I think my cat may be blind

Today my cat Tokki suddenly started behaving as if she cannot see. Her pupils seem dilated and glassy. She doesn't respond to her toys like she normally does. She just keeps glancing and sniffing around the room as if she really cannot see. Every time I pick her up she meows a little bit. I'm very worried. Just this morning she was playing with our other cat and took a nap. When she woke up she started behaving this way. She just stands in the same position and just seems very nervous. She's around 6 months old, she was fixed about 2 months ago, has been seen by the vet a few times (an initial exam and shots when we first found her, then when she was fixed and finally for treatment of a uti she acquired post op) other than she has no significant medical history that we are aware of. Could it be she suddenly went blind and if so what could be the cause and how soon should she see the vet? It's Saturday night and not sure if this would count as an emergency visit. Please any input is greatly appreciated.Thanks for taking the time to read.

I would consider it an emergency based on her young age and that healthy cats do not normally go blind unless there is a medical issue or exposed to something.  I would rather run a blood panel now then see if it gets worse.  May be fixable at this moment.  Blood sugar spike could make her vision very bad and that could be one of the easier fixes(insulin and a low carb canned food)

You can take the flat side of your hand and push it fairly rapidly towards one eye and the other and see if she blinks or reacts. Seizures and other neurological events are other causes of blindness but I agree with catsallaround that this is very unusual and serious and medical treatment as soon as you can is indicated.