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Lim S, Kim C, Jafari S, Park J, Garcia SS, Demer JL. Postmortem Digital Image Correlation and Finite Element Modeling Demonstrate Posterior Scleral Deformations during Optic Nerve Adduction Tethering. Bioengineering (Basel) 2024; 11:452. [PMID: 38790319 PMCID: PMC11117839 DOI: 10.3390/bioengineering11050452] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2024] [Revised: 04/25/2024] [Accepted: 04/28/2024] [Indexed: 05/26/2024] Open
Abstract
Postmortem human eyes were subjected to optic nerve (ON) traction in adduction and elevated intraocular pressure (IOP) to investigate scleral surface deformations. We incrementally adducted 11 eyes (age 74.1 ± 9.3 years, standard deviation) from 26° to 32° under normal IOP, during imaging of the posterior globe, for analysis by three-dimensional digital image correlation (3D-DIC). In the same eyes, we performed uniaxial tensile testing in multiple regions of the sclera, ON, and ON sheath. Based on individual measurements, we analyzed eye-specific finite element models (FEMs) simulating adduction and IOP loading. Analysis of 3D-DIC showed that the nasal sclera up to 1 mm from the sheath border was significantly compressed during adduction. IOP elevation from 15 to 30 mmHg induced strains less than did adduction. Tensile testing demonstrated ON sheath stiffening above 3.4% strain, which was incorporated in FEMs of adduction tethering that was quantitatively consistent with changes in scleral deformation from 3D-DIC. Simulated IOP elevation to 30 mmHg did not induce scleral surface strains outside the ON sheath. ON tethering in incremental adduction from 26° to 32° compressed the nasal and stretched the temporal sclera adjacent to the ON sheath, more so than IOP elevation. The effect of ON tethering is influenced by strain stiffening of the ON sheath.
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Affiliation(s)
- Seongjin Lim
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
| | - Changzoo Kim
- Department of Ophthalmology, Kosin University, Busan 49267, Republic of Korea;
| | - Somaye Jafari
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
| | - Joseph Park
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
| | - Stephanie S. Garcia
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
| | - Joseph L. Demer
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
- Neuroscience Interdepartmental Program, University of California, Los Angeles, CA 90095, USA
- Department of Neurology, University of California, Los Angeles, CA 90095, USA
- Department of Bioengineering, University of California, Los Angeles, CA 90095, USA
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Kim CZ, Lim S, Demer JL. Biomechanics Explains Variability of Response of Small Hypertropia to Graded Vertical Rectus Tenotomy. Am J Ophthalmol 2024; 265:21-27. [PMID: 38614193 DOI: 10.1016/j.ajo.2024.03.025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2024] [Revised: 03/18/2024] [Accepted: 03/25/2024] [Indexed: 04/15/2024]
Abstract
PURPOSE Small angle hypertropia in sagging eye syndrome is conveniently treated by graded vertical rectus tenotomy, yet an adjustable technique under topical anesthesia has been recommended because of variability of effect. We performed graded tenotomy in an experimental model to elucidate the reason for variability of response to this surgical procedure. DESIGN Experimental study. METHODS Thirty-two fresh bovine rectus musculotendon specimens were prepared including continuity with insertional sclera, and extending for a total 40 mm length to the proximal muscle bellies, and trimmed to 16 mm width. Specimens were anchored by the clamps at the scleral insertion and muscle belly ends within a physiological chamber. After preconditioning and elongation to 10% strain was imposed by a linear motor, tensile force was allowed to stabilize at a plateau state. Then 25%, 50%, 75%, 90%, and 100% marginal tenotomies were performed progressively as remnant forces were measured. RESULTS Tendon thickness averaged 0.29 ± 0.05 mm and width 19.71 ± 2.25 mm. On average, remnant force decreased linearly (R2 = 0.985) from 4.23 ± 1.34, 2.76 ± 0.88, 1.70 ± 0.73, 1.01 ± 0.49, 0.39 ± 0.10, and 0 N, at 0%, 25%, 50%, 75%, 90%, and 100% tenotomy. However, there was marked individual variability in effect among specimens, with coefficients of variation of 32%, 32%, 43%, 49%, and 27%, respectively. CONCLUSION On average, there is a linear relationship between graded rectus tenotomy and percentage force reduction, but the effect among individual tendons is large, paralleling the reported variation in surgical effect. This explains and implies continued advisability of adjustable technique in this procedure.
