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Transient terahertz time-domain spectroscopy (THz-TDS) imaging has emerged as a novel non-ionizing and noninvasive biomedical imaging modality, designed for the detection and characterization of a variety of tissue malignancies due to their high signal-to-noise ratio and submillimeter resolution. We report our design of a pair of aspheric focusing lenses using a commercially available lens-design software that resulted in about 200 × 200-µm2 focal spot size corresponding to the 1-THz frequency. The lenses are made of high-density polyethylene (HDPE) obtained using a lathe fabrication and are integrated into a THz-TDS system that includes low-temperature GaAs photoconductive antennae as both a THz emitter and detector. The system is used to generate high-resolution, two-dimensional (2D) images of formalin-fixed, paraffin-embedded murine pancreas tissue blocks. The performance of these focusing lenses is compared to the older system based on a pair of short-focal-length, hemispherical polytetrafluoroethylene (TeflonTM) lenses and is characterized using THz-domain measurements, resulting in 2D maps of the tissue refractive index and absorption coefficient as imaging markers. For a quantitative evaluation of the lens effect on the image resolution, we formulated a lateral resolution parameter, R2080, defined as the distance required for a 20-80% transition of the imaging marker from the bare paraffin region to the tissue region in the same image frame. The R2080 parameter clearly demonstrates the advantage of the HDPE lenses over TeflonTM lenses. The lens-design approach presented here can be successfully implemented in other THz-TDS setups with known THz emitter and detector specifications.

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PURPOSE: This study aimed to report the pattern of contact lens prescribing from the Gulf Cooperation Council (GCC) countries. METHODS: Optometrists in the GCC region were contacted to participate in a web-based survey hosted on Qualtrics XM (Provo, Utah, USA). The survey methodology was adapted from the International Contact Lens Prescribing Consortium, and participants were asked to report their last five lens fits. It collected information on practitioner demographics (age, gender, nationality, qualification, country of practice, and number of years of experience), CL user demographics (age and gender) and on lens specific details such as lens type, lens design, lens material, replacement plan, and modality of lens wear. Descriptive statistics were used to analyse and report the data. RESULTS: This study reports 739 contact lens fits by 174 practitioners from six GCC countries. The average age of the patients was 29.72 ± 9.07 (Mean ± SD) years and 64 % of them were females. The majority (80.2 %) were fitted with soft contact lenses, with 59 % preferring silicone hydrogels, 20 % wearing them for cosmetic purposes and nearly half of them disposed of their lenses daily (55 %). Among the RGP lenses, 41 % were scleral lenses. This survey demonstrated a greater proportion of new lens fits (55 % vs. 37 %), disposable hydrogel lens use (21 % vs. 13 %), and a preference for cosmetic contact lenses (20 % vs. 4 %) compared to the international data. CONCLUSION: The pattern of CL prescriptions in the GCC region closely resembled the global trend. The survey observed a higher preference towards frequent replacement soft lenses, a greater proportion of silicone hydrogel lenses, a higher percentage of rigid lens fits, a greater affinity for cosmetic contact lenses, and a higher percentage of new fits. These trends suggest that contact lens prescription habits in the region are likely to continue evolving in the future.

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Microendoscopes are commonly used in small lumens in the body, for which a focus near to the distal tip and ability to operate in an aqueous environment are paramount for navigation and disease detection. Commercially available distal optic systems below 1mm in diameter are severely limited, and custom micro lenses are generally very expensive. Gradient index of refraction (GRIN) singlets are available in small diameters but have limited optical performance adjustability. Three-dimensional (3D) printed monolithic optical systems are an emerging option that may be suitable for enabling high performance, close-focus imaging. In this manuscript, we compared the optical performance of three custom distal optic systems; a custom-pitch GRIN singlet, 3D-printed monolithic doublet, and 3D-printed monolithic triplet, with a nominal working distance (WD) of 1.5mm, 0.5mm and 0.4mm in 0.9% saline. These short WDs are ideal for microendoscopy in collapsed or flushed lumens such as pancreatic duct or fallopian tube. The GRIN singlet had performance limited only by the fiber bundle relay over 0.9mm to 1.6 mm depth of field (DOF). The 3D printed doublet was able to achieve a comparable DOF of 0.71mm, while the 3D printed triplet suffered the most limited DOF of 0.55mm. 3D printing enables flexible design of monolithic multi-element systems with aspheric surfaces of very short WDs and relative ease of integration.

