The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Jost B Jonas - One of the best experts on this subject based on the ideXlab platform.
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relationship between the alignment of a non mydriatic fundus camera anterior chamber depth and axial length
Eye science, 2012Co-Authors: Yaqin Zhang, Liang Xu, Yaxing Wang, Xin Wang, Jost B JonasAbstract:Purpose:To evaluate the relationship between the position of the focal adjustment knob of a fundus camera and Refractive error and biometric data as measured in the same eye.Methods:Normal eyes of patients presenting to clinics at the Beijing Tongren Hospital were examined with a non-mydriatic fundus camera.The position on the focal scale of a knob adjusting the distance between the camera lens and film plane,used to adjust focus the image of the patients fundus relative to the Refractive Power of the eye,was recorded in degrees.Ocular biometry and refractometry were performed on the same eyes.Results:The study included 136 subjects with a mean age of 36.5 ±19.6 years and a mean Refractive error of-1.31 ±2.77 diopters.In univariate analysis,the position of the adjustment knob was significantly associated with Refractive error.(P < 0.001;correlation coefficient r=-0.77),axial length.(P<0.001;r=0.65) and anterior chamber depth (P<0.001;r=0.48).After adjustment for age,anterior chamber depth decreased by 0.01 mm(95% confidence interval:0.003,0.017) for change per degree in the position of the adjustment knob.Conclusion:A fundus camera can be used to estimate anterior chamber depth,axial length and Refractive error.In a screening setting,a fundus camera operated by a technician may be helpful to detect a shallow anterior chamber and evaluate a potential risk factor for primary angle closure.
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Crystalline Lens Power and Refractive Error
Investigative ophthalmology & visual science, 2012Co-Authors: Rafael Iribarren, Ian G. Morgan, Vinay Nangia, Jost B JonasAbstract:PURPOSE To study the relationships between the Refractive Power of the crystalline lens, overall Refractive error of the eye, and degree of nuclear cataract. METHODS All phakic participants of the population-based Central India Eye and Medical Study with an age of 50+ years were included. Calculation of the Refractive lens Power was based on distance noncycloplegic Refractive error, corneal Refractive Power, anterior chamber depth, lens thickness, and axial length according to Bennett's formula. RESULTS The study included 1885 subjects. Mean Refractive lens Power was 25.5 ± 3.0 D (range, 13.9-36.6). After adjustment for age and sex, the standardized correlation coefficients (β) of the association with the ocular Refractive error were highest for crystalline lens Power (β = -0.41; P < 0.001) and nuclear lens opacity grade (β = -0.42; P < 0.001), followed by axial length (β = -0.35; P < 0.001). They were lowest for corneal Refractive Power (β = -0.08; P = 0.001) and anterior chamber depth (β = -0.05; P = 0.04). In multivariate analysis, Refractive error was significantly (P < 0.001) associated with shorter axial length (β = -1.26), lower Refractive lens Power (β = -0.95), lower corneal Refractive Power (β = -0.76), higher lens thickness (β = 0.30), deeper anterior chamber (β = 0.28), and less marked nuclear lens opacity (β = -0.05). Lens thickness was significantly lower in eyes with greater nuclear opacity. CONCLUSIONS Variations in Refractive error in adults aged 50+ years were mostly influenced by variations in axial length and in crystalline lens Refractive Power, followed by variations in corneal Refractive Power, and, to a minor degree, by variations in lens thickness and anterior chamber depth.
