I am a mother of a now three year old daughter with a facial PWS in the same areas as your child. I felt the same way that you and your wife do when my daughter Josie was born. It can be so overwhelming, mostly because a lot of the questions about your child's future are left up to fate. It can be so tough - I still worry about my daughter and her birthmark, even though we have had three years without any complications.
I am not a medical expert, but I can tell you what our pediatric dermatologist and other docotrs have told us about Port Wine Stains and Sturge Weber.
The PWS can be located in three different areas of the face: V1 , V2, and V3. The V refers to the 5th cranial nerve, which is the trigeminal. V1 is above the eyes, V2 is midface, and V3 is the lower face/chin. Children with PWS on the V2 and V3 regions have little-no risk for Sturge Weber. The risk increases when the birthmark is on the V1 region. However, most children with PWS on the V1 region do not have Sturge Weber.
My daughter has a tiny bit of the PWS on the area above the eye and a bit on the temple, which are V1 regions. However, because it is so minimal in this area, the doctors decided that an MRI was not warranted. Of course, I still kept an eye out for seizures, but we did not have an MRI. At age 3, she has had no signs of Sturge Weber syndrome, and she is perfectly happy and healthy and bright!
Because your child, like mine, has a bit of PWS above the eye, you will probably want to talk to your doctor about eye examinations for glaucoma in that eye. Children with PWS on and around the eye region are at increased risk for glaucoma. Josie received her first eye examination under anesthesia in conjunction with her first pulsed-dye laser treatment at 3 months old. She continues to get regular eye examinations to check for glaucoma. She does not have glaucoma or any increased pressure to date. She does, however, wear glasses (neither my husband nor myself do), and ironically her birthmark eye is the normal one!
In short, although it is necessary for you to take precautions in proper treatment and diagnosis of your child, it is also okay to take a breath of relief knowing that things will more than likely be okay. If you are taking to doctors that you trust and educating yourself on the subject, then you are already ensuring the best possible outcome, no matter what.
Best of luck in finding your answers!