Tuesday, December 23, 2008

You'll shoot your eye out

(A Christmas Story, Warner Bros, 1983)
(Click arrow to start the video)

Merry Christmas and
Happy New Year!

9.12 Panda myopia

Two giant pandas, Tuan-Tuan and Yuan-Yuan, both from Sichuan arrived in Taiwan today.

Panda-mania now begins. Kids are overjoyed. And adults are busy analyzing the political implications of such precious gifts.

The happiest people are the merchants who peddle everything panda, from cookies, candies, to clothing.

What, pandas are near-sighted? -4.00D? Based on cycloplegic refraction?

Friday, December 5, 2008

9.11 Lobster eyes

On the left is a normal 2-clawed Maine lobster. Newport Daily News (12/3/2008) reports that a 1.5-lb 4-clawed lady lobster is caught this week by a Mr Patrick Marks in the waters 60 miles south of Newport, RI. It has one crusher claw and three pincher claws, all functional. After showing it off most of the day, Mr Marks let her go, explaining that he "sometimes lets lobsters go out of guilt when they look at him funny."

Yes!! Lobster vision at work.

Lobster eyes are structurally very different from that of other animals (including the mantis shrimp). The cornea actually contains an array of mirror-like reflectors, each arranged at a specific angle, that ultimately focus incoming light rays onto the retina.

The optics is reflection rather than the more conventional refraction.

Presumably in the dim deep sea where sharp vision is less important than acute sense of smell and touch, the lobsters do not rely on vision to hunt, they only need to detect motion.

Under bright lights, the lobsters probably cannot not see much as everything is blended into the background and "washed out". Lights reflected from their eyes, on the other hand, will give you an impression that you are being stared at, inquisitively. If you were a lobsterman, you'd probably let them go, too.

Earlier this summer, another 4-clawed lobster was caught by a Mr Jimmy Whitty based in Morell, PEI, Canada. It was nicknamed Mothra and kept in an aquarium at a restaurant. It was, alas, lost to follow-up.

And in Taiwan (local news, 11/25/2008, reported in www.nownews.com), fisherman Mr Chen caught a 3-kg male crab with a 50-cm "wing" span, estimated at 10 years old, at the mouth of Chen-wen Brook in Tainan Hsien (台南曾文溪河口). When caught with a net, it protested loudly with a hissing sound, fought gallantly with its claws, and with the eyes extending from the protective grooves, it was looking to escape at the same time. Mr Chen eventually let him go, so it can continue to propagate.

Wednesday, November 26, 2008

The first Thanksgiving

(In November of 1621) when the Wampanoags helped the Pilgrims (who had arrived on the Mayflower, in 1620) bring in their first crop in the new world, there was a great feast during that harvest time. According to the Pilgrims, about 90 Wampanoags crashed the party and brought with them all sorts of delicacies. The Wampanoags usually celebrated their harvests, with food and rejoicing. They brought venison (deer meat), wild turkey, rabbit, woodchuck, lobster, clams, mussels, potatoes, sea bass, bluefish and many other delicious foods. Wampanogas also brought corn, beans, and squash to the feast, and even showed the Pilgrims how to cook the food. The Pilgrims were very appreciative of the gifts, and the 90 Wampanoags who crashed the party had a wonderful time (extracted from http://content.scholastic.com/browse/article.jsp?id=7587).

Thanksgiving is celebrated in the US on the 4th Thursday of November every year. Happy Thanksgiving !!

Friday, November 21, 2008

9.10 Eye popping

Occasionally, patients claim they can do "crazy" things with their eyes. One of them can indeed move her eyes independently, for example. So much for coordinated binocularity. A burning question is: Can the eyes actually pop out of the eye sockets. The video below answers the question in part. It shows voluntary globe luxation, another of those crazy things, which presumably is a painless maneuver. Strictly speaking, it is a form of exophthalmos. Exophthalmos, as we all know, is most commonly seen in Graves disease.

Warning: The following video is a bit on the gruesome side:

(Click on arrow to start the video)

There are all kinds of catastrophic injuries involving the whole eyeglobes. One of them has the eyeball hanging outside of the socket with the eyelids closing behind the eyeball. This is not a pleasant topic; however, from the eyecare point of view, a review is still necessary.

As far as this type of involuntary eye popping, there are two varieties: (1) traumatic avulsion of the globe and (2) traumatic globe luxation. The difference between the two is really the extent of the damages: avulsion involves completely or partially severed extraocular muscles and the optic nerve, whereas in luxation, the muscles and the optic nerve are retained (hence a potentially total recovery after proper care). Luxation can be from a simple act of sneezing - often the patient has shallow eye sockets and weak ligaments.

With globe avulsion, there is very little or in fact zero chance of sight restoration. The 1999 movie, Oliver Stone's Any Given Sunday, has a scene that depicts some hapless football player's eyeball flying across the end-zone when tackled. This is actually probable despite common disbelief. There were indeed incidences of such injuries from through-the-windshield car accidents and blow-to-the-head martial-art competitions.

