An anterior chamber depth that is generally normal, a crowded angle, and a flat iris are all indicative of plateau iris syndrome (PIS). The peripheral iris base of the iris inserts more anteriorly on the ciliary body, resulting in PIS. The iridocorneal angle becomes smaller as a consequence, making it more likely to get blocked during mydriasis. Patients with PIS thus remain at risk for AACG despite having a patent iridotomy.

It is important to note that the greatest anatomical risk factor for angle closure is depth of the anterior chamber [11]. Other risk factors for AACG include an anteriorly positioned lens, short axial length, thick lens, and plateau iris configuration [10]. The risk of drug-induced AACG in space is increased as many of the anticholinesterase or cholinergic medications used by NASA to manage space motion sickness (such as scopolamine and promethazine) cause mydriasis which increases the risk of AACG, due to anterior displacement of lens-iris diaphragm [12]. With space tourism, individuals traveling to space may also be taking a variety of medications which are known as possible AACG precipitants, including α1-adrenergic agonists, β2 adrenergic agonists, sulfonamides, serotonergic agents, and antihistamines [10]. In addition to these risk factors, a dimly lit environment can also precipitate AACG, which may occur during spaceflight.

Ionizing radiation during long-duration spaceflight may cause cataracts, from exposure to galactic comic radiation or solar particle events. Radiation-induced cataract is a dose-dependent phenomena, and as the ionizing radiation dosage is increased, the lens becomes more opaque [13]. Local changes in the organized arrangement of lens cells caused by oxidation of protein sulfhydryl groups and the creation of high-molecular-weight complexes can lead to phacolytic glaucoma. Thus, cataract is a known risk factor for AACG. Although there have been no reported cases of astronauts developing AACG during or post-spaceflight, one additional rational for protective countermeasures against radiation exposure includes reduced risk for radiation-induced cataracts [14].

While the risks of AACG are rare with an estimated prevalence of 0.5–0.8% and have yet to be clearly defined in spaceflight, if AACG were to occur, the resulting visual loss and ocular pain could impact critical astronaut function and the mission [15]. Secondary optic nerve damage and visual loss if not rapidly treated aggressively and early can be permanent in AACG.

In the case of AACG in space, an immediate reduction in intra-ocular pressure via medical management would be the first step but on Earth depending on etiology a bilateral laser or surgical peripheral iridotomy may be necessary. As laser iridotomy is not available, medication to lower the IOP including topical ophthalmic beta blockers and muscarinic agonists is absolutely critical for future spaceflight.

Lower-body negative pressure (LBNP) is an emerging countermeasure for SANS by mitigating the cephalad fluid shifts in microgravity. However acute usage of LBNP in spaceflight did not impact choroidal thickness, which suggests that choroidal engorgement may occur secondary to cerebral venous congestion [16]. Gonioscopy is the gold standard method to examine the drainage angles and assess AACG risk, which can be performed quickly and with little patient discomfort. For objective measurement of the angle, ultrasound biomicroscopy or Visante OCT (Zeiss, Germany) can also be used for imaging. Further studies are required on the structural and functional effects on ocular structure on long-duration spaceflight [17,18,19].

Based on these considerations, we recommend that assessment of the angle be included in any ophthalmic screening prior to spaceflight in the era of civilian spaceflight and SANS. This includes a detailed medical history (including risk factors and current medications), optic nerve examination [20], and gonioscopy to identify for anatomical AACG risk factors. As we prepare for a future where spaceflight is more accessible to a civilian population with diverse physiology and anatomy, it becomes increasingly important to take into the considerations to reduce the risk of acute medical risks such as acute, sight-threatening glaucoma.