The device may not be applicable to those with difficulty in hand tremor ; or those who fail to understand or perceive the phosphene ; or those with moderate to advanced glaucoma who will have too little optic nerve function to perceive any useful phosphene . " the key to a successful self - tonometry is proper technique and training 然而，对于手震的病人、不能理解及读取闪光现象的病人，或因青光眼已达中期至严重阶段，大部份视神经已经受损而无法有效读取闪光现象的病人，皆未必适用。
