Biology subjects

Tan, R. K. Y.

Publications and source records attributed to Tan, R. K. Y..

3 recordsLinked to original sources

bioRxiv2022

A duration-dependent interaction between high-intensity light and optical refocus in the drive for myopia control

PURPOSETo evaluate the duration-dependent and synergetic impact of high-intensity light (HL) and optical refocus (RF) on lens-induced myopia (LIM) development in chickens. METHODSMyopia was induced in one eye in chicks (10 groups, n=126) from day 1 post- hatching (D1) until D8 using -10D lenses. Fellow eyes remained uncovered as controls. Nine groups were exposed daily to continuous 2 hours (h), 4h, or 6h of either HL (15,000 lux); RF (removal of -10D lens); or both (HL+RF). One group served as the LIM group without any interventions. Ocular axial length (AL), refractive error, and choroidal thickness were measured on D1, D4, and D8. Outcome measures are expressed as inter-ocular difference (IOD= experimental - control eye) {+/-}SEM. RESULTSBy D8, LIM increased AL (0.36{+/-}0.04 mm), myopic refraction (-9.02{+/-}0.37D), and choroidal thinning (-90.27{+/-}16.44 {micro}m) in the LIM group (all, P<0.001). Compared to the LIM group, exposure to 2h, 4h, or 6h of HL, RF, or HL+RF reduced myopic refraction in a duration-dependent manner, with RF being more effective than HL (P<0.05). Only 6h of HL+RF (not 2h or 4h) prevented LIM and was more effective than RF (P=0.004) or HL (P<0.001) in reducing myopic refraction, and more effective than HL (P<0.001) in reducing axial elongation. CONCLUSIONDaily exposure to 2h, 4h, or 6h of HL, RF, or HL+RF reduced lens-induced myopic refraction in a duration-dependent manner in chickens. Only 6h of HL+RF completely stopped LIM development. The synergetic effect of HL and RF is dependent on the duration of the interventions.

neuroscience↗

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

Changes in Iris Stiffness and Permeability in Primary Angle Closure Glaucoma

PurposeTo evaluate the biomechanical properties of the iris by evaluating iris movement during pupil constriction and to compare such properties between healthy and primary angle-closure glaucoma (PACG) subjects. MethodsA total of 140 subjects were recruited for this study. In a dark room, the anterior segments of one eye per subject were scanned using anterior segment optical coherence tomography (AS-OCT, SS-1000 CASIA, Tomey Corporation, Nagoya, Japan) imaging during induced pupil constriction with an external white light source of 1700 lux. Using a custom segmentation code, we automatically isolated the iris segments from the AS-OCT images, which were then discretized and transformed into a three-dimensional point cloud. For each iris, a finite element (FE) mesh was constructed from the point cloud, and an inverse FE simulation was performed to match the clinically observed iris constriction in the AS-OCT images. Through this optimization process, we were able to identify the elastic modulus and permeability of each iris. ResultsFor all 140 subjects (95 healthy and 45 PACG of Indian/Chinese ethnicity, Age: 60.2{+/-}8.7 for PACG subjects and 57.7{+/-}10.1 for healthy subjects), the simulated deformation pattern of the iris during pupil constriction matched well with OCT images. We found that the iris stiffness was higher in PACG than in healthy controls (24.5{+/-}8.4 kPa vs 17.1{+/-}6.6 kPa with 40 kPa of active stress specified in the sphincter region; p < 0.001), whereas iris permeability was lower (0.41{+/-}0.2 mm2/kPa.s vs 0.55{+/-}0.2 mm2/kPa.s; p = 0.142). ConclusionThis study suggests that the biomechanical properties of the iris in PACG are different from those in healthy controls. An improved understanding of the biomechanical behavior of the iris may have implications for the understanding and management of angle-closure glaucoma.

bioengineering↗