Intraocular length measuring instrument capable of avoiding errors in

Abstract

An intraocular length measuring instrument according to the invention can avoid errors in measurement caused by the movement of a subject's eye, such as a blink or involuntary eye movement, and improve the accuracy of the measurement of an intraocular length of the eye. The intraocular length measuring instrument includes a pattern image projecting and receiving optical system for projecting a pattern image onto the cornea of the eye and receiving the pattern image into a two-dimensional image sensor; an interferometric system for producing interference light in such a way that measuring light is projected onto a surface of an intraocular object to be measured while reference light is projected onto a reference surface corresponding to the object surface and interference is caused between light reflected by the object surface and light reflected by the reference surface and causing a photosensor to receive the interference light and output an interference signal; a device for determining the position of the object surface by sampling interference signals output by the photosensor; a device for reading the data concerning the pattern image received by the two-dimensional image sensor at any point of time of the duration of the sampling in order to memorize the pattern image data in a memory medium; and means for determining the position of a corneal vertex from the pattern image data memorized in the memory medium.