Comparison of the influence of pupil dilation on predicted postoperative refraction and recommended intraocular lens power among Barrett Universal II, Haigis, and SRK/T calculation formulas: a retrospective study CURRENT STATUS:

Background We investigated the effect of pupil dilation on and (IOL) power calculated using three power calculation formulas: Barrett Universal II (Barrett) (new generation), Haigis (4th generation), and SRK/T (3rd generation).Methods This retrospective study included 150 eyes. The following variables were measured and calculated using an optical biometer before and after dilation: anterior chamber depth (ACD), lens thickness (LT), white-to-white (WTW), mean absolute change (MAC) in PPR, and recommended IOL power. PPR and recommended IOL power were calculated by Barrett, Haigis, and SRK/T IOL calculation formulas. Correlations between all changes were analyzed. The influence of pupil dilation on recommended IOL power calculated by each formula was also analyzed.Results MAC in PPR before and after dilation was highest in Barrett, followed by Haigis and SRK/T. Significant differences were found among each MAC. Significant changes were observed before and after dilation in ACD and LT but not in WTW. In Barrett and Haigis, there was a significant positive correlation between change in PPR and change in ACD and a negative correlation between change in PPR and change in LT. Correlations were strongest in Barret followed by Haigis, especially in LT. Change in PPR in Barrett also demonstrated a significant positive correlation with change in WTW. The recommended IOL power using Barrett and Haigis changed before and after dilation in 23.3% and 19.3% cases; SRK/T showed no change.Conclusions In PPR and recommended IOL power, pupil dilation influenced Barrett most strongly, followed by Haigis and SRK/T. Given the stronger correlation between the change in PPR in Barrett and the change in ACD, LT, and WTW, the change of ACD, LT, and WTW is more important to the influence of dilation on Barrett. The influence of dilation on each formula and variables, including ACD, LT, and WTW is key to improving IOL calculation.

