Comparison of Refractive Power and Astigmatism between Digital Keratometer and Autorefractor

PURPOSE: To compare the corneal refraction, astigmatism, and corneal marking for toric intraocular lens measured with a VERION® Image Guided System and an autorefractor in order to precisely determine the toric intraocular lens target. METHODS: The medical records of 29 eyes of 29 patients were retrospectively reviewed to compare the corneal refraction, axis, and amount of astigmatism measured with a VERION® Image Guided System and an autorefractor. We compared the difference in marked axis for toric intraocular lenses as measured by a VERION Digital Marker and a manual marker. RESULTS: The average corneal refraction and amount of astigmatism were greater with the VERION® Image Guided System than with the autorefractor. The average difference in axis of astigmatism was 9.62°. The difference in axis of astigmatism in patients with more than 1.0 D of astigmatism (18 eyes) was 2.82 ± 2.27°, while that in patients with less than 1.0 D of astigmatism (11 eyes) was 20.27 ± 28.14°. The average difference in marked axis for toric intraocular lens measured by the VERION® Digital Marker and manual marker was 2.50° (0°-9.27°). CONCLUSIONS: The corneal refraction and amount of astigmatism were significantly higher with the VERION® Image Guided System, so careful concern and comparison of surgical outcomes between the two devices is needed in biometry.

Paying attention to precision correcting surgery for cataract associated with corneal astigmatism / 中华实验眼科杂志

Corneal astigmatism in patients with cataract is very common,but it could not be accurately corrected during previous cataract surgery,which usually affects the visual quality seriously.The accurate measurement of corneal astigmatism power and meridian before surgery is key to the effective correction of astigmatism during the cataract surgery by either the determination of astigmatic keratotomies or the selection and implantation of toric intraocular lenses (IOL).The combination of IOL Master for sphere,the Pentacam for the total corneal refractive power and VERION Digital Marker for surgical orientation can provide promising refractive examination,treatment and good postoperative outcomes.Preexsisting astigmatism can be corrected during cataract surgery by modifying incision,performing arcuate keratotomy,or implanting a toric IOL.Femtosecond laser arcuate keratotomy combined with phacoemulsification is an effective,safe and precise method for the correction of low to moderate corneal astigmatism power,and it can improve visual acuity in cataract surgery candidates.Further work is required to establish corneal biomechanics numerical simulation and nomography protocol for cataract refractive surgery so as to improve the predictability and accuracy of femtosecond laser-assisted astigmatic keratotomy during refractive cataract surgery.

Digital marker tracing combined with center-of-mass algorithm in measuring pelvic displacement / 第二军医大学学报

Objective: To evaluate the reliability of the digital marker tracing method combined with center-of-mass algorithm in measuring human pelvic displacement. Methods: Six cadaveric specimens of the third lumbar vertebra to the proximal 1/3 part of femur were used in present study. The specimens had no structural abnormality and all the soft tissues were dissected, reserving the hip joint capsules and the ligaments of the pelvic ring and floor. Markers with black dots against white back-ground were used to mark the key points of the pelvis. Axial loadings from the proximal lumbar (simulating the two-legged stance) were applied by MTS in the gradient of 0 N to 500 N. Images of the front and lateral views were obtained using two CCD cameras. Using Image J software, we calculated the vertical displacement of S1, (the first sacral vertebrae) in the front view and the micro-angular rotation of sacroiliac joint in the lateral view by measuring the marker's movement. Results: There was good correlation between the marked points before and after deformation of the pelvis, with the average correlation coefficient being 0. 983. Based on the 768 X 576 pixels, pixel size (mm) 0. 681 5 X 0. 681 5 image,the accuracy of the displacement was about 0. 018 pixels and the comparative error could reach 1. 11‰. The load-displacement curves obtained in this study accorded well with the clinical results. The pelvic load-displacement curve exhibited approximately a linear behavior; the sacroiliac joint load-angular rotation curve in the sagittal plane exhibited a non-linear behavior. Under a vertical load of 500 N,the average vertical displacement of S1, of the pelvis was (0. 835 6 ± 0. 283 0) mm and the average micro-angular rotation of sacroiliac joint in lateral view was (0. 584 ±0. 221). Conclusion: Digital marker tracing method combined with the center-of-mass algorithm is a simple, accurate method for measurement of pelvic displacement, which can be widely used in biomechanical research.