Delayed Appearance of High Altitude Retinal Hemorrhages

When closely examined, a very large amount of climbers exhibit retinal hemorrhages during exposure to high altitudes. The incidence of retinal hemorrhages may be greater than previously appreciated as a definite time lag was observed between highest altitude reached and development of retinal bleeding. Retinal hemorrhages should not be considered warning signs of impending severe altitude illness due to their delayed appearance

Ocular blood flow assessment using continuous laser Doppler flowmetry

This article describes the technique of continuous laser Doppler flowmetry (LDF) as applied to the measurement of the flux of red blood cells in the optic nerve head, iris and subfoveal choroid. Starting with the exposition of the physical principles underlying LDF, we first describe the various devices developed to perform LDF in these vascular beds. We then discuss the clinical protocols, blood flow parameters, calibration procedures, reproducibility and limitations of the LDF technique. Various problems still need to be solved in order to bring to light the full potential of LDF in the assessment of microcirculatory haemodynamics

Choroidal blood flow in the foveal region of the human ocular fundus

Purpose. To develop a noninvasive method for the investigation of choroidal blood flow (ChBF) and its regulation in the foveal region of the human ocular fundus. Methods. Measurement of ChBF was based on the technique of laser Doppler flowmetry (LDF). Sixteen normal subjects (age range, 20 to 64 years), with normal eye examination results, were asked to fixate on a diode laser beam (wavelength = 811 nm, 60 //W at the cornea) delivered to the undilated eye through a fundus camera. Light scattered by red blood cells in the tissue volume sampled by the incident laser beam was detected at the fundus image plane of the camera by an optical fiber. The diameter of the beam at the fundus of the emmetropic eye was about 300 fxm. Relative ChBF was measured in both eyes by analyzing the Doppler signal with commercial skin blood flowmeters. The average pulsatile component of ChBF, ChBFp, was determined over the cardiac cycle, and its value was compared to the average total ChBF, ChBF AV . Responses of ChBF to various physiological stimuli, such as increased blood O 2 and CO2 concentrations, rapid increases in intraocular pressure, and valsalva maneuvers, were documented. Results. Significant correlations were obtained between the ChBF AV values measured with both flowmeters (P < 0.001) and between the ChBF AV values measured in the right and left eye (P < 0.001). ChBFp represented less than 23% of ChBF AV . ChBF AV was not significantly affected by 5 minutes of breathing 100% oxygen. Raising end-tidal CO2 in one subject from 37 to 59 mm Hg increased ChBF AV by approximately 40%. Acute elevation of the intraocular pressure by suction cup or finger pressure on the globe reduced ChBF AV by as much as 90%. Valsalva maneuvers induced reproducible responses that were very different from those recorded from the skin microcirculation. Conclusions. Although LDF of the choroidal circulation is still at an early stage of development, this noninvasive method appears to provide continuous and sensitive measurements of relative choroidal blood flow in the foveal region of the human fundus. Near-infrared laser diodes enable measurements through undilated pupils. Examples of responses suggest new avenues in the investigation by LDF of the effect of various physiological stimuli, pharmacologic agents, and pathologic processes on the choroidal circulation in man. Invest Ophthalmol Vis Sci. 1994; 35:4273-4281. JL he lack of a noninvasive technique to measure choroidal blood flow (ChBF) in humans has compelled researchers to acquire information on this important hemodynamic parameter from studies in anesthetized animals. Numerous techniques have been used for thi

Effect of dark adaptation on retinal blood flow

PURPOSE: Laser Doppler measurements performed immediately after the transition from dark adaptation (DA) to light led to the hypothesis that retinal blood flow, Fret, is increased during DA, but the use of visible lasers had prevented measurements during DA. Our aim was to test this hypothesis by measuring Fret during and after DA. MATERIAL AND METHODS: Fret in retinal vessels at the optic disk surface was recorded quasi-continuously in one eye of 6 normal subjects (age 27 to 60 years) using a laser Doppler flowmeter in the near-infrared (810 nm). Measurements were performed during light (baseline), various periods of DA and again during light. DA lasted between 2 and 32 min. RESULTS: Average Fret for the 6 subjects did not change significantly (-2.7 +/- 8% sd, p > 0.05) during the various periods of DA, as determined from linear regressions of the flux versus time. Following the transition from DA to light, there was, in most cases, a rapid transient increase of the flux, which reached an average value of 37 +/- 10% above the pre-transition value and peaked at 30-60 sec after the transition. CONCLUSIONS: These results do not support the hypothesis that Fret in normal volunteers is increased during DA. Rather, they strongly suggest that the transient increase in flux observed after DA is induced by the transition from dark to light (FNSRS #3200-043157 et CNR, It. #95.01715.CT04)

Noninvasive Measurements and Analysis of Blood Velocity Profiles in Human Retinal Vessels

The blood velocity profile across the retinal vessel lumen was analyzed to enable better calculation of average blood flow rate

Intraocular pressure during a very high altitude climb

Reports on intraocular pressure (IOP) changes at high altitudes have provided inconsistent and even conflictin

Graphs describing hemorrhages in both groups of climbers at different altitudes.

<p>Panel A: total number of hemorrhages; panel B: total area of hemorrhages; panel C: percentage of mountaineers with hemorrhages in at least 1 eye.</p

Fundus photographs of a climber from group 1 showing the development of retinal hemorrhages during the course of her climb.

<p>Note the white-centered hemorrhage localized at the temporal inferior branch of the retinal artery.</p

Summary of total number, total area of retinal hemorrhages (in optic disc areas) and percentage of climbers with hemorrhages per group at different altitudes.

<p>Summary of total number, total area of retinal hemorrhages (in optic disc areas) and percentage of climbers with hemorrhages per group at different altitudes.</p