Nucleus management for MSICS
Everything you ever wanted to know about manual small incision cataract surgery (MSICS) - Part 2
A: The prolapsed pole of the nucleus is dialed out; B: The nucleus lies completely within the anterior chamber; C: Viscoexpression of the nucleus; D: First postoperative day shows a clear cornea and round pupil.
This column is in continuation of my last column, which dealt with wound construction in MSICS.
Superior rectus bridle suture taken while constructing the tunnel is released to allow the globe to move to primary position. Prior to creating the internal tunnel incision, a side port is constructed in the horizontal meridian on the right side for right-handed surgeons to allow a rhexis to be created under closed-chamber conditions. Though can-opener capsulotomy can also be done and the nucleus extracted safely in MSICS, a rhexis is preferred as it allows in-the-bag IOL placement. Unless the nucleus is small, a rhexis larger (6-7mm) than that conventionally created for phaco is required. The larger the nucleus, the larger the rhexis required to allow easy expression from the bag. Hard brunescent and black cataracts require relaxing incisions on the superior rhexis margin to safely prolapse the pole into the anterior chamber (AC).
After completing rhexis, the tunnel is opened and extended to either side. Internal incision of the tunnel is longer than the external incision.
HYDRODISSECTION AND HYDRODELINEATION:
Hydrodissection and hydrodelineation are done under the rhexis margin to help delineate the nucleus to a smaller size and to aid in later cortex aspiration. The nucleus is then hydroprolapsed out by injecting multiple gentle fluid waves under the epinuclear shell while gently depressing on one side. Increased pressure behind the nucleus causes one pole to tilt out of the rhexis rim. If a can-opener capsulotomy was used, the nucleus is prolapsed by inserting a Sinskey hook carefully under the capsular margin to engage one pole of the nucleus and bring it out of the capsular bag.
NUCLEUS PROLAPSE INTO AC:
Once one pole is out, viscoelastic is injected under the prolapsed pole to help tilt it further up. Viscoelastic is also injected to depress and contour the iris around the prolapsed pole to make it easier to dial it out above the iris. It also coats and protects the cornea during the subsequent nuclear manoeuvres. A Sinskey hook is then used to engage the pole of the nucleus and dial the nucleus completely out of the bag and into the AC.
The classical Blumenthal Mininuc technique uses fluid pressure from an anterior chamber maintainer and a Sheets glide for guiding and expressing the nucleus out of the tunnel. An irrigating vectis may also be used to engage and express the nucleus. Care should be taken not to accidentally entrap the inferior iris between the vectis and the nucleus, which can result in an iridodialysis.
Viscoexpression using HPMC 2% is the author’s preferred technique. Once the nucleus is entirely within the anterior chamber, both anterior and posterior surfaces of the nucleus and cornea are coated liberally with viscoelastic. The superior rectus bridle suture is then tugged gently and a 23-gauge viscoelastic cannula is inserted under the nucleus beyond its centre. Viscoelastic is then injected under the nucleus with the cannula gently depressing the posterior scleral lip. The increased intra-cameral pressure together with the open corneo-scleral tunnel allows the nucleus to be expressed out. It engages the larger internal scleral lip, moulds to the tunnel and comes out through the smaller sized external lip. The cannula should be brought out together with the nucleus to avoid a posterior capsular rent when the chamber suddenly shallows after nucleus expression. Hard brown nuclei that cannot mould require a larger external incision. If the nucleus appears stuck in the tunnel at its widest, a cystitome can be used to rotate it out gently. However, if the nucleus appears too large for the incision, forcible attempts should not be made to avoid endothelial loss, posterior capsular blow-out and nucleus drop. In case of difficulty, either the nucleus can be broken into smaller pieces that are extracted individually or the incision should be extended. If part of the nucleus is seen outside the wound, it can be debulked, pushed back into the AC, rotated to engage along the narrower diameter and then expressed.
Phacofracture with the bisector, trisector or a second instrument is possible. However, these require two instruments within the AC and skill in performing the fracture. Uncontrolled movements of the hard nucleus or instruments against the endothelium and inadvertent damage to surrounding structures should be avoided. A stainless steel snare can also be used effectively to divide a large nucleus.
With viscoexpression of the nucleus, the epinucleus and some cortex also generally express out through the incision. Attempting cortex aspiration through the tunnel can lead to shallowing of the AC and possible posterior capsular rent.
Cortex should instead be removed with the Simcoe cannula passed through the side port. This allows cortex aspiration in a closed chamber and also gives easy access to sub-tunnel cortex.
Under cover of viscoelastic, the leading haptic of a rigid IOL can be implanted into the bag through the main port and the trailing haptic dialled in with the Sinskey hook passed through the side port. Alternatively, the trailing haptic can be flexed into the bag.
Another alternative here is to inject a foldable IOL into the bag through the paracentesis after extending it with a keratome.
Viscoelastic is removed with the Simcoe cannula passed through the side port. The integrity of the incision is then checked. Adequate pressurisation of the AC with air or BSS helps seal the internal valve more effectively. Length, depth, shape and distance of tunnel from the limbus all affect the amount of astigmatism. Sutures may be applied if the tunnel leaks or to decrease against the rule astigmatism. Conjunctival cut ends can generally be apposed well by lightly applying cautery to the edges held together by a forceps. Doing this at either end allows good conjunctival closure. Alternately, injecting the antibiotic steroid injection into the cut conjunctiva balloons it up such that it covers the exposed sclera beneath. Sutures or fibrin glue may also be used to close conjunctiva.
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