Went for mri last year for tinnitus and found out i have arachnoid cyst and chiari malformation recently have worsening tinnitus blurry vision, why?

Blurred vision &, : less commonly, tinnitus,can be symptoms of a Chiari Type I from the cerebellar tonsils' causing pressure on the brainstem &/or spinal cord or blocking flow of CSF. Arachnoid cysts may have no symptoms or may cause pressure on the parts of the brain they overlie, especially if there is an increase in size of the fluid-filled sac. Thorough medical & neurological re-evaluations are warranted.