Mean Cylinder Research Articles

Effects of EGR rates on combustion and emission characteristics in a diesel engine with n-butanol/PODE3-4/diesel blends

An experimental investigation is conducted on the influence of EGR (Exhaust Gas Recirculation) rates (0–40%) on the combustion and emission characteristics of n-butanol/diesel/PODE3-4 blends at low-temperature combustion mode in diesel engine. The results show that at identical EGR rate, compared to D100 (diesel fuel), the peak values both of the mean cylinder pressure and the heat release rate of BD20 (20% butanol and 80% diesel in volume) are increased, ignition delay is extended, and the brake thermal efficiency is enhanced. Concerning BD20 blended with PODE3-4, the ignition delay is shortened, while both the brake thermal efficiency and the combustion efficiency increase. At the EGR rate below 30%, as the EGR rate grows, the effects on emission of soot, CO and HC are not significant, while the emission of NOx is sharply reduced; when the EGR rate is above 30%, as it grows, the emissions of soot, CO, and HC drastically rise. As EGR rate grows, the total particulate matter (PM) number concentrations of four fuels firstly decline and then rise, the total PM mass concentrations keep stable firstly and then rise drastically. As the proportion of added PODE3-4 in BD20 grows, the particle geometric mean diameters further decrease.

Outcomes of Re-treatment by LASIK After SMILE.

To report the outcomes of LASIK re-treatments after small incision lenticule extraction (SMILE). Retrospective review of all eyes to have undergone a re-treatment by LASIK after primary SMILE between September 2013 and January 2016. Thin-flap LASIK was used in most cases as long as sufficient tissue was available for safe flap creation between the maximum epithelial thickness and minimum cap thickness. Otherwise, the SMILE interface was converted into a LASIK flap by the Circle technique or side cut only. The multivariate nomogram for LASIK re-treatments was used, including sphere, cylinder, age, and primary spherical equivalent (SEQ) as variables. Patients were observed for 1 year after surgery and standard outcomes analysis was performed. A total of 116 LASIK re-treatments were performed in a population of 2,643 consecutive SMILE procedures, indicating a re-treatment rate of 4.39%. Mean attempted SEQ was -0.05 ± 0.99 diopters (D) (range: -1.88 to +1.50 D). Mean cylinder was -0.70 ± 0.55 D (range: 0.00 to -2.25 D). Postoperative uncorrected distance visual acuity was 20/20 or better in 81% of eyes, for a population with corrected distance visual acuity (CDVA) of 20/20 or better in 95% before re-treatment. Mean postoperative SEQ relative to the target was +0.19 ± 0.49 D (range: -0.88 to +2.13 D), with 74% within ±0.50 D. Mean postoperative cylinder was -0.29 ± 0.24 D (range: 0.00 to -1.25 D). There was one line loss of CDVA in 15% of eyes, but no eyes lost two or more lines. There was a small increase in contrast sensitivity (P < .05). Overcorrection was identified in myopic re-treatments (n = 20) of -1.00 D or more; mean postoperative SEQ was +0.59 ± 0.64 D (range: -0.63 to +2.13 D). Re-treatment after SMILE by LASIK achieved excellent visual and refractive outcomes, although these results indicate that myopic LASIK retreatment after primary myopic SMILE requires a different nomogram than for myopic LASIK re-treatment after primary myopic LASIK. [J Refract Surg. 2018;34(9):578-588.].

Three-year outcomes after high hyperopia correction using photorefractive keratectomy with a large ablation zone

AimTo evaluate refractive and visual outcomes of photorefractive keratectomy (PRK) to treat high hyperopia using an aberration-neutral profile and large ablation zone.MethodsThis was a retrospective, consecutive observational case series at...

Customized Toric Intraocular Lens Implantation in Eyes with Cataract and Corneal Astigmatism after Deep Anterior Lamellar Keratoplasty: A Prospective Study.