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corneal Refractive Power and its associations with ocular and general parameters the central india eye and medical study
Ophthalmology, 2011Co-Authors: Jost B Jonas, Vinay Nangia, Ajit Sinha, Rajesh GuptaAbstract:Purpose To investigate the normal distribution of corneal Refractive Power (CRP) and its associations with other ocular and systemic parameters in the Central Indian population. Design Population-based study. Participants The Central India Eye and Medical Study is a population-based study performed in a rural region of Central India. The study comprised 4711 subjects aged 30+ years. Methods A detailed ophthalmic and medical examination was performed. Horizontal and vertical CRP were measured using a non-automatic keratometer. Main Outcome Measures Corneal Refractive Power. Results After excluding pseudophakic or aphakic eyes, keratometric measurements were available on 9024 eyes of 4617 study participants (98.0%) with a mean age of 49.1±13.2 years (range, 30–100 years) and a mean Refractive error of −0.20±1.52 diopters (D). Mean horizontal CRP was 44.60±1.68 D (mean ± standard deviation; range, 36.5–52.0 D), and vertical CRP was 44.62±1.74 D (range, 37.75–52.0 D) with no significant difference between both parameters ( P =0.27). In multivariate analysis, CRP was significantly ( P P P =0.02), and lower body height ( P P P P P Conclusions Horizontal CRP increased with higher age, lower level of education, lower body height, thinner central cornea, deeper anterior chamber, shorter axial length, and myopic Refractive error. The association with age may be of importance for Refractive surgery. The association of a steeper cornea with a shorter body stature and a shorter axial length parallels an association between shorter body length and shorter axial length without association with Refractive error. The association among steeper cornea, shorter body length, and lower educational level complements the association between shorter body length and lower educational level. The correlation between steeper cornea and deeper anterior chamber may be explained geometrically. Financial Disclosure(s) The author(s) have no proprietary or commercial interest in any materials discussed in this article.
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central corneal thickness and its association with ocular and general parameters in indians the central india eye and medical study
Ophthalmology, 2010Co-Authors: Vinay Nangia, Jost B Jonas, Ajit Sinha, Arshia Matin, Maithili KulkarniAbstract:Purpose To evaluate the distribution of central corneal thickness (CCT) and its associations in an adult Indian population. Design Population-based study. Participants The Central India Eye and Medical Study is a population-based study performed in a rural region close to Nagpur in Central India; it included 4711 subjects (ages 30+ years) of 5885 eligible subjects (response rate, 80.1%). Methods The participants underwent a detailed ophthalmic and medical examination, including 200 standardized questions on socioeconomic background, lifestyle, social relations, and psychiatric depression. This study was focused on CCT as measured by sonography and its associations. Intraocular pressure was measured by applanation tonometry. Main Outcome Measures Central corneal thickness and intraocular pressure. Results Central corneal thickness measurement data were available on 9370 (99.4%) eyes. Mean CCT was 514±33 μm (median, 517 μm; range, 290–696 μm). By multiple regression analysis, CCT was associated significantly with younger age ( P P P = 0.006), lower corneal Refractive Power ( P P = 0.02), thicker lens ( P = 0.02), and shorter axial length ( P = 0.006). Central corneal thickness was not associated significantly with Refractive error ( P = 0.54) or cylindrical Refractive error ( P = 0.20). If eyes with a corneal Refractive Power of 45 or more diopters were excluded, the relationship between CCT and axial length was no longer statistically significant ( P >0.05), whereas all other relationships remained significant. Intraocular pressure readings increased significantly ( P Conclusions Indians from rural Central India have markedly thinner corneas than do Caucasians or Chinese, and, as in other populations, CCT is greater in men. CCT was associated with younger age, higher body mass index, lower corneal Refractive Power, deeper anterior chamber, thicker lens, and shorter axial length. Intraocular pressure readings were associated with CCT, with high readings in those eyes that had thick corneas or steep corneas. Central corneal thickness and steepness of the anterior corneal surface may thus both have to be taken into account when applanation tonometry is performed. Financial Disclosure(s) The author(s) have no proprietary or commercial interest in any materials discussed in this article.
Masatoshi Ishikawa - One of the best experts on this subject based on the ideXlab platform.
