Double-pass Technique Research Articles

Novel approach in manufacturing aluminum-based alternate layered composite material via friction stir additive manufacturing route

The majority of today’s metal additive manufacturing techniques involve the transition of phases from liquid to solid, affecting their performance due to the microstructures formed during solidification. Employing novel solid-state additive manufacturing techniques like friction stir additive manufacturing (FSAM) helps to overcome these constraints. This study employed alternative layers of AA 6061-T6 and AA 7075-T6 aluminum alloys to construct defect-free alternate layered composite material (ALCM) via FSAM route using a single-pass (SP) weld strategy and double-pass (DP) weld strategy. The experiments were conducted by selecting the tool traverse speed, tool rotation speed and tool tilt angle as 40 mm/min, 1200 rpm and 2⁰ when AA 6061-T6 was set over AA 7075-T6 and 50 mm/min, 1100 rpm and 2⁰ when AA 7075-T6 was set over AA 6061-T6. A comprehensive investigation of the mixing of these dissimilar materials, changes in microstructure and microhardness, and variations in strength along the longitudinal direction in the stir zone (SZ) are evaluated in this study. Microstructures that evolved during both strategies were observed to be non-uniform, and equiaxed refined grains were identified in the SZ, which was recognized as the build’s most functional part. Repetitive stirring by the rotating tool decreased the average grain size and low-angle grain boundaries (LAGBs) along the SZ. The hardness and strength in the final build increased from lower layers to upper layers primarily due to the variation in grains and precipitate size. The highest value of hardness of 215.7 HV was identified in the topmost layer of DP technique, which was 15% higher when compared with the SP technique. Similarly, a 15% increase in strength was also observed in the topmost slice in the DP technique, whose value corresponds to 364 MPa. This study presents a summary of the results indicating that the use of a composite material consisting of alternating layers of AA 6061-T6 and AA 7075-T6 materials, which possess enhanced hardness and tensile strength, may serve as a viable replacement for the typical AA 6061 material often employed in automotive components. This substitution offers the potential for improved performance and increased lifespan.

Forward-scattered and backward-scattered light in moderate keratoconus.

To evaluate the backscattered light, objective scatter index (OSI) and retinal straylight in patients with moderate keratoconus and healthy control subjects. A prospective observational study was developed with 33 patients in the moderate-keratoconus group (KC) and 34 in the non-keratoconus group (NKC). Corneal densitometry was obtained using Scheimpflug corneal tomography and measurements were expressed in grayscale units (GSU) over four zones within a 12.00 mm diameter around the corneal apex. A straylight meter was used to determine the amount of intraocular straylight under scotopic conditions, and the straylight parameter (LOG(s)) and test duration were recorded. The Optical Quality Analysis System based on the double-pass technique determined the OSI value. Significant differences were observed between the KC and NKC groups for corneal densitometry (except in the 6-10 mm zone), OSI and retinal straylight. A moderate and significant correlation was found between OSI and retinal straylight LOG(s) (r=0.52, p=0.002). Weaker and non-significant correlations were found between corneal densitometry and the other parameters analysed (i.e., OSI, retinal straylight LOG(s) and retinal straylight times). Backscattered light, retinal straylight and the OSI show clear differences between healthy eyes and those with moderate KC. The changes present in the stages of KC evaluated in the current study (stages II and III according to the Amsler-Krumeich classification) might alter the scattering of the light entering the eye.

Study on the double-pass electrochemical discharge machining process

ABSTRACT Electrochemical discharge machining (ECDM) is a nontraditional machining process applied to nonconductive and brittle materials such as glass and ceramic. In recent years, investigations have focused on improving machining efficiency, especially the material removal rate (MRR). In this regard, different techniques, including chemical and physical phenomena, have been employed on different components of the ECDM system. Current research applies a new and straightforward method to improve the MRR without the consequent complexity of other techniques (improved machining efficiency). In this way, the machining process applies in two sequential passes (double-pass machining) to shape the final geometry. In the typical ECDM process, the whole geometry is machined by one pass process. Results showed that by employing the double-pass technique, the maximum depth reached 660 µm, which was 35% higher than the single-pass (SP) process (the total machining time of SP was the same as double-pass). In addition, a significant average improvement percentage of 45% was achieved. The optimum diameter difference of the tools in the double-pass process was 300 µm, which led to the highest depth values. Depending on the tool changing time, the double-pass process is economically efficient in machining depths of more than 250 µm.

