HOAs especially corneal HOAs were studied in several previous articles and found to be increased in patients with KCN [19–22]. Naderan et al.  reported that the ocular aberration, i.e., vertical and total coma and total HOA, increases in KCN and FFKC, and Colak et al.  showed that anterior corneal HOAs are significantly increased in eyes with moderate and advanced KCN. To the best of our knowledge, corneal aberrations are the predominant cause of vision dysfunction in KCN. Few articles studied corneal HOAs in different grades of KCN. The present study was designed to investigate the corneal HOAs of the anterior surface, posterior surface, and total cornea in KCN eyes with and without Vogt’s striae to explore which part of the HOA is prone to increase with the progress of KCN.
Vogt’s striae or stress lines are a typical clinical sign of progressive KCN . Significant correlations between the appearance of Vogt’s striae and changes in diopters and between visual acuity and corneal morphological parameters are observed . Our study also confirmed the same results by comparing corneal morphological parameters between eyes with and without Vogt’s striae. The UCVA and BCVA in KCN eyes with Vogt’s striae were significantly lower than those in eyes without Vogt’s striae.
As presented in Table 2, the vertical coma, spherical aberration, RMS (total), and RMS (HOA) in the front and back corneal surfaces and total cornea in KCN eyes with Vogt’s striae were significantly higher compared with those in KCN eyes without Vogt’s striae. These results were similar to those in previous studies [16, 26, 27] and due to the inferior position of the corneal cone in most patients with KCN [14, 28] and cone protrusion as the disease progresses. Feizi et al.  demonstrated that vertical and horizontal coma in the KCN group were significantly higher than those in normal cases. However, this finding was not consistent with our research. In the present study, the horizontal coma in the front and back corneal surfaces and total cornea in KCN eyes with and without Vogt’s striae was not significantly different. We believe that the horizontal coma may have less to do with the severity of KCN and that the appearance of Vogt’s striae in KCN eyes may significantly affect the vertical coma and has minimal influence on the horizontal coma.
The other finding of our study is that the vertical coma and spherical aberration of the back corneal surface are the opposite of that of the front corneal surface and total cornea in KCN eyes with and without Vogt’s striae. Similar findings were observed by Shokrollahzadeh et al. , who reported that the changes in the vertical coma of the front and back corneal surfaces have opposite signs because the front corneal surface converges, and the posterior surface diverges . Although the aberrations of front and back corneal surfaces compensate each other, the exact relationship remains uncertain.
In the association between the presence of Vogt’s striae and corneal HOAs, the front and total corneal 3rd-order vertical coma and spherical aberration were negatively correlated with K1, K2, Km, Kmax, ACE, and PCE. Given that the vertical coma on the front corneal surface and total cornea was negative, the RMS of 3rd-order vertical coma was positively correlated with K1, K2, Km, Kmax, ACE, and PCE. Colak et al.  compared corneal morphological parameters and front corneal HOAs in KCN and concluded a high correlation between the corneal curvature and total aberrations. In the present study, we evaluated corneal topographic indices and found that RMS (total) and RMS (HOA) were positively correlated with K1, K2, Km, Kmax, ACE, and PCE in front and back corneal surfaces and total cornea. Interestingly, these correlations were consistent with corneal morphological parameters and corneal HOAs comparisons between the KCN eyes with and without Vogt’s striae. These observations indicated that the appearance of Vogt’s striae may change the corneal shapes, further lead to increased corneal HOAs, and trigger visual diminution.
One limitation of our study is that grouping was not performed on the basis of corneal curvature, which may lead to potential bias. However, our study focuses on the influence of Vogt’s striae on corneal HOAs and the potential correlations between corneal HOAs and corneal morphological indices in KCN eyes with Vogt’s striae. Therefore, the curvature has little effect on our study.
In conclusion, we demonstrated that corneal HOAs especially vertical coma and spherical aberration in front and back corneal surfaces and total cornea may increase when Vogt’s striae appears in the KCN eyes. The scale of corneal HOAs is significantly related to changes in corneal shapes.