Relative optic cup depth assessments using three stereo photograph viewing methods.

PURPOSE: A consistent stereoscopic (stereo) effect in disc photographs is important to be certain that apparent depth changes are real and are not the result of artifact caused by a variable stereo angle. The purpose of this study is to compare the accuracy of relative depth assessments using three different stereo photo viewing methods. METHODS: We evaluated the ability of 12 observers to arrange sets of simultaneous stereo photographs (Nidek 3-Dx split-frame slides, Lentec transparencies) and sequential stereo photographs (Zeiss full-frame slides) according to apparent cup depth. Observer arrangements of each set of 10 photographs were compared to a "reference standard" sequence determined from cup depth measurements made by the Imagenet optic nerve analyzer. RESULTS: The median number of sequence errors (n = 6) made by all examiners in arranging the Nidek 3-Dx simultaneous stereo slides was significantly lower than the median number of errors (n = 12) with the Zeiss sequential stereo slides. CONCLUSIONS: Simultaneous stereo slides provide significantly more interobserver consistency for judgements of cup depth than sequential stereo slides.

Resolution of nidek 3-dx, zeiss, canon, and topcon fundus cameras.

The limiting factor in resolution in modern fundus photography may be the fundus camera itself. We therefore wanted to measure the ideal resolution of several popular brands of fundus cameras. A standard U.S. Air Force high-contrast resolution test target was photographed in-air with the Nidek 3-Dx, Zeiss FF3, Canon CF-60U, Canon CF-60UV, and Topcon TRC-50X fundus cameras. Resolution was determined after correction for magnification. Resolution was similar on all properly aligned cameras we tested. Presumably because of the fundus camera's prism optics, resolution of vertically oriented targets with all cameras was consistently worse than those directed horizontally. Processing of the simultaneous stereo image from the Nidek 3-Dx camera into a 3.5 x 5-in lenticular transparency (LenTec Corporation, Duluth, GA, U.S.A.) not requiring a stereo viewer caused minor additional degradation in resolution of vertically oriented targets. Fundus camera users may easily check the resolving power of their camera using the method described, to detect deficiencies that could adversely affect the quality of clinical fundus photographs. They should be aware of orientational differences in resolution, especially in lenticular transparencies.

Microaerosol formation in noncontact 'air-puff' tonometry.

Attention has been directed recently to appropriate methods for sterilizing tonometers to inactivate the human immunodeficiency virus and other viruses that have been found in tears. Noncontact tonometry, utilizing a brief pulse of pressurized air, is an alternative that avoids the need for sterilization procedures. We used a camera and flash electrically coupled to an American Optical Non-Contact II tonometer (Cambridge Instruments Inc, Cambridge, Mass) or a Keeler Pulsair tonometer (Keeler Instruments Inc, Broomall, Pa) to photograph the corneal profile during tonometry. Most eyes revealed some degree of tear film dehiscence and microaerosol formation. While tears have not been implicated as a source of human immunodeficiency virus infection, the ease with which droplets, potentially contaminated with human immunodeficiency virus and other viruses, are dispersed is disturbing. "Air-puff" tonometry may not be aseptic as previously presumed.