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Silverman RH. Principles of Ophthalmic Ultrasound. EXPERT REVIEW OF OPHTHALMOLOGY 2023; 18:379-389. [PMID: 38370284 PMCID: PMC10871633 DOI: 10.1080/17469899.2023.2277781] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/14/2023] [Accepted: 10/27/2023] [Indexed: 02/20/2024]
Abstract
Introduction Ultrasound imaging of the eye was introduced over 50 years ago. While the physical principles of ultrasound imaging have not changed, technology has undergone tremendous and ongoing development. Areas covered The fundamentals of ultrasound physics, biometry (A-scan), structural imaging (B-scan) and blood-flow imaging and measurement (Doppler) will be described. Emphasis will be placed on technological development and potential future advances. Expert opinion While A- and B-scan ultrasound of the eye has traditionally been performed with focused single-element transducers, the introduction of annular and linear arrays has enhanced clinical utility. Future advances, especially in multielement arrays, and point-of-care systems promise amazing new capabilities for diagnostic imaging of the eye and orbit.
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A-scan ultrasound in ophthalmology: A simulation tool. Med Eng Phys 2021; 97:18-24. [PMID: 34756334 DOI: 10.1016/j.medengphy.2021.09.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Revised: 09/14/2021] [Accepted: 09/17/2021] [Indexed: 11/22/2022]
Abstract
In the present study, we developed a computational tool for simulating the ophthalmological applications of A-scan ultrasound, including cataract characterisation and biometry. A-scan biometry is used to measure the axial length (AL) of the eye before cataract surgery to calculate the refractive power of the intraocular lens to be implanted. Errors in the measurement of the AL lead to post-surgical refractive errors. The simulation tool was developed using the k-Wave Matlab toolbox, together with a user-friendly interface developed in Matlab. Diverse error sources were evaluated. Constant ultrasound speed assumptions may introduce refractive errors of up to 0.6 D; by contrast, probe positioning errors had a lower impact, of up to 0.11 D. The correct identification of the Bruch's membrane is limited not only by axial resolution constraints but also by the low reflection coefficient at the retina/choroid interface. Regarding cataract characterisation, the amplitudes of the echoes reflected at the lens interfaces are sensitive to diverse cataract types and severities, and a more realistic representation could be obtained by using a higher resolution in the eye grid; however, the required computational times would make simulations impracticable when using personal computers. The simulation tool shows good versatility for evaluating diverse aspects of A-scan biometry.
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Abstract
The use of focused ultrasound to obtain diagnostically significant information about the eye goes back to the 1950s. This review describes the historical and technological development of ophthalmic ultrasound and its clinical application and impact. Ultrasound, like light, can be focused, which is crucial for formation of high-resolution, diagnostically useful images. Focused, single-element, mechanically scanned transducers are most common in ophthalmology. Specially designed transducers have been used to generate focused, high-intensity ultrasound that through thermal effects has been used to treat glaucoma (via ciliodestruction), tumors, and other pathologies. Linear and annular transducer arrays offer synthetic focusing in which precise timing of the excitation of independently addressable array elements allows formation of a converging wavefront to create a focus at one or more programmable depths. Most recently, linear array-based plane-wave ultrasound, in which the array emits an unfocused wavefront and focusing is performed solely on received data, has been demonstrated for imaging ocular anatomy and blood flow. While the history of ophthalmic ultrasound extends back over half-a-century, new and powerful technologic advances continue to be made, offering the prospect of novel diagnostic capabilities.