Efficacy and safety of intense pulsed light direct eyelid application

To describe the efficacy and safety of intense pulsed light (IPL) applied directly on the eyelids of patients with Meibomian gland dysfunction (MGD) without corneal shield protector. Observational retrospective single centre study where patients underwent 3 treatment sessions of IPL with 2 weeks of interval. The IPL was carried out with Lumenis OPT M22 with a double pass technique of 12 impacts on the infraorbital/lower eyelid region with the 15 × 35 mm guide light (step 1) and a double pass technique of 3 impacts over the upper eyelids with the 8 × 15 mm guide light (step 2). The follow up was conducted through Oculus Keratograph 5 M. 30 patients were enrolled in the study. Although there were no significant differences (p > 0.05), non-invasive tear break-up time, ocular redness, and OSDI questionnaire improved during the 3 IPL sessions. A significant improvement (p = 0.024) in the percentage of meibomian gland loss was also observed. Regarding tear meniscus, it was found similar measurements before and after treatment. No serious adverse effects were reported during the procedure or in subsequent follow-up. Preliminary results suggest that IPL therapy applied directly on the eyelids without corneal shield could be safe and effective in the treatment of MGD.

Commentary: Low-dose atropine: How clear is the view?

Myopia is an under acknowledged epidemic which has already affected nearly 30% of the world population in 2020. According to current projections, this number is expected to rise to 50% by 2050, of which 10% will be contributed by high myopia.[1] Myopia adversely impacts an individual’s quality of life, particularly high myopia, which can be potentially blinding. It may increase the risk of cataract, glaucoma, and various posterior segment complications such as myopic maculopathy, retinal degenerations, posterior staphyloma, retinal detachment, choroidal neovascularization, and so on.[2] With predicted increase in myopia prevalence, one can only imagine its socioeconomic impact globally. Needless to say, various pharmacological, behavioral, or optical measures have been tried and tested worldwide in order to halt or slow down its progression. Among these, atropine is the only medication found to be consistently effective.[34] Various low-to-moderate concentrations of atropine eye drops (e.g., 0.01, 0.025, 0.05, and 0.1%) have been tried with varying efficacy, and it is also known that side effects and rebound effects are dose dependent. Five-year results from ATOM2 study supported application of 0.01% atropine as the safest and most effective dose for restricting myopia.[5] However, does atropine therapy have any side effects on the vision quality? In the following article, the authors have compared the optical quality of vision between two doses of atropine eyedrops, namely, 0.05 and 0.01%, using the Optical Quality Analysis System™ (OQAS; Visiometrics, Terrassa, Spain). The optical quality of retinal image is mainly affected by higher-order aberrations and scattered light. Traditionally, wavefront aberrometry systems have been used to measure these objectively. OQAS uses a newer technology of double-pass technique based on recording images from a point-source object after reflection on the retina and a double pass through the ocular media.[6] This system has already been used to evaluate optical quality in patients undergoing keratorefractive and phakic IOL surgery,[7] patients with keratitis,[8] and presbyopic patients after photorefractive keratectomy.[9] Several studies have evaluated the side effects of low-dose atropine drops as they are used in control of myopia progression, but till date, there is no study which has objectively evaluated the optical quality of vision after commencing atropine treatment. The authors have illustrated that the optical quality after 2 weeks following treatment with 0.01% atropine eye drops did not change, while it decreased with 0.05% eye drops. This further strengthens our rationale for using lower dose of atropine (0.01%) in myopic children in order to halt or slow-down myopia progression. A small percentage of children in the LAMP study (trials using 0.05, 0.025, and 0.01%) reported reduction in accommodation amplitude by 0.26D and dilation of pupils by 0.5 mm with 0.01% atropine, neither of which are clinically significant.[10] However, the authors of the current study, while comparing 0.01 and 0.05% atropine, found that children with mild myopia may need to begin wearing glasses while using 0.05% atropine eye drops. The decrease in predicted visual acuity at 20 and 9% contrast indicates that children treated with 0.05% atropine eye drops had poorer vision when reading materials with poor contrast. These effects were not seen with 0.01% atropine. Most recent studies advocate the course of treatment of at least 2 years initially, with follow-up every 3 months with cycloplegic refraction. For myopic children, treatment with atropine 0.01% can be commenced as a night-time dose after discussing the potential side effects and expected benefits. Cycloplegic refraction must be repeated at 3–6 monthly intervals during this period of treatment. The required myopic correction should be worn at all times. If the child experiences near blurring, bifocal glasses may be offered. If photophobia occurs, tinted glasses or sunglasses may be used outdoors. As the authors have already pointed out, children on 0.05% atropine treatment may need better contrast conditions. Increased outdoor time and reduced screen time should be encouraged. During the follow-up visits, possible local side effects such as red eyes, allergy, and even systemic effects such as headache and tachycardia should be looked for. In case of continued myopia progression ≥ 0.5 D after 6 months, one may consider using a higher dose (0.05%) of atropine, keeping in mind the side effects and high discontinuation rate. In conclusion, low dose (0.01%) atropine is the recommended concentration when commencing atropine treatment for myopia because its benefits clearly outweigh the side effects. Both children and parents need to be motivated for long-term compliance by educating them about consequences of high myopia. After all, the clinical and economic burden of this condition is only expected to increase in the near future.

