Types Of Contact Lenses Research Articles

Comparison of Tear Film Stability and Correction for Improvement by Toric Soft Contact Lens Materials

Purpose : The Purpose of this study was to compare the degree of axial rotation and NIBUT of toric soft contact lenses which were three types of different materials and axial stability designs. Methods : The three types of toric soft contact lenses (hereinafter toric SCL) were worn on 19 subjects. One of them was double thin zone design lens (A-lens), the second was ASD lens (B-lens), and the third was prism ballast design lens (C-lens). Subjects were wearing the toric SCL to find out NIBUT for tear film stability and degree of the rotation for axial stability. All examinations were conducted after wearing SCL for two different wearing times such as 20 minutes (short time) and 8 hours (long time). Results : The “A-lens” corrected visual acuity was moderate at the initial wearing, and excellent after long time wearing. The result of NIBUT showed that “B-lens” was the best in initial wearing(p 0.050). The best axial stability was “A-lens” in the initial wearing(p 0.050). Conclusion : While the “A-lens” was best corrected visual acuity, it was worn for a long time, reducing tear film stability and surface wetting tendency. “B-lens” had better tear film stability and axial stability than the others in the early stage of lens wearing due to wet treatment on the surface and ASD design. In the C-lens with silicone hydrogel material, the corrected visual acuity was good, but the tear film stability and axial stability the poorest. It is considered that the great improvement for a method of surface treatment of silicone hydrogel is necessary.

Effects of lysosomal deposition on the friction coefficient of hydrogel contact lenses

When a contact lens is in contact with the eyelid and the cornea, tear proteins start to be accumulated on the lens and may subsequently undergo conformational changes. Protein adsorption or conformational changes on the lens may lead to discomfort, red eye, or even inflammatory reactions. Although measuring the friction coefficient of contact lens has been linked to comfort degree in vivo, there is not much research about the effects of tear protein deposition on the friction coefficient of the contact lens. Therefore, we investigated the friction coefficient of three distinct materials of contact lenses in two different lysosomal concentrations. We also studied lysozyme deposition on the lens without the influence of friction. The results demonstrated that although the amount of lysozyme deposition was high on all the materials we tested, it was not corresponded to higher friction coefficient. In addition, we investigated the effect of the contact lens care solution we developed on friction coefficient and lysozyme deposition of three different materials of contact lenses. The results showed that the care solution could reduce the increased friction coefficient caused by high lysosomal concentration. Therefore, we proposed a potential mechanism of why lysosomal deposition may result in high friction coefficient for certain types of hydrogel contact lenses.

Zeta potential of tear samples: A tool to explore the effects of wear of contact lenses

PurposeThe aim was to develop a method to assess the electrostatic properties of human tear samples, and to evaluate their modifications induced by the wear of contact lenses (CLs). MethodThe barrier method was developed for the measurement of the isoelectric point (IEP) on relatively small quantities. The method was applied to compare three groups: tears (TNW) of non-wearers, tears (TW_etaf) of regular wearers of etafilcon A CLs, and tears (TW_omaf) of regular wearers of omafilcon A CLs. Zeta potential (ζ) as a function of pH was measured by a Zetasizer Nano ZS90 (Malvern Instruments) on 40%-diluted samples, obtained by mixing 57 μL of tears of different subjects of the same group with 85 μL of HCl aqueous solution. IEP was deduced as the pH at which ζ is zero, i.e. the net electric charge on tear constituents being neutralized. ResultsWithin an error of about 0.05, IEPs were found to be 2.90 (TNW), 2.80 (TW_omaf), and 3.16 (TW_etaf). On average, a lower H+ concentration is needed to neutralize the surface charge of the tear components of etafilcon A wearers, compared to both TNW and TW_omaf. ConclusionIEP measurements on tear samples of wearers of different types of CLs are proposed in order to enhance the knowledge on the modifications of the profile of charged species in tears. The TW_etaf results, compared to those of the other groups, are compatible with an increase, due to the wear of etafilcon A CLs, of the relative concentration of high-IEP proteins.

