The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform
Richard Potvin - One of the best experts on this subject based on the ideXlab platform.
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Toric intraocular Lens orientation and residual refractive astigmatism: an analysis.
Clinical Ophthalmology, 2016Co-Authors: Richard Potvin, Brent A. Kramer, David R. Hardten, John P. BerdahlAbstract:PURPOSE: To analyze intraocular Lens (IOL) orientation data from an online Toric back-calculator (astigmatismfix.com) for determining if differences were apparent by Lens type. METHODS: A retrospective review of astigmatismfix.com Toric back-calculations that included IOL identification and intended orientation axis. RESULTS: Of 12,812 total validated calculation records, 8,229 included intended orientation and Lens identification data. Of the latter, 5,674 calculations (69%) involved Lenses oriented 5° or more from their intended position. Using estimated Toric Lens usage data, the percentage of Lenses with orientation ≥5° from intended was 0.89% overall, but the percentage varied significantly between specific Toric Lens brands (P
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Toric intraocular Lens orientation and residual refractive astigmatism an analysis
Clinical Ophthalmology, 2016Co-Authors: Richard Potvin, Brent A. Kramer, David R. Hardten, John P. BerdahlAbstract:PURPOSE: To analyze intraocular Lens (IOL) orientation data from an online Toric back-calculator (astigmatismfix.com) for determining if differences were apparent by Lens type. METHODS: A retrospective review of astigmatismfix.com Toric back-calculations that included IOL identification and intended orientation axis. RESULTS: Of 12,812 total validated calculation records, 8,229 included intended orientation and Lens identification data. Of the latter, 5,674 calculations (69%) involved Lenses oriented 5° or more from their intended position. Using estimated Toric Lens usage data, the percentage of Lenses with orientation ≥5° from intended was 0.89% overall, but the percentage varied significantly between specific Toric Lens brands (P<0.05). The percentage of back-calculations related to Lenses that were not oriented as intended was also statistically significantly different by Lens brand (P<0.05). When IOLs were misoriented, they were significantly more likely to be misoriented in a counterclockwise direction (P<0.05). This was found to be due to a bias toward counterclockwise orientation observed with one specific brand, a bias that was not observed with the other three brands analyzed here. CONCLUSION: The percentage of eyes with Lens orientation ≥5° from intended in the Toric Results Analyzer data set was <1% of Toric IOLs in general, with the relative percentage of Tecnis® Toric IOLs significantly higher than AcrySof® Toric IOLs. Both of these had higher rates than the Staar® Toric and Trulign® Toric Lenses, with the availability of higher Tecnis and AcrySof cylinder powers a likely contributing factor. The AcrySof Toric IOL appears to be less likely than the Tecnis Toric IOL to cause residual astigmatism as a result of misorientation. The Tecnis Toric IOL appears more likely to be misoriented in a counterclockwise direction; no such bias was observed with the AcrySof Toric, the Trulign® Toric, or the Staar Toric IOLs.
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comparison of visual outcomes after implantation of diffractive trifocal Toric intraocular Lens and a diffractive apodized bifocal Toric intraocular Lens
Clinical Ophthalmology, 2016Co-Authors: K Gundersen, Richard PotvinAbstract:PURPOSE: The aim of this study was to compare a new diffractive trifocal Toric Lens with an apodized diffractive bifocal Toric Lens in terms of refractive and visual acuity (VA) outcomes, including low-contrast VA (LCVA), as well as the patient's visual function 3 months after implantation. PATIENTS AND METHODS: This is a randomized prospective study involving bilateral implantation of a trifocal Toric or a bifocal Toric Lens. At 3 months postoperatively, the subject's vision was tested both uncorrected and with his/her best distance correction at: distance (4 m), intermediate (63 cm), and near (40 cm). Binocular defocus curves were measured with no correction and with the subject's best distance correction in place. Quality of vision was measured using the National Eye Institute Visual Function Questionnaire. RESULTS: A total of 22 patients were enrolled (eleven in each group). There was no statistically significant difference in the absolute change in measured rotation between 1 month and 3 months postoperatively between the two intraocular Lens (IOL) groups (P=0.98). At 3 months, the postoperative refraction and distance VA by eye were similar between groups. There was no statistically significant difference in the measured LCVA between groups (P=0.39). The defocus curve showed that at 67 cm, the trifocal Toric Lens had statistically significantly better VA when compared to the bifocal Toric Lens. There were no statistically significant differences by group for any of the National Eye Institute Visual Function Questionnaire scores (P>0.26 in all cases). CONCLUSION: The trifocal Toric IOL improved the intermediate vision without negatively impacting visual function and distance, near, or low-contrast VA when compared to a bifocal Toric IOL. The Toric component of the trifocal Lens effectively reduced astigmatism and provided good rotational stability.
