Contact Lens Manufacturing Research Articles

Establishing optimal conditions for catalytic obtaining of allyl-1,3,4-trimethylcyclohex-3-encarboxylate

Kinetics of the reaction of the catalytic cyclic addition of 2,3-dimethylbuta-1,3-diene and allyl methacrylate by the Diels-Alder reaction was studied. Reaction rate constants k=0.9·10 -3 l/(mol·s) at T=303 K; k=1.6·10 -3 l/(mol·s) at T=313 K; k=2.3·1 -3 l/(mol·s) at T=323 K; k=2.9·10 -3 l/(mole·s at T=333 K and the activation parameters of the reaction E akt =32.6 kJ/mol, ΔS=−203.7 J/(mol·K), ΔH=30.0 kJ/mol were determined. Influence of temperature, molar ratio of reagents and catalyst on the yield of the target product was investigated. At temperature increase from 303 to 333 K, ATMCGC yield increases from 58 % to 76 %. With further increase in temperature, DMB boils and AMA remains in a liquid state, accordingly it is not expected that the target product yield will materially increase. An increase in the excess of DMB:AMA=from 1.5:1 to 4:1 makes it possible to increase yield of ATMCGC from 54 % to 76 %. According to decreasing of the catalytic activity in the reactions of [4+2]-cyclic addition of DMB and esters of acrylic acids, the catalysts are placed in an order: Ag n.p. >Cu 2 Cl 2 >Pd n.p. >Au n.p. . At the established optimal conditions of catalytic production of allyl-1,3,4-trimethylcyclohex-3-enecarboxylate are: temperature of 323−333 K and molar ratio of reagents DMB:AMA=4:1 in the presence of Ag n.p. catalyst (0.25 % mol), the yield of ATMCGC reaches 72−76 % at productivity of 111−117 g/(l/h). Based on the obtained reaction rate constants and the activation parameters of the catalytic [4+2]-cyclic addition of 2,3-dimethylbuta-1,3-diene and allyl methacrylate, it was found that the reaction under study is subject to the kinetic law of the second order. It was established that in the presence of Agn.p. catalyst, the reaction of [4+2]-cyclic addition of 2,3-dimethylbuta-1,3-diene and esters of acrylic acids proceeds through a two-stage mechanism with the initial stage of formation of a catalytic complex which activates the reaction by reducing its energy barrier by 44 kJ/mol. The synthesized alkyl esters of alkylcyclohexenecarbonic acids have the ability of polymerization and can be used as a raw material for preparation of polymeric materials, compositions and hyper plasticizers for concrete mixtures. Polymer compositions made with allyl-1,3,4-trimethylcyclohex-3-enecarboxylate are recommended for manufacture of contact lenses and artificial crystalline lenses

Modelling of Surface Roughness in Ultra-High Precision Turning of an RGP Contact Lens Polymer

Contact lens manufacture requires high accuracy and surface integrity. Surface roughness an important response because it has direct influence toward the part performance and the production cost. Hence, choosing optimal cutting parameters will not only improve the quality measure but also the productivity. This research work is therefore aimed at developing a predictive surface roughness model and investigate a finish cutting conditions of ONSI-56 contact lens polymer with a monocrystalline diamond cutting tool. In this work, a novel surface roughness prediction model, in which the feed rate, cutting speed and depth of cut are considered is developed. This combined process was successfully modeled using a Box–Behnken design (BBD) with response surface methodology (RSM). The effects of feed rate, cutting speed and depth of cut were investigated. Analysis of variance (ANOVA) showed that the proposed quadratic model effectively interpreted the experimental data with coefficients of determination of R2 = 0.89 and adjusted R2 = 0.84. The worse surface value was obtained at high feedrate and low spindle speed.

