Order RMS Research Articles

Higher order aberrations and retinal image quality during short-term accommodation in myopic and non-myopic children.

Despite the known associations between near work and myopia, and retinal image quality and eye growth, accommodation-induced changes in higher order aberrations (HOA's) and retinal image quality in children with different refractive errors are poorly understood. Ocular HOA's were measured using a Hartmann-Shack wavefront sensor (COAS-HD, Wavefront Sciences) in 18 myopic and 18 age- and sex-matched non-myopic children during short-term accommodation tasks (four demands of 0, 3, 6 and 9 D) presented using a Badal optometer. Eighth order Zernike polynomials were fitted across a 2.3 mm pupil diameter to determine refractive power vectors (M, J180 and J45 ) and the accommodation error, and a 4 mm pupil was used for HOA analyses. Retinal image quality was examined using the visual Strehl ratio based on the optical transfer function (VSOTF) for third to eighth radial orders only. Most refractive error group differences were observed for the 6 and 9 D demands. Myopic children underwent greater changes in with-the-rule astigmatism (J180 ), higher order and third order RMS values, primary vertical ( ) and horizontal coma ( ), and several other individual Zernike coefficients compared with non-myopic children (all refractive error group by demand interaction p-values of ≤0.02). Non-myopic children exhibited a greater negative shift in primary ( ) and positive shift in secondary spherical aberration ( ) (both refractive error group by demand interaction p-values of ≤0.002). The VSOTF degraded for the 6 and 9 D demands in both groups, but the myopic children underwent a greater mean (SE) reduction from 0 D of -0.274 (0.048) for the 9 D demand, compared with -0.131 (0.052) for the non-myopic children (p = 0.001). These results may have implications for the association between near work, accommodation and myopia development, particularly related to the use of short working distances during near tasks.

Ocular and corneal aberrations changes in controlled randomized clinical trial MiSight\xae Assessment Study Spain (MASS)

BackgroundTo compare ocular and corneal inherent aberrations in the naked eyes of randomly selected children fitted with MiSight contact lenses (CL) for myopia control, versus children corrected with single-vision spectacles (control), over a 24-months period.MethodsChildren aged 8 to 12 years, with myopia (-0.75 to -4.00 D sphere) and astigmatism (< -1.00 D cylinder) were randomly assigned to the lens study group (MiSight) or the control group (single-vision spectacles). The root mean square aberration (RMS) was determined as corneal (RMS_C), corneal high order RMS (HO_RMS_C), corneal low order RMS (LO_RMS_C), ocular (total) RMS (RMS_T), ocular high order RMS (HO_RMS_T), ocular low order RMS (LO_RMS_T), corneal spherical aberration (SA_C) and ocular SA (SA_T) were calculated by aberrometry measures at the baseline, on 12-months and 24-months visits. A 5 mm diameter was defined for the analysis in all visits for all subjects. Only the dominant eye was analyzed.ResultsSeventy-four subjects completed the clinical trial: 41 subjects from the MiSight group (age: 11.01 ± 1.23 years) and 33 from the single-vision group (age: 10.12 ± 1.38 years). RMS_T significantly changed (0.57 ± 0.20 µm, p = 0.029) after 24-months in the control group. In the MiSight group no significant changes were registered (p > 0.05). The SA_C and SA_T did not reveal significant changes between visits or between groups (p > 0.05).ConclusionsAlong 2 years, MiSight CL did not induce significant changes in RMS of anterior cornea or total ocular RMS. Contrary, in control group the RMS_T significantly changed as response of greater eye growth and myopia progression. The results obtained in present study allow to predict corneal or total aberration changes, in children, in response of wearing of MiSight lens along the time.Trial registration: ClinicalTrials.gov Identifier: NCT01917110.