Effects of senofilcon A and lotrafilcon B bandage contact lenses on epithelial healing and pain management after bilateral photorefractive keratectomy

PurposeThe purpose of this study was to compare postoperative epithelial healing time and ocular discomfort score in patients wearing two types of silicon hydrogel bandage contact lenses (BCLs) following bilateral photorefractive keratectomy (PRK). MethodsFor the study’s contralateral eye comparison, 43 patients who underwent bilateral PRK were randomized to be fitted for a senofilcon a lens in one eye and a lotrafilcon B lens in the other. The patients were masked to the specific BCL in each eye. On the first 3 days after PRK, the epithelial defect size was calculated, and patients reported their level of ocular discomfort, including pain, epiphora, and photophobia, on a visual analog scale (0 = no pain or discomfort, 10 = highest level of pain and discomfort). ResultsEpithelial defect size (mm2) did not differ significantly between the BCLs on Day 1 (senofilcon A vs. lotrafilcon B: 14.15 ± 5.59 vs. 14.93 ± 5.72, p = .327), Day 2 (senofilcon A vs. lotrafilcon B: 7.43 ± 4.67 vs. 7.04 ± 3.82, p = .586), or Day 3 (senofilcon A vs. lotrafilcon B: 0.59 ± 1.44 vs. 0.38 ± 1.08, p = .348) postoperation. By Day 3, re-epithelialization was complete in 35 eyes (81.3%) with senofilcon A lenses and 36 eyes (83.7%) with lotrafilcon B lenses. Patients reported less pain in eyes with senofilcon A lenses during the first 3 days postoperation (for all, p < .001) and less epiphora during the first 2 days postoperation (Day 1: p = .008, Day 2: p < .001, Day 3: p = .267) than in eyes with lotrafilcon B lenses. No significant difference in photophobia emerged between the BCLs postoperatively (for all, p > .05). ConclusionsAlthough duration of corneal re-epithelialization after PRK between the two BCLs did not differ significantly, senofilcon A lenses caused significantly less pain and epiphora after PRK.

Effects of eye rotation and contact lens decentration on horizontal peripheral refraction.

Peripheral refraction is important in design of myopia control therapies. The aim was to investigate the influence of contact lens decentration associated with eye rotation on peripheral refraction in the horizontal visual field. Participants were 10 emmetropes and 10 myopes in good general and ocular health. Right eyes underwent cycloplegic peripheral refraction, using a Grand-Seiko WAM-5500 Autorefractor, in 5° steps to ±35° eccentricities along the horizontal visual field. Targets were fixated using eye rotation only or head rotation only. Refractions were measured without correction and with three types of contact lenses: single vision, a multifocal centre-distance aspheric with +2.50D add and NaturalVue aspheric. Photographs of eyes during lens wear were taken for each eye rotation. Effects of visual field angle, lens type and test method (head or eye rotation) on vector components of relative peripheral refraction were evaluated using repeated measures anovas. Test method for each visual field angle/lens combination were compared via paired t-tests. Horizontal decentration ranges across the visual field were 1.2±0.6mm for single vision and 1.2±0.4mm for multifocal lenses but smaller at 0.7±0.4mm for NaturalVue lenses. There were only two significant effects of test method across the visual field angle/lens type combinations (single vision: for emmetropes horizontal/vertical astigmatism component at 35° nasal with mean difference -0.38D and for myopes spherical equivalent refraction at 20° temporal with mean difference +0.24D). Upon eye rotation the contact lenses decentred on the eye, but not enough to affect peripheral refraction. For the types assessed and for the horizontal visual field out to ±35° when measurements were performed with the Grand-Seiko WAM-5500 autorefractor, it is valid to use eye rotations to investigate peripheral refraction.

Raman Analysis of Tear Fluid Alteration Following Contact Lense Use.

Tear fluid is a heterogeneous solution containing mainly proteins, lipids, mucins and electrolytes, which regulates the physiology of the human eye. The complex composition of tears can be altered in the presence of eye inflammations. The use of contact lenses is one of the most frequent causes of inflammatory responses of the eye, with the related discomfort often causing the wearer to give up using them. In this paper, we exploit the potentiality of Raman Spectroscopy to analyse the biochemical changes in tear fluid in a contact lens wearer. In particular, we analysed the tear fluid collected from a volunteer as a function of the wearing time for two types of monthly contact lenses (Hydrogel and Si-Hydrogel). Our experimental results show an alteration of the relative concentrations of proteins and lipids in both of the analysed cases. More importantly, our results highlight the diagnostic sensitivity of Raman analysis to select the proper contact lens type for each wearer and optimise the lens wearing conditions.

