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Swimming with snakes


Even when on vacation, scientific discoveries never cease to amaze

Dr. McDonnell

By Peter J. McDonnell, MD

A few weeks ago, I escaped from the cold weather of Baltimore and went snorkeling with a friend off a beach in Costa Rica. One of the most beautiful and visitor-friendly countries in the world, this nation has protected the habitats of its native plants and animals. Sea turtles, monkeys, tree frogs, and orchids are all plentiful here.

On this sunny day, the warm, clear Pacific Ocean was teeming with colorful, interesting fish of all shapes and sizes, singly and in large schools. Most of them were just swimming around, while others were hard at working gnawing at the coral of the reef or plant life on the sea floor.

That’s when I happened upon one more very colorful form of life-one that was about as welcome as Michael Jordan at a Hair Club for Men Convention (or, if the reader prefers, as a mosquito at a nudist colony). Cruising along the sea floor, just a few feet below me, was a very colorful sea snake, about 1 meter in length.

Having grown up on a beach along the Atlantic Ocean, where sea snakes do not live, all I knew about these creatures had come from books.

In the Pacific and Indian oceans, I knew, sea snakes are quite venomous. What I did not know was whether they were aggressive, whether they could swim faster than me with my flippers, and whether this particular species was poisonous.

Fortunately, while I pondered, this chap just ignored me and slithered beneath my floating body, headed off to do whatever business he or she had on her agenda for that day.

After a while, we were back on shore and my friend asked, “I saw snakes out there. Did you?”

We compared notes and learned that, based upon the coloring, we had actually seen different snakes.

“Are they poisonous?” she asked.

“I don’t know,” was my reply.

‘Ignorance is bliss’

Sadly, the Internet reaches even to the pristine beaches of Central America, and quickly my snorkeling companion had researched this life form.

Thankfully, they are generally not aggressive, but are quick to defend themselves if molested. Pelamis platurus, extending from Pacific islands to Costa Rica and Panama, is indeed possessed of venom that can cause death. Based on LD50, the venom is more potent than that of any terrestrial snake in Costa Rica, but human fatalities are much less common. After 30 minutes to several hours, ptosis and paralysis of voluntary muscles occurs, followed by rhabdomyolysis, severe hyperkalemia, and cardiac arrest.

“I’m glad I didn’t know this before I went snorkeling,” my friend said.

“Ignorance is bliss” was all that occurred to me.

Even if, like me, you are creeped out by snakes, when you see them up close you have to admit they are very colorful. Equipped with their venom, they must feel no need to hide themselves.

Sea snakes have small eyes with round pupils. As a rule, they do not leave the water. That makes sense because presumably their eyes, adapted to see underwater, would render them severely myopic on land.

Also, sea snakes like Aipysurus laevis have photoreceptors in the skin of their tails, allowing them to detect light. This ability is thought to let the snake know that it is completely hidden from prying eyes when it wants to be, or it might make it easier to avoid being surprised by creatures (like vacationing ophthalmologists) swimming above.


• Campbell JA, Lamar WW. 2004. The venomous reptiles of the Western Hemisphere. Comstock Publishing Associates, Ithaca and London.



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