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Dr. Lloyd's blog has now been retired. We appreciate all the wisdom and support Dr. Lloyd has brought to the WebMD community throughout the years.

Tuesday, November 18, 2008

When Things Appear Clear but Different

Sometimes it can be very difficult for a person to describe something like a visual symptom.

“…it’s kinda green and it looks like it is on fire”

“…I see a repeat image but it begins 30 seconds afterwords”

“…think of it like a bright halo with a big upside-down X in the middle” (hey, isn’t an upside-down X still an X?)

Having practiced medicine for nearly 30 years I have witnessed many valiant attempts. Fortunately, most of the time, there is a nondangerous explanation to describe whatever the patient saw. On the other hand, specific symptoms are highly informative clues to the eye doctor.

“…my right eye just sees things differently than the left eye”. Such a disclosure may indicate a genuine problem.

Take a look at the top picture of colorful fall foliage. The vibrant colors jump out of the top photo. Imagine seeing that image with your left eye, but after covering the left eye the image in the right eye resembles the bottom picture. It’s still clear, the image is still crisp, but the colors appear washed-out. The medical term for this change is color desaturation. Acquired color desaturation often signals a problem in the affected eye or in the attached optic nerve. Here’s some comfort, a brain problem would not preferentially cause one-sided color desaturation.

Such a great disparity between the two eyes may not be noticed unless one eye is temporarily covered – like during an eye exam. There are some simple, painless clinic tests that can evaluate color desaturation complaints. Remember, the cause is likely inside the affected eyeball or its optic nerve. Cataract, for example, commonly causes this symptom and its presence is easy to confirm.

If the retina or optic nerve is the culprit then it is likely that other vision tests will be similarly abnormal. The penlight test of pupil behavior is a great example. A person with color desaturation due to an optic nerve problem like undiagnosed glaucoma will also demonstrate an abnormal pupil response to a swinging penlight test. On the other hand, if the pupils behave normally then the cause is localized to the eyeball and likely a fixable problem.

Here’s what you should know:

  • It’s a good idea to check the vision in each eye separately every so often
  • See your eye doctor if you sense color desaturation in one eye
  • Don’t give up if the first eye doctor cannot explain your unusual symptoms. Consider letting a second specialist listen to your story.

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Posted by: Bill Lloyd MD at 3:55 pm

Monday, November 17, 2008

Next Millennium Drug Delivery

Drug researchers have a lot to consider when they create new medical treatments. Besides chemical formulation, bioavailability and potential adverse effects, these scientists also want to optimize the delivery of the new drug to where it is needed most.

The eye is a particular challenge because eyedrops don’t simply migrate across the clear cornea and enter the eye – although at times we wish they could! If this were the case the eye would double in size everytime we swam underwater without goggles!

A variety of biochemical barriers and microscopic membranes interfere with direct drug transport. Clever drug researchers invented eyedrop formulations that allowed the medicine to alter its identity (electrical charge, lipid and water affinity, and pH) as the compounds make their way across the cornea.

When eye specialists needed a way to deliver high doses of antiviral medication to people with CMV retinitis (a blinding eye infection) inventors created tiny drug wafers that could be surgically implanted deep inside the eyeball. Some intravenous drugs are inert until stimulated by infrared, microwave or RF energy that is externally applied to the target organ. Again, put the drug where its needed.

Other medical specialists grapple with similar challenges. Powerful drugs used to treat colon cancer or severe intestinal inflammation can make people very sick as the drug circulates throughout the bloodstream. A team at the Dutch electronics conglomerate Philips has unveiled the intelligent pill – the iPill. Think of the iPill as a robot dumptruck with a built-in cellphone. It has its own wireless transmitter and measures 1.0 by 0.5 inches (bigger than a ‘Mike & Ike’ candy) and it cannot be chewed!

Gulp! Once it is on its way the iPill broadcasts the acidity of the surrounding contents. Since acidity drops as intestinal contents travel south of the stomach this is an accurate way to map its location. I don’t think consumer-grade GPS gear is that precise yet but I’m sure NASA is already working on it.

Once the iPill is at the desired location (duodenum, ileum, acsending colon, transverse colon, descending colon) it electronically releases the perfect dose of the prescribed medication. The rest of the body is unaffected. With traditional medicines you may need to consume 500mg in order to get 50mg to reach the target organ. The rest of the body has to deal with the leftovers!

Okay, I know what you’re thinking: how much will it cost? The prototype versions run $1000 per iPill (equivalent to 4 iPods!) Over time, like all electronic gadgets, the price will drop significantly…perhaps down to $10 per swallow. In the meantime I just hope Philips does not license the technology to Apple!

