[A study on the consistency of measuring corneal astigmatism and refractive astigmatism with different instruments]

Objective: To investigate the differences and consistency in measuring corneal astigmatism between autorefractors and corneal topographers, as well as in assessing total ocular astigmatism among autorefractors, wavefront aberrometers, and subjective refraction devices, so as to provide a basis for clinical instrument selection for astigmatism measurements. Methods: A retrospective study was conducted. A total of 245 patients (245 right eyes) who underwent corneal refractive surgery and related examination at the Department of Ophthalmology, The Second Affiliated Hospital of Chongqing Medical University and Chongqing Mingda Eye Hospital from January 2015 to November 2023 were enrolled, including 85 males and 160 females, aged (32.17±10.16) years, with astigmatism degrees ranging from -4.50 to -0.25 D. The patients were divided into three age groups: 17-29 years (96 cases), 30-39 years (77 cases), and 40-50 years (72 cases). They were also classified based on the astigmatism degree:-0.25 to -0.75 D (131 eyes), -1.00 to -1.75 D (65 eyes), and ≤-2.00 D (49 eyes). Corneal astigmatism was measured using an autorefractor and a corneal topographer, while total ocular astigmatism was measured using an autorefractor, a wavefront aberrometer, and a subjective refraction device. The horizontal-vertical astigmatism vector (J₀) and 45° oblique astigmatism vector (J₄₅) of the cornea and the entire eye were calculated. Differences in corneal and total ocular astigmatism were compared. The Pearson correlation analysis of results from different instruments was performed, and the consistency was evaluated using the Bland-Altman analysis. Results: For corneal astigmatism, there were no statistically significant differences in J₀ measurements in the 30-39 years group and J₄₅ measurements in the 40-50 years group between the two instruments; however, statistically significant differences in J₀ and J₄₅ measurements were observed in other age groups and the overall population (all P<0.05). Moreover, no statistically significant differences were found in J₀ and J₄₅ measurements between the instruments in the ≤-2.00 D group, while statistically significant differences were present in other astigmatism groups and the overall population (all P<0.05). The results presented in a polar coordinate system showed that the measurement values of the two instruments were close in all groups and the overall population. The Pearson analysis indicated that J₀ and J₄₅ in all groups and the overall population were significantly correlated (all P<0.05). The consistency analysis revealed relatively good consistency in the 95% confidence interval (CI) of the 95% limits of agreement (LoA) for the overall results presented in a polar coordinate system. For total ocular astigmatism, statistically significant differences in J₀ measurements among the three instruments were observed in all age groups and the overall population (all P<0.05). Regarding J₄₅ measurements, only the 30-39 years group showed no significant difference among the autorefractor (P>0.05). In addition, there were statistically significant differences in J₀ measurements among the three instruments in all astigmatism groups and the overall population (all P<0.05). Regarding J₄₅ measurements, no significant difference was observed in the overall population and the -1.00 D to-1.75 D group (P>0.05). J₀ and J₄₅ in all groups and the overall population showed significant correlations between each pair of the three instruments (all P<0.05). The consistency analysis demonstrated that the upper limit of the 95%CI of 95% LoA for J₀ in all groups and the overall population was <0.50 D, and most of the lower limits were <0.50 D; the 95%CI of 95% LoA for J₄₅ in all measurements was within 0.50 D, indicating good consistency among the three instruments. Conclusions: In the undilated pupil state, the autorefractor and corneal topographer have a high correlation and relatively good consistency in measuring corneal astigmatism and can be mutually referential in clinical practice. The autorefractor, subjective refraction device, and wavefront aberrometer have a high correlation and good consistency in the measurements of total ocular astigmatism. Among them, the autorefractor and wavefront aberrometer (objective refraction) can provide references for the subjective refraction device (subjective refraction). Clinically, the selection can base on the applicable scope of the instruments and clinical requirements.