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Affiliation(s)
- Ronald H Silverman
- Department of Ophthalmology, Columbia University Medical Center
- F.L. Lizzi Center for Biomedical Engineering, Riverside Research, New York, NY, USA
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Meister U, Ohnesorge B, Körner D, Boevé MH. Evaluation of ultrasound velocity in enucleated equine aqueous humor, lens and vitreous body. BMC Vet Res 2014; 10:250. [PMID: 25312851 PMCID: PMC4205291 DOI: 10.1186/s12917-014-0250-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Accepted: 10/06/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Sonographic ophthalmic examinations have become increasingly important in veterinary medicine. If the velocity of ultrasound in ocular tissues is known, the A-mode ultrasound method may be used to determine the axial intraocular distances, such as anterior chamber depth, lens thickness, axial length of the vitreous and axial globe length, which are required for intraocular lens (IOL) power calculations. To the authors' knowledge, the velocity of ultrasound in the ocular tissues of the horse was not previously determined. In the present study, 33 lenses, 29 samples of aqueous and 31 of vitreous from 35 healthy equine eyes have been examined. The corresponding ultrasound velocities are reported in dependence of age, temperature, gender and elapsed time after enucleation. RESULTS The velocity of ultrasound at 36°C in equine aqueous, lens and vitreous are 1529 ±10 m/s, 1654± 29 m/s and 1527 ±16 m/s respectively, and the corresponding conversion factors are 0.998± 0.007, 1.008 ±0.018 and 0.997 ±0.010. A linear increase of the speed of ultrasound with increasing temperature has been determined for aqueous and vitreous. No temperature dependence was found for the speed of ultrasound in the lens. The ultrasound velocity did not significantly differ (95%) on the basis of gender, age or time after enucleation during the first 72 hours after death. CONCLUSIONS Compared to human eyes, the ultrasound velocity in equine lental tissue deviates by one percent. Therefore, axial length measurements obtained with ultrasound velocities for the human eye must be corrected using conversion factors. For the aqueous and vitreous, deviations are below one percent and can be neglected in clinical settings.
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Affiliation(s)
- Ulrike Meister
- Stiftung Tierärztliche Hochschule Hannover, Klinik für Pferde, Bünteweg 9, 30559, Hannover, Germany.
| | - Bernhard Ohnesorge
- Stiftung Tierärztliche Hochschule Hannover, Klinik für Pferde, Bünteweg 9, 30559, Hannover, Germany.
| | - Daniel Körner
- Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universität Jena, 07743, Jena, Germany.
| | - Michael H Boevé
- Stiftung Tierärztliche Hochschule Hannover, Klinik für Pferde, Bünteweg 9, 30559, Hannover, Germany.
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Peyman GA, Ingram CP, Montilla LG, Witte RS. A High-Resolution 3D Ultrasonic System for Rapid Evaluation of the Anterior and Posterior Segment. Ophthalmic Surg Lasers Imaging Retina 2012; 43:143-51. [DOI: 10.3928/15428877-20120105-01] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Accepted: 10/28/2011] [Indexed: 11/20/2022]
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Tang J, Liu J. Variance of speed of sound and correlation with acoustic impedance in canine corneas. ULTRASOUND IN MEDICINE & BIOLOGY 2011; 37:1714-1721. [PMID: 21821348 DOI: 10.1016/j.ultrasmedbio.2011.06.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2011] [Revised: 06/16/2011] [Accepted: 06/20/2011] [Indexed: 05/31/2023]
Abstract
The clinical standard for measuring corneal thickness is ultrasound pachymetry that assumes a constant speed of sound. The purpose of this study was to examine the variance of speed of sound and its relationship with acoustic impedance in healthy eyes of canines with a large age span. Corneal speed of sound and acoustic impedance were measured in 34 canine eyes at room temperature (21 ± 1°C). The mean speed of sound was 1577 ± 10 m/s ranging from 1553 to 1594 m/s. There was a strong correlation between speed of sound and acoustic impedance (R = 0.84, p < 0.001). Corneal speed of sound had a small variance in healthy canines over 1-year-old, but was significantly lower in younger canines suggesting an age effect. The strong correlation between corneal speed of sound and acoustic impedance may offer a potential means to noninvasively detect abnormal speed of sound for more accurate corneal thickness estimation.
