Brian, optometrists are not immune form urban legends. As the two related questions indicated, it's not bad. It's no worse than a camera operating in low light. Here are some relevant links that may apply more specifically to your question:
Eye exercise and other care myths:
It’s time we put those myths to rest. Dr. Theodore Lawwill of the American Academy of Ophthalmology said TV won’t do any lasting harm to your eyes even if you sit close to it. Kids, he said, like to be as close to the set as possible but nothing bad will come out of this habit. That’s because their eyes can easily focus whether the object is far or two inches or less away from them.
Should you worry if the room is too dark? Not really. On the contrary, people with mild cataracts may even see better in dim light. But this can cause eyestrain. To remedy this, simply adjust the set to get a better picture.
"The contrast between a bright set and a dark room temporarily tires some people’s eyes as does the reflective glare off the screen from a poorly placed lamp, but neither situation will lead to long-term damage," said Deborah Franklin in Health magazine.
"Choose a seat in relation to a movie or television screen at whatever distance is most comfortable to you. As long as you do that, you will not harm your eyes," Rosenfeld added.
Snopes.com forum discussion.
Also found an article on ScienceDaily that talks about this:
“Eyestrain can occur when the eyes are fixed on an object for a long period of time, there is poor lighting, or there is glare,” explains John Bullough, Ph.D., lighting scientist at the LRC and lead researcher on the television study. “One scenario believed to cause eyestrain is watching television in a dark room. In this case, visual discomfort is caused by the large difference in luminance between the television screen and the room’s dark background.”
Even though the effects were modest, they were measurable. The results are consistent with prior literature supporting the concept of limiting luminance ratios between a visual task and its surround, according to LRC researchers.
In all cases, they key word is fatigue, not damage. So the bottom line, it will make your eyes more tired, but it won't harm them.