Adhesion of tungsten particles on rough tungsten surfaces using Atomic Force Microscopy

Adhesion forces between tungsten spherical microparticles and tungsten substrates with different roughnesses have been measured using the Atomic Force Microscopy (AFM) colloidal probe technique. Mean roughnesses of the tungsten substrates were measured by AFM and were ranked in three categories i.e. nanoscale, sub-microscale and microscale roughnesses. Experimental Hamaker constant of 37±3.5×10−20 J has been obtained using a spherical tungsten particle of 10.5 μm in radius and a tungsten substrate with nanoscale root-mean-square roughness of rms=11.5 nm. It was shown that larger roughness of the order rms=712 nm induces a two order of magnitude decrease on the adhesion of tungsten microparticles compared to a smooth tungsten surface with nanoscale roughness. Comparison with the van der Waals-based adhesion force model of Rabinovich which integrates the roughness of surfaces showed good agreement with experimental pull-off forces even when roughness of the substrate is close to the micrometer range. In such case, measurements have shown that dependency of adhesion force with particle size (in the micrometer range) has a secondary influence compared to the roughness of surfaces.

ADVANCED KERATOCONUS WITH LOW REFRACTIVE ERROR

In this report we are presenting a 28-year-old female with right keratoconus grade3 and leftkeratoconus grade 2 with low degree refraction (spherical equivalent in right eye = -2.25 and+0.75D in left eye). Axial length measurement revealed short axial length (RE=19.63mm,LE=19.97 mm). After counseling the patient, the decision was to go for right simultaneousfemtosecond intracorneal ring segments implantation with corneal collagen cross linking. UCVA,BCVA, sphere, cylinder, spherical equivalent, RMS total high order aberrations(HOA), RMS coma,and RMS astigmatism were measured pre- and postoperatively in the first week, 1 month, 3 month, 6month. The results were favorable as regards improvement in UCVA, BCVA, with mild hyperopic shiftin the sphere as expected with decrease in the cylinder, and induced flattening. As for HOA, comaand astigmatism; there was marked decrease.

Influence of overnight orthokeratology lens fitting decentration on corneal topography reshaping

BackgroundThis retrospective study was designed to investigate the sole influence of orthokeratology (OK) lens fitting decentration on the Zernike coefficients of the reshaped anterior corneal surface.MethodsThis study comprised a review of 106 right eyes and measurements of corneal topography both before OK and at 1-month follow-up visit. A routine was designed to calculate local corneal surface astigmatism and assist the determination of OK lens fitting decentration from pupil center. The pupil-centered corneal Zernike coefficients of baseline (PCCB) and post-treatment (PCCP) were calculated. Meanwhile, the OK-lens-centered corneal Zernike coefficients of post-treatment (OCCP) were also calculated and considered as the presumptive ideal fitting group without decentration. Relationships between lens fitting decentration and the change of Zernike coefficients including (PCCP − PCCB) and (PCCP − OCCP) were analyzed.ResultsPatients with a mean age of 11 ± 2.36 years old had an average spherical equivalent refractive error of −3.52 ± 1.06 D before OK. One month after treatment, OK lens fitting decentration from pupil center was 0.68 ± 0.35 mm. RMS of 3rd-order (P < 0.05), RMS of 4th-order (P < 0.001) and RMS of total high order (P < 0.001) corneal Zernike coefficients were increased in PCCP by comparing with OCCP, which was solely caused by lens fitting decentration. Nevertheless, no significant difference was observed in {C}_2^0 (P > 0.05). For the high order corneal Zernike coefficients in (PCCP – OCCP), radial distance of decentration was correlated with {C}_3^{-1} (r = −0.296, P < 0.05), {C}_3^1 (r = −0.396, P < 0.001), and {C}_4^0 (r = 0.449, P < 0.001), horizontal decentration was significantly correlated with {C}_3^1 (r = 0.901, P < 0.001) and {C}_5^1 (r = 0.340, P < 0.001), and vertical decentration was significantly correlated with {C}_3^{-1} (r = 0.904, P < 0.001).ConclusionsOK lens fitting decentration within 1.5 mm hardly influenced the change of corneal spherical power for myopia correction, but significantly induced additional corneal high order Zernike coefficients including {C}_3^{-1} , {C}_3^1 , {C}_4^0 , and {C}_5^1 .

Miniscleral lens wear influences corneal curvature and optics.

