Videokeratoscopic assessment of silicone hydrogel contact lens wettability using a new in-vitro method

PurposeThe aim of the study was to assess the surface wettability of new-generation silicone hydrogel (SiH) contact lenses (CLs) videokeratoscopically using a new in-vitro method under office conditions.MethodVideokeratoscopic methodology was used to compare time-dependent CL wettability on an in-vitro cornea model. The model cornea was a polished chrome surface coating a Teflon form. It was prepared with a base curve of 8.7 mm and a diameter of 15 mm. Laboratory temperature and humidity were controlled. Before and after placing CLs on the on the model cornea, Bausch + Lomb Biotrue® multi-purpose solution (MPS) was dropped to simulate the pre-lens and post-lens film layer. Fanfilcon A, Senofilcon A, Samfilcon A, and Lotrafilcon B CLs with -3.00D were used, and images were taken with the videokeratoscopic method for testing. In the control group, the same procedure was performed without placing CLs. The images of CLs at 0, 60, 90, 120, 150, and 180 s were taken. Distortions and gaps seen in rings were recorded. The areas in rings were calculated in pixels using İmageJ.ResultsWhen CLs were examined, statistical differences were found among average pixel values (p < 0,001). The average pixel value was 131877.4 in the Samfilcon group, 116125.5 in the Senofilcon group, 137893.2 in the Fanfilcon group, 125578.3 in the Lotrafilcon group, and 124984.6 in the control group. No difference was found between the average values of the Lotrafilcon group and the control group. Differences were found between the average values of all other groups.DiscussionThe results obtained showed that videokeratoscopy was an effective method for in-vitro testing of CL wettability. It was found that SiH lenses displayed different performance under office conditions depending on materials and technologies used for wetting the lens surface. It was shown that lens surface wettability could be measured with a repeatable and new method when the factors affecting surface wetness and image quality were ruled out.     

Impact of meibomian gland width on successful contact lens use

PurposeTo evaluate meibomian gland (MG) width and determine its impact on successful contact lens (CL) use and ocular health.MethodsA five-site study was conducted by recruiting 18- to 45-year-old subjects who had dropped out of CLs because of discomfort. CL dropouts were compared to age- and sex-matched successful CL wearers. Right eyes were evaluated for tear break-up time, tear meniscus height, MG expressibility, meibum quality, and meibography. Central MG widths were evaluated with a custom MATLAB program.ResultsCL dropouts (n = 56) and successful CL (n = 56) wearers had similar grades for upper (p = 1.0) and lower (p = 0.22) MG atrophy, upper (p = 0.07) and lower (p = 0.89) MG tortuosity, and upper (p = 0.92) and lower (p = 0.97) MG widths. Upper eyelid MG widths were narrower than lower eyelid MG widths (p = 0.03). Upper and lower MG tortuosity (p < 0.001) and widths (p = 0.03) were associated, but not atrophy (p = 0.42). Lower eyelid MG widths were associated with MG expressibility (p = 0.01), but MG widths were not with any other factors.ConclusionsSuccessful CL wear does not appear to be clinically influenced by MG width or other measures of MG structural integrity. Lower eyelid MGs were wider than upper eyelid MGs and narrower lower eyelid MGs were associated with worse MG expressibility, suggesting that narrower MGs may produce abnormal meibum. Data also suggests that MG factors of both eyelids should be evaluated in practice.     

Patients’ and prescribers’ perception of contact lenses as a potential ocular drug delivery system

Contact lenses (CLs) designed to deliver medication gradually to the eye are being developed and investigated for the use in ocular drug delivery. The aim of the current research is to determine patients’ acceptance of the use of lenses for ocular drug delivery. In addition, the study aimed to seek the views and perceptions of healthcare professionals (HCPs) on CLs as a method of ocular drug delivery and whether it will be prescribed to treat ocular conditions.This was a cross-sectional survey targeted at patients and HCPs. Two separate questionnaires were created with open-closed ended and multiple response questions, gauging the perceptions and acceptance of CLs as drug delivery tool. The patients’ survey was distributed in John Radcliffe (JR), Oxford and Moorfields eye hospital (MEH), London, UK. The HCPs’ questionnaire was manually distributed and was also devised on Survey Monkey and sent by email to ophthalmologists, optometrists, opticians, GPs and hospital and community pharmacists. The data were analysed using SPSS statistical software and Excel.Over 60% (92/151) of patients would accept the use of CLs for their ocular treatment with the highest acceptance being reported by patients in the age group of 30–49 years old. The most frequently used conventional treatment formulation was eye drops as indicated by 87% (131/151) of the responses. More than half of eye drop users (57%, 75/131) indicated that they would accept using CLs expecting them to reduce the frequency of application of the medicine and be less time consuming. Interestingly, half of HCPs were not aware of CLs as an ocular drug delivery method; nevertheless, a total of 65 HCPs out of the 112 surveyed stated that they would prescribe/dispense CLs to treat ocular disease.     

