An alkyl ether derivative represented by the following general formula [1] or its salt: wherein R1 and R2 represent each a substituent such as hydrogen, halogeno or alkyl; R3 represents alkylamino, amino or hydroxyl; the ring A represents a 5- or 6-membered aromatic heterocycle or a benzene ring; m and n are each an integer of from 1 to 6; and p is an integer of from 1 to 3; shows an effect of protecting retinal nerve cells and, therefore, is useful as a preventive and/or a remedy for retinal nerve diseases such as glaucoma, diabetic retinopathy, retinal artery obstruction, retinal venous obstruction, macular degeneration and retinopathy of prematurity.