Production of orbital angular momentum states of optical vortex beams using a vortex half-wave retarder with double-pass configuration

Higher orders of orbital angular momentum states (OAMs) of light have been produced with a double-pass configuration through a zero-order vortex half-wave retarder (VHWR). This double-pass technique can reduce the number of VHWR plates used, thus reducing costs. The OAM states of the vortex beams are identified by the near-field Talbot effect. Polarization dependence of the vortex states can also be demonstrated with this VHWR using Talbot effect. Without using the Talbot patterns, this effect of the polarization on the vortex beam can not be recognized. A theoretical validation has also been provided to complement the experimental results. Our study gives an improved understanding of this approach to use a VHWR plate.

Comparing the vision quality using double-pass technique in eyes with corrected refractive errors and emmetropic eyes.

To evaluate the vision quality by measuring the objective light scatter index and objective optical quality parameters (Strehl Ratio and Modulation Transfer Function) in patients with emmetropia and ametropia. This prospective, cross-sectional study included 408 eyes. The ametropic group comprised of eyes with best-corrected visual acuity of 0.0 logMAR or better and present at least a refractive error of ≥0.25 D. Patients underwent slit lamp examination, visual acuity, refraction, and vision quality using the HD Analyzer. The mean objective light scatter indices were 0.62 ± 0.63, 0.77 ± 0.70, 0.74 ± 0.30, 0.93 ± 0.55, and 0.85 ± 0.61, and mean Strehl Ratio and Modulation Transfer Function scores were 38.17 ± 10.4, 37.37 ± 10.06, 29.84 ± 9.71, 33.2 ± 12.11, and 33.13 ± 10.09 in emmetropes, myopia, hyperopia, spherical equivalent of ≥0, and spherical equivalent of <0, respectively. Differences in all variables were significant between emmetropic and corrected hyperopic and between spherical equivalent of ≥0, and spherical equivalent of <0 eyes (p<0.05). In spectacle-corrected conditions (with trial frames), emmetropic and simple myopic eyes had significantly better vision quality compared to hyperopic and astigmatic eyes. The clinical significance of these results should be investigated in further studies.

Implementation of the Frequency Scatter Index in Clinical Commercially Available Double-pass Systems

ABSTRACTA previous work has reported a methodology to quantify intraocular scattering using a high sensitivity double-pass instrument with a robust index, the frequency scatter index. The purpose of our study was to evaluate an adaptation of the frequency scatter index for use in clinical double-pass systems. A prospective observational study was carried out in a group of patients with nuclear cataracts (n = 52) and in a control group (n = 11) using conventional double-pass systems. The frequency scatter index and the objective scatter index were used to assess the scattering. The Spearman coefficient was calculated to assess the correlation between both indexes, obtained from the double-pass images. Simultaneous measurements were performed with a double-pass and with a Hartmann-Shack wavefront sensor in the control group. The root-mean-square wavefront error and the full width at half maximum of the double-pass image were used to quantify the residual aberrations introduced by the variations in pupil size and retinal eccentricity. Measurement in eyes with different grades of cataracts shows a strong correlation (ρ = 0.929, p < .0001) between the frequency scatter index and the objective scatter index. A certain degree of correlation was observed between the objective scatter index and the root-mean-square and between the objective scatter index and the full width at half maximum, both for measurements with a different pupillary diameter and with a different retinal eccentricity (p < .05). No relationship was observed between the frequency scatter index and the root-mean-square or between the frequency scatter index and the full width at half maximum (p > .05). We have introduced and evaluated an adaptation of a methodology proposed recently for the measurement of intraocular scattering using the double-pass technique with a robust index, which is less affected by ocular aberrations. The frequency scatter index can be applied to conventional double-pass instruments available in clinical environments.

