Effect of high-altitude exposure on myopic laser in situ keratomileusis.

PURPOSE: To study the effect of high-altitude exposure on visual acuity after myopic laser in situ keratomileusis (LASIK). SETTING: Aconcagua, Mendoza, Argentina. METHODS: In the early postoperative period after uneventful myopic LASIK, 2 physicians prospectively assessed their visual acuity during an ascent of Aconcagua (22841 feet). The distance uncorrected visual acuity (UCVA) and peripheral oxygenation were measured at approximately every 2000 feet of altitude. RESULTS: Both climbers developed a moderate loss of distance UCVA but described normal near and pinhole acuity consistent with a myopic shift. The distance UCVA diminished to 20/100 in the right eye and 20/125 in the left eye of Climber A and to 20/160 and 20/30, respectively, of Climber B. The vision loss worsened with increased altitude, duration of exposure, and decreased peripheral oxygenation. One week after the climb, the manifest refraction demonstrated a small myopic shift in both eyes of Climber A; these subsequently resolved. CONCLUSIONS: Two climbers, 8 and 14 weeks after myopic LASIK, experienced vision loss consistent with a temporary myopic shift in the refractive error with ascent to high altitude. Climbers who have LASIK, particularly those in the early postoperative period, should be prepared for visual acuity fluctuations with high-altitude exposure.

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.

Effects of povidone-iodine chemical preparation and saline irrigation on the perilimbal flora.

PURPOSE: To analyze the effects of 5% povidone-iodine preparation and saline irrigation on the species composition of perilimbal flora. METHODS: Cultures were taken from the perilimbal conjunctiva in 100 eyes before preparation for ophthalmic surgery, after instillation of povidone-iodine solution, and after saline irrigation. RESULTS: Bacteria were isolated in 75% of eyes before preparation, in 28% after povidone-iodine instillation, and in 24% after saline irrigation. Fifty-one culture-positive eyes became negative with povidone-iodine, while only four culture-negative eyes became culture-positive (P < 0.001). The number of eyes yielding coagulase-negative staphylococci, Staphylococcus aureus, and Propionibacterium were significantly decreased after povidone-iodine instillation. Twenty-three culture-positive eyes became negative after saline irrigation, while 19 culture-negative eyes became culture-positive (P > 0.25). CONCLUSION: Povidone-iodine solution is effective in reducing bacterial recovery from the perilimbal conjunctiva, where most incisions for intraocular surgery occur. Saline irrigation after povidone-iodine preparation has no significant effect.