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high speed liquid lens with 2 ms response and 80 3 nm root mean square wavefront error
Proceedings of SPIE the International Society for Optical Engineering, 2010Co-Authors: Hiromasa Oku, Masatoshi IshikawaAbstract:A liquid lens structure with a step response time of 2 ms, a Refractive Power range of 52 D, and a root-meansquare (RMS) wavefront error of 80.3 nm is reported. This lens uses a liquid-liquid interface with a pinned contact line as a variable Refractive surface, and its shape is controlled by a piezo stack actuator via a built-in hydraulic amplifier. The potential applications of this device include axial focus scanning of microscopes and focusing/zooming of camera lenses and machine vision systems.
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high speed liquid lens with 2 ms response and 80 3 nm root mean square wavefront error
Applied Physics Letters, 2009Co-Authors: Hiromasa Oku, Masatoshi IshikawaAbstract:A liquid lens structure with a step response time of 2 ms, a Refractive Power range of 52 D, and a root-mean-square (rms) wavefront error of 80.3 nm is reported. This lens uses a liquid-liquid interface with a pinned contact line as a variable Refractive surface, and its shape is controlled by a piezostack actuator via a built-in hydraulic amplifier. The measured wavefront error suggests that the method of pinning the contact line to a precise shape is an important factor in achieving higher optical performance.
Douglas D Koch - One of the best experts on this subject based on the ideXlab platform.
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comparison of intraocular lens Power calculation methods in eyes that have undergone lasik
Ophthalmology, 2004Co-Authors: Li Wang, Marc A Booth, Douglas D KochAbstract:Abstract Objective To compare methods of calculating intraocular lens (IOL) Power for cataract surgery in eyes that have undergone myopic LASIK. Design Noncomparative case series. Participants Eleven eyes of 8 patients who had previously undergone myopic LASIK (amount of LASIK correction [±standard deviation], −5.50±2.61 diopters [D]; range, −8.78 to −2.38 D) and subsequently phacoemulsification with implantation of the SA60AT IOLs (Alcon Surgical, Inc., Fort Worth, TX) were included (Refractive error after cataract surgery, −0.61 ± 0.79 D; range, −2.0 to 1.0 D). Methods We evaluated the accuracy of various combinations of: (1) single-K versus double-K (in which pre-LASIK keratometry is used to estimate effective lens position) versions of the IOL formulas; the Feiz–Mannis method was also evaluated; (2) 4 methods for calculating corneal Refractive Power (clinical history, contact lens overrefraction, adjusted effective Refractive Power [EffRP adj ], and Maloney methods); and (3) 4 IOL formulas (SRK/T, Hoffer Q, Holladay 1, and Holladay 2). The IOL prediction error was obtained by subtracting the IOL Power calculated using various methods from the Power of the implanted IOL, and the F test for variances was performed to assess the consistency of the prediction performance by different methods. Main outcome measures Mean arithmetic IOL prediction error, mean absolute IOL prediction error, and variance of the IOL prediction error. Results Compared with double-K formulas, single-K formulas predicted lower IOL Powers than the Power implanted and would have left patients hyperopic in most cases; the Feiz–Mannis method had the largest variance. For the Hoffer Q and Holladay 1 formulas, the variances for EffRP adj were significantly smaller than those for the clinical history method (0.43 D 2 vs. 1.74 D 2 , P = 0.018 for Hoffer Q; 0.75 D 2 vs. 2.35 D 2 , P = 0.043 for Holladay 1). The Maloney method consistently underestimated the IOL Power but had significantly smaller variances (0.19–0.55 D 2 ) than those for the clinical history method (1.09–2.35 D 2 ; P Conclusions The most accurate method was the combination of a double-K formula and corneal values derived from EffRP adj . The variances in IOL prediction error were smaller with the Maloney and EffRP adj methods, and we propose a modified Maloney method and second method using Humphrey data for further evaluation.