Purpose To investigate the effectiveness of toric intraocular lenses (IOLs) for treating corneal astigmatism in patients with cataract and previous deep anterior lamellar keratoplasty (DALK). Setting San Giovanni-Addolorata Hospital, Rome, Italy. Design Prospective interventional case series. Methods Patients undergoing cataract surgery after DALK for keratoconus were enrolled. Total corneal astigmatism (TCA) was assessed by a rotating Scheimpflug camera combined with Placido-disk corneal topography (Sirius; CSO, Firenze, Italy). A customized toric IOL (FIL 611 T, Soleko, Rome, Italy) was implanted in all eyes. One year postoperatively, refraction was measured, the IOL position was recorded, and vectorial and nonvectorial analyses were performed to evaluate the correction of astigmatism. Results Ten eyes of 10 patients were analyzed. The mean preoperative TCA magnitude was 4.92 ± 1.99 diopters (D), and the mean cylinder of the IOL was 6.18 ± 2.44. After surgery, the difference between the planned axis of orientation of the IOL and the observed axis was ≤10° in all eyes. The mean surgically induced corneal astigmatism was 0.35 D at 20°. The mean postoperative refractive astigmatism power was 1.13 ± 0.94 D; with respect to preoperative TCA, the reduction was statistically significant (p < 0.0001). The mean change in astigmatism power was 3.80 ± 1.60 D, corresponding to a correction of 77% of preoperative TCA power. Nine eyes out of 10 had a postoperative refractive astigmatism power ≤ 2D. Conclusions Toric IOLs can effectively correct corneal astigmatism in eyes with previous DALK. The predictability of cylinder correction is partially lowered by the variability of the surgically induced changes of TCA. This trial is registered with NCT03398109.

Comparison of dosimetric and clinical outcomes between short- and long-channel cylinder applicators for vaginal brachytherapy in intermediate- and high-risk endometrial cancer

PurposeVaginal brachytherapy (VBT) using a cylinder applicator is a standard treatment of intermediate- and high-risk endometrial cancer. We conducted a retrospective study of the dosimetric and clinical outcomes at our institution with 2 single-channel applicators in patients receiving VBT. Methods and MaterialsOne hundred thirty-six patients with endometrial cancer treated from 2006 to 2016 receiving VBT after definitive surgery were evaluated. Two cylinders were used with the distal dwell position 7.1–12.8 mm from the apex varying by diameter (short channel), and 3.2 mm from the apex (long channel). We prescribed 18–26 Gy in 3–4 fractions at 0.5 cm depth. Measurements of the distance from the apex to the prescription isodose line were taken from CT imaging. Student's t test and the Wilcoxon rank-sum test were used with corrections for multiple comparisons. ResultsPatients had International Federation of Gynecology and Obstetrics 2009 Stage I-II disease (70 Stage IA, 58 Stage IB, 9 Stage II). Mean cylinder apex dose was 95.2% and 154.7% of prescription (p < 0.001), and mean distance from apex to the prescription isodose line was 0.54 mm and 3.5 mm (p < 0.001) for the short- and long-channel cylinders, respectively. There were no significant differences in any toxicity between cylinders. Four patients (2.9%) had vaginal recurrence, all of whom were treated with the short-channel cylinder. Cylinder type was not associated with vaginal recurrence (p = 0.27). ConclusionsA cylinder applicator with a distal dwell position closer to the apex results in higher doses to the vaginal cuff and increased D2cc to the bladder. All four recurrences were in the short-channel cylinder. Additional investigation into applicator design and impact on patient outcomes in larger cohorts with sufficient followup is warranted.

Photorefractive keratectomy after cataract surgery in uncommon cases: long-term results.