Corneoscleral junction angle in healthy eyes assessed objectively

PurposeTo introduce a fully objective method to measure corneoscleral junction (CSJ) angle and evaluate the CSJ angle in healthy eyes.MethodsCorneoscleral topography (Eye Surface Profiler, ESP) was acquired from the right eye of 105 healthy Caucasian subjects, ranging from 18 to 59 years old. From the raw anterior eye height data, the topographic limbus was automatically demarcated in 360 semi-meridians. Further, in limbal location, the CSJ angle was automatically calculated from corneoscleral height data using neighbouring auxiliary points for angle calculation. Additionally, CSJ angle was statistically analysed regionally.ResultsThe mean CSJ angle was 177.5 ± 1.1°. There is a mean difference of 7.7 ± 3.7° between the steepest (smallest) and flattest (largest) CSJ angle within the same eye. There exist statistically significant differences between temporal (178.2 ± 1.4°) and nasal (176.4 ± 1.1°) regions (paired t-test, p < 0.001), and between superior (178.1 ± 1.1°) and inferior (177.9 ± 1.1°) regions (p = 0.038). CSJ angle is correlated with limbus position (r = 0.43, p < 0.001).ConclusionCSJ angle is rotationally asymmetric. CSJ varies regionally, being the smallest (steepest) in the nasal region. Significant rough changes in CSJ angle were observed for some healthy individuals.     

Does placebo effect exist in contact lens discomfort management?

PurposeTo study the effect of daily disposable contact lens (DDCL) refitting in monthly contact lens (CL) wearers suffering from contact lens discomfort (CLD), and to assess if there is a placebo effect associated with this CLD intervention.MethodsSymptomatic CL wearers, according to the Contact Lens Dry Eye Questionnaire 8 (CLDEQ-8 ≥ 12 points), were divided into two groups. The study group was provided with DDCLs (delefilcon A) and the control group with a masked pair of their habitual monthly CLs (placebo effect) and were assessed after one month. Then, the control group was provided with the same DDCLs and evaluated one month later. The symptoms were recorded with the CLDEQ-8 and global rating of change scale (GRCS). Non-invasive tear break-up time (NITBUT), conjunctival hyperaemia, fluorescein staining, and lid wiper epitheliopathy (LWE) were evaluated. Changes between visits, groups, and the effect of each intervention were analysed.ResultsThirty-one participants (mean age: 23.2 ± 5.3 years) were recruited. The study group (n = 14) showed an improvement of -39.6 ± 25.8 % (p < 0.001) in CLDEQ-8 and 31.3 ± 14.6 points in GRCS (p < 0.001) after one month of DDCL use, while no changes in clinical tests were found. In the control group (n = 17), symptoms improved significantly after wearing the masked monthly CL (CLDEQ-8: -26.1 ± 31.0 %, p = 0.03; GRCS: 14.9 ± 17.0, p = 0.002), however a worsening in bulbar (26.5 ± 40.0 %; p = 0.02) and limbal hyperaemia (21.6 ± 34.7 %, p = 0.02) and an improvement of -19.1 ± 37.0 % (p = 0.049) in LWE was found. When the control group was fitted with the DDCL, improvements in GRCS (20.5 ± 25.5, p = 0.02), NITBUT (37.9 ± 42.3 %, p = 0.002), and conjunctival staining (-47.1 ± 59.9 %, p = 0.005) were noted.ConclusionsRefitting symptomatic monthly CL wearers with Delefilcon A DDCL is effective in reducing symptoms related to CLD. However, clinicians and researchers must be aware of the existence of a placebo effect when assessing the effectiveness of any CL refitting.     

