Customized aspheric intraocular lenses calculated with real ray tracing.

PURPOSE: To calculate the exact geometry of custom intraocular lenses (IOLs) for pseudophakic eyes and theoretically predict the residual wavefront error by real ray tracing based on Snell's law. SETTING: Centre for Ophthalmology, University Hospital, Tübingen, Germany. METHODS: Individual computer models were constructed based on measurements, including corneal topography and axial length. The geometry of custom spherical, aspheric, toric, and toric aspheric IOLs was calculated in an optimization process with real ray tracing to provide the minimum root mean square wavefront error. The geometric optical properties in terms of residual wavefront error was simulated and approximated by Zernike polynomials. RESULTS: Data from 45 pseudophakic eyes were used to construct the models. Defocus was almost completely corrected by the spherical IOL and astigmatism, by the toric IOL. The aspheric IOL strongly reduced spherical aberration but only slightly reduced total higher-order aberrations (HOAs); both theoretical predictions corresponded to clinical investigations of wavefront measurements in pseudophakic eyes with a spherical or aspheric IOL. CONCLUSIONS: Real ray tracing calculated the exact geometry of custom IOLs to provide the minimum wavefront error, going beyond simple diopter information. Results show spherical aberration can be significantly reduced with aspheric IOLs. However, the limited possible reduction of total HOAs, even perfectly positioned custom aspheric IOLs, may be a reason for the unclear results in studies assessing the potential benefit to visual performance of currently used aspheric IOLs.

Virtual reality training improves wet-lab performance of capsulorhexis: results of a randomized, controlled study.

PURPOSE: To investigate, whether capsulorhexis training on the EYESi surgical simulator improves wet-lab operating performance of surgical novices. METHODS: Randomized, masked experimental study. Thirty-one medical students and 32 ophthalmological residents were randomized to either virtual reality (VR) training, or control. Initially and after 3 weeks each participant performed three capsulorhexis tasks in a porcine wet-lab. In between, participants from the VR training groups completed two training trials on the EYESi surgical simulator (VRmagic, Mannheim, Germany). VR training consisted of basic skill tasks and capsulorhexis tasks of increasing difficulty, and preset performance goals had to be reached for each task. All wet-lab procedures (n = 372) were recorded on DVD, and assessed by a masked observer. Each wet-lab capsulorhexis was evaluated with regard to five criteria (circularity, size, centering, time, tissue protection) using a predefined scoring system with a maximum overall score of 10 points (2 per criterion). The primary outcome measure was the intra-individual difference in the average overall performance score between the first and second wet-lab capsulorhexis procedures. Ten operation videos were additionally assessed by three further investigators to determine interobserver agreement. RESULTS: Inter-observer agreement regarding the overall performance score was high (ICC = 0.91). Compared to control groups, VR-trained students and residents showed significant improvement in their median wet-lab capsulorhexis overall performance score compared to controls (+3.67 vs +0.33 points, P = 0.001 and +3.33 vs +/-0.00 points, P < 0.0001). The capsulorhexis performance of VR-trained students and residents was also more consistent with a lower standard deviation of scores compared to controls (SD 1.3 vs 2.1 and 1.2 vs 1.7 points respectively). CONCLUSIONS: Structured capsulorhexis training on the EYESi to reach specific target criteria significantly improved wet-lab capsulorhexis performance.

Comparison of the new perimetric GATE strategy with conventional full-threshold and SITA standard strategies.

PURPOSE: A new, fast-threshold strategy, German Adaptive Thresholding Estimation (GATE/GATE-i), is compared to the full-threshold (FT) staircase and the Swedish Interactive Thresholding Algorithm (SITA) Standard strategies. GATE-i is performed in the initial examination and GATE refers to the results in subsequent examinations. METHODS: Sixty subjects were recruited for participation in the study: 40 with manifest glaucoma, 10 with suspected glaucoma, and 10 with ocular hypertension. The subjects were evaluated by each threshold strategy on two separate sessions within 14 days in a randomized block design. RESULTS: SITA standard, GATE-i, and GATE thresholds were 1.2, 0.6, and 0.0 dB higher than FT. The SITA standard tended to have lower thresholds than those of FT, GATE-i, and GATE for the more positive thresholds, and also in the five seed locations. For FT, GATE-i, GATE, and SITA Standard, the standard deviations of thresholds between sessions were, respectively, 3.9, 4.5, 4.2, and 3.1 dB, test-retest reliabilities (Spearman's rank correlations) were 0.84, 0.76, 0.79, and 0.71, test-retest agreements as measured by the 95% reference interval of differences were -7.69 to 7.69, -8.76 to 9.00, -8.40 to 8.56, and -7.01 to 7.44 dB, and examination durations were 9.0, 5.7, 4.7, and 5.6 minutes. The test duration for SITA Standard increased with increasing glaucomatous loss. CONCLUSIONS: The GATE algorithm achieves thresholds that are similar to those of FT and SITA Standard, with comparable accuracy, test-retest reliability, but with a shorter test duration than FT.