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monte carlo simulation of expected outcomes with the acrysof Toric intraocular Lens
BMC Ophthalmology, 2008Co-Authors: Warren Hill, Richard PotvinAbstract:Background To use a Monte Carlo simulation to predict postoperative results with the AcrySof® Toric Lens, evaluating the likelihood of over- or under-correction using various Toric Lens selection criteria.
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Monte Carlo simulation of expected outcomes with the AcrySof^®Toric intraocular Lens
BMC Ophthalmology, 2008Co-Authors: Warren Hill, Richard PotvinAbstract:Background To use a Monte Carlo simulation to predict postoperative results with the AcrySof^® Toric Lens, evaluating the likelihood of over- or under-correction using various Toric Lens selection criteria. Methods Keratometric data were obtained from a large patient population with preoperative corneal astigmatism
John P. Berdahl - One of the best experts on this subject based on the ideXlab platform.
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Toric intraocular Lens orientation and residual refractive astigmatism: an analysis.
Clinical Ophthalmology, 2016Co-Authors: Richard Potvin, Brent A. Kramer, David R. Hardten, John P. BerdahlAbstract:PURPOSE: To analyze intraocular Lens (IOL) orientation data from an online Toric back-calculator (astigmatismfix.com) for determining if differences were apparent by Lens type. METHODS: A retrospective review of astigmatismfix.com Toric back-calculations that included IOL identification and intended orientation axis. RESULTS: Of 12,812 total validated calculation records, 8,229 included intended orientation and Lens identification data. Of the latter, 5,674 calculations (69%) involved Lenses oriented 5° or more from their intended position. Using estimated Toric Lens usage data, the percentage of Lenses with orientation ≥5° from intended was 0.89% overall, but the percentage varied significantly between specific Toric Lens brands (P
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Toric intraocular Lens orientation and residual refractive astigmatism an analysis
Clinical Ophthalmology, 2016Co-Authors: Richard Potvin, Brent A. Kramer, David R. Hardten, John P. BerdahlAbstract:PURPOSE: To analyze intraocular Lens (IOL) orientation data from an online Toric back-calculator (astigmatismfix.com) for determining if differences were apparent by Lens type. METHODS: A retrospective review of astigmatismfix.com Toric back-calculations that included IOL identification and intended orientation axis. RESULTS: Of 12,812 total validated calculation records, 8,229 included intended orientation and Lens identification data. Of the latter, 5,674 calculations (69%) involved Lenses oriented 5° or more from their intended position. Using estimated Toric Lens usage data, the percentage of Lenses with orientation ≥5° from intended was 0.89% overall, but the percentage varied significantly between specific Toric Lens brands (P<0.05). The percentage of back-calculations related to Lenses that were not oriented as intended was also statistically significantly different by Lens brand (P<0.05). When IOLs were misoriented, they were significantly more likely to be misoriented in a counterclockwise direction (P<0.05). This was found to be due to a bias toward counterclockwise orientation observed with one specific brand, a bias that was not observed with the other three brands analyzed here. CONCLUSION: The percentage of eyes with Lens orientation ≥5° from intended in the Toric Results Analyzer data set was <1% of Toric IOLs in general, with the relative percentage of Tecnis® Toric IOLs significantly higher than AcrySof® Toric IOLs. Both of these had higher rates than the Staar® Toric and Trulign® Toric Lenses, with the availability of higher Tecnis and AcrySof cylinder powers a likely contributing factor. The AcrySof Toric IOL appears to be less likely than the Tecnis Toric IOL to cause residual astigmatism as a result of misorientation. The Tecnis Toric IOL appears more likely to be misoriented in a counterclockwise direction; no such bias was observed with the AcrySof Toric, the Trulign® Toric, or the Staar Toric IOLs.