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methods of estimating corneal Refractive Power after hyperopic laser in situ keratomileusis
Journal of Cataract and Refractive Surgery, 2002Co-Authors: Li Wang, David W Jackson, Douglas D KochAbstract:Purpose: To evaluate and compare methods of estimating corneal Refractive Power after hyperopic laser in situ keratomileusis (LASIK). Setting: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Methods: Using the clinical history method (HisRP) as the standard, the accuracy of values of corneal Refractive Power derived from the EyeSys Corneal Analysis System or Humphrey Atlas computerized videokeratography, the thin lens formula, and corneal topographic measurements modified according to the amount of LASIK-induced Refractive change were evaluated. Results: Thirty-four eyes of 19 patients were evaluated using EyeSys and 27 eyes of 16 patients were examined using Humphrey Atlas. Although the values derived from corneal topography and the thin lens formula correlated well with HisRP, the differences between HisRP and topographic values increased significantly with increasing hyperopic correction. When the values of corneal topographic measurements were modified according to the amount of LASIK-induced Refractive change, the accuracy was significantly improved (all P < .05) and the percentages of eyes within 0.5 diopter (D) and 1.0 D of the HisRP values exceeded 71% and 94%, respectively. Conclusion: Using the clinical history method as the standard, the most accurate method for determining corneal Refractive Power in hyperopic LASIK eyes was to adjust the postoperative corneal topographic measurement according to the amount of LASIK-induced Refractive change.
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a comparative analysis of five methods of determining corneal Refractive Power in eyes that have undergone myopic laser in situ keratomileusis
Ophthalmology, 2002Co-Authors: Abdelmonem M Hamed, Li Wang, Manjula Misra, Douglas D KochAbstract:Abstract Objective To evaluate the accuracy of computerized videokeratography, keratometry, and the Gaussian optics formula for measuring corneal Refractive Power in patients after myopic laser in situ keratomileusis (LASIK). Design Noncomparative case series. Participants One hundred eyes of 63 patients (mean age, 45.0 ± 10.9 [standard deviation] years) who underwent LASIK were included in the study. Methods Using the clinical history method as the standard, we evaluated the accuracy of values of corneal Refractive Power derived from computerized videokeratography (the EffRP value of the EyeSys Corneal Analysis System, which averages corneal Refractive Power over the central 3 mm), keratometry (K), the Gaussian optics formula (GauRP), and values of EffRP and keratometry as modified according to the amount of LASIK-induced Refractive change. Main outcome measures Correlation of measured corneal Power values to those obtained using clinical history method (HisRP). Results Although the values for HisRP were significantly correlated with postoperative EffRP and K values and with GauRP, postoperative EffRP and K values were higher than HisRP (0.87 ± 0.68 diopters [D] and 1.16 ± 1.10 D, respectively), and GauRP were lower than HisRP (0.44 ± 0.66 D) ( P Conclusions Using the clinical history method as the standard, we found that the most accurate method for determining corneal Refractive Power in post-LASIK eyes was to adjust the postoperative corneal measurement according to the amount of LASIK-induced Refractive change.
Vinay Nangia - One of the best experts on this subject based on the ideXlab platform.
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Crystalline Lens Power and Refractive Error
Investigative ophthalmology & visual science, 2012Co-Authors: Rafael Iribarren, Ian G. Morgan, Vinay Nangia, Jost B JonasAbstract:PURPOSE To study the relationships between the Refractive Power of the crystalline lens, overall Refractive error of the eye, and degree of nuclear cataract. METHODS All phakic participants of the population-based Central India Eye and Medical Study with an age of 50+ years were included. Calculation of the Refractive lens Power was based on distance noncycloplegic Refractive error, corneal Refractive Power, anterior chamber depth, lens thickness, and axial length according to Bennett's formula. RESULTS The study included 1885 subjects. Mean Refractive lens Power was 25.5 ± 3.0 D (range, 13.9-36.6). After adjustment for age and sex, the standardized correlation coefficients (β) of the association with the ocular Refractive error were highest for crystalline lens Power (β = -0.41; P < 0.001) and nuclear lens opacity grade (β = -0.42; P < 0.001), followed by axial length (β = -0.35; P < 0.001). They were lowest for corneal Refractive Power (β = -0.08; P = 0.001) and anterior chamber depth (β = -0.05; P = 0.04). In multivariate analysis, Refractive error was significantly (P < 0.001) associated with shorter axial length (β = -1.26), lower Refractive lens Power (β = -0.95), lower corneal Refractive Power (β = -0.76), higher lens thickness (β = 0.30), deeper anterior chamber (β = 0.28), and less marked nuclear lens opacity (β = -0.05). Lens thickness was significantly lower in eyes with greater nuclear opacity. CONCLUSIONS Variations in Refractive error in adults aged 50+ years were mostly influenced by variations in axial length and in crystalline lens Refractive Power, followed by variations in corneal Refractive Power, and, to a minor degree, by variations in lens thickness and anterior chamber depth.
