Possible Causes for Ocular Changes During Space Flight
It has been hypothesized that these observed ocular changes are a direct result of the cephalid fluid shifts previously reported during exposure to microgravity. These negative effects, which correlate with increased intraocular pressure during space flight, have been predicted by mathematical simulations and demonstrated in rat studies.
More recently, it has been speculated that cephalid fluid shifts in microgravity may induce a phenomenon similar to an earth-bound condition known as idiopathic intracranial hypertension. Intriguingly, a recent report of ground-based persons undergoing 10˚ head-down tilt (an analogue for producing cephalid fluid shifts akin to microgravity exposure) reported increased intraocular pressure and ophthalmic vein distention after only 30 minutes of tilt. In an earlier study, Mader and colleagues also demonstrated an increase in intraocular pressure in participants exposed to 30 minutes of 10˚ head-down tilt. These observations also suggest that changes in intracerebral fluid pressure can occur very early after entering microgravity.
Although it has been known for years that cephalic fluid shifts occur upon entry into microgravity, the potential deleterious consequence of this maladaptive interaction between human and machine is only beginning to be more widely acknowledged. On earth, chronic idiopathic intracranial hypertension can eventually lead to blindness. Whether this may occur at a higher frequency in astronauts, especially among those with the longest continuous or cumulative exposure to microgravity, remains to be determined.
Ideally, careful measurements of intraocular pressure before, during, and after flight may be required to better identify astronauts who may be particularly susceptible to the visual decrement induced by microgravity exposure. Of interest is whether Russian cosmonauts (who, on average, have an even longer duration of exposure to microgravity with repeated exposures) have experienced similar decrements in visual acuity, with accompanying ophthalmologic findings.
Medscape Family Medicine © 2012 WebMD, LLC
Cite this: Eleanor A. O'Rangers, Kieran T. Smart. Ocular Changes After Space Travel - Medscape - May 23, 2012.