PALS, MIR and UV–vis–NIR spectroscopy studies of pHEMA hydrogel, silicon- and fluoro-containing contact lens materials

Studies on polymeric materials used in contactology for manufacturing of contact lenses are presented in the paper. Different types of brand new contact lenses were investigated: hydrogel, silicone-hydrogel and rigid gas permeable. Positron annihilation lifetime spectroscopy (PALS) was used to characterize geometrical sizes and fraction of the free volume holes in the investigated samples. Measurements reveal significant differences between the materials. Namely differences in size and fraction of free volume were observed. These changes are strongly correlated with oxygen permeability in contact lenses. Middle infrared (MIR) spectroscopy was carried out in order to investigate the internal structure of materials. Furthermore, UV–vis–NIR studies were performed in order to determine the transmittance properties of contact lenses.

Practitioner Perceptions of Patients Wearing Decorative Contact Lenses Purchased Through Unauthorized Sellers.

To describe practitioner experiences regarding ocular complications in patients wearing decorative contact lenses, and to investigate the compliance of unauthorized distributors of decorative contact lenses to current Food and Drug Administration (FDA) and Federal Trade Commission (FTC) regulations. Also, to provide data to support a more targeted public health approach to reducing the incidence of illegal contact lens sales and associated ocular complications. An institutional review board-approved online survey was distributed through mass email to a list of 98 optometrists in the Boston, MA area. Concurrently, an empirical evaluation of independent, online decorative contact lens sellers who were not associated with FDA-approved contact lens manufacturers was performed to determine their adherence to FDA and FTC guidelines. The first 18 noncoincidental websites that resulted from a Google search for "costume contact lens sellers" and "cosmetic contact lens sellers" were examined as to the brands and parameters of lenses being sold, whether or not a valid prescription was required or verified, and if consumer education was provided. Twenty-two optometrists completed the online survey. Seventy-seven percent of respondents reported having patients with complications from decorative contact lenses that were purchased both legally and illegally. The most common age group for complications was 18 to 25 years (61%). One third of complications were seen in first-time lens wearers, half of whom never received proper care instructions or were unaware that care instructions existed. One quarter of the lenses were purchased illegally with unlicensed stores being the most common place of purchase. Of the 18 online sites examined, 72% of sellers failed to adhere to FTC and FDA regulations. A significant number of individuals who obtain contact lenses illegally from unauthorized sources are young adults. Most unauthorized sellers reviewed did not adhere to the proper protocol for selling contact lenses or instruct their customers on proper lens wear and care. A significant percentage of optometrists responding to the survey reported complications associated with contact lenses purchased through unauthorized sources, suggesting that the risk of contact lens-related complications increases when the lenses are purchased from one of these sources.

Contact Lens-Related Corneal Infections - United States, 2005-2015.

Keratitis (inflammation of the cornea) can result from contact lens wear or other causes. Keratitis from all causes, including contact lens wear, results in approximately 1 million clinic and emergency department visits annually, with an estimated cost of $175 million in direct health care expenditures in 2010 (1). Approximately 41 million U.S. residents wear contact lenses, and in 2014, >99% of contact lens wearers surveyed reported at least one behavior that puts them at risk for a contact lens-related eye infection (2). The Center for Devices and Radiological Health at the Food and Drug Administration (FDA) regulates contact lenses as medical devices, and certain adverse events related to contact lenses are reported to FDA's Medical Device Report (MDR) database. To describe contact lens-related corneal infections reported to the FDA, 1,075 contact lens-related MDRs containing the terms "ulcer" or "keratitis" reported to FDA during 2005-2015 were analyzed. Among these 1,075 reports, 925 (86.0%) were reported by a contact lens manufacturer and 150 (14.0%) by an eye care provider or patient. Overall, 213 (19.8%) reports described a patient who had a central corneal scar, had a decrease in visual acuity, or required a corneal transplant following the event. Among the reports, 270 (25.1%) described modifiable factors known to be associated with an increased risk for contact lens-related corneal infections, including sleeping in contact lenses or poor contact lens hygiene; the remainder did not provide details that permitted determination of associated factors. Continued efforts to educate contact lens wearers about prevention of contact lens-related eye infections are needed.