Transient changes in corneal topography associated with soft and conventional or reverse geometry rigid contact lens wear have been well documented; however, only a few studies have examined the influence of scleral contact lens wear upon the cornea. Therefore, in this study, we examined the influence of modern miniscleral contact lenses, which land entirely on the sclera and overlying tissues, upon anterior corneal curvature and optics. Anterior corneal topography and elevation data were acquired using Scheimpflug imaging (www.pentacam.com) immediately prior to and following 8 h of miniscleral contact lens wear in 15 young healthy adults (mean age 22 ± 3 years, eight East Asian, seven Caucasian) with normal corneae. Corneal diurnal variations were accounted for using data collected on a dedicated measurement day without contact lens wear. Corneal clearance was quantified using an optical coherence tomographer (RS-3000, www.nidek.com) following lens insertion and after 8 h of lens wear. Although corneal clearance was maintained throughout the 8-h lens wear period, significant corneal flattening (up to 0.08 ± 0.04 mm) was observed, primarily in the superior mid-peripheral cornea, which resulted in a slight increase in against-the-rule corneal astigmatism (mean +0.02/-0.15 × 94 for an 8 mm diameter). Higher order aberration terms of horizontal coma, vertical coma and spherical aberration all underwent significant changes for an 8 mm corneal diameter (p ≤ 0.01), which typically resulted in a decrease in RMS error values (mean change in total higher order RMS -0.035 ± 0.046 μm for an 8 mm diameter). There was no association between the magnitude of change in central or mid-peripheral corneal clearance during lens wear and the observed changes in corneal curvature (p > 0.05). However, East Asian participants displayed a significantly greater reduction in corneal clearance (p = 0.04) and greater superior-nasal corneal flattening compared to Caucasians (p = 0.048). Miniscleral contact lenses that vault the cornea induce significant changes in anterior corneal surface topography and higher order aberrations following 8 h of lens wear. The region of greatest corneal flattening was observed in the superior-nasal mid-periphery, more so in East Asian participants. Practitioners should be aware that corneal measurements obtained following miniscleral lens removal may mask underlying corneal steepening.

V39. Repetitive magnetic stimulation (rMS) leads to NMDA receptor-dependent metaplasticity in hippocampal slices in vitro

Long-term potentiation (LTP) is widely accepted as a major mechanism of information storage in the brain. Experimentally, LTP is induced by electrical stimulation of afferent fibers using various high-frequency stimulation paradigms. We have previously shown that repetitive magnetic stimulation (rMS) can also elicit LTP at Schaffer collateral-CA1 pyramidal cell synapses, which was N-methyl- d -aspartate (NMDA) receptor-dependent. In the current study, we investigated the priming effect of rMS on the subsequent magnitude of electrically induced LTP in the CA1 region of rat hippocampal slices. To this end, we first stimulated the afferent fibers using rMS, and then started the recording of field excitatory postsynaptic potentials (fEPSPs). Electrical stimulation (ES) was administered at 30 min after rMS in order to induce LTP. Under control conditions, ES could reliably induce LTP in naive slices. In contrast, the same ES protocol resulted in long-term depression when rMS was delivered to the slice 30 min prior to ES. Thus, rMS-priming prevented subsequent ES-induced LTP. The effect of rMS-priming was significantly diminished when applied in the presence of the metabotropic glutamate receptor antagonists(RS)-α-methylserine-O-phosphate (MSOP) and (RS)-α-methyl-4-carboxyphenylglycine (MCPG). In order to study the effects of rMS on CA1 hippocampal synapses directly,we conducted another set of experiments starting the fEPSP recording before rMS. In this case, rMS itself led to a significant enhancement of the fEPSP which was then reduced to baseline level by decreasing the stimulation strength before ES was administered. Under these conditions, ES did increase the fEPSP, but the magnitude of LTP in rMS-primed slices was significantly lower than the LTP obtained in unprimed slices. Moreover, when rMS was delivered in the presence of the NMDA receptor-antagonist D-2-amino-5-phosphonovalerate (50 μM) which itself completely blocked the rMS-induced fEPSP enhancement, ES-induced LTP was again as high as under control conditions in slices without priming. These results demonstrate that rMS-priming significantly reduced the propensity of subsequent electrical LTP, and show that both metabotropic glutamate and NMDA receptor activation were involved in this form of rMS-induced metaplasticity.

