I spoke to a couple of Doctors who fully understand mixed gas diving. Basically they said it was ‘probably’ a reaction of the lung to the high Oxygen content in the mix. Sort of an irritation.
No one is sure, but Oxygen at high percentages is quite bad for you, the inside of the lung inflames and is unable to absorb the gas.
Following that the next day I reduced the final Deco mix to a much lower O2. I was OK.
Further dives I used a max of 70% O2, which also has the added benefit of being a gas that you can get onto early in the deco. Should the dive go wrong it gives you more flexibility
I’ve never liked using pure O2 as its only useful from about 6m upwards – which is no good if you need gas at say 20m.
How the gas affects you is very individual, I’ve altered my deco gradient after lots of experiments.
Still got bent a few times, but it was more of a skin rash rather than losing sight in one eye – which was alarming to say the least.