There are many reasons why the eyes can’t see clearly after looking at something for a long time, such as presbyopia, dry eye, visual fatigue and so on. 1. Presbyopia: Presbyopia occurs in middle-aged and old people, due to the age increase, resulting in the gradual decline of the eye’s adjustment function, so it will cause the eyes to see things for a long time can not see the phenomenon. 2. Dry eye: dry eye is more dry eyes, after a long time of eye use, the phenomenon of blurred vision will appear suddenly, due to various reasons caused by the quality and quantity of tears or abnormal dynamics of the tear film stability decline, and will be accompanied by foreign body sensation in the eye, dryness and other symptoms. 3. Visual fatigue: prolonged use of the eyes will cause visual fatigue, which will cause the eyes to see things for a long time can not see, mainly for a transient blurred vision. There are many reasons that cause the eyes to look at things for a long time, it is recommended to use the eyes reasonably, if there are symptoms of discomfort, it is recommended to consult a doctor in a timely manner, a clear diagnosis, and follow the doctor’s instructions for treatment.