Effects of Blink Rate on Tear Film Optical Quality Dynamics with Different Soft Contact Lenses.

Objective The aim of this study was to investigate tear film optical quality dynamics for four types of silicone hydrogel contact lenses (SHCLs) for daily wear over a 15-day period and for different blink rate (BR) patterns. Methods A prospective randomized, double-blind, cross-over pilot study including four SHCLs (A: lotrafilcon B (Air Optix plus HydraGlyde, Alcon Laboratories); B: samfilcon A (Ultra, Bausch & Lomb); C: comfilcon A (Biofinity, CooperVision); and D: filcom V3 (Blu:gen, Mark'Ennovy)). Serial measurements of Objective Scatter Index (OSI) using the HD Analyzer (Visiometrics S.L., Terrassa, Spain) were taken at different blinking patterns: blinking every 2.5 seconds (high BRs) and every 9 seconds (low BRs). They were performed during the first visit before CL insertion (baseline), after 20 minutes of CL wear (Day 1), and during the last visit after 8 hours of CL wear on day 15 of use (Day 15). Results Normal young healthy subjects were recruited and fitted with the four lenses. For low BRs, the mean OSI value increased over time for all CLs and the slope of the curve also increased for all CLs, except for CL D. However, for high BRs, the mean OSI value increased only for CLs B and C and the slope of the curve did not change over time for any of them. Conclusions These results suggest that the tear film optical quality dynamics after wearing SCHLs for 15 days seems to undergo a slight deterioration only for lowest BR.

Pengaruh Penggunaan Lensa Kontak, Kelembapan, dan Pengetahuan Terhadap Dry Eyes Syndrome

Objective: The Effect of Contact Lenses, humidity, and knowledge on the dry eyes syndrome.Methods: The type of reserach used is observation. The dimensions of study time are cross sectional because of data collection and outcome at one time. Humidity variables were measured using thermohygrometer and users’characteristic were obtained by questionnaire. The statistical test used is multiple logistic regression to find out effect of Contact Lenses Type, length of lens usage, humidity, and knowledge on the dry eyes syndrome.Results: Respondents were students Faculty of Public Health UNAIR from 2014-2017. Based on the type of lens, 90.9% of respondents used daily wear and 9.1% of respondents used overnight wear or extended wear. Based on the length of use of the lens 84.8% using a lens more than 4 hours and 15.2% less than 4 hours. Based on knowledge of 51.5% having high knowledge and 48.5% having low knowledge. Based on the humidity of the space of 54.5% the humidity level of the air conditioned lecture hall is appropriate and 45.5% is not suitable.Logisti regression test results obtained value of 4.732 Wald with a probability of 0.030, which means that there is a significant effect of moisture on the dry eyes syndrome while the user characteristics there is no significant effect. Conclusion: Based on the results of research conducted Students of the Faculty of Public Health, there are some conclusions that most respondents use the type of daily wear lens. Respondents use contact lenses more than 4 hours and users' knowledge in the high category. Humidity of spaces in the Faculty of Public Health is 54.5% stated to be appropriate and 45.5% is declared inappropriate.

Miniscleral lenses in the treatment of patients with dry eye syndrome (first own experience)

Background. Scleral lenses, due to their benefits, hold a specific position among all types of contact lenses. Some years ago, they began to be used successfully not only for the correction of complex types of refractive errors, when other types of correction failed to achieve satisfactory visual function and visual rehabilitation of patients, but also as a therapeutic system in the management of ocular surface disease.&#x0D; Purpose. To evaluate the efficacy of rigid gas permeable miniscleral contact lenses as a therapeutic system in the management of patients with dry eye syndrome by filling the space under the lens with a non-preserved sodium hyaluronate solution.&#x0D; Materials and methods. In the study, 7 patients (11 eyes) with keratectasias after corneal surgery and concomitant dry eye syndrome were included. In the treatment and rehabilitation of these patients, miniscleral contact lenses were used during daytime with additional filling of the space under the lens with a non-preserved sodium hyaluronate solution.&#x0D; Results. As a criterion of the effectiveness of miniscleral contact lens use for therapeutic purposes, along with a significant increase in visual function in patients with complex corneal pathology, the elimination of discomfort due to restoration of the corneal epithelium integrity and improvement of their quality of life is considered.

