scholarly journals Contralateral Eye Study On The Characteristics of Corneal Aberration In Patients With Bilateral Keratoconus And Unilateral Corneal Vogt’s Striae

2021 ◽  
Author(s):  
Jing Li ◽  
Yaohua Zhang ◽  
Yong Li ◽  
Yan Cai ◽  
Jing Du ◽  
...  
Keyword(s):  
Spherical Aberration ◽  
Front Surface ◽  
High Order ◽  
Back Surface ◽  
Morphological Parameters ◽  
High Order Aberration ◽  
Contralateral Eye

Abstract Purpose: To assess the corneal high-order aberration(HOA) and its correlation with corneal morphological parameters in patients with bilateral keratoconus (KCN) and unilateral Vogt’s striae.Methods: A total of 168 eyes of 84 patients with KCN, whose corneas had definite signs of unilateral Vogt’s striae were enrolled. Corneal HOA and morphological parameters were measured using Pentacam HR.Results: The corneal morphological parameters between KCN eyes with and without Vogt’s striae were evidently different (P < 0.001). The 3rd coma 90°, 4th spherical aberration, 5th coma 90°, RMS (total), and RMS (HOA) in the front, back surfaces and total cornea in KCN eyes with Vogt’s striae were significantly higher than those in KCN eyes without Vogt’s striae (P < 0.001). In KCN eyes with Vogt’s striae, the 3rd coma 90° and 4th spherical aberration in the front surface and total cornea were negatively correlated with K1, K2, Km, Kmax, ACE, and PCE (P < 0.05). The 3rd coma 90° , 4th spherical aberration in back surface and RMS (total), RMS (HOA) in the front, back surfaces, total cornea were positively correlated with K1, K2, Km, Kmax, ACE, and PCE (P < 0.05).Conclusions: Corneal HOA especially vertical coma and spherical aberration may increase when Vogt’s striae appeared in KCN eyes. The scale of increase was significantly related with changes in corneal shapes.

scholarly journals Simultaneously measuring ocular aberration and anterior segment biometry during accommodation

2015 ◽  
Vol 08 (02) ◽  
pp. 1550005 ◽  
Author(s):  
Yuanyuan Wang ◽  
Yilei Shao ◽  
Yimin Yuan
Keyword(s):  
Anterior Segment ◽  
Crystalline Lens ◽  
Front Surface ◽  
High Order ◽  
Human Vision ◽  
Wavefront Aberrations ◽  
High Order Aberration ◽  
Key Factor ◽  
Set Up

In the human eye, accommodation is essential for functional vision. However, the mechanisms regulating accommodation and the ocular parameters affecting aberrations remain to be explored. In order to measure the alterations of ocular aberration and crystalline lens biometry during dynamic accommodative stimuli, we designed an optical coherence tomography with ultra-long penetration depth (UL-OCT) combined with a Shack–Hartmann wavefront sensor (SHWFS). This integrated set up measures human eye's anterior segment as well as monochromatic high-order aberrations (HOAs) with 6 μm resolution and (1/20) λ accuracy. A total of 10 healthy volunteers without ocular diseases were examined. Upon exposure to accommodative stimuli, the wavefront aberrations became larger. Among the anterior segment biometry, the anterior crystalline lens demonstrated significant curvature during accommodation and was the major cause of high-order aberration. These findings suggest that the front surface of the crystalline lens can significantly affect variation among aberrations, which is a key factor underlying the quality of human vision.

scholarly journals High Order Aberration Outcomes of Corneal Collagen Crosslinking in Eyes with Keratoconus and Post-LASIK Ectasia

2014 ◽  
Vol 3 (3) ◽  
pp. 107-112
Author(s):  
Adam Muzychuk ◽  
Victor Penner ◽  
Guillermo Rocha
Keyword(s):  
Visual Acuity ◽  
Spherical Aberration ◽  
Retrospective Chart Review ◽  
High Order ◽  
Collagen Crosslinking ◽  
Distance Visual Acuity ◽  
High Order Aberration ◽  
Manifest Refraction ◽  
Corneal Collagen Crosslinking ◽  
Corneal Collagen