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Affiliation(s)
- Junhua Tang
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH 43210, USA
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Kao CY, Richdale K, Sinnott LT, Grillott LE, Bailey MD. Semiautomatic extraction algorithm for images of the ciliary muscle. Optom Vis Sci 2011; 88:275-89. [PMID: 21169877 PMCID: PMC3030281 DOI: 10.1097/opx.0b013e3182044b94] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
PURPOSE To develop and evaluate a semiautomatic algorithm for segmentation and morphological assessment of the dimensions of the ciliary muscle in Visante Anterior Segment Optical Coherence Tomography images. METHODS Geometric distortions in Visante images analyzed as binary files were assessed by imaging an optical flat and human donor tissue. The appropriate pixel/mm conversion factor to use for air (n = 1) was estimated by imaging calibration spheres. A semiautomatic algorithm was developed to extract the dimensions of the ciliary muscle from Visante images. Measurements were also made manually using Visante software calipers. Interclass correlation coefficients and Bland-Altman analyses were used to compare the methods. A multilevel model was fitted to estimate the variance of algorithm measurements that was due to differences within- and between-examiners in scleral spur selection vs. biological variability. RESULTS The optical flat and the human donor tissue were imaged and appeared without geometric distortions in binary file format. Bland-Altman analyses revealed that caliper measurements tended to underestimate ciliary muscle thickness at 3 mm posterior to the scleral spur in subjects with the thickest ciliary muscles (t = 3.6, p < 0.001). The percent variance due to within- or between-examiner differences in scleral spur selection was found to be small (6%) when compared with the variance because of biological difference across subjects (80%). Using the mean of measurements from three images, achieved an estimated interclass correlation coefficient of 0.85. CONCLUSIONS The semiautomatic algorithm successfully segmented the ciliary muscle for further measurement. Using the algorithm to follow the scleral curvature to locate more posterior measurements is critical to avoid underestimating thickness measurements. This semiautomatic algorithm will allow for repeatable, efficient, and masked ciliary muscle measurements in large datasets.
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Affiliation(s)
- Chiu-Yen Kao
- Department of Mathematics and Mathematical Biosciences Institute, College of Mathematics and Physical Sciences, The Ohio State University, Columbus, Ohio 43210, USA
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JANSSON F. Measurement of intraocular distances by ultrasound and comparison between optical and ultrasonic determinations of the depth of the anterior chamber. Acta Ophthalmol 2009; 41:25-61. [PMID: 13957439 DOI: 10.1111/j.1755-3768.1963.tb02420.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Oksala A, Lehtinen A. EXPERIMENTAL RESEARCHES ON VITREOUS HAEMORRHAGES AND ON THE ECHOGRAM EMITTED BY THEM. Acta Ophthalmol 2009. [DOI: 10.1111/j.1755-3768.1959.tb03397.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Oksala A, Varonen ER. EXPERIMENTELLE UND KLINISCHE UNTERSUCHUNGEN ZUR DICKENMESSUNG DER LEDERHAUT MIT ULTRASCHALL***. Acta Ophthalmol 2009. [DOI: 10.1111/j.1755-3768.1965.tb06371.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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LEHTINEN A, OKSALA A. A new quick method for measuring distances between ultrasonic echoes on echograms of the eye. Acta Ophthalmol 2009; 39:50-4. [PMID: 13760511 DOI: 10.1111/j.1755-3768.1961.tb02338.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Silverman RH, Patel MS, Gal O, Sarup A, Deobhakta A, Dababneh H, Reinstein DZ, Feleppa EJ, Coleman DJ. Effect of corneal hydration on ultrasound velocity and backscatter. ULTRASOUND IN MEDICINE & BIOLOGY 2009; 35:839-46. [PMID: 19195769 PMCID: PMC2705943 DOI: 10.1016/j.ultrasmedbio.2008.11.009] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2008] [Revised: 11/13/2008] [Accepted: 11/14/2008] [Indexed: 05/20/2023]
Abstract
The cornea's acoustic properties (speed-of-sound, backscatter, attenuation) are related to its state of hydration. Our aim was to determine these properties as a function of corneal hydration using high-frequency ultrasound. Bovine corneas were suspended in a Dexsol-equivalent corneal preservation medium at 33 degrees C and then immersed successively in 75%, 50% and 25% medium and distilled water. Using a 38-MHz focused ultrasound transducer, we measured speed-of-sound and corneal thickness (n = 8) and stromal backscatter (n = 6) after 45-min immersion in each medium. Corneal speed-of-sound was modeled as a function of corneal thickness. We found the mean speed-of-sound to be 1605.4 +/- 2.9 m/s in normotensive medium. The maximum observed speed-of-sound was 1616 m/s. As we decreased medium tonicity, the cornea swelled and the speed-of-sound decreased, reaching 1563.0 +/- 2.2 m/s in water. Average corneal thickness increased from 969 +/- 93 microm in 100% medium to 1579 +/- 104 microm in water. Going from 100% medium to water, stromal backscatter (midband-fit) increased from -60.0 +/- 0.8 dBr to -52.5 +/- 3.5 dBr, spectral slope increased from -0.119 +/- 0.021 to -0.005 +/- 0.030 dB/MHz and attenuation coefficient decreased from 0.927 +/- 0.434 to 0.010 +/- 0.581 dB/cm-MHz. The observed correlation between acoustic backscatter and attenuation with the speed-of-sound offers a potential means for more accurate determination of speed-of-sound and, hence, thickness in edematous corneas.