To evaluate the efficacy and safety of the excimer laser correction of the residual refractive errors after cataract extraction with intraocular lens (IOL) implantation in uncommon cases. Totally 24 patients with high residual refractive error after cataract surgery with IOL implantation were examined. Twenty-two patients had a history of phacoemulsification and IOL implantation, and two had extra-capsular cataract extraction with IOL implantation. Detailed examination of preoperative medical records was done to explain the origin of the post-cataract refractive errors. All patients underwent photorefractire keratectomy (PRK) enhancement. The mean outcome measures were refraction, uncorretted visual acuity (UCVA), best corrected visual acuity (BCVA) and corneal transparency and follow up ranged from 1 to 8y. The principal causes of residual ametropia was inexact IOL calculation in abnormal eyes with high myopia and congenital lens abnormalities, followed by corneal astigmatism both suture induced and preexisting. After cataract surgery and before the laser enhancement the mean spherical equivalent (SE) was -0.56±3 D ranging from -4.62 to +2.25 D in high myopic patients, instead it was -1±1.73 D ranging from -3.25 to +3.75 D in the astigmatic eyes, with a mean cylinder of -3.75±0 ranging from -3 to +5.50 D. After laser refractive surgery the mean SE was 0.1±0.73, ranging from -0.50 to +1.50 in the myopic group, and it was -0.50±0.57 ranging from -1.25 to +0.50 in astigmatic patients, with a mean cylinder of -0.25±0.75. In myopic patients the mean UCVA and BCVA were 0.038±0.072 logMAR and 0.018±0.04 respectively, both ranging from 0.10 to 0.0. In astigmatic patients, the mean UCVA and BCVA were 0.213±0.132 and 0.00±0.0 respectively, UCVA ranging from 0.50 to 0.22 and BCVA was 0.00. All patients presented normal corneal transparency. No ocular hypertension was detected and no corneal haze was observed. All registered values remained stable also at the end line evaluation. The excimer laser treatment of residual refractive errors after cataract surgery with IOL implantation in abnormal eyes resulted in satisfactory and stable visual outcome with good safety and efficacy.

Capturing Pressure Oscillations in Numerical Simulations of Internal Combustion Engines

In an earlier publication (Jupudi et al., 2016, “Application of High Performance Computing for Simulating Cycle-to-Cycle Variation in Dual-Fuel Combustion Engines,” SAE Paper No. 2016-01-0798), the authors compared numerical predictions of the mean cylinder pressure of diesel and dual-fuel combustion, to that of measured pressure data from a medium-speed, large-bore engine. In these earlier comparisons, measured data from a flush-mounted in-cylinder pressure transducer showed notable and repeatable pressure oscillations which were not evident in the mean cylinder pressure predictions from computational fluid dynamics (CFD). In this paper, the authors present a methodology for predicting and reporting the local cylinder pressure consistent with that of a measurement location. Such predictions for large-bore, medium-speed engine operation demonstrate pressure oscillations in accordance with those measured. The temporal occurrences of notable pressure oscillations were during the start of combustion and around the time of maximum cylinder pressure. With appropriate resolutions in time steps and mesh sizes, the local cell static pressure predicted for the transducer location showed oscillations in both diesel and dual-fuel combustion modes which agreed with those observed in the experimental data. Fast Fourier transform (FFT) analysis on both experimental and calculated pressure traces revealed that the CFD predictions successfully captured both the amplitude and frequency range of the oscillations. Resolving propagating pressure waves with the smaller time steps and grid sizes necessary to achieve these results required a significant increase in computer resources.

Astigmatism in Chinese primary school children: prevalence, change, and effect on myopic shift.

To study the prevalence, type, and progression of astigmatism in primary school children, and its effect on myopic shift. A prospective study carried out in a primary school in southern Taiwan. The study was performed on a subset of children, one year after initial examination. Refractive error measured by cycloplegic autorefraction was the main study outcome. Astigmatism was recorded as negative cylinder form, and we defined clinical significant astigmatism (CSA) as cylinder refraction -1.0 D or greater. Myopia was defined as a spherical equivalent refraction (SER) of -0.50 D or greater. Three hundred sixty-two children, mean age was 8.97 y/o (SD 1.41; range 7 to 11 y/o) participated in the study. One hundred nineteen (32.9 %) subjects had CSA at the initial screening. The mean cylinder refraction was -0.80 + 0.84 diopters (D) (-5.25 D to 0.00 D), with predominant with rule astigmatism (69.7%). In the 183 children studied longitudinally, the mean cylinder refraction was reduced from -0.74 D to -0.58 D (p< 0.05). The cylinder refraction in the initial CSA group was not associated with SER change (p=0.99) or axial length change (p=0.55). Compared to the initial non-CSA group, the initial CSA group had no significant difference in axial length elongation (p=0.20). The prevalence of astigmatism was not low in the Chinese primary school children and with-the-rule astigmatism was predominant. The astigmatism decreased during the 1 year follow-up. The CSA was not associated with myopia progression (p=0.99).