Performance Analysis on Single- and Double-Pass Ytterbium-Doped Fiber Amplifier in the 1 µm Region

ABSTRACT In this work, single- and double-pass configurations of ytterbium-doped optical fiber amplifiers (YDFAs) have been investigated. This low quantum defect rare-earth dopant and their performance near 1 µm region has been comprehensively investigated on the basis of gain and noise figure in relation with input signal power and input pump power. The obtained results showed that at an input pump power of 100 mW, the gain was proportionally increased with ytterbium-doped fiber (YDF) length for both proposed configurations, but double-pass regime scored higher gain. This is due to the double-propagation of the forwarded and amplified spontaneous emission (ASE) signal into the active medium and hence will maximize the attainable gain near the 1 µm wavelength region. At YDF length of 5 m, the double-pass technique showed better amplification performance at a lower input signal power of −20 dB compared to the higher input signal power of 0 dB. The maximum gain and optical signal-to-noise ratio (OSNR) attained by double-pass configuration were 24.6 dB and 53.4 dB, respectively. Double-pass amplification at input signal power of −20 dB has increased the gain by 11.2 dB in comparison with the single-pass technique.

Feasibility of optical quality analysis system for the objective assessment of accommodation insufficiency: a phase 1 study

PurposeTo assess differences in a new objective metric obtained with a double-pass technique between a group with accommodation insufficiency (AI) and a control group and to explore the diagnostic capabilities of this new tool in comparison to conventional procedures. MethodsRetrospective cross-sectional case-control phase 1 study. Two groups with ages ranging from 8 to 18 years were recruited: AI and control group. The diagnostic criterion of AI was based on monocular accommodative amplitude (AA), 2 D below Hofstetter’s calculation for minimum AA, and monocular accommodative facility (MAF), failing with minus lens and cut-off at ≤ 6 cycles per minute. Accommodative response with a double pass device (HD Analyzer, Visiometrics) was measured, performing an evaluation from +1.00 D to −3.50D (−0.5D steps), offering the width of the profile at 50% (WP) in minutes of arc. ResultsDifferences were found between groups for the AA, MAF and MEM retinoscopy (p < 0.0001, p < 0.001, p = 0.037). The discriminative capacity of MEM retinoscopy for AI diagnosis was significant and the cut-off that maximized the sensitivity and specificity was > 0.5 D. Considering WP 50% in different points, the discriminative AI diagnosis capacities for the points of 2.0 D and 2.50 D were significant (ROC-AUC 0.78; p = 0.03 and p = 0.02). ConclusionsDouble-pass system metric differed between patients with AI and control group, therefore the aim of a Phase I study was achieved. Further steps with higher sample sizes are required to evidence if the system really provides any advantage versus conventional methods in the diagnosis of AI.

Extraction of bridge information based on the double-pass double-vehicle technique

To identify the bridge information from the response of test vehicles passing on it (also known as the indirect approach) has aroused the interest of many researchers thanks to its economy, easy implementation and less disruption to traffic. The surface roughness of bridge remains an obstacle for such method as it contaminates the vehicle response severely and thereby renders many vehicle-response-based bridge identification methods ineffective. This study aims to eliminate such effect with the responses of two different test vehicles. The proposed method can estimate the surface profile of a bridge based on the acceleration data of the vehicles running on the bridge successively, and obtain the normalized contact point response, which proves to be relatively immune to surface roughness. The frequencies and mode shapes of bridge can be further extracted from the normalized contact point acceleration with spectral analysis and Hilbert transform. The effectiveness of the proposed method is verified numerically with a three-span continuous bridge. The influence of measurement noise is also examined.

