Nucleus management for MSICS
Everything you ever wanted to know MSICS Part 3 – Complications
A: A long straight tunnel can leak and may require sutures. B: A good internal corneal valve allows cortex aspiration without iris prolapse. C: A poorly constructed internal corneal valve leaks and allows iris to prolapse out. D: A leaking tunnel should be sutured and cortex aspiration done through a separate paracentesis in a formed AC
In the final part of this three-part series on MSICS, we will discuss complications and their management.
Buttonholing, wound gape and excessive astigmatism can occur secondary to dissecting a shallow tunnel (<50% scleral depth) or by not following the curve of the globe while dissecting. A buttonholed tunnel is not self-sealing and does not yield a stable anterior chamber (AC) for subsequent manoeuvres. Too deep a tunnel (>75% depth) can lead to premature entry. Unintentionally going full scleral thickness (100%) can cause uveal show, haemorrhage, scleral disinsertion and ciliary prolapse. Initiating and maintaining appropriate depth (50-75% scleral thickness) is therefore important.
The globe is curved, and its curvature should be followed in forward and sideward dissection. The blade should be angled to follow the curvature forwards and the lateral edge of the blade should be tilted downwards slightly to match the sideward contour of the globe. The tunnel must be initiated on one side and continued over to the other side while maintaining the same plane. Starting dissection at either end to try and meet in the middle can lead to inadvertent dissection in different planes with ensuing bridge of undissected tissue. Deep and superficial tunnels are managed by either reinitiating the dissection at the right plane or by creating a new tunnel at a different site. Reinitiating at a different plane should be done carefully to avoid a free tongue of scleral tissue that can compromise tunnel integrity.
Premature entry can occur with deep dissection or if the crescent dissector is not angled more anteriorly at the limbus to follow the steeper corneal curvature. This leads to loss of valvular effect and iris prolapse with consequent iris chafing. Premature entry can also lead to iridodialysis, haemorrhage or, rarely, Descemet’s detachment. Suturing at the end of surgery is a must to avoid a leaking wound, hyphema and ectatic cicatrix.
Too anterior a corneal entry leads to excessively long tunnel and difficulty in manoeuvring instruments. Ideal length of the tunnel is 2mm on the scleral aspect and 1.5mm on the corneal aspect.
Significant against-the-rule astigmatism can arise from MSICS incisions unless care is taken. Remaining within the astigmatic neutral funnel and avoiding incisions too close to the limbus, shallow tunnels, large tunnels and straight tunnels can prevent this.
Excessive wound distortion while expressing the nucleus or while inserting the IOL can also cause wound gape and subsequent astigmatism. Holding the tunnel with forceps while dissecting can lead to loss of tunnel integrity. Gaping or leaking incisions require sutures.
The anterior capsular opening needs to be large enough to allow the nucleus delivery into AC. With a rhexis, it is important to make relaxing incisions before attempting to bring large, hard nuclei out. Failure to do this can cause zonulodialysis and damage to the entire bag. Excessive hydrodissection and hydrodelineation carry the risk of a capsular blow-out just as in phacoemulsification. Gentle, multi-quadrant hydrodissection with intermittent decompression should be done.
Softer nuclei can be hydroprolapsed, but attempting this with large, bulky nuclei through an intact rhexis can cause capsular blow-out. Repeated attempts to bring the nucleus into the AC, even with relaxing incisions, may cause capsular tear run-around, vitreous loss and nucleus drop.
A small pupil hinders nucleus delivery. MSICS may therefore be better avoided in small rigid pupils and in cases of zonulodialysis or zonular weakness, especially by beginners. Difficulty may also be encountered while dialling the nucleus out of the bag. Repeated attempts without adequate viscoelastic protecting the corneal endothelium can result in corneal oedema and striate keratopathy.
Once the nucleus is in the AC and ready to be expressed out, corneal endothelial protection should again be ascertained by injecting viscoelastic both above and below the nucleus.
Nucleus expression may become impossible if the tunnel length is inadequate. In this case, the tunnel has to be extended to either side with a keratome or needs to be converted into an extracapsular incision by cutting either end of the incision.
The width of the internal incision should be larger than the external incision in order to allow the nucleus to mould and exit out. Few undissected scleral fibres anywhere in the tunnel or premature entry with iris plugging the tunnel can also obstruct nuclear expression. In either case, the tunnel should be made complete and extended if required.
An inferior iridodialysis with intra-cameral bleeding and hyphema can occur while attempting to deliver the nucleus with a vectis if the vectis is accidentally inserted under the iris instead of above it. This needs to be repaired through a Hoffman pocket using a double-armed 10-0 prolene suture.
In case of a superior iridodialysis, the iris root can be sutured to the inner scleral lip of the MSICS tunnel. Techniques like phaco-sandwich and phaco-fracture can cause collateral damage to the iris and endothelium because of the greater manipulations required within the AC.
Attempting to aspirate cortex through the tunnel leads to shallowing of the AC, forward movement of posterior capsule and increased risk of posterior capsular rent. A separate side port should therefore be used for manoeuvres requiring a formed AC such as rhexis and cortex aspiration. Sub-tunnel cortex can be easily approached this way.
Dialling the IOL within the bag can help dislodge residual small stubborn cortex. Single-piece or three-piece PMMA IOLs are implanted through the tunnel. Foldable single piece or three-piece acrylic IOLs may be injected through an enlarged side port for in-the-bag IOL implantation if the rhexis is intact.
A leaking wound can cause a shallow AC and predispose to endophthalmitis. Severe against-the-rule astigmatism from wound gape may require opening the conjunctiva and suturing the incision. Increased iris manipulation can cause iritis and cystoid macular oedema. Corneal oedema, striate keratopathy and even corneal decompensation can arise from rough manipulations of the nucleus and instruments within the AC.
Dr Soosan Jacob is Director and Chief of Dr Agarwal’s Refractive and Cornea Foundation at Dr Agarwal’s Eye Hospital, Chennai, India and can be reached at firstname.lastname@example.org.