Exploring non-adherence to contact lens wear schedule: Subjective assessments and patient related factors in children wearing single vision and myopia control contact lenses

PurposeTo determine factors associated with non-adherence to contact lens wear schedule involving single vision and myopia control contact lenses in children.MethodsData from 379 children enrolled in a prospective, double masked, randomized clinical trial, aged 8–13 years, cycloplegic spherical equivalent of -0.75 to -3.50D and wearing either: single vision silicone hydrogel (SiH) CL (control lens); two anti-myopia SiH CL that incorporated relative plus in the central and periphery in a stepped manner (test lens I and II); and two extended depth of focus hydrogel CL (test lens III and IV) was considered. A questionnaire was administered to the participants at every scheduled visit and gathered information on days of wear/week and subjective assessments of ocular comfort and visual quality on an analog scale of 1–10.Participants were categorized as “Adherent” when lens wear was ≥ 6 days/week or “Non-adherent” when lens wear ≤ 5 days/week. Categorized adherence data was summarized as a percentage across visits for each CL type. Differences between the two groups were analyzed using linear mixed model.ResultsFor the control lens, 79.6 % participants were adherent as compared to 63.7%–74.6% with test lenses (p=0.026). Non-adherence was greater in those that discontinued (p<0.001). Subjective ratings of visual quality for static and dynamic tasks were lower with non-adherent wearers and more variable between visits. Ocular comfort was also poorer in non-adherent wearers irrespective of lens material or lens design. Male gender, lower baseline myopia, lower high contrast visual acuity and esophoria were associated with a higher risk of non-adherence.ConclusionsThe study identified a wide range of factors associated with non-adherence to lens wear schedule. Paying specific attention to these factors when evaluating patients for CL wear and taking steps to ensure satisfaction in lens wear may promote longer term continuation of wear.     

The eyelids and tear film in contact lens discomfort

Purpose

To investigate characteristics of the eyelid margins, meibomian glands and the tear film of contact lens wearers, and to determine whether these characteristics were related to symptoms of contact lens discomfort.

皮带轮疲劳强度的数值计算分析

针对一种车用皮带轮,运用有限元技术进行了该皮带轮的疲劳强度分析。由于皮带-皮带轮传动系统的复杂性,在皮带轮的疲劳强度分析中考虑了皮带和皮带轮之间的接触问题。皮带轮和皮带之间的接触采用了常用的点-面接触模型,并应用拉格朗日乘子法来描述整个接触问题。最后通过该型皮带轮-皮带系统的分析得到了该皮带轮的疲劳强度的具体分布。整个分析过程可以为皮带轮-皮带系统的强度优化设计提供良好的分析依据。     

A surface wear model for hypoid gear pairs

In this paper, a methodology was proposed for simulation of surface wear of face-milled or face-hobbed hypoid gear pairs. The methodology combines Archard's wear model with a finite-element based hypoid gear contact model. The wear model requires the sliding distances and contact pressures to be computed along the contact zones at each rotational gear position. Formulations were proposed for computation of sliding distance along the tooth contact zones based on hypoid gear kinematics and geometry of the tooth surfaces, and the contact model was used to predict the normal contact pressure distributions. An example hypoid gear pair was analyzed for its wear behavior. Influences of gear position errors on wear patterns were demonstrated. An approximate method that is computationally more efficient was also proposed at the end.     

Hybrid Atomistic/Continuum Study of Contact and Friction Between Rough Solids

A hybrid simulation method is used to study the effect of atomic structure and self-affine roughness on non-adhesive contact and friction between two-dimensional surfaces. Rough-on-flat and rough-on-rough contact are compared as a function of system size up to several micrometers. In order to contrast elastic and plastic behavior, interactions within the deformable substrate are either harmonic or Lennard-Jones. The ratio of lattice constants in the solids is varied to examine the effect of commensurability. In all cases the true area of contact rises linearly with load, but the slope is much larger than expected from continuum calculations. These calculations considered a continuous distribution of surface heights that is appropriate for large scales, rather than the discrete height distribution of the crystalline surfaces used here. The ratio of contact area to load depends on the ratio of lattice constants in the solids and varies with system size in small systems that deform plastically. While some dislocations are observed, plasticity is dominated by an asperity flattening mechanism where surface atoms are displaced into a lower layer. The kinetic friction rises linearly with load and is independent of system size, as predicted by Amontons’s laws. Variations in friction with commensurability are smaller for rough surfaces than for flat surfaces, because most of the contact area is in small patches. Asperity flattening increases patch sizes and thus the effect of commensurability on friction. Rough-on-rough contact leads to additional friction associated with the local slope of the contacting regions.