Comparative study of induced changes in effective lens position and refraction after Nd:YAG laser capsulotomy according to intraocular lens design.

PurposeTo evaluate and compare the changes in refraction and effective intraocular lens (IOL) position between a plate-haptic IOL and a c-loop single-piece IOL after neodymium-doped yttrium aluminium garnet (YAG) laser posterior capsulotomy.MethodsIn a prospective study, anterior chamber depth and subjective refraction were measured in 110 pseudophakic eyes from 110 patients, before and 1 month after YAG laser capsulotomy. Patients were divided into 2 groups according to the IOL design: group 1 (plate-haptic acrylic hydrophilic AT LISA tri 839MP®) and group 2 (c-loop acrylic hydrophobic single-piece AcrySof® SA60AT). Lens position was obtained through optical coherence biometry (Biograph WaveLight OB820®).ResultsYAG laser capsulotomy was performed 37.8±9.8 months after surgery in group 1 and 40.6±8.6 months in group 2 (p=0.125). Significant changes were found in the lens effective position after treatment in the 2 groups. The YAG posterior capsulotomy led to a change of anterior chamber depth in group 1 from 4.03±0.32 mm to 3.86±0.34 mm (p=0.02) and in group 2 from 4.03±0.37 mm to 4.14±0.45 mm (p=0.025). After YAG laser posterior capsulotomy, no significant changes were observed in mean spherical equivalent, sphere or cylinder for both groups (p>0.05).ConclusionYAG laser posterior capsulotomy can induce a significant change in the IOL position according to the IOL type; however, the refractive change after treatment is clinically insignificant.

Visual and Refractive Outcomes of Topography-guided Laser-assisted In Situ Keratomileusis in Virgin Eyes.

IntroductionWe wanted to assess the efficacy, predictability, and stability of topography-guided, laser-assisted in situ keratomileusis (TGL) on normal untreated eyes with a preoperative best corrected visual acuity (BCVA) of 20/20.MethodsThis was a retrospective, non-randomized, and single arm study evaluating the outcomes of TGL in eyes with a preoperative BCVA of 20/20. We included 50 eyes of 50 patients who presented to the Hashmanis Hospital, Pakistan and were followed for six months postoperatively. All eyes underwent treatment using the Alcon Wavelight Allegro Topolyzer (Alcon Laboratories, Inc., TX, USA).ResultsThe mean preoperative sphere, cylinder, and spherical equivalent (SE) values were -4.3 ± 1.6 dioptres (D), -1.0 ± 0.8 D, and -4.8 ± 1.8 D. On day one these values were 0.2 ± 0.8 D, -0.5 ± 0.3, and 0.3 ± 0.8, respectively, and on month six they were -0.1 ± 0.6, -0.5 ± 0.3, and -0.4 ± 0.6 D, respectively. On postoperative day one and month six, 86% and 94% of eyes had a UCVA of 20/20 or better, respectively. Two eyes (4%) had an SE change of greater than 0.5 D from three to six months.ConclusionOur study demonstrates good efficacy, predictability, and stability of eyes undergoing TGL with a follow-up of six months.

Visual and Refractive Outcomes and Tomographic Changes after Femtosecond Laser-assisted Intrastromal Corneal Ring Segment Implantation in Patients with Keratoconus.

