Wednesday, September 21, 2005

How is colorblindness tested?

My first color vision test ever, I think, was an article in Popular Science that my dad thrust in front of me. I was 7 or 8, and I had just commented about the orange-ness of the grass. By that point I had already made skies purple in coloring books, but this magazine confirmed it for my dad.

My next test, administered by my opthalmologist a few years later, consisted of his pointing to the woven pattern on his office wallpaper and asking me to identify a strand or two of color. "Red-green colorblind," he said.

I've since failed a number color plate tests in books, on Web sites, in science museums, but I haven't really been tested as an adult, and I've felt like I've been missing some important self-knowledge--especially now that I'm in art school.

So a month ago I asked my opthalmologist, who handed me a booklet of Ishihara plates (circles made up of colored dots, some of which form letters, numbers or curved lines from one edge to the other). Some numbers and lines were obvious, others nearly invisible. I stared at some plates, certain I could figure out the path of dots if I could just have a moment alone with them. But my doctor grew impatient; she started turning the pages for me. Her professional opinion: "You're colorblind."

"Can you be more specific?" I asked.

"You'll have to come in again for a more in-depth evaluation."

That in-depth evaluation, the Farnsworth Dichotomous something-or-other, took place today. Here's how it works: in a long narrow box lies a row of 15 pastel-colored pegs (like little plastic game pieces). The first peg is immobile; your task is to choose the peg among the others that most closely matches it and place that one second. Then you choose the peg that most closely resembles the second, and place it third.

A lab technician administered the test--rather unscientifically. First of all, she casually allowed me to see the pegs before she mixed them up. What I saw was a spectrum of colors from bluish-purplish something on one end to yellowish-orangish-greenish something in the middle to bluish-purplish something on the other end. I averted my eyes and tried to ignore what I'd seen. She put a patch over my right eye, scrambled the pegs and handed the box back to me.

Peg #1 looked blue to me. Or purple. Several others looked similar, in value if not in hue, so I placed those next. After I had ordered 4 or 5 pegs, the test administrator said, "You understand what you're supposed to do, right? You choose the one that looks most like the first one and place it second."

Clearly I was bombing. My arrangement looked different from what I had seen minutes earlier, but I thought I should ignore that and just try to follow the directions. At some point I reached what I would call the "from here on out, one guess is as good as another" moment, and I handed the box back to her.

She flipped the pegs over and started copying numbers down on a form. "You've got some real color problems," she said with a laugh. I asked her how often she administers the test.

"Oh, it goes in waves," she said. "We always get the guys from the police academy. That's awful. They go through the whole training, and then they have to take this test. If they fail it, they can't graduate. I've seen men in tears."

She moved my patch to the other eye and rescrambled the pegs. "Actually," she said, "you've pretty well scrambled them up yourself!"

This time I decided to use my head. The yellowish ones go in the middle, I thought, and the darker ones look either blue or reddish. They must go from cool to warm. It must go from blues to greens to yellows to oranges to reds, like a counter-clockwise trip around the color wheel. I took my time, comparing pegs, looking for hints of warmth and coolness.

"You did much better this time," she said. "If you want, you can do the first eye over again."

So I did, following the same strategy.

"Wow," she said. "I've never seen so much improvement." My score was nearly perfect with the left eye the second time around.

She asked me which results I wanted her to submit to her director for the formal report. "Do you want the results to be better or worse?" she asked, thinking I might need the poor results to get some accommodations at school. "Whichever is more accurate," I answered.

But I'm not really sure which would be more accurate. Obviously her feedback helped me, but it didn't change my color vision--it just changed my understanding of what I was supposed to do. We decided to submit the first try, since the resulting report would probably be more interesting.

In any case, the results suggest that I have this problem, to lesser or greater degree:

PROTAN (red, blue green)

"What does that mean?" I asked.

"It means you confuse red, blue and green. Or red and blue-green." So she didn't know.

"I think I might be an anomolous trichomat," I said. She gave me a blank look. "This form says dichotomous, but isn't that also a type of color blindness?" I asked. "Anomolous trichomat?"

"Could be," she said.

OK, so was that a waste of time? In the hands of a less clueless technician, would my results have been different? Will the report tell me something I don't already know, something that can help me negotiate expectations with my art teachers?

We'll see--it should arrive in the mail in a week.