrectomy was introduced3 in 2002 by Fujii followed by the 23 gauge in 2005 by Eckardt and Stanley Chang which combined the benefits of 20 and 25 gauge. In 2010, Oshima introduced even smaller, 27-gauge instrumentation. As a result of these advances, vitreoretinal surgeons now have multiple choices when determining their operative approach.

Instrumentation

 In MIVS, three micro-cannulas are inserted in the pars plana (with the help of insertion trocar) through the conjunctiva and sclera through a two-step incision. The infusion line and vitreoretinal instruments are then introduced into the vitreous cavity through these cannulas. At the end of the procedure, the cannulas are removed without suturing either the sclera or the conjunctiva. The inner diameters of the 25- and 23-gauge cannulas are 0.57 and 0.65 mm, respectively,3,4 in contrast to the 0.9 mm diameter of a conventional 20-gauge incision while that of the 27-gauge cannula is 0.4 mm. These narrow incisions do not need to be sutured, thus providing minimal surgical trauma and brief recovery times. A smaller port and a proximity closer to the tip maybe advantageous when performing complex manoeuvres, such as shaving of the vitreous base, working near detached mobile retina, membrane segmentation or delamination. The MIVS system also comes equipped with higher cutting rates extending up to 5000–8000 cpm; which reduces the likelihood of uncut vitreous fibres going through the cutter port, thereby reducing dynamic vitreoretinal traction with less chance of iatrogenic retinal tears and damage to the retinal surface. To achieve this high cutting rate without vibrations for better stability and precision cutting newer cutters do not have spring to drive the guillotine.

Illumination

Reducing the diameter of a light pipe by 20% theoretically reduces the amount of illumination by ∼35%. The conventional illumination (halogen) used in 20-gauge PPV is not adequate for MIVS. Currently, with the new-generation xenon and mercury vapor illumination sources, illumination inside the vitreous cavity has greatly improved. When combined with chandelier illuminators or multifunction instruments, these sources have made bimanual microincision vitrectomy a reality.

Complications

Wound leakage

Post-operative wound leak has always been a concern with MIVS. These issues can be addressed by proper wound construction. Displacement of the conjunctiva before entry so that the conjunctival and scleral incisions are misaligned has found to reduce wound leakage. Oblique/angled entry has less incidence of wound leakage as compared to perpendicular entry and biplanar incisions are advantageous over uniplanar ones. Previous sclerotomy sites are structurally weaker because of scarring and fibrosis and reduced rigidity of the sclera could increase the likelihood of wound leakage.

Post-operative endophthalmitis

Kaiser et al. in their presentation at the 2007 Vail Vitrectomy meeting reported 0.23% incidence of endophthalmitis in 3103 consecutive eyes undergoing MIVS. This is in contrast to only one case of endophthalmitis in 5498 consecutive 20-gauge vitrectomies (an incidence of 0.0018%) performed by the same surgeons, at the same institution, over the same period. However, four other studies (three with level II evidence) that compared rates of acute endophthalmitis between 20- and 25-gauge vitrectomy did not show a statistically significant difference in incidence of endophthalmitis. In a similar comparative study of 23-gauge and 20-gauge cases, no case of endophthalmitis was observed among 943 eyes after 23-gauge PPV.

Indications of MIVS

23 Gauge

Though it can be used universally, 23-gauge system is ideally suited for Rhegmatogenous retinal detachment surgery and for diabetic vitrectomies. It can also be used in cases of endophthalmitis and trauma especially foreign body removal.

25 and 27 Gauge

They are more suitable for macular surgery (Macular hole/macular pucker/epiretinal mem Four-port vitrectomy for ROP using MIVS brane) and simple cases of vitreous haemorrhage. Branch vein decompression (sheathotomy) can also be performed. 25G instruments are also preferred in paediatric cases.

Advantages of MIVS over conventional 20 gauge

• Sutureless procedure: so better patient comfort.
• Less inflammation: faster healing and recovery of visual acuity.
• Less surgery induced refractive error.
• Reduced conjunctival scarring: Useful for patients requiring multiple surgeries and also prior to or anticipated glaucoma filtering surgeries or candidates with ocular surface disorders.
• Port design helps in more complete vitrectomy and easier dissection of proliferative membranes.
• Higher cut rates and smaller port aperture reduces the chances of inadvertent retinal breaks. Disadvantages of MIVS when compared to 20 gauge
• Actual time for performing vitrectomy may be longer
• Not suitable for cases where extensive dissection is needed and in eyes where fragmatome have to be used
• Higher infusion pressure may cause optic nerve damage
• Smaller incision may limit the maximum flow across the port
• Flimsy instruments which may deform or break during surgery
• With long trocar blade, there is an increased risk of retinal injury in eyes with anteriorly displaced retina
• Increased risk of post-operative hypotony, choroidal detachments and endophthalmitis due to gaping wounds

Conclusion

The development of MIVS has provided surgeons with new options in the surgical treatment of vitreoretinal diseases. Each system has its advantages and disadvantages. The optimum gauge and settings have to be selected after careful deliberation to provide the best possible surgical outcome.