Clinical evaluation of different types of contact lenses in keratoconus management

PurposeTo compare the clinical and topographical findings of the keratoconus patients according to the prescribed contact lens type and to investigate the effects of corneal collagen cross-linking (CXL) and cone location on lens selection. MethodsThe records of 301 eyes of 195 keratoconus patients who were prescribed contact lenses were analyzed retrospectively. The eyes were grouped according to the lens type: Soft toric contact lens (STCL), rigid gas-permeable contact lens (RGPCL), hybrid contact lens (HCL) and mini-scleral contact lens (MSCL). The history of having CXL, ophthalmological examination findings, and the topographical findings were compared between the groups. Brown-Forsythe, Chi-square, and post-hoc tests were used to compare the groups. Mann-Whitney U test was used for subgroup analysis. Comparison of the lens-corrected visual acuity (LCVA) and spectacle-corrected visual acuity (SCVA) levels was made with Wilcoxon signed-ranks test. ResultsThere was no significant difference between the groups regarding topographical cone location, CXL history, spherical refraction, and LCVA. The difference between spectacle-corrected visual acuity and LCVA was higher in RGPCL and MSCL groups than STCL group (p=0.01). Keratometry of RGPCL and MSCL groups were higher than STCL and HCL groups (p=0.01, p<0.001). In RGPCL group, eyes with central cones had a higher increase in visual acuity with contact lenses compared to eyes with paracentral cones (p=0.043). STCL and MSCL were mostly prescribed in mild and severe keratoconic eyes, respectively. In RGPCL group, the increase in visual acuity with contact lens was higher in eyes treated with CXL (p= <0.01). ConclusionsWhile STCL and HCL were mostly prescribed in mild keratoconus, RGPCL and MSCL were selected for moderate or advanced disease. If appropriately chosen, all types of contact lenses could result in a good visual acuity level. CXL history did not affect the prescribed lens type. Having central cone location and CXL history in RGPCL group improved visual acuity more efficiently.

Visual rehabilitation of patients with irregular cornea

Purpose: To estimate the possibility of optical correction of an irregular surface of a cornea at primary ectasia (keratoconus) and secondary ectasia (a consequence of radial keratotomy (RKT) and Keratoplasty) for improvement of the maximum of visual acuity. Material and methods: In the study the scleral gas-permeable lenses (SGCL) were fitting by the 60 patients, it was 45 men and 15 women from them. The 46 patients had various stage of keratoconus and 14 patients had the keratectasia after RKT. On the 5 eyes of the patients was carried out keratoplasty earlier. Criteria of successful selection of SGCL considered achievement of steadily high visual acuity, comfort of carrying and the optimal clearance in apical zone, in the limbal and landing zone on the conjunctiva also. The results: In the course of the study, the maximum visual acuity in all patients was achieved with mini-SGKL correction irrespective of type of keratoektasia. All patients observed visual comfort compared with spectacle correction or correction with other types of contact lenses. Conclusion: Scleral gas-permeable contact lenses are the main method of correction at patients with irregular corneas and provide the best visual acuity.

