Pinhole focused optics for locating visual axis of the eye for ultrasonic interior measurement
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United States of America Patent
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Jun 19, 1990
Grant Date -
N/A
app pub date -
Sep 9, 1988
filing date -
Sep 9, 1988
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A prior art ultrasonic eye measuring device is fitted with pinhole optics. A fixation target is provided with the pinhole optics. The instrument is used to measure the dimension of the eye typically preparatory to cataract surgery. In use of the instrument, the patient has the cornea anesthetized. The patient is thereafter told to fixate on the spot of light leaking from the pinhole optics as the eye examiner brings the instrument into contact with the cornea of the eye. The point source of light approaches the eye. As it approaches, the point source increases in size. When the light source becomes sufficiently large, the fixation target becomes visible. Upon touching of the instrument to the eye, ultrasound measurement of the dimension of the eye preferably along the visual axis occurs. By the expedient of aligning the interrogating ultrasound axis to the line of sight of the fixation target, measurement of the visual axis length of the eye occurs. The appearance of the fixation target immediately before eye measurement minimizes undesired off axis measurement. In a preferred embodiment of the instrument, the conjugate image of a pinhole light source is relayed by optics through the lens of the eye. Consequently, the fixation target is not diffraction limited.
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