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Purpose: Ocular pathology may be reduced by slowing myopia progression. The purpose of this study was to evaluate the potential of a novel custom-designed rigid gas permeable (RGP) contact lens to control high myopia by comparing the efficacy of multifocal RGP lenses and single-vision spectacles for high myopia control. Methods: The medical records of children fitted with spectacles or multifocal rigid gas-permeable lenses between January 2018 and May 2020 were retrospectively reviewed. Children (5-17 years) with non-cycloplegic spherical equivalent refraction of ≤ -6.00 D or spherical equivalent refraction > - 6.00 D with baseline axial length ≥ 26.5 mm, and astigmatism of ≥ -2.00 D were included. Axial length and refraction were measured at baseline, before fitting the participants with multifocal rigid gas-permeable lenses or spectacles, and at 1- and 2-year follow-up visits. Changes in axial length were compared between the groups. Results: Among the 77 children with 1-year follow-up data, the mean axial elongation was 0.20 ± 0.17 mm and 0.21 ± 0.14 mm in the multifocal rigid gas-permeable and control groups, respectively, without significant differences between groups (F = 0.004, p = 0.835). Among the 41 patients who completed 2 years of follow-up, the mean axial elongation values in the multifocal rigid gas-permeable and control groups were 0.21 ± 0.15 mm and 0.24 ± 0.13 mm, respectively, at the 1-year follow-up, and 0.37 ± 0.27 mm and 0.43 ± 0.23 mm, respectively, at the 2-year follow-up, without significant between-group differences at either time point (p = 0.224). Conclusion: Axial length increased at a similar rate in both the control (spectacles) and multifocal rigid gas-permeable lens groups, suggesting that multifocal rigid gas-permeable lenses have no significant impact on controlling high myopia progression compared with spectacles.

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To ascertain the theoretical impact of optical design variations of the intraocular lens (IOL) on the accuracy of IOL power formulas based on a single lens constant using a thick lens eye model. This impact was also simulated before and after optimization. We modeled 70 thick-lens pseudophakic eyes implanted with IOLs of symmetrical optical design and power comprised between 0.50 D and 35 D in 0.5-step increments. Modifications of the shape factor resulting in variations in the anterior and posterior radii of an IOL were made, keeping the central thickness and paraxial powers static. Geometry data from three IOL models were also used. Corresponding postoperative spherical equivalent (SE) were computed for different IOL powers and assimilated to a prediction error of the formula due to the sole change in optical design alone. Formula accuracy was studied before and after zeroization on a uniform and non-uniform realistic IOL power distribution. The impact of the incremental change in optic design variability depended on the IOL power. Design modifications theoretically induce an increase in the standard deviation (SD), Mean Absolute Error (MAE), and Root Mean Square (RMS) of the error. The values of these parameters reduce dramatically after zeroization. While the variations in optical design can affect refractive outcomes, especially in short eyes, the zeroization of the mean error theoretically reduces the impact of the IOL's design and power on the accuracy of IOL power calculation.

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The study assessed the contact lens prescribing patterns and associated factors in a university optometry clinic in Trinidad and Tobago. The data relating to habitual or new contact lens (CL) prescribing patterns among wearers over a two-year period were reviewed. Pearson's chi-squared test and logistic regression models were used to analyze the findings. The Hosmer-Lemeshow goodness-of-fit test was used to examine the model calibration. A total of 243 CL fits were analyzed, and the Homeshow-Lemeshow goodness-of-fit test indicated a good fit (χ2 (7) = 7.296, p = 0.399). The mean age of lens wearers was 29.6 ± 12.4 (mean ± SD); the majority, 155 (63.8 %) of whom, were 21 to 40 years old. Most lenses were fitted on females (64.2% of fits overall) and about half of the wearers (n = 122, 50.2%) were prescribed lenses for cosmetic purposes. Conventional soft CL were the most prescribed modality of wear, accounting for 129 (53.1%) of the fits. Age from 21 to 40 years was the predictor of lens type prescribed, and those in that age range were four times more likely to be prescribed soft lenses compared to other ages. The patterns of CL prescribing in a university optometry clinic in Trinidad and Tobago are similar to the global market trends with slight variations.

