This could be a sign of many things but it is always best to get the vet to actually check over the rabbit. In extreme cases it could be a form of cancer as any change in a rabbits eyes can be a sign of cancer. If not caught early enough, cancer can lead to several outcomes including the eye may need to be removed.
However, another and a more likely reason could be that your rabbit is getting cataracts. This is caused through age and the eyes become cloudier as time goes on. This can mean that your rabbit's vision will eventually deteriorate and vision will be a problem. While you can have laser surgery for your rabbit, if the change in their eyesight is gradual, they often adjust quite well and don't need surgery.
Whatever problem your rabbit has it could be painful or uncomfortable so it should be seen by a vet as soon as possible.
However, another and a more likely reason could be that your rabbit is getting cataracts. This is caused through age and the eyes become cloudier as time goes on. This can mean that your rabbit's vision will eventually deteriorate and vision will be a problem. While you can have laser surgery for your rabbit, if the change in their eyesight is gradual, they often adjust quite well and don't need surgery.
Whatever problem your rabbit has it could be painful or uncomfortable so it should be seen by a vet as soon as possible.