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corneal Refractive Power and its associations with ocular and general parameters the central india eye and medical study
Ophthalmology, 2011Co-Authors: Jost B Jonas, Vinay Nangia, Ajit Sinha, Rajesh GuptaAbstract:Purpose To investigate the normal distribution of corneal Refractive Power (CRP) and its associations with other ocular and systemic parameters in the Central Indian population. Design Population-based study. Participants The Central India Eye and Medical Study is a population-based study performed in a rural region of Central India. The study comprised 4711 subjects aged 30+ years. Methods A detailed ophthalmic and medical examination was performed. Horizontal and vertical CRP were measured using a non-automatic keratometer. Main Outcome Measures Corneal Refractive Power. Results After excluding pseudophakic or aphakic eyes, keratometric measurements were available on 9024 eyes of 4617 study participants (98.0%) with a mean age of 49.1±13.2 years (range, 30–100 years) and a mean Refractive error of −0.20±1.52 diopters (D). Mean horizontal CRP was 44.60±1.68 D (mean ± standard deviation; range, 36.5–52.0 D), and vertical CRP was 44.62±1.74 D (range, 37.75–52.0 D) with no significant difference between both parameters ( P =0.27). In multivariate analysis, CRP was significantly ( P P P =0.02), and lower body height ( P P P P P Conclusions Horizontal CRP increased with higher age, lower level of education, lower body height, thinner central cornea, deeper anterior chamber, shorter axial length, and myopic Refractive error. The association with age may be of importance for Refractive surgery. The association of a steeper cornea with a shorter body stature and a shorter axial length parallels an association between shorter body length and shorter axial length without association with Refractive error. The association among steeper cornea, shorter body length, and lower educational level complements the association between shorter body length and lower educational level. The correlation between steeper cornea and deeper anterior chamber may be explained geometrically. Financial Disclosure(s) The author(s) have no proprietary or commercial interest in any materials discussed in this article.
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central corneal thickness and its association with ocular and general parameters in indians the central india eye and medical study
Ophthalmology, 2010Co-Authors: Vinay Nangia, Jost B Jonas, Ajit Sinha, Arshia Matin, Maithili KulkarniAbstract:Purpose To evaluate the distribution of central corneal thickness (CCT) and its associations in an adult Indian population. Design Population-based study. Participants The Central India Eye and Medical Study is a population-based study performed in a rural region close to Nagpur in Central India; it included 4711 subjects (ages 30+ years) of 5885 eligible subjects (response rate, 80.1%). Methods The participants underwent a detailed ophthalmic and medical examination, including 200 standardized questions on socioeconomic background, lifestyle, social relations, and psychiatric depression. This study was focused on CCT as measured by sonography and its associations. Intraocular pressure was measured by applanation tonometry. Main Outcome Measures Central corneal thickness and intraocular pressure. Results Central corneal thickness measurement data were available on 9370 (99.4%) eyes. Mean CCT was 514±33 μm (median, 517 μm; range, 290–696 μm). By multiple regression analysis, CCT was associated significantly with younger age ( P P P = 0.006), lower corneal Refractive Power ( P P = 0.02), thicker lens ( P = 0.02), and shorter axial length ( P = 0.006). Central corneal thickness was not associated significantly with Refractive error ( P = 0.54) or cylindrical Refractive error ( P = 0.20). If eyes with a corneal Refractive Power of 45 or more diopters were excluded, the relationship between CCT and axial length was no longer statistically significant ( P >0.05), whereas all other relationships remained significant. Intraocular pressure readings increased significantly ( P Conclusions Indians from rural Central India have markedly thinner corneas than do Caucasians or Chinese, and, as in other populations, CCT is greater in men. CCT was associated with younger age, higher body mass index, lower corneal Refractive Power, deeper anterior chamber, thicker lens, and shorter axial length. Intraocular pressure readings were associated with CCT, with high readings in those eyes that had thick corneas or steep corneas. Central corneal thickness and steepness of the anterior corneal surface may thus both have to be taken into account when applanation tonometry is performed. Financial Disclosure(s) The author(s) have no proprietary or commercial interest in any materials discussed in this article.
