Systems and methods for monitoring properties of the cornea and controlling the crosslinking treatment. The thickness of the cornea during crosslinking may be measured by using ultrasonic reflections to determine an anterior distance (Di') between a reference location (37) on a device resting on the eye and an anterior surface (66) of the cornea and to determine a posterior distance (D3') between a posterior surface (63) of the cornea and an element of the eye such as an anterior surface (72) of the lens of the eye. These distances are subtracted from a reference distance (Do) between the reference location and the element of the eye. The reference distance (Do) may be determined using ultrasonic reflections to determine the corresponding anterior and posterior distances and the thickness (D2) of the cornea prior to crosslinking. The speed of sound in the cornea during crosslinking may be derived using the thickness (D2') and time of flight of ultrasound through the cornea. The position of the cornea relative to a reference location may be determined. In still other embodiments, location of a surface of demarcation (86) within the cornea formed as a result of crosslinking may be determined. Still other embodiments provide for determination of one or more resonant frequencies of the cornea, and for measurement of responses of the cornea to applied forces, such as displacement and rebound velocity. The properties of the cornea may be used as proxies for the extent of crosslinking, and a light source (48, 348) used to induce crosslinking may be controlled in response to such proxies.L'invention concerne des systèmes et des procédés de contrôle de propriétés de la cornée et de contrôle du traitement de réticulation. L'épaisseur de la cornée pendant la réticulation peut être mesurée par des réflexions ultrasoniques pour déterminer une distance antérieure (Di') entre un emplacement de référence (37) sur un dispositif reposant sur l'œil et une surface antérieure (66) de la
