Monday, May 24, 2010

Visual Evoked Potential test

Summer had an appointment with Ophthalmology for a Visual Evoked Potential (VEP) test on the 12th.  I didn't post right away because Jason and I were a little confused about the results, but I talked to the ophthalmology technician this morning and got some clarification.

The purpose of this test was to find out what level of damage, if any, she had to her optic nerves as a result of the brain tumor. The results will provide a baseline for her brain's response to visual stimuli, now that most of the swelling in her brain is gone. She'll have this test every 3-6 months (probably closer to 6), and they'll compare future results back to the one from today in an attempt to detect any problems early.

For the test, the doctor glued electrodes all around her head (which she did NOT like) and then sat Summer and I down in front of a TV screen. He played 30-second segments of flashing black and white patterns - one segment had  black and white lines, another had a checkerboard pattern, etc. - and dangled a small figurine in front of the TV. As the segment played, he sang a song and jerked the figurine up and down in front of the screen. Meanwhile, the electrodes measured her brain activity in response to the changes in pattern on the TV and the motion of the figurine.

Summer did way better than Jason or I expected her to with this test since it required her to sit still and focus on the screen without distraction. That's not a problem for her when Caillou is on, but a flashing checkerboard is not quite so interesting.

She made it through several of the brief segments, so the doctor decided to try and push his luck to get one or two more in, but Summer was done at that point. They got enough information from the ones she did sit through to give us a better idea of what her vision is like.

She can see, and her visual clarity is in the normal range - we already knew this. This means that things look just as clear or fuzzy to her as they should for any 20 month old kid.

That said, there was some damage to her optic nerve. The optic nerve is pretty inflexible and damage isn't usually reversible. We are incredibly lucky that it wasn't worse, especially when you consider that three weeks earlier she wasn't really able to see at all.

When it came to the smaller checkerboard patterns, her brain wasn't reacting the same way it had for the larger checkerboard patterns. This, combined with a normal visual clarity rating tells us that Summer can't see contrast as well as the rest of us. We won't know exactly what level of contrast she can see until she is old enough to tell us.

It could mean that she'll only have difficulty telling the difference between two very similar shades of the same color, or it could mean that she won't be able to recognize bigger differences in shades - like between red and orange. Until she can tell us there's a difference between two colors, we won't know.

The reduced ability to see contrast may make it a little harder when she's learning to read. This is where Jason and I were confused - black letters on white paper seems like pretty significant contrast to us. Well, it is - but small fonts make it harder to see the contrast and identify the shape of the letters. Also, a lot of children's books have text written over image backgrounds, rather than on a white background.

We can help her by getting books with large fonts on white paper (think the 'I Can Read' style), and by paying attention to lighting when we're reading to her or teaching her to read. She might outgrow those needs once she has learned to read, or she may need the large-print books for the rest of her life.We'll just have to wait and see.

At first, Jason and I weren't sure how to feel about these results. Everything had been so positive so far, that it has been easy to forget where we were three and a half weeks ago. Even this tiny bit of slightly negative news made us feel sad for her. But then we remembered. Three and a half weeks ago, Summer was essentially blind. Now, she can point out planes in the sky again and spot a flower to smell from across the street. We just have to keep reminding ourselves how lucky we are!

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