welcome to health care magic
is a degenerative condition of conjunctiva
which may grow towards cornea and make hindrance to proper vision..
because of exposure to uv rays or in sun light or due to dust it may develop,more commonly in the elderly aged people like your dad..
regarding the treatment as long as it reaches the cornea no treatment is required except for cosmetic purposes..when it encroaches upon cornea you need surgical excision to prevent double vision
,improper vision,halos etc..
in surgery,surgeon removes the excess part,,
Very rarely it may transform into malignant melanoma
for further suggestions..hope you get satisfied with my suggestion..