Okay, okay, I know what you are really thinking: what happens to the iPill once the journey is complete? It enters the iToilet and heads for the iSewer. Folks are already concerned that there is too much excreted Prozac in our drinking water, what happens when thousands (or millions of Americans start swallowing iPills? The iPill team at Philips says they don’t have a good answer yet. For now they are still working on a solution. I’m not too worried. Having seen all of the bizarre things my children have accidentally dropped in the potty I’ve never seen them reappear from my kitchen faucet.

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Posted by: Bill Lloyd MD at 3:29 pm

Tuesday, November 11, 2008

Permanently Pain-Free…Feel Good to You?

Scratches, abrasions and other very superficial injuries to the clear cornea often feel worse than a gunshot wound: super intense, burning, boring discomfort. It often persists even after the eyelids close.

There is a complex layer of sensory nerves that serve the outer cornea. These tiny nerves reside right beneath the epithelial cells and are immediately exposed following any trauma to those outer protective cells. These same nerves activate the instantaneous blink reflex whenever anything approaches our eyeballs, slamming those eyelids closed like a bank vault.

Fortunately, since the nerves are so close to the surface they are very accessible to topical anesthetics. These eyedrops temporarily block the sensory fibers’ ability to conduct a pain signal back to the brain – the problem is still there, your brain just doesn’t get the word.

Attention medical history buffs: Topical anesthetics (drugs like novocaine, lidocaine and tetracaine) derive from the same chemical family as cocaine. In fact, the first reported legitimate medical use for cocaine was for performing eye surgery over a century ago. A lot of history articles depict an oral surgery procedure but the scientist behind topical local anesthesia was Dr. Karl Koller, an Austrian ophthalmologist.

Since these eyedrops numb the pain why not prescribe them for continuous use until the patient recovers? There are several wise reasons that condemn that practice.

Pain is useful to the clinician. If the patient’s symptoms persist the doctor may want to explore other diagnostic possibilities. Pain relief also signals clinical improvement.

There is no guarantee the patient will return. Why should they? Their pain is gone, at least until they run out of eyedrops. In the meantime an abrasion may become an infected ulcer and permanent visual loss may result.

Topical anesthetics can inhibit healing. Additionally, chronic use of topical anesthetic eyedrops is toxic to the eye and can lead to irreversible corneal changes.

For these reasons eye doctors do not usually dispense topical anesthetics to their patients. A comfortable eye patch with a generous amount of ointment will usually work. Savvy, suffering patients may attempt to swipe a bottle of topical anesthetic when nobody is looking. Yes, this happens all the time.

Remember, ignorance is not bliss and anesthesia is not a treatment. Numbing the cornea does little to heal the underlying problem and, in some cases, actually creates new problems.

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Posted by: Bill Lloyd MD at 4:31 pm

Tuesday, November 4, 2008

How Does Squinting Improve Eyesight?

A recent visitor to our WebMD Vision & Eye Disorder message board posted an inquiry about his mother who had just recently had cataract surgery. I could immediately sense the worry in his posting.

During the post-op clinic visit the woman could see very the vision chart very clearly when using the familiar pinhole occluder. It uses a movable plastic flap with lots of small holes. Once the pinholes were removed the woman’s vision was very blurry. Was there cause for concern? I was able to offer some much-needed reassurance.

As I teach ophthalmology residents, the answer to every question regarding the eyes and vision is based entirely on either anatomy or optics – sometimes both!

The pinhole occluder imitates the most precise pair of eyeglasses ever made. The individual pinholes (Trivia Alert! Each hole is 1.2mm in diameter!) only permit straight rays of light to pass through. Therefore, only straight light rays enter the eye.

The optics of corrective spectacles work to straighten bent light rays – to reverse a refractive error. Now, if the rays are already straight no refracting is necessary. This explains why folks often see better when using the pinhole occluder (with or without their eyeglasses). People who can already see 20/20 without correction do not experience any improvement with the pinhole. A person with spectacles who sees better with the pinhole likely needs a change to their correction. In the case of the post-op cataract patient, she can expect an excellent visual result once healing is complete and postoperative astigmatism resolves.

Can you make a pinhole occluder at home? Sure! Unbend a standard paper clip and use one end of the wire to poke multiple holes in a index card – perhaps one-quarter inch apart. When you peek through the pinhole you should be able to read the time on a clock across the room.

We instinctively create a pinhole every time we squint. By narrowing the opening through which light can enter the eye we eliminate many nonaxial (not straight) light rays.

Pinholes and squinting are not a long-term solution for improved vision. They markedly constrict the visual field and reduce total illumination. Even so, both help us see better until our refractive errors can be corrected.

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Posted by: Bill Lloyd MD at 11:43 am

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