Patent ID: 8852175

Claim:
A system for locating tissue layer transitions within a cornea having an anterior surface, a posterior surface, and a photodisruption threshold, the system comprising: a laser subsystem configured to scan a laser spot at varying focal positions between the anterior surface of the cornea and the posterior surface of the cornea, the laser spot having an energy level of 0.2 μJ such that the irradiance of the laser spot is below the photodisruption threshold, a harmonic signal being produced as the laser spot propagates in the cornea, wherein the cornea has adjacent tissue layers with different harmonic signals, the adjacent tissue layers comprising one or more of the group consisting of an epithelium, a Bowman's layer, a stroma, a Descemet's membrane and an endothelium, and wherein the change in the harmonic signal indicates the tissue layer transition; a sensor configured to detect the harmonic signal; and a processor coupled to the sensor and the laser subsystem, the processor configured to: monitor a location of the laser spot within the cornea; measure a change in the harmonic signal; correlate the location of the laser spot within the cornea with the change in the harmonic signal to determine a tissue layer transition within the cornea; determine a thickness of the tissue layers based on the harmonic signal; and determine a distance between the tissue layer transition and the anterior surface of the cornea or the posterior surface of the cornea; wherein the laser subsystem comprises a femtosecond laser configured to produce a non-ultraviolet pulsed laser beam with a wavelength of about 400 nm to about 3000 nm, the spot corresponding to a focal spot of the beam; and wherein the harmonic signal has an intensity; and the change in the signal is based on a change in the intensity of the harmonic signal.