BACKGROUND: This article documents the stability of photorefractive keratectomy (PRK) and laser -assisted in situ keratomileusis (LASIK) in two astronauts during 6-mo missions to the International Space Station. CASE REPORTS: Ocular examinations including visual acuity, cycloplegic refraction, slit lamp examination, corneal topography, central corneal thickness, optical biometry (axial length/keratometry), applanation tonometry, and dilated fundus examination were performed on each astronaut before and after their missions, and in-flight visual acuity testing was done on flight day 30, 90, and R-30 (30 d before return). They were also questioned regarding visual changes during flight. DISCUSSION: We documented stable vision in both PRK and LASIK astronauts during liftoff, entry into microgravity, 6 mo on the International Space Station, descent, and landing. Our results suggest that both PRK and LASIK are stable and well tolerated during long -duration spaceflight.

BACKGROUND: The purpose of this report is to document the first use of a single piece, posterior chamber phakic implantable collamer lens (ICL) with a central port in the right eye (OD) of a spaceflight participant (SFP) during a 12-d Soyuz mission to the International Space Station (ISS). We also briefly document the stability of a pre-existing pachychoroid pigment epitheliopathy (PPE) in the macula of his left eye (OS) during this mission.CASE REPORT: Ocular examination, including refraction, slit lamp examination, macular examination by optical coherence tomography (OCT), and tonometry were performed before and after his mission and he was questioned regarding visual changes during each portion of his flight.DISCUSSION: We documented no change in ICL position during his spaceflight. He reported stable vision during liftoff, entry into microgravity, 12 d on the ISS, descent, and landing. Our results suggest that the modern ICL with a central port is stable, effective, and well tolerated during short duration spaceflight. His PPE also remained stable during this mission as documented by OCT.Gibson CR, Mader TH, Lipsky W, Brown DM, Jennings R, Law J, Sargsyan A, Brunstetter T, Danilichev SN, Maezawa Y. Implantable collamer lens use in a spaceflight participant during short duration spaceflight. Aerosp Med Hum Perform. 2023; 94(1):48-50.

Posterior globe flattening has been well-documented in astronauts both during and after long-duration space flight (LDSF) and has been observed as early as 10 days into a mission on the International Space Station. Globe flattening (GF) is thought to be caused by the disc centred anterior forces created by elevated volume and/or pressure within the optic nerve sheath (ONS). This might be the result of increased intracranial pressure, increased intraorbital ONS pressure from compartmentalisation or a combination of these mechanisms. We report posterior GF in three astronauts that has persisted for 7 years or more following their return from LDSFs suggesting that permanent scleral remodelling may have occurred.

We read with great interest the article by Mader et al (1) entitled “Persistent asymmetric optic disc swelling after long-duration space flight: implications for pathogenesis.” Mader et al point out that ophthalmic abnormalities including optic disc swelling, optic nerve sheath distention, globe flattening, and choroidal folds have been reported in astronauts after long-duration space flight. They emphasize 2 potential mechanisms to explain optic disc edema observed in astronauts. The first explanation is that optic disc swelling results from elevated intracranial pressure (ICP) secondary to cephalad fluid shifts. The second is compartmentation of cerebrospinal fluid (CSF) in the orbital subarachnoid space (SAS). We provide a possible additional explanation of how microgravity, at least in part, may cause optic disc edema due to an imbalance between ocular glymphatic inflow and outflow. In 2012, the glymphatic system was discovered in mice by Iliff et al (2). Their findings suggested that a brain-wide network of paravascular pathways along which a large proportion of subarachnoid CSF recirculates through brain parenchyma, facilitating the clearance of interstitial solutes, including amyloid-β, from the brain. CSF enters the brain along para-arterial channels to exchange with interstitial fluid which is, in turn, cleared from the brain along paravenous pathways. Intriguingly, other reports (3) together with preliminary data from our own postmortem study (4) suggest that a similar paravascular transport system is present in the human optic nerve and retina. We examined cross-sections of human optic nerves by light microscopy after injecting India ink into the SAS of the optic nerve. Our results showed a striking accumulation of India ink in paravascular spaces around the central retinal artery and vein, whereas the lumens of these vessels and the surrounding axons remained unlabeled. We speculated that a “paravascular communication” may exist between the surroundings of the retinal vascular system and the surroundings of the central retinal vessels in the optic nerve. Such a para-arterial “retino-orbital” pathway would include a paraarterial CSF influx route around the central retinal artery to enter the paravascular spaces of the retina, followed by a paravenous efflux route around the central retinal vein. Normally, intraocular pressure exceeds ICP, and, on average, there is a small force (mean 4 mm Hg) directed posteriorly across the lamina cribrosa (5). This trans-lamina cribrosa pressure difference (TLCPD) would ensure effective paravenous outflow from the eye. However, in long-duration space flight–induced increased ICP, paravenous outflow may fail to match ocular para-arterial inflow due to the reduction of the normal TLCPD. Ocular paravenous outflow may be completely impeded if there is reversal of the TLCPD. This may result in glymphatic stasis predominantly within the prelaminar region of the optic nerve head, which could contribute to the optic disc edema seen in astronauts. The accumulation of toxic metabolites due to glymphatic stasis then may cause further disc swelling. Although this mechanism is speculative, it is important to note that Denniston et al (6) provided support for the importance of the ocular glymphatic system in the pathogenesis of papilledema secondary to idiopathic intracranial hypertension (IIH). Using spectral domain optical coherence tomography in a cohort of patients with IIH, they demonstrated a number of structural differences not seen in healthy controls, including the presence of perivascular “black holes.” This was observed both in the optic nerve head and within the retinal nerve fiber layer, and the authors hypothesized that this represents dilated ocular perivascular glymphatic channels. There seemed to be a relationship between the degree of papilledema and the extent of these changes. In healthy controls, the authors did not detect these features. Given these findings, we believe that our proposed theory deserves further study and may ultimately contribute to the field of space health research.

