A large pupil usually means one of the following: glaucoma, nerve damage, use of dilating medication, physiological phenomena, etc. Normally, the diameter of the pupil is around 2mm to 4mm, but if it is larger than 4mm, it means that the pupil is dilated. Dilated pupils can be caused by a variety of reasons, usually related to glaucoma, nerve damage and other conditions. 1. Glaucoma attacks. Increased intraocular pressure in patients with glaucoma can lead to paralysis of the pupil sphincter, thus dilating the diameter of the pupil. 2. Nerve damage. Damage to the optic nerve can cause the pupil to lose the light reflex, causing the pupil diameter to expand. Damage to the motor nerve can also cause paralysis of the pupil sphincter, resulting in pupil dilation. Diseases of the central nervous system, such as cerebral hemorrhage, cerebral infarction, etc., may also affect the higher center that governs the movement of the pupil, thus causing the pupil to dilate. 3. Pupil dilation caused by the use of dilating drugs. If you order dilating drugs, such as atropine eye drops, compound tropicamide eye drops, etc., it will also lead to pupil sphincter paralysis, causing pupil dilation. 4. Physiological phenomenon. Physiologic pupil dilation occurs when the patient looks at something in a dim environment, allowing more light to enter the interior of the eye, thus creating clear vision. If the symptoms of pupil dilation persist and are accompanied by eye discomfort, it is necessary to consult a doctor to rule out pathological causes.