Patent Document ID: 4705045
Application ID: 06832763
Patent Status: 1

Claim One:
1. A non-contact type tonometer having an orifice tube for discharging a fluid to deform a cornea of an eye under test, and an alignment optical system for aligning an axis of the orifice tube with the vertex of the cornea and for indicating a predetermined working-distance between a tip of the orifice tube and the vertex of the cornea, said alignment optical system comprising: first projection means having a first optical axis thereof for projecting a first target image on the focal point of said cornea; second projection means having a second optical axis thereof for projecting a second target image on the focal point of said cornea; imaging optical means having a focal point and an alignment optical axis which is coaxial with said axis of said orifice tube for forming an image of specularly reflected light rays of said first and second projecting means from said cornea, said first and second optical axes of said projection means being obliquely arranged with respect to said alignment optical axis; means for detecting said images formed by said imaging optical means; said first and second projection means being configured such that said first and second optical axes and said alignment optical axis intersect with each other at a first intersection point on said alignment optical axis and said first and second projection means being further adapted to form said first and second target images at said intersection point; and said tonometer being operable such that where no alignment error exists between the vertex of the cornea and the central axis of the orifice tube, and no working-distance error exists between the vertex of the cornea and the tip of the orifice tube, said first target light ray projected by said first projection means toward the cornea, and said second target light ray projected by said second projection means toward the cornea intersect at the focal point of the cornea, and a portion of the target light rays are reflected from the cornea and become parallel to said alignment optical axis of said imaging optical means, and said first and second reflected target light rays are imaged by said imaging optical means on said image detecting means and are coincident with each other at said focal point of said imaging optical means.