Control de la temperatura para la prevención de plagas poscosecha en la conservación de granos

The postharvest insect plagues are the main cause of grain quality lost during storage period, fundamentally in tropical climate zones due to the high values of temperature and humidity. The storage in Refrigerated Metallic Storehouses (rms) is one of the principal technologies for the conservation of large grain quantities during long time period. The atmospheric variables are modified by using vehicles equipped with cool air compressors which are shared among several storehouses. The inadequate usage of these cold carts causes that temperature and/or humidity in the rms run out of the specifications for the maize conservation. This research aims to analyse and forecast the temperature and humidity behavior in a rms in order to evaluate and to improve the cooling process. A forecasting model for the temperature in the rms is built using trend lines, which is employed to plan the adequate usage of the cold carts.

Influence of higher order aberrations and retinal image quality in myopisation of emmetropic eyes.

Refractive error, higher order aberrations (HOA), axial length (AL), anterior chamber depth (ACD) and average corneal radius of curvature were measured after cycloplegia from 166 emmetropic participants at the Sydney Myopia Study (SMS, 2004-2005, age 12.63 ± 0.48 years). Measurements were repeated approximately 5 years later at the Sydney Adolescent Vascular and Eye Study (SAVES, 2009-2010, age 17.08 ± 0.67 years). The baseline spherical equivalent (M) did not differ significantly between the participants lost to follow-up (65%) and the participants enrolled in SAVES study (p = 0.932). Refractive error and HOA were measured using a Shack-Hartmann aberrometer for a pupil diameter of 5 mm and AL, ACD and average corneal curvature measured using IOL Master at both visits. Retinal image quality in terms of Visual Strehl ratio (VSOTF) for a 5 mm pupil diameter was determined using on-axis lower and HOA. General linear model was used to determine the association of HOA and retinal image quality with change in refraction. Of the 166 emmetropes, 41 (25%) had myopic change (change in M > -0.50 D) and 125 (75%) had no change in refraction (change in M between +0.49 D and -0.49 D). Change in C[4, 0] (p < 0.001, R² = 0.236), fourth order RMS (p = 0.003, R² = 0.097) and coma RMS (p = 0.004, R² = 0.056) from baseline were significantly correlated with change in refraction. More positive change in C[4, 0] was associated with lesser myopic change in refraction. The eyes with myopic change in refraction decreased in positive C[4, 0] (at baseline = +0.049 ± 0.05 μm, at follow-up = +0.024 ± 0.05 μm, p < 0.05). In comparison, eyes with no change increased in positive C[4, 0] (at baseline = +0.033 ± 0.04 μm, at follow-up = +0.047 ± 0.04 μm, p < 0.05). Thus in conclusion, no significant association was observed between HOA and retinal image quality at baseline and development and progression of myopia among emmetropic eyes. The change in spherical aberration (C[4, 0]) with myopic change is possibly associated with changes occurring in crystalline lens during ocular growth.

OCT 3-D surface topography of isolated human crystalline lenses.

Quantitative 3-D Optical Coherence Tomography was used to measure surface topography of 36 isolated human lenses, and to evaluate the relationship between anterior and posterior lens surface shape and their changes with age. All lens surfaces were fitted to 6th order Zernike polynomials. Astigmatism was the predominant surface aberration in anterior and posterior lens surfaces (accounting for ~55% and ~63% of the variance respectively), followed by spherical terms, coma, trefoil and tetrafoil. The amount of anterior and posterior surface astigmatism did not vary significantly with age. The relative angle between anterior and posterior surface astigmatism axes was on average 36.5 deg, tended to decrease with age, and was >45 deg in 36.1% lenses. The anterior surface RMS spherical term, RMS coma and 3rd order RMS decreased significantly with age. In general, there was a statistically significant correlation between the 3rd and 4th order terms of the anterior and posterior surfaces. Understanding the coordination of anterior and posterior lens surface geometries and their topographical changes with age sheds light into the role of the lens in the optical properties of the eye and the lens aging mechanism.

