Growth rates of icicles

Experimental and theoretical studies on the growth rate of an icicle were carried out as a function of temperature, water-supply rate and wind speed; the relative humidity was also taken into account. The length of an icicle increases by the downward growth of thin dendritic crystals into the supercooled pendant water drop at the tip, and thus the growth is in the crystallographic a-axis direction. The diameter, on the other hand, increases by the freezing of a water film flowing down along the icicle wall. The ratio of measured length-and diameter-growth rates was large, namely 8–32.Both growth rates increased with decreasing temperature and increasing wind speed. The increase in water-supply rate led to the decrease in the length-growth rate but no significant change in the diameter-growth rate. These results could be well described by a numerical model of icicle growth which takes account of the dendritic growth at the tip and the wall and the effective heat transfer within the turbulent boundary layer around the icicle. A formation mechanism of ribs and hollows is discussed in relation to the flowing and freezing process of water on an icicle wall

Similarity of eyes in a cataractous population—How reliable is the biometry of the fellow eye for lens power calculation?

Background In some situations it is necessary to use biometry from the fellow eye for lens power calculation prior to cataract surgery. The purpose of this study was to analyse the lateral differences in biometric measurements and their impact on the lens power calculation. Methods The analysis was based on a large dataset of 19,472 measurements of 9736 patients prior to cataract surgery with complete biometric data of both left and right eyes extracted from the IOLMaster 700. After randomly indexing the left or right eye as primary (P) and secondary (S), the differences between S and P eye were recorded and analysed (Keratometry (RSEQ), total keratometry (TRSEQ) and back surface power (BRSEQ)), axial length AL, corneal thickness CCT, anterior chamber depth ACD, lens thickness LT). Lens power was calculated with the Castrop formula for all P and S eyes, and the refraction was predicted using both the P and S eye biometry for the lens power calculation. Results Lateral differences (S-P, 90% confidence interval) ranged between -0.64 to 0.63 dpt / -0.67 to 0.66 dpt / -0.12 to 0.12 dpt for RSEQ / TRSEQ / BRSEQ. The respective difference in AL / CCT / ACD / LT ranged between -0.46 to 0.43 mm / -0.01 to 0.01 mm / -0.20 to 0.20 mm / -0.13 to 0.14 mm. The resulting difference in lens power and predicted refraction ranged between -2.02 to 2.00 dpt and -1.36 to 1.30 dpt where the biometry of the S eye is used instead of the P eye. The AL and RSEQ were identified as the most critical parameters where the biometry of the fellow eye is used. Conclusion Despite a strong similarity of both eyes, intraocular lens power calculation with fellow eye biometry could yield different results for the lens power and finally for the predicted refraction. In 10% of cases, the lens power derived from the S eye deviates by 2 dpt or more, resulting in a refraction deviation of 1.36 dpt or more

Calculation of ocular magnification in phakic and pseudophakic eyes based on anterior segment OCT data

Purpose The purpose of this study is to develop a straightforward mathematical concept for determination of object to image magnification in both phakic and pseudophakic eyes, based on biometric measures, refractometry and data from an anterior segment optical coherence tomography (OCT). Methods We have developed a strategy for calculating ocular magnification based on axial length measurement, phakic anterior chamber and lens thickness, keratometry and crystalline lens front and back surface curvatures for the phakic eye, and axial length measurement, anterior chamber and lens thickness, keratometry and intraocular lens power, refractive index and shape factor for the pseudophakic eye. Comparing the magnification of both eyes of one individual yields aniseikonia, while comparing the preoperative and postoperative situation of one eye provides the gain or loss in ocular magnification. The applicability of this strategy is shown using a clinical example and a small case series in 78 eyes of 39 patients before and after cataract surgery. Results For the phakic eye, the refractive index of the crystalline lens was adjusted to balance the optical system. The pseudophakic eye is fully determined and we proposed three strategies for considering a potential mismatch of the data: (A) with spherical equivalent refraction, (B) with intraocular lens power and (C) with the shape factor of the lens. Magnification in the phakic eye was −0.00319 ± 0.00014 and with (A) was −0.00327 ± 0.00013, with (B) was −0.00323 ± 0.00014 and with (C) was −0.00326 ± 0.00013. With A/B/C, the magnification of the pseudophakic eye was on average 2.52 ± 2.83%/1.31 ± 2.84%/2.14 ± 2.80% larger compared with the phakic eye. Magnification changes were within a range of ±10%. Conclusions On average, ocular magnification does not change greatly after cataract surgery with implantation of an artificial lens, but in some cases, the change could be up to ±10%. If the changes are not consistent between the left and right eyes, then this could lead to post‐cataract aniseikonia.</p