Purpose:To evaluate the visual, refractive, and tomography changes after femtosecond laser-assisted intrastromal corneal ring segment (ICRS; Intacs® SK) implantation in patients with keratoconus.Methods:In this prospective interventional case series, Intacs SK ICRSs were inserted using a femtosecond laser into eyes with stage I–IV keratoconus. Visual, refractive, and corneal tomography changes, along with surgical complications, were analyzed 1 week, 2 months, and 6 months postoperatively.Results:The study evaluated 71 eyes of 52 patients (mean age: 27.5 years). Six months postoperatively, the spherical equivalent, mean sphere, and mean cylinder were decreased by 2.07, 1.47, and 1.13 diopters (D), respectively. The mean preoperative uncorrected distance visual acuity (UDVA) increased from 0.87 ± 0.26 to 0.46 ± 0.19 LogMAR and the mean preoperative corrected distance visual acuity (CDVA) increased from 0.55 ± 0.21 to 0.28 ± 0.17 LogMAR (P < 0.001). Flat and steep keratometry decreased by a mean corneal power in the 3-mm zone, and mean anterior elevation decreased by 0.91 D, 2.52 D, and 1.03 microns (P < 0.001), respectively. Among all eyes, 93.0% gained one or more lines of CDVA. Mean internal anterior chamber depth decreased from 3.25 ± 0.33 to 3.14 ± 0.45 mm (P = 0.001), and mean irregularity in the 3-mm zone decreased from 5.63 ± 1.71 to 5.24 ± 1.82 (P = 0.006). However, mean posterior elevation and irregularity in the 5-mm zone did not change significantly.Conclusion:Implantation of one or two Intacs SK segments is safe and effective to treat keratoconus, leading to significant improvement in UDVA, CDVA, and refractive error.

Development of Four-Zone Segmented Transitional Model for Reciprocating Internal Combustion Engine Analysis Using Gasoline

A four zone model based on the first law of thermodynamics has been developed for analysis of combustion in an internal combustion engine. The four zones included an unburned zone and two regions of burned zone, (namely burned gas1 and burned gas 2) and unburned burned zone described as a transitory zone which is a mixture of burned and unburned gases. Arbitrary constant for each of burn (CC2) and unburned (CC1) zone leakages in unburned burned zone was evaluated at optimally predetermined values of 0.005 and 0.00025 respectively, while mass fraction burned from burned gas1, x1 and burned gas 2, x2 were also evaluated at predetermined optimal values of 0.6 and 0.4 respectively. The model was used to analyse an SI engine operating with a gasoline fuel. The engine operating conditions were set at engine speed of 2000 rpm, -35bTDC ignition time and burn duration at 60°. The temperature distribution from the arbitrary constants (CC2, CC1, x1 and x2) for the newly developed four zone model was compared to the two zone model and literature experimental temperature value. The obtained indicated mean effective pressure (IMEP), thermal efficiency (η), cylinder pressure and emission characteristics from the developed model and those of two zone analysis were both compared with literature values.

Characteristics of astigmatism in Black South African high school children.

Astigmatism impairs vision at various distances and causes symptoms of asthenopia which negatively impacts reading efficiency. The aim of conducting this study was to determine the prevalence and distribution of astigmatism and its relationship to gender, age, school grade levels and spherical ametropia. Using a multi-stage random cluster sampling, 1589 children who included 635 (40%), males, and 954 (60%), females were selected from 13 out of a sample frame of 60 schools. Their ages ranged between 13 and 18 years with a mean of 15.81±1.56 years. The parameters evaluated included visual acuity using the LogMAR chart and refractive errors measured using an autorefractor and then refined subjectively. Axis of astigmatism was presented in the vector method where positive values of J0 indicated with-the-rule, negative values described against-the-rule and J45 represented oblique astigmatism. The mean cylinder power was -0.09 ± 0.27 and mainly with-the-rule, J0 = 0.01 ± 0.11. The overall prevalence of clinically significant astigmatism (≤ - 0.75 cylinder) in the sample was 3.1% [(95% Confidence interval = 2.1-4.1%)]. Cylinder of at least - 0.25 power was considered to classify astigmatism types. Thus, the estimated distributions of types of astigmatism were: axis- 11.5%, sphero-astigmatism 10.1% and magnitude-astigmatism 11.2% while 67.2% had no cylinder of any magnitude. The prevalence of astigmatism is relatively low in this population studied. Older children and those in high school grade levels were more likely to have with-the-rule or against-the-rule astigmatism. The prevalence of astigmatism were comparable within but not across regions.

Visual outcomes of the second eye in keratoconic patients who have a corneal graft in the first eye: analysis at 12 years.