Optical Assessment of Soft Contact Lens Edge-Thickness.

To assess the edge shape of soft contact lenses using Gabor-Domain Optical Coherence Microscopy (GD-OCM) with a 2-μm imaging resolution in three dimensions and to generate edge-thickness profiles at different distances from the edge tip of soft contact lenses. A high-speed custom-designed GD-OCM system was used to produce 3D images of the edge of an experimental soft contact lens (Bausch + Lomb, Rochester, NY) in four different configurations: in air, submerged into water, submerged into saline with contrast agent, and placed onto the cornea of a porcine eyeball. An algorithm to compute the edge-thickness was developed and applied to cross-sectional images. The proposed algorithm includes the accurate detection of the interfaces between the lens and the environment, and the correction of the refraction error. The sharply defined edge tip of a soft contact lens was visualized in 3D. Results showed precise thickness measurement of the contact lens edge profile. Fifty cross-sectional image frames for each configuration were used to test the robustness of the algorithm in evaluating the edge-thickness at any distance from the edge tip. The precision of the measurements was less than 0.2 μm. The results confirmed the ability of GD-OCM to provide high-definition images of soft contact lens edges. As a nondestructive, precise, and fast metrology tool for soft contact lens measurement, the integration of GD-OCM in the design and manufacturing of contact lenses will be beneficial for further improvement in edge design and quality control. In the clinical perspective, the in vivo evaluation of the lens fitted onto the cornea will advance our understanding of how the edge interacts with the ocular surface. The latter will provide insights into the impact of long-term use of contact lenses on the visual performance.

A Study on the Manufacturing of Photochromic Contact Lenses using Spiropyran Derivatives

Purpose: The purposes of this study are to synthesize spiropyran derivatives for the development of photochromic contact lens using both casting-mould and sandwich processes and to investigate their photochromic and physical properties. Methods: The casting-mould method was performed by a manufacturing process in which monomers including spiropyran, HEMA, EGDMA, NVP and MMA were introduced into a solid mold and polymerized to solidify. The sandwich process producing triple-layered structures started with the 1st-copolymerization of HEMA, EGDMA, NVP and MMA. The resulting substrate was coated with a mixture of binder and spiropyran derivative, followed by 2nd-copolymerization with the same monomer ratio as the 1st-copolymerization process. The water content, contact angle, and optical properties of the manufactured lenses were investigated. The photochromic properties of the lenses such as color change behavior and absorbance were investigated under UV-light exposure for 1 min or in dark-room for 10 min. Results: The contact lenses prepared by casting-mould method showed water content of 35.21% and contact angle of 70.80° with a non-photochromic property. For the sandwich process, the lenses exhibited water content of 35.21% and contact angle of 70.80° with a good photochromic property. The lenses showed deep purple in color after exposure of UV light while they became colorless in dark-room. Conclusions: The contact lenses prepared by casting-mould method showed a non-photochromic property. The application of sandwich process exhibited a photochromic behavior without changes in the water content and contact angle of the lenses, suggesting that this method has practical and potential applications in contact lens industry.

Investigation of the Degree of Disorder of the Structure of Polymer Soft Contact Lenses Using Positron Annihilation Lifetime Spectroscopy PALS.