Perhaps the most disturbing are reports of eyeballs hanging by the threads (i.e., remnants of the optic nerve) in many A-bomb victims in Hiroshima on Aug 6, 1945. The blast force was a "mere" 15 kilo-tons, far less than the warheads in the arsenals of super-powers today, e.g., 300 kT. Destruction on such a scale is beyond imagination/comprehension. Let's not even try.

Tuesday, November 11, 2008

9.9 One-eyed dragons

Ah, yes, this 1956 movie based on Leo Tolstoy's epic tome of the same title. And Audrey Hepburn (1929-1993) remains a perennial favor of many movie fans all over the world, even today.

One of the supporting characters in the movie, while in fact the chief architect of the Moscow defense, or more accurately, the Non-Defender of Moscow, General Mikhail Kutuzov had lost his right eye to head injuries, sustained while fighting against the Turks early in his career.

In 1812, France invaded Russia. With Kutuzov's scorched-earth strategy, Napoleon entered a deserted Moscow. His Grand Armée eventually succumbed to the bitter winter. Of the 450,000 men, only 10,000 returned to France, barely alive.

There were a few one-eyed generals. In the Eastern culture, they are known as one-eyed dragons (or 独眼竜 in Japanese and 獨眼龍 in Chinese). In the Chinese Red Army, there was General Liu Po-cheng (劉伯承, 1892-1986) who had also lost his right eye to a bullet wound. He led successful guerrilla warfare against the Nationalist Army in the late 1940s.

Beyond military operations, and far more interesting is the founding of Sendai City (仙台市) in the Northeast region of Japan in 1600 by Lord Da-Té Masa-Mu-né (伊達 政宗, 1567-1636) who had also lost one eye. The right eye, of course.
In this case, however, the loss was not owing to war injuries but to an eye infection of unknown etiology. Some proposed small pox, others claim that he later gouged out his diseased eye on purpose. And it is doubtful that any anesthetic was used at that time.

Lord Daté was a patron of Christianity in Japan. He actually built sea-worthy ships and with which, sent emissaries to Rome to establish diplomatic relations with the Pope. Five members of the expedition stayed in Coria (now Seville) in Spain to avoid religious persecution ordered by the Tokugawa government back home. The descendants adopted a last name "Japón" who now number 600+.

It would appear that generals who had lost their right eyes were great visionaries.

To make the story complete, the earliest known one-eyed general was Antigonus I Monophthalmus (382BC - 301BC) under the command of Alexander the Great. Unfortunately, it is unknown as to which eye he had lost. Judging from his life-long military successes, probably the right eye as well. He finally lost a battle at age 81, killed by a javelin.

King Philip II (360-336BC, father of Alexander the Great) also had lost his right eye, but then he was not a general.

Tuesday, October 21, 2008

Happy Halloween!!

It is that time of the year again... Temperatures start to drop. Leaves begin to turn colors and fall on the ground. And in the early evening of Oct 31, kids from around the neighborhood, dressed up as little goblins and ghouls, come and ring your doorbell. They'll yell "Trick or treat!!" when you open the door, and gleefully collect candies from your hands. [Mental note: one of them has peanut allergies.]

And a Jack-o'-lantern on your porch? Yes, a tradition around here in the Northeast (or wherever modern-day Celts congregate).

Why are the eyes triangular in shape? No one really knows. Maybe the all-seeing eye housed in a pyramid, an icon of the Freemasons, can tell us.

A Happy Halloween to all!!

Monday, October 6, 2008

9.8 Baby formula

By now, 53,000 babies in China have been sickened by melamine-tainted milk and 4 have already died (left: a baby holding a can of Sanlu powdered milk). And milk products from China are now banned in many countries around the World.

Ideally, there should not be any melamine in any food anywhere. Unfortunately, melamine is ubiquitous. Chances are the favorite plastic dish/cup of yours or the counter top in your kitchen was made in part from melamine. The upper safety limit in food set by both the EU and the US is now 2.5 ppm (or 2.5 mg/kg). For babies, 1 ppm in China [in Taiwan, the upper limit for powder milk for babies is at a far more stringent 0.05 ppm]. In the US, the tolerable daily intake is set, for now, at 0.63 mg/kg body weight/day.

Let's do some simple math: Assuming you weigh 50 kg, the daily melamine limit is then 0.63 x 50 = 31.5 mg. Then even if you consume 31.5/2.5 = 12.6 kg of milk powder everyday, it is still "safe". And for a 12-month-old baby weighing 10 kg at the 1 ppm limit, it'll be a 1 kg consumption per day - still quite a lot of milk. Unfortunately, the melamine content in Sanlu powdered milk putatively was as high as a mind-boggling 2,560 ppm. So forget the math, the stuff is highly toxic all right.

The most logical alternative to powdered cow milk is of course mother's milk. While this may not always be possible, for those making the switch, more about milk and the eyes:

The following are extracted from an interesting article by Hoffman et al: "Maturation of visual acuity is accelerated in breast-fed term infants fed baby food containing DHA-enriched egg yolk". J Nutr 134:2307-2313, 2004:

The authors divided 6-month-old breast-feeding babies into two groups: (1) the DHA group that received each day, one jar of baby food (113 g) containing egg yolk enriched with 115 mg/100 g DHA (docosahexaenoic acid) and (2) the same but no DHA (i.e., the control group).

