Distribution and related factors of corneal regularity and posterior corneal astigmatism in cataract patients

Purpose: To study the distribution of posterior corneal astigmatism (PCA) and its influencing factors in Chinese patients before cataract surgery. Patients and methods: A retrospective study was conducted in the First Affiliated Hospital of Soochow University, Suzhou, China. In all, this study enrolled 121 eligible eyes of 121 cataract patients. The astigmatism, aberrations and Q value of anterior, posterior and total cornea and anterior segment parameters (ACD, CCT, WTW, ATA) were measured by the Sirius System, and AL was measured by Lenstar LS 900. Cataract was diagnosed using slit-lamp examination. Results: The mean age of patients was 67.44 +/- 10.66 years old. Mean PCA was 0.31 +/- 0.17 (range 0.05-1.09) D and 85.9% eyes had PCA values <0.5 D. With-the-rule (WTR) astigmatism predominated the anterior cornea astigmatism (ACA) (48.8%) and total corneal astigmatism (TCA) (61.2%), while against-the-rule (ATR) astigmatism predominated posterior (86.0%). Significant positive correlation was found between the astigmatic power vector (APV) of ACA and PCA (Pearson correlation=0.318, P<0.001); TCA and PCA (Pearson correlation=0.204, P=0.025); keratometric astigmatism and PCA (Pearson correlation=0.356, P< 0.001); this study also found a positive correlation between primary spherical aberration (Z4 degrees) of the total cornea and PCA (Pearson correlation=0.266, P=0.003); primary spherical aberration (Z4 degrees) of the corneal front surface and PCA (Pearson correlation=0.260, P=0.004); total corneal aberrations (Total cornea root mean square [RMS]) and PCA (Pearson correlation=0.327, P< 0.001); total corneal higher-orderaberrations (Total HOA RMS) (Pearson correlation=0.232, P=0.011); total corneal lower-order aberrations (Total LOA RMS) (Pearson correlation=0.250, P=0.006). A positive linear correlation between Q value of corneal front surface and PCA, either 6 mm pupil diameter (Pearson correlation=0.264, P=0.003) or 8 mm pupil diameter (Pearson correlation=0.184, P=0.043) was found in this study. Conclusion: Corneal aberration, Q value (front surface specifically) was essential that we need to take into consideration when we conduct PCA and intraocularlens measurement in clinics.