Objective Quantification of Image Quality and Optical Scatter Before and After Nd:YAG Capsulotomy Using a Double-Pass Technique.

PurposeThe purpose of this study is to evaluate and compare the correlation between changes in vision and HD Analyzer dual-pass metrics versus changes in vision and conventional subjective slit lamp gradings in pseudophakic patients with posterior capsular opacity undergoing neodymium:yttrium-aluminum-garnet (Nd:YAG) capsulotomy.Patients and MethodsHigh contrast (HC) and low contrast (LC) best spectacle-corrected distance visual acuity (BCVA) and HD Analyzer evaluation were prospectively performed on patients with mild-to-moderate posterior capsular opacification (PCO) and monofocal and accommodating intraocular lens implants. Differences between pre- and post-operative measurements were calculated, along with the correlation of HD Analyzer metrics and slit lamp grading to changes in visual acuity.ResultsFollowing Nd:YAG capsulotomy (n=29), there was statistically significant improvement in HC-BCVA and LC-BCVA, decrease in optical scatter, and corresponding improvement in Strehl ratio and HD Analyzer values at all contrast levels tested (p≤0.05). Pearson test showed a high correlation between the improvement in HC-BCVA (r coefficient = 0.78) and LC-BCVA (r coefficient = 0.71) to the improvement in Objective Scatter Index (OSI). There was a higher correlation of change in HC-BCVA to pre-op OSI (r2=0.61) than to the subjective PCO grading score (r2 = 0.19). There was also a higher correlation of change in LC-BCVA to pre-op OSI (r2 = 0.49) than to subjective grading (r2 = 0.16).ConclusionThe HD Analyzer provides objective measurements of forward light scatter (ie, light directed towards the retina) that can assist with both PCO grading and prediction of improvement of visual quality after YAG laser capsulotomy with higher accuracy than conventional slit lamp assessment based upon backscatter (ie, light traveling to the observer) in patients tested with monofocal and accommodating intraocular lens implants.

Non-invasive Instrument-Based Tests for Quantifying Anterior Chamber Flare in Uveitis: A Systematic Review

ABSTRACT Purpose: Anterior chamber (AC) flare is a key sign for anterior uveitis. New instrument-based techniques for measuring AC flare can offer automation and objectivity. This review aims to identify objective instrument-based measures for AC flare. Methods: In this systematic review, we identified studies reporting correlation between instrument-based tests versus clinician AC flare grading, and/or aqueous protein concentration, as well as test reliability. Results: Four index tests were identified in 11 studies: laser-flare photometry (LFP), optical coherence tomography, ocular flare analysis meter (OFAM) and the double-pass technique. The correlation between LFP and clinician grading was 0.40–0.93 and 0.87–0.94 for LFP and protein concentration. The double-pass technique showed no correlation with clinician grading and insufficient information was available for OFAM. Conclusion: LFP shows moderate to strong correlation with clinician grading and aqueous protein concentration. LFP could be a superior reference test compared to clinician AC flare grading for validating new index tests.

Five-Year Outcomes of Ultrathin Descemet Stripping Automated Endothelial Keratoplasty.

To report 5-year outcomes of ultrathin Descemet stripping automated endothelial keratoplasty (UT-DSAEK) with a central graft thickness intended to be <100 μm. This retrospective, consecutive, interventional case series included 354 eyes with endothelial decompensation due to various causes (Fuchs endothelial dystrophy, pseudophakic or aphakic bullous keratopathy, failed previous graft, herpetic endothelitis, or buphthalmos). Donor tissue was prepared using the microkeratome-assisted double-pass technique aiming at a graft thickness <100 μm. The Descemet membrane was stripped under air. The graft was delivered into the anterior chamber using the pull-through technique through a 3.2-mm clear corneal incision using a modified Busin glide. The best spectacle-corrected visual acuity (BSCVA), endothelial cell loss, graft survival rates, and immunologic rejection rates were evaluated. Follow-up data at 1, 2, 3, and 5 years after UT-DSAEK were collected from 214, 172, 147, and 105 eyes, respectively. After excluding eyes with comorbidities, BSCVA better than or equal to 20/20 was recorded in 36.3%, 37.4%, 46.4%, and 53.4% of eyes, respectively, whereas BSCVA better than or equal to 20/40 was documented in 95.5%, 95.3%, 96.0%, and 96.6% of eyes, respectively. The mean endothelial cell loss was 35.4%, 42.3%, 43.3%, and 52.3%; Kaplan-Meier graft survival probability was 99.1%, 96.2%, 94.2%, and 94.2%, and Kaplan-Meier cumulative probability of a rejection episode was 3.4%, 4.3%, 5%, and 6.9% at 1, 2, 3, and 5 years, respectively. UT-DSAEK grafts allow excellent 5-year outcomes, including BSCVA, endothelial cell density, and survival rates comparable with those recorded post-Descemet membrane endothelial keratoplasty, but with a higher immunologic rejection rate.