Both groups continued to breast-feed for a mean of 9 months. In the control group, the red cell DHA levels decreased significantly between 6 and 12 months (from 3.8 to 3.0 g/100 g total fatty acids), whereas in the DHA group, the levels increased from 4.1 to 5.5 g/100 g.

VEP (visually evoked response) acuity at 6 months was 0.49 logMAR (minimum angle of resolution) which improved to 0.29 logMAR by 12 months in the control group. In the DHA group, VEP acuity was 0.48 logMAR at 6 months and which matured to 0.14 logMAR at 12 months. In other words, 1.5 lines (on the eye chart) better visual acuity than the controls. So an adequate dietary supply of DHA throughout the first year of life maybe necessary for visual maturation. The stereo-acuity on the other hand was not affected by DHA.

Interestingly, DHA concentration in human milk varies from as little as 0.1% of total fatty acids in women on Western diets to as much as 1.4% in Inuit women in North America and 2.78% in Chinese women from a fishing village, both of the latter consumed large amounts of marine animal foods.

Hmm... So the old-wives' tale of "fish is brain food", by way of DHA, is quite profound and is actually scientifically accurate! [We don't need to repeat that the brain is the extension of the eyes, do we.]

Saturday, September 20, 2008

9.7 Beethoven's Symphony No 9 in D-minor

It is a well-known story: When his 9th (the Choral) Symphony premiered on May 7, 1824, in the Kärntnertortheater in Vienna, the audience went wild. Ludwig van Beethoven (1770-1827) by then, however, was totally deaf. Contralto soloist, Karoline Unger, had to help turn him around to face the cheering crowd. There were 5 ovations all together, the ultimate respect for a common man (the police stopped further ovations in deference to the royalties who customarily were accorded three). It must have been quite a moving sight.

Beethoven indeed had put all his heart and soul into this symphony. In fact, despite the common belief that the vocal part of the 4th movement, Ode to Joy, was a poem borrowed from Frederich Schiller (1759-1805), Beethoven himself actually wrote portions of it. For example, at the very beginning of the vocal part, i.e., the baritone solo starting on bar 216:
O Freunde, nicht diese Töne!
Sondern laßt uns angenehmere anstimmen,
und freudenvollere.
Freude! Freude!
This symphony is of course remembered forever for its 4th movement. However, IMHO, the 3rd movement beginning with Adagio molto e cantabile is positively celestial that deserves even more attention.

Something about Beethoven's eyes? Ah, yes, we are just coming around to that.

The etiology of Beethoven's deafness has never been clear. Several possibilities have been put forth including otosclerosis, syphilis, noise trauma, Paget’s disease, sarcoidosis, and otitis media. None of them was conclusive, however.

It is known that Beethoven suffered from digestive diseases plus rheumatism, various skin abscesses and recurrent infections, ophthalmia, jaundice, and anemia. Ophthalmia? An old term for inflammation of the membranes/coats of the eye, i.e., iritis/uveitis. This, plus Beethoven's own admission of "constant belly aches, diarrhea and bloody stools" suggests that he might have a bad case of ulcerative colitis or Crohn's disease - both of which are associated episodically with deafness.

So the best guess is then: Beethoven's deafness was an immunopathic manifestation of Inflammatory Bowel Disease (IBD). And iritis/uveitis no doubt flared up from time to time. Unfortunately, after the autopsy, the coroner's report concentrated on the liver and the abdominal fluid, with nothing on the intestines. So we'll never know for sure.

There is a lesson here, though: Patients with IBD need to have their eyes (especially the retina) and ears (at least the hearing) examined regularly - particularly for musicians and composers.

Friday, September 12, 2008

9.6 Diving and retinal breaks

Guo Jingjing is the Gold medalist of Women's 3-m springboard diving of the 2008 Olympics. She took up diving since age 7. And now at age 27, she is the most decorated Olympic female diver ever.

And the price she has paid as far as the eyes? Retinal tears or breaks:
They lead up to the more severe sight-threatening retinal detachment. Which was probably what has happened to Ms Guo. In 2002, a retinal break was discovered in her right eye. After a successful surgical repair, her vision or visual field dropped to 20% of normal anyway. In 2004, right before the Olympics in Athens, the retina apparently has re-detached. She went on to win two gold medals nonetheless. After the 2008 Games, both eyes now require surgery.

Sudden physical impacts or blunt trauma to the eyes in, e.g., boxing, car accidents, baseball or hockey games, can disrupt the retinal (and sometimes choroidal) structure. Even if there is no detectable blow-out detachment when the eyes are examined immediately after the injury, it does not mean that the patient is out of the woods. Unfortunately, the latency for retinal detachment is quite long, often in years. Diving apparently involves repetitive impacts on the top portion of the eye. In other words, when the diver's head enters the pool water, the contact force will have been transmitted to the eyeballs. And the latency of retinal detachment will have been considerably shortened. Even worse if there are other pre-disposing factors, e.g., high myopia and/or family history of retinal detachment.

Athletes in competitive diving should probably have their retinas examined at least once every 6 months.

