Integrated High-Accuracy Correction Technology of Radio-Wave Refraction for Deep-Space (High-Orbit) Targets

The radio-wave refraction error caused by the troposphere and ionosphere badly affects accuracy in terms of the navigation, positioning, measurement, and control of a target; it is the main source of errors in high-accuracy measurement and control systems. The high-accuracy technology needed for radio-wave refraction error correction (mainly in the troposphere and ionosphere) has been the focus of research for a long time. At present, the correction methods used for radio-wave refraction errors have a low accuracy. For an S-band radio-wave signal, the accuracy of refraction error correction can generally only reach m-level (elevation angle of 15° and above), and thus has difficulty meeting the requirements of dm-level accuracy refraction error correction for deep-space and high-orbit targets. To improve the accuracy of radio-wave refraction error correction for deep-space and high-orbit targets, a novel correction method for tropospheric and ionospheric range error due to refraction is proposed in this study, on the basis of the measured data from a water vapor radiometer and dual-frequency Global Navigation Satellite System (GNSS). The comprehensive calibration test is conducted in combination with the Chinese Area Positioning System (CAPS) in Kunming. Results show that this method can effectively correct the range error due to refraction that is caused by the troposphere and ionosphere. For an S-band radio-wave signal, the accuracy of refraction error correction can reach dm-level accuracy (elevation angle of 15° and above), which is 50% higher than that achieved with traditional methods. This work provides an effective support system for major projects, such as lunar exploration and Mars exploration.

Comparing the Effect of Monofocal and Multifocal Intraocular Lenses on Macular Surgery

Aim. To compare the effects of previously implanted monofocal and multifocal intraocular lenses (IOL) on macular surgery. Methods. Seventy eyes of 70 patients with epiretinal membrane (ERM) and symptomatic vitromacular traction syndrome that previously had IOL implantation for cataract surgery were included in this prospective randomized clinical trial. Cases were divided into two groups. Group 1 and Group 2 were composed of eyes with monofocal and multifocal IOLs, respectively. The effects of refraction error and IOL decentration at the time of macular surgery performed for ERM and ILM peeling, according to the lens type, were investigated. Pars plana vitrectomy (PPV) was performed to peel ERM and ILM in all cases. Complete ophthalmological examination, fundus fluorescein angiography, and optical coherence tomography imaging were made to all cases, preoperatively and postoperatively. Results. The mean BCVA in Group 1 and Group 2 improved from 0.69 ± 0.15 and 0.38 ± 0.14 logMAR to 0.40 ± 0.14 and 0.10 ± 0.04 logMAR, respectively, at the 6th month. There was no statistically significant difference between the groups in terms of the mean spherical refraction error (P>0.05) and IOL decentration level (P>0.05). The mean time required for macular surgery in Group 2 was statistically significantly longer than that for Group 1 (P<0.05). There was no statistically significant relationship between IOL decentration and macular surgery time in Group 1 (P>0.05), but there it was found in Group 2 (P<0.05). In Group 2, there was a positive correlation between IOL decentration and macular surgery time. Conclusion. In cases with multifocal IOL implants, especially with lens decentration, the time of macular surgery for ERM and ILM peeling during PPV is longer than that of eyes with monofocal IOL due to fluctuations in the clarity of the surgeon’s view.

Retinal Fibre Layer Thickness Measurement in Normal Paediatric Population in Sweden Using Optical Coherence Tomography

Purpose. To evaluate the correlation between peripapillary retinal nerve fibre layer (RNFL) thickness and both age and refraction error in healthy children using optical coherence tomography (OCT). Patients and Methods. 80 healthy children with a mean age of 9.1 years (range 3.8 to 16.7 years) undergoing routine ocular examination at the orthoptic section of the Ophthalmology Department were recruited for this cross-sectional study. After applying cycloplegia, the peripapillary RNFL thickness was measured in both eyes using the Topcon 3D OCT 2000 device. Results. 138 eyes were included in the analysis. The average refractive error (SE) was +1.7 D (range −5.25 to +7.25 D). The mean total RNFL thickness was 105 μm ± 10.3, the mean superior RNFL thickness was 112.7 μm ± 16.5, and the mean inferior RNFL thickness was 132.6 μm ± 18.3. We found no statistically significant effect of age on RNFL thickness (ANOVA, f=0.33, p=0.56). Refraction was proven to have a statistically significant effect (ANOVA, f=67.1, p<0.05) in RNFL measurements. Conclusions. Data obtained from this study may assist in establishing a normative database for a paediatric population. Refraction error should be taken into consideration due to its statistically significant correlation with RNFL thickness.