Retinal-image quality and contrast sensitivity function in eyes with epiretinal membrane: a cross-sectional observational clinical study

BackgroundTo investigate the effect of idiopathic epiretinal membrane (ERM) on the retinal-image quality and psychophysical contrast sensitivity function (CSF).MethodsForty-four subjects with diagnosis of idiopathic unilateral ERM were enrolled in this cross-sectional observational clinical study. The fellow unaffected eyes were set as the control group. For retinal-image quality assessment, an Optical Quality Analysis System (OQAS) based on double-pass technique was used to evaluate objective scatter index (OSI) and Strehl ratio. For visual performance, the CSF under photopic condition was measured.ResultsFor retinal-image quality, the result of double-pass device revealed a significant lower Strehl ratio and larger OSI in the ERM eyes compared to the fellow eyes (all P < 0.05). For visual performance, the CSF at all spatial frequencies under photopic condition were also significantly degraded in the ERM eyes compared to the fellow eyes (all P < 0.05). For the ERM eyes, the reduction of Strehl ratio and CSF was 29.41 and 54.39%, respectively, and the increase of OSI was 164.10% compared to the fellow eyes. Besides, BCVA significantly correlated to the total CSF (ERM eyes, r = − 0.53, P < 0.001; the fellow eyes, r = − 0.467, P = 0.002) and Strehl ratio (ERM eyes, r = − 0.485, P = 0.001; the fellow eyes, r = − 0.311, P = 0.043) in both of the ERM and the fellow eyes.ConclusionEyes affected with ERM showed poorer retinal-image quality and visual performance than the normal eyes. Retinal-image quality measured by OQAS based on double-pass technique could be useful for assessing the retinal-image quality for ERM-affected eyes, in which retinal scattering was significantly increased.

Long-Term Changes in Straylight Induced by Overnight Orthokeratology: An Objective Measure Using the Double-Pass System

ABSTRACTPurpose: To map the time course of changes in intraocular straylight of the human eye 1 year after initial lens wearing for orthokeratology treatment using the objective double-pass technique.Materials and Methods: A total of 35 subjects (19 males and 16 females) completed the study. The mean age was 11.46 ± 2.33 years (range, 8–16 years). All subjects were fitted with spherical four-zone orthokeratology lenses following the procedures recommended by the lens manufacturer. The subjects were required to wear the lens for at least eight consecutive hours at night. After lens removal during the daytime, objective scattering index (OSI) was evaluated using the double-pass technique (OQAS-II, Visiometrics, Terrassa, Spain) prior to lens dispatch (baseline), followed by evaluations at 1 week, 1 month, 6 months, and 12 months after the initial lens wearing. Longitudinal changes were fitted to a model containing both an impairing and recovery component, and the results were based on an extrapolation between the visits.Results: OSI rose quickly following lens wearing, reaching its highest level (double that of baseline values) by approximately 1.47 months. However, the recovery phase was slow and modest. One year after the initial lens wearing, OSI exhibited a 20% recovery from the peak level, but remained 63% higher than the baseline level.Conclusions: Intraocular straylight immediately increased flowing lens wearing, and this change reaches maximal level around 1 month after lens wearing. Slow but significant recoveries of optical quality subsequently followed.

Intraocular light scatter in patients on topical intraocular pressure-lowering medication.