ABSTRACT Purpose To evaluate the effect of riboflavin and ultraviolet- A-induced corneal collagen crosslinking (CXL) on high order aberrations (HOA) up to third-order at 6 months using the iTrace wavefront aberrometer in patients with progressive keratoconus and post-LASIK ectasia. Materials and methods Ongoing retrospective chart review of patients having undergone CXL. The iTrace (Tracey Technologies, Houston, TX) was used to evaluate HOA. Patient data was collected from a single clinical site pre- and 6 months postoperatively. Data collected included logMAR uncorrected distance visual acuity (UDVA), logMAR corrected distance visual acuity (CDVA), manifest refraction, and HOA measurements. Data was analyzed with paired two-tailed student's t-test. Results 18 eyes (9M:4F, mean age 29.2 years, range 16-45) had 6 months of follow-up. Total HOAs, total coma and total trefoil were significantly reduced at 6 months by 16, 33 and 26% respectively (p < 0.05). Nonsignificant trends toward improvement were seen in spherical aberration, secondary astigmatism and UDVA. There were no statistically significant changes in manifest refraction or CDVA. Conclusion Improvement in high order aberration profile is one mechanism by which corneal collagen crosslinking enhances visual function in ectatic corneas. Total HOA and total coma measures are the most commonly reported improvements in HOA measures in previous studies, while total trefoil has only been observed in one other study. The improvements seen in HOAs remain fairly modest which likely accounts for the lack of measureable improvement in high-contrast visual acuity measures, such as Snellen UDVA and CDVA. This study is the first to report HOA outcomes with the iTrace wavefront aberrometer. How to cite this article Muzychuk A, Penner V, Rocha G. High Order Aberration Outcomes of Corneal Collagen Crosslinking in Eyes with Keratoconus and Post-LASIK Ectasia. Int J Kerat Ect Cor Dis 2014;3(3):107-112.

scholarly journals Evaluation of Corneal Higher-Order Aberrations by Scheimpflug–Placido Topography in Patients with Different Refractive Errors: A Retrospective Observational Study

2019 ◽  
Vol 2019 ◽  
pp. 1-5 ◽  
Author(s):  
Mohamed Anbar ◽  
Engy Mohamed Mostafa ◽  
Ashraf Mostafa Elhawary ◽  
Islam Awny ◽  
Mahmoud Mohamed Farouk ◽  
...  
Keyword(s):  
Observational Study ◽  
High Myopia ◽  
Spherical Aberration ◽  
High Order ◽  
Retrospective Observational Study ◽  
Refractive Errors ◽  
Ophthalmological Examination ◽  
High Order Aberration ◽  
Myopic Astigmatism ◽  
High Order Aberrations

Purpose. To report the characteristics of anterior and posterior corneal high-order aberrations in patients with different refractive errors.Setting. This study was conducted at Sohag Refractive Center, Sohag, Egypt.Design. This is a retrospective observational study.Methods. This study evaluated 750 patients (750 eyes) who were seeking refractive surgery. The eyes were stratified into five groups (150 eyes/group) based on refractive error: mild-to-moderate myopia, high myopia, hyperopia, simple myopic astigmatism, and simple hypermetropic astigmatism. All patients were subjected to comprehensive ophthalmological examination including corneal topography and corneal aberrometry using the Scheimpflug–Placido topography (Sirius, CSO, Italy).Results. Coma aberration was statistically significant when compared in all five groups (P=0.01). It was highest in the hypermetropia group (0.26 ± 0.12 μm) but lower in the moderate myopia, high myopia, myopic astigmatism, and hypermetropic astigmatism groups. Spherical aberration was lowest in the hypermetropia group and significantly different from that in the other groups. Trefoil was statistically insignificant when all groups were compared (P=0.062) but was highest in the myopic astigmatism group (0.24 ± 0.25 μm). Total RMS peaked in the hypermetropia group (0.99 ± 0.70).Conclusions. In normal corneas and regular refractive errors, the cornea-induced high-order aberration was minimal, and all types of refractive errors were associated with certain types of high-order aberrations, with a significant increase in spherical aberration in the hypermetropia group.