Survey on a Disposal Method of Contact Lenses after Use

Purpose : To investigate a disposal method of disposing contact lenses and the recognition of environmental pollution by micro plastics which may be caused by the wrong disposal method of domestic contact lens wearers.Methods : Two hundred sixty one adults(124 males, 137 females, mean age 21.48±3.14 years) were participated in this study. They were given the questionnaire survey on contact lenses purchasing place, type of contact lenses, duration of wearing contact lenses, the disposal method of disposing contact lenses and the recognition of the occurrence of environmental pollution.Results : It appeared that eyeglass shop(50.0%) and contact lens shop(48.3%) were the main purchasing places, and the most common type of contact lenses were disposable lenses(38.5%) and daily wearing lenses(52.5%). On the duration of wearing contact lenses they answered more than 5 years(29.3%), less than 1 year (26.0%), less than 1 year to less than 3 years (26.0%), and on wearing a contact lens during a week they did 1-2 days (32.0%), 1 week (28.0%), 5-6 days (22.4%) and 3-4 days (17.6%). It was shown “no(78.3%)” and “yes(21.7%)” to the questionnaire of whether they received information or education about a disposal method at the place where the contact lens was purchased, and “no(87.5%)” and “yes(12.5%)” to the questionnaire of whether they received information or education from schools, public institutions or public media such as the internet. As for the disposal methods, landfill waste(45.6%), recycled garbage(29.6%), and drainage(16.8%) from the sink or toilet responded in order. Although men were more educated and informed about disposal than women (t=3.63189, p<0.00001), women were more aware of environmental pollution(t=2.44269, p=0.01605).Conclusion : In order to reduce the environmental pollution issue caused by the contact lens which does not decompose at the sewage treatment facility and become micro plastics, it is urgent to provide information about correct disposal methods after using contact lenses and to educate contact lens wearers.

Impact of a Hyaluronic Acid-Grafted Layer on the Surface Properties of Model Silicone Hydrogel Contact Lenses

The introduction of high oxygen transmissibility silicone hydrogel lenses ameliorated hypoxia-related complications, making them the most prescribed type of contact lens (CL). Despite the progress made over the last 2 decades to improve their clinical performance, symptoms of ocular dryness and discomfort and a variety of adverse clinical events are still reported. Consequently, the rate of CL wear discontinuation has not been appreciably diminished by their introduction. Aiming to improve the interfacial interactions of silicone hydrogel CLs with the ocular surface, a biomimetic layer of hydrophilic glycosaminoglycan hyaluronic acid (HA) (100 kDa) was covalently attached to the surface of model poly(2-hydroxyethyl methacrylate- co-3-methacryloxypropyl-tris-(trimethylsiloxy)silane) (pHEMA- co-TRIS) silicone hydrogel materials via UV-induced thiol-ene "click" chemistry. The surface structural changes after each modification step were studied by Fourier transform infrared spectroscopy-attenuated total reflectance and X-ray photoelectron spectroscopy (XPS). Successful grafting of a homogeneous HA layer to the surface of the model silicone hydrogels was confirmed by the consistent appearance of N (1s) and the significant decrease of the Si (2p) peaks, as determined by low-resolution angle-resolved XPS. The HA-grafted surfaces demonstrated reduced contact angles, dehydration rate, and nonspecific deposition of lysozyme and albumin, while maintaining their optical transparency (>90%). In vitro studies demonstrated that the HA-grafted pHEMA- co-TRIS materials did not show any toxicity to human corneal epithelial cells. These results suggest that surface immobilization of HA via thiol-ene "click" chemistry can be used as a promising surface treatment for silicone hydrogel CLs.

Contact lens complications : Diagnosis and treatment

Contact lens complications are all pathological alterations of the eyes caused by wearing contact lenses. Clinical manifestations particularly affect the cornea and conjunctiva. Adifferentiation is made between undesired manifestations and disease conditions that at least temporarily make the further wearing of contact lenses impossible. The decisive factor is that for every irritation of the anterior segment of the eye the possibility of contact lens complications is considered and investigated. This article describes the most important contact lens types, the physiology and pathology of corneal metabolism, clinical manifestations and the corresponding treatment.

In Vitro Evaluation of Adhesion of Two Acanthamoeba Strains to Cosmetic Contact Lenses.

