I have used warm water and cotton ball to gently wipe from corner to corner. If there is something in the eye, which is often the case, this will help dislodge it if you can soak it long enough to un-seal the eye. If this doesn't work you will need to consult a vet to see what is wrong. It is possible that something caused a scratch and the eye has gotten infected. If this is the case the infection will have to be treated. Only a vet would be able to determine whether the infection is isolated to the eye or if it is systemic, meaning in the blood stream. This would determine what kind of treatment would be best.
On the flip side, I sold and shipped a young dragon who apparently had injured or lost an eye. I think something happened in shipping but am not certain. Anyway, the new owner was quite concerned and decided that since his wife was already very attached to the new baby he would keep it and see what happened. I told him I would replace it if it didn't make it and if he decided to take it to the vet I would reimburse him. He kept the eye clean and hand fed for a while. The eye never did open and the last I heard the baby was doing great, growing and had adjusted to having only one eye. So, as long as you can rule out infection, even if the eye was injured your MHD may have a good chance at a healthy life.
Keep us posted,
Marcia