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PURPOSE: To evaluate factors related to myopia progression in children wearing either orthokeratology (OK) lenses or single-vision spectacles (SVS) for 2 years. STUDY DESIGN: Pooled-analysis retrospective intervention study. METHODS: This study involved 105 school-aged children wearing SVS who participated in the multi-center Myovision Study and 89 school-aged children wearing one of 3 OK lens types [Menicon Z Night (M, n = 27), αORTHO®-K (A, n = 32), and Emerald™ (E, n = 30)]. In the OK-lens patients, last examination was performed at ≥ 3-weeks post lens-wear discontinuation. Of the subjects, 102 SVS-Group and 79 OK-Group (M: n = 24, A: n = 28, and E: n = 27) children completed all examinations. A relationship between refractive error (RE) change and 7 factors (correction methods, baseline age, baseline RE, baseline axial length, gender, right or left eye, and follow-up period) was derived by multiple regression modeling. Via those same methods, we investigated the relationship between RE change and 7 factors including 3 OK-lens corrections. RESULTS: Related influence factors were correction method (0.85 D myopia reduction in the OK Group, P < 0.001), baseline age (0.16 D myopia reduction in older-age patients, P < 0.001), and baseline RE (0.12 D myopia reduction per 1 D myopia, P = 0.01). No relationship was found between RE change and OK-lens type. No serious adverse events occurred. CONCLUSION: Regardless of OK lens design, myopia progression in school-aged children was suppressed. The effect was examined not only via axial-length elongation but also RE change, and the myopia control effect by OK lenses was found to be 0.85 D over the 2-year period.

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PURPOSE: In absence of scleral lens standards, this article aims to provide an official definition of terms related to scleral lens fitting and manufacturing, in order to make more uniform the use of appropriate terms when describing, writing or lecturing about scelral lenses. Adoption of a common terminology may also favor more fruitful exchanges between eyecare practitioners and manufacturers. METHODS: A committee of 12 advances scleral lens clinicians met and develop a list of terms related to scleral lens fit and manufacturing. Litterature review was made using PubMed database with the keywords "scleral lenses" and "terminology". Other related publications such as textbooks were also considered valid references. Validation of the terms selected and their suggested definition was made by consultation of other experts in the field, over 2 years. A final version was adopted by the Scleral Lens Education Society late in 2018. RESULTS: This article contains three main sections. Section I provides the definition of a scleral lens. Section II addresses the general terminology habitually applied to contact lens field but in the context of scleral lens usage. Finally, Section III suggests a decription of terms specifically used when fitting or manufacturing scleral lenses. At the end, recommendations are made to manufacturers about the essential elements to provide to eyecare practitioners in order to help them understanding the lens design and to customize their fit. CONCLUSION: A common language is key to advancing the science and clinical practice of scleral lens fitting. The current terminology will help standardize this field, helping eyecare practitioners, educators, speakers and manufacturers to talk with the same language.

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A 54-year-old woman presented with recurrent redness and blurred vision of the left eye with elevated intraocular pressure (IOP) for one year. She was treated as "iridocyclitis" and ``Posner-Schlossman syndrome'' at the local hospitals. However, the patient developed intermittent ocular inflammation and hyphema. Patient had a cataract surgery and intraocular lens (IOL) implantation in the left eye one year before at the local hospital. A diagnostic procedure was performed and the possible pathogenesis was discussed.

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PURPOSE: Radial Refractive Gradient (RRG) spectacles are lenses specifically designed to minimize peripheral hyperopic defocus typically found in conventional spectacles. Our goals were: (1) to demonstrate a method to design such lenses; and (2) to quantify the exact foveal vision power errors induced by them. METHODS: The design procedure was based on a point-by-point sequential surface construction algorithm that designs a front aspheric surface (back surface is spherical) to achieve a given overall tangential focal length of the lens. A peripheral refraction model was built based on average peripheral refractive errors from a set of eyes. We designed four negative lenses with optical powers: -2.5, -5.0, -7.5 and -10.0 D, so that the tangential focal length of the lens matches the retinal conjugate surface. RESULTS: The lenses induce very small sagittal power errors in a wide range of off-axis field angles (30°), solving the problem of peripheral hyperopic defocus. However, such designs introduce non-negligible mean power errors (above 0.25 D from 7°, 6.8°, 7.1° and 7.8° for the -2.5, -5.0, -7.5 and -10.0 D lenses, respectively) for foveal vision in a rotating eye. CONCLUSION: Our results show the unavoidable errors introduced by RRG spectacles when used for dynamic foveal vision. The described method offers valuable information towards determining the best trade-off between controlling power errors for peripheral and foveal vision.

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With an explosive increase in the worldwide prevalence of presbyopia, development of an accommodating intraocular lens (IOL) with expansive accommodative amplitude remains the holy grail in lens-based refractive surgery. A dynamic change in the dioptric power of the eye can be accomplished by various strategies alone or in combination, including changes in the position, shape, or refractive index of a single- or dual- optic IOL. This article reviews the cumulative advances in these various lens designs, along with clinical outcomes and complications of those that have been implanted. The challenges that remain in each cat-egory are also highlighted.

