"38 CFR 70.4 - Criteria for approval
(c) When a claimant requests payment for beneficiary travel for care or services that were not scheduled with VHA prior to arrival at the facility and were not emergency treatment and the travel did not include a special mode of transportation, VA will not approve round-trip payment under this part but will approve payment for the return trip if VHA actually provided care or services."
According to this statement, VA is supposed to pay 1-way travel for medical services that do not require an appointment. I have been searching Title 38 and have found no exceptions for picking up eyeglasses or prosthetic equipment.
VA, time after time, does not follow its own regulations. They have a fox guarding the hen house with the VAOIG. However, Im unaware of a regulation which requires them to mail out glasses or pay you travel pay to pick them up.