The value or benefit of something that must be given up to gain something else is known as . The worth or importance of something is its . describes the limited supply of goods, resources, or services. A person who pays for goods or services is a , while a person or group of people who use resources to make goods or provide services is a .

True blindness may be caused by trauma to the eye, severe conjunctivitis due to  ibr (infectious bovine rhinoceros) or pink eye or other infections, leptospirosis, lead poisoning, selenium toxicity, fungal infections, vitamin a  deficiencies, rabies, vitamin b12 deficiency, neoplastic of the orbit or  conjunctiva, cataracts, congenital malformations, etc.