Sorry but I think you’re better off seeing a doctor than asking me. Sometimes it’s only seasonal though.
Or caused by staring at a computer screen for too long. You can also try supplementing with fish oil capsules or eating more fatty fish.
The Mayo Clinic has a good online article listing aging and vitamin A deficiency among other causes.
There are OTC eye drops to alleviate it, but if it’s persistent you should really see an eye doctor to be safe.
If it’s related to diet or dry air they can sometimes go together.
BUT AGAIN I’M NOT A DOCTOR.