Diurnal Pattern of Intraocular Pressure is Affected by Microgravity When Measured in Space With the Pressure Phosphene Tonometer (PPT)

Chung, Ki-Young; Woo, Se Joon; Yi, Soyeon; Choi, Gi-Hyuk; Ahn, Changwoo; Hur, Gang-chul; Lim, Jung-gu; Kim, Tae Woo

doi:10.1097/ijg.0b013e3181f464d2

Cited by 16 publications

(11 citation statements)

References 11 publications

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“…The so-called Cherenkov effect, which shows as a characteristic blue glow resulting from electromagnetic radiations emitted when charged particles pass through the vitreous medium at a speed greater than that of light, is a repeatedly reported explanation for phosphenes in astronauts [ 10 , 11 ]. Alternate explanations include physiological mechanisms involving retinal stimulation and/or damage (including mitochondrial oxidative processes [ 12 ] and bioluminescent ultraweak photons), microgravity [ 10 ], or pressure phosphenes [ 13 ]. Similarly, irradiated patients commonly report anomalous visual perceptions after therapeutic irradiation of the CNS, head and neck and the eye [ 14 – 18 ].…”

Section: Introductionmentioning

confidence: 99%

Mechanisms of phosphenes in irradiated patients

et al. 2017

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Anomalous visual perceptions have been reported in various diseases of the retina and visual pathways or can be experienced under specific conditions in healthy individuals. Phosphenes are perceptions of light in the absence of ambient light, occurring independently of the physiological and classical photonic stimulation of the retina. They are a frequent symptom in patients irradiated in the region of the central nervous system (CNS), head and neck and the eyes. Phosphenes have historically been attributed to complex physical phenomena such as Cherenkov radiation. While phosphenes are related to Cherenkov radiation under high energy photon/electron irradiation conditions, physical phenomena are unlikely to be responsible for light flashes at energies used for ocular proton therapy. Phosphenes may involve a direct role for ocular photoreceptors and possible interactions between cones and rods. Other mechanisms involving the retinal ganglion cells or ultraweak biophoton emission and rhodopsin bleaching after exposure to free radicals are also likely to be involved. Despite their frequency as shown in our preliminary observations, phosphenes have been underreported probably because their mechanism and impact are poorly understood. Recently, phosphenes have been used to restore the vision and whether they might predict vision loss after therapeutic irradiation is a current field of investigation. We have reviewed and also investigated here the mechanisms related to the occurrence of phosphenes in irradiated patients and especially in patients irradiated by proton therapy for ocular tumors.

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Section: Introductionmentioning

confidence: 99%

Mechanisms of phosphenes in irradiated patients

et al. 2017

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“…visual impairment and intracranial pressure; intraocular pressure; choroidal area; hydrostatic gradient UNDERSTANDING THE IMMEDIATE response of the eye to alterations in the gravity vector is important because it likely initiates the ocular adaptation to prolonged microgravity exposure. Compared with both the upright and supine positions on Earth, intraocular pressure (IOP) is increased initially upon entering microgravity (6,9,10,21,22; Draeger J., personal communication). IOP increases 50 -90% shortly after entering microgravity (11,21).…”

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confidence: 99%

“…The additional increase in microgravity has been attributed to a cephalad fluid shift caused by the removal of hydrostatic gradients (10,22). Underlying the assumption that a fluid shift in microgravity raises IOP above supine levels is the presumption that the fluid shift in microgravity elevates ocular venous pressures (episcleral, vortex, and choroidal) well above supine values (6). Two lines of evidence, however, suggest this is not the case.…”

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confidence: 99%

Acute effects of changes to the gravitational vector on the eye

Anderson

Swan

Phillips

et al. 2016

Journal of Applied Physiology

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Intraocular pressure (IOP) initially increases when an individual enters microgravity compared with baseline values when an individual is in a seated position. This has been attributed to a headward fluid shift that increases venous pressures in the head. The change in IOP exceeds changes measured immediately after moving from seated to supine postures on Earth, when a similar fluid shift is produced. Furthermore, central venous and cerebrospinal fluid pressures are at or below supine position levels when measured initially upon entering microgravity, unlike when moving from seated to supine postures on Earth, when these pressures increase. To investigate the effects of altering gravitational forces on the eye, we made ocular measurements on 24 subjects (13 men, 11 women) in the seated, supine, and prone positions in the laboratory, and upon entering microgravity during parabolic flight. IOP in microgravity (16.3 ± 2.7 mmHg) was significantly elevated above values in the seated (11.5 ± 2.0 mmHg) and supine (13.7 ± 3.0 mmHg) positions, and was significantly less than pressure in the prone position (20.3 ± 2.6 mmHg). In all measurements,P< 0.001. Choroidal area was significantly increased in subjects in a microgravity environment (P< 0.007) compared with values from subjects in seated (increase of 0.09 ± 0.1 mm(2)) and supine (increase of 0.06 ± 0.09 mm(2)) positions. IOP results are consistent with the hypothesis that hydrostatic gradients affect IOP, and may explain how IOP can increase beyond supine values in microgravity when central venous and intracranial pressure do not. Understanding gravitational effects on the eye may help develop hypotheses for how microgravity-induced visual changes develop.

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“…DieverfügbarewissenschaftlicheEvidenz zu IOD-Messungen in Schwerelosigkeit ist begrenzt, veröffentlichte Daten beziehen sich auf Einzelfallberichte von Astronautinnen und Astronauten [2]. So zeigte ein koreanischer Astronaut einen Druckanstieg von im Mittel 26 % unter Schwerelosigkeit im Vergleich zu den Vormessungen auf der Erde [44]. Auch andere Berichte bestätigen diesen IOD-Anstieg und zeigten zudem eine Normalisierung bis Reduktion nach einigen Tagen [45].…”

Section: Augeninnendruck Im Weltall Unter Schwerelosigkeitunclassified