A cat's eyes are good at signalling trouble early, provided you know what normal looks like for your own cat: bright, clear, evenly open, with matching pupils and only the smallest amount of sleep in the corners. Eye problems disturb that picture in recognisable ways, and because some eye conditions can damage vision fast, the timeline of what changed and when is unusually important with this category of signs.
Squinting, redness and discharge
Squinting is the classic first flag. A cat may hold one eye half closed, blink one side more than the other, or turn that side of the face away from bright light. Redness can appear in the white of the eye or along the inner eyelids, and discharge ranges from clear watering to thicker yellow or green material that crusts the lashes and needs wiping away repeatedly through the day. Pawing or rubbing at the eye is common and worth discouraging gently, since claws and rough rubbing can scratch a surface that is already sore. Note whether one eye or both are affected: a single squinting eye with pawing often points to something local like irritation or a scratch, while both eyes watering alongside sneezing suggests a wider respiratory picture. Either way, the detail helps the vet narrow the starting point.
Cloudiness, third eyelid and pupil changes
Cloudiness is a sign to take seriously. It can look like a bluish or grey haze over the front of the eye, a white spot on the surface, or an eye that simply stops looking clear and shiny in photographs. The third eyelid, the pale membrane in the inner corner, may slide partly across the eye in a cat who is unwell or whose eye is painful. Pupils deserve a look too: a difference in size between the two pupils, or a pupil that stays wide in bright light, is not normal. An eye that suddenly looks enlarged, bulging or different in colour from its pair also needs prompt attention. Photographing the eyes in the same light, without flash close to the face, creates a comparison that shows whether cloudiness or redness is progressing.
Vision and behaviour clues
Sometimes the first evidence is not in the eye itself but in how the cat moves. A cat losing vision may hesitate at doorways, misjudge jumps she knows well, startle when approached from one side, or become unusually cautious in a dim room. She may bump furniture that has not moved, or walk more slowly with her head carried lower, whiskers forward. These changes are easy to blame on age or mood, so test your impression gently: watch whether the difficulty is worse on one side, and whether toys waved silently on that side get less response than on the other. Do not shine bright lights into the eyes to test them; your observations of everyday behaviour are the useful evidence.
When an eye sign is urgent
Contact a vet the same day for an eye held shut, obvious cloudiness, a swollen or bulging eye, pupils of different sizes, or any eye problem alongside bumping into things. Eye pain in cats can escalate quickly, and problems involving pressure inside the eye or damage to the surface are far easier to help early. Tell the clinic exactly when you first noticed the change and whether it is improving or worsening hour by hour. Having that onset time and progression recorded in your KinsLe Pet Passport, which keeps a cat's health records together for vet visits, lets the vet judge urgency from facts instead of estimates.