Fig 1.
Schematic diagram of the experimental setup, including an SD-OCT system and a perfusion unit.
The perfusion unit can be used to induce pressure transients. A single reservoir can control static pressures in the cannula inserted into Schlemm’s canal (SC), while switching between two reservoirs provides a means of examining dynamic changes. A radial limbal segment is placed with the trabecular meshwork facing upward toward the OCT imaging beam and a cannula is inserted into SC.
Fig 2.
Schematic illustration of the OCT scanning protocol.
B-scans are performed as a parallel series of sequential cross sections along the Y-axis, which represents the circumferential direction along Schlemm’s canal. A-scans are performed sequentially along the X-axis in the plane of the B-scan. The A-scans traverse along the Z-axis from the trabecular meshwork surface to the surface of the sclera with each A-scan oriented orthogonal to the X-axis. Scanning dimensions in each axis are as indicated.
Fig 3.
The SD-OCT system provides detailed images of microstructures within the AOS system.
(a) A representative OCT cross-sectional image cut longitudinally through SC at a pressure of 10 mmHg, and (b) the corresponding cross-section at 50 mm Hg. Images (c) and (d) are the 3D reconstructions of SC, CCE and ISCC within the same specimen under the pressures of (a) 10 and (b) 50 mm Hg, respectively. With the increase of pressure, the ISCCs move out of the 2D plane and are oriented closer to the observer in the 3D sections. Yellow color identifies the region of SC, pink the CCE, and green the ISCC. In image (c) at 10 mm Hg pressure, SC and the ISCC are smaller and in some areas absent in comparison with image (d) at 10 mm Hg.
Fig 4.
High-resolution volumetric SD-OCT dataset permits detailed examination of the trabecular meshwork (TM), Schlemm’s canal (SC) (red arrow) and the collector channels (CC) (white arrow).
Images shown are obtained from dissecting the scanned tissue volume at a plane that gives optimal identification of collagen flaps to show the hinged flap or leaflet-like organization at the collector channel entrance. (a-f) Images are each oriented to provide an optimal view of collector channel relationships to SC, and the associated hinged collagen flaps (asterisks) that separate the collector channel from SC.). Each CC has a relatively long flap at its entrance creating the appearance of a hinged configuration. The hinged flaps or leaflets are each attached to the TM by means of thin cylindrical attachment structures (CAS) (black arrows) spanning SC. Some sections through the CAS revealed the presence of a lumen (green arrows).
Fig 5.
3D OCT imaging provides the ability to quantify the response of Schlemm’s canal to controlled perfusion pressures ranging from 0 of 50 mm Hg.
(a) A composite cross-sectional image permits visualization of the entire length of ~8 mm of a limbal segment while maintaining a perfusion pressure of 50 mm Hg; SC is dilated along its entire length. A cannula is visible in SC at the right edge of the image of the segment and the trabecular meshwork (TM) is visible superior to the canal. OCT images (b1-b4) representing radial cross-sections through SC demonstrate progressive dilation of the canal as pressure increases from 0 to 50 mm Hg. (c) The curves represent the measured SC area at 10um intervals along the 2 mm limbal segment under pressures as indicated in the legend. (d) Elastance curve generated from measured SC volume increases resulting from changes in applied pressure.
Fig 6.
(a)–(f) OCT cross-sectional images under the steady state pressures of 0, 5, 10, 20, 30 and 50 mmHg, respectively.
OCT imaging resolution is high enough to permit quantification of the configuration changes in Schlemm’s canal, collector channel entrances and intrascleral collector channels and their relationship under steady state pressure conditions. The ISCC in (d) and the HCF in (f) are outlined in red. Trabecular Meshwork (TM), Hinged Collagen Flap (HCF), Ciliary Body (CB).
Fig 7.
(A), (B), and (C) are boxplots of the data for Schlemm’s canal (SC) area, height and height change respectively.
Data is from 14 quadrants of 4 eyes in A & B and from 13 quadrants in C. SC height changes in C are reflected in the data of Fig 7, which displays normalized differences of individual quadrants. The boxplot central lines represent the median, and the box borders the interquartile distance. Means are represented by the small squares. Maximum value are shown as Δ, while minimum as inverted Δ. *p<0.05. The whiskers represent the 99% and 1% range of Tukey.
Fig 8.
OCT images (a-c) represent a section through the limbus while maintaining cannula pressures of 10, 30, and 50 mm Hg respectively; the images represent the static configuration after having switched to the respective reservoir pressures from a baseline of 0 mm Hg pressure. The ciliary body (CB), trabecular meshwork (TM), Schlemm’s canal (SC), collector channel (CC) and intrascleral collector channels (ISCC) undergo progressive changes in shape in response to pressure increases. Red asterisks indicate the base of a hinged collagen flap. Height changes with time of the lumen of SC, CC and ISCC are depicted in (d) (e) and (f); time was determined from the initiation of height change following switching from a baseline reservoir height of 0 to a height of 10, 30 or 50 mm Hg respectively. The bar chart (g) depicts maximum velocities of SC, CC and ISCC lumen height change following pressure changes from the 0 baseline to the10, 30, or 50 mm Hg reservoir height.
Fig 9.
OCT cross-sectional images sequentially acquired at static progressively increasing perfusion pressures of 5, 10, 20 and 30 mmHg (top row) and then sequential acquisition in the reverse direction (bottom row).
Ciliary Body (CB), TM Trabecular Meshwork (TM), Schlemm’s canal (SC), Collector Channel (CC).