Post-anaesthetic blindness historically was thought to be associated with poor perfusion and oxygenation. However, a paper by Stiles et al in 2012 showed that the use of a mouth gag was a risk factor for blindness following anaesthesia in cats. The paper reviewed 20 cases of blindness. Three occurred following cardiac arrest. Of the remaining 17, all but one used a spring-held mouth gag at full extension. Their hypothesis that spring-held mouth gags can reduce blood flow to the brain by stretching of the maxillary artery was confirmed by Barton-Lamb et al in 2013.
Happily 70% of these cats regained "useful" vision. However please consider avoiding the use of spring-held gags. And adopting a "less is more" attitude when holding a cats mouths open for dental or other procedures.
I'm busy working on my blog posts. Watch this space!