Tuesday, September 2, 2008

9.5 You are left-eyed?

No one can spin a better yarn about the eyes as the ancient Egyptians. In the Egyptian mythology, the right eye, aka the Eye of Re (or Ra), symbolizes the Sun. And the left eye, aka the Eye of Horus, is the Moon.

The Eye of Re has a mind of its own and frequently wanders around by itself. On one of the fun-filled outings, it refuses to return, so Re (the father of all gods) sends Shu and Tefnut, two underlings, to retrieve it. The eye stubbornly refuses. And in the ensuing struggle, the eye sheds tears and from which, men emerge.

Another story has it differently, Re actually sends Thoth to fetch it back. And upon returning, the eye discovers that it has been replaced by another eye and becomes quite indignant. To pacify it, Re places the right eye in the shape of the uraeus serpent on his own brow - to show that the eye is now the ruler of the world. This serpent is worn by all Egyptian Pharaohs on their headgears. The right eye later becomes an entity and its association with many goddesses is of course the basis of many other stories.

The story of the left eye, the Moon, is even more complex.

The lunar cycle actually represents the eternal battle between Horus and Seth. They are fighting for the inheritance of Horus's father, Osiris. Seth steals the eye and damages it - cuts it up into six pieces. Thoth, with the help of other gods, puts the eye back together on the 6th lunar day. The healed eye is known as Wadjet. It symbolizes a re-established order after disturbances. The lunar cycle is essentially a description of how the eye is injured and repaired. The latter performed by 14 gods.

For the mere mortals such as you and I, the two eyes also behave somewhat differently - in the form of ocular dominance. About 2/3 of the population sight with the right eye. Ocular dominance seems to correlate with the handedness, i.e., a right-handed person sights with the right eye. However, there are always exceptions; you can be right-handed but sight with the left eye and so on. The reason is simple, each retina is controlled by both hemispheres of the brain, whereas each limb by only one side.

Ocular dominance is actually quite interesting and practical at the same time. It is often why a patient notices a change in vision (i.e., when the dominant eye is seeing less well than the fellow eye) and seeks help. In monovision contact lens fitting, the first attempt is always to fit the dominant eye for distant vision and the fellow eye for reading. Sometimes, this does not work out and the patient actually does better with the dominant eye for reading. In monovision laser vision correction, the dominant eye is also selected for distant vision. You are of course stuck if this arrangement does not work.

Being very capable archers, the ancient Egyptians must have queried their eye doctors why some sighted with one eye vs the other. The mythology of the eyes, on the other hand, is a true testament to their vivid imagination.

Evidence of eye surgery in ancient Egypt? See the lower eyelid of the right eye in this mummy portrait:

An attempt at repairing entropion, it seems.

Saturday, August 23, 2008

Exemplary Olympians

In the wheelchair is Su Li-Wen of Chinese-Taipei (Taiwan). She competed with an injured left knee in the women's 57-kg Taekwondo and fought in excruciating pain to the end. In the last round, she fell 11 times yet refused to concede.

Robina Muqimyar of Afghanistan who competed in the 100 meters. She came to Beijing despite the mysterious disappearance of teammate Mehboba Ahadyar (around July 4, while training in Italy), who was to run in the women's 1500- and 3000-m events.

Monday, August 11, 2008

9.4 Valsalva retinopathy

Lu Ying-Chi of Chinese Taipei won a bronze medal of women's 63kg weightlifting
event at Beijing 2008 Olympic Games, Aug 11, 2008.

Chen Xiexia (C) of China, Sibel Ozkan (L) of Turkey and Chen Wei-Ling (R) of Chinese Taipei wave to spectators at the awarding ceremony of the women's 48kg of weightlifting event at Beijing 2008 Olympic Games at the Beijing University of Aeronautics & Astronautics Gymnasium in Beijing, China, Aug 9, 2008. Chen Xiexia, Sibel Ozkan and Chen Wei-Ling won the gold, silver and bronze medals respectively. (From news/xinhuanet.com)

Weight-lifting can injure the eyes. No kidding.

Once a patient came in and complained that his vision in the right eye was suddenly lost when he tried to lift some heavy boxes in his basement. Valsalva retinal hemorrhage immediately comes to mind. However, fundus exam reveals a cellophane membrane over a "wrinkled" macula. A macular pucker, it turned out to be. This is entirely different from the first suspect which occurs when one holds breath performing physically strenuous tasks, e.g., heavy weight-lifting, giving birth, passing stool, etc. The increase in the intrathoracic/abdominal pressure raises the venous pressure which in turn causes rupture of retinal capillaries. The blood accumulates between the retina and the vitreous. And vision changes if the hemorrhages occur within the visual axis. Often the history and a retinal exam confirm the diagnosis:

(Image from Digital Ophthalmology)

The above is an unusually large pre-retinal hemorrhage in a case of Valsalva retinopathy. More common than not, the hemorrhages are much smaller of about 1 disc diameter often found near the disc itself; although they can extend into the macula and obscure vision.

Luckily, most cases of simple Valsalva retinopathy heal quickly, spontaneously, and completely. Some cases, usually those with pre-existing vascular disorders, may require the Nd:YAG laser/surgical intervention.

