The Eyes Have It

That bastion of science-y wonder has stumbled upon an incredible discovery. Teresa Conrick, at the Age of Autism, discovered something absolutely amazing, that apparently no one else has learned before. She did some in-depth investigation after noticing a peculiar change in her daughter. You see, Teresa's daughter's eyes were blue when she was born, but they gradually changed to a "brownish green".

This puzzled Ms. Conrick so much that she decided to look into just why her daughter's eyes could have gone from "beautiful blue" to apparently less beautiful brownish green. Anyone familiar with AoA will not be surprised at what she discovered. The cause?

Mercury!

Yep, according to Ms. Conrick, mercury (presumably from thimerosal) changed her daughter's eye color, as she discusses in a post title "Look Them In the Eyes". Kim Wombles already beat me to the punch on this one over at Countering, but I thought I'd take a stab at it, too.

Now, normal people understand that babies' eyes change color as they age. The color of the eye is due to a substance called melanin. Melanin is the pigment that makes our skin various colors. Darker-skinned people have more melanin than lighter-skinned people. It also happens to make our eyes the color that they are. Since lighter-skinned people, such as Ms. Conrick and her daughter, produce less melanin than those with darker skin, their eyes tend to be blue or blue-grey at birth. As they age, their body continues to produce melanin in the eye, leading to a gradual changing of the color of the iris. Pretty cool, huh?

Ah, but Ms. Conrick did research! She found that mercury can change the color of the eye! What was this research?

Let's start with "A Clinical Pathologic Study of Mercurialentis Medicamentosus" (PDF). This paper discuss lens pigmentation changes among individuals who worked in the thermometer, meter repair, felt hat and battery industries (all of which were exposed to inorganic mercury, not ethylmercury) and people who used phenyl-mercuric nitrate (again, not ethylmercury) containing eye drops. The route of exposure for these individuals is gaseous (for the workers) and topical (for the eye drop users). In other words, this paper does not support thimerosal-containing vaccines (TCVs) (intramuscular exposure to a different mercuric compound) as a cause for eye color change.

Next up, she links to "The Whole Book" (PDF). She quotes the following:

Chronic exposure usually occurs from inorganic mercury salt ingestion, inhalation of industrial or agricultural vapours or exposure to mercurial fungicides in paint. Mercury vapour exposure to the eyes can cause conjunctivitis and eyelid tremor. Chronic exposure may lead to grey or brown lens discolouration or band keratopathy.

Chronic exposure to mercury vapors can lead to lens discoloration. Again, TCVs are an acute, not a chronic, exposure, and the exposure is intramuscularly, not vapor. That makes 0 for 2 for Ms. Conrick's supporting research.

Let's continue. Maybe she has something else that actually supports her idea. "Effects of mercury intoxication on the response of horizontal cells of the retina of thraira fish (Hoplias malabaricus)" is a study looking at what happens when one injects methylmercury (again, not ethylmercury) into fish. The study found changes in function of the eyes, but does not mention changes in eye color, except for a passing reference to mercury vapor leading to concentrations in pigment epithelium in monkeys. Not only does this study not use the same form of mercury as in TCVs, it doesn't even look at eye color. If this were baseball, Ms. Conrick would be out.

But this isn't baseball. Either that, or Teresa's making up her own rules for the game. She continues with "Uveal Melanocytes, Ocular Pigment Epithelium, and Müller Cells in Culture: In Vitro Toxicology," a study that discusses how melanin in the eyes binds with "organic amines and metal ions". The abstract doesn't actually mention mercury in any form, nor does it address route of exposure, since they're more interested in in vitro cultures to examine toxic effects of various substances. No ethylmercury, not intramuscular exposure, no support for Ms. Conrick's idea.

Next, "Localizing organomercury uptake and accumulation in zebrafish larvae at the tissue and cellular level" actually mentions ethylmercury! In this study, the researchers exposed zebrafish to either methylmercury or ethylmercury in water for anywhere from 20-84 hours. They found that the greatest concentration was in the eyes of the fish. The amount of ethylmercury used was 100 μM (micromoles). I can't say what this translates to as far as total exposure, though, as I do not know the proper conversion method, nor did the researchers specify in how much water this was diluted. At any rate, This amounts to 20µg/mL for 20 hours (thanks, Science Mom, for the conversion). The exposure here is largely topical, though one can imagine that some would also be ingested. I'll give Teresa half a point for this one for actually getting the compound correct, but she missed the correct route of exposure. I'm also betting that the amount of thimerosal was significantly higher than would be found in TCVs.

