Yes heat exhaustion can cause complete temporary blindness in both eyes and it means that it's leading to heat stroke.
If you're out in the heat and you start noticing your eyes getting blurry or you're getting double vision or you begin to not be able to see that's a sure sign of heat exhaustion that's leading up to heat stroke.
If you can get inside a cool place or into some shade and call 911 just to be safe.
It's better to get help and not need it than not get help and need it.
Heat exhaustion can lead to heat stroke which is a serious life threatening condition and is a medical emergency.
When I had heat exhaustion last summer I had blurred vision in both eyes and it gradually got worse and after I got help and cooled off my vision came back .