Including posterior corneal astigmatism (PCA) into consideration may increase the accuracy of astigmatism correction after corneal refractive surgery. In the present study we aim to investigate the distribution pattern of PCA in a large number of myopic patients from multiple ophthalmic centers. There were 7829 eyes retrospectively included in the study. Pentacam data of the eyes were retrieved from the machine and only results with image quality labelled with ‘OK’ were included. Distribution of PCA was slightly positively skewed (Skewness = 0.419, Kurtosis = 0.435, KS P < 0.0001). Mean PCA was 0.34 ± 0.14 D (range: 0.00 D-0.99 D). PCA was ≥ 0.25 D in 74.91% of the eyes and was ≥ 0.50 D in 11.61% of the eyes. In 97.55% of the eyes the steep meridian of PCA was vertical (SMV). PCA magnitude was significantly higher in eyes with SMV PCA (P < 0.0001) or high manifest astigmatism (MA, P < 0.0001). There was a significant correlation between anterior corneal astigmatism (ACA) magnitude and PCA magnitude in all of the eyes (r = 0.704, P < 0.0001). There was also a trend of decreasing frequency and magnitude of SMV PCA with aging (both P < 0.0001). In conclusion, PCA is present in myopic patients having corneal refractive surgery and PCA magnitude is increased with higher MA or ACA. Consideration of the impact of PCA on laser astigmatism correction may be necessary.

Purpose: To investigate the distribution of white-to-white (WTW) corneal diameter and anterior chamber depth (ACD) in Chinese myopia patients.Methods: This was a cross-sectional observational study conducted at five ophthalmic centers. Anterior segment biometry was performed in 7,893 eyes of the 7,893 myopic patients using Pentacam, and the WTW and ACD were recorded. The distribution patterns of WTW and ACD were evaluated and the correlation between WTW and ACD was analyzed statistically.Results: There were 4416 (55.95%) males and 3477 (44.05%) females. The age of the study population was 25.14 ± 5.41 years. Distribution of WTW was slightly positively skewed (Skewness = 0.0076, Kurtosis = 0.3944, KS P = 0.020) with a mean of 11.65 ± 0.38 mm and a 95% normal range of 10.91–12.39 mm. A significant difference in WTW was found among different myopia groups (P &lt; 0.001). The ACD was normally distributed (Skewness = 0.899, Kurtosis = 0.027, KS P = 0.086). The mean ACD was 3.25 ± 0.26 mm and the 95% normal range of was 2.74–3.75 mm. A significant difference in ACD was also found among different myopia groups (P = 0.030). There was a significant correlation between WTW and ACD (r = 0.460, P &lt; 0.001).Conclusions: In our study, 95% of the Chinese myopic patients had a WTW within 10.91–12.39 mm and an ACD within 2.74–3.75 mm. ACD and WTW were significantly different among different myopia, gender and age groups. WTW was positively correlated with ACD.

It is essential to know the normal range of the interocular symmetry of the cornea (ISC) for keratoconus diagnosis and corneal substitutes design. In the present study we investigated the interocular symmetry of corneal biometrics in 6,644 Chinese myopic patients from multiple ophthalmic centers. Corneal biometrics of both eyes were exported from the Pentacam instrument. Interocular symmetry of the corneal biometrics was analyzed by Spearman’s correlation test, intraclass correlation coefficient (ICC) analysis and Bland–Altman plot. Significantly strong interocular correlations were found in anterior and posterior corneal curvatures, corneal diameter, corneal thickness, corneal volume, corneal eccentricity, and corneal asphericity (r = 0.87–0.98, all P < 0.001). Moderate interocular correlations were observed in whole corneal astigmatism (r = 0.78) and posterior corneal astigmatism (r = 0.73). ICC between the right and left eyes was 0.94–0.98 for anterior and posterior corneal curvatures, corneal diameter, corneal thickness and corneal volume, 0.80–0.88 for corneal eccentricity and asphericity, and 0.73–0.79 for corneal astigmatism (all P < 0.001). Bland–Altman plot showed that the 95% limit of agreement between both eyes was narrow and symmetric in most of the corneal biometrics, suggesting strong interocular agreements in these corneal biometrics. In conclusion, significant interocular symmetry of corneal biometrics is observed in Chinese myopia patients. Extra attention should be paid to patients with interocular corneal asymmetry.

We aimed to evaluate the posterior corneal and anterior chamber changes following small incision lenticule extraction (SMILE) and femtosecond laserassisted laser in situ keratomileusis (FS-LASIK). This retrospective study included 93 eyes for SMILE and 228 eyes for FS-LASIK. Posterior corneal curvature, anterior chamber biometrics, and posterior corneal aberrations preoperatively and at 1 week and 3 months after surgery were evaluated. The correlation between surgical-related factors and posterior corneal morphology changes, posterior corneal morphology changes, and posterior corneal aberration alterations were determined. There was an increase in mean posterior corneal radius (PCC R) and flat posterior corneal radius (PCC R1) and decrease in anterior chamber depth and anterior chamber volume in the SMILE and FS-LASIK group (all p < 0.05). A significant difference was observed in posterior corneal higher-order aberrations before and after the FS-LASIK (p = 0.006). A negative correlation was found between alterations of PCC R and changes of posterior corneal spherical aberrations in the SMILE (r = −0.289) and FS-LASIK group (r = −0.383). In conclusion, posterior corneal and anterior chamber biometrics are changed after SMILE and FS-LASIK. Innovatively, we find that changes in posterior corneal morphology are correlated with posterior corneal aberration alterations.

Aims To predict posterior corneal astigmatism (PCA) magnitude and flat axis using other corneal parameters. Methods In this multicenter cross-sectional study, sex, age, eye laterality, and eight selected corneal parameters were input, and PCA magnitude and flat axis were output of the ridge regression (RR) models. Data from two centers were used for RR models construction and internal validation, and data from the other three centers were for external validation. Mean absolute error (MAE), root mean square error (RMSE) and area under the receiver operating characteristic curve (AUC) were used to evaluate the prediction accuracy. Results A total of 10448 subjects (17538 eyes) were included (5943 males and 4505 females, mean age: 24.84 ± 5.38 years). An RR equation was generated for prediction of PCA magnitude in all eyes (R2 = 0.501) with an MAE and an RMSE of 0.065-0.080D and 0.083-0.102D in external validation, respectively. Another RR equation was generated for prediction of PCA flat axis in all eyes (R2 = 0.157) with an MAE and an RMSE of 6.254–8.518° and 9.052–12.612° in external validation, respectively. Binary prediction of eyes with a PCA ≥ 0.50D was performed with a mean AUC of 0.900-0.928 in external validation. For eyes with a PCA ≥ 0.50D, in external validation an MAE of 0.049-0.059D and an RMSE of 0.058-0.076D were achieved in prediction of PCA magnitude, with an MAE of 2.863–4.010° and an RMSE of 3.755–5.263° in prediction of PCA flat axis. Conclusions Accurate prediction of PCA magnitude and flat axis based on other corneal parameters can be achieved by RR models. The RR models may be useful in refractive surgery to improve personalized astigmatism correction and prevent residual astigmatism.