BACKGROUNDThe purpose of this paper is to report the first use of an intraocular lens (IOL) in an astronaut during long duration spaceflight (LDSF). An astronaut developed a unilateral cataract and underwent phacoemulsification with insertion of an acrylic IOL. Approximately 15 mo later he flew on a Soyuz spacecraft to the International Space Station (ISS), where he successfully completed a 6-mo mission.CASE REPORTOcular examination, including ultrasound (US), was performed before, during, and after his mission and he was questioned regarding visual changes during each portion of his flight.DISCUSSIONWe documented no change in IOL position during his space mission. This astronaut reported excellent and stable vision during liftoff, entry into microgravity (MG), 6 mo on the ISS, descent, and landing. Our results suggest that modern IOLs are stable, effective, and well tolerated during LDSF.Mader TH, Gibson CR, Schmid JF, Lipsky W, Sargsyan AE, Garcia K, Williams JN. Intraocular lens use in an astronaut during long duration spaceflight. Aerosp Med Hum Perform. 2018; 89(1):63-65.

BACKGROUND:Several ophthalmic findings including optic disc swelling, globe flattening and choroidal folds have been observed in astronauts following long-duration space flight. The authors now report asymmetric choroidal expansion, disc swelling and optic disc morphologic changes in a 45-year-old astronaut which occurred during long-duration space flight and persisted following his space mission.METHODS:Case study of ocular findings in an astronaut documented during and after a long-duration space flight of approximately 6 months. Before, during and after his spaceflight, he underwent complete eye examination, including fundus photography, ultrasound, and optical coherence tomography.RESULTS:We documented asymmetric choroidal expansion inflight that largely resolved by 30 days postflight, asymmetric disc swelling observed inflight that persisted for over 180 days postflight, asymmetric optic disc morphologic changes documented inflight by OCT that persisted for 630 days postflight and asymmetric globe flattening that began inflight and continued 660 days postflight. Lumbar puncture opening pressures obtained at 7 and 365 days post-mission were 22 and 16 cm H20 respectively.CONCLUSION:The persistent asymmetric findings noted above, coupled with the lumbar puncture opening pressures, suggest that prolonged microgravity exposure may have produced asymmetric pressure changes within the perioptic subarachnoid space.

This report documents the effects of photorefractive keratectomy (PRK) in an astronaut during a 12-day Russian Soyuz mission to the International Space Station in 2008. Changing environmental conditions of launch, microgravity exposure, and reentry create an extremely dynamic ocular environment. Although many normal eyes have repeatedly been subject to such stresses, the effect on an eye with a relatively thin cornea as a result of PRK has not been reported. This report suggests that PRK is a safe, effective, and well-tolerated procedure in astronauts during space flight.Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2012; 38:1486-1491 (C) 2012 ASCRS and ESCRS

Purpose: To describe the history, clinical findings, and possible etiologies of ophthalmic findings discovered in 7 astronauts after long-duration space flight, and document vision changes in approximately 300 additional astronauts.Design: Retrospective, observational examination of ophthalmic findings in 7 astronauts and analysis of postflight questionnaires regarding in-flight vision changes in approximately 300 additional astronauts.Participants: Seven astronauts with ophthalmic anomalies upon return from long-duration space missions to the International Space Station and 300 additional astronauts who completed postflight questionnaires regarding in-flight vision changes.Methods: Before and after long-duration space flight, all 7 subjects underwent complete eye examinations, including cycloplegic and/or manifest refraction and fundus photography. Six underwent postmission optical coherence tomography (OCT) and magnetic resonance imaging (MRI); 4 had lumbar punctures (LP). Approximately 300 astronauts were queried regarding visual changes during space missions.Main Outcome Measures: Refractive change, fundus photograph examination, retina OCT, orbital MRI, LP opening pressures, and examination of visual acuity data.Results: 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. Five of 7 with near vision complaints had a hyperopic shift >= + 0.50 diopters (D) between pre/postmission spherical equivalent refraction in 1 or both eyes (range, +0.50 to +1.75 D). These 5 showed globe flattening on MRI. Lumbar punctures performed in the 4 with disc edema documented opening pressures of 22, 21, 28, and 28.5 cm H2O performed 60, 19, 12, and 57 days postmission, respectively. 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. Some of these vision changes remain unresolved years after flight.Conclusions: We hypothesize that the optic nerve and ocular changes we describe may result from cephalad fluid shifts brought about by prolonged microgravity exposure. The findings we report may represent parts of a spectrum of ocular and cerebral responses to extended microgravity exposure.Financial Disclosure(s): The authors have no proprietary or commercial interest in any of the materials discussed in this article. Ophthalmology 2011; 118: 2058-2069 (C) 2011 by the American Academy of Ophthalmology.

A 36-year-old woman with retinitis pigmentosa was scheduled for removal of posterior subcapsular cataracts and experienced inadvertent retrobulbar administration of hypertonic saline. The patient developed retrobulbar pain and ophthalmoplegia that slowly improved over time. Hypertonic saline may cause ophthalmoplegia and pain if inadvertently given as a retrobulbar injection.