Biology subjects

Nongpiur, M. E.

Publications and source records attributed to Nongpiur, M. E..

4 recordsLinked to original sources

bioRxiv2024

Iris Morphological and Biomechanical Factors Influencing Angle Closure During Pupil Dilation

PurposeTo use finite element (FE) analysis to assess what morphological and biomechanical factors of the iris and of the anterior chamber are more likely to influence angle narrowing during pupil dilation. MethodsThe study consisted of 1,344 FE models comprising of the cornea, sclera, lens and iris (stroma, sphincter and dilator tissues) to simulate pupil dilation and to assess changes in angle. For each model, we varied the following parameters: anterior chamber depth (ACD = 2 -4 mm) and width (ACW = 10-12 mm), iris convexity (IC = 0-0.3 mm), thickness (IT = 0.3-0.5 mm), stiffness (E = 4-24 kPa) and Poissons ratio (v = 0-0.3), and simulated pupil dilation. We evaluated for the change in anterior chamber angle ({bigtriangleup}{angle}) and the final dilated anterior chamber angles ({angle}f) from baseline to dilation for each parameter. ResultsThe final dilated AC angles decreased with a smaller ACD ({angle}f = 53.4{degrees}{+/-}12.3{degrees} to 21.3{degrees}{+/-}14.9{degrees}), smaller ACW ({angle}f = 48.2{degrees}{+/-}13.5{degrees} to 26.2{degrees}{+/-}18.2{degrees}), larger IT ({angle}f = 52.6{degrees}{+/-}12.3{degrees} to 24.4{degrees}{+/-}15.1{degrees}), larger IC ({angle}f = 45.0{degrees}{+/-}19.2{degrees} to 33.9{degrees}{+/-}16.5{degrees}), larger E ({angle}f = 40.3{degrees}{+/-}17.3{degrees} to 37.4{degrees}{+/-}19.2{degrees}) and larger v ({angle}f = 42.7{degrees}{+/-}17.7{degrees} to 34.2{degrees}{+/-}18.1{degrees}). The change in AC angle increased with larger ACD ({bigtriangleup}{angle} = 9.37{degrees}{+/-}11.1{degrees} to 15.4{degrees}{+/-}9.3{degrees}), smaller ACW ({bigtriangleup}{angle} = 7.4{degrees}{+/-}6.8{degrees} to 16.4{degrees}{+/-}11.5{degrees}), larger IT ({bigtriangleup}{angle} = 5.3{degrees}{+/-}7.1{degrees} to 19.3{degrees}{+/-}10.2{degrees}), smaller IC ({bigtriangleup}{angle} = 5.4{degrees}{+/-}8.2{degrees} to 19.5{degrees}{+/-}10.2{degrees}), larger E ({bigtriangleup}{angle} = 10.9{degrees}{+/-}12.2{degrees} to 13.1{degrees}{+/-}8.8{degrees}) and larger v ({bigtriangleup}{angle} = 8.1{degrees}{+/-}9.4{degrees} to 16.6{degrees}{+/-}10.4{degrees}). ConclusionsThis parametric study offered valuable insights into the factors that could influence angle closure. The morphology of the iris (IT and IC) and its innate biomechanical behavior (E and v) were crucial in influencing the way the iris deformed during dilation, and angle closure was further exacerbated by decreased AC biometry (ACD and ACW).

bioengineering↗

bioRxiv2022

The Structural Layers of the Porcine Iris Exhibit Inherently Different Biomechanical Properties

PurposeTo isolate the structural components of the ex vivo porcine iris tissue and to determine their biomechanical properties. MethodsThe porcine stroma and dilator tissues were separated, and their dimensions were assessed using optical coherence tomography (OCT). The stroma underwent flow test (n = 32) to evaluate for permeability using Darcys Law ({Delta}P = 2000 Pa, A = 0.0391 mm2), and both tissues underwent stress relaxation experiments ({varepsilon} = 0.5 with initial ramp of {delta}{varepsilon} = 0.1) to evaluate for their viscoelastic behaviours (n = 28). Viscoelasticity was characterised by the parameters {beta} (half width of the Gaussian distribution), {tau}m(mean relaxation time constant), E0 (instantaneous modulus) and E{infty} (equilibrium modulus). ResultsFor the stroma, the hydraulic permeability was 9.49 {+/-} 3.05 x 10-6 mm2/Pa{middle dot}s, and the viscoelastic parameters were {beta} = 2.50 {+/-} 1.40, and {tau}m = 7.43 {+/-} 4.96 s, with the two moduli calculated to be E0= 14.14 {+/-} 6.44 kPa and E{infty} = 6.08 {+/-} 2.74 kPa. For the dilator tissue, the viscoelastic parameters were {beta} = 2.06 {+/-} 1.33 and {tau}m = 1.28 {+/-} 1.27 s, with the two moduli calculated to be E0 = 9.16 {+/-} 3.03 kPa and E{infty} = 5.54 {+/-} 1.98 kPa. ConclusionWe have established a new protocol to evaluate the biomechanical properties of the structural layers of the iris. Overall, the stroma was permeable and exhibited smaller moduli than those of the dilator muscle. An improved characterisation of iris biomechanics may form the basis to further our understanding of angle closure glaucoma.