Chris Hunt - One of the best experts on this subject based on the ideXlab platform.
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Clinical evaluation of factors affecting soft Toric Lens orientation.
Optometry and Vision Science, 2009Co-Authors: Graeme Young, Roberta Mcilraith, Chris HuntAbstract:PURPOSE: To evaluate the comparative orientation characteristics of currently available silicone hydrogel Torics. METHODS: The re-orientation characteristics of four Toric Lenses were assessed: three prism-ballasted (PB) designs, Purevision Toric (PVT), Air Optix Toric (AOT), Proclear Toric (PCT), and an "Accelerated Stabilization Design" (ASD) ACUVUE ADVANCE for Astigmatism (AAfA). In the first part of the study, the Toric Lenses were rotated, approximately 45 degrees in the infero-temporal direction and a video recording of Lens reorientation was made from which blink-by-blink measurements of Lens orientation were taken. In the second part of the study, subjects were positioned with their head orientated 90 degrees to the vertical and Lens orientation photographed once it had settled. RESULTS: In Part 1, the speed of re-orientation from oblique mis location was similar for the four designs tested and ranged from 22°/min (PVT) to25°/min (AOT). Lenses showed more rotation during rather than between the blink (p
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clinical evaluation of factors affecting soft Toric Lens orientation
Optometry and Vision Science, 2009Co-Authors: Graeme Young, Roberta Mcilraith, Chris HuntAbstract:PURPOSE: To evaluate the comparative orientation characteristics of currently available silicone hydrogel Torics. METHODS: The re-orientation characteristics of four Toric Lenses were assessed: three prism-ballasted (PB) designs, Purevision Toric (PVT), Air Optix Toric (AOT), Proclear Toric (PCT), and an "Accelerated Stabilization Design" (ASD) ACUVUE ADVANCE for Astigmatism (AAfA). In the first part of the study, the Toric Lenses were rotated, approximately 45 degrees in the infero-temporal direction and a video recording of Lens reorientation was made from which blink-by-blink measurements of Lens orientation were taken. In the second part of the study, subjects were positioned with their head orientated 90 degrees to the vertical and Lens orientation photographed once it had settled. RESULTS: In Part 1, the speed of re-orientation from oblique mis location was similar for the four designs tested and ranged from 22°/min (PVT) to25°/min (AOT). Lenses showed more rotation during rather than between the blink (p<0.0001). Between blinks, AAfA and AOT showed significantly more rotation than PCT and PVT (p0.04). There were no significant differences between Lenses for rotation during the blink. The PB Lenses showed faster re-orientation further away from the zero position.AAfA showed no significant difference in rotation speed with varying orientation position. In Part 2, all the PB Lenses rotated significantly more under the effect of gravity than the ASD Lenses.The mean total rotation of the AAfA Lenses,from their settled position, was 11.4° compared with 25.9° for PVT (p0.01), 18.4° with AOT (p0.02) and 37.4° with PCT (p0.0002) [corrected]. The mean total rotation of the AAfA Lenses, from their settled position, was 11.2 degrees compared with 32.8 degrees for PVT (p < 0.001), 16.1 degrees with AOT and 33.1 degrees with PCT (p < 0.001). CONCLUSIONS: The four Lens designs show similar re-orientation speeds. In the recumbent position, PB Lenses rotate more from their normal settled position than ASD Lenses.
