Objective To observe the morphological characteristics of corneal topography in patients with keratoconus using the ALLEGRO Oculyzer for measurements； to provide data for early diagnosis and screening of keratoconus and an analysis of the pathogenesis of keratoconus. Methods This was a retrospective case control study. Sixty-two clinical keratoconus patients （66 eyes）， 57 subclinical keratoconus patients （57 eyes） and 35 healthy people （70 eyes） were enrolled in this research. All of them were examined using the Oculyzer for measurements. Posterior surface topography classifications for elevation were divided into 6 types： island， incomplete island， increasing bridge， decreasing bridge，incomplete bridge and irregular type. The morphological features of the elevation pattern maps and the position of the cornea at the thinnest point were studied by observing the pachometer apex and the pupil center. The collected data were analyzed with one-way ANOVA and a nonparametric test. Results The types of topography of the posterior surface in the normal eyes （group 1） were mainly an incomplete bridge （61%） and decreasing bridge （26%）， the topography of the subclinical keratoconus eyes （group 2） were mainly an increasing bridge （40%） and an incomplete island （25%）， and the clinical keratoconus eyes （group 3） were mainly an incomplete island （33%） and island （56%）. The thinnest points were located in the inferior temporal region in 81%， 86%， and 76%， respectively. The distance between the thinnest point and corneal apex in groups 1， 2， and 3 were 0.59±0.20 mm， 0.77±0.27 mm， 0.66±0.32 mm， respectively， and the differences were statistically significant （F=6.903， P<0.01）. The angles in the inferior temporal region in groups 1， 2， and 3 were （41.96±17.30）°， （49.14±18.83）°， （49.40±16.77）°， respectively， and the differences were statistically significant （F=3.112， P<0.05）. Conclusion The posterior surface of the cornea in patients at risk for keratoconus ranged from the development of an incomplete bridge type to an incremental type. Moreover， the increases in distance between the thinnest corneal position and the corneal apex are related to the development of keratoconus. More attention should be paid to this condition.