Biomedical subjects

Gregory T Smedley

Publications and source records attributed to Gregory T Smedley.

3 recordsLinked to original sources

PubMed2005

A refractive tilting-plate technique for measurement of dynamic contact angles.

The contact angle is a critical parameter in liquid interface dynamics ranging from liquid spreading on a solid surface on earth to liquid motion in partially filled containers in space. A refractive tilting-plate technique employing a scanning laser beam is developed to conduct an experimental study of a moving contact line, with the intention of making accurate measurements of the contact angle. The technique shows promise as an accurate and potentially fully automated means to determine the velocity dependence of the contact angle at the intersection of the interface between two transparent fluids with a transparent solid surface. Ray tracing calculations are included to reinforce the measurement concept. The principal experiments were conducted at speeds ranging from 0.05 to 1.00 mm/s, both advancing and receding, using an immiscible liquid pair (nonane/formamide) in contact with glass. The contact angle was found to depend for practical purposes only on the sign of the velocity and not on its magnitude for the range of velocities studied. Other observations revealed a bimodal behavior of the contact line that depends on which liquid first contacts the glass, with resulting drift in the dynamic contact angle with time.

Journal Article↗

PubMed2005

A trabecular bypass flow hypothesis.

PURPOSE: To introduce a hypothesis that theorizes the effect of a trabecular bypass, a channel created through the trabecular meshwork, on the facility of outflow and the intraocular pressure (IOP). METHODS: Equations that govern the pressure and circumferential flow in Schlemm's canal are established, based on the linear relationships between pressure drop and flow, the balance of flows in the canal, and a uniform leaking structure of collector channels. Two types of bypasses permitting either unidirectional or bidirectional flow are incorporated through boundary conditions to solve the equations and to derive the facility of outflow and the reduced IOP. RESULTS: In normal healthy eyes, the facility of outflow increases by 13% and 26% in the presence of a unidirectional and bidirectional bypass, respectively. The circumferential flow is significant only in the immediate quadrant to the bypass. The elevated IOP due to the abnormally high resistance in trabecular meshwork in open angle glaucoma is substantially reduced with a single bypass. Mean physiological level of IOP is attained if the bidirectional bypass is placed; slightly higher IOP is attained if a unidirectional bypass is placed. In either case, the higher the baseline IOP, the greater the reduction. The effectiveness of the bypass on IOP reduction is related to the resistances in the canal and the collector channels. Multiple bypasses can be used to further reduce the IOP. CONCLUSION: It is theoretically demonstrated that a single patent trabecular bypass can enhance the facility of outflow and reduce the IOP to physiological levels.

Aqueous Humor↗

PubMed2004

Trabecular bypass stents decrease intraocular pressure in cultured human anterior segments.

PURPOSE: To determine the effect on intraocular pressure (IOP) of bypassing the trabecular meshwork in cultured human anterior segments. DESIGN: Prospective laboratory investigation using normal human eyes obtained at autopsy. METHODS: Anterior segments from 21 eyes were placed in perfusion culture, and trabecular bypass stents were inserted through the trabecular meshwork, with the lumen of the tube opening into Schlemm's canal. Eyes received from one to four stents, placed equidistant apart. In eyes receiving one or two stents, additional stents were later added to a maximum of four per eye. RESULTS: Intraocular pressure was lowered after placement of a single stent, from 21.4 +/- 3.8 mm Hg to 12.4 +/- 4.2 (P < .001). This corresponded to an 84% increase in facility of outflow. Eyes receiving more than one stent had final IOP of 11.9 +/- 3.7 mm Hg. Nine eyes had sequential addition of stents, and seven of these had a further decrease of IOP (13.6 +/- 4.1 to 10.0 +/- 4.3; P = .02). Excision of the entire meshwork, between stents, dropped IOP to 6.3 +/- 3.2 mm Hg, indicating some residual meshwork or canal resistance remained even after placement of three stents. CONCLUSIONS: Bypass of the trabecular meshwork lowers IOP in cultured human anterior segments. One stent produced the greatest change in pressure. The sequential addition of more stents further lowered pressure in seven of nine eyes. This technique holds promise as a new clinical surgery for glaucoma.

Anterior Eye Segment↗