Abstract
Purpose :
Posterior corneal astigmatism (PCA) is an important contributor to total corneal astigmatism. Its magnitude and direction has been previously elucidated using Scheimpflug imaging. However, its relationship to anterior corneal astigmatism (ACA) and other biometric variables like axial length has not been well described. The purpose of this study is to investigate the relationship between ACA and PCA using a swept-source OCT biometer.
Methods :
Biometric measurements obtained between February 2020 and May 2021 were exported from a SS-OCT device (IOLMaster 700, Carl Zeiss Meditec AG). Chart review was preformed to associate the exported data with clinical variables and determine any comorbidities at the time of scan. Inclusion criteria were male or female, age 18 or older at the time of measurement. Exclusion criteria included any significant corneal or intraocular media opacity other than cataract, abnormal corneal findings, any anterior segment pathology that could significantly impact astigmatism, history of intraocular or corneal surgery, and failed or poor quality measurements as determined by the device’s internal image quality metrics.
Results :
Of 385 eyes, 283 eyes from 170 patients met the criteria for inclusion in the analysis. Of all eyes, 106 eyes had with-the-rule (WTR) ACA, 57 had oblique ACA, and 120 had against-the-rule (ATR) ACA. The average ACA magnitude was 1.12±0.86, 0.67±0.50, and 0.94±0.63 D in eyes with WTR, oblique, and ATR ACA, respectively (p = 0.0002). The average PCA magnitude was 0.30±0.16, 0.20±0.08, and 0.16±0.08 D in eyes with WTR, oblique, and ATR ACA, respectively (p < 0.0001). The proportion of eyes that had the PCA steep axis oriented vertically was 96%%, 91%, and 70% in eyes with WTR, oblique, and ATR astigmatism, respectively. In eyes with WTR and oblique ACA, there was a significant positive linear correlation between the magnitude of ACA and PCA (R2=0.58 and 0.36 respectively). There was no significant linear relationship between ACA and PCA in eyes with ATR ACA.
Conclusions :
The correlation between ACA and PCA magnitude is strongest in eyes with WTR ACA, weaker in those with obliquely oriented ACA, and weakest in those with ATR ACA. Increasing the number of eyes in the analysis will allow us to further elucidate how ACA and PCA relate in vector space, change with age, and correlate with other variables like axial length.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.