Complications of cataract surgery
There are ways of avoiding corneal wound burn and corneal incisional contracture.
Back-and-forth movement of the phaco tip generates heat. A: Flow of fluid around the tip through the silicone sleeve; B: unoccluded continuous flow through the phaco tip; C: and leakage through the incision; D: all help in cooling the tip and preventing wound burn
The corneal incision used in phacoemulsification plays a vital role in maintaining the self-sealing nature of the tunnel thereby preventing wound leak, shallow anterior chamber (AC) and endophthalmitis postoperatively. The self-sealing architecture of the tunnel is also extremely crucial to avoid high postoperative astigmatism and to maintain the normal shape of the cornea. Though rare, corneal incisional contracture or wound burn is a complication that every surgeon needs to be aware of as it results in irreversible damage to incisional architecture, fish-mouthing and loss of integrity.
CAUSES OF WOUND BURN
Back-and-forth movement of the metallic phaco tip within the sleeve that occurs during application of phaco power generates stress on the metal and creates friction that generates heat, which can be translated to the incision leading to a wound burn. Thermal damage to the collagen fibres occurs at a temperature of 60 degrees centigrade and leads to contracture and wound distortion. The phaco tip is continuously cooled by fluid entering the AC around the tip through the phaco sleeve as well as aspirated fluid exiting through the hollow bore of the tip. In addition, incisional leakage through the wound around the sleeve also helps prevent rise in temperature of corneal collagen.
Phacoemulsification in the absence of adequate fluid flow through the sleeve, secondary to a tight incision or kinking of the sleeve against the wound, can lead to a corneal burn. A tight incision also decreases incisional leakage resulting in localised temperature rise at the corneal incision.
AVOIDING WOUND BURN
Corneal wound burn can be avoided by decreasing the heat built-up at the incision. This can be achieved by using lower phaco power settings, larger incisions, adequate fluid flow, modified tips and modified sleeves. High vacuum and low power with suitable power modulations avoid excessive temperature rise. The process of cavitation generates heat. Certain phaco modes are more prone to heat generation. Under similar conditions of power, stroke length and energy, longitudinal ultrasound generates more heat than torsional secondary to a lower operating frequency as well as decreased stroke length at the incision. Similarly, continuous mode phaco creates more heat than pulse mode.
The off period in pulse mode allows the tip to cool in between two pulses as well as reducing the total amount of power used and thus also the heat generated. Using a lower duty cycle minimises heat production, allows better cooling of the tip and allows aspiration of the emulsified nuclear fragments, thus decreasing heat production. Handpiece frequency and stroke length are other important factors. Higher power utilisation generates more heat. Similarly, prolonged phaco time can cause wound burns.
Modifications in phaco tip design – thinner tips, microtips, titanium tips with the same inner bore but smaller outer bore as well as modified sleeve designs with straight or spiral ribbing or other textured designs, using polyimide insulator, aspiration bypass system and making sleeves stiffer to allow greater flow can help decrease wound burn. Different phaco machines employed under similar conditions with similar settings often have differing amounts of heat generation due to differences in make and design.
In addition, nucleus removal technique also determines the amount of heat produced. Chop techniques use manual energy for nuclear disassembly and therefore cause less heat generation than divide and conquer, stop and chop or other techniques using ultrasonic disassembly.
Free flow of fluid in and around the phaco tip is a prerequisite for efficient cooling. A tight wound can restrict fluid flow both within the sleeve as well as around the sleeve. Needle size, sleeve size and incision size should be appropriate to each other. Higher bottle height and higher aspiration flow rate both increase fluid turnover in the AC thus promoting cooling.
Retention of air or viscoelastic near the phaco tip decreases efficiency of cooling mechanisms at play thus predisposing to wound burn. Clogging of the phaco needle, handpiece or tubing by viscoelastic or a dense nuclear piece leading to blocked aspiration flow can cause sudden release of heat and a corneal burn. Using ultrasound energy within viscoelastic releases heat and the incidence is higher with Healon 5, Ocucoat and Viscoat.
Listening to audible sounds from the machine indicating occlusion and also making sure not to run out of irrigating fluid inadvertently are important. Viscoelastic overfill should be avoided and it should be cleared from around the phaco tip before proceeding with nuclear emulsification. Confirming free flow of fluid into the phaco tip is important before initiating ultrasound. If occluded, either I/A mode should be used to clear clogged material or the phaco needle should be removed and outflow flushed to remove any clogs.
RECOGNISING WOUND BURN
Lens milk is a sign of decreased flow and stagnant emulsification near the phaco tip and is seen as a cloudiness secondary to milky lenticular material with no substance seen evacuating out of the eye through the phaco tip. Phacoemulsification should immediately be stopped to avoid further worsening.
Whitening and coagulation of the incision is another sign that should be recognised immediately and is secondary to damage to adjacent corneal stroma and endothelium. Other signs include incisional fish mouthing, difficult wound closure, wound leak and an unstable anterior chamber.
Postoperatively, continuing leakage, shallow AC, corneoscleral melt, corneal fistula, increased risk of endophthalmitis, high postoperative astigmatism, poor uncorrected and best-corrected visual acuity, irregular astigmatism and poor ocular surface are some of the difficulties encountered.
MANAGEMENT OF WOUND BURN
Multiple interrupted sutures or running cross-sutures may be needed. Special “gape sutures” as described by Robert Osher can help seal the incision and minimise induced astigmatism. Tissue adhesive, bandage contact lens and aqueous suppressants may help. Seidel negativity should be confirmed. Leaving iris incarcerated has been proposed as a solution followed at a later date by separation of iris.
The author has used a SMILE® lenticule as a filler graft to avoid an overly tight incision. Astigmatism can decrease after suture removal and over longer follow-up. Various means to tackle astigmatism include contact lenses, glasses, arcuate keratotomy, topography-guided LASIK, small-aperture IOL, pin-hole pupilloplasty etc.
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