When you stand up from your seat, it is normal for you to feel blackout in front of your eyes because of the rushed pressure at the eyes. You need to have a rest for a while to wait for the clear-headed situation. You should keep calm. This situation is temporary which will get recover soon. Thus you just wait for the recovery. Next time you need to stand up slowly from your seat.
The problem is not in the eyes but in the brain. One reason is due to low blood glucose, and the other is anemic and the third is caused by cerebral vascular insufficiency. Standing up suddenly can cause low blood pressure in the brain which can cause parts of it to selectively shut-down momentarily. To avoid this problem get yourself a little excited before standing up, such as pump your muscles, stretch your legs.
Generally speaking, there would be some causes that lead to your problem, such as low BP, diabetes, obesity, lack of vitamins, bad physical conditions, etc. So, you must figure out where went wrong with your body. And you must try to take actions against the problem. Try to consult a doctor in the hospital and take his sincere suggestions.