The effect of different optical zone diameters on the results of high-order aberrations in femto-laser-assisted in situ keratomileusis

2019 ◽  
Vol 30 (6) ◽  
pp. 1272-1277
Author(s):  
Kemal Özülken ◽  
Ahmet Kaderli
Keyword(s):  
Medical Records ◽  
Spherical Aberration ◽  
High Order ◽  
High Order Aberration ◽  
Optical Zone ◽  
The Mean ◽  
Coma Aberration ◽  
Myopic Astigmatism ◽  
High Order Aberrations

Purpose: To evaluate the postoperative high-order aberration differences of femto-LASIK surgery in 6.5 and 7 mm optic zones. Patients and Methods: We retrospectively reviewed 80 eyes of 40 patients with myopia or myopia with astigmatism who underwent femtosecond LASIK surgery. Q values, z3, 3 (h. trefoil), z3, –3 (v. trefoil), z3, 1 (h. coma), z3, –1 (vertical coma), z4, 0 (spherical aberration), z5, –1 (second other v. coma), aberration coefficients were evaluated 3 months after surgery. Central corneal thicknesses, intraocular pressures, patient ages and genders, optical zone diameters and ablation depths are collected from patients’ medical records. Results: The mean age was 28.4 ± 0.69 years (range, 20–47 years). Lower z4, 0 spherical aberrations and aberration coefficient values were associated with larger optical zones (7 mm) (z4, 0 spherical aberrations = 1.25, p = 0.01; coefficient value = –1.21, p < 0.01). Although a smaller optical zone (6.5 mm) was associated with an increase in most of the wave-front aberration variables, measurements were not statistically different between the two groups other than z4, 0 spherical aberrations and aberration coefficients. Discussion: LASIK treatment with 6.5 and 7 mm optical zones is safe and effective for correcting myopia and myopic astigmatism and has statistically similar visual outcomes. Moreover, larger optical zone (7 mm) was found to be associated with lower spherical aberration induction and smaller aberration coefficient values compared to 6.5 mm optical zone. This can be important for decision-making in femto-LASIK surgery for better postoperative results.

scholarly journals Comparison of correcting myopia and astigmatism with SMILE or FS-LASIK and postoperative higher-order aberrations

2021 ◽  
Vol 14 (4) ◽  
pp. 523-528
Author(s):  
Peng-Fei Zhao ◽  
◽  
Yue Wang ◽  
Cai-Yun Fu ◽  
Jing Zhang ◽  
...  
Keyword(s):  
Visual Acuity ◽  
Spherical Aberration ◽  
Higher Order ◽  
High Order ◽  
Controlled Study ◽  
Spherical Equivalent ◽  
Higher Order Aberrations ◽  
Post Surgery ◽  
Significant Difference ◽  
High Order Aberration

AIM: To compare the effect of myopia and astigmatism correction and postoperative change in higher-order aberration as results of receiving small-incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK). METHODS: A prospective and non-randomized controlled study was conducted. The subjects are divided into two groups according to different operations received: 229 eyes of 116 patients in the SMILE group and 168 eyes of 86 patients in the FS-LASIK group. All subjects were followed up for 3mo by monitoring their uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), spherical equivalent, higher-order aberrations, and the preoperative and postoperative complications. RESULTS: At 1wk, 1, and 3mo post-surgery, 224 eyes (97.8%), 227 eyes (99.1%) and 229 eyes (100%) had UCVA≥20/20 in the SMILE group, while 165 eyes (98.2%), 167 eyes (99.4%) and 167 eyes (99.4%) had UCVA≥20/20 in the FS-LASIK group, respectively (χ2=0.146, 2.135, and 1.124; all P&#x0026;#x003E;0.05). BCVA reduction was not observed in both groups at 1 and 3mo of post-surgery (χ2=0.734 and 1.898, P&#x0026;#x003E;0.05). There was no statistically significant difference in the spherical equivalent between the two groups at 1 and 3mo post-surgery, though the percentage of the spherical equivalent within ±0.50 D at 3mo post-surgery was 98% in the SMILE group, which was higher than that of the FS-LASIK group (92%, χ2=1.872, P&#x0026;#x003E;0.05). The root mean square (RMS) values of total high-order aberration, coma, and spherical aberration of the two groups increased significantly in the early postoperative period and decreased after 3mo, but the values were still higher than the preoperative levels (P&#x0026;#x003C;0.05); there was no significant difference between the two groups in the RMS values of total higher-order aberrations and specific higher-order aberrations (P&#x0026;#x003E;0.05). The incidence of complications in the SMILE group was lower than that in the FS-LASIK group (χ2=14.52, P&#x0026;#x003C;0.05). CONCLUSION: SMILE and FS-LASIK can effectively treat myopia, significantly improve visual acuity, and increase the total high-order aberration, spherical aberration, and coma. The incidence of complications after SMILE is relatively low.

