34 EyeWorld Asia-Pacific | September 2024 Dr. Anwar stated that IOP recovery can occur in about 200 ms while still being independent of the vacuum limit or IOP level. Additionally, the pump provides active incisional leakage compensation, meaning there is real-time pumping of fluid to make up for any leakage volume. In a 2023 paper by Fanney et al,5 Dr. Anwar discussed the results which showed that the QUATTRO Pump® demonstrated higher surge peak values and shorter surge duration times as compared to the Centurion® system. The time the IOP remained below 90% of the target IOP was 408.1 ms for the QUATTRO Pump® and 913 ms for the Centurion® pump. Dr. Anwar also emphasized the feature of “Power on Demand,” saying that the QUATTRO Pump® can use up to 50% less ultrasound upon occlusion, and there is no need to constantly press and release the foot control pedal to modulate the ultrasound. “This provides a much more relaxed surgical experience,” he stressed. In his own study, Dr. Anwar compared 50 eyes using the QUATERA® 700 with high parameters (aspiration flow rate 70-90 cc/min, vacuum 500-700 mmHg, and IOP 30-60 mmHg) and 50 eyes using Centurion® with low parameters (aspiration flow rate 25-30 cc/min, vacuum 250-400 mmHg, and IOP 20-50 mmHg). He found that the total phacoemulsification time was faster with the QUATERA® 700 than the Centurion®. Although macular thickness and endothelium cell count six weeks after surgery was not statistically significantly different in either group, the effective emulsification time was significant for the QUATERA® 700 (24 seconds vs. 37 seconds). “What I feel is that it is not just finishing a surgery; it’s a journey,” Dr. Anwar remarked. “A good surgery is not enough for the patients now.” He explained that many patients may not understand the concept of IOP, but his myopic patients are aware. “These patients,” he said, “can feel the high IOP. If you are able to reduce IOP for them, it really makes them feel comfortable.” The Importance of Total Keratometry in IOL Calculations Yeo Tun Kuan, FRCOphth, FAMS (Singapore) “We know that standard keratometry (K) estimates corneal power by measuring the anterior corneal radius,” Yeo Tun Kuan, FRCOphth, FAMS (Singapore) stated. However, Total Keratometry (TK) combines anterior corneal power with posterior corneal power and central corneal thickness measured by swept source optical coherence tomography (OCT). “Total Keratometry values can be used for the Barrett and EVO formulas,” Dr. Yeo explained. “However, because they are thick lens IOL formulas, you should not use TK directly in place of K. Instead, the correct way would be to input K and posterior corneal power (PK) as separate parameters.” When using the Barrett formulas on the IOLMaster® 700 with TK, it is actually utilizing standard K and PK as separate inputs. Similarly, on the online Barrett calculators, to utilize measured posterior cornea, one must select “measured PCA” to input PK values and indicate that the values are from IOLMaster® 700. The most important question is of course: Is Total Keratometry beneficial and does it help to provide more accurate outcomes? In some of the earliest publications on this topic, studies found that there was a trend towards a lower mean absolute error for TK compared to K, and there was a slightly higher proportion of eyes within ± 0.25, 0.50, and 1.00 D.6,7 However, Dr. Yeo also discussed how some recent studies found lower refractive prediction accuracy when using TK instead of K and that TK was not superior compared to K with comparable prediction outcomes.8,9 “This is to be expected,” Dr. Yeo explained. “Since TK was designed to be very similar to K, you should not expect any significant advantages of TK over K in normal eyes,” he stressed. So when is TK beneficial? “In eyes with atypical corneas,” Dr. Yeo said. “TK has been proven to be very useful in post-refractive surgery eyes.” A 2020 study10 found that the Barrett True-K TK provided the lowest mean refractive prediction error (RPE) and variance for patients with either prior myopic or hyperopic laser vision correction (LVC). The latest study11 in 2024 on eyes with prior myopic LVC showed that the EVO 2.0 PK, Barrett True-K TK and PEARLDGS formulas performed the best, achieving better results than the Hoffer QST and legacy formulas such as Haigis-L and Shammas-PL. “You can see the trend that using TK or PK values provide better outcomes in eyes with previous myopic LVC,” Dr. Yeo said. “The top formulas were the ones that used total keratometry or posterior cornea measurements from the IOLMaster® 700.” Dr. Yeo then explained his multicenter study involving the Singapore National Eye Center and Tan Tock Seng Hospital comparing the accuracy of existing and new post-myopic LVC formulas. There were 900 eyes with standard keratometry values and 517 eyes with TK and PK values. With standard keratometry, the accuracy of the top performing formula was 62.0% within 0.5D. “But, if you use total keratometry, the accuracy increases to 66.5%. Overall, the TK/PK formulas perform better,” Dr. Yeo said. “Looking at axial length bias, the EVO PK and Barrett True-K PK formulas did not have any error bias against axial length and performed well for fairly short to very long eyes.” If one looks at the other formulas, though, there is significantly greater axial length bias. Fanney et al (2023)5 showed that the mean surge duration, the time the IOP remained below 90% of target IOP, for the Quattro Pump® was 408.1 ms and while the Centurion® pump had a surge duration time of 913 ms. Copyright 2024 APACRS. All rights reserved. The views expressed here do not necessarily reflect those of the editor, editorial board, or publisher, and in no way imply endorsement by EyeWorld, Asia-Pacific or APACRS. Supplement to EyeWorld Asia-Pacific September 2024 Introducing the Forefront Technologies in Refractive and Cataract Surgery
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