Having a spinal tap, as you have found out, is not without its side-effects. I would be more inclined to have one if my doctor really thought that I had intracranial pressure not because he did not know what else to test for. To test just for a tests sake is not a good idea! Perhaps discussing what the symptoms are for increased pressure would help you decide. Also “visual disturbances” as a side-effect is a bit vague, more precision is encouraged. Can an opthamologist look at your eyes and tell? I do not know.
What I do know about Chiari and visual disturbances is that Chiari’s pressure on the spinal cord and its contents can affect brain function - before and continuing after surgery too. Various systems can compensate, but if further challenged later in life (illness, blow to the head, medications, ageing, stress), the brain’s ability to perform well can be compromised. Vision is incredibly complicated and one of the first brain function to deteriorate with Chiari both pre and post surgery.
By all means explore other options with your doctor to rule out other conditions. We cannot blame everything on Chiari.
If nothing else is to blame, and doctors are finished investigating, you may want to consider visual therapy. I am 6 years post surgery and ended up doing a couple of long stints of daily exercises to get my visual perception in good shape. Of course doctors blamed vestibular migraines, psychological disturbances, and stress as a cause of my vision concerns prior to me finding a wonderful vision therapist.
Keep us posted!