Hydrogel and silicone-hydrogel polymeric materials are widely used in ophthalmology for the manufacture of contact lenses. An important aspect is the investigation of the structure of these materials. This study has been conducted in order to compare the degree of disorder and presence of free volumes in the internal structure of the polymeric soft contact lenses Omafilcon A (hydrogel) and Comfilcon A (silicone-hydrogel). Differences in the occurrence of trapping centers for positrons and free volumes between the types of investigated contact lenses have been demonstrated. Two types of polymeric contact lenses were used as materials: Omafilcon A (hydrogel) and Comfilcon A (silicone-hydrogel). The study was performed using positron annihilation lifetime spectroscopy (PALS). When the results of the measurements has been obtained, a graphical curve has created to describe the relationship of the number of annihilation acts in time. Significant changes were observed between the contact lenses investigated in positron trapping in macropores (based on a two-state model) and the presence of free volumes (based on the Tao-Eldrup model). The use of the positron annihilation two-state model made it possible to demonstrate that a higher positron trapping rate in macropores occurs in the silicone-hydrogel contact lens. Additionally, calculations using the Tao-Eldrup model show the existence of free volumes in both types of materials. The size and fraction of free volumes is much larger in the silicone-hydrogel contact lens.

Evaluation of surface water characteristics of novel daily disposable contact lens materials, using refractive index shifts after wear.

PurposeContact lens wearers today spend much time using digital display devices. Contact lens manufacturers are challenged to develop products that account for longer periods of time where blink rate is reduced and tear-film evaporation rate is increased, affecting both visual acuity and comfort. Two manufacturers recently introduced novel daily disposable contact lenses with high surface water content. The objective of the present study was to compare surface water characteristics before and after initial wear of recently introduced nesofilcon A and delefilcon A high surface water lenses with those of etafilcon A lenses.Patients and methodsTwenty healthy subjects wore each of the three lens types studied in a randomly determined order for 15 minutes. After each wearing, lenses were removed and the surface refractive index (RI) of each lens was immediately measured.ResultsThe mean RI of the unworn delefilcon A lens was 1.34, consistent with water content in excess of 80%. After 15 minutes of wear, the surface RI shifted to 1.43, consistent with its reported 33% bulk water content. In contrast, the mean surface RI of the nesofilcon A lens was 1.38, both initially and after 15 minutes of wear, and that of the etafilcon A lens was 1.41 initially and 1.42 after 15 minutes of wear.ConclusionThe surface of the delefilcon A lens behaves like a high water hydrogel upon insertion but quickly dehydrates to behave like its low-water silicone-hydrogel bulk material with respect to surface water content during wear, while both nesofilcon A and etafilcon A lenses maintain their water content during initial wear. The nesofilcon A lens appears unique among high water lenses in maintaining high surface and bulk water content during wear. This is important because changes in surface RI due to dehydration are reported to lead to visual aberration affecting user experience.

Evolution of High Precision Manufacturing of Contact Lenses

Today’s contact lens professionals must familiarise themselves with the various contact lens manufacturing methodologies that are capable of producing high accuracy optical products for their patients. Contact lens manufacturing dates back to the 19thcentury with the development of glass contact lenses and later evolved to various types of optical polymeric materials. The recent advances in the manufacturing of contact lenses can be attributed to the development of advanced polymeric materials and high precision processing technologies. Two basic techniques are identified for contact lens manufacturing. They are moulding method and ultra-high precision machining. Ultra-high precision machining is employed for direct shaping of contact lenses or for making mould inserts that will be used further in lens injection. Mould inserts can be made from high hardness steel, nickel plated steel, aluminium or other nonferrous alloys. Advanced light metal optical aluminium alloys provide a high integrity mould with fine microstructures for optical lens production. This review paper provides a chronological view of the evolution of contact lens manufacturing and identifies the importance of a recently developed aluminium alloy in the production of mould inserts for high quality contact lenses.

Advances in scleral lenses for refractive surgery complications.

The last two decades have brought advances in materials and manufacturing of large diameter rigid gas-permeable contact lenses, and a greater appreciation of the role of scleral lenses for therapeutic indications. The purpose of this review is to provide an update on the use of rigid gas-permeable scleral lenses in the management of patients with complications after refractive surgery. There are recent reports on clinical experience with specific scleral lens designs from single institutions in cohorts that include patients who have undergone refractive surgery. Typically, these are patients with 'irregular corneas' after radial keratotomy or LASER assisted in-situ keratomileusis, but patients with keratectasia, dry eye syndrome, and corneal neuralgia are also reported. Visual outcomes and wearing success rates are high in these reports, although outcomes for refractive surgery patients are not reported separately. Clinicians who encounter patients with complications after corneal refractive surgery should be aware of advances in scleral lenses. Scleral lenses are an alternative to surgical intervention in patients who might otherwise be considered poor contact lens candidates.

