Contact Lens Prescription Research Articles

Globe Subluxation in the Specialty Contact Lens Practice

Purpose. This report documented the occurrence of globe subluxation (GSL) during the insertion of a scleral contact lens (SL) and described the management of two keratoconus patients, in need of a gas permeable contact lens prescription and experiencing GSL. Furthermore, an anatomical explanation for the occurrence of spontaneous GSL is attempted. Material and Methods. Two separate case reports of GSL were evaluated and described. In case 1, the patient experienced GSL secondary to insertion of a trial SL and in case 2 the patient had experienced multiple GSLs secondary to Grave’s disease. Different management strategies were taken to help to provide functional vision for these patients. In case 1, the patient was fitted with a smaller corneal gas permeable lens to minimize lid manipulation needed to insert a lens and provide effective correction. In case 2, the patient’s existing Prosthetic Replacement of the Ocular Surface Ecosystem (PROSE) SL was designed to increase vertical lens steepness to tighten the lens fit and minimize the chance of losing the lens during wear. Results. With the help of the individually fitted contact lenses, it was possible to achieve visual rehabilitation in accordance with the patient’s specific needs. Conclusion. SL are fitted with increasing frequency and tend to require excessive lid manipulation, which may lead to GSL. This small case series demonstrated different lens design and selection maybe utilized to minimize the occurrence of GSL. The superior septum orbitale is perforated several times across the width of the upper lid by the aponeurosis of the levator. This structural arrangement weakens the superior septum orbitale and, postulated here, predisposes the eye to GSL by a herniation primarily of the superior septum orbitale.

Machine learning-based prediction of tear osmolarity for contact lens practice.

This study addressed the utilisation of machine learning techniques to estimate tear osmolarity, a clinically significant yet challenging parameter to measure accurately. Elevated tear osmolarity has been observed in contact lens wearers and is associated with contact lens-induced dry eye, a common cause of discomfort leading to discontinuation of lens wear. The study explored machine learning, regression and classification techniques to predict tear osmolarity using routine clinical parameters. The data set consisted of 175 participants, primarily healthy subjects eligible for soft contact lens wear. Various clinical assessments were performed, including symptom assessment with the Ocular Surface Disease Index and 5-Item Dry Eye Questionnaire (DEQ-5), tear meniscus height (TMH), tear osmolarity, non-invasive keratometric tear film break-up time (NIKBUT), ocular redness, corneal and conjunctival fluorescein staining and Meibomian glands loss. The results revealed that simple linear regression was insufficient for accurate osmolarity prediction. Instead, more advanced regression models achieved a moderate level of predictive power, explaining approximately 32% of the osmolarity variability. Notably, key predictors for osmolarity included NIKBUT, TMH, ocular redness, Meibomian gland coverage and the DEQ-5 questionnaire. In classification tasks, distinguishing between low (<299 mOsmol/L), medium (300-307 mOsmol/L) and high osmolarity (>308 mOsmol/L) levels yielded an accuracy of approximately 80%. Key parameters for classification were similar to those in regression models, emphasising the importance of NIKBUT, TMH, ocular redness, Meibomian glands coverage and the DEQ-5 questionnaire. This study highlights the potential benefits of integrating machine learning into contact lens research and practice. It suggests the clinical utility of assessing Meibomian glands and NIKBUT in contact lens fitting and follow-up visits. Machine learning models can optimise contact lens prescriptions and aid in early detection of conditions like dry eye, ultimately enhancing ocular health and the contact lens wearing experience.

EVALUATION OF WEAR EXPERIENCE WITH WATER SURFACE DAILY DISPOSABLE LENSES IN SATISFIED REUSABLE SOFT CONTACT LENS WEARERS.