All those previous "supporting" sources appear to have just been warm-up. Let's see what we have next. "Distributions of Elements in the Human Retinal Pigment Epithelium" (PDF). Ms. Conrick only provides this one quote from the paper:

It is likely that melanosomes may continue binding metal ions throughout the life of an individual, ultimately reaching a concentration that is demonstrable.

She failed to note that copper was found in greater amounts in the eyes than mercury (82% vs. 72% binding to melanin). Perhaps copper is the actual cause of autism? If I thought like Ms. Conrick does about mercury, this might actually make sense. At any rate, does this study mention ethylmercury? Nope. Nor does it mention route of exposure. In fact, the authors don't really talk much at all about the form of mercury, except for a few mentions of methylmercury. Once more, this study does not support Teresa's assertion that TCVs can cause eye color to change.

Maybe she'll have luck with her final source, "Mercury accumulation in the squirrel monkey eye after mercury vapour exposure." Well, the title doesn't bode well. We know right off the bat that we are dealing with vapor exposure, not intramuscular or subcutaneous exposure. Any mention of ethylmercury in the abstract? Hmmm...nope.

Ms. Conrick presents seven sources to support her notion that thimerosal in vaccines caused her daughter's eyes to change color. Of those, only one mentions ethylmercury (thimerosal), but does not use the amounts or route of exposure that would be found in TCVs.

When it comes to mercury (in varying forms), melanin does bind it, and it can cause damage to the eye in sufficient quantities. Furthermore, chronic exposure to mercury vapor can result in the eyes changing colors. However, there is no evidence that exposure to thimerosal from vaccines can cause changes to the color or function of the eyes.

She asks:

Are the eyes of autism possibly revealing a very big truth about a mechanism of injury?

Well, Teresa. When it comes to eye color, the answer is no. The most likely explanation is that she went through the same thing that happens to just about every human being: melanin production continues after birth, resulting in gradual changing of eye color.

Edited to add: Another thing Teresa failed to do was this: if TCVs cause eye color to change, and if this is an indication of autism, then there should be very few autistic individuals with blue eyes (among light-skinned populations). Out of curiosity, I googled "eye color autism" and found this, admittedly non-scientific, poll. The majority of respondents had blue eyes!

Addendum: I did some digging around to find some scientific articles discussing the change of eye color in infants to see how early it was noted, as well as some other info. Here's what I found:

•  The color of the iris during infancy - article mentioning changing iris color in infants from 1919 (8 years before invention of thimerosal and 11 before its use in vaccines)
•  Diagnosis from the Eye, Chapter IV: "The Teachings of Diagnosis from the Eye", p.15 - mentions blue eyes in infancy and changing color of the iris with age, from a 1904 text (23 years before thimerosal) whose author believes that blue is the normal eye color for Caucasians and any other color means the individual is diseased (darker eyes meaning worse the sickness)
•  Infants, Their Chronological Progress, p.16 - a text from 1887 (40 years before thimerosal) states the following about eye color and hair changes in children:
  

  The eyes of the new-born are always, as is alleged, a dark blue. A high authority states that the eyes generally begin to change color from the sixth to the eighth week. Galton teaches that the eyes begin to change within a few days; that " the color of eyes and hair is liable to change during childhood and youth;" that the color of the eyes is more persistent than of the hair; and that " the hair of children darkens considerably as they grow older, even up to the time when it begins to turn gray." Topinard says that "it is common for the hair, and in a less degree for the eyes, to become darker during the second period of childhood (7 to 14 years) or later." Authorities also teach that eyes and hair darken to less extent in females than in males; that the hair of females has less tendency to turn gray; that more girls have red hair than boys; and that dark hair tends to turn gray earlier than hair of other colors. As is well known, far more men than women are bald.

That last one has something interesting. Notice that it has been observed that eye color can change as late as 7 to 14 years of age.

What we can see from these few selections is that at least as far back as 1887, though likely much earlier (the first one also mentions that color changes have been noted for several hundred years), children's eye color gradually changes as the child grows. This just adds more evidence that what Teresa and many of the commenters at AoA observed is just normal childhood development. They are finding connections where there actually are none, like faces in the wood grain of a door.

Addendum, the third: Some of the terminology from the studies Teresa Conrick linked to have been nagging at me. So, I decided to see if I could find a good diagram of the eye with the parts labeled all nice and neat, so I could get a better sense of what was meant by "pigmented epithelium" and "lens" and how these differ from what we usually associate with eye color: the iris. Here is just such a diagram. Notice, if you will, that for the most part, the studies are looking at changes in the coloration of parts other than the iris. Teresa? Research; you're doing it wrong.