Prevention of phaco wound burns needed during cataract surgery
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The cornea is a delicate tissue. It is thin, clear, avascular and susceptible to damage, particularly from the heat that is generated by the phaco probe.
Think of the corneal tissue like the albumin of an egg: With heat, these clear proteins denature, become opaque and contract. In the cornea, application of heat will cause the tissue to opacify and contract, which will induce a large degree of astigmatism and prevent the incision from sealing well.
During cataract surgery, the phaco probe generates heat due to friction. Ultrasound means that the frequency of the vibration is above the range of human hearing, which is in the range of 20 Hz to 20,000 Hz (this higher limit declines with age). Most of our phaco probes vibrate between 28,500 Hz and 40,000 Hz in the longitudinal as well as torsional directions. The phaco tip moves back and forth at this fixed high rate of speed, with the “phaco power” setting being a way of increasing the stroke length while the frequency stays the same. The stroke creates a mechanical impact, cavitation and implosion at the tip, and a fluid and particle wave. But the phaco probe stroke also creates heat from friction.
To mitigate the heat buildup from ultrasonic energy, we use a silicone sleeve around the phaco needle, and we have the infusion of balanced salt solution come into the eye bathing the phaco needle. This is also why we intentionally use a slightly leaky incision for increased fluid egress and phaco needle cooling.
Some of the factors that put us at risk for a corneal wound burn include using a high amount of ultrasound energy, such as for a dense nuclear cataract; lack of phaco power modulations, such as pulse mode, burst mode or lower duty cycles; having an improperly fitted silicone sleeve that is too tight for the incision; and failing to pivot in the incision while pushing the phaco needle against the sides, roof or floor of the corneal incision (Figure 1).
Source: Uday Devgan, MD
If there is blockage of the bore of the phaco needle, then the fluid flow will decrease dramatically, and the heat will build up quickly. A warning sign is a white cloud of emulsified lens material at the phaco tip (Figure 2). If this is noted, immediately stop delivering ultrasound energy, take the probe safely out of the eye and check it for blockage. Sometimes this blockage of the phaco needle can be due to excess viscoelastic occluding the tip.
Once you notice a phaco wound burn, it is already too late. At this point, care should be taken to finish the surgery and not cause more corneal burning or trauma. The incision will leak more during the rest of the surgery and will cause anterior chamber instability and a higher risk for posterior capsule rupture. It may be wise to abandon the burned incision, suture it securely and then create another incision through which to finish the case.
Securing this burned incision is not easy, and it requires patience and multiple sutures to achieve a watertight closure (Figure 3). Keep in mind that there are irregular surfaces created from the burn that will not appose well. The key suture is the horizontal mattress suture that helps pull the roof of the incision down to the floor across the entire width of the corneal tunnel (Figure 4). These sutures should be left in the eye for many months until wound healing is sufficient to keep the tissues closed. The phaco wound burn will also cause an astigmatic effect that can be pronounced in the postop period. This will tend to decrease with time, but it can take months or longer.
Fortunately, phaco wound burns are uncommon, but keep in mind that they can happen, especially when we do cataract surgery on dense nuclear cataracts. Optimize your phaco ultrasound settings, make your incision precise, and be sure to pivot and float within the incision. That will limit the risks and help ensure a great visual outcome for our patients.
See full video of this case at cataractcoach.com.
- For more information:
- Uday Devgan, MD, is in private practice at Devgan Eye Surgery, Chief of Ophthalmology at Olive View UCLA Medical Center and Clinical Professor of Ophthalmology at the Jules Stein Eye Institute, UCLA School of Medicine. He can be reached at 11600 Wilshire Blvd. #200, Los Angeles, CA 90025; email: devgan@gmail.com; website: www.CataractCoach.com.
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