Determining radiant exposure at the retina during an ophthalmic procedure

An ophthalmic laser system, comprising:

• a laser device configured to direct a laser beam towards a target within an eye, the eye having a retina, an axis of the eye defining a z-axis, a z-position being a position relative to the z-axis;
• an ophthalmic microscope configured to receive light from a focal point within the eye to provide an image of an object at the focal point;
• a z-direction sensor configured to determine the z-position corresponding to the focal point of the ophthalmic microscope by detecting the z-position of a base of the ophthalmic microscope;
• and
• a controller configured to:
• determine a position Z0, the z-position where the focal point of the ophthalmic microscope is at the retina of the eye by:
• autofocusing the focal point of the ophthalmic microscope at the retina of the eye or receiving user input that the focal point of the ophthalmic microscope is at the retina of the eye;
• and
• determining, from the z-direction sensor, the z-position corresponding to the focal point;
• determine a position Z, the z-position where the focal point of the ophthalmic microscope is at the target within the eye, by:
• autofocusing the focal point of the ophthalmic microscope at the target within the eye or receiving user input that the focal point of the ophthalmic microscope is at the target within the eye;
• and
• determining, from the z-direction sensor, the z-position corresponding to the focal point;
• calculate a target-to-retina distance ΔZ according to a difference between the position Z and the position Z0;
• calculate a radiant exposure He at the retina according to the target-to-retina distance ΔZ by:
• determining a laser spot size of the laser beam on the retina;
• and
• calculating the radiant exposure He according to the target-to-retina distance ΔZ and the laser spot size of the laser beam:
• calculate a closest target-to-retina distance ΔZ at which the eye can be treated, given a laser pulse energy E of the laser beam;
• calculate a maximum laser pulse energy E at which the eye can be treated, given the target-to-retina distance ΔZ;
• calculate a range of laser pulse energy E values and a range of target-to-retina distance ΔZ values at which the eye can be treated;
• determine whether the radiant exposure He exceeds a maximum radiant exposure;
• if the radiant exposure He exceeds a maximum radiant exposure, prevent the laser device from directing the laser beam towards the target within the eye;
• and
• otherwise, allow the laser device to direct the laser beam towards the target within the eye.