Evaluation of visual quality of spherical and aspherical intraocular lenses by Optical Quality Analysis System

AIM： To evaluate the impact of spherical and aspherical intraocular lenses on the postoperative visual quality of age-related cataract patients using Optical Quality Analysis System （OQAS）. METHODS： Seventy-four eyes with age-related cataracts were randomly divided into spherical and aspherical lens implantation groups. Best-corrected visual acuity （BCVA） was measured preoperatively, one day, one week, two weeks, one month and two months after surgery. A biometric systems analysis using the OQAS objective scattering index （OSI） was performed. RESULTS： There were no significant differences in visual acuity （P〉0.05） before and after spherical and aspheric lens implantation. There was a negative linear correction between the OSI value and BCVA （t-=-0.634, P=-0.000）, and positive corrections between the OSI value and the lens LOCUS III value of nucleus color （NC）, nucleus opacity （NO）, cortex （C） and posterior lens capsular （P） （r=0.704, P=0.000; r=0.514, P=0.000; r=0.276, P=0.020; r=0.417, P=-0.000, respectively）. OSI values of spherical vs aspherical lenses were 11.5±3.6 vs 11.8±3.4, 4.1±0.9 vs 3.3±0.8, 3.5±0.9 vs 2.7±0.7, 3.3±0.8 vs 2.6±0.7, 3.2±0.7 vs 2.5±0.8, and 3.2±0.8 vs 2.50.8 before and ld, 1, 2wk, 1 and 2mo after surgery, respectively. All time points varied significantly （P〈0.01） between the two groups. CONCLUSION： Aspherical IOLs does not significantly affect visual acuity compared with spherical IOLs. The OSI value, was significantly lower in the aspherical lens group compared with the spherical lens. This study shows that objective visual quality of aspheric IOLs is better than that of the spherical lens by means of OQAS biological measurement method.

SOFTWARE-CONTROLLED SYSTEM OF ULTRA-PRECISION MACHINING AXISYMMETRIC ASPHERIC MIRROR

In order to improve machining accuracy and efficiency, a software-controlled system of ultra-precision machining for axisymmetric aspheric mirror, using techniques of error compensation, remote transmission and modularization, is designed based on industrial PC, Windows 2000 work platform and Visual Basic 6.0. By experiments, this system realizes functions of ultra-precision machining, machining error compensation, remote data transmission and automatic data transformation among first machining, compensation machining and accuracy measurement. The actual application shows that error compensation improves machining accuracy, remote transmission improves machining efficiency while modularization avoids repeated work and improves design efficiency. Therefore, the system has met ultra-precision machining need for aspheric mirror.

Research on Large Depth Diameter Ratio Ultra-precision Aspheric Grinding System

In this paper, the factors of affecting surface roughness and profiles accuracy of the machined larege depth diamter ratio aspheric surfaces in ultra-precision grinding process are analyzed theoretically. An ultra-precision aspheric grinding system is then designed and manufactured. Aerostatic form is adopted to build the spindle of the workpiece, transverse guideway, longitudinal guideway and the spindle of the grinder in this system. The following specification is achieved, such as the turning accuracy of the spindle of the workpiece is 0.05 μm, radial rigidity of the spindle is GE 220N/μm, axial rigidity is GE 160 N/μm, radial rigidity of the guideway is GE 200N/μm, the highest rotational speed of the grinder is 80 000 rev/min and its turning accuracy is 0.1 μm, the resolution of linear displacement of the transverse and longitudinal guideway is 4.9 nm. Adjusting range of this adjusting mechanism is 2 mm in the Y direction, the adjusting accuracy of the precise adjusting mechanism is 0.1 μm. Micro displacement measuring system of this ultra-precision aspheric grinding adopts two-backfeed strategy, and angle displacement back-feed is realized by photoelectric encoder, it’s resolution is 655 360 pulse/rev. after 4 frequency multiplication, it’s angle displacement resolution is achieved 2 621 440 pulse/rev. Straight-line displacement is monitored by single frequency laser interferometer (DLSTAX LTM-20B, made in Japan). This CNC system adopts inimitable bi-arc step length flex CN interpolation algorithm, it’s CN system resolution is 5 nm.So this aspheric grinding system ensures profile accuracy of the machined part. The resolution of this interferometer is 5 nm. Finally, lots of ultra-precision grinding experiments are carried out on this grinding system. Some optical aspheric parts, with profiles accuracy of 0.3 μm, surface roughness less than 0.01 μm, are obtained.