Soft contact lens wearers are often prescribed the same lens material and modality for multiple years if patients express satisfaction and no significant problems with lens fit or ocular health are noted upon evaluation. Despite their satisfaction, it is possible that other lenses exist that could provide additional health or convenience benefits and still provide satisfied lens wear experience. In this study, wearers of a specific monthly replacement lens brand (comfilcon A) were recruited for an open-label study. The habitual contact lens prescription was optimized for 2 weeks of wear and participants confirmed that they were satisfied with their habitual lenses before being refit with daily disposable lenses (verofilcon A). Participants responded to visual analog scale (VAS) survey about their initial impressions of the lenses. After 2 weeks of lens wear, participants completed a final study visit and completed surveys about lens wear experiences with the daily disposable study lenses. Fifteen male and 15 female participants completed the study. Median (IQR) binocular LogMAR visual acuity was -0.20(0.12), which is equivalent to 10/12.5 Snellen acuity. Initial impression surveys revealed median (interquartile range) of 92.5(22.3) for quality of vision; 95.0(19.3) for comfort; and 91.5(19.3) for satisfaction. At the final visit, median scores for EOD quality of vision was 86.5(24.0); EOD comfort was 84.5(30.3), and EOD dryness 25.5(47.0). Median overall VAS scores were 92.5(16.0) for vision; 88.0(18.3) for comfort, and 17.5(25.8) for dryness. Median satisfaction with the study lenses was scored 9(2.8) on a 1-10 scale. In this study, satisfied wearers of comfilcon A reusable lens were refit with Verofilcon A daily disposable lenses and showed high satisfaction scores with the new lenses, showing that refitting these patients can allow patients to have lenses with more frequent replacement and maintain satisfaction with daily lens wear.

Characterization of rotational symmetry and noise in multifocal contact lens power maps

AbstractPurpose: Spherical multifocal contact lenses are typically designed with a rotationally symmetrical power profile. Imperfections in the raw material, manufacturing and measurement process can break this symmetry, altering the intended lens design. The purpose of this work is to develop a method to separate the intended symmetric design profile from the asymmetries and to give the spatial distribution of the measurement noise uncertainty in diopters.Methods: NIMO TR1504 (Lambda‐X) version V.2.13.2 has been used to measure the local power map of various multifocal contact lenses. From the map, a set of radial power profiles is obtained for different angles (0°, 180°), (0°, 360°). A symmetrical lens should show a constant radial profile for different angles, while asymmetries manifest as differences in the set of radial power profiles. They are analysed using a Principal Components Method (PCA) implemented in MATLAB.Results: The method displays a map of the symmetric radial profile of the lens, another map of the deviations with spatial structure indicating the angles where the deviations are stronger (rotational asymmetries), and noise with three separated components (spatially random variations). Asymmetries of the order of 0.17D (with maximums of 0.4D), and random noise values of 0.12D were found in some lenses.Conclusions: The characterization of multifocal contact lens prescription is important in visual optics. The prescription perceived by the patient depends on the distribution of the radial power profile on the pupil. That is the reason why asymmetries and imperfections estimation is important. The method developed in this work allows to calculate a diopter equivalent number for them.

Current Trends in Scleral Lens Prescription, Management, and Evaluation.

To report current trends in scleral contact lens prescription and management, including lens designs prescribed, care products recommended, and procedures performed during routine scleral lens (SL) evaluation. An online survey was designed by the Scleral Lenses in Current Ophthalmic Practice Evaluation study team and administered to eye care practitioners attending a specialty contact lens meeting. The survey was available from November 8, 2019, through March 31, 2020. Participants' demographic data were collected, along with information on lens diameters, landing zone (LZ) designs, recommended care products, and components of routine SL evaluation. In total, 715 participants responded to at least one of the survey items of interest. Most lenses prescribed (63%) were 16 mm or more in diameter. Lenses with toric LZs were the most frequently prescribed (48%), followed by spherical (40%), quadrant-specific (8%), and impression-based or image-based designs (3%). Most participants (61%) recommended hydrogen peroxide products for lens care. Nonpreserved saline in a single-use vial was most frequently recommended to fill the bowl of the lens before application. Intraocular pressure was measured during SL evaluation by 45% of participants; 38% of participants routinely measured corneal thickness. Practitioners increasingly are prescribing SLs with advanced LZ designs. Most practitioners recommend hydrogen peroxide-based disinfection systems and single-use vials of nonpreserved saline for lens care and application. Because differences in components of routine SL evaluations were reported, clinicians may benefit from reaching a consensus on essential components of SL evaluation.