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Toric Lens orientation and visual acuity in non-standard conditions.
Contact Lens and Anterior Eye, 2009Co-Authors: Roberta Mcilraith, Graeme Young, Chris HuntAbstract:Purpose: To evaluate and compare the effect of gravity and gaze direction on Toric Lens orientation and visual acuity (VA). Method: This was a 14 subject, randomised, unmasked, non-dispensing study, relating to the effect of gaze direction and posture on Toric Lens orientation and VA. Four Lens types were assessed: Acuvue TM Oasys 1 for Astigmatism (AOfA), Purevision 1 Toric (PVT), Air Optix 1 for Astigmatism (AOT) and Proclear 1 Toric (PCT). In the first part of the study, subjects were positioned on their side and once Lenses had settled, VA was measured and photographs taken of the Lens orientation position. In the second part, the subjects were positioned at a slit-lamp and video-recordings taken as they changed from the primary gaze position to the eight cardinal directions of gaze. Results: In Part 1, all Lenses rotated as a result of change in posture and head position. With subjects in a recumbent position mean rotation ranged from 11.08 with AOfA to 29.18 with PCT. The consequent mean reduction in VA ranged from 0.05 logMAR for AOfA to 0.15 logMAR for PVT and was significantly worse with PVT and PCT compared with AOfA (P < 0.05). In Part 2, Lenses tended to show inferio-nasal rotation on upgaze and inferio-nasal rotation on downgaze. The AOfA Lenses showed less rotation on inferio-nasal version than each of the other designs (P < 0.005). The AOT Lenses showed significantly less rotation on superior-temporal version than PVT (P = 0.01). Conclusion: Toric soft contact Lens stability in extreme versions and postural positions can affect orientation and VA.
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clinical evaluation of factors influencing Toric soft contact Lens fit
Optometry and Vision Science, 2002Co-Authors: Graeme Young, Chris Hunt, Mike CoveyAbstract:Purpose. Some knowledge of the orientation position of Toric soft Lenses is required as part of the fitting process. Although it is known that factors such as lid anatomy, Lens design, and fit are important, there is little detailed understanding of how these relate to Toric Lens orientation. The purpose of this study was to evaluate various patient and Lens factors that might influence Toric soft Lens fit and to determine the predictor variables for Lens orientation. Methods. This was a clinical study in which 45 subjects were fitted with a prism-stabilized, mid-water, cast-molded, back surface Toric soft Lens. The Lens was representative of commonly used designs for frequent replacement Toric soft Lenses. Patient and Lens fit variables were assessed, including a range of lid topography features, which were measured using a digital photographic technique. Results. The main patient factors associated with Lens orientation and stability were degree of myopia, palpebral aperture, and several angles relating to lid anatomy. Greater upward incline of the temporal lids was associated with increasing inferior-temporal Lens orientation; lower myopia and smaller palpebral aperture size were associated with more stable Lens orientation. The principal Lens fit characteristics affecting Lens orientation were postblink movement and Lens tightness. Less movement was associated with more stable Lens orientation, and increased tightness was associated with slower reorientation speed. Weaker but significant correlations were also shown between a number of other patient and Lens variables. Conclusions. A number of patient factors and Lens fit characteristics influencing Toric soft Lens orientation were identified. The findings fall short of allowing practitioners to accurately predict Toric Lens orientation; however, they do provide some factors to consider when fitting Toric soft Lenses.
Samir I. Sayegh - One of the best experts on this subject based on the ideXlab platform.
