After pursuing an undergraduate degree in Chemistry from Baylor University, he attended the University of Texas Southwestern Medical School. He graduated at the top of his class and became a member of Alpha Omega Alpha – Honor Medical Society. His training continued at Presbyterian Hospital of Dallas in an Internal Medicine internship, followed by an ophthalmology residency. He is presently board-certified in Ophthalmology.

Dr. Gilliland is actively engaged in teaching resident doctors in Ophthalmology, Maxillofacial Surgery, and several other specialties at Baylor Medical Center and the University of Texas Southwestern Medical Center.

Dr. Gilliland is an expert on orbital surgery and has extensive experience in the evaluation and surgical treatment of meningiomas with invasion of the orbit. His expertise has been crucial in the comprehensive care offered at the Meningioma Center, particularly in the management of patients with vision loss caused by meningioma involvement of the optic nerves or when there is orbital invasion by the tumor.  He often works in tandem with the neurosurgical team in the surgery of meningiomas affecting the intracranial and orbital compartments of the skull base.