To quantify ocular light scattering in patients under treatment with intraocular pressure-lowering eye-drops. In this prospective, observational, cross-sectional case series study, 160 eyes of 160 patients with primary open angle glaucoma or primary ocular hypertension were consecutively recruited from our Glaucoma Department over 7 months. In total, 46 eyes of 46 healthy volunteers matched for age and sex served as the control group. The variables recorded in a single visit were as follows: drug and number of drops per day, treatment duration, OXFORD corneal staining grade, lower tear meniscus height as measured by spectral domain optical coherence tomography, ocular redness and non-invasive tear breakup time measured with the Oculus Keratograph 5M, ocular surface disease index questionnaire score and objective scatter index through a double-pass technique (Optical Analysis System II). Objective scatter index was higher in the patient group (3.1, interquartile range = 1.8-5.47) than in the control group (1.95; interquartile range = 0.7-5; p = 0.017). In a multiple linear regression model, non-invasive tear breakup time was identified as the most influential variable on light scatter (mean ratio = -1.015; p = 0.003; 95% confidence interval = -1.025 to -1.005). No correlation with objective scatter index was observed for number of daily eye-drops, preservative concentration or treatment duration. Participants on anti-glaucoma medication showed a significantly higher objective scatter index than control group individuals. In the treated patient group, a lower non-invasive tear breakup time was associated with a higher objective scatter index. This suggests that lubricating eye-drops to improve tear breakup time could also improve vision quality in these patients by diminishing light scattering.

A dynamic double pass technique for characterizing internal noise during binocular rivalry

A dynamic double pass technique for characterizing internal noise during binocular rivalry

Ultrathin Descemet's Stripping Automated Endothelial Keratoplasty Using the Double-pass Technique with the Microkeratome versus Standard Descemet's Stripping Automated Endothelial Keratoplasty

Purpose The aim of the present study was to compare the results of Descemet's stripping automated endothelial keratoplasty (DSAEK) and ultrathin Descemet's stripping automated endothelial keratoplasty (UT-DSAEK) that were performed with a standardized technique at a single institution. Design The present study was designed as a single-center, prospective, randomized nonblinded study. Participants and methods Sixty-one and 51 eyes underwent DSAEK and UT-DSAEK, respectively, for any endothelial disease at the ‘Villa Igea’ Center. Patients with pre-existing ocular comorbidity that impacted visual potential such as macular degeneration, amblyopia, advanced glaucoma, and other optic neuropathies were excluded from the study. Best-corrected visual acuity (BCVA) (in Snellen acuity chart) was obtained and specular microscopy of donor corneal tissue was performed before surgery. Postoperative complications, BCVA, and the percent of endothelial cell loss (ECL) recorded at 1, 3, 6 months, and 1 year were compared. Main outcome measures Visual acuity improvement, ECL, intraoperative postoperative complications, iatrogenic primary graft failure, and rebubbling were the main outcome measures in this study. Results Mean ± SD BCVA improved from 0.17 ± 0.13 and 0.19 ± 0.13 before surgery to 0.75 ± 0.18 and 0.88 ± 0.19 at 1 year after DSAEK and UT-DSAEK, respectively (P = 0.001). ECL was 33.88 ± 17.74% after DSAEK and 36.37 ± 13.10% after UT-DSAEK (P = 0.4080). There were no iatrogenic primary graft failures after the two procedures but there were two late endothelial failures after DSAEK. Rebubbling was performed for four of 51 eyes after UT-DSAEK and for none after DSAEK (P = 0.04). Conclusion Compared with DSAEK, UT-DSAEK provided better visual recovery and comparable ECL. The UT-DSAEK group had a higher percentage of rebubbling procedures but less rejection and failure rate.

Binocular open-view system to perform estimations of aberrations and scattering in the human eye.

We present a system that integrates a double-pass (DP) instrument and a Hartmann-Shack (HS) wavefront sensor to provide information not only on aberrations, but also on the scattering that occurs in the human eye. A binocular open-view design permits evaluations to be made under normal viewing conditions. Furthermore, the system is able to compensate for both the spherical and astigmatic refractive errors that occur during measurements by using devices with configurable optical power. The DP and HS techniques provide comparable data after estimating wavefront slopes with respect to the intersections of an ideal grid and compensating for residual errors caused by the optical defects of the measuring system. Once comparable data is obtained, it is possible to use this combined manner of assessment to provide information on scattering. Measurements in an artificial eye suggest that the characteristics of the ocular fundus may induce deviations of DP with respect to the HS data. These differences were quantified in terms of the modulation transfer function in young, healthy eyes measured in infrared light to demonstrate the potential use of the system in visual optics studies.