Explicitly correlated composite thermochemistry of transition metal species

Atomization energies were calculated using explicitly correlated coupled cluster methods with correlation consistent basis sets for a series of 19 small molecules containing 3d transition metal atoms. The atomization energies were calculated using a modified Feller-Peterson-Dixon approach in which CCSD(T) complete basis set (CBS) limits were obtained using extrapolations of aVTZ∕aVQZ CCSD(T)-F12b correlation energies, and then a series of additive contributions for relativity, core correlation, higher order correlation, and zero-point vibrations were included. The frozen-core CBS limits calculated with F12 methods closely matched the more computational expensive conventional awCVQZ∕awCV5Z CBS extrapolations, with a mean unsigned deviation of just 0.1 kcal∕mol. In particular, the CCSD(T∗)-F12b∕aVDZ and aVTZ atomization energies were more accurate on average than the conventional CCSD(T)∕aVQZ and aV5Z results, respectively. In several cases the effects of higher order correlation beyond CCSD(T), as judged by CCSDT and CCSDT(Q)Λ calculations, were greater than 1 kcal∕mol, reaching 4.5 kcal∕mol for CrO3. For the 16 molecules of this study with experimental uncertainties of ∼3.5 kcal∕mol or less, the final composite heats of formation have a mean unsigned deviation (MUD) from experiment of just 1.3 kcal∕mol, which is slightly smaller than the average of the experimental uncertainties, 1.8 kcal∕mol. The root mean square deviation (RMS) is only slightly larger at 1.7 kcal∕mol. Without the contributions due to higher order correlation effects, the MUD and RMS rise to 2.1 and 2.8 kcal∕mol, respectively. To facilitate the F12 calculations, new (aug-)cc-pVnZ∕MP2Fit (n = Q, 5) and (aug-)cc-pwCVTZ∕MP2Fit auxiliary basis sets were also developed for the transition metal atoms.

Pilot study of hyperopic LASIK using the solid-state laser technology

To evaluate and report the visual, refractive, and aberrometric outcomes of LASIK for the correction of low to moderate hyperopia in a pilot group using a commercially available solid-state laser Prospective pilot study including 11 consecutive eyes with low to moderate hyperopia of six patients undergoing LASIK surgery using the Pulzar Z1 solid-state laser (CustomVis Laser Pty Ltd., currently CV Laser). Visual, refractive, and aberrometric changes were evaluated. Potential complications were evaluated as well. Mean follow-up time was 6.6 months (range, 3 to 11 months). A significant improvement in LogMAR uncorrected distance visual acuity (UDVA) was observed postoperatively (p = 0.01). No significant change was detected in LogMAR corrected distance visual acuity (CDVA) (p = 0.21). Postoperative LogMAR UDVA was 0.1 (about 20/25) or better in ten eyes (90.9 %). Mean overall efficacy and safety indices were 1.03 and 1.12. Postoperatively, no losses of lines of CDVA were observed. Postoperative spherical equivalent was within ± 1.00 D in ten eyes (90.9 %). With regard to aberrations, no statistically significant changes were found in higher order and primary coma RMS postoperatively (p ≥ 0.21), and only minimal but statistically significant negativization of primary spherical aberration (p = 0.02) was observed. No severe complications were observed. LASIK surgery using the solid-state laser technology seems to be a useful procedure for the correction of low to moderate hyperopia, with minimal induction of higher order aberrations.

Rolling Contact Fatigue Damage Detected by Correlation between Experimental and Numerical Analyses

A study on vibrations related to rolling contact fatigue test bench and a possible way to correlate this mechanical behavior and damage of the specimens is presented. In particular it has been evaluated the possibility to detect and quantify, thanks to vibration analysis, the damage on two discs subjected to rolling contact fatigue in different working conditions. Paper is divided in two parts. In the first part there is a description of test bench and results of its static and modal analyses. Then, some tests were carried out changing working conditions and specimens' parameters and a procedure that allowed both to monitor the specimen's damage state and to record accelerometric data was implemented. A set of piezoaccelerometers was placed on the machine and a virtual instrument for automatic data handling and analysis was performed. Taking into account the FEM results derived from the first part of work, data were analyzed both using a standard approach and by implementing custom digital weighting filters for a windowed RMS in order to define, real-time during the measurement, a good estimator for the specimen damage state development.