To analyze demographic, clinical, and keratometric outcomes of the second eye in keratoconic patients when the first eye has already been grafted, initially and finally at 12 years. Retrospective analysis of initial and 12 years visual and keratometric outcomes of the second eye in keratoconic patients when the first one has already been grafted. A total of 107 patients were included: 66 patients were analyzed at the beginning of the follow-up and at 12 years. There were no statistically significant differences with regard to the correction method from the beginning to the end of the follow-up; 3% of patients underwent crosslinking and 4.5% an intracorneal ring segments implantation. There was no significant progress in corneal opacities (1.5% vs 3.0% at 12 years) or visual comfort (90.9% vs 87.9%). The mean values of best-corrected visual acuity (BCVA) (0.69 vs 0.71 at 12 years, on a decimal scale), cylinder (-2.64 D vs -3.13 D), spherical equivalent, and keratometry (46.34 D vs. 46.49 D) had not significantly changed during the follow-up period. During the follow-up, 41 patients (38.3%) received a penetrating or lamellar keratoplasty on the contralateral eye (63% in the 5 years after the first corneal graft). At the time of the keratoplasty procedure, corneal opacities were seen in 7 patients (17.1%), mean BCVA was 0.26 ± 0.16, spherical equivalent mean was -3.70 D, mean cylinder was 3.89 D, mean keratometry values were 52.65 ± 6.80 D, and mean pachymetry value was 335.50 µm. This study suggests that the period of risk of keratoplasty in the second eye is significant in the first 5 years following the first keratoplasty. New therapeutic treatments have been made available, allowing for stabilization of the keratoconus decreasing the impact of transplantation.

Femtosecond laser implantation of a 340-degree intrastromal corneal ring segment in keratoconus: Short-term outcomes

To evaluate the short-term outcomes of femtosecond laser-assisted implantation of a 340-degree intracorneal ring (ICR) (Keraring) in patients with keratoconus. Four centers in Iran. Prospective case series. All cases had implantation of the 340-degree ICRafter tunnel creation with a femtosecond laser. The uncorrected (UDVA) and corrected (CDVA) distance visual acuities, sphere, cylinder, manifest refraction spherical equivalent (MRSE), mean keratometry (K), steep K, and flat Kwere evaluated preoperatively and 1, 3, and 6months postoperatively. Eighteen eyes of 17 patients were included. The mean follow-up was 4.33months (range 1 to 6months). The mean UDVA improved from 0.95 logarithm of the minimum angle of resolution (logMAR)±0.33 (SD) to 0.53±0.35 logMAR (P=.001) and the mean CDVA from 0.39±0.22 logMAR to 0.26±0.21 logMAR (P=.09). The mean sphere decreased from -5.08±3.74 diopters (D) to -1.67±2.59 D, the mean cylinder from -5.83±2.02 D to -2.72±1.81 D, and the mean MRSE from -8.03±3.88 D to -3.01±2.82 D (P<.001). The mean K decreased from 51.43±3.59 D to 47.42±3.59 D (P<.001). All patients with a preoperative mean K greater than 55.0 D had worse CDVA. Implantation of a 340-degree ICR using femtosecond laser improved the visual, refractive, and topographic parameters in keratoconic patients. The findings indicate that patients with severe keratoconus (mean K >55.0 D) are not good candidates for this type of ICR.

Inflatable penile prosthesis as tissue expander: what is the evidence?

