You may have a condition called central serous retinopathy (CSR). This condition is commonly seen in young men and thought to be induced by stress. Fortunately, this condition resolves on its own over a month or two without treatment. Sometimes lasers and injections can make the fluid resorb faster, but ultimate vision recovery is similar between treatment and no treatment.
From your description, it is likely CSR but I would recommend you confirm with your eye doctor in Vietnam.
CSR is generally not associated with pain. If you have inflammation of the optic nerve called optic neuritis, this can cause pain on eye movement. This generally resolves within 6 weeks, but tests should be done to make sure it is not related to infections or other autoimmune diseases.
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Do you have pain with eye movement?
How bad is your vision in that eye?
Did the doctors say a name for the condition?
Yes, it's unlikely a retina detachment from your description.
For CSR, usually just wait until it resolves on its own. The drops may help, but efficacy is not known.
You vision should improves as the fluid goes away. I describe as similar to a blister in the back of the eye.
In some cases, laser or injection of medicines into the eye helps to speed up the recovery.
Yes, that can happen since it has medicine in it.
Yes, that is possible.
It is thought to help, but not proven.