Vibration based diagnostics on rolling contact fatigue test bench

The paper presents the first results of a study on vibrations associated with a rolling contact fatigue test bench and how this mechanical behavior may be correlated to the fatigue damage of the specimens. In particular, the aim of this study was to evaluate the possibility to detect and quantify, thanks to vibration analysis, the damage on two discs subjected to rolling contact fatigue. The first part of this work regards a description of the bench with a focus on the results acquired by its static and modal fem analyses. Then, some pure rolling and sliding condition tests were carried out and a procedure to monitor both the specimens damage state and to record accelerometric data was implemented by placing a set of piezoaccelerometers on the machine and developing a virtual instrument for automatic data handling and analysis. Tests were also periodically stoppedand the rolling contact surface profile was acquired by means of a linear video camera in order to evaluate its progressive damage. Data acquired were analyzed, considering also the results from the first part of work, both using a standard approach, such as a spectral analysis (FFT, PSD and waterfall), and by implementing custom digital weighting filters for a windowed RMS in order to estimate, realtime during the measurement, a good estimator for the specimen damage state development.

Dynamics of ocular aberrations in keratoconus

Background: The aim was to investigate the fluctuations in monochromatic ocular aberrations with accommodation and tear‐film changes in moderate keratoconic eyes.Methods: We measured the changes in ocular higher‐order aberrations in 10 moderate keratoconic and 10 visually normal eyes to accommodative stimuli ranging from zero to 5.00 DS using a Hartmann‐Shack aberrometer. In addition, the changes in ocular higher‐order aberrations were measured for up to 15 seconds after a blink in eight keratoconic and eight visually normal eyes.Results: These results show that ocular spherical (p = 0.68) and coma‐like (p = 0.71) aberrations did not change significantly with accommodation from zero to 5.00 DS in keratoconic eyes. In contrast to normal eyes, the ocular higher‐order RMS error tended to decrease in magnitude after a blink in keratoconic eyes. Vertical coma became less negative with time after a blink in the keratoconic group, therefore, reducing the manifest ocular higher order RMS error by counteracting the negative vertical coma of the cornea.Conclusions: Compared to the manifest monochromatic higher‐order aberrations, any dynamic fluctuations in ocular aberrations with accommodation and tear film changes are relatively small in moderate keratoconic eyes. This implies that the correction of monochromatic higher‐order aberrations in keratoconus using customised soft contact lenses will not be significantly hindered by such dynamic aberrational changes.

Alignment sensing and control in advanced LIGO

The advanced LIGO detectors are currently in their final design stage, and the installation phase will start at the end of 2010: they will have about 10 times better sensitivity than initial LIGO, with a sensitive band ranging from 10 Hz to 10 kHz. As compared with previous LIGO detectors, there will be increased complexity in the optical configuration, improved seismic isolation system and significantly higher power circulating in the arm cavities. In the new detectors, the control of the angular orientation of the mirrors will be particularly challenging. The advanced LIGO (aLIGO) mirrors need to have a residual angular motion of the order of 1 nrad RMS in order to achieve high sensitivity. In the high power regime, the torque induced by radiation pressure effects will be comparable with the restoring torque of the mirror suspension, such that we must think of the opto-mechanical response, instead of just the mechanical response. These modifications have to be considered in order to design the control strategy for keeping the mirrors well aligned. Moreover, to meet the sensitivity target the alignment control noise coupled to the gravitational-wave channel must be well below at 10 Hz. We developed a model of the alignment sensing and control scheme of aLIGO which takes into account radiation pressure effects and meets the noise target.