Predictive Modelling of Cutting Force and its Influence on Surface Accuracy in Ultra-high Precision Machining of Contact Lenses

Abstract The successful application of contact lenses is heavily dependent on their form accuracy and surface integrity. Cutting forces play a key role in the diamond turning of contact lenses as they have direct influence on their form accuracy and surface integrity. In addition, the cutting forces are also important for other aspects of diamond turning of contact lenses such as tool wear. Therefore, the prediction of cutting forces in contact lens manufacturing is deemed essential for the sake of high quality optical surfaces. One way to manage the effect of the cutting force and reduce its negative effect on surface finish could be realised through optimisation and modelling techniques. There are several factors that affect the extent of the cutting force developed in diamond turning. An example of these factors is the selection of cutting parameters. The establishment of a statistical model for the reliable prediction of cutting forces which is linked to a specific optical quality characteristic could be a way for understanding the behaviour of cutting force and its effect. In this study, a cutting force model based on response surface statistical method is developed for reliably predicting the values of cutting force based on its relationship to cutting parameters in the high-precision machining of contact lenses. The model obtained from fifteen experimental tests determines the effects of cutting speed, feed rate and depth of cut on force and how various combinations of parameters affect cutting force and thus surface quality. Results indicate that feed rate is a significant factor in the generation of high cutting force and low surface roughness. The study concludes that high feed rates and high cutting speeds cause an increase in cutting force and thus adversely affect the quality of the diamond-machined surface in the high precision machining of contact lenses.

Resale Price Maintenance after Leegin: The Curious Case of Contact Lenses

Resale price maintenance (RPM) is a controversial pricing practice for managing retail distribution channels. In Leegin Creative Leather Products, Inc. v. PSKS, Inc. (2007), the Supreme Court abolished a nearly century-old per se rule against RPM established in Dr. Miles Medicine Co. v. John D. Park & Sons (1911). Henceforth, RPM will be judged under federal antitrust law by the rule of reason – a less restrictive standard that requires courts to weigh all the relevant circumstances of a case to assess whether a practice unreasonably restrains trade. Despite that the decision in Leegin leaves many unanswered questions, the decision has prompted an increasing number of consumer goods manufacturers to adopt RPM in the management of their retailer relationships. Recently, the widespread use of restrictive pricing practices in the retail distribution of contact lenses have drawn attention and elevated debate over the practice. Pending lawsuits in the industry have been identified as an important “test case” for antitrust’s new vertical pricing regime following Leegin. Drawing upon relevant literatures from law, economics, and business, together with publically available information, important questions in the debate and related cases that share significance for scholarship and practice are elaborated upon and examined. This examination reveals insights helpful to understanding the antitrust implications of contact lens manufacturers’ pricing practices and for advancing academic knowledge, marketing practice, and competition policy involving RPM.AAI Working Papers are typically works in progress that will eventually be revised and published elsewhere. They do not necessarily represent the position of the American Antitrust Institute. This Working Paper represents the work of the authors and does not necessarily represent the views of the American Antitrust Institute or their affiliated institutions.

