Detection of optical surface of patient interface for ophthalmic laser applications using a non-confocal configuration
An ophthalmic laser system uses a non-confocal configuration to determine a laser beam focus position relative to the patient interface (PI) surface. The system includes a light intensity detector with no confocal lens or pinhole between the detector and the objective lens. When the objective focuses the light to a target focus point inside the PI lens at a particular offset from its distal surface, the light signal at the detector peaks. The offset value is determined by fixed system parameters, and can also be empirically determined by directly measuring the PI lens surface by observing the effect of plasma formation at the glass surface. During ophthalmic procedures, the laser focus is first scanned insider the PI lens, and the target focus point location is determined from the peak of the detector signal. The known offset value is then added to obtain the location of the PI lens surface.
1. An ophthalmic laser system comprising:
a laser source configured to generate a parallel light beam;
an objective lens configured to focus the parallel light beam to a focus point;
an objective lens movement structure configured to move the objective lens in a Z direction which is parallel to an optical path of the ophthalmic laser system;
a light intensity detector;
a beam splitter disposed to guide a portion of the light beam from the laser source to the objective lens and to guide a portion of a back-reflected light beam, which has been reflected back by a reference reflective surface disposed in front of the objective lens and has passed through the objective lens, to the light intensity detector, wherein the reference reflective surface is a surface attached to the laser system other than any anatomical structure of an eye of a patient,
wherein the optical path is free of any lens between the objective lens and the light intensity detector;
a controller electrically coupled to the light detector and the objective lens movement structure, the controller being configured to control a movement of the objective lens and to analyze a corresponding light intensity signal detected by the light intensity detector, which represents an intensity of the light which has been reflected back by the reference reflective surface and is incident on the light intensity detector, including to determine that a position of the objective lens in the Z direction is at a predefined position with respect to the reference reflective surface by determining a peak of the light intensity signal detected by the light intensity detector.
2. The ophthalmic laser system of claim 1 , wherein the light intensity detector has an effective detection area of 1 mm 2 or less.
3. The ophthalmic laser system of claim 1 , wherein the objective lens is configured to focus the parallel light beam to the focus point having a size of 2 μm or less.
4. The ophthalmic laser system of claim 1 , wherein the objective lens has a numerical aperture of 0.4 or higher.
5. The ophthalmic laser system of claim 1 , further comprising:
a housing, wherein the light intensity detector is mounted in the housing at a fixed location, and wherein the objective lens is moved relative to the housing; and
a patient interface optical element mounted on the housing and having an optical surface disposed to receive the light beam from the objective lens and to reflect a part of the received light beam back to the objective lens, wherein the optical surface of the patient interface optical element forms the reference reflective surface.
6. The ophthalmic laser system of claim 5 , wherein the controller is further electrically coupled to the laser source, the controller being further configured to:
set a power of the light beam to a first power below a plasma threshold for the patient interface optical element, and while the power is set to the first power:
control the objective lens movement structure to move the objective lens in the Z direction;
control the light intensity detector to measure a light that has been reflected back by the optical surface of the patient interface optical element and has passed through the objective lens;
analyze a light intensity signal produced by the detector while the objective lens is moved; and
determine a first position of the objective lens that corresponds to a peak position in the light intensity signal;
set the power of the light beam to a second power above the plasma threshold for the patient interface optical element, and while the power is set to the second power:
control the objective lens movement structure to move the objective lens in the Z direction to move the light focus point from a position outside of the patient interface optical element through the optical surface to a position inside the patient interface optical element;
control the light intensity detector to measure a light that has been reflected back by the optical surface of the patient interface optical element and has passed through the objective lens; and
determine a second position of the objective lens that corresponds to a sudden decrease in the light intensity signal; and
calculate a difference between the first and second positions as an offset value and store the offset value.
7. The ophthalmic laser system of claim 6 , wherein the optical surface is a distal optical surface of the patient interface optical element.
8. The ophthalmic laser system of claim 5 , wherein the controller is further electrically coupled to the laser source, the controller being further configured to:
control the objective lens movement structure to move the objective lens in the Z direction;
control the light intensity detector to measure a light that has been reflected back by the optical surface of the patient interface optical element and has passed through the objective lens;
analyze a light intensity signal produced by the detector while the objective lens is moved;
determine a first position of the objective lens that corresponds to a peak position in the light intensity signal;
calculate a second position of the objective lens based on the first position, an offset value pre-stored in the controller, and a depth value, wherein the offset value represents a distance between the optical surface of the patient interface optical element and a light focus position that corresponds to the peak position in the light intensity signal;
move the objective lens to the second position; and
operate the laser source to scan the focus point of the light beam according to a scan pattern.