Research on CNC Turning System of Aspheric Machining Grinding Wheel

The technology of machining aspheric surface with high precision is the premise for the application of aspheric surface. The grinding machining with error compensation is a commonly used method to machine aspheric surface, which will directly influence the quality of aspheric workpiece surface. Multifunctional CNC grinding wheel truing system is a four-axis CNC truing system which can be applied to grinding wheel truing. In this system, DSP-based multi-axes motion control card is adopted as the controller, and visual C++ is used as development tool. When the design of hardware and software is completed, the system can implement truing of various grinding wheel with high precision aspheric machining such as plane grinding wheel, arc grinding one, and sphere grinding one.

A Novel Method of Testing Aspherical Surface

A set-up based on a special shadow method, pinhole method, was made and some experiments were done. The results show that this novel method is simple, easy to operate,and suitable for testing large aspherical surfaces quantitatively.

RESEARCH ON PARALLEL GRINDING METHOD OF NON-AXISYMMETRIC ASPHERIC LENS

In order to resolve the problems of machining non-axisymmetric aspheric lens,which is short of flexibility in mould grinding and needs high accuracy CNC machine center in globediamond wheel grinding, a new parallel grinding method that utilizes common arc diamond wheel isput forward. Base on the approach calculation of machining locus, the advantages of parallelgrinding that machines non-axisymmetric aspheric lens by 2.5-axis CNC machine center have beenobtained. The results of grinding experiment show the new method can meet the need of grinding highaccuracy non-axisymmetric aspheric lens.

Comparison of visual quality after implantation of Al-UV and SN60WF aspheric intraocular lens

AIM:To compare the visual performance of pseudophakic eyes implanted with Al-UV and SN60WF aspheric intraocular lens(IOL),and to investigate the correlations between visual quality parameters and pupil size.METHODS:This prospective comparative study included 105 eyes of 90 patients with age-related cataract who underwent uneventful phacoemulsification.The subjects were divided into two groups according to the implanted IOL type.Three months postoperatively,visual acuity and contrast sensitivity were measured,wave-front aberrations were assessed using a KR-IW aberrometer(Topcon),and objective optical quality parameters were performed using an optical quality analysis system-OQAS Il(Visiometrics).Independent sample Mest and Spearman correlation analysis were used for data analysis.RESULTS:There were no significant differences found in visual acuity,contrast sensitivity and visual quality parameters between the two groups(P>0.05).The measured intraocular spherical aberration(SA)in Al-UV IOL eyes of-0.19±0.05 pm was close to the designed SA value of-0.20 pm.The modulation transfer function cutoff,Strehl ratio and OQAS values were negatively correlated with pupil size in both groups(P<0.01).CONCLUSION:The subjective and objective visual quality in pseudophakic eyes with A1-UV and SN60WF IOLs are comparable.For aspheric IOL eyes,visual quality decreases with increasing pupil size.

Visual function and higher order aberration after implantation of aspheric and spherical multifocal intraocular lenses:a meta-analysis

AIMTo assess the visual outcomes of aspheric multifocal intraocular lenses (IOLs) compared with spherical multifocal IOL after cataract surgery.

Computer Controlled Polishing of the Off-axis Aspheric Mirrors

In this paper, the manufacturing and testing procedures to make large off-axis aspherical mirrors are presented. The difficulties in polishing and testing for both circular aperture and rectangular aperture mirrors are previewed, and a possible solution is given. The two mirrors have been polished by means of CCOS, and the final accuracy is 25nm rms for 770mm×210mm rectangular mirror and 20nm rms for φ600mm circular mirror. These results just meet the optical tolerances specified by the designer, and the manufacturing and testing procedures presented here show good ability to make the large off-axis aspherical mirrors.