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A Direct Method for Determining Toricity Ratios of Toric Intraocular Lens Calculators
Scientific Reports, 2018Co-Authors: Lauren G. Gabra, Samir I. SayeghAbstract:This study develops a method to determine Toricity ratios used by arbitrary Toric intraocular Lens calculators. Access to this information allows for the improvement of refractive results. We derive the Sayegh-Gabra formula, which uses input and output parameters in a Toric calculator to extract Toricity ratios that are typically not disclosed. We illustrate the method on a number of commercial calculators. For each calculator, high, average, and low axial length values are crossed with high, average, and low mean corneal power values to generate a 3 × 3 matrix. A Toricity ratio is generated for each axial length and mean corneal power pair. We thus identify several Toric Lens manufacturers’ calculators that use a constant Toricity ratio, often 1.46. Some others use a variable ratio centered at 1.46, but varying as axial length and mean K increases over a range of values corresponding to physiological myopia and hyperopia. There is an emerging trend away from constant Toricity ratios. Using our methodology, it is possible to extract the Toricity ratio used by specific calculators/manufacturers, distinguish those using constant versus variable Toricity ratios, and use this information to improve surgical outcomes by refining current and future Toric intraocular Lens calculators.
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Development of a universal Toric intraocular Lens calculator
Proceedings of SPIE, 2014Co-Authors: David Hjelmstad, Samir I. SayeghAbstract:We present a method for calculating the ideal Toric Lens to implant in astigmatic patients following cataract surgery. We show that the online calculators provided by major Toric IOL manufacturers are insufficient for both theoretical and practical reasons. We reveal important theoretical shortcomings in their approach, illustrated by a number of cases which demonstrate how the approach can lead to errors in Lens selection. Our approach combines the spherical and cylindrical power calculations into one, and allows for Lens data from any manufacturer to be used, eliminating the reliance on multiple programs.
Nathan Efron - One of the best experts on this subject based on the ideXlab platform.
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An international survey of Toric contact Lens prescribing
2020Co-Authors: Philip B. Morgan, Nathan Efron, Craig A. WoodsAbstract:Objectives To characterize Toric contact Lens prescribing worldwide. Methods Up to 1,000 survey forms were sent to contact Lens fitters in up to 39 countries between January and March every year for 5 consecutive years (2007–2011). Practitioners were asked to record data relating to the first 10 contact Lens fits or refits performed after receiving the survey form. Only data for Toric and spherical soft Lens fits were analyzed. Survey data collected since 1996 were also analyzed for 7 nations to assess Toric Lens fitting trends since that time. Results Data were collected in relation to 21,150 Toric fits (25%) and 62,150 spherical fits (75%). Toric prescribing ranged from 6% of Lenses in Russia to 48% in Portugal. Compared with spherical fittings, Toric fittings can be characterized as follows: older age (29.8 ± 11.4 years vs. 27.6 ± 10.8 years for spherical Lenses); men are overrepresented (38% vs. 34%); greater proportion of new fits (39% vs. 32%); use of silicone hydrogel Lenses (49% vs. 39%); and lower proportion of daily disposable Lenses (14% vs. 28%). There has been a continuous increase in Toric Lens prescribing between 1996 and 2011. The proportion of Toric Lens fits was positively related to the gross domestic product at purchasing power parity per capita for year 2011 (r2 = 0.21; P=0.004). Conclusions At the present time, in the majority of countries surveyed, Toric soft contact Lens prescribing falls short of that required to correct clinically significant astigmatism (≥0.75 diopters) in all Lens wearers.