Research on the visual performance and effects of higher order aberration after Epi-LASIK for myopia

To investigate changes of visual performance and effects of higher order aberration on visual performance after Epi-LASIK for myopia. In this prospective study, 102 patients were included. The trial group had 52 patients with Epi-LASIK, and 50 cases with LASIK as the control group. Ocular higher order aberrations were measured with the Hartman-shack wavefront analyzer, and high (100%), moderate (25%), low contrast (10%) and very low contrast (5%) visual acuity with and without glare were measured with Multi-Function Visual Acuity Tester under mesopic condition preoperatively and 4 - 6 months after surgery. 35 subjects in Epi-LASIK and 33 cases in LASIK were followed up 4 - 6 months later. Paired t test were used to analyze different contrast visual acuity before and after Epi-LASIK. Multiple linear regression analysis was performed to find the explanatory aberrations which contributed to the visual acuity. The Pearson correlation was used to explore the correlation between high- and low-contrast visual acuity and the explanatory higher order aberrations. The independent t test was used to analyze the difference of refraction power and visual acuity between Epi-LASIK and LASIK. There were significantly statistical differences at 5% and 10% contrast level compared to preoperation with glare and with no glare. With no glare, the mean logMAR visual acuity at 5% and 10% contrast level were 0.32 + or - 0.14 and 0.21 + or - 0.12 preoperatively, and 0.47 + or - 0.15 and 0.33 + or - 0.16 postoperatively (t = -4.863, 3.950; P = 0.000, 0.000). With glare, the mean logMAR visual acuity were 0.37 + or - 0.20 and 0.22 + or - 0.13 preoperatively, and 0.46 + or - 0.18 and 0.30 + or - 0.17 postoperatively (t = -1.949, -2.283; P = 0.047, 0.029). Using stepwise multiple linear regressions to evaluate which higher order aberration was significantly associated with each contrast VA. For each order RMS, S(4) was positive correlated with 5% contrast visual acuity (r(2) = 0.282;P = 0.025); S(4) was positive and S(5) was negative correlated with 10% contrast visual acuity (r(2) = 0.192;P = 0.033). None of the higher order RMS can significantly affect the 25% and 100% contrast visual acuity. For each Zernike coefficients, C(4)(0) and C(6)(4) were positive correlated with 5% contrast visual acuity (r(2) = 0.233; P = 0.024); C(4)(-4) was negative, C(4)(0) and C(5)(-5) were positive correlated with 10% contrast visual acuity (r(2) = 0.289; P = 0.013); None of Zernike coefficients had a significant correlation with 25% and 100% contrast visual acuity. The Pearson correlated coefficients between S(4), C(4)(0) and each contrast visual acuity increased as the contrast level decreased. S(4) and C(4)(0) were associated significantly with 5% contrast visual acuity, the correlation coefficients were 0.378 and 0.390 (P = 0.025 and 0.021). The visual acuity under 100% contrast with no glare was a little poorer than in LASIK. At the early stage after Epi-LASIK, the visual acuity for lower contrast level was worse compared to preoperative with glare and with no glare. Spherical aberration and the spherical-like aberration may contribute to this.

Lateral shearing interferometry, dynamic wavefront sensing, and high-speed videokeratoscopy for noninvasive assessment of tear film surface characteristics: a comparative study

There are several noninvasive techniques for assessing the kinetics of tear film, but no comparative studies have been conducted to evaluate their efficacies. Our aim is to test and compare techniques based on high-speed videokeratoscopy (HSV), dynamic wavefront sensing (DWS), and lateral shearing interferometry (LSI). Algorithms are developed to estimate the tear film build-up time T(BLD), and the average tear film surface quality in the stable phase of the interblink interval TFSQ(Av). Moderate but significant correlations are found between T(BLD) measured with LSI and DWS based on vertical coma (Pearson's r(2)=0.34, p<0.01) and higher order rms (r(2)=0.31, p<0.01), as well as between TFSQ(Av) measured with LSI and HSV (r(2)=0.35, p<0.01), and between LSI and DWS based on the rms fit error (r(2)=0.40, p<0.01). No significant correlation is found between HSV and DWS. All three techniques estimate tear film build-up time to be below 2.5 sec, and they achieve a remarkably close median value of 0.7 sec. HSV appears to be the most precise method for measuring tear film surface quality. LSI appears to be the most sensitive method for analyzing tear film build-up.