Wearer Experience and Eye Care Professional Acceptance with a 1 Day Multifocal Contact Lens.

A large observational survey was undertaken to determine eye care professional (ECP) and patient experience of stenfilcon A multifocal soft contact lens (MyDay multifocal) when prescribed in a real-world setting. A total of 196 ECPs from eleven countries fit up to ten presbyopes with stenfilcon A multifocal. Data were collected on fit success at the initial visit, patient satisfaction with comfort, vision at distance, intermediate, and near, overall vision, overall satisfaction, and handling at the initial and follow-up visits after 1-2 weeks of wear. ECPs completed questionnaires on multifocal fitting experience and expectations before and after the fitting period. A total of 196 pre-fitting and 141 post-fitting ECP surveys were collected. A total of 1505 initial fits (mean age 53.4, range 38 to 81 years, 73% female, 27% neophytes) and 1440 follow-up visits were completed. The mean distance vision contact lens prescription was -1.32DS (range -12.00DS to +8.00DS) with Add powers: Low 56%, Medium 24%, and High 21%. At the follow-up visit 77% (n=1108) of trials were successful. Mean patient satisfaction ratings (1-10 scale, where 1 is not at all satisfied, and 10 extremely satisfied) at the initial visit were higher than eight out of ten for comfort, vision, and overall satisfaction, and were not significantly different after 1-2 weeks of wear. Stenfilcon A multifocal was preferred by 66% of patients over their habitual correction. In most cases mean satisfaction scores and the proportion of patients highly satisfied were not significantly different between myopes and hyperopes, across Add range, between new and habitual wearers, and wearers of frequently replaced and 1 day contact lenses. ECPs in real-world clinical settings found stenfilcon A multifocal contact lenses easy to fit to a wide range of patients, with a high fit success rate and high levels of patient satisfaction for overall comfort, vision, satisfaction, and handling.

Corneal RGP Contact Lens Fitting Software for Keratoconus Built-In Anterior Segment Optical Coherence Tomography.

To assess the performance of the contact lens fitting software built into anterior segment optical coherence tomography (AS-OCT). This retrospective study enrolled patients with keratoconus prescribed with spherical corneal rigid gas-permeable contact lenses based on a contact lens fitting software. Subjects were classified into four subgroups based on corneal morphology: nipple, oval, globus, and marginal type. Software performance was evaluated according to the correlation between the back optical zone radius (BOZR) calculated by the contact lens fitting program and the BOZR of the lens prescribed, and the number of trial lens replacements required.Results:A total of 340 eyes of 254 patients with a mean age of 40.4 ± 13.6 years were included. The oval type was the most common (61.8%), followed by the nipple type (26.2%). Linear regression analysis revealed a significant correlation between the prescribed and the calculated BOZR in all subgroups (R 2 = 0.92, P < 0.01 for the nipple type; R 2 = 0.76, P < 0.01 for the oval type; R 2 = 0.93, P < 0.01 for the globus type; and R 2 = 0.79, P < 0.01 for the marginal type). Furthermore, the globus type had the highest proportion of cases requiring at least one trial lens replacement (36.3%), followed by the nipple group (27.0%). There were no significant differences among the subgroups ( P = 0.14). In conclusion, our findings reveal that the contact lens fitting software built into AS-OCT may be useful for accurate contact lens prescription for any corneal shape.

