Non-arteritic central retinal artery occlusion (CRAO) causes sudden, severe vision loss. The metabolically active retina sustains irreversible damage within 97 minutes after CRAO onset.^{Reference Hayreh1} The central retinal artery branches off the ophthalmic artery to supply the inner retina. The posterior ciliary circulation also branches off the ophthalmic artery but supplies the outer retina and choroid. Under normal physiologic conditions, 50% of inner retinal oxygen comes from the outer retina through passive diffusion. This increases up to 97% with hyperbaric oxygenation.^{Reference Mac Grory2}

Reperfusion therapies such as intravenous thrombolysis are still debated.^{Reference Mac Grory3} Alternatively, treatment focused on enhancing the oxygen diffusion from the outer to inner retina may prevent ischemic damage and improve vision. Elfil M. et al. performed a systematic review and meta-analysis to determine the efficacy of hyperbaric oxygen therapy (HBOT) for acute CRAO.^{Reference Elfil4}

The approximate incidence of CRAO is 1–2 in 100,000 ^{Reference Dattilo5} so the authors must be commended on including 499 patients from 9 studies. This low prevalence likely explains the heterogeneity between studies. Best corrected visual acuity improved with HBOT, but only when correcting for heterogeneity, and studies reporting visual acuity without mention of correction did not show benefit. This creates confusion because visual acuity should always be “best corrected” by convention. For Snellen line reading, several studies showed improvement, but there was no significant difference between the HBOT and non-HBOT groups.

Interestingly, benefits of HBOT may go beyond visual outcomes. Patients who received HBOT had lower rates of neovascular glaucoma (15.79% vs. 7.89%) and stroke (16.6% vs. 4.3%). Neovascular glaucoma is a particular concern.^{Reference Călugăru and Călugăru6} Retinal ischemia promotes vasoproliferative growth factors that cause fragile angiogenesis and inflammation. The resulting angle-closure glaucoma is progressive, with further vision loss and intractable pain requiring invasive procedures or even enucleation.

HBOT may not be an option for some patients. Adverse events included confinement anxiety, seizure, asymptomatic bradycardia, epistaxis and ear barotrauma. The rates of incisional myringotomies or other surgical interventions were not reported. Patients had multiple comorbidities with mean age of 62.5–73.67 years, so transferring patients with severe vision loss into the machines must also be considered.

HBOT requires specialized equipment and technical knowledge, which is not always immediately available at CRAO onset. Time from CRAO onset to HBOT varied between studies from hours to days. Treatment duration and total sessions also varied and were not described in some studies. Timely treatment with standardized HBOT protocols would be needed when designing future randomized controlled trials.