Carl Zeiss Meditec IOL Master
IOLMaster — White-to-White Measurement (WTW).
Determination of "White-to-White" (optional)
Fig. 34, White to White determination
Each time the joystick knob is pressed, an image of the eye is displayed, in which the detected iris edge is marked. After checking that the iris and fixation point have been correctly recognized, confirm with OK. Only then will the data be valid and available for further processing.
The WTW value is the horizontal diameter of the iris. In addition to the WTW value, the deviation of the visual axis from the center of the iris (x, y) will also be displayed (as seen above).
The values are stated in millimeters with reference to a Cartesian coordinate system, the zero point of which is assumed to be in the established center of the iris or pupil. If the visual axis is above the iris or pupil center, the Y value will be positive; if it is below, the value will be negative. X values to the left of the center are negative; those to the right are positive.