![Fig. 1; [Top group; upper row] Preflight fundus images of the right and left posterior pole. [Top group; lower row] Postflight return to Earth + 19 days (R+19) images of the right and left posterior pole showing choroidal folds below the optic disc (top arrow) and a “cotton-wool” spot (bottom arrow) in the inferior arcade of the right eye. Optic disc imaging did not show presence of observable disc edema. [Bottom group] Postflight return to Earth + greater than 5 year (R+ >5 years) spectral domain optical coherence tomography (SD-OCT) images showing the presence and persistence of the choroidal folds (arrows) inferior to the right optic disc. Choroidal folds are now only detectable with SD-OCT. OD=right eye, OS=left eye.](/figures/fig-1-top-group-upper-row-preflight-fundus-images-of-the-pzszjtk9.webp)
Q2. Why is the IOP dependent on the intraocular fluid volume?
Because ocular liquids within the eye are incompressible, the IOP depends on the intraocular fluid volume and the rather rigid elastic properties of the cornea and sclera.
Q3. What is the reason for the sudden increase in IOP?
Choroidal volume changes in microgravity may be responsible for the abrupt increase in IOP (within 30 seconds) in orbital and KC-135 parabolic flights as well as head-down studies.
Q4. What are the common ophthalmic procedures performed on astronauts?
Several ophthalmic procedures were initiated on astronauts, including dilated fundus examinations with binocular ophthalmoscopy, cycloplegic refraction, optical coherence tomography (OCT), magnetic resonance imaging (MRI) of orbits, and fundus photos of astronauts before and after space missions.
Q5. How many astronauts experienced a degradation in vision after a short flight?
The 300 postflight questionnaires documented that approximately 29% and 60% of astronauts on short and long-duration missions, respectively, experienced a degradation in distant and near visual acuity.
Q6. How many astronauts had near vision complaints after 6 months of space flight?
After 6 months of space flight, 7 astronauts had ophthalmic findings, consisting of disc edema in 5, globe flattening in 5, choroidal folds in 5, cotton wool spots (CWS) in 3, nerve fiber layer thickening by OCT in 6, and decreased near vision in 6 astronauts.
Q7. What is the effect of choroidal pooling on the retina?
This choroidal pooling may gradually expand the delicate collagen lamella of the choroid beyond its normal anatomic structural boundaries such that the choroid becomes permanently distended even on return to the 1-G environment and in the presence of normal venous back-pressure.
Q8. What is the effect of choroidal expansion on the retina?
When choroidal expansion occurs and this attachment is not present, the pigment epithelium slips easily over the choriocapillaris, the folds are not produced, and the fundus has a smooth appearance despite choroidal thickening.
Q9. What is the reason for the hyperopic shifts observed in astronauts?
It may be that choroidal expansion and presumably a commensurate hyperopic shift may be quite common during space flight and may exist for months to years after return to Earth.
Q10. What was the grade of the edema?
An intracranial magnetic reso-CSF cerebral spinal fluid; MRI magnetic resonance imaging; NFL retinal nerve fiber layer; OCT optical coherence tomography; OD right; Disc edema was graded with the modified Frisén scale.
Q11. What was the result of the MRI?
MRI of the brain and orbits, performed 8 days after return, documented bilateral posterior globe flattening, distended ON sheaths, and tortuous ONs.
Q12. What is the likely explanation for the hyperopic shifts?
It is also possible, although unlikely, that the fluid shifts within the eye could result in lenticular changes, which may lead to alterations in refractive error.
Q13. What is the first possible explanation for the findings?
The first possible explanation is that the findings the authors describe resulted from increased ICP brought about by prolonged microgravity exposure.
Q14. How many astronauts complained of near vision difficulties?
As seen in Table 2, data from postflight questionnaires completed by approximately 300 astronauts after their short- and longduration space missions showed that approximately 23% of the short-duration and 48% of the long-duration mission astronauts complained of near vision difficulties.
Q15. What is the way to explain the changes in IOP?
It is well established that there is an initial spike in intraocular pressure (IOP) on exposure to microgravity followed by a decrease in IOP over a period of days.