Contact Lens Prescribing Trends for Keratoconus at an Academic Medical Center: Increased Utilization of Scleral Lenses for Severe Disease.

To describe contact lens prescription trends for patients with keratoconus. Demographics, corneal curvature, visual acuity, and type of contact lens prescribed were reviewed for all patients with keratoconus evaluated in the contact lens service in 2010 and 2020. There were 292 patients in 2010 and 217 in 2020. In 2010, 69% were using corneal gas-permeable lenses (GP), 16% soft toric, 13% hybrid, and 2% soft sphere with no scleral lens (SL). In 2020, 60% were using corneal GP, 22% SL, 12% soft toric, 5% hybrid, and 1% soft sphere. Mean log of minimum angle of resolution visual acuities with manifest refraction were (represented in mean [SD, range]) 0.42 (0.33, 0-1.3) in 2010 and 0.35 (0.33, 0-1.6) in 2020 improving to 0.19 (0.18, 0-1.3; P≤0.01) and 0.13 (0.14, 0-0.60; P<0.01) with contact lenses. Mean keratometry measurement in patients using SLs was 53.0 diopters (D) (9.9, 42.1-84.5), which was steeper than 46.6 D in patient's using all other lens types in 2010 and 2020 (3.9, 40.9-57.9; P<0.01). Scleral lens prescription increased during the past decade; however, corneal GP lenses remain the most frequent lens prescribed for patients with keratoconus in this cohort. Despite being prescribed for patients with the most advanced disease, SLs provide good visual acuity.

The use of a modern web-application to assist reusable toric lens fitting success

Purpose: Increasing numbers of online tools are available to assist ECPs in fitting contact lenses. In this study, the contact lens prescription of a reusable toric silicone hydrogel lens was determined using a traditional fitting guide and the results were compared to the prescription recommended by the lens fitting app OptiExpert™.

Toric lens fitting success supported by an online fitting App

Purpose: Increasing numbers of online tools are available to assist ECPs in fitting contact lenses. In this study, the contact lens prescription of a reusable toric silicone hydrogel lens was determined using a traditional fitting guide and the results were compared to the prescription recommended by the lens fitting app OptiExpert™.

Evaluation of Visual Performance according to Multifocal Contact Lens Prescription Methods in Presbyopia

Evaluation of Visual Performance according to Multifocal Contact Lens Prescription Methods in Presbyopia

The Survey on Refraction Protocol for Optical Aids to be More Accurate

Purpose : This study was to investigate the refraction protocal ongoing in the clinics when conducted dispensing, refraction and prescribing contact lens optical aids to be more accurate. Methods : A questionnaire covered three items refraction, dispensing and prescription of contact lenses and was conducted by 53 optometrists in Gyeonggi-do. Results : In the item refraction, 50(94.3%) optometrists answered checking visual acuity with habitual correction. When asked measuring the interpupillary distance, 24(45.3%) optometrists used a P.D. meter and 21(39.6%) used the value measured by the auto-refractometer. 23(43.4%) optometrists did not use the Jackson cross-cylinder after correcting astigmatism. The reasons were diverse; ‘not aware of the methods’(17.4%), ‘unnecessary to do(52.2%)’, ’not enough time(26.1%)’ and ‘unspecified(4.3%)’. 8(15.1%) optometrists did not doublecheck after prescribing contact lenses. Conclusion : In order to provide the best correction, the accurate refraction, dispensing and prescribing contact lenses must be fulfilled as well as the eye examinations required in the clinic.

Passive Verification: A Flawed System Putting Patients' Sight at Risk.

