What are some infectious diseases that cause vision loss?

There are many: Most common would be corneal infections, like herpes simplex, contact-lens related infections or ulcers and subsequent scarring, acanthamoeba (rarely) etc. Retinal infections like cytomegalovirus (cmv), toxoplasmosis, histoplasmosis etc can also affect the vision. Rare but serious infections like endophthalmitis following trauma or spread from the bloodstream are also possible infectious causes.