Wondering if anyone has any ideas on what may have caused this. I was on the second dive of the day on my JJ when I noticed that I couldn't really see the rightmost LED on my HUD. It was like I was getting tunnel vision. I then also noticed that I had disturbances in my vision. This was only a 20m dive I was playing with some new video lights so at this point I bailed out but the disturbances remained. It was very strange I've never experienced anything like this before while diving, what I can say was that at the time I felt completely fine and didn't feel like I had impaired decision making. I ascended to 6m on my BO but subsequently decided that since the symptoms remained I didn't want to be underwater anymore, since I had no deco obligation I ascended straight to the surface after about a 1min stop at 6m.
After getting back to the car and de-kitting I started to get a splitting headache which lasted for several hours post dive, it only went after taking some paracetamol and going asleep for a few hours.
What I can conclude:
It probably wasn't anything to do with my O2 or Dil, this was the second dive of the day and the 3rd dive in total on this set of cylinders, all previous dives were without incident.
I had a fresh scrubber packed that day and at this point only had about 1hr 20min on it doing very low stress/low exertion dive.
When I noticed the problem with my vision I made a conscious effort to check my breathing encase of CO2, it was completely steady and I was not finding it difficult to breathe.
Although the water is very cold this time of year I was warm, I was wearing fourth element xerotherms with a heated vest and a fourth element halo undersuit, with heated gloves. The only part that was slightly cold was my feet.
This was only my third dive with a new hood, I can't think of any reason why this would make a difference but that is one part of my kit that has changed recently.
At the moment my only conclusion is that I started to get a migraine underwater, I do get them about once a year but never while diving before.
I have left the rebreather together and I am going to breathe off it tomorrow for 20mins to check for CO2 breakthrough but since my breathing remained steady I am not expecting this to teach me anything.