So who/why/what is "Valsalva"? Well, Mr Antonio Maria Valsalva (1666-1723) was an Italian physician specializing in ear anatomy. He had also described the (original) Valsalva maneuver (i.e., what happens physiologically when you forcibly exhale against a closed glottis). He also coined the term, the Eustachian tube (which connects the middle ear and the pharynx). When you travel by air, when the airplane descends for landing, your ears tend to "pop". The reason is the rapid increase in the atmospheric pressure causes the Eustachian tube to collapse (or become pinched). Gum-chewing works the best in opening this tube and restoring the pressure balance. If you don't have any chewing gums handy, try opening your jaws with the lips closed instead.

Saturday, August 2, 2008

9.3 Centrifuges and reading in space

This is a standard desktop centrifuge. Each "hole" accommodates an Eppendorf centrifuge tube. The centrifugal force is about 2,000 x g, strong enough for separating most particulate matters from the solvents. For comparison, 1 x g is what most of us experience on the surface of Earth everyday.

Humans occasionally subject themselves to higher Gs. For example, most rides in amusement/theme parks are actually centrifuges or variations of centrifuges. While most are in the less than 2 x g range (an example is shown below), some in the form of roller-coasters, e.g., the Space Mountain in Disney World, can reach 4 x g.

(An amusement park centrifuge)

Momentary exposure to 4 x g (or even higher) is relatively harmless, unless there is an undiagnosed pre-existing medical condition - then it can end in tragedy. Indeed, heart attacks and brain hemorrhages are known to occur on some high-G rides.

NASA has the ultimate centrifuge for the humans:
This is NASA's 20 x g centrifuge used for testing the physiologic responses of astronauts. And this is where you see the astronauts' faces start to melt, among other things.

Technically, the g-force is calculated thus:

where g = Relative centrifugal force (RCF)
r = rotational radius (centimeters, cm)
N = rotating speed (revolutions per minute, rpm)

Of course, g is also the basic unit of the gravitational force. Without gravity (i.e., zero-g), as that in the outer space, some human reflexes that have worked previously now begin to unravel. And one of them is the simple vestibulo-ocular reflex (VOR).

Now pick one object in your room, stare at it, and then move/rotate your head to left and right, you'll notice the object remains in the same stable position. In other words, the image of the object is stabilized on your retina. This is the VOR at work.

The sensory aspect of VOR is handled in the inner ear by the semicircular canals (which sense angular acceleration to detect head rotation) and the otolith organs (which sense linear acceleration to detect both head translation and the position of the head relative to gravity). The information is processed centrally and the output sent to extraocular muscles.

In zero-G, the semicircular canals do not work well because the fluid contained within no longer convects effectively. So the coordination between head motion and eye movement is now disturbed. If you read too fast, the text lines will appear jerky. Effective reading can be achieved only at voice speed. Whether VOR eventually adapts to long periods of zero-G and normalizes is still yet to be tested. In a long journey to other galaxies, catching up on your reading will become an integral part of mental exercise. Certainly beats looking out of the window into darkness 24/7.

Of course, large centrifuges can be incorporated into space stations and star ships. The centrifugal force will provide simulated gravitation that can make the astronauts' lives easier.

The (presumably) rotating space station shown below is in 3D. You'll need to borrow a pair of red-green glasses from your eye doctor to see the effect.

(From http://farm3.static.flickr.com/2351/2130591814_53d9037897.jpg?v=0)

Monday, July 14, 2008

9.2 Mars

No one can forget the excitement upon seeing this image, taken in 1976 by the Viking spacecraft then orbiting Mars. Clearly it is a face complete with eyes (well, at least one), nose, and mouth. Some claimed that computer enhancement showed an eyeball with the pupil (the right eye) plus a tear drop below the eye. In 1998, the Mars Global Surveyor re-photographed the same region and the face now looked somewhat different, the "eye", sadly, either was never there or had disappeared:

So the Martians most likely did not construct the site, if there had been Martians in the first place.

Now the Phoenix Mars Lander tells us, there is ice on Mars and the Martian soil is similar to that found in our backyards. For those who grew up with Ray Bradbury's the Martian Chronicles (1950), the new info is simply a re-affirmation of what maybe, even though no Martians are found just yet. Of course, Marvin the Martian (and his eyes) has been around to entertain us for a long long time:
Now, remember this 1990 movie, "Total Recall", starring Arnold
Fast forward your DVD to the part when Douglas Quaid and Melina get blown out of the enclosures onto the surface of Mars and are now exposed to the Martian environment, i.e., the vacuum. Their bodies begin to bloat. The change of their eyes is especially alarming as they begin to bulge out of the eye sockets. However, as soon as the alien machine starts to alter the Mars atmosphere to that resembling the Earth, both Quaid and Melina recover nicely. Their eyes look entirely normal with no loss in function - as if nothing untoward has happened. Right there is your clue that something is amiss in this explosive decompression episode. If the eyeball can expand at all, it'll only be the conjunctiva. The retina does not have the elasticity to allow stretching and is certain to disrupt, just like wet tissue paper. So an episode such as that depicted in the movie can lead to blindness.