To assess the rate of erroneous or expired (invalid) contact lens prescriptions submitted for passive verification at two practice sites in Cleveland, OH. Passive verification facsimile (FAX) requests were collected from office staff at a county hospital (MetroHealth [MH]), and at a private ophthalmology group office (University Ophthalmology Associates [UOA]) in Cleveland, Ohio, from January 2013 to January 2018. A total of 415 verification requests were evaluated (339 MH, 75 UOA), 28.2% (104 MH, 13 UOA) were expired, 11.8% (48 MH, one UOA) were not under the care of the doctor to whom the request was directed, 8.9% (32 MH, 5 UOA) were incorrect, and 3.9% (16 MH, 0 UOA) did not complete fitting. The total rate of invalid prescriptions was 52.8% (200 MH, 19 UOA). There is a high rate of invalid prescriptions presented for passive verification. Although the majority of prescriptions are simply expired, there is a fraction of prescriptions that contain incorrect specification of lens parameters or no record of prescription by that doctor. The current mechanism of passive verification, with the burden on the provider for denial within a short time window, makes it likely that such prescriptions would be filled, potentially putting patient comfort and safety at risk.

Value of routine evaluation in asymptomatic soft contact lens wearers

ObjectivesLimited literature supports the value of routine contact lens examinations. The purpose of this study is to document complications diagnosed when subjectively successful planned replacement soft contact lens patients are evaluated to renew their existing contact lens prescriptions. MethodsAsymptomatic soft contact lens patients who presented to the University Eye Center at Ketchum Health (Anaheim, CA) and the Eye and Vision Center at the Massachusetts College of Pharmacy and Health Sciences (Worcester, MA) for routine contact lens comprehensive exams to renew existing contact lens prescriptions were professionally evaluated and their complications documented. All subjects presented without complaint and had a history of subjectively successful planned replacement soft lens wear for at least 1 year. ResultsA total of 202 subjects were recruited from both sites (age range 16–72 years; 76 male, 126 female; spherical contact lens optical power equivalent range: +7.75D to −19.25D). Considering health issues, one hundred and five (52%) patients were found to exhibit at least one undiagnosed complication (95% CI: 0.45-0.59): 70% were diagnosed with contact lens driven ocular complications; 54% were diagnosed with non-contact lens driven ocular health issues; and 4% showed signs of undiagnosed systemic disease. Of note, complication prevalence increases to 72% overall if both contact lens fit issues and contact lens care compliance problems are included as complications in analysis. ConclusionsA striking ocular health and contact lens complication rate in asymptomatic soft contact lens wearers is demonstrated across two different study sites. This data suggests that asymptomatic as well as symptomatic contact lens wearers require routine professional evaluations.

A survey on knowledge and attitude of Saudi female students toward refractive correction

BackgroundTo assess the general knowledge and attitude of refractive error correction methods among female Saudi university students.MethodsOne thousand, one hundred and sixty‐five female university students, between 17 and 32-years of age were randomly interviewed using self‐administered questionnaires with open and closed‐ended questions. The questions collected information on demographics (gender, age, educational status, college of study, and occupation), addressed general knowledge/perception of the difference between the professions of ophthalmology and optometry, and attitudes toward spectacle, contact lens (CL) usage, including coloured prescription CLs, and refractive surgery for correcting refractive errors.ResultsThe response rate was 90-per cent (1,052/1,165). Fifty‐two per cent had never had an eye examination and only 28-per cent correctly identified the difference between an ‘ophthalmologist’ and ‘optometrist’. Eighty‐one per cent knew that CLs instead of spectacles (81.8-per cent), and coloured CLs (89.7-per cent) can be used for correcting refractive errors. Concerning refractive surgery, although a majority (90-per cent) knew that the technique corrects refractive error and reduces dependency on spectacles/CLs, only five-per cent had experienced refractive surgery. Approximately, 46-per cent and 47-per cent used spectacles and CLs, respectively, and while the optometrist was the main source of CL prescriptions (41-per cent), most people visited the ophthalmologist for their eye examination (68-per cent). Surprisingly, 52-per cent had never had an eye examination, or had only had one or two eye examinations (50-per cent) in their lifetime. While 23-per cent of spectacle wearers chose to continue with spectacles at the end of the study, 64-per cent and 12-per cent preferred refractive surgery and CLs, respectively, for refractive correction. Lack of information and fear of complications, but not cost, hindered most people from uptake of CLs and refractive surgery.ConclusionThe students demonstrated high levels of knowledge and awareness of refractive correction methods, especially for refractive surgery. Although many consulted the optometrist or ophthalmologist for their eye examinations and corrective devices, many remain uncorrected and unaware of the main difference between both professions. The lack of information about correction methods and fear of complications may have affected their interest in uptake of eye services and should be addressed to increase uptake and prevent avoidable vision loss.