To evaluate the factors affecting the adhesion of Acanthamoeba trophozoites to the surface of cosmetic contact lenses (CCLs). Acanthamoeba castellanii and A. hatchetti trophozoites were inoculated onto CCLs (hema copolymer [HM] [38.5% H2O], phemfilcon [PF] [55% H2O], polymacon [PM] [38% H2O], polyhema [PH] [%42 H2O], and hema [HM55] [55% H2O]), and the number of trophozoites adhered to the lens surfaces was assessed over time, that is, at 15 min, 1, and 24 hr. In addition, scanning electron microscopy (SEM) analysis of the lens surfaces was performed to evaluate the effect of lens surface topology on adhesion. The number of amoeba adhered to the contact lens surface was found lower with PF and PH production materials, than lenses with HM, PM, and HM55 production materials (P<0.05). No significant difference was detected in amoebic strains adhered in all the contact lens types (P>0.05). No significant difference was found on average amoeba adhesion between contact lenses with hema production material but with different water contents (45%, 55%), to see the effect of water content on amoebic adhesion (P>0.05). As a result of SEM analysis, surface topology showed no effect on adhesion. (1) Chemical composition of lenses seemed to be mostly responsible for the adhesion of Acanthamoeba. (2) Different numbers of trophozoites, obtained after the adhesion experiment, could also indicate that adherence capacity can also differ among Acanthamoeba species.

Mechanical Properties of Contact Lens Materials.

To evaluate the mechanical properties of commonly available soft contact lens materials and compare results using custom-built MicroTensometer. The Young modulus, parameters for stress relaxation, and toughness of 18 types of single vision soft contact lenses were measured using custom-built MicroTensometer. Five lenses of each type were soaked in standard phosphate buffered saline and measured at a temperature of 35°C. Each lens was flattened and sliced into a rectangular strip sample using two parallel blades. The Acuvue Moist 1-Day and SofLens Daily lenses measured lowest moduli, whereas Air Optix Night & Day Aqua and Premio measured the highest. The measured moduli for silicone hydrogel materials were generally higher compared with the hydrogels except for Dailies AquaComfort Plus. The exponential curve fitted over the decay in stress showed a consistent time constant of approximately 10 sec for most lens types measured. However, the amplitude constant varied from 2.84% for SofLens Daily to 22.39% for Acuvue TruEye 1-Day. The toughness results showed that Dailies AquaComfort Plus is strong but not necessarily tough. The mechanical properties of commonly prescribed soft contact lens materials were measured using a dedicated instrument. Its reliability was demonstrated, and modulus results were compared against published data from manufacturers and other research groups. Agreement was generally good, with only a few exceptions exceeding 15% difference. The more recently released silicone hydrogel lens types have reduced modulus, approaching that of medium or high water content hydrogel materials.

Digital Eye Strain in a Population of Young Subjects.

The main goal of our study was to prove short-term objective influence of near addition and relieving prism on accommodative and vergence facility in group of young healthy persons. Further, we wanted to prove objective and subjective difference between two types of soft contact lenses during working with digital device. We had in total 37 subjects in our study. The first group contained 37 subjects with average age 23 years without important eye pathology. The second group contained 8 subjects with the same average age without important eye pathology. In the first group of subjects, we measured binocular accommodative facility (BAF) and binocular vergence facility (BVF) with and without addition 1 D and with and without relieving prism 2 pD BO at working distance 45 cm. In the second group, we evaluated BAF, BVF and standardized questionnaire (Computer Vision Syndrome Questionnaire - CVS-Q, Sequí M. 2015) during usage of two types of soft contact lenses. The first type of contact lenses (type 1) contained relieving prism for PC working and type 2 was soft contact lens with aspheric design. In the first group of subjects, we measured these values: BAF without addition = 12.78 cpm, BAF with addition = 11.57 cpm, BVF without prism = 12.32 cpm, BVF with prism = 11.59 cpm. In the second group of subjects, we measured with contact lens type 1 these values: BAF = 12.13 cpm, BVF = 13.63 cpm and questionnaire score 9.43 points. With contact lens type 2 we measured BAF = 11.75 cpm, BVF = 11.63 cpm and questionnaire score 12.86 points. We proved statistically important different between two variable only in the first group between BAF with and without addition and BVF with and without relieving prism. In conclusion, we found statistically important decrease in variable BAF and BVF with usage of addition and relieving prism. We found that neither addition nor prism have positive influence on increase of BAF and BVF. Subjects in second group had higher BAF and BVF values with both types of contact lenses in comparison with natural values. We found that with contact lens type 1 (with addition) subjects had higher BAF and BVF values in comparison with contact lens type 2 (aspheric). Subjects with contact lens type 1 had also lower (better) questionnaire score, i.e. 9.43 versus 12.86 point. Key words: Digital eyestrain syndrome, accommodative and vergence facility, addition, relieving prism.

