The eyes that undergo vitrectomy and SO implantation usually have suffered from severe eye diseases, as shown in the current study. Accurate biological measurement before IOL implantation is important for this kind of eyes, to obtain a good visual effect after the operation. Inaccurate measurement of AL and keratometry leads to 36% and 22% errors in predicting IOL refraction using optical biometrics, respectively20.
Measuring AL in SO-filled eyes brings additional challenges: artifacts caused by oil droplets may complicate the measurement, and insufficient SO filling in different degrees may lead to deviations in the results, especially in ultrasound biometry where patients are in a prone position7, 21. CoV can be used to indicate the accuracy and repeatability of measurement22. The lower the CoV value, the higher the precision. Auffarth et al. 22used Pentacam AXL and IOLMaster 700 to measure the AL of pseudophakic SO-filled eyes. Their research showed that the CoV of Pentacam AXL and IOLMaster 700 were 0.26% and 0.09% respectively. The CoV of IOLMaster 700 was similar to our results (0.029%). Our research showed that the CoV of the AL measured by OA-2000 was 0.042%, indicating that these two devices could still provide high repeatability despite more difficult conditions.
Cataract extraction with SO injection is necessary for patients with severe cataracts, since previous studies have shown that about 10% and 20% of eyes with severe cataracts couldn't be measured by PCI-based optical biometer23, 24. Therefore, the patients enrolled in this study were aphakic SO-filled eyes. However, as reported, the success rate of the new SS-OCT-based biometric instruments for measuring AL has greatly improved in various lens opacities. Reitblat et. 25showed that the significant advantage of OA-2000 was the high success rate for AL measurement. Among the 6465 patients, 301 eyes whose ALs could not be measured by IOLMaster 500 were successfully measured by OA-2000 in 284 eyes (94. 35%), and the success rate for AL measurement by OA-2000 was 99. 7%. This is important for SO-filled eyes with cataracts, which can help reduce some postoperative complications after combined surgeries of anterior and posterior ocular segments. However, the success rate and accuracy of OA-2000 for cataract SO-filled eye measurement need further study in the future.
For SO-filled eyes, previous studies showed that the PCI-based IOLMaster had good accuracy in measuring the AL. Parravano et al. 6measured the ALs of 10 SO-filled eyes before and one week after SO removal. They found that there was no statistical difference in the ALs of SO-filled eyes before and after surgery, and IOLMaster had good accuracy in measuring the AL. Kunavisarut et al. 26measured 34 cataractous SO-filled eyes with IOLMaster and A-ultrasound before and 3 months after removing SO combined with cataract surgery and IOL implantation, and found that the AL measurement by IOLMaster also was more accurate than A-ultrasound by Pearson’s correlation (0.966 vs 0.410). A-ultrasound 's prediction of postoperative refractive error (average 1.79 ± 1.04d) was higher than that of IOLMaster (average 0.60 ± 0.23d), with a statistically significant difference (P = 0.049). Similarly, El-Baha et al.7 used IOLMaster and A-ultrasound to measure the ALs of 22 cataractous SO-filled eyes, which underwent removing SO, cataract removal and IOL implantation. Unlike Kunavisarut et al.' s research, in El-Baha et al.' s research, A-ultrasound measured the AL after removing SO during operation. There was no statistical difference between the two instruments in measuring the ALs, and the two instruments showed a small predictive postoperative refractive error. There was no statistical difference in the predictive error between the two techniques.
The current research showed that the measured values of OA-2000 and IOLMaster 700 had good correlation and consistency in SO-filled eyes. This study showed that there was a slight difference between OA-2000 and IOLMaster 700 in measuring the AL. The average AL measured by OA-2000 was 0.124mm shorter than that measured by IOLMaster 700, and the difference was clinically acceptable. According to SRK-T formula, the 0.12mm error of AL will lead to an error of 0. 30 ~ 0.51D27. This difference may be caused by the different algorithms or analysis programs of the boundary measured by the two devices. Previous studies showed that IOLMaster 700 and OA-2000 had little difference and good consistency in measuring the ALs of normal subjects, which was consistent with our research in SO-filled aphakia eyes eyes12, 28. Huang et al. 12compared the AL measurement and success rate of cataract patients with two kinds of optical biometers based on SS-OCT (IOLMaster 700, OA-2000 and Argos) and PCI (IOLMaster v 5.4). They found that compared with IOLMaster v5.4, these three SS-OCT biometers had significantly higher success rates in measuring the AL of the eyes in various lens opacity. Three SS-OCT biometers had high consistency with IOLMaster v5.4 in measuring for the AL. Compared with IOLMaster 700, OA-2000 had an average shorter AL of 0.01mm, and the difference had no clinical significance. Goebels et al. 28used OA- 2000, IOL Master 500 and Lenstar 900 to measure the ALs in cataract patients, and found that the three instruments had a good correlation. The differences between OA-2000, IOLMaster 500 and Lenstar 900 in measuring the AL were quite small (0. 05mm and 0. 03mm respectively), which was statistically significant but not clinically significant. In addition, their research also showed that OA-2000 and IOL Master 500 were in good agreement in measuring AL, CCT and K values, which was consistent with our research in SO-filled aphakia eyes.
The limitation of this study was that we didn't use instruments to predict the refractive error of SO-filled eyes after SO was removed and IOL implantation. Next, we will conduct research. In a word, the first clinical comparative study between OA-2000 and IOLMaster 700 in SO-filled aphakia eyes showed that Al, Kf, Ks, Ax1 and CCT had good consistency between the two devices. This study proves the possibility that OA-2000 can reliably and repeatedly obtain the most important parameters needed for IOL implantation in patients with SO-filled aphakia eyes.