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PURPOSE: To understand long-term contact lens prescribing habits of Canadian optometrists. METHODS: One thousand optometrists were surveyed annually from 2000 to 2015. Information was requested on the first ten patients examined after receiving the survey. RESULTS: Over the 16-year survey period, 1987 optometrists provided information on 19,143 patients. Mean age of the patients was 32.7±14.4years. Ratio of females to males was 2:1, the ratio of new fits to refits was 2:3. Soft contact lenses represented 94.5% of all fits. Rigid lenses were more often used as a refit compared to a new fit. Over the 16 years, market share for silicone hydrogel materials grew from 0% to 69.6%, mid-water content materials declined from 75.7% to 14.1%. The multifocal market share grew at the expense of spherical designs, with no change in toric lens fitting. Monthly soft lens replacement remained the preferred option at 48.2%, followed by daily disposable at 40.8%; two-weekly replacement declined to less than10% of patients by 2015. Extended wear was likely used to refit and only to a small proportion of wearers, representing 2.6% of SCL by 2015. The lens care system of choice throughout the period was multipurpose solutions, although the proportion for peroxide systems more than doubled by 2015 from 9.6%, to 21.1%. CONCLUSIONS: Over the 16-year period, SCL material preference changed to silicone hydrogels with monthly replacement being preferred; daily disposables replacing 2-weekly as the alternate. Lens care preference continued to be multipurpose solutions. Rigid lenses appear to be sustained for specialist fitting.

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Posterior capsule opacification (PCO) is the most common complication after cataract surgery, with an incidence of 30%. It tends to be considered a normal event in the natural history of cataract surgery. Better understanding of its pathophysiology and advancement of intraocular lens material and design along with the improvement of phacoemulsification technique have contributed to decrease the incidence of PCO. Although treatment by Nd: YAG laser posterior capsulotomy is quick and non-invasive, the opening of the posterior capsule may be associated with numerous complications. Prevention remains the best measure for controlling this pathology.

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PURPOSE: To compare lens orientation and rotational recovery of five currently available soft toric lenses. METHODS: Twenty subjects were recruited and trialed with each of the study lenses in a random order. Study lenses were PureVision(®) Toric (B&L), Air Optix(®) for Astigmatism (Alcon), Biofinity(®) Toric (CooperVision), Acuvue(®) Advance for Astigmatism (Vistakon), and Proclear(®) Toric (CooperVision). Lens orientation in primary position to determine the lens rotation form the vertical position and rotational recovery to primary gaze orientation following a 45° manual misorientation for the different lenses was compared. RESULTS: The Biofinity Toric showed the lowest rotation from the vertical position and the Proclear Toric the highest. Also, the highest and the lowest reorientation speed were related to the Biofinity Toric and the Acuvue Advance for Astigmatism, respectively. The Repeated Measures ANOVA showed a significant difference in the lens rotation (P=0.004) and rotational recovery (P<0.001) among different contact lenses and the performed multiple comparisons indicated differences in rotation and also in reorientation speed were only seen between the Biofinity Toric when compared to four other lenses (P<0.05). CONCLUSION: Although there was appropriate fitting, based upon lens orientation and reorientation speed, with each of the study lenses it would appear that the optimized ballast technique used in the design of the Biofinity Toric helps reduce lens rotation and improve rotational recovery compared to others.

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This study was performed to evaluate the correlationship between posterior capsular opacification and optic configuration of intraocular lens in extracapsular lens extraction with In-the-bag implantation of posterior chamber lens. We retrospectively studied the 455 cases of cataract operations that were performed between January 1993 and January 1995. All were in-the-bag placement and their optic designs were divided into two groups: a group of biconvex lens and a group of convex-plano lens with continuous laser ridge. The incidence of PCO in bicovex lens group was 7.0% and that of convex plano lens with laser ridge group was 7.1%. The difference in the rate of posterior capsular opacification between two groups was not statistically significant. The incidence of Nd: YAG laser posterior capsulotomy revealed 0.0% in continuous ridged group and 2.6% in biconvex group(p>0.05).

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Posterior capsule opacification(PCO) is a common complication of cataract surgery. The presence of a posterior chamber intraocular lens has been shown to decrease the incidence of the development of PCO. Moreover, there are evidences that the design of intraocular lens may also alter its development. Extracapsular lens extraction with implantation of posterior chamber lens were operated on a consecutive series of 230 eyes. These were evaluated in the viewpoint of PCO development after surgery. All were sulcus fixed and their optic designs were devided into two groups; a group of convex-plano lens with continuous laser ridge including convex-concave lens and a group of biconvex lens. The incidence of PCO was lower in convex-plano lens with continuous laser ridge group(6.7%) than that of boconvex lens group(18.9%). The incidence of Nd:YAG posterior capsulotomy marked 0.0% in continuous ridged group and 1.8% in biconvex group(p<0.05, p

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