ABSTRACTObjective:Many patients who undergo inflatable penile prosthesis (IPP) replacement are often upsized to larger cylinders, suggesting the IPP may serve as a tissue expander and increase internal penile length. The objective of this study is to evaluate whether cylinder length increases with subsequent IPP insertion.Materials and Methods:We queried American Medical Systems and Coloplast Patient Information Form databases to identify patients who underwent IPP placement and replacement between 2004-2013. Patients were grouped by device type and time to replacement (<2 or ≥2 years). We selected the 2-year mark for subgroup analysis to allow time for tissue expansion to occur and to exclude patients who underwent early explantation (e.g. erosion or infection).Results:Two thousand, seven hundred and forty nine patients (1,532 AMS 700 LGX, 717 AMS 700 CX, and 500 Coloplast Titan) met the inclusion criteria. Mean time between implants was earlier for LGX (29 months) than CX (39 months) and Titan (48 months) patients (p<0.001). Patients who underwent device replacement at <2 years did not experience an increase in mean cylinder length. On the contrary, patients who underwent device replacement at ≥2 years did experience significant increases in mean cylinder length (LGX 1.2 cm, CX 1.1 cm, and Titan 0.9 cm, p<0.001). The mean increases in length at ≥2 years were similar between the 3 devices (p=0.20). Sixty percent of patients demonstrated increases of >0.5 cm and 40% demonstrated increases of ≥1 cm.Conclusions:As demonstrated, the IPP may provide tissue expansion over time. Further evaluation is needed to determine if increased cylinder length correlates to increased functional length and patient satisfaction.

The effects of the engine design and operation parameters on the performance of an Atkinson engine considering heat-transfer, friction, combustion efficiency and variable specific-heat

Atkinson cycle engines have become particularly popular because of high energy efficiency. A novel model considering heat-transfer, friction, and variable specific-heat has been established for an Atkinson cycle engine based on the finite-time thermodynamics. Different from the ones in previous investigations, the heat-transfer and friction losses are computed considering the effects of the cycle conditions, and the design and operation parameters. In this way, the study can have practical physical meanings and is closer to real conditions. The effects of mean piston speed, friction coefficient, cylinder bore, stroke length, stroke-to-bore ratio, equivalence ratio, and compression ratio on the energy losses and cycle performance have been investigated. The results show that there are the optimum values of compression and equivalence ratios making the cycle performance the best; the energy losses from friction, heat-transfer and exhaust process monotonously increase or decrease with respect to increasing the compression ratio. Increasing the friction loss, cylinder bore and stroke length has negative effects on the cycle performance. Increasing the mean piston speed has positive effect on the power output and the power density but less effect on the energy efficiency. The study results could provide significant guidance for designing a real Atkinson cycle engine and optimizing the performance.

LASIK for the Correction of High Hyperopic Astigmatism With Epithelial Thickness Monitoring.

To evaluate outcomes of high hyperopic LASIK using the MEL 80 excimer laser (Carl Zeiss Meditec, Jena, Germany). Retrospective analysis of 830 consecutive high hyperopic LASIK procedures using the MEL 80 excimer laser and either the VisuMax femtosecond laser (Carl Zeiss Meditec) or zero compression Hansatome microkeratome (Bausch & Lomb, Rochester, NY). Inclusion criteria were attempted hyperopic correction of +4.00 diopters [D] or higher in one axis and corrected distance visual acuity (CDVA) of 20/20 or better. Patients were observed for a minimum of 1 year. Epithelial thickness monitoring by Artemis very high-frequency (VHF) digital ultrasound (ArcScan Inc., Morrison, CO) was used to evaluate potential for further steepening as a re-treatment. One-year data were available for 785 eyes. Mean attempted spherical equivalent refraction (SEQ) was +4.52 ± 0.84 D (range: +2.00 to +6.96 D) for the primary treatment and mean cylinder was 1.05 ± 0.86 D (range: 0.00 to 5.25 D). Mean age was 50 ± 12 years (range: 18 to 70 years) and 61% were women. Postoperative SEQ was ±0.50 D in 50% and ±1.00 D in 77% of eyes after primary treatment. After re-treatment, 67% of eyes were within ±0.50 D and 89% were within ±1.00 D. Uncorrected distance visual acuity was 20/20 or better in 76% of eyes after final treatment. One line of CDVA was lost in 25% of eyes and two lines were lost in 0.4%. There was a clinically insignificant but statistically significant decrease (P < .05) in contrast sensitivity (CSV-1000) by less than 1 log unit at 3 and 6 cycles per degree (cpd) and by 1 log unit at 12 and 18 cpd. Diurnal fluctuation in refraction was identified in 2 eyes, proven by VHF digital ultrasound to be due to diurnal epithelial remodeling overnight and unrelated to maximum postoperative keratometry induced. LASIK for hyperopia by cumulative treatment of up to +8.33 D with the MEL 80 excimer laser was found to satisfy accepted criteria for safety, efficacy, and stability when applying specialized protocols, including epithelial monitoring. [J Refract Surg. 2017;33(5):314-321.].