It is often assumed that a person explodes when exposed to the non-pressure of the outer space. In reality, for a human being to decompress from 1 atm to zero, nothing much happens, because the skin is tough enough to withstand such a small change. The sclera of the eyeglobe is especially strong because it is constituted of overlaying collagen fibers. A slight inflation, yes. Explosion, no. Oh, the death is from asphyxiation, naturally.

There has been only one catastrophic explosive decompression of unimaginable force. That is the Byford Dolphin diving bell accident of 1983. In which, 4 divers inside the bell died from a sudden pressure drop from 8 to 1 atm owing to the sudden opening of a hatch (the diver who opened the hatch also died). The Byford Dolphin is a Norwegian oil exploration rig then operating in the North Sea. The divers were undergoing gradual decompression when the accident occurred. One of them closest to the hatch literally did explode. The others showed blood lipoprotein denaturation, organ hemorrhages, and large amount of gas in blood vessels. One diver had a large sub-conjunctival blister suggesting a separation of the conjunctiva from the sclera.

It is possible that the script writers of "Total Recall" had perused the Byford Dolphin forensic reports, hence the eye scene.

Unfortunately, in a world now starving for oil, we foresee a rush to off-shore oil exploration and deep-sea drilling. We must all remember that safety for the workers/divers is a first priority and deservedly so.

Friday, July 4, 2008

Happy 4th of July !!

A quick report (11:00PM): Boston celebrates 4th of July in style, again. The Boston Pop under Keith Lockhart performs at the Half-Shell on the Esplanade for a crowd of half a million with music that combines country and pop, the 1812 Overture by Tchaikovsky complete with canon firing and church bell ringing, Puccini's Nessun Dorma from Tourandot, John Philip Sousa's Star and Stripes Forever - just to name a few. The event is MC'd by Craig Ferguson. And the fireworks are simply breathtaking that light up the dark summer sky with spectacular reflection from the Charles River.

It is a great city, Boston. Please come and visit.

Incidentally, Red Sox 6, Yankees 4, today.

Thursday, July 3, 2008

9.1 Shrimp's auntie

No, this is not a cockroach. It is a mantis shrimp (shown above is one of the less colorful varieties), also known as 蝦姑 (the shrimp's auntie) in Chinese.

A more colorful one is shown below:
It is more a crab than a shrimp. The taste is rather bland, though - probably the reason why it has never made it into the menu of Chinese restaurants. The Italians do have a way of preparing it (recipe below quoted from here):

Canocchie (or Panocchie) alla Pezza - Mantis Shrimp Pezza Style

To serve 4:
16 Mantis shrimp, about 2 1/4 pounds (1 k) in all
A small clove of garlic, minced
A small bunch parsley
A lemon (optional)
Olive oil
Salt to taste

Lightly oil a deep skillet large enough to contain all the shrimp, and lay them flat in it with the garlic and a pinch of salt. Sprinkle a little water over the shrimp, cover the skillet with a wet cloth, and cook over very high heat for 2-3 minutes. Serve the shrimp at once, garnished with sprigs of parsley and, if you like, lemon wedges.

Note: It goes without saying that it'll be a messy sitting, as the shrimp shell is a bit hard to crack.

There are always people who look at the shrimp differently. A few have noticed the unusual eyes:
And a close-up (by Roy Campbell, from www.wired.com):
In the 3/20/2008 issue of Current Biology, Cronin, Marshall, and Caldwell reported that the mantis shrimp had a 4th mode of vision. Really, unlike everybody else, it sees circular polarization light. (Note: the other three modes of vision: black & white, color, and linear polarization). So what does that mean? Let's look at the polarization process first (below quoted from here).

"Light in the form of a plane wave in space is said to be linearly polarized...If light is composed of two plane waves of equal amplitude by differing in phase by 90°, then the light is said to be circularly polarized. If two plane waves of differing amplitude are related in phase by 90°, or if the relative phase is other than 90° then the light is said to be elliptically polarized."

In other words, if one can see the tip of the vector, circularly (or elliptically) polarized light would appear to rotate. It can be produced by passing linearly polarized light through a quarter-wave plate at a 45° angle to the optic axis of the plate. For the transmission of electromagnetic waves, circular polarization has almost no signal loss. It will be a great way of cell phone communication - no more dropped signals. Of course, for the mantis shrimp, this "technology" has been in use for more than 400 million years. Human electrical engineers are still yet to catch up.

It is fair to assume that the mantis shrimp uses circularly polarized light to communicate for mating and/or staking territorial claims - as in other animals. Its shell then must be the source of the reflected polarization light. Its compound eyes already contain thousands of rows of light-detecting units called ommatidia - a mix of photoreceptors and filters.

If you think about it, the mantis shrimp will survive long pass other species on earth: It looks un-appetizing, in fact, not much taste, has a hard shell for protection, and communicates with polarized light which no one else can see. Not bad at all. In fact, it is also known as the shrimp from Mars.

Speaking of Mars...

Monday, June 23, 2008

8.7 Plastic brain

(From ewake.wfubmc.edu. IMHO, a pickled sheep brain is more fun to play with.)

