Biology subjects

Perera, S. A.

Publications and source records attributed to Perera, S. A..

3 recordsLinked to original sources

bioRxiv2025

Iris Crypts Could Reduce the Chance of Angle Closure: A Computational Biomechanics Study Derived from Clinical and Human Iris Data

PurposeTo investigate the effect of crypts during pupil constriction and dilation on the potential for angle closure by performing finite element analysis using clinical and experimental data on human tissues. MethodsA computational model was developed to determine the influence of small crypts (surface area of [~]0.015 mm2) and large crypts (surface area of 0.300 mm2) on the anterior chamber angles during pupil dilation. The model needed permeability data from human subjects, hence 21 enucleated human eyes (72 hours post-mortem) were procured and subjected to a flow set-up previously reported. Finally, 66 subjects were recruited to measure pupil constriction and dilation levels from optical coherence tomography (OCT) videos. ResultsThe hydraulic permeability of the human iris stroma was determined to be 2.55 {+/-} 1.93 x 10-5 mm2/Pa{middle dot}s. The average iris constriction and dilation durations were 0.710 {+/-} 0.213 seconds and 1.24 {+/-} 0.401 seconds, respectively, with pupil diameter changes of 1.16 {+/-} 0.39 mm and 0.75 {+/-} 0.27 mm, respectively. The computational models had starting anterior chamber angles of 51.30{degrees} and final anterior chamber angles of 26.81{degrees} once steady state has been reached. In an extreme case with decreased anterior border layer (ABL) permeability, the anterior chamber angle narrowed to 12.37{degrees}, but the presence of crypts kept the angle above 20.36{degrees}, highlighting the potential of crypts in preventing angle closure. ConclusionsOur findings on the biomechanics of crypts in the iris may drive the development of novel treatments by altering ABL morphology, providing an alternative bypass for angle closure prevention in high-risk patients.

bioengineering↗

bioRxiv2019

Effect of Changing Heart Rate on the Ocular Pulse and Dynamic Biomechanical Behavior of the Optic Nerve Head

PurposeTo study the effect of changing heart rate on the ocular pulse and the dynamic biomechanical behaviour of the optic nerve head (ONH) using a comprehensive mathematical model.\n\nMethodsIn a finite element model of a healthy eye, a biphasic choroid consisted of a solid phase with connective tissues and a fluid phase with blood, and the lamina cribrosa (LC) was viscoelastic as characterized by a stress-relaxation test. We applied arterial pressures at 18 ocular entry sites (posterior ciliary arteries) and venous pressures at four exit sites (vortex veins). In the model, the heart rate was varied from 60 bpm to 120 bpm (increment: 20 bpm). We assessed the ocular pulse amplitude (OPA), pulse volume, ONH deformations and the dynamic modulus of the LC at different heart rates.\n\nResultsWith an increasing heart rate, the OPA decreased by 0.04 mmHg for every 10 bpm increase in heart rate. The ocular pulse volume decreased linearly by 0.13 {micro}L for every 10 bpm increase in heart rate. The storage modulus and the loss modulus of the LC increased by 0.014 MPa and 0.04 MPa, respectively, for every 10 bpm increase in heart rate.\n\nconclusionsIn our model, the OPA, pulse volume, and ONH deformations decreased with an increasing heart rate, while the LC became stiffer. The effects of blood pressure / heart rate changes on ONH stiffening may be of interest for glaucoma pathology.\n\nSupportSingapore Ministry of Education, Academic Research Fund, Tier 2 (R-397-000-280-112).\n\nCommercial relationshipNone

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↗