METHODS: A cross-sectional study. Three hundred and forty-five eyes of 247 consecutive keratoconus patients diagnosed in Henan Eye Hospital were enrolled during September 2018 to December 2020. The mean age was(24.51±6.38)years. According to age, the subjects were divided into ≤20 years group, 21-30 years group and ≥31 years group. The severity of keratoconus was divided into AK1, AK2, AK3 and AK4 by Amsler krumeich(AK)classification method. The visual acuity, corneal flat curvature(K1), corneal steep curvature(K2), average corneal curvature(Km)and the thinnest corneal thickness(TCT)were measured. The SP-A1, intraocular pressure(IOP), deformation amplitude max(DA Max), velocity at the first applanation(A1V), time at the first applanation(A1T), time at the second applanation(A2T), velocity at the second applanation(A2V), biomechanical corrected IOP(bIOP), and Radius were measured by Corneal Visualization Scheimpflug Technology(Corvis ST). The correlation between SP-A1 and other parameters were analyzed by Spearman rank correlation, and one-way ANOVA was used to analyze the difference of SP-A1 among different age groups or disease severity groups.

RESULTS: No statistically differences of gender, visual acuity, IOP, K1, K2, Km, TCT and disease severity classification were found among different age groups(P>0.05). The SP-A1 was positively related to age(r_s=0.137, P=0.011). The SP-A1 of keratoconus patients in the ≥31 years group was significantly higher than that in the ≤20 years group and 21-30 years group(P<0.05). SP-A1 was negatively correlated with K1, K2 and Km in patients in the ≤20 years group and 21-30 years group, while SP-A1 was negatively correlated with K2 in patients in the ≥31 years group(P<0.05). In addition, SP-A1 was negatively correlated with DA Max, A1V and A2T, and positively correlated with TCT, IOP, bIOP, A1T, A2V and Radius. With the increase of disease severity, the SP-A1 values gradually decreased in patients in the ≤20 years group and 21-30 years group(P<0.05). The values of SP-A1 between AK1 and AK4, AK2 and AK3, AK2 and AK4 were statistically different(P=0.008, 0.035, 0.001).

CONCLUSION: The value of SP-A1 in keratoconus was positively correlated with age. In patients less than 30 years old, the SP-A1 decreased with the increase of disease severity.