개시제와 교차결합제 농도의 변화에 따른 소프트콘택트렌즈의 물리적 성질과 약물용출 농도의 변화

목적: 개시제와 교차결합제의 농도에 따른 소프트콘택트렌즈의 재질을 변화시켜서 재질변화에 대한 물리적 특성 및 약물의 용출량 및 속도를 비교하였다. 방법: HEMA에 개시제인 AIBN과 교차결합제인 EGDMA의 농도을 변화시켜서 콘택트렌즈를 제작하였다. 항균물질인 노플록사신(norfloxacin)은 고분자 중합 시 0.1% 농도로 단량체와 함께 혼합하였다. 재질변화에 따른 물리적 성질 변화를 확인하기 위해 약물용출 농도, 함수율, 굴절률, 단백질 흡착량 등에 대한 실험을 통하여 비교하였으며, 통계분석을 통해 유의성을 확인하였다. 결과: 개시제의 농도을 변화 시킨 콘택트렌즈는 함수율의 변화가 거의 없으며, 굴절률의 값에도 별 변화가 없었다. 교차결합제 농도이 증가하면 함수율이 낮아지고 굴절률이 높아졌다. 약물용출의 농도를 살펴보면 개시제의 변화에 의해서는 많은 변화를 보이지 않았으며, 함수율이 높을수록 용출되는 농도가 증가하였다. 단백질 흡착양은 개시제에 의한 변화는 거의 없었으며 함수율이 낮을수록 흡착되는 양이 증가하였다. 결론: 개시제의 농도에 대한 변화는 특성 변화에 영향력이 거의 없었으며, 교차결합제 농도에 따라서는 많은 변화를 보였다. 교차결합제의 농도가 증가할수록 함수율은 감소하며 굴절률은 증가하였다. 또한 함수율의 증가에 따라 약물이 많이 용출되었으며 단백질의 흡착량은 감소되었다. Purpose: The material properties of contact lenses were measured by varying the amounts of an initiator and a cross-linking agent that are the basis for the manufacture of contact lenses, and the drug delivery effects depending on the material properties of contact lenses were compared. Methods: Contact lens samples were manufactured using HEMA by varying the concentration of the cross-linking agent and the initiator. To investigate the changes in physical characteristics depending on the material properties, the results of the experiments on the amount of drug elution, water content, refractive index, and the amount of protein adsorption were compared. Results: For the contact lenses manufactured by varying the amount of the initiator, the water content hardly changed, and the refractive index also hardly changed. The amount of drug elution was not much affected by the changes in the initiator, but the amount of elution increased as the water content increased. The amount of protein adsorption was hardly affected by the changes in the initiator, but the amount of adsorption increased as the water content decreased. Conclusions: The changes in the properties were hardly affected by the changes in the amount of the initiator, but were significantly affected by the changes in the amount of the cross-linking agent. As the amount of the cross-linking agent increased, the water content decreased, while the refractive index increased. Also, when the water content increased, the amount of drug elution increased, while the amount of protein adsorption decreased.

Competitive analysis of a contact lens market

Purpose – This paper aims to present a broader industry-level competitive analysis of a contact lens market. Design/methodology/approach – Porter’s Five Forces model can be used for a broader and rigorous competitive analysis of a contact lens market to determine the competitive intensity and to form a well-rounded business strategy. Findings – The contact lens market is highly competitive and unattractive. Because growth has been stagnant, traditional competition has become more intense to steal share from each other. However, the competition in the market could not be defined narrowly between traditional competition but is broad with substitutes, and bargaining power of customers and distributors. A contact lens manufacturer has to look beyond the traditional competition to not only compete with traditional competitors within the industry but also with substitutes, and bargaining power of customers and distributors. Practical implications – This paper will benefit contact lens manufacturers/businesses in forming a well-rounded business strategy.

Building strategic elements to increase contact lens sales

Purpose – This paper aims to build important strategic elements to penetrate deeper into the contact lens market and increase sales. Design/methodology/approach – The contact lens market is highly competitive and unattractive. Because contact lens market growth has slowed, competitors have become more alike. To survive or make more than normal profits, a contact lens manufacturer has to differentiate and compete on wider dimensions. Findings – In a complex, competitive and ever-changing vision care industry environment, a contact lens manufacturer must compete on wider dimensions to gain strategic advantage and increase sales. Practical implications – To survive, a contact lens manufacturer’s strategic game plan may not look simple and form wider strategic components. Originality/value – Provides a unique look at the contact lens market.

