It can mean 2 different things. If it was just one hen I would suggest first that you look at maybe something in her eye. You can rinse her eye to try and remove whatever is in it although many times something gets lodged in their eye lids and needs to be removed.
The second reason is much more serious and it's contagious, Mycoplasma infection. Since two of them have it I would lean in that direction. Are they sneezing at all or do they have any respiratory discharge?
Can you take them to a vet? Are your chickens pets or livestock?
Mycoplasma can result in blindness if untreated. If it is Mycoplasma you will need to treat to pretect them from blindness and to keep it from spreading.