bioengineering↗

bioRxiv2021

Adduction Induces Large Optic Nerve Head Deformations in Subjects with Normal Tension Glaucoma

Purpose: To assess optic nerve head (ONH) deformations and strains during adduction, abduction, and intraocular pressure (IOP) elevation in subjects with high-tension glaucoma (HTG) and normal-tension glaucoma (NTG). Design: Clinic-based cross-sectional study. Participants: 114 HTG subjects and 114 NTG subjects. Methods. We recruited 228 subjects (114 subjects with HTG [pre-treatment IOP > 21mmHg] and 114 with NTG [pre-treatment IOP < 21mmHg]). For each subject, we imaged the ONH using spectral-domain optical coherence tomography (OCT) under the following conditions: (1) primary gaze, (2) 20 degree adduction, (3) 20 degree abduction, and (4) primary gaze with acute IOP elevation (to approximately 33 mmHg) achieved through ophthalmodynamometry. For each OCT volume, we automatically segmented the prelaminar tissue (PLT), the choroid, the sclera and the lamina cribrosa (LC) using a deep learning algorithm. We also digitally aligned the OCT volumes obtained from (2)-(4) to the primary gaze volume (1) before performing digital volume correlation (DVC) analysis to quantify IOP- and gaze-induced ONH tissues three-dimensional displacements and effective strain (a local measure of tissue deformation) for all scenarios. Main Outcome Measures: Three-dimensional ONH displacements and strains. Results: Across all subjects, adduction generated high effective strain (4.2 {+/-} 1.4%) in the ONH tissues with no significant difference (p>0.05) with those induced by IOP elevation (4.5 {+/-} 1.5%); while abduction generated significantly lower (p = 0.014) effective strain (3.8 {+/-} 1.1%). Interestingly, the LC of HTG subjects exhibited significantly higher effective strain than those of NTG subjects under IOP elevation (HTG:4.6 {+/-} 1.7% vs NTG:4.1 {+/-} 1.5%, p = 0.047). Conversely, the LC tissue of NTG subjects exhibited significantly higher effective strain than those of HTG subjects under adduction (NTG: 4.9 {+/-} 1.9% vs HTG: 4.0 {+/-} 1.4%, p = 0.041). Conclusion: We found that adduction produced comparable strains and displacements as IOP elevation. We also found that NTG subjects experienced higher strains due to adduction than HTG subjects, while HTG subjects experienced higher strain due to IOP elevation than NTG subjects - and that these differences were most pronounced in the LC tissue.

bioengineering↗

bioRxiv2018

Optic Nerve Tortuosity and Globe Proptosis in Normal and Glaucoma Subjects

PurposeTo assess the difference in optic nerve tortuosity during eye movements and globe proptosis between primary open angle glaucoma and normal subjects using orbital magnetic resonance imaging.\n\nMethods10 Chinese subjects matched for age, ethnicity and refractive errors were recruited, including five normal controls and five patients with primary open angle glaucoma. All subjects underwent magnetic resonance imaging to assess their optic nerves and globes for three eye positions: primary gaze, adduction and abduction. Optic nerve tortuosity (optic nerve length divided by the distance between two ends) and globe proptosis (maximum distance between cornea and interzygomatic line) were measured from magnetic resonance imaging images.\n\nResultsIn adduction, the tortuosity of normal eyes was significantly larger than that of the glaucomatous eyes. Optic nerve tortuosity in adduction in the control and glaucoma groups were 1.004{+/-}0.003 (mean {+/-} standard deviation) and 1.001{+/-}0.001, respectively (p=0.037). Globe proptosis (primary gaze) in glaucoma subjects (19.14{+/-}2.11 mm) was significantly higher than that in control subjects (15.32{+/-}2.79 mm; p = 0.046).\n\nConclusionsIn this sample, subjects with glaucoma exhibited more taut optic nerves and more protruding eye globes compared to normal eyes. This may impact optic nerve head deformations in anatomically predisposed patients.\n\nPrecisEyes with glaucoma have tauter optic nerves compared with normal eyes, which may exert more force on the optic nerve head tissues during eye movements.

pathology↗