Had an eye ultrasound (fine) and an eye exam (fine) due to a nerf gun. but the dr said i still should be worried for 3mths for a detached retina, why?

The force of : The hit to the eye transmits energy to all the tissues. Because of the energy there can be a delayed response in form of a retinal detachment. This is very rare but risks are real.

Correct: The vitreous can contract post-trauma weeks later and cause retinal problems. Follow-up as recommended, sooner if new/worse symptoms.

Not common, fixable: Minor to moderate trauma to the eye rarely causes retinal tears and detachment. When it occurs, retinal reattachment surgery with vitrectomy or scleral buckle (types of surgery) can fix retinal detachments. When the trauma is severe, retinal detachments are more common, and the success rate decreases with increased severity of the trauma. It all starts with an exam by an eyemd.