Oxygen myopia & Skin bends on rebreather

[Hootis]

Two seperate issues, first is optical illusions following repeated exposure to PPO2's of 1.4 for a couple of dive days while rebreather diving. Both times this phenomon have occured, the oxygen exposure limits were not extreme. The first occurance was on day two of a week long dive trip. Dive was to 100fsw for 60 min flying my rebreather at 1.4. Decompression was minimal and I was very conservative. After two hours out of the water...feeling fine....I began to have optical disturbances best described as 10-20 spots of blur about 1" in diameter, arms length away, moving like a swarm of bees through my field of view. Subsided after 15-30 minutes. The next time this occured (year later) I was 6 dives into a two week trip. Biggest exposure prior to the occurance was 175fsw for 30 minutes bottom time with conservative decompression and with no symptoms. The next dive (following day) was 100fsw for 20 min again at a setpoint of 1.4. Again, the visual disturbances were noted approx 2 hours after leaving the water...no other symptoms noticed. I've read some reports of oxygen myopia....not sure if this is consistent with the accounts that I've read. Another idea by a doctor friend of mine, was minor bends in the region of the optic nerve (brain.) Anyone else experience these symptoms, or have any other ideas.

Next issue I've noticed, is that I occasionally will get a stinging feeling in the skin (or tissues just below) in the region of my stomache. I believe this to be a from of skin bends. Some other (very well known and experienced) technical divers I've talked to privately about this issue have also experienced it. Anyone have any information on this? Seems to occur on deeper/longer dives, but without reason or rhyme. I've had it occur twice in my 12 year diving career...both times on dives that were not nearly what I would consider extreme. (but both times beyond the limits of recreational) Both times this occured, I could not attribute the occurance to any obvious outside factor. (Hydration, medications, lack of conservatisim in the decompression profile, etc.) Anybody else experience this?

 

[sagascuba]

Happened to me a few days ago, after a 15min dive at 90 meters (260fsw?). Nice purple bruises (no pain) on the right shoulderblade. Completely disapeared after 1 hour at the surface.
It was a relaxed Trimix CCR dive (no exertion) in warm water (Red Sea). Dive plan generated by RGBM with a lot of extra conservatism.

 

[Otter]

I remember reading that Howard Hall and some eye issues after multiple days of diving on RBs due to elevated ppos. I'll take a look around and see if I can find the post.

 

[Saturation]

Two seperate issues, first is optical illusions following repeated exposure to PPO2's of 1.4 for a couple of dive days while rebreather diving. Both times this phenomon have occured, the oxygen exposure limits were not extreme. The first occurance was on day two of a week long dive trip. Dive was to 100fsw for 60 min flying my rebreather at 1.4. Decompression was minimal and I was very conservative. After two hours out of the water...feeling fine....I began to have optical disturbances best described as 10-20 spots of blur about 1" in diameter, arms length away, moving like a swarm of bees through my field of view. Subsided after 15-30 minutes. The next time this occured (year later) I was 6 dives into a two week trip. Biggest exposure prior to the occurance was 175fsw for 30 minutes bottom time with conservative decompression and with no symptoms. The next dive (following day) was 100fsw for 20 min again at a setpoint of 1.4. Again, the visual disturbances were noted approx 2 hours after leaving the water...no other symptoms noticed. I've read some reports of oxygen myopia....not sure if this is consistent with the accounts that I've read. Another idea by a doctor friend of mine, was minor bends in the region of the optic nerve (brain.) Anyone else experience these symptoms, or have any other ideas.

Next issue I've noticed, is that I occasionally will get a stinging feeling in the skin (or tissues just below) in the region of my stomache. I believe this to be a from of skin bends. Some other (very well known and experienced) technical divers I've talked to privately about this issue have also experienced it. Anyone have any information on this? Seems to occur on deeper/longer dives, but without reason or rhyme. I've had it occur twice in my 12 year diving career...both times on dives that were not nearly what I would consider extreme. (but both times beyond the limits of recreational) Both times this occured, I could not attribute the occurance to any obvious outside factor. (Hydration, medications, lack of conservatisim in the decompression profile, etc.) Anybody else experience this?

