Novel approaches to model effects of subconjunctival blebs on flow pressure to improve clinical grading systems after glaucoma drainage surgery

Autoři: Yann Bouremel aff001;  Richard M. H. Lee aff001;  Ian Eames aff001;  Steve Brocchini aff001;  Peng Tee Khaw aff001
Působiště autorů: National Institute for Health Research (NIHR) Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom aff001;  UCL Department of Mechanical Engineering, London, United Kingdom aff002;  UCL School of Pharmacy, London, United Kingdom aff003;  Chelsea and Westminster Hospital NHS Foundation Trust, London, United Kingdom aff004
Vyšlo v časopise: PLoS ONE 14(10)
Kategorie: Research Article


Clinical grading systems following glaucoma filtration surgery do not include any effects of the bleb on the intra-ocular pressure and are relatively subjective, therefore carrying the risk of inter and/or intra-observer variability. The main objective of the study is to quantify and model the effect of subconjunctival bleb on flow pressure for assessment of clinical grading following glaucoma surgery. Subconjunctival bleb was created by inserting a tube into ex vivo rabbit eyes via an ab externo approach through the anterior chamber and exiting into the subconjunctival space. Sterile dyed water was injected through the tube into the developing bleb. For the in vitro approach a silicone bleb was created by clamping a circular silicone sheet, injecting dyed water through a fixed resistance outlet tube. Photographic measurements of the bleb height, planform area and pressure were taken as a function of time. Clinical blebs were also collected over a few months. Mathematical algorithm software was used to build the bleb model. Bleb height and volume increase as pressure in the bleb increases. The bleb planform area tended to a constant determined by the section of conjunctiva prior to shunt insertion. These increases were in accordance with the bleb model developed in the Appendix. They show that the pressure in the bleb is related to the resistance of the outflow. The linearity of clinical grading systems is reviewed and a new grading approach is proposed. The pressure in the bleb has a strong dependence on bleb extent, height and a weak dependence on conjunctival thickness. The pressure in a bleb can be estimated from bleb height, radius, and flow rate inlet in agreement with the bleb flow model. These results provide support for an improved bleb categorization system.

Klíčová slova:

Eyes – Flow rate – Glaucoma – Medical devices and equipment – Ophthalmic procedures – Rabbits – Surgical and invasive medical procedures – Silicones


1. Kingman S. Glaucoma is second leading cause of blindness globally. Bulletin of the World Health Organization. 2004;82(11):887–888. doi: /S0042-96862004001100019 15640929

2. Bouremel Y, Henein C, Lee RMH, Eames I, Brocchini S, Khaw PT. A novel 3D printed eye flow resistance model for intraocular pressure after glaucoma surgery: R1, R2 and R3. 2018; 59: ARVO E-abstract 2000.

3. Wells AP, Ashraff FNN, Hall RC, Puride G. Comparison of Two Clinical Bleb Grading Systems. Ophthalmology. 2006;113:77–83. doi: 10.1016/j.ophtha.2005.06.037 16389104

4. Cantor LB, Mantravadi A, WuDunn D, Swamynathan K Cortes A. Morphologic Classification of Filtering Blebs after Glaucoma Filtration Surgery: The Indiana Bleb Appearance Grading Scale. Journal of Glaucoma. 2003;12: 266–271. 12782847

5. Marks JR, Siriwardena D, Wells A, Frangouli A, Khaw PT. A comparison of two grading systems for filtering blebs. Invest Ophthalmol Vis Sci. 2000;41(4):S581.

6. Furrer S, Menke MN, Funk J, Töteberg-Harms M. Evaluation of filtering blebs using the “Wuerzburg bleb classification score” compared to clinical findings. BMC Ophthalmology. 2012;12: 24. doi: 10.1186/1471-2415-12-24 22805056

7. Picht G, Grehn F. Classification of filtering blebs in trabeculectomy: biomicroscopy and functionality. Curr Opin Ophthalmol. 1998;9(2):2–8. 10180508

8. Picht G, Grehn F. Development of the filtering bleb after trabeculectomy. Classification, histopathology, wound healing process. Ophthalmologe. 1998;95(5):W380–W387. 9643029

9. Ross C, Pandav SS, Li YQ, Nguyen DQ, Beirne S, Wallace GG et al. Determination of Bleb Capsule Porosity With an Experimental Glaucoma Drainage Device and Measurement System. JAMA Ophthalmol. 2015;133:549–554. doi: 10.1001/jamaophthalmol.2015.30 25719729

10. Nguyen DQ, Ross CM, Li YQ, Pandav S, Gardiner B, Smith D et al. A Model to Measure Fluid Outflow in Rabbit Capsules Post Glaucoma Implant Surgery. Invest Ophthalmol Vis Sci. 2012;53:6914–6919. doi: 10.1167/iovs.12-10438 22956615

11. Gardiner BS, Smith DW, Coote M, Crowston JG. Computational Modeling of Fluid Flow and Intra-Ocular Pressure following Glaucoma Surgery. PLoS ONE. 2010;5(10): e13178. doi: 10.1371/journal.pone.0013178 20957178

12. Lee RMH, Bouremel Y, Eames I, Brocchini S, Khaw PT. The implications of an ab interno versus ab externo surgical approach on outflow resistance of a subconjunctival drainage device for intraocular pressure control. Translational Vision Science & Technology. 2019; 8(3): Article 58.

13. Khaw PT, Chiang M, Shah P, Sii F, Lockwood A, Khalili A. Enhanced trabeculectomy–The Moorfields Safer Surgery System. Dev Ophthalmol. 2012; 50:1–28. doi: 10.1159/000334776 22517170

14. Dhingra S, Khaw PT. The Moorfields Safer Surgery System. Middle East Afr J Ophthalmol. 2009; 16(3): 112–115. doi: 10.4103/0974-9233.56220 20142973

15. Zhang X, Li Q, Liu B, Zhou H, Wang H, Zhang Z et al. In vivo cross-sectional observation and thickness measurement of bulbar conjunctiva using optical coherence tomography. Invest Ophthalmol Vis Sci. 2011;52(10):7787–7791. doi: 10.1167/iovs.11-7749 21873655

16. Chiba T, Takahashi H, Chiba N, Lijima H. In vivo thickness measurements of conjunctiva and tenon’s capsule with optical coherence tomography in healthy subjects. IOVS. 2014; 55: ARVO E-Abstract 4873.

17. Read SA, Alonso-Caneiro D, Vincent SJ, Bremner A, Fothergill A, Ismail B et al. Anterior eye tissue morphology: Scleral and conjunctival thickness in children and young adults. Scientific Reports. 2016;6: 33796 EP. doi: 10.1038/srep33796 27646956

18. Eberwein P, Nohava J, Schlunck G, Swain M. Nanoindentation Derived Mechanical Properties of the Corneoscleral Rim of the Human Eye. Key Engineering Materials. 2014;606:117–120.

19. Ressiniotis T, Khaw PT. Procedural treatments: Trabeculectomy. In: Giaconi JA, Law SK, Coleman AL, Caprioli J, eds. Pearls of Glaucoma Management. Berlin: Springer-Verlag, Heidelberg, 2010:271–278.

20. Weissten, EW. Spherical Cap. MathWorld—A Wolfram Web Resource.

21. Bouremel Y, Madaan S, Lee R, Eames I, Wojcik A, Khaw PT. Pursing of planar elastic pockets. Journal of Fluids and Structures. 2017;70:261–275.

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2019 Číslo 10
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