14 September 2010
An individual should furnish a copy of the certificate issued by the medical board constituted either by the Central government or a state government in the prescribed form, along with the return of income of the year for which the deduction is claimed.
The term 'dependent' here refers to the spouse, children, parents and siblings of the assessee who are dependent on him for maintenance and who themselves haven't claimed a deduction for the disability in computing their total incomes.
14 September 2010
Blindness or low vision is a disability for the purpose of the referred section. However, grand parents are not included in the definition of dependents under section 80DD. In view of that, if you are trying for 80DD,you are not eligible for the claim.