3 papers studying the accuracy of the predictability of different IOL calculation formulas have been published. 4,5) Most researchers say that Barrett Universal II may be one of the most reliable IOL calculation formulas. Some studies analyzed the influence of preoperative anterior chamber depth (ACD) on PPR in different IOL calculation formulas. 6,7) They concluded that the influence of preoperative of ACD on PPR varies from formula to formula. There is also some research which examined the influence of pupil dilation on biometric parameters such as ACD, lens thickness (LT), white-towhite (WTW), and recommended IOL power using different IOL calculation formulas. 8,9,10) . Thus, there are a small number of research papers which conducted the comparison of the influence of pupil dilation on PPR and recommended IOL power calculated using the different generation IOL calculation formulas, and different biometric parameters, such as ACD, LT and WTW. However, to the best of our knowledge, this is the first study which researched the correlation between PPR and recommended IOL power in three different generation IOL calculation formulas, and change in the different biometric parameters, ACD, LT and WTW. Given that the different generation IOL calculation formulas include different biometric parameters, and they can be influenced by pupil dilation, further research in this area could be interesting.
The purpose of this study was to analyze the influence of pupil dilation on biometric variables and recommended IOL power calculated using Barrett Universal II, Haigis, and SRK/T. Additionally, the correlation among all variables was investigated. Methods 150 eyes in 81 patients were analyzed in this retrospective study. The average age was 72.9 ± 7.7 years (range: 51-87 years), and 39.6% of patients were men (Table 1). Cataract operations without any unexpected events were performed at two eye clinics (Yokosuka Chuoh Eye Clinic and Tsurumi Chuoh Eye Clinic). For all patients, monofocal acrylic single piece IOLs (SN60WF, Alcon Laboratories, Inc., Fort Worth, TX, USA) were inserted. This study was approved by the ethical committees of both eye clinics. Consent to use their medical data for this research was given by all patients whose postoperative best-correction vision was higher than 20/40 without any history of eye problems and intraocular or corneal operations. This research followed the tenets of the Declaration of Helsinki in the entire data collection process. After the pre-dilation examination, topical tropicamide and phenylephrine (Midrin-P®, Santen, Osaka, Japan) were applied every 15 minutes. After full dilation, the post-dilation examination was performed.
The mean change in ACD, LT, and WTW and mean absolute change (MAC) in PPR in each formula were analyzed. The correlation of the variables above was also investigated. Additionally, the difference in coincidence rate of recommended IOL power in each formula between before and after pupil dilation was checked. Finally, based on the collected data above, the influence of pupil dilation on all variables was analyzed.
To compare change in ACD, LT, and WTW and change in PPR in each formula before and after dilation,
The coincidence rates of recommended IOL power before and after pupil dilation in each formula are displayed in   In many studies, AL and corneal curvature radius are not affected by pupil dilation. [10][11][12] However, ACD was reported to be influenced by pupil dilation. [10][11][12][13][14]  Haigis and SRK/T. This suggests that Barrett Universal II was the most sensitive to pupil dilation, followed by Haigis, and then SRK/T. The difference in the sensitivity to pupil dilation among the 9 formulas was significant. This tendency was also seen in the coincidence of recommended IOL power in each formula before and after dilation. The recommended IOL power calculated by Barrett Universal II changed most frequently among the formulas, although it was not statistically significant between Barrett Universal II and Haigis. Although some studies demonstrated that the recommended IOL power in Haigis was significantly affected by pupil dilation but not in SRK/T 10),12), 16) , our research was the first to show that Barrett Universal II may be even more sensitive to pupil dilation than Haigis, considering PPR and recommended IOL power.
The analysis of correlation between the change in PPR and the biometric variables indicated that the newer generation formula is more sensitive to pupil dilation. The change in PPR in Barrett Universal II and Haigis showed a significant positive correlation with the change in ACD and a significant negative correlation with the change in LT, but not in SRK/T. This tendency was more remarkable in Barrett Universal II. This result indicated that the change in ACD and LT significantly influenced the change in PPR in the formulas, which included ACD as a biometric parameter, and it was even more influential on the formula that included both ACD and LT as biometric variables. Additionally, the change in PPR in Barrett Universal II indicated a significant positive correlation with the change in WTW, but not in Haigis and SRK/T. This outcome was persuasive since Barrett Universal II was the only formula that included WTW as a biometric factor. Given the fact that all biometric factors, ACD, LT, and WTW, could be significantly influenced by pupil dilation, it is convincing that the more biometric parameters IOL calculation formula includes, the more influential pupil dilation is on the formula. As a result, recommended IOL power calculated by Barrett Universal II changed in many more cases after pupil dilation compared to Haigis and SRK/T.
Thus, there are biometric factors in the IOL calculation formula that are influenced by pupil dilation. In general, the more modern generation formula is, the more biometric parameters are included. Barrett Universal II is said to be one of the most reliable IOL calculation formulas. However, this study demonstrated that, since it includes many more such biometric variables compared to previous generation formulas; eye specialists have to be familiar with these phenomena to improve the accuracy of IOL calculation.
One of the limitations of this study is that the influence of pupil dilation on prediction error in refraction was not analyzed. This additional research can enable optimization of the constant for measurement with or without pupil dilation. This idea may be more useful to improve the accuracy of IOL power calculation. We plan to analyze this investigation in our future research.

Conclusions
In our study, pupil dilation influenced Barrett most strongly, followed by Haigis and SRK/T, in PPR and recommended IOL power. Given the stronger correlation between the change in PPR in Barrett

ETHICS APPROVAL AND CONSENT TO PARTICIPATE
This study was approved by the ethical committee at Yokosuka Chuoh Eye Clinic and Tsurumi Chuoh Eye clinic.

CONSENT FOR PUBLICATION
Written informed consent for publication of their clinical details and/or clinical images was obtained from the patients. A copy of the consent form is available for review by the editor of this journal.

AVAILABILITY OF DATA AND MATERIALS
The datasets used and/or analysed during the current study are available from the corresponding author upon reasonable request.

COMPETING INTERESTS
The authors declare that they have no competing interests

FUNDING
This research was unfunded.

AUTHORS' CONTRIBUTIONS
TT conceived the concept, designed, analyzed and interpreted the data, and was a major contributor in writing this manuscript. AM analyzed the data and interpreted the analyzed data. NM supervised the entire process in this study. All authors approved the final manuscript.