"The Texas sales tax and motor vehicle sales tax laws allow people with disabilities to purchase certain items and services tax free.
Many items and services are specifically tax exempt by law. Some normally taxed items are exempt when purchased with a prescription. Others require an exemption certificate from the State Comptroller."
You may receive a refund for tax paid on an exempt item up to four years after the date of purchase.
For detailed information on specific exemptions the Texas Comptroller of Public Accounts has published on the internet "State Tax Exemptions for People with Disabilities".