Shifting of the Line of Sight in Keratoconus Measured by a Hartmann-Shack Sensor

To evaluate ocular wavefront aberrations owing to keratoconus compared with normal controls and to describe the changes in the axis of line of sight (LoS) among keratoconic patients. Prospective case-control study. Fifty-five eyes of 30 patients with keratoconus and 100 eyes of 50 refractive surgery candidates with normal corneas. Ocular aberrations over a 4.5 mm (undilatated) pupil were measured with a Hartmann-Shack sensor. Corneal topographic measurement was performed with a Tomey corneal topographer. The axis of the displacement of LoS was calculated by vector analysis. Root mean square (RMS) and higher order RMS values, ocular aberrations up to the 6th Zernike order and the distance of the LoS from the pupillary center (x and y offset values) in keratoconic and normal eyes were measured with aberrometry. The steepest and average keratometric values and the axis of the steepest meridian were measured in keratoconic eyes with topography. Correlations were made between the size and the direction of the shift in the LoS and ocular aberrations. The following parameters were significantly higher in the keratoconus group compared to the control group: higher order RMS (P<0.001), Z(3)(-1) (P<0.001), Z(3)(-3) (P<0.002), Z(3)(3) (P = 0.001), Z(4)(-2) (P<0.001), Z(4)(2) (P<0.001), Z(4)(4) (P = 0.016), Z(5)(-5) (P = 0.03), Z(5)(-1) (P = 0.04), Z(5)(3) (P = 0.01), and y offset value (P<0.001). In keratoconic patients there was a significant correlation between the axis of the shift in the LoS and the steepest keratometric axis on topography (r = 0.59; P<0.001), the distance of the LoS from pupil center and vertical coma (r = -0.39; P = 0.004), and spherical aberration (SA; r = 0.29; P<0.04). There was also a significant correlation between the average keratometry value measured by topography and SA (r = -0.49; P<0.001). A factorial regression model testing the interactive effects of vertical coma and SA on the shift of LoS had a good fit on our data (r(2) = 0.69; P<0.001). A significant displacement of the LoS is observed in keratoconus and relates to the position of the cone on topography and the induced vertical coma measured by aberrometry. The authors have no proprietary or commercial interest in any of the materials discussed in this article.

Posterior Corneal Aberrations and Their Compensation Effects on Anterior Corneal Aberrations in Keratoconic Eyes

To characterize posterior corneal aberrations in keratoconic (KC) eyes and investigate compensatory effects between anterior and posterior corneal surfaces. The corneal topography of 113 eyes (37 advanced KC, 31 moderate KC, 14 mild KC, and 31 normal eyes) was used to compute the corneal aberrations. The central 6-mm diameter of both anterior and posterior corneal topographies was decomposed into Zernike polynomials. The magnitude and the orientation of each posterior corneal aberration were calculated by vector analysis. The compensation effects between anterior and posterior corneal aberrations were also assessed quantitatively with a linear regression model. The average higher order RMS wavefront errors for the posterior corneas were 1.04, 0.54, 0.24, and 0.19 microm in the advanced, moderate, and mild KC and normal eyes, respectively. In the advanced KC eyes, posterior corneal coma was oriented in the superior-nasal direction with a mean orientation angle of 75 degrees +/- 19 degrees OD and 78 degrees +/- 20 degrees OS. On average, 22%, 24%, and 14% of the anterior corneal coma were compensated by the posterior cornea in the advanced, moderate, and mild KC eyes, respectively. However, no significant higher order aberration (HOA) compensation effects were found in normal corneas. Significantly larger amounts of posterior corneal aberrations and stronger compensation effects were observed in KC eyes than in normal eyes. The uncorrected posterior corneal aberration in KC eyes was substantial and degraded retinal image quality. This may explain the relatively poor visual acuity obtained in eyes with rigid gas permeable (RGP) lenses, which correct only anterior corneal aberrations.