Actually, the topic here is Brain Plasticity (or the more authoritatively sounding "Neuroplasticity"), a red-hot theme in brain research today. This post will only give you a quick introduction of what it is. Ideally, another blog should be created to cover this subject in much greater detail. Perhaps in the future.

Only a few decades ago, it was generally agreed that the lower brain and neocortical areas were immutable/unchangeable. In other words, the brain functions are fixed in certain areas:

Indeed, developmentally, it has been shown that the sensory pathways are fixed after a certain critical period. However, it has gradually become clear that the continued re-wiring of the brain, throughout life, largely influenced by the environment, is also operational. (A grand unification theory is needed here.)

Simplistically speaking, beyond the basic developmental plasticity, there are at least two other types of plasticity: one induced by injury repair and the other simply from learning and memory. In brain repair, the functions can move to different locations, and in learning/memory, specific brain areas can expand.

Neurologists have long observed that spontaneous recovery from brain lesions is common. For example, in an fMRI study (Pantano et al, Brain 125: 1607-1615, 2002), MS patients who had suffered a single attack of hemiparesis, there are adaptive changes involving both the symptomatic and asymptomatic hemispheres - during a simple motor task. And the extent of these changes increased with the lapsed time and the severity of damage .

There are simply too many such examples to cite, so we won't even attempt. Readers are encouraged to google their own.

And in this news article: "Taxi drivers' brains 'grow' on the job" (BBC News, 14 March, 2000): "...The hippocampus is at the front of the brain and was examined in Magnetic Resonance Imaging (MRI) scans on 16 London cabbies. The tests found the only area of the taxi drivers' brains that was different from the 50 other "control" subjects was the left and right hippocampus... One particular region of the hippocampus, the posterior or back, was bigger in the taxi drivers..."

These Knowledge Boys/Girls are special, aren't they.

Notice in the above, the research methodology was based on MRI yet again. In fact, both morphometric and functional MRI.

Let's not stray too far from the eye. If you recall "3.3.1 Who's being lazy" and "3.3.2 Squint", here is something extra that is relevant to brain plasticity:

"...The gray matter volume in strabismic adults was smaller than that in normal subjects at the areas consistent with the occipital eye field (OEF) and parietal eye field (PEF). However, greater gray matter volume was found in strabismic adults relative to normal controls at the areas consistent with the frontal eye field (FEF), the supplementary eye field (SEF), the prefrontal cortex (PFC), and subcortical regions such as the thalamus and the basal ganglia. These opposite gray matter changes in the visual and the oculomotor processing areas are compatible with a hypothesis of plasticity in the oculomotor regions to compensate for the cortical deficits in the visual processing areas..." (See Chan et al, Neuroimage 22:986-94, 2004.)
(Esotropia OS. From eye.ac.cn)

The next step is confirmation with fMRI. Time to write a grant application, then.

Maybe an introductory paragraph starting with:

"Visual deficits can be correlated to less gray matter at the striate and extra-striate visual cortex. In particular, visual motion deficits can be correlated to less gray matter at the parietal eye field, and normal saccade responses can be correlated to more gray matter at the rest of the oculomotor regions..."

Then again, maybe not.

Friday, June 13, 2008

8.6 Perivenous syndrome

First, all sons and daughters, take your father out to dinner on Sunday.

Happy Father's Day!

We will now touch upon the "perivenous syndrome". Perhaps the best explanation is that in Prof Philip James's " Hyperbaric oxygenation in fluid microembolism", Neurol Res, 29(2): 156-161(6), 2007:

[Abstract] "...Studies of bubbles formed on decompression in diving have demonstrated the importance of pulmonary filtration in the protection of the nervous system and that filtration is size dependant, as small bubbles may escape entrapment. Fluid and even small solid emboli, arresting in or passing through the cerebral circulation, do not cause infarction, but disturb the blood-brain barrier inducing what has been termed the 'perivenous syndrome'. The nutrition of areas of the white matter of both the cerebral medulla and the spinal cord depends on long draining veins which have been shown to have surrounding capillary free zones. Because of the high oxygen extraction in the microcirculation of the gray matter of the central nervous system, the venous blood has low oxygen content. When this is reduced further by embolic events, tissue oxygenation may fall to critically low levels, leading to blood-brain barrier dysfunction, inflammation, demyelination and eventually, axonal damage. These are the hallmarks of the early lesions of multiple sclerosis where MR spectroscopy has also shown the presence of lactic acid..."

Having already gone over the principle and practice of NMR, now a quick review of the current treatment of multiple sclerosis (MS):

MS, despites years of research, still does not have an agreed upon etiology. Since the principal symptom is inflammation, treatments thus far have targeted it by using anti-inflammatories. For acute relapses, patients with relapse-remitting MS are treated with steroids usually intravenous methylprednisolone (IVMP). For longer-term maintenance, there are the interferons, IFN1a and INF1b, that can block immune factors known as class II MHC molecules. With this treatment, the T cells can no longer breach the blood-brain barrier to cause cerebral damages.