Contact lenses for vision correction in children and adolescents (literature review)

The use of contact lenses (CLs) in children and adoles¬cents is a topical subject that attracted even more atten¬tion during recent years due to the improvement of ma¬terials and types of CLs. According to research, more than 2 million children and adolescents use soft CLs in the USA alone. This results from both broad medical indications for the prescription of CLs and social reasons. The age at which contact lenses can be recommended for children is also an important subject that is being under debate. While some ophthalmologists believe that children can be introduced to soft contact lenses from the age of 12 years old, others think that the minimum age should be 14 years old. Some doctors, however, are against using contact lenses in children. Optometrists, not having the right to conduct cycloplegia, prefer to prescribe contact lenses to adolescents over 14 years old. On the other hand, the selection of CLs for children and adolescents does not depend on age, but on the indications for their application.

A survey of contact lens-related complications in a tertiary hospital in China.

To describe the type of complications related to contact lens (CL) wear in a tertiary hospital in XX, China. A retrospective study of 141 patients who complained discomfort after wearing contact lens on an outpatient basis of XX Hospital were conducted from the January 2012 to December 2015. The data included patients' demographics, lens type, history, slit-lamp examination, reports of corneal scrapings, culture, and examination of in vivo confocal microscopy. Binary logistic regression was used to analyse the possible factors which were associated with more severe corneal complications and superficial punctuate keratitis (SPK). About 86.52% were female and 13.48% were male, the age varied between 12 and 56 years old. Of the 141 patients, 82.27% were soft CL wearers, 2.84% were rigid gas permeable lens (RGP) wearers, and 14.89% patients used overnight orthokeratology. The most common complication was dry eye (36.88%), followed by SPK (36.17%) during these cases. Blepharitis and meibomian gland dysfunction (MGD) were noted in 31.91% of cases. Microbial keratitis was seen in 15 patients including 7 cases of Acanthamoeba keratitis. Age was a significant factor to be a case of corneal infection or inflammation [Exp (B)was 0.918, p=0.030], MGD and blepharitis was found to be significantly associated with being a case of SPK [Exp(B)was2.276, p=0.047]. The commonest complication was dry eye in this study, followed by SPK. Lid margin and meibomain gland should be paid attention to before contact lens prescription. Younger CL wearers need follow-up examinations.

소프트 콘택트렌즈 착용자의 피팅 상태에 따른 각막 이심률과 곡률반경과의 상관관계

Purpose. Because of a recent increase in use of soft contact lens at younger ages, in the present study, the correlation between corneal eccentricity and radius of curvature and fitting types of contact lens was investigated. Methods. The study evaluated the fitting status of targets through lens centration, push-up test, dynamic lag test and static lag test of lenses usually worn by 49 men and women (98eyes) in their 20s to 30s who put on soft contact lenses. After evaluation, the subjects were classified into 3 categories by fitting status(steep, aligment and flat). The radius of corneal curvature in the naked eyes was measured by using keratometer. Moreover the corneal eccentricity in the nasal side, temporal side, superior side and inferior side was measured by using the device capable of measuring the corneal eccentricity. Results. The radius of corneal curvature and corneal eccentricity of soft lenses worn by subjects were higher in the order of steep fitting and flat fitting, and the higher average corneal curvature radius and corneal eccentricity is intend to be more steep fitting(p=0.051, p=0.052). The corneal eccentricity showed a tendency to nasal fitting type at the higher eccentricity and temporal fitting type at the smaller eccentricity, statistically significant difference was observed(p<0.05). The study showed there were low correlation that nasal and temporal side at steep fitting, superior side at normal fitting and 4side(nasal, temporal, superior, inferior) at flat fitting, therefore when the corneal eccentricity changed the radius of corneal curvature also changed. The corneal eccentricity and the radius of corneal curvature showed statistically significant difference at 4side and each fitting types(p<0.05). Conclusions. The results of this study, the fitting status, of wearer are based on radius of corneal curvature and corneal eccentricity, and if lens fitting would be done considering that, it seems to be useful in a soft contact lens prescription.