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Contact Lens practice
2020Co-Authors: Nathan EfronAbstract:Part 1 Introduction HisTorical perspective. The anterior eye Visual optics Clinical instruments Part 2 Soft contact Lenses Soft Lens materials Soft Lens manufacture Soft Lens optics Soft Lens measurement Soft Lens design and fitting Soft Toric Lens design and fitting Soft Lens care systems Part 3 Rigid contact Lenses Rigid Lens materials Rigid Lens manufacture Rigid Lens optics Rigid Lens measurement Rigid Lens design and fitting Rigid Toric Lens design and fitting Rigid Lens care systems Part 4 Lens replacement modalities Unplanned Lens replacement Daily soft Lens replacement Planned soft Lens replacement Planned rigid Lens replacement Part 5 Special Lenses and fitting considerations Scleral Lenses Tinted Lenses Presbyopia Continuous wear Sport Keratoconus High ametropia Paediatric fitting Therapeutic applications Post-refractive Surgery Post-keratoplasty Orthokeratology Diabetes Part 6 Patient examination and management History taking Preliminary examination Patient education Aftercare Complications Digital imaging Compliance Practice management Appendices Index
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An international survey of Toric contact Lens prescribing
Eye & Contact Lens-science and Clinical Practice, 2013Co-Authors: Philip B. Morgan, Nathan Efron, Craig A. WoodsAbstract:OBJECTIVES: To characterize Toric contact Lens prescribing worldwide. METHODS: Up to 1,000 survey forms were sent to contact Lens fitters in up to 39 countries between January and March every year for 5 consecutive years (2007-2011). Practitioners were asked to record data relating to the first 10 contact Lens fits or refits performed after receiving the survey form. Only data for Toric and spherical soft Lens fits were analyzed. Survey data collected since 1996 were also analyzed for 7 nations to assess Toric Lens fitting trends since that time. RESULTS: Data were collected in relation to 21,150 Toric fits (25%) and 62,150 spherical fits (75%). Toric prescribing ranged from 6% of Lenses in Russia to 48% in Portugal. Compared with spherical fittings, Toric fittings can be characterized as follows: older age (29.8 ± 11.4 years vs. 27.6 ± 10.8 years for spherical Lenses); men are overrepresented (38% vs. 34%); greater proportion of new fits (39% vs. 32%); use of silicone hydrogel Lenses (49% vs. 39%); and lower proportion of daily disposable Lenses (14% vs. 28%). There has been a continuous increase in Toric Lens prescribing between 1996 and 2011. The proportion of Toric Lens fits was positively related to the gross domestic product at purchasing power parity per capita for year 2011 (r = 0.21; P=0.004). CONCLUSIONS: At the present time, in the majority of countries surveyed, Toric soft contact Lens prescribing falls short of that required to correct clinically significant astigmatism (≥ 0.75 diopters) in all Lens wearers.
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soft Toric contact Lens prescribing in different countries
Faculty of Health; Institute of Health and Biomedical Innovation, 2010Co-Authors: Nathan Efron, Philip B. Morgan, Eef Van Der Worp, Magne Helland, Motozumi Itoi, Deborah Jones, Jason J Nichols, Craig A. WoodsAbstract:There have been significant improvements in Toric soft contact Lens design over the past decade. Data from our international contact Lens prescribing survey were mined to assess recent trends in Toric soft contact Lens fitting. This survey was conducted by sending up to 1000 survey forms to contact Lens fitters in Australia, Canada, Japan, the Netherlands, Norway, the UK and the USA each year between 2000 and 2009. Practitioners were asked to record data relating to the first 10 contact Lens fits or refits performed after receiving the forms and to return them to us for analysis. The data revealed a gradual increase in the extent of Toric soft Lens fitting this century. Excluding Japan – which had a consistently low rate of soft Toric Lens fitting over the survey period – soft Toric Lenses now represent over 35% of all soft Lenses prescribed; it can be assumed that, on average (and again excluding Japan), all cases of astigmatism 0.75 D or less remains uncorrected among contact Lens wearers. Toric Lenses are fitted more to those who are older, full-time wearers and reusable Lens wearers, and less to those wearing silicone hydrogel and extended wear Lenses.
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Prescribing soft contact Lenses for astigmatism.
Contact Lens and Anterior Eye, 2009Co-Authors: Philip B. Morgan, Nathan EfronAbstract:There have been continued improvements in Toric soft Lens design over the past three decades. Data that we have gathered from annual contact Lens fitting surveys demonstrate a commensurate increase in Toric Lens fitting as a proportion of all soft Lenses fitted. The current Toric Lens prescribing rate (34% of all Lenses when cosmetic tints, monovision and multifocal Lenses are ignored) is roughly equivalent to the rate that would be achieved if all cases of astigmatism 1.00 D or more were fitted with Toric Lenses. Toric Lenses tend to be fitted more to males and prescribed for monthly rather than daily replacement.