AIM: To investigate the diagnostic value of the difference of binocular biological parameters of the anterior segment in early keratoconus.

METHODS: Retrospective case-control study. A total of 183 patients(366 eyes)who visited our hospital from March 2022 to November 2023 were included, including 107 cases(214 eyes)in the control group(patients with simple refractive error), 40 cases(80 eyes)in the subclinical keratoconus group, and 36 cases(72 eyes)in the clinical keratoconus group. All of the patients were examined by the Pentacam anterior segment analyzer to determine the inferior-superior 3 mm of the posterior corneal surface(I-S), corneal posterior elevation of the thinnest point(P.E.), maximum posterior elevation of the best fit sphere(MPE from BFS), the maximum posterior elevation of the best fit toric ellipsoid(MPE from BFTE), posterior aspherical asymmetry index(AAI), central corneal thickness(CCT), thinnest corneal thickness(TCT), pachymetric progression index average(PPIavg), Ambrósio relational thickness maximum(ARTmax), Belin/ Ambrósio enhanced ectasia display(BAD-D), and the binocular difference of each test was calculated separately for each patient. The control group was further divided according to corneal diameter: 21 cases(42 eyes)with corneal diameter <11.2 mm in group A, 54 cases(108 eyes)with 11.2 mm≤ corneal diameter ≤11.8 mm in group B, and 32 cases(64 eyes)with corneal diameter >11.8 mm in group C.

RESULTS: There was significant differences in the binocular I-S, P.E., MPE from BFS, MPE from BFTE, AAI, CCT, TCT, PPIavg, ARTmax and BAD-D between the clinical keratoconus group and the control group(P<0.05). The difference of binocular I-S, P.E., MPE from BFS, MPE from BFTE, AAI, CCT, TCT, PPIavg, and BAD-D were of high diagnostic value(AUC≥0.900), with the best diagnostic ability for P.E. and BAD-D, and an AUC as high as 0.999 and 0.995, respectively. The difference of binocular P.E. and ARTmax between the subclinical keratoconus group and the control group were statistically significant(P<0.05). The difference of binocular I-S, P.E. and BAD-D had high diagnostic value for subclinical keratoconus(AUC≥0.900). In the control group A, B and C, there were no significant difference in binocular I-S, CCT, TCT, MPE from BFS, MPE from BFTE, AAI, PPIavg and ARTmax(all P>0.05), and none of them had correlation with corneal diameter(P>0.05); however, there were statistical significant differences in binocular P.E. and BAD-D in the control group A, B and C(P=0.007, 0.003), while the P.E. differences had no correlation with corneal diameter(P=0.270), and binocular BAD-D differences were negatively correlated with corneal diameter(r=-0.230, P=0.017).

CONCLUSION: Pentacam anterior segment analyzer can accurately measure a variety of corneal biological parameters. Difference of binocular corneal I-S, P.E. and BAD-D are sensitive indexes for the early diagnosis of keratoconus. Among them, difference of binocular I-S and P.E. are less affected by corneal diameter, thus being significant for the early diagnosis of keratoconus with different cornea diameters.