scholarly journals Effect of Surface Roughness on Ultrasonic Testing of Back-Surface Micro-Cracks

2018 ◽  
Vol 8 (8) ◽  
pp. 1233 ◽  
Author(s):  
Zhe Wang ◽  
Ximing Cui ◽  
Hongbao Ma ◽  
Yihua Kang ◽  
Zhiyang Deng
Keyword(s):  
Surface Roughness ◽  
Ultrasonic Testing ◽  
Amplitude Ratio ◽  
Ultrasonic Inspection ◽  
Front Surface ◽  
Signal Amplitude ◽  
Back Surface ◽  
Element Analysis ◽  
Arithmetic Average ◽  
Micro Cracks

Surface roughness is one of the main factors that affect the ultrasonic testing of micro-cracks. This article theoretically analyzes the relationship between the changes in the energy intensity of crack echo waves and roughness-modified transmission coefficients. A series of simulations are carried out using two-dimensional sinusoidal curves as rough surface. Then, parallel experiments are performed on sample surfaces with different arithmetic average heights (Ra). The signal amplitude ratio factor (SARF) is defined to assess the ultrasonic detection capacity for micro-cracks. Both finite element analysis and experimental results show that signal amplitude decreases with an increase in Ra, resulting in signal-to-noise ratio loss. Amplitude attenuation caused by the rough back surface is less than that caused by the rough front surface. It is difficult to identify the signal of micro-cracks with a depth less than 400 μm when the Ra of the front surface is larger than 15 μm. Cracks with depths of more than 200 μm can be distinguished when the back-surface roughness is less than 24 μm. Furthermore, the amplitude of the micro-crack signal increases slightly with variation in the horizontal parameter (Rsm). This study provides a valuable reference for the precision evaluation of micro-cracks using ultrasonic inspection.

High-Order Aberration Measurement Method for Hyper-NA Lithographic Projection Lens

2017 ◽  
Vol 37 (4) ◽  
pp. 0412003
Author(s):  
诸波尔 Zhu Boer ◽  
王向朝 Wang Xiangzhao ◽  
李思坤 Li Sikun ◽  
孟泽江 Meng Zejiang ◽  
张恒 Zhang Heng ◽  
...  
Keyword(s):  
Measurement Method ◽  
High Order ◽  
Projection Lens ◽  
High Order Aberration

Average Residual Stresses in Hard Physical Vapor Deposited (PVD) Coatings

2019 ◽  
Vol 799 ◽  
pp. 20-25
Author(s):  
Harri Lille ◽  
Alexander Ryabchikov ◽  
Jakub Kõo ◽  
Valdek Mikli ◽  
Eron Adoberg ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Front Surface ◽  
Back Surface ◽  
Length Variation ◽  
Pvd Coatings ◽  
Cross Sectional ◽  
Average Residual ◽  
Thin Walled ◽  
Compressive Residual Stresses ◽  
Very High

In this study we determined average residual stresses in hard nitride PVD AlCrN, TiAlN and TiCN coatings through simultaneous measurement of length variation in thin-walled tubular substrates and of the curvature of plate substrates. A device for measurement of the length of the tube was developed. Inside the depositing chamber the tube and the plate were fixed parallel in the relation to the axis of the rotating cathode. One batch of plate samples was produced by deposition on front surface (facing the cathode) and the other batch, by deposition on back surface (with back to the cathode). The cross-sectional microstructure and thickness of the coatings were investigated by means of scanning electron microscopy (SEM). The thicknesses of the coatings deposited on front and back surfaces of the plates and on the tube were significantly different. The values of average compressive residual stresses, determined by both methods, were very high irrespective of coating thickness. It was found that the values of compressive residual stresses in the coating were dependent on the shape of the substrate and on its position in the relation to the axis of the rotating cathode.

Sign in / Sign up

Export Citation Format

Share Document