LORI,
My son's eyes are red ALL the time and he has constant headaches. He reads huge books and he reads all the time which is very hard on his eyes. His eyes can't keep up and they tire within 15 minutes. He needs to wear glasses when reading. Although he has 20/20 vision, his eyes cave in when he focuses up close. So the more he reads...the more headaches. He actually only used both eyes together ONCE while being tested. Other than that he is constantly switching eyes. The glasses help relax his muscles during up close work so he can go longer without the headache.

It would be interesting to see what your son would do on the test if it was taking in segments. When the optometrist was done testing him (it took two hours), when my son looked up at me, he literally looked like he had the flu. It worked his eyes so hard he looked sick. He was physically and emotionally done. He was exhausted and really couldn't do much for the rest of the day. Which makes me wonder how the poor kid makes it through a school day with all the close up work. It may explain some of his 'quiet defiance' issue. I think he may just quit working when he can't see or function anymore.
My son's IQ test (WISC IV) was not the best testing environment. It was done by a substitute school psychologist (very great guy), but we were at the end of a hall that comes to a circle which has 5 classrooms. The test started as school was getting ready to start. It was the last 2 days of school and it was bedlam. The teachers were yelling up and down the halls, the kids were yelling up and down the halls, the announcements went on for I think 7 minutes and I was trying to read outside the little closet room my son was in and I couldn't even concentrate it was so loud. The psychologist left the door wide open during the first half of the test. I got up and asked him if he would close it. He didn't want to, I think for the child safety concerns - no adult will be with a kid behind a closed door... for molestation type concerns. I worked in a school here and that was the rule. However, even with the noise etc for half of the test he still did pretty good, getting an overall 121 and a VCI of 130.
I bet your kid would do even better on the test if done in short segments.