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A medical instrument for phacoemulsification with which the biological tissue of a lens of the eye is comminuted by the introduction of energy, the comminuted product is sucked out through an incision in the cornea, while intraocular pressure is maintained by supplying an irrigating liquid. In an in

A medical instrument for phacoemulsification with which the biological tissue of a lens of the eye is comminuted by the introduction of energy, the comminuted product is sucked out through an incision in the cornea, while intraocular pressure is maintained by supplying an irrigating liquid. In an instrument of the type mentioned above, two cannulas are provided for sucking out the ablated lens material and for supplying the irrigating liquid and are connected, via feed lines, with the suction device and with the supply device. A switchable directional valve is provided in the feed lines between the cannulas and the suction device and supply device, by means of which, in a first valve position, a first cannula is connected with the suction device and the second cannula is connected with the supply device and, in a second valve position, the second cannula is connected with the suction device and the first cannula is connected with the supply device.

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A medical instrument for phacoemulsification with which the biological tissue of a lens of the eye is comminuted by the introduction of energy, the comminuted product is sucked out through an incision in the cornea, while intraocular pressure is maintained by supplying an irrigating liquid. In an in

A medical instrument for phacoemulsification with which the biological tissue of a lens of the eye is comminuted by the introduction of energy, the comminuted product is sucked out through an incision in the cornea, while intraocular pressure is maintained by supplying an irrigating liquid. In an instrument of the type mentioned above, two cannulas are provided for sucking out the ablated lens material and for supplying the irrigating liquid and are connected, via feed lines, with the suction device and with the supply device. A switchable directional valve is provided in the feed lines between the cannulas and the suction device and supply device, by means of which, in a first valve position, a first cannula is connected with the suction device and the second cannula is connected with the supply device and, in a second valve position, the second cannula is connected with the suction device and the first cannula is connected with the supply device. associated chain of an associated chain drive system; a tensioning spring connected to said blade, said spring having opposite first and second ends located respectively adjacent said first and second opposite end portions of said blade, said spring contacting and exerting a biasing force on said central portion of said blade; a hub defined by said first end portion of said blade, said hub connected to said central portion of said blade by a first end wall and defining a through-bore adapted for receipt of an associated pin for pivotably connecting said blade to an associated mounting bracket; and, a rib projecting outwardly from said first end wall in a direction moving away from said second end portion of said blade. 2. The apparatus as set forth in claim 1, wherein said first end of said rib is smoothly blended into said exterior chain guide surface. 3. The apparatus as set forth in claim 2, wherein said second end of said rib is smoothly blended into said hub. 4. The apparatus as set forth in claim 3, wherein said rib, at an outermost end that is spaced a maximum distance outwardly away from said first end wall, defines a smoothly curved outermost surface. 5. The apparatus as set forth in claim 1, wherein blade defines a rear face adapted to lie adjacent the associated mounting bracket and defines a front face opposite said rear face, and wherein said rib is centrally located between said front and rear faces. 6. The apparatus as set forth in claim 1, wherein said blade defines a first slot adapted for receipt of said first end of said tensioning spring and defines a second slot adapted for receipt of said second end of said tensioning spring, wherein said first end wall separates said rib from said first slot. 7. The apparatus as set forth in claim 6, wherein said first slot is defined by a first floor surface, a first ceiling surface spaced from said first floor surface and said first end wall, said first end wall extending between said first floor surface and said first ceiling surface at a closed end of said first slot, and wherein a maximum height of said rib relative to said first end wall is generally aligned with said first slot. 8. The apparatus as set forth in claim 7, further comprising: a first projection located in said first slot and projecting outwardly from said first floor surface toward said first ceiling surface, said first end of said tensioning spring defining a first slot adapted for receipt of said first projection when said first end of said tensioning spring is located in said first slot. 9. The apparatus as set forth in claim 6, wherein said second slot is defined by a second floor surface, a second ceiling surface spaced from said second floor surface and a second end wall, said second end wall extending between said second floor surface and said second ceiling surface at a closed end of said second slot. 10. The apparatus as set forth in claim 9, further comprising: a second projection located in said second slot and projecting outwardly from said second floor surface toward said second ceiling surface, said second end of said tensioning spring defining a second slot adapted for receipt of said second projection when said second end of said tensioning spring is located in said second slot. 11. The apparatus as set forth in claim 1, wherein said blade is defined from a material comprising one of a plastic and a filled plastic. 12. A chain tensioner apparatus comprising: a mounting bracket adapted for connection to an associated engine block, said mounting bracket defining a pivot point and a support surface; a blade comprising: (i) first and second opposite end portions joined together by a central portion; (ii) a hub defined by said first end portion; and, (iii) a first end wall connecting said hub to said central portion, said hub of said blade pivotably connected to said bracket adjacent said pivot point and said second end of said blade abutting said support surface, said b