Sometimes the attachment to the center of the vision
does not release and the jelly pulls on the central retina. This causes the retina at this location to swell, resulting in decreased vision. Sometimes the attachment releases with time but if it does not the pulling/swelling eventually cause scarring
and damage to the retina. The vision may improve if the pulling releases on its own, but otherwise the vision will likely worsen with time. Surgical therapy (vitrectomy
with membrane pealing) is usually considered but if your father is not a candidate there are some intravitreal injections which have some efficacy in cases such as this. I would recommend discussing these options with your current retina specialist or getting a second opinion to explore these options.