Most divers expect sore calves, sunburned noses, and a touch of post-trip fatigue after a week of repetitive diving. Blurry vision is not usually on the list. Yet an increasing number of divers report subtle changes in eyesight after intensive dive schedules, particularly on liveaboards or during nitrox-heavy trips.
A recently published medical review and case report in a peer-reviewed journal has brought renewed attention to a little-known phenomenon known as hyperoxic myopia, a temporary shift toward short-sightedness linked to repeated exposure to elevated oxygen levels. While the condition has long been recognised in clinical hyperbaric oxygen therapy, this research asks an important question for the dive community, could the same effect occur in recreational scuba diving?
A Case That Will Sound Familiar to Many Divers
The paper, published in the medical research archive PubMed Central, documents a recreational diver who experienced a noticeable increase in myopia after an extended period of repetitive dives. The diver had normal, stable vision before the trip. Following many days of diving with elevated oxygen exposure, his distance vision deteriorated enough to be measurable during eye examination.
Importantly, this was not permanent damage. Over time, the diver’s vision gradually returned toward baseline, a hallmark of hyperoxic myopia. The authors then examined existing medical literature to see whether similar effects had been documented elsewhere, including in divers, hyperbaric patients, and animal studies.
Their conclusion was cautious but clear, prolonged exposure to high partial pressures of oxygen can cause temporary changes in the eye’s refractive system, particularly the lens.
What Is Hyperoxic Myopia?
Hyperoxic myopia is a temporary increase in short-sightedness caused by exposure to elevated oxygen levels. In medical settings, it is a well-documented side effect of hyperbaric oxygen therapy, where patients breathe pure oxygen at pressures higher than normal atmospheric levels.
Under these conditions, oxygen alters the biochemical balance inside the eye’s crystalline lens. This affects how light is bent as it enters the eye, shifting focus forward and making distant objects appear blurred.
Crucially, this is not oxygen toxicity in the classic sense, and it is not associated with eye pain, inflammation, or structural damage. It is a functional change, and in most documented cases, it resolves after oxygen exposure is reduced.
Why This Matters to Divers
Recreational scuba diving does not involve breathing pure oxygen, but it can involve repeated exposure to elevated oxygen partial pressures, especially when diving nitrox or conducting multiple dives per day.
On a typical liveaboard itinerary, divers may complete four or five dives daily for a week or more. Even within accepted recreational limits, the cumulative oxygen exposure can be significant.
As explained in guidance published by Shearwater Research, hyperoxic myopia has been observed in divers operating at partial pressures around 1.3 to 1.4 ATA, values commonly used for nitrox dive planning. While most divers will never notice any change, those with heavy exposure profiles may experience subtle effects.
The key takeaway is not that nitrox is unsafe, but that oxygen exposure has effects beyond CNS and pulmonary toxicity, and vision changes may be one of them.
What Divers Might Notice
Divers affected by hyperoxic myopia typically describe:
- Difficulty focusing on distant objects after a dive trip
- A sense that glasses or mask lenses feel “wrong”
- Blurred distance vision that improves gradually over days or weeks
Near vision often remains unaffected or may even seem sharper, which can delay recognition of the problem.
Because the change is temporary, many divers never seek medical advice, assuming fatigue or dehydration is to blame.
What This Is Not
It is important to be clear about what hyperoxic myopia is not.
- It is not decompression sickness
- It is not mask squeeze or barotrauma
- It is not permanent vision loss
- It is not a reason to stop diving
The authors of the study emphasise that the evidence base remains limited, and no changes to recreational diving guidelines are currently warranted.
Practical Takeaways for Divers
This research is best viewed as an awareness tool rather than a warning.
Divers who regularly undertake high-intensity dive schedules may want to:
- Be aware of subtle vision changes after trips
- Avoid changing prescription glasses immediately after a dive holiday
- Mention recent diving history to optometrists if vision seems off
- Plan nitrox use sensibly rather than defaulting to the highest oxygen mix
As always, conservative dive planning and adequate surface intervals remain good practice, not just for decompression safety, but for overall physiological stress.
A Reminder That Diving Affects the Whole Body
Diving medicine has traditionally focused on the lungs, brain, and joints. This study is a useful reminder that the eyes are also sensitive to pressure and gas exposure, even when dives are well within recreational limits.
For most divers, the effect will never be noticeable. For others, especially those diving intensively, it may explain a post-trip experience that previously seemed puzzling.
Research like this does not make diving more dangerous. It makes divers more informed.
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