1.Frequent blinking of eyes 2.For every 20 minutes look far away for 20 sec 3.Drink more water 4.Do not sit in front of air conditioner 5.Take Adequate break in between 6.computer screen should be 16-30inches away 7.ensure the screen is neither too bright nor dim 8.get good sleep 9.use lubricating eye drops 6 times per day 10.ensure there is no glare from your screen.

In all probability,  you may have mild number...as you are nearing presbyopia age n have difficulty in near work .. Get yourself checked !