9. The ophthalmic laser system of claim 8 , wherein the offset value is a fixed value determined by a focal length of the objective lens and a fixed length of the optical path from the light intensity detector to the optical surface of the patient interface optical element.
10. The ophthalmic laser system of claim 8 , wherein the optical surface is a distal optical surface of the patient interface optical element.
11. A method implemented in an ophthalmic laser system, the ophthalmic laser system comprising a laser source for generating a light beam, a moveable objective lens for focusing the light beam, a light intensity detector for detecting a light signal from the objective lens, and a controller, the method comprising:
mounting a patient interface device on the ophthalmic laser system, the patient interface device having an optical element with a distal optical surface;
using the objective lens to focus the light beam generated by the laser source to a focus point located inside the patient interface optical element;
moving the objective lens to move the focus point;
using the light intensity detector, detecting a back-reflected light that has been reflected by the distal optical surface of the patient interface optical element and has passed through the objective lens, to generate a light intensity signal, wherein the back-reflected light travels from the objective lens to the light intensity detector without passing through any other lens;
analyzing the light intensity signal to determine a first position of the objective lens that corresponds to a peak position in the light intensity signal;
calculating a second position of the objective lens based on the first position, a pre-stored offset value, and a depth value, wherein the offset value represents a distance between the distal optical surface of the patient interface optical element and a light focus position that corresponds to the peak position in the light intensity signal;
moving the objective lens to the second position; and
operating the laser source to scan the focus point of the light beam according to a scan pattern.
12. The method of claim 11 , wherein the light intensity detector has an effective detection area of 1 mm 2 or less.
13. The method of claim 11 , wherein the focus point has a size of 2 μm or less.
14. The method of claim 11 , wherein the objective lens has a numerical aperture of 0.4 or higher.
15. An ophthalmic laser system comprising:
a laser source configured to generate a light beam;
an objective lens configured to focus the light beam to a focus point;
an objective lens movement structure configured to move the objective lens in a Z direction which is parallel to an optical path of the ophthalmic laser system;
a housing, wherein the objective lens is moved relative to the housing;
a patient interface optical element mounted on the housing and having an optical surface disposed to receive the light beam from the objective lens and to reflect a part of the received light beam back to the objective lens;
a light intensity detector disposed to receive a portion of a light reflected or scattered by the optical surface;
a controller electrically coupled to the laser source, the light intensity detector and the objective lens movement structure, wherein the controller is configured to:
set the power of the light beam to a predetermined power;
while the power of the light beam is set to the predetermined power, control the objective lens movement structure to move the objective lens in the Z direction to move the light focus point from a position outside of the patient interface optical element through the optical surface to a position inside the patient interface optical element;
while moving the objective lens in the Z direction, control the light intensity detector to measure a light that has been reflected or scattered by the optical surface; and
based on a light intensity signal measured by the light intensity detector during movement of the objective lens, determine whether or not a sudden change in the light intensity signal occurred which indicates that a glass burn has occurred.
16. The ophthalmic laser system of claim 15 , wherein the predetermined power is above a plasma threshold for the patient interface optical element, and wherein the light beam is configured to burn the optical element when the focus point is inside the optical element,
wherein the controller is further configured to:
upon detecting a sudden change in the light intensity signal measured by the light intensity detector, determine a position of the objective lens that corresponds to the sudden change in the light intensity signal; and
store the determined position of the objective lens as a reference position corresponding to a Z direction position of the optical surface.
17. The ophthalmic laser system of claim 15 , wherein the controller is further configured to determine whether or not the ophthalmic laser system is in an optimum condition based on whether or not a glass burn has occurred.
18. The ophthalmic laser system of claim 15 , wherein the optical surface is a distal optical surface of the patient interface optical element.
19. The ophthalmic laser system of claim 15 , further comprising a beam splitter disposed to guide a portion of the light beam from the laser source to the objective lens and to guide a portion of a back-reflected light beam, which has been reflected back by the reference reflective surface disposed in front of the objective lens and has passed through the objective lens, to the light intensity detector.