Characteristics of Posterior Corneal Astigmatism in Different Stages of Keratoconus
PurposeTo evaluate the magnitudes and axis orientation of anterior corneal astigmatism (ACA) and posterior corneal astigmatism (PCA), the ratio of ACA to PCA, and the correlation between ACA and PCA in the different stages of keratoconus (KCN).
MethodsThis retrospective study comprised 161 eyes of 161 patients with KCN (104 men, 57 women; mean age, 22.35±6.10 years). The participants were divided into 4 subgroups according to the Amsler‑Krumeich classification. A Scheimpflug imaging system was used to measure the magnitude and axis orientation of ACA and PCA. The posterior‑anterior corneal astigmatism ratio was also calculated. The results were compared among different subgroups.
ResultsThe average amounts of anterior, posterior, and total corneal astigmatism were 4.08±2.21 diopters (D), 0.86±0.46 D, and 3.50±1.94 D, respectively. With‑the‑rule, against‑the‑rule, and oblique astigmatisms of the posterior surface of the cornea were found in 61 eyes (37.9%), 67 eyes (41.6%), and 33 eyes (20.5%), respectively; corresponding figures in the anterior corneal surface were 55 eyes (32.4%), 56 eyes (34.8%), and 50 eyes (31.1%), respectively. A strong correlation was found between ACA and PCA in the different stages of KCN (P≤ 0.001, r = 0.839); the correlation was weaker in eyes with grade 3 (P≤ 0.001, r = 0.711) and grade 4 (P≤ 0.001, r = 0.717) KCN. The maximum posterior‑anterior corneal astigmatism ratio (PCA/ACA, 0.246) was found in patients with stage 1 KCN.
ConclusionCorneal astigmatism in anterior surface was more affected than posterior surface by increasing in the KCN severity, although PCA was more affected than ACA in an early stage of KCN.
Journal of Ophthalmology Bina, Volume:23 Issue:1, 2017
49 - 56
روشهای دسترسی به متن این مطلب
در سایت عضو شوید و هزینه اشتراک یکساله سایت به مبلغ 300,000ريال را پرداخت کنید. همزمان با برقراری دوره اشتراک بسته دانلود 100 مطلب نیز برای شما فعال خواهد شد!
به کتابخانه دانشگاه یا محل کار خود پیشنهاد کنید تا اشتراک سازمانی این پایگاه را برای دسترسی همه کاربران به متن مطالب خریداری نمایند!