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Affiliation(s)
- Chang Zoo Kim
- From the Stein Eye Institute and Department of Ophthalmology, University of California, Los Angeles (C.K., S.L., J.L.D.), Los Angeles, California, USA; Department of Ophthalmology, College of Medicine, Kosin University (C.K.), Busan, Korea
| | - Seongjin Lim
- From the Stein Eye Institute and Department of Ophthalmology, University of California, Los Angeles (C.K., S.L., J.L.D.), Los Angeles, California, USA
| | - Joseph L Demer
- From the Stein Eye Institute and Department of Ophthalmology, University of California, Los Angeles (C.K., S.L., J.L.D.), Los Angeles, California, USA; Department of Neurology, University of California, Los Angeles (J.L.D.), Los Angeles, California, USA; Bioengineering Department, University of California, Los Angeles (J.L.D.), Los Angeles, California, USA.
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Moon S, Park J, Lim S, Suh SY, Le A, Demer JL. Scanning Laser Ophthalmoscopy Demonstrates Pediatric Optic Disc and Peripapillary Strain During Horizontal Eye Rotation. Curr Eye Res 2024; 49:437-445. [PMID: 38185657 DOI: 10.1080/02713683.2023.2295789] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2023] [Accepted: 12/08/2023] [Indexed: 01/09/2024]
Abstract
Purpose: We employed automated analysis of scanning laser ophthalmoscopy (SLO) to determine if mechanical strains imposed on disc, and retinal and choroidal vessels during horizontal duction in children differ from those of adults.Methods: Thirty-one children aged 11.3 ± 2.7 (standard deviation) years underwent SLO in central gaze, and 35° ab- and adduction. Automated registration with deep learning-based optical flow analysis quantified vessel deformations as horizontal, vertical, shear, and equivalent strains. Choroidal vessel displacements in lightly pigmented fundi, and central disc vessel displacements, were also observed.Results: As in adults, strain in vessels during horizontal duction was greatest at the disc and decreased with distance from it. Strain in the pediatric disc was similar to published values in young adults,1 but in the peripapillary region was greater and propagated significantly more peripherally to at least three disc radii from it. During adduction in children, the nasal disc was compressed and disc vessels distorted, but the temporal half experienced tensile strain, while peripapillary tissues were compressed. The pattern was similar but strains were less in abduction (p < .001). Choroidal vessels were visualized in 24 of the 62 eyes and shifted directionally opposite overlying retinal vessels.Conclusions: Horizontal duction deforms the normal pediatric optic disc, central retinal vessels, peripapillary retina, and choroid, shearing the inner retina over the choroid. These mechanical effects occur at the sites of remodeling of the disc, sclera, and choroid associated with typical adult features that later emerge later, including optic cup enlargement, temporal disc tilting, and peripapillary atrophy.
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Affiliation(s)
- Sunghyuk Moon
- Department of Ophthalmology, Stein Eye Institute, University of California, Los Angeles, CA, USA
- Department of Ophthalmology, Busan Paik Hospital, Inje University College of Medicine, Busan, Republic of Korea
| | - Joseph Park
- Department of Ophthalmology, Stein Eye Institute, University of California, Los Angeles, CA, USA
| | - Seongjin Lim
- Department of Ophthalmology, Stein Eye Institute, University of California, Los Angeles, CA, USA
- Department of Mechanical Engineering, University of California, Los Angeles, CA, USA
| | - Soh Youn Suh
- Department of Ophthalmology, Stein Eye Institute, University of California, Los Angeles, CA, USA
| | - Alan Le
- Alcon Research, Ltd, Lake Forest, CA, USA
| | - Joseph L Demer
- Department of Ophthalmology, Stein Eye Institute, University of California, Los Angeles, CA, USA
- Bioengineering Department, University of California, Los Angeles, CA, USA
- Neuroscience Interdepartmental Program, University of California, Los Angeles, CA, USA
- Department of Neurology, University of California, Los Angeles, CA, USA
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Kawai M, Goseki T, Hirasawa K, Ishikawa H, Shoji N. Changes in Optic Nerve Head Blood Flow During Horizontal Ocular Duction. Invest Ophthalmol Vis Sci 2024; 65:7. [PMID: 38170537 PMCID: PMC10768701 DOI: 10.1167/iovs.65.1.7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2023] [Accepted: 11/29/2023] [Indexed: 01/05/2024] Open
Abstract
Purpose In this study, we aimed to compare blood flow changes in the optic nerve head (ONH) during horizontal ocular duction among normal, primary open-angle glaucoma (POAG), and normal-tension glaucoma (NTG) eyes. Methods In this cross-sectional study, we included 90 eyes from 90 participants (30 control eyes, 30 POAG eyes, and 30 NTG eyes). ONH blood flow was measured with laser speckle flowgraphy using an external fixation light to induce central gaze, abduction, and adduction at 30 degrees for each eye. The mean blur rate (MBR) of the entire ONH area (MA), vascular region (MV), and tissue region (MT), and the change ratio were analyzed. The change ratio was defined as abduction or adduction value/central gaze value. Results In the control group, MA significantly decreased during adduction (22.9 ± 3.7) compared with that during central gaze (23.6 ± 3.9, P < 0.05). In the POAG group, MA (adduction = 17.4 ± 3.8 and abduction = 17.3 ± 3.6) and MV (adduction = 37.9 ± 5.6 and abduction = 38.0 ± 5.6) significantly decreased during adduction and abduction compared with those during central gaze (18.0 ± 4.1 and 39.5 ± 6.3, respectively, P < 0.05). In the NTG group, MA significantly decreased during adduction (17.4 ± 4.2) compared with that during central gaze (18.1 ± 4.6) and abduction (18.1 ± 4.8, P < 0.05). The change ratio did not differ between the glaucoma and control groups. Conclusions ONH blood flow decreased during horizontal ocular duction regardless of normal or glaucoma states; however, the change ratio was comparable between the normal and glaucoma groups.