The search for a better alternative to interferons culminated in 2004 when natalizumab, a monoclonal antibody, was approved for MS treatment. However, shortly after, reports of a rare progressive multifocal leukoencephalopathy (PML) surfaced. This new drug was withdrawn from the market in Feb, 2005. And after extensive reviews, in June, 2006, the FDA allowed natalizumab to return to the market with certain safety restrictions. The benefits of natalizumab, either by itself or in conjunction with IFNa1 seem to outweigh the risks according to several 2006 reports. So MS patients actually do have treatment choices and many are well-managed by their neurologists.

Of course, there are always other drugs being developed and tested, for example, the immunosuppressants, the statins, estrogen, even the cannabinoids. Also being tested are stem-cell implants and plasmapheresis. Preliminary results are somewhat mixed in most if not all cases.

Most intriguing, however, is the hyperbaric oxygen treatment (HBOT) of MS. In fact, the efficacy of HBOT has been reported in as early as 1983 (for details, see: Fischer BH et al. Hyperbaric oxygen in the treatment of multiple sclerosis; a randomised placebo-controlled double-blind trial. New Eng J Med 1983;308:181-186).

Because of the venous leakage that causes inflammation in the surrounding area, the treatment principle is to provide the repairing process the best environment before sclerosis sets in. And one of the major environmental factors is indeed oxygen. Logically, then HBOT should be employed urgently as it it the best way of delivering oxygen.

Treating early stage MS is now possible with the advent of MRI and MRS (and eventually, the 4-dimensional NMR spectroscopy). To firmly establish HBOT as the treatment of choice, large-scale double-blind studies based on MR technology must be conducted. The focus will be on the level of lactate, the 1.35-ppm resonance [note: its chemical shift is pH-dependent], th index of anaerobic glucose metabolism.

In fact, all eye doctors should be on the lookout for patients with early MS - pay more attention to a complaint of diplopia for one thing, and do take retrobulbar pains seriously. A judicious referral for MRI scan is mandatory. The treatment choices also must be presented and explained to the patients.

Ideally, those microemboli that cause focal ischemia in MS in the first place should be definitely identified and the method for their removal developed. Something for the near future, perhaps.

Lest we forget: many devastating ocular diseases are ischemic in nature, for example, primary open-angle glaucoma, age-related macular degeneration, and diabetic retinopathy. Is there a role for HBOT in the treatment of these diseases? You tell me.

Wednesday, May 28, 2008

8.5 Optic neuritis

(The above is a fundus photo of optic neuritis, notice the blurred disc margin. This is not always seen, however. Image from meded.ucsd.edu.)

Sometimes a patient's chief complaint is this: Over the past few weeks, vision fades in and out and the patient is now experiencing "pain behind the eye" especially when looking about. Also, there is now a loss of vision. A quick visual acuity test does confirm the patient's own observation. And the swinging penlight test also reveals an afferent pupillary defect. Ophthalmoscopy, however, shows a normal optic disc. You are entertaining a diagnosis of optic neuritis but how to confirm it in the absence of any obvious signs of disc change?

Contrast MRI, naturally:
The above is a T1-weighted coronal image of the brain after intravenous GdDTPA, a contrast agent, to provide enhancement of the lesion. And in this case, a hyperintense left optic nerve (on the right side of the image, the white spot next to the caption) suggesting a leaky optic nerve sheath resulting from, most likely, inflammation. In contrast, the right optic nerve shows no such enhancement. This clinches the diagnosis of left optic neuritis. A course of intravenous steroid treatment is then in order. Unfortunately for the patients, optic neuritis is often an early manifest of multiple sclerosis (MS):

In fact, 15 years after the onset of optic neuritis, ca 75% of women and ca 34% of men will have developed MS (see above, the hyperintense areas) which is characterized by exacerbations and remissions of motor and/or sensory functions over a period of time. Conversely, up to 50% of MS patients will develop one episode of optic neuritis. Both types of patients are seen in the eye doctor's office.

Metabolically, proton MRS of MS brain lesions shows a decrease in the NAA/Cr ratio and an increase in the Cho/Cr ratio. MRS in conjunction with MRI therefore can help distinguish early lesions that might respond to therapy from late irreversible ones. In theory, other resonances such as lipids, lactate, glutamate, and inositol, could potentially help in the staging of MS. Certainly, any successful treatment will be evidenced by the normalization of the NMR spectra.

A more specific water-suppressed proton MRS study of an MS patient (see Narayana et al. Serial proton magnetic resonance spectroscopic imaging, contrast-enhanced magnetic resonance imaging, and quantitative lesion volumetry in multiple sclerosis. Ann Neurol 1998;43:56–71) is cited here:

The spectra shown above were obtained on Days 98 (A), 147 (B), 189 (C), and 259 (D) of a longitudinal study. The volume of interest is exhibited in the MR images. The resonance at 2 ppm is NAA. (A) is the baseline. (B) and (C) reflect transient changes, chiefly a decrease in NAA. And (D) total recovery back to baseline as that in (A).

Notice in (B), the resonance at 1.32 ppm, designated as lipids in the original report, is actually lactate [to be further verified of course]. This is consistent with the general observation that lactate accumulates abnormally during necrosis, inflammation, or other tissue injury. In other words, whenever ischemia occurs, cellular metabolism is forced into anaerobic glycolysis with lactate as the principal end-product.

We will next examine the etiology and treatment of MS.