title: In Vivo 3-Dimensional Strain Mapping of the Optic Nerve Head Following Intraocular Pressure Lowering by Trabeculectomy.
abstract: To map the 3-dimensional (3D) strain of the optic nerve head (ONH) in vivo after intraocular pressure (IOP) lowering by trabeculectomy (TE) and to establish associations between ONH strain and retinal sensitivity.
  
  
  
  Observational case series.
  
  
  
  Nine patients with primary open-angle glaucoma (POAG) and 3 normal controls.
  
  
  
  The ONHs of 9 subjects with POAG (pre-TE IOP: 25.3±13.9 mmHg; post-TE IOP: 11.8±8.6 mmHg) were imaged (1 eye per subject) using optical coherence tomography (OCT) (Heidelberg Spectralis, Heidelberg Engineering GmbH, Heidelberg, Germany) before (<21 days) and after (<50 days) TE. The imaging protocol was repeated for 3 controls in whom IOP was not altered. In each post-TE OCT volume, 4 tissues were manually segmented (prelamina, choroid, sclera, and lamina cribrosa [LC]). For each ONH, a 3D tracking algorithm was applied to both post- and pre-TE OCT volumes to extract IOP-induced 3D displacements at segmented nodes. Displacements were filtered, smoothed, and processed to extract 3D strain relief (the amount of tissue deformation relieved after TE). Strain relief was compared with measures of retinal sensitivity from visual field testing.
  
  
  
  Three-dimensional ONH displacements and strain relief.
  
  
  
  On average, strain relief (averaged or effective component) in the glaucoma ONHs (8.6%) due to TE was higher than that measured in the normal controls (1.07%). We found no associations between the magnitude of IOP decrease and the LC strain relief (P > 0.05), suggesting biomechanical variability across subjects. The LC displaced posteriorly, anteriorly, or not at all. Furthermore, we found linear associations between retinal sensitivity and LC effective strain relief (P < 0.001; high strain relief associated with low retinal sensitivity).
  
  
  
  We demonstrate that ONH displacements and strains can be measured in vivo and that TE can relieve ONH strains. Our data suggest a wide variability in ONH biomechanics in the subjects examined in this study. We further demonstrate associations between LC effective strain relief and retinal sensitivity.
authors.affiliation: Ophthalmic Engineering & Innovation Laboratory, Department of Biomedical Engineering, National University of Singapore, Singapore; Singapore Eye Research Institute, Singapore National Eye Centre, Singapore. Electronic address: mgirard@nus.edu.sg.
authors.forename: Michaël J A
authors.initials: MJ
authors.lastname: Girard
authors.affiliation: Ophthalmic Engineering & Innovation Laboratory, Department of Biomedical Engineering, National University of Singapore, Singapore.
authors.forename: Meghna R
authors.initials: MR
authors.lastname: Beotra
authors.affiliation: Ophthalmic Engineering & Innovation Laboratory, Department of Biomedical Engineering, National University of Singapore, Singapore.
authors.forename: Khai Sing
authors.initials: KS
authors.lastname: Chin
authors.affiliation: NIHR Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom.
authors.forename: Amanjeet
authors.initials: A
authors.lastname: Sandhu
authors.affiliation: NIHR Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom.
authors.forename: Monica
authors.initials: M
authors.lastname: Clemo
authors.affiliation: NIHR Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom.
authors.forename: Eleni
authors.initials: E
authors.lastname: Nikita
authors.affiliation: NIHR Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom.
authors.forename: Deborah S
authors.initials: DS
authors.lastname: Kamal
authors.affiliation: NIHR Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom.
authors.forename: Maria
authors.initials: M
authors.lastname: Papadopoulos
authors.affiliation: Université de la Polynésie française, Tahiti, French Polynesia.
authors.forename: Jean Martial
authors.initials: JM
authors.lastname: Mari
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore.
authors.forename: Tin
authors.initials: T
authors.lastname: Aung
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; NIHR Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom; Discipline of Clinical Ophthalmology and Eye Health, University of Sydney, Sydney, NSW, Australia.
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Strouthidis
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D001696:Biomechanical Phenomena; D005260:Female; D005902:Glaucoma, Open-Angle / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D021621:Imaging, Three-Dimensional; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009898:Optic Disk / Q000000981:diagnostic imaging / Q000503:physiopathology*; D009901:Optic Nerve Diseases / Q000000981:diagnostic imaging / Q000503:physiopathology*; D012160:Retina / Q000503:physiopathology; D041623:Tomography, Optical Coherence; D014065:Tonometry, Ocular; D014130:Trabeculectomy; D014786:Vision Disorders / Q000175:diagnosis; D014794:Visual Fields / Q000502:physiology