The characteristics of a preservative-free contact lens care solution on lysozyme adsorption and interfacial friction behavior

The population of soft contact lens wearers is increasing, thus the issues of feeling comfortable and contact lens-induced clinical symptoms are concerned. Both lysozyme deposition and mechanical friction among contact lens and the eye can induce discomfort and eye conditions. Therefore, we characterized our developed preservative-free contact lens care solution on lysozyme adsorption and lubrication. Two distinct lens materials were washed with the care solution after being soaked in lysozyme, as well as were rubbed against the glass in the presence of lysozyme and the care solution for measuring the friction coefficient. Our results demonstrated that the preservative-free contact lens care solution can be applied as a potential lubricant for a specific type of soft contact lenses.

Ocular residual and corneal astigmatism in a clinical population of high school students.

PurposeTotal refractive astigmatism is usually the first consideration that guides the selection of contact lens type (e.g., spherical or toric), while the ocular source of the astigmatism is a second, but more important consideration, for the final clinical decision. This study was conducted to provide detailed data on this topic by evaluating astigmatic components in Chinese adolescents.MethodsParticipants were recruited from healthy high school students undergoing an annual ocular examination at a local hospital. Total astigmatism (TA), corneal astigmatism (CA), and ocular residual astigmatism (ORA) were determined by a Hartmann-Shack wavefront analyzer system (KR-1W, Topcon) with the natural pupil. The axis relationship between CA and ORA was placed into three categories: on-axis, defined as an axis with a difference of 0 ± 10°; opposite-axis, a difference of 90 ± 10°; and the rest defined as oblique-axis.ResultsThe study consisted of 1,466 students (57.84% girls, age: 16.49 ± 1.05 years). ORA was present in 83.97%, 66.64%, and 45.23% of participants, according to the various criteria for astigmatism (≥ 0.50 D, ≥ 0.75 D, and ≥ 1.00 D, respectively). While with-the-rule was the most common axis orientation for both TA (76.28%) and CA (89.94%), against-the-rule predominated in ORA (93.82%; χ2 = 1688.544, p < 0.001). Opposite-axis was the major type of axis difference (90.96%) of clinical significance (i.e., ≥ 1.00 D) between CA and ORA, which also prevailed in all levels of TA (range: 56.25–82.26%).ConclusionsORA is common in high school students and usually demonstrates a compensation relationship with CA, which should be taken into consideration when determining the design of contact lenses to correct refractive error.

Hydrogel Contact Lens Water Content is Dependent on Tearfilm pH

Based on clinical inferences, investigators theorized in situ soft lens hydration was linked to the precorneal tearfilm pH. Forty-one myopic subjects at Fort Rucker, AL, USA were fitted with one of two types of extended-wear soft contact lenses, and were followed quarterly for a period of 33 mo. The anterior soft contact lens surface pH was measured in situ, while the in vitro lens water content was measured immediately after lens removal, using a hand-held refractometer on one lens, and a gravimetric means of hydration measurement on the other lens. The in situ pH increased logarithmically across extended wearing time, reaching an asymptote at approximately 5 d' wearing time at a pH of 7.45 ± 0.03. Lens water content was shown to similarly decrease at an inversely logarithmic rate, leveling off at 4-5 d' extended wearing time. Both means of hydration assessment correlated well with each other across days' extended wearing time (R = 0.98; p < 0.0001). A log-log dual conversion yielded significantly different linear slopes (p < 0.001), based on a multifactorial analysis of both lens types, by the pH, and by their water content. The differing ionic status of each material accentuated their varied polar attraction characteristics. Two soft lenses, identical in all patient-based parameters, could provide differing oxygen availability, as well as differing physical fits in patients of identical physical characteristics, as a result of their unique tearfilm pH differences. The in situ hydrogel lens water content is directly dependent on the precorneal tearfilm pH.