AIM: To explore the diagnostic value of combining the corneal stress-strain index(SSI)with corneal biomechanical parameters for early keratoconus.

METHODS:A retrospective study was conducted on 34 patients(53 eyes)with early keratoconus diagnosed and treated in our hospital from March 2022 to February 2024. Additionally, 112 normal volunteers(112 eyes)who underwent physical examinations in our hospital during the same period were selected as a healthy control group. The CorvisST equipment was utilized for measurement and recorded deformation with Scheimpflug camera to obtain 10 biomechanical parameters: first applanation time(A1T), first applanation length(A1L), velocity of initial applanation(Vin), second applanation time(A2T), second applanation length(A2L), velocity of outward applanation(Vout), highest concavity time(HCT), highest concavity depth of applanation(HCDA), highest concavity radius(HCR), and peak distance(PD), as well as stress-strain index(SSI), and the corneal biomechanical parameters of the two groups were compared. Furthermore, Logistic regression analysis was used to identify the risk factors for keratoconus, and ROC curves were plotted to analyze the biomechanical parameters of the cornea for early diagnosis of keratoconus.

RESULTS:The SSI(0.77±0.17)in patients with keratoconus was lower than that in healthy controls(1.01±0.24; P<0.001). Patients with keratoconus had lower A1T, A1L, A2L, and HCR, and higher Vout, HCDA, and PD compared to healthy controls(all P<0.001). Logistic regression analysis showed that decreased SSI, A1T, A1L, A2L, and HCR, as well as increased Vout, HCDA, and PD, were risk factors for the development of keratoconus(P<0.001). ROC curve analysis showed that the AUC value for combined diagnosis of early keratoconus was 0.997, with a Youden's index of 0.954, sensitivity and specificity of 98.1% and 97.3%, respectively, and a 95% CI of 0.994-1.000.

CONCLUSION:The combination of SSI and corneal biomechanical parameters holds diagnostic significance for early keratoconus, and the joint diagnostic value is even higher. It can be considered as a diagnostic or screening indicator for early keratoconus.