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Affiliation(s)
- Ronald H Silverman
- Department of Ophthalmology, Weill Medical College of Cornell University, New York, NY 10065, USA.
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Hayden BC, Kelley L, Singh AD. Ophthalmic Ultrasonography: Theoretic and Practical Considerations. ACTA ACUST UNITED AC 2008. [DOI: 10.1016/j.cult.2008.04.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Lafon C, Khokhlova VA, Kaczkowski PJ, Bailey MR, Sapozhnikov OA, Crum LA. Use of a bovine eye lens for observation of HIFU-induced lesions in real-time. ULTRASOUND IN MEDICINE & BIOLOGY 2006; 32:1731-41. [PMID: 17112959 DOI: 10.1016/j.ultrasmedbio.2006.07.035] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2005] [Revised: 07/13/2006] [Accepted: 07/27/2006] [Indexed: 05/12/2023]
Abstract
Study of coagulative lesion formation by high intensity focused ultrasound (HIFU) in tissue usually requires performing a sequence of experiments under different exposure conditions followed by tissue sectioning. This paper, inspired by the pioneering work of Frederic L. Lizzi, reports on the use of the bovine eye lens as a laboratory model to observe visually the development of HIFU-induced lesions. The first part of this work describes the measurement of the lens shape, density, sound speed and attenuation. The measured values were within the range of previously published values. In the second part, HIFU-induced lesion development was observed in real-time and compared with good agreement with theoretical simulation. Theoretical modeling included acoustic propagation, absorptive heating and thermal dose, as well as the experimentally measured lens characteristics. Thus, the transparent eye lens can be used as a laboratory phantom to facilitate the understanding of HIFU treatment in other tissues.
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Affiliation(s)
- Cyril Lafon
- Inserm, Université Claude Bernard Lyon 1, Lyon, France
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OKSALA A, LEHTINEN A. Use of the echogram in the location and diagnosis of intra-ocular foreign bodies. Br J Ophthalmol 1998; 43:744-52. [PMID: 14428551 PMCID: PMC509891 DOI: 10.1136/bjo.43.12.744] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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JANSSON F, SUNDMARK E. Determination of the velocity of ultrasound in ocular tissues at different temperatures. Acta Ophthalmol 1998; 39:899-910. [PMID: 14451255 DOI: 10.1111/j.1755-3768.1961.tb07754.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Hamidzada WA, Osuobeni EP. Ultrasound velocity in the aqueous and vitreous humours of the one-humped camel (Camelus Dromedarius). Clin Exp Optom 1998; 81:222-227. [PMID: 12482323 DOI: 10.1111/j.1444-0938.1998.tb06739.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/06/1998] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND: There are no previous reports on the velocity of ultrasound through the aqueous and vitreous humours of the one-humped camel. This information is required for determination of the depth of the aqueous and vitreous chambers and therefore the axial length. This knowledge together with other, yet to be determined, ocular dimensions will ultimately be used in drawing up a schematic eye for the camel. This will provide a tool for studying the visual capability of this animal. METHOD: A-mode ultrasonography was used to determine the velocity of sound through the aqueous and vitreous fluids of the one-humped camel. The fluids were obtained from freshly enucleated eyes. RESULTS: The average velocity of ultrasound through 20 aqueous and 22 vitreous humour samples kept at 20 degrees Celsius was 1,499 +/- 23 m/s and 1,497 +/- 24 m/s, respectively. CONCLUSION: We recommend that at 20 degrees Celsius a common value of 1,498 m/s should be adopted as the velocity of ultrasound through the aqueous and vitreous humours of the one-humped camel. This value is slower than in humans but similar to that of the cow and pig.
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Affiliation(s)
- Wali A Hamidzada
- Department of Biomedical Technology, College of Applied Medical Sciences, King Saud University, PO Box 10219, Riyadh 11433, Saudi Arabia.