Ivan Pelivanov - One of the best experts on this subject based on the ideXlab platform.
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nearly incompressible transverse isotropy niti of cornea elasticity model and experiments with acoustic micro tapping oce
Scientific Reports, 2020Co-Authors: John J Pitre, Mitchell A Kirby, Tueng T Shen, Ruikang K Wang, Matthew Odonnell, Ivan PelivanovAbstract:The cornea provides the largest Refractive Power for the human visual system. Its stiffness, along with intraocular pressure (IOP), are linked to several pathologies, including keratoconus and glaucoma. Although mechanical tests can quantify corneal elasticity ex vivo, they cannot be used clinically. Dynamic optical coherence elastography (OCE), which launches and tracks shear waves to estimate stiffness, provides an attractive non-contact probe of corneal elasticity. To date, however, OCE studies report corneal moduli around tens of kPa, orders-of-magnitude less than those (few MPa) obtained by tensile/inflation testing. This large discrepancy impedes OCE’s clinical adoption. Based on corneal microstructure, we introduce and fully characterize a nearly-incompressible transversely isotropic (NITI) model depicting corneal biomechanics. We show that the cornea must be described by at least two shear moduli, contrary to current single-modulus models, decoupling tensile and shear responses. We measure both as a function of IOP in ex vivo porcine cornea, obtaining values consistent with both tensile and shear tests. At pressures above 30 mmHg, the model begins to fail, consistent with non-linear changes in cornea at high IOP.
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nearly incompressible transverse isotropy niti of cornea elasticity model and experiments with acoustic micro tapping oce
arXiv: Biological Physics, 2020Co-Authors: John J Pitre, Mitchell A Kirby, Tueng T Shen, Ruikang K Wang, Matthew Odonnell, Ivan PelivanovAbstract:The cornea provides the largest Refractive Power for the human visual system. Its stiffness, along with intraocular pressure (IOP), are linked to several pathologies, including keratoconus and glaucoma. Although mechanical tests can quantify corneal elasticity ex vivo, they cannot be used clinically. Optical coherence elastography (OCE), which launches and tracks shear waves to estimate stiffness, provides an attractive non-contact probe of corneal elasticity. To date, however, OCE studies report corneal moduli around tens of kPa, orders-of-magnitude less than those (few MPa) obtained by tensile/inflation testing. This large discrepancy impedes OCE's clinical adoption. Based on corneal microstructure, we introduce and fully characterize a nearly-incompressible transversally isotropic (NITI) model depicting corneal biomechanics. We show that the cornea must be described by two shear moduli, contrary to current single-modulus models, decoupling tensile and shear responses. We measure both as a function of IOP in ex vivo porcine cornea, obtaining values consistent with both tensile and shear tests. At pressures above 30 mmHg, the model begins to fail, consistent with non-linear changes in cornea at high IOP.