Personalized aspheric intraocular lens implantation based on corneal spherical aberration: a review

With the evolution of cataract surgery from visual rehabilitation to refractive surgery, aspheric intraocular lenses(IOLs) are being increasingly used in the field of ophthalmology. This increased use can be attributed to negative or zero spherical aberrations with unique optical designs, which counteract some of the positive spherical aberrations of the cornea. These alterations reduce the total spherical aberration of human eyes and improve the visual acuity in patients with cataract postoperatively. At present, various types of aspheric IOLs are used worldwide. Although the implantation of aspheric IOL is beneficial to the patients who need correction of spherical aberrations, much controversy is still associated with ocular residual spherical aberrations that facilitate the best visual quality for patients postoperatively. In order to provide reference for future clinical work and scientific research, this report reviews the relationship between the ocular residual spherical aberration of human eyes and visual quality.

Higher order aberration comparison between two aspherical intraocular lenses: MC6125AS and Akreos advanced optics

AIM: To compare higher order aberrations in two aspherical intraocular lenses(IOLs): Akreos advanced optics(AO) and Dr. Schmidt Microcrystalline 6125 aspheric anterior surface(MC6125AS) with each other. METHODS: Forty eyes of 39 patients underwent phacoemulsification and Akreos AO and MC6125 AS were implanted in their eyes in a random manner. Three months post-operatively, higher order aberrations including spherical aberration, coma aberration, and total aberrations were measured and compared.RESULTS: The total aberration was 0.24±0.17 in eyes with Dr. Schmidt and 0.20 ±0.01 in eyes with Akreos AO(P =0.361). The mean of coma aberration was 0.17 ±0.21 and 0.09 ±0.86 in Dr. Schmidt and Akreos lenses,respectively(P =0.825). Total spherical aberration was almost the same in both groups(mean: 0.05, P =0.933).Best corrected visual acuity in Akreos AO(0.10±0.68) and Dr. Schmidt(0.09±0.67) did not differ significantly(P =0.700). CONCLUSION: There is no statistically significant difference in the higher order aberrations between these two aspherical lenses.

Clinical study inpatient-reported outcomes after binocular implantation of aspheric intraocular lens of different negative spherical aberrations

Objective: To compare patient-reported outcomes after implantation of the ZA9003 intraocular lens(IOLs), or the MCX11 ASP IOLs or the spherical IOLs(HQ-201HEP). Methods: Prospective nonrandomized controlled trial was used. A total of 105 patients(210 eyes) were divided into three groups according to the type of IOLs: ZA9003(35 patients, 70 eyes), MCX11 ASP(35 patients, 70 eyes) or HQ-201HEP(35 patients, 70 eyes). The main outcome was scores of Catquest nine-item short-form questionnaire. Additional outcome was best corrected visual acuities, spherical aberration(SA) and total higher-order aberrations(HOAs). Results: The global score was significantly lower in the spherical IOL group than the aspherical IOL group of-020 μm SA(P < 0.05) and the aspherical IOL group of-027 μm SA(P < 0.05), and no significant difference was found in the global score between the aspherical IOL group of-020 μm SA than the aspherical IOL group of-027 μm SA(P > 0.05). Significant differences were also found in question 2, question 5, question 6 and question 8 between the spherical IOLs and the aspherical IOLs. Conclusion: Implantation of an aspherical IOL could improve vision-related quality of life compared with a spherical IOL. However, there were no statistically significant differences in vision-related quality of life between aspheric IOLs with different negative spherical aberrations.

Theoretical and Experimental Research on Error Analysis and Optimization of Tool Path in Fabricating Aspheric Compound Eyes by Precision Micro Milling