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El-Maghraby HM, Nyland TG, Bellhorn RW. ULTRASONOGRAPHIC AND BIOMETRIC EVALUATION OF SHEEP AND CATTLE EYES. Vet Radiol Ultrasound 1995. [DOI: 10.1111/j.1740-8261.1995.tb00236.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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Thijssen JM. The history of ultrasound techniques in ophthalmology. ULTRASOUND IN MEDICINE & BIOLOGY 1993; 19:599-618. [PMID: 8134966 DOI: 10.1016/0301-5629(93)90068-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The history of 50 years of applications of ultrasound in ophthalmology is described. This period started in 1938 with a study of the possible effects of high intensity ultrasound on eyes. The measurement of biological effects for the assessment of potential hazards characterizes the first decades. More recently, the therapeutic use of ultrasound by hyperthermia has gained much interest in ophthalmology. Further topics are: the measurement of acoustic characteristics of ocular tissues; the biometry of the eye ball, the results of which are used to calculate the optical power of artificial lens implants; the development of diagnostic instruments in various parts of the world; and ultrasonic tissue characterization for the differential diagnosis of pathology. The final topic is concerned with some recent developments which present a look into the future.
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Affiliation(s)
- J M Thijssen
- Biophysics Laboratory, University Hospital St. Radboud, Nijmegen, The Netherlands
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Shugar JK, de Juan E, McCuen BW, Tiedeman J, Landers MR, Machemer R. Ultrasonic examination of the silicone-filled eye: theoretical and practical considerations. Graefes Arch Clin Exp Ophthalmol 1986; 224:361-7. [PMID: 3519372 DOI: 10.1007/bf02150030] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
As the use of silicone oil in the treatment of complex retinal detachment becomes more frequent, an accurate assessment of ocular structures in these eyes by ultrasonic imaging is increasingly important. Because of the ultrasonic properties of silicone oil, the interpretation of ultrasound images of the silicone-filled eye is difficult. We have developed a mathematical model of ultrasound propagation in the eye. Using a computer simulation with graphic output, we have been able to make calculations concerning the interpretation and limitations of ultrasound examination in patients with intraocular silicone oil.
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Chivers RC, Round WH, Zieniuk JK. Investigation of ultrasound axially traversing the human eye. ULTRASOUND IN MEDICINE & BIOLOGY 1984; 10:173-188. [PMID: 6390896 DOI: 10.1016/0301-5629(84)90216-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
A ray tracing model for ultrasonic propagation through the human eye, including the lens, has been developed on the assumptions of lossless media and non-reflecting interfaces. Measurement of the distribution of an ultrasonic beam before and after traversing specimens of human eyes in vitro, and of the velocity of ultrasound in the various dissected media, has permitted some comparison of the predictions of the model with experiment. The agreement is good although there are significant limitations involved and these are discussed. For imaging systems the effect of the eye arises largely from the lens which acts as a defocussing lens of focal length approx. 13.5 cm. Although the experiments were performed at approx. 4 MHz, the validity of the ray tracing model is largely frequency independent and will be appropriate at the higher frequencies commonly used in ophthalmology.
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Abstract
The power of an intraocular lens can be calculated before surgery to make the eye emmetropic or ametropic. The physiological mechanism of accommodation however, cannot be restored with an inelastic lens. An increased depth of focus in the implanted eye can be predicted through optical principles alone, if the postoperative ametropia of the implanted eye is a simple myopic astigmatism. This increased depth of focus without accommodation was tested in artificial ametropia and found to be used in nature by the seal. To increase the precision of intraocular lens calculation the average change in corneal power induced at surgery is used to predict the postoperative corneal power. By controlled suture release in the postoperative phase, the amount of induced corneal astigmatism is adjusted to obtain a simple myopic astigmatism. Patients with an intraocular lens and a simple myopic astigmatism as a residual ametropia, are spectacle independent most of the time. They need their glasses only for driving or prolonged reading. The methods used to calculate the postoperative cornea, the postoperative anterior chamber depth and the intraocular lens are described with the corresponding calculator programs for the HP 41C calculator. Clinical results and measurements of the depth of focus are shown in a series of 50 successive implant cases.
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STALLKAMP H, NOVER A. Diagnostische Ultraschalluntersuchungen am gesunden Auge. Graefes Arch Clin Exp Ophthalmol 1962; 164:399-410. [PMID: 13916128 DOI: 10.1007/bf00682360] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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