Uday Devgan MD posted: " Increasing lens thickness indicates danger in cataract surgery because liquefied lens cortex can pressurize the capsular bag, increasing the risk for capsular runout. When looking at the biometry for our cataract surgery patients, the axial lengt" Cataract Coach
Increasing lens thickness indicates danger in cataract surgery because liquefied lens cortex can pressurize the capsular bag, increasing the risk for capsular runout.
When looking at the biometry for our cataract surgery patients, the axial length, keratometry and anterior chamber depth are usually what we gravitate toward. These values are used in the IOL power calculations, and the anterior chamber depth gives us an idea of the working room while performing phacoemulsification. However, we should also look carefully at the lens thickness.
As the cataract develops and nuclear sclerosis progresses, the anterior-posterior dimension of the human lens increases. A typical cataract surgery patient will have a lens thickness of about 4 mm to 5 mm, with 4.5 mm being average. However, there are cases in which the lens thickness can increase dramatically, such as when the lens cortex becomes liquefied and the capsular bag becomes pressurized. This intumescent lens fluid will cause an outward push on the lens capsule as the intralenticular pressure rises.
The case featured here was submitted by Richard Schulze, MD, of Savannah, Georgia, and it illustrates this situation (Figure 1). His patient was seen in June 2021 with a 3+ nuclear cataract and a lens thickness of 4.53 mm. The patient elected to wait and then returned in September 2022 with an intumescent white cataract. Optical biometry was unable to penetrate the opaque lens, so ultrasound A-scan was used to measure the eye, and the lens thickness was confirmed to be 6.34 mm, which is an increase of 40%. This indicates that the capsular bag is highly pressurized, and the risk for capsular runout, known as the Argentinian flag sign, is increased dramatically.
Figure 1: lens thickness increased by 40% from 4.53mm to 6.34mm as the cortex liquefied and the capsular bag became highly pressurized.
The biggest surgical challenge in this eye is the capsulorhexis because any attempt to depressurize the capsular bag may result in an uncontrolled capsular runout. This can even extend to the posterior capsule and cause vitreous prolapse and retained lens material. Many techniques have been described to decompress the capsular bag in cases like this, such as needle aspiration, phaco puncture, double capsulorrhexis and femtosecond laser capsulotomy. However, there are issues with each of these because the time required to perform these may allow a sudden rupture of the anterior lens capsule. Dr. Schulze elected to use the Zepto device (Centricity Vision) to perform a precision pulse capsulotomy, which can be created in just 4 milliseconds. Another advantage is that the edge of the capsular opening is very strong and more resistant to runout.
The Zepto device is placed on the anterior lens capsule and centered by the surgeon over the visual axis or desired position. It has a nitinol ring that enters the eye collapsed and then expands in the eye using a finger-slide button. Gentle suction is automatically applied to adhere the Zepto device to the capsular surface, and then a brief 4 millisecond pulse of energy is used to instantly create a 5.2-mm diameter capsular opening. The suction is stopped, and the device can be collapsed and removed from the anterior chamber. The rest of the cataract case can be performed normally because the capsular bag is fully decompressed and the capsulotomy is strong and precise.
At the end of the surgery, the IOL is implanted in the capsular bag, and we can see that the 5.2-mm capsulotomy is precisely centered over the 6-mm optic of the lens (Figure 2). This ensures secure placement of the IOL and great long-term stability. The capsulotomy covers the optic edge 360° and ensures a precise effective lens position, which gives a more predictable refractive outcome compared with a case in which there was a runout of the capsulorhexis.
Figure 2: great result at the end of surgery and stable at 1 month post-op.
When examining patients before cataract surgery, we must take the extra step to carefully look at the biometry, including lens thickness data, in order to be better prepared for the surgery. When you see a patient with a white cataract and an increased lens thickness, you can be sure that lens proteins have liquefied and the capsular bag is pressurized. Special maneuvers or equipment as shown in this case can be helpful to give patients the best outcomes with the lowest risks.
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