Your description sound like lens 02 toxicity but its not possible to say with more certaintiy: in the events experienced by Hall and others [and possibly Pyle] published in MEDLINE, it took weeks to resolve. Significant DCS worsens with time until it peaks then subsides, while 02 related toxicity improves continuously with time, once the 02 exposure terminated.

There is a possibility you experienced a type of CNS 02 toxicity instead, called retinal toxicity. Its more consistent with the scotoma like distribution and the retina is more sensitive to high pp02 exposures. It was shown experimentally the retina exibits electrical changes before overt visual symptoms. That the symptoms resolved quickly supports 02 toxicity.

A bottom setpoint of 1.4 is high. Its preferrably for bottom pp02 to be <=1.2, in rebreathers or OC.

 

[DepartureDiver]

Just to add an experience of mine ... during a mild smoothly executed 200' dive (total time less than 60 minutes with deco), I started getting a little blurry vision in one eye during a stop at around 50'. At first I thought it was my mask fogging up. As I progressed through my stops, both eyes started getting a little blurry. Now I'm starting to think about a tox issue. I should also point out that I wear rigid gas permeable hard contact lenses. So the thought that the gas wasn't exchanging well for some reason also entered my mind. When I reached the surface, I took my mask off and my eyes were still blurry and had gotten worse. I informed our team of what was going on, but this resolved within 30 minutes. Naturally I re-checked my mixes and they were right were supposed to be. We target our deco mixes with a ppO2 of about 1.35 (except for 02 ... which is also 1.4 since we are using it at 20' at reduced atmospheric pressure at altitude). My bottom mix was also at about 1.3. This incident never made sense to me other than what I perceived to be an undeserved tox. Any thoughts?

 

[Saturation]

Just to add an experience of mine ... during a mild smoothly executed 200' dive (total time less than 60 minutes with deco), I started getting a little blurry vision in one eye during a stop at around 50'. At first I thought it was my mask fogging up. As I progressed through my stops, both eyes started getting a little blurry. Now I'm starting to think about a tox issue. I should also point out that I wear rigid gas permeable hard contact lenses. So the thought that the gas wasn't exchanging well for some reason also entered my mind. When I reached the surface, I took my mask off and my eyes were still blurry and had gotten worse. I informed our team of what was going on, but this resolved within 30 minutes. Naturally I re-checked my mixes and they were right were supposed to be. We target our deco mixes with a ppO2 of about 1.35 (except for 02 ... which is also 1.4 since we are using it at 20' at reduced atmospheric pressure at altitude). My bottom mix was also at about 1.3. This incident never made sense to me other than what I perceived to be an undeserved tox. Any thoughts?

Hi DD, are you back from the West coast? Will PM you about other issues we discussed a while back, good to read you back on board.

As these are transient episodes of visual disturbances, the physiologic data do show the eyes to manifest early effects of high pp02, and that there are no lasting effects once it resolves, its very hard to say for sure.

There are 2 anecdotes, few to no divers report symptoms once the bottom setpoint is pp02 of 1.2 or less, and that there are few reports of possible fatal 02 toxicity on OC divers diving to bottom pp02 of >= 1.3.

When VENTID was put as a prodrome of symptoms of 02 toxicity, and often taught to nitrox students, they studies were based on symptoms reported by Navy rebreather divers using very high pp02 in shallow depths. The subtle symptoms you and other describe are consistent with their data.

I have yet to hear an open water diver report any VENTID symptoms breathing OC with high pp02 ... its more commonly a rebreather phenomenon. Unfortunately, 02 convulsions in OC is commonly fatal, so if they had a VENTID before they convulsed, we'll never know.

 

[Dr Deco]

Thanks for all the comments. I do not have any further insight on this issue.

Dr D.