Tribo-electric Charging in the Ultra-high Precision Machining of Contact Lens Polymers

The manufacture of precision optics with diver custom surface profile is in high demand in contact lens manufacturing. Ultra- high precision diamond turning is an adequate manufacturing technique with the ability to produce freeform optics of various custom surface profiles. However, during polymers machining, adhesion of the tool chip around the tool dictates the presence of an electrostatic force field. This phenomenon known as tribo-electric charging is responsible for tool wear and poor surface finish. Attaining a clear understanding of tribo-electricity in polymer machining, its occurrence and causing agents is important to ensure surface integrity of optical profiles. This study observes static charging during the ultra-high precision machining of contact lens polymers and identifies machining parameters and environmental factors influencing the static buildup. The influence of relative humidity and certain cutting parameters such as cutting feed rates were observed as factors in static charging.

Multifocal contact lenses: Power profiles and their interpretation

Purpose: Many contact lens (CL) manufacturers produce simultaneous-image (vision) lenses in which power varies either smoothly or discontinuously with zonal radius. We present in-vitro measurements of some current CLs and discuss their performance in terms of distance corrections and near addition powers.

Editorial

You will be forgiven if you have not heard of EUROMCONTACT. It is a non-profit organization and represents the European Federation of National Associations and International Companies of Contact Lens (and Lens Care) Manufacturers. It has three types of members: 1.National Associations of Manufacturers, such as SYFFOC (France), SPECTARIS (Germany), NAC (The Netherlands), ASSOTTICA (Italy), AEO (Spain), OPTICS Swiss Suppliers Association (Switzerland) and the ACLM (United Kingdom). 2.International Companies, such as Alcon, AMO Ltd., Bausch & Lomb, CooperVision, Johnson & Johnson Vision Care, Mark Ennovy and Menicon. 3.European Federation for the Contact Lens Industry, with about 100 members in 30 countries.

Power Profiles of Multifocal Contact Lenses and Their Interpretation

Many contact lens (CL) manufacturers produce simultaneous-image lenses in which power varies either smoothly or discontinuously with zonal radius. We present in vitro measurements of some recent CLs and discuss how power profiles might be approximated in terms of nominal distance corrections, near additions, and on-eye visual performance. Fully hydrated soft, simultaneous-image CLs from four manufacturers (Air Optix AQUA, Alcon; PureVision multifocal, Bausch & Lomb; Acuvue OASYS for Presbyopia, Vistakon; Biofinity multifocal- "D" design, Cooper Vision) were measured with a Phase focus Lens Profiler (Phase Focus Ltd., Sheffield, UK) in a wet cell and powers were corrected to powers in air. All lenses had zero labeled power for distance. Sagittal power profiles revealed that the "low" add PureVision and Air Optix lenses exhibit smooth (parabolic) profiles, corresponding to negative spherical aberration. The "mid" and "high" add PureVision and Air Optix lenses have bi-aspheric designs, leading to different rates of power change for the central and peripheral portions. All OASYS lenses display a series of concentric zones, separated by abrupt discontinuities; individual profiles can be constrained between two parabolically decreasing curves, each giving a valid description of the power changes over alternate annular zones. Biofinity lenses have constant power over the central circular region of radius 1.5 mm, followed by an annular zone where the power increases approximately linearly, the gradient increasing with the add power, and finally an outer zone showing a slow, linear increase in power with a gradient being almost independent of the add power. The variation in power across the simultaneous-image lenses produces enhanced depth of focus. The through-focus nature of the image, which influences the "best focus" (distance correction) and the reading addition, will vary with several factors, including lens centration, the wearer's pupil diameter, and ocular aberrations, particularly spherical aberration; visual performance with some designs may show greater sensitivity to these factors.