Rubella in your 20s is unlikely to have caused an eye lesion as it is more often seen in congenital syndrome( characterised by cataract , glaucoma
, retinopathy ) . The corneal scar could have been due to co-existing infection of the cornea ( could be bacterial or viral ) . You are right that a corneal scar causes irregular astigmatism but then it is more gradual and is not so obvious as in few weeks. It would not be correct to attribute a recent decrease in vision to an old corneal scar. The eye will have to be examined in detail for other causes of reduced visual acuity related to anterior segment ( uveitis
/ glaucoma ), posterior segment ( retina / optic nerve related ) . Further course of action for corneal scar depends on its location on the cornea( from which clock hour to which clock hour eg 4o'clock to 8o'clock) , its depth ( whether superficial or deep ) , central or peripheral in location. If any signs of inflammation are found , it is treated with steroid eye drops . If no inflammatory signs are seen , then only corneal scar can be treated with either partial thickness keratoplasty for superficial scars or full thickness graft for deep scars. If the scar is very faint ( nebular grade ) , steroids are tried for a few months to see whether the scar heals. PTK
( phototherapeutic keratectomy) laser has been done for corneal scars too .
Thanks and best wishes
If you are satisfied with the answer , please press the accept
button so that I get my dues.
A bonus and positive feedback are welcome.