The invention relates to the use of brimonidine for treating ocular pain. The apparatus includes a communication control device that can be inserted into a signal receiving device. The particle flow is advantageously further reinforced in the direction of the gas sink by an oppositely arranged gas supply device. Light transmittance through the pixel part is changed based on movement of a fluid within the pixel part. The EKM then responds to the key request by issuing a new key ) or an existing key.