Keithley Instruments Inc. of Cleveland has expanded its business presence in southeast Asia by enlarging its Singapore office and opening two new offices in Malaysia for direct sales and support of its electrical test and measurement solutions. The company says more than half of its sales currently come from outside the US and it can work more effectively with its Asian customers from the new offices.    . . .    Horsham, Pa.-based Avo Photonics, a manufacturer of photonic and microelectronic packaging, assembly and test solutions for the communications, military/aerospace and medical/industrial markets, has added 500 sq. ft of Class 100 clean space to its existing 6000 sq. ft of Class 10000 space to meet the design and manufacturing demands of advanced medical product makers.    . . . IntraLens Vision Inc. of Lake Forest, Calif., has changed its name to ReVision Optics Inc. as it targets the refractive surgery market and the treatment of presbyopia, or the inability to focus on near objects after the age of 40. The company also announced that femtosecond laser maker IntraLase Corp. of Irvine, Calif., has developed specialized software to allow ReVision to produce customized corneal flaps that will assist eye surgeons in injecting ReVision's intracorneal vision-correction lenses, now undergoing clinical trials in the US. As part of this agreement with ReVision, IntraLase will acquire full rights to the name IntraLens.    . . .    Austin, Texas-based Molecular Imprints Inc., (MII) a manufacturer of nanolithography systems and developer of imprint lithography technology, today announced that President and CEO Norman Schumaker has retired. Mark Melliar-Smith, the company's chief operating officer, has been appointed CEO. MII has also named John Doering as its new vice president of marketing. Doering most recently worked as global director of strategic marketing at ASML, a manufacturer of photolithography systems.