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Affiliation(s)
- Manami Kawai
- Department of Ophthalmology, Kitasato University School of Medicine, Kanagawa, Japan
| | - Toshiaki Goseki
- Department of Ophthalmology, Kitasato University School of Medicine, Kanagawa, Japan
- Department of Ophthalmology, International University of Health and Welfare Atami Hospital, Shizuoka, Japan
| | - Kazunori Hirasawa
- Department of Ophthalmology, Kitasato University School of Medicine, Kanagawa, Japan
| | - Hitoshi Ishikawa
- Department of Orthoptics and Visual Science, Kitasato University School of Allied Health Sciences, Kanagawa, Japan
| | - Nobuyuki Shoji
- Department of Ophthalmology, Kitasato University School of Medicine, Kanagawa, Japan
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Park J, Moon S, Lim S, Demer JL. Scanning Laser Ophthalmoscopy Demonstrates Disc and Peripapillary Strain During Horizontal Eye Rotation in Adults. Am J Ophthalmol 2023; 254:114-127. [PMID: 37343739 DOI: 10.1016/j.ajo.2023.06.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2023] [Revised: 06/05/2023] [Accepted: 06/08/2023] [Indexed: 06/23/2023]
Abstract
PURPOSE We used automated image analysis of scanning laser ophthalmoscopy (SLO) to investigate mechanical strains imposed on disc, and retinal and choroidal vessels during horizontal duction in adults. DESIGN Deep learning analysis of optical images. METHODS The peripapillary region was imaged by SLO in central gaze, and 35° abduction and adduction, in younger and older healthy adults. Automated image registration was followed by deep learning-based optical flow analysis to track determine local tissue deformations quantified as horizontal, vertical, and shear strain maps relative to central gaze. Choroidal vessel displacements were observed when fundus pigment was light. RESULTS Strains in the retina and disc could be quantified in 22 younger (mean ± SEM, 26 ± 5 years) and 19 older (64 ± 10 years) healthy volunteers. Strains were predominantly horizontal and greater for adduction than for abduction. During adduction, maximum horizontal strain was tensile in the nasal hemi-disc, and declined progressively with distance from it. Strain in the temporal hemi-retina during adduction was minimal, except for compressive strain on the disc of older subjects. In abduction, horizontal strains were less and largely confined to the disc, greater in older subjects, and generally tensile. Vertical and shear strains were small. Nasal to the disc, choroidal vessels shifted nasally relative to overlying peripapillary retinal vessels. CONCLUSIONS Strain analysis during horizontal duction suggests that the optic nerve displaces the optic canal, choroid, and peripapillary sclera relative to the overlying disc and retina. This peripapillary shearing of the optic nerve relative to the choroid and sclera may be a driver of disc tilting and peripapillary atrophy.
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Affiliation(s)
- Joseph Park
- From the Department of Ophthalmology (J.P., S.M., S.L., J.L.D.), Stein Eye Institute, Los Angeles, California, USA
| | - Sunghyuk Moon
- From the Department of Ophthalmology (J.P., S.M., S.L., J.L.D.), Stein Eye Institute, Los Angeles, California, USA; Department of Ophthalmology (S.M.), Busan Paik Hospital, Inje University, Busan, Republic of Korea
| | - Seongjin Lim
- From the Department of Ophthalmology (J.P., S.M., S.L., J.L.D.), Stein Eye Institute, Los Angeles, California, USA; Department of Mechanical Engineering (S.L.), University of California Los Angeles, Los Angeles, California, USA
| | - Joseph L Demer
- From the Department of Ophthalmology (J.P., S.M., S.L., J.L.D.), Stein Eye Institute, Los Angeles, California, USA; Neuroscience Interdepartmental Program (J.L.D.), University of California Los Angeles, Los Angeles, California, USA; Department of Neurology (J.L.D.), University of California Los Angeles, Los Angeles, California, USA; Department of Bioengineering (J.L.D.), University of California Los Angeles, Los Angeles, California, USA.
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