Purpose: To investigate the effect of head tilt on keratometric measurement using the IOLMaster.
Methods: Twenty-seven right eyes of 27 volunteers were examined using a manual keratometer (MK), automated keratometer (AK), and an IOLMaster. MK and AK measurements were performed in the upright head position, whereas IOLMaster measurements were performed in five different head positions (upright, 5° or 15° clockwise head tilt, and 5° or 15° counter-clockwise head tilt). The repeatability of IOLMaster was compared with MK and AK. The keratometric measurements (mean keratometric power, magnitude of astigmatism, and steep meridian) in different head positions were compared.
Results: The IOLMaster showed good repeatability of keratometric measurement comparable to MK or AK. 15° and 5° clockwise head tilt resulted in 12.09 ± 9.51 (mean ± SD) (P<0.001 vs upright) and 5.51 ± 5.97 (mean ± SD) degrees (P<0.001) of clockwise rotation of steep meridian, respectively. 15° and 5° counter-clockwise head tilt resulted in 12.49 ± 7.07 (mean ± SD) (P<0.001) and 6.08 ± 5.09 (mean ± SD) degrees (P<0.001) of counter-clockwise rotation of steep meridian, respectively.
Conclusions: The patient's head tilt (5° or 15°, clockwise or counter-clockwise) significantly changed the steep meridian of astigmatism measured using IOLMaster and the steep meridian generally shifted to the direction of head tilt. The importance of maintaining the upright head posture during IOLMaster measurement is demonstrated.