Structure design and fabricating methods of three-dimensional （3D） artificial spherical compound eyes have been researched by many scholars. Micro-nano optical manufacturing is mostly used to process 3D artificial compound eyes. However, spherical optical compound eyes are less at optical performance than the eyes of insects, and it is difficult to further improve the imaging quality of compound eyes by means of micro-nano optical manufacturing. In this research, nonhomogeneous aspheric compound eyes （ACEs） are designed and fabricated. The nonhomogeneous aspheric structure is applied to calibrate the spherical aberration. Micro milling with advantages in processing three-dimensional micro structures is adopted to manufacture ACEs. In order to obtain ACEs with high imaging quality, the tool paths are optimized by analyzing the influence factors consisting of interpolation allowable error, scallop height and tool path pattern. In the experiments, two kinds of ACEs are manufactured by micro-milling with different too path patterns and cutting parameter on the miniature precision five-axis milling machine tool. The experimental results indicate that the ACEs of high surface quality can be achieved by circularly milling small micro-lens individually with changeable cutting depth. A prototype of the aspheric compound eye （ACE） with surface roughness （Ra） below 0.12 p.m is obtained with good imaging performance. This research ameliorates the imaging quality of 3D artificial compound eyes, and the proposed method of micro-milling can improve surface processing quality of compound eyes.

Effect of intracorneal ring segment implantation on corneal asphericity

AIM： To evaluate the visual, refractive and corneal asphericity changes after intrastromal corneal ring segment（ICRS） implantation for visual rehabilitation of keratoconus.METHODS： A total of 42 eyes of 32 patients were included. After creation of intrastromal tunnels of 5.01±0.03 mm inner diameter, 5.71±0.03 mm outer diameter and at 384.21±34.12 μm depth, 1 or 2 ICRS of 150-300 μm thickness and 90°-210° arc length were implanted. Changes in uncorrected distance visual acuity（UDVA）, corrected distance visual acuity（CDVA）, refractive errors, mean simulated keratometry readings SimK_（avg）, anterior and posterior corneal asphericity values（Q_（ant） and Q_（post）, respectively） measured with Scheimpflug topography were evaluated retrospectively. RESULTS： There was a significant improvement in UDVA and CDVA, along with a significant decrease in refractive spherical equivalent（SE）, cylinder and SimK_（avg） postoperatively（P〈0.001 for all）. Mean Qant increased from-1.06±0.48 to-0.57±0.58 postoperatively（P〈0.001）. Change in mean Qpost was insignificant（P=0.92）. Postoperative changes in UDVA and CDVA were not correlated with the postoperative changes in SE and cylinder（P〉0.05 for all）; but were correlated with the preoperative SimK_（avg） and Q_（ant） values（P〈0.001 for all）. CONCLUSION： ICRS implantation seems to approximate the anterior corneal asphericity of ＂advanced prolate＂ shape to ＂optimal prolate＂ shape and an ＂ideal Q value＂ of-0.46; which may have a role in improved UDVA and CDVA postoperatively, besides decreased refractive cylinder values.

Wheel Setting Error Modeling and Compensation for Arc Envelope Grinding of Large-Aperture Aspherical Optics

Precision grinding is a key process for realizing the use of large-aperture aspherical optical elements in laser nuclear fusion devices,large-aperture astronomical telescopes,and high-resolution space cameras.In this study,the arc envelope grinding process of large-aperture aspherical optics is investigated using a CM1500 precision grinding machine with a maximum machinable diameter ofΦ1500 mm.The form error of the aspherical workpiece induced by wheel setting errors is analytically modeled for both parallel and cross grinding.Results show that the form error is more sensitive to the wheel setting error along the feed direction than that along the lateral direction.It is a bilinear function of the feed-direction wheel setting error and the distance to the optical axis.Based on the error function above,a method to determine the wheel setting error is proposed.Subsequently,grinding tests are performed with the wheels aligned accurately.Using a newly proposed partial error compensation method with an appropriate compensation factor,a form error of 3.4μm peak-to-valley(PV)for aΦ400 mm elliptical K9 glass surface is achieved.

Interchangeability of corneal curvature and asphericity measurements provided by three different devices