Visual and refractive outcomes and glistenings occurrence after implantation of 2 monofocal, aspheric, hydrophobic acrylic IOLs

PURPOSE: To compare the Clareon intraocular lens (IOL) with the Tecnis PCB00 IOL in terms of visual performance, refractive outcomes, glistenings occurrence, and quality-of-life outcomes. SETTING: Guy's and St Thomas' NHS Foundation Trust, London, England. DESIGN: Single-center, single-masked, prospective, randomized, controlled trial. METHODS: One hundred thirty-nine patients with bilateral cataracts were randomized to receive the Clareon (C IOL) or Tecnis (T IOL) IOL. Visual acuity, refraction, central corneal thickness (CCT), endothelial cell loss, contrast sensitivity, and mesopic gap acuity, evaluation of glistenings and rates of perioperative and postoperative complications were recorded. Quality-of-life outcomes were measured with the EuroQOL-5 Dimension questionnaire and the Patient-Reported Outcome Measures questionnaire. Optimised A-constants were available for the T IOL but not the C IOL. RESULTS: Seventy-one patients (140 eyes) received the C IOL and 68 patients (134 eyes) received the T IOLs. Data were analysed for the first implanted eye. At 12 months, mean uncorrected distance visual acuity (logarithm of the minimum angle of resolution) was 0.02+/-0.10 and 0.01+/-0.08 (mean+/- SD; P=0.49; 95% CI -0.02, 0.04) in the C IOL and T IOL groups, respectively. Corrected visual acuity was -0.02+/-0.09 and -0.03+/-0.06, respectively (P=0.45; 95% CI -0.02, 0.04). The increase in CCT was 14+/-19 and 16+/-28 μm, respectively (P=0.63;95% CI -10.16, 6.16). Mean absolute refraction spherical equivalent error from target refraction was 0.41+/-0.28 for the C IOL and 0.25+/-0.2 for the T IOL groups (P=0.002; 95% CI 0.08, 0.24). Glistenings were minimal (median grade 0), with no difference in grades between groups (P=0.2). PROMS improved postoperatively and were similar in both groups. CONCLUSIONS: There were no differences in visual outcomes between the Clareon IOL and Tecnis PCB00 IOLs. Glistenings were rarely observed in either IOL with no difference in grades. There was no difference in perioperative or postoperative complications. Surgeon optimization of the A-constant for the Clareon IOL is recommended

Posterior capsule opacification: What's in the bag?

Cataract, a clouding of the lens, is the most common cause of blindness in the world. It has a marked impact on the wellbeing and productivity of individuals and has a major economic impact on healthcare providers. The only means of treating cataract is by surgical intervention. A modern cataract operation generates a capsular bag, which comprises a proportion of the anterior capsule and the entire posterior capsule. The bag remains in situ, partitions the aqueous and vitreous humours, and in the majority of cases, houses an intraocular lens (IOL). The production of a capsular bag following surgery permits a free passage of light along the visual axis through the transparent intraocular lens and thin acellular posterior capsule. Lens epithelial cells, however, remain attached to the anterior capsule, and in response to surgical trauma initiate a wound-healing response that ultimately leads to light scatter and a reduction in visual quality known as posterior capsule opacification (PCO). There are two commonly-described forms of PCO: fibrotic and regenerative. Fibrotic PCO follows classically defined fibrotic processes, namely hyperproliferation, matrix contraction, matrix deposition and epithelial cell trans-differentiation to a myofibroblast phenotype. Regenerative PCO is defined by lens fibre cell differentiation events that give rise to Soemmerring's ring and Elschnig's pearls and becomes evident at a later stage than the fibrotic form. Both fibrotic and regenerative forms of PCO contribute to a reduction in visual quality in patients. This review will highlight the wealth of tools available for PCO research, provide insight into our current knowledge of PCO and discuss putative management of PCO from IOL design to pharmacological interventions

Vortr\ue4ge. cber die Structur und Zusammensetzung der Krystalle des prismatischen Kalkhaloides, nebst einem Anhange \ufcber die Structur der kalkigen Theile einiger wirbellosen Thiere

Volume: 19Start Page: 10End Page: 3

Ueber die Krystall-Bildung im gew\uf6hnlichen Glase und in den verschiedenen Glasfl\ufcssen

Volume: 8Start Page: 261End Page: 27

Vortr\ue4ge. cber den Meteorstein von Borkut

Volume: 20Start Page: 398End Page: 40

Vortrag. cber eine neue Methode, die Stuctur und Zusammensetzung der krystalle zu unteruchen, mit besonderer Ber\ufccksichtigung der Variet\ue4ten des rhomboedrischen Quarzes

Volume: 15Start Page: 59End Page: 8