A visible nictating membrane can indicate a cat that doesn't feel well, which wouldn't be that out of line with having a URI. As well, some URIs manifest with eye problems. How do your cat's eyes look otherwise? Any redness or tearing? Is your cat eating normally?
"To close your eyes will not ease another's pain." ~ Chinese Proverb
“We must not refuse to see with our eyes what they must endure with their bodies.” ~ Gretchen Wyler