Surgical induced astigmatism in phaecoemulsification cataract surgery

Abstract Purpose: Surgical induced astigmatism is often-neglected issue in phaecoemulsification cataract surgery. It is a significant problem resulting in poor refractive outcome and patients’ satisfaction. The objective of this study was to describe the preoperative astigmatism and the postoperative surgical induced astigmatism and its contributing factors. Design: Retrospective study on the Malaysian Cataract Surgery Registry between year 2008 and 2011. Method: Data on phaecoemulsification cataract surgery from 37 Ophthalmology Units were studied and filtered. Patients more than 50 year-old with complete refractive assessment results and with no ocular comorbidity were included. Contributing factors namely patients’ age, race, gender, laterality of the operated eye, surgeon’s status and intraoperative complications were analyzed. Results: The mean age of the 5350 patients was 68.0 years with majority Chinese patients. The mean postoperative cylinder was 1.19D (SD=0.91) compared to the preoperative mean cylinder of 0.88D (SD=0.83D). Multivariate regression analysis on postoperative data revealed statistically significant high cylinder power (&gt;1.0 Dioptre) for older patients, Chinese race, left operated eyes (p&lt;0.001), performed by trainee ophthalmologists (p&lt;0.001), and for those with intraoperative complications (p&lt;0.001). The overall difference of cylinder power before and after phaecoemulsification cataract surgery was high; signifying high degree of surgical induced astigmatism. Conclusion: Surgical induced astigmatism could result in significant postoperative astigmatism with poor refractive outcome. The contributing factors are old age, Chinese race, left operated eyes, operated by trainee ophthalmologists and intraoperative complications.

Small Incision Lenticule Extraction (SMILE) for Hyperopia: Optical Zone Centration.

To evaluate optical zone centration of hyperopic small incision lenticule extraction (SMILE). This prospective study of 60 consecutive hyperopic SMILE procedures used the VisuMax femtosecond laser and matched LASIK procedures with the VisuMax and MEL 80 excimer lasers (Carl Zeiss Meditec AG, Jena, Germany). Inclusion criteria were maximum attempted hyperopic meridian of between +1.00 and +7.00 diopters (D) and astigmatism up to 6.00 D. For SMILE, the optical zone was between 6.3 and 6.7 mm, with a 2-mm transition zone. Two LASIK control groups (6.5- and 7-mm optical zone) were generated matched for spherical equivalent treated. In SMILE, the corneal vertex of the coaxially fixating eye was aligned with the vertex of the curved contact glass. In LASIK, the treatment was centered on the coaxially sighted corneal light reflex (first Purkinje image) with the contralateral eye (Seiler method). A tangential (instantaneous) curvature preoperative to 3 months postoperative difference map was generated for each eye. A fixed grid and set of concentric circles were superimposed on the difference map to measure the offset between the optical zone center and corneal vertex (0,0), and vector analysis was used for comparative analysis. Mean attempted spherical equivalent was +5.61 ± 0.96 D (range: +3.20 to +6.50 D) and mean cylinder was -0.96 ± 0.62 D (range: 0.00 to -2.75 D) in the SMILE group. Mean age was 29 ± 7 years (range: 19 to 52 years) in the SMILE group. Mean centration offset was 0.23 ± 0.15 mm (range: 0 to 0.61 mm) for the SMILE group, 0.33 ± 0.14 mm (range: 0.14 to 0.85 mm) for the 6.5-mm LASIK group, and 0.31 ± 0.19 mm (range: 0.05 to 0.85 mm) for the 7-mm LASIK group. The mean centration offset for SMILE was less than that of both LASIK groups (P < .05). Optical zone centration of hyperopic SMILE was found to be similar to eye-tracker-centered hyperopic LASIK with the MEL 80 laser. [J Refract Surg. 2017;33(3):150-156.].