Generating realistic retinal image for whole visual system modeling

Recent progress and improvements on optical technology have enabled us to measure the characteristics of the eye in great detail. It has also been shown that, even when myopia and astigmatism are completely corrected with spectacle, the retinal image is still blurred due to uneven refraction power of the cornea and the crystalline lens [1][2], an effect known as “irregular astigmatism”. However, almost all researches in visual science assume sharp images as input. Currently, a large-scale whole visual system models is being developed on a supercomputer to elucidate its complex function [3]. Moreover, it has been demonstrated that the blurred retinal images are gradually compensated at both, the retina and the cortex [4]. Therefore, we have developed an eye optics model which can calculate the blurred retinal image based on known physiological evidences to provide a more realistic input to retinal and visual cortex model. The proposed model is described by the linear image filter based on Artal's model [5]. It can process multi-spectral image for reproducing the spectral characteristics of photoreceptors. OTF (Optical transfer function) calculated from the wavefront aberration with spectral transmittance of the lens is used for image processing filter. The wavefront aberration is defined by Zernike Coefficients values (measured by wavefront aberrometer such as OPD-Scan or Shack-Hartman Sensor systems) or SCA values (power of sphero-cylindrical lens with its axis for spectacle lens or contact lens prescriptions). To consider the effects of diffraction, OTF is designed to vary depending on pupil diameter and wavelength. To account for aging effects, the spectral transmittance of the lens [6] was also implemented. As inputs of the model, multispectral images taken by multispectral camera or converted from RGB image can be utilized. We simulated a closed-loop system connecting the proposed model to a simple eye movement model and pupil model. The eye movement model generates random saccades and the pupil model modifies pupil diameter according to the mean luminance of retinal image. As a result, our model could reproduce the effect of chromatic aberration, pupil diameter and age on the blurred retinal image. By applying our model to the large-scale visual system model, it is expected to be able to evaluate the phenomena, for example, age dependent perception on visual illusions, blur compensation in retina or visual cortex, and so on.

RGP Material Selection Strategy and the Gel/RGP oxygen “Gap”

Three clinical strategies for optimizing corneal oxygenation by selection of rigid gas permeable (RGP) materials were inspected for validity, and corneal oxygenation supplied by a prototypical nonconventional hydrogel contact lens was comparatively assessed. Greater equivalent oxygen percentage (EOP) resulted with a hyperpermeable material (Dk > ]00) despite the larger critical thickness necessary for lens stability. For RGP lenses having significant refractive power and/or prism, it was found that selection of RGP materials with the highest available oxygen permeability also resulted in the flattest EOP profile. Superpermeable materials (60 < Dk ⩽ 100) could be used to approach the EOP profiles of hyperpermeable materials when refractive power remained low and lenses were cut more thinly than normally performed. A nonconventional hydrogel material (Dk = 35) greatly reduced, if not eliminated, the “oxygen advantage” of RGP over gel materials at points of critical thickness. Yet its EOP profile depended much more on additional thickness induced by incorporation of refractive and/or prismatic power. Therefore, a significant “oxygen gap” between the hydrogel and some RGP materials remained when refractive power and/or prism was required in the contact lens prescription.