AIM: To evaluate the interchangeability of keratometric and asphericity measurements provided by three measurement systems based on different optical principles.METHODS: A total of 40 eyes of 40 patients with a mean age of 34.1 y were included. In all cases, a corneal curvature analysis was performed with IOL-Master(IOLM), iDesign 2(ID2), and Sirius systems(SIR). Differences between instruments for flattest(K1) and steepest(K2) keratometric readings, as well as for magnitude and axis of corneal astigmatism were analyzed. Likewise, differences in asphericity(Q) between SIR and ID2 were also evaluated. RESULTS: Mean differences between devices for K1 were 0.20±0.21(P<0.001),-0.12±0.36(P=0.046) and-0.32±0.36 D(P<0.001) for the comparisons IOLM-SIR, IOLM-ID2 and SIR-ID2, respectively. The ranges of agreement for these comparisons between instruments were 0.41, 0.70, and 0.70 D. For K2, mean differences were 0.31±0.33(P<0.001),-0.08±0.43(P=0.265) and-0.39±0.38 D(P<0.001), with ranges of agreement of 0.65, 0.84, and 0.74 D. Concerning magnitude of astigmatism, ranges of agreement were in the limit of clinical relevance(0.49 D, P=0.011; 0.55 D, P=0.386; 0.43 D, P=0.05). In contrast, ranges of agreement were clinically relevant for astigmatic axis(26.68o, 33.83o and 18.37o, P≥0.121) and for Q between SIR and ID2(0.16, P<0.001). CONCLUSION: The keratometric corneal power, astigmatic axis and asphericity measurements provideby the three systems evaluated cannot be considered as interchangeable, whereas measurements of corneal astigmatism obtained with SIR and ID2 can be considered as interchangeable for clinical purposes.

Study on Injection Moulding of High Precision Aspheric Plastic Lens

With the rapid development of information and multi me dia technologies, the demand for the optical plastic aspheric elements used in o pto-electronic devices, camera, optical disc and projector lens etc. has been i ncreased rapidly in the recent years. The key technologies of fabrication of asp heric plastic lens are the design and manufacturing moulds, selection of proper injection moulding equipment, and optimization of injection moulding parameters etc. In this paper, the effect of injection pressure, moulding temperature, cool ing time and injection speed on the surface profile of the lenses during injecti on and holding process is investigated. Surface quality of plastic lenses is mea sured by Talysurf Texture Measuring System. The experimental results showed that the injection pressure and moulding temperature are important parameters compar ing to cooling time and injection speed. A bit change of injection pressure or m oulding temperature will affect the property of the surface profile. Either incr easing injection pressure or mould temperature can achieve less shrinkage. Other wise, a lower injection pressure will produce more shrinkage, more air traps and a lower mould temperature results greater warp and higher shrinkage. The dynami c process of injection for optical plastic lenses is simulated by 3D Moldflow pl astic Insight software (MPI). The MPI will help us to optimize injection mouldin g parameters.

ASPHERICITY AND PROLATENESS OF LINEAR AND CIRCULAR MACROMOLECULES

The shape asymmetry of gaussian models of linear and circular macromolecules has been numerically investigated in terms of asphericity and prolateness parameters. These parameters are found to decrease with increasing length for the macromolecule either confined to a plane or in three dimensions. The effect of dimensionality on these parameters is visible only for low dimensions and is generally weak. As dimensionality goes to infinity, it is found that asphericity and prolateness for both chains and rings approach slowly yet descendingly values of corresponding asphericity and prolateness factors, with the exception of the chain which shows a minimum value of asphericity when the embedding space has a dimensionality of four.

Use of Virtual Medium in Designing of the CGH Wave Front Generator for Aspheric Testing

Design method and procedures of computer-generated hologram （CGH） used for aspheric test are in- troduced in detail. For CGH phase calculation, virtual medium which has zero refractive index at given wavelength is used to model ideal aspheric wavefront. Reflective Fresnel zones located in a ring area concentric to the CGH structure is designed to reduce or eliminate alignment errors. Substrate figure error, pattern distortion, etching and duty cycle variations that influence the reconstructed wavefront are quantitatively analyzed in theory and corresponding error equations are obtained to guide the tolerance distribution during CGH fabricating. A design example is given and the uncertainty of t achieves λ20.

Designing of Quasi-universal Compensator for Testing Aspherical Surface

According to the theory of testing aspherical surface by normal aberration compensation method,the designing method of quasi-universal compensator is studied.On the basis of third-order aberration theory,after calculating and optimizing with an optical design program,the structure parameters of a compensator are obtained.This new compensator could be used in Twyman-Green interferometer,and in measurement of a certain range of paraboloid ellipsoid and hyperboloid.The compensation accuracy is more than 0.02 λ .