Photosensitive Epilepsy

With the premiere of the long-awaited (by some) Twilight: Breaking Dawn Part 1, several individuals have reported experiencing photosensitive epileptic seizures as a result of the flashing lights during the tense birthing scene in the movie. The instances occur due to the bright flashing lights of red and white, which can cause what are known as photosensitive epilepsy or photosensitive seizures.

Understanding Photosensitive Epilepsy

Photosensitive epilepsy is when your brain has an abnormal response to a certain sequence of flashing lights. The exact mechanism is not well understood, but it seems to be caused when flashing lights trigger a synchronized response in brain cells dedicated to processing visual signals. This synchronized response works like a laser to cause overexcitement in adjacent nerve clusters, which soon leads to the entire brain becoming seized, which results in blackouts and often motor responses.

What Light Triggers Photosensitive Epilepsy?

There is no single light or pattern of light that triggers photosensitive epilepsy. Many photosensitives will have trouble with a specific pattern of light. The chief frequencies for risk seem to be 15-20 Hz, but what frequency will stimulate an epileptic response varies from person to person and even from instance to instance for the same person.

One key seems to be the relaxation rate of the visual processing center of the brain. If processing cells remain excited for longer, it allows an accumulation of excited cells that ultimately leads to seizures.

Other photosensitives will experience problems with only a certain wavelength of light. Light of ~700 nm has been identified as a specific trigger for seizures. This is in the red part of the spectrum, so flashing red lights are often to blame for photosensitive seizures. Scientists suspect this is because light of this wavelength is processed by a special type of cone which is visually separate from other light-sensitive cones on the retina. There are three types of color-sensitive cones in the retina: red, blue, and green. Blue and green cones obviously have a significant amount of spectral overlap, but red is separate. According to the theory, when cones of one color are stimulated without stimulation of adjacent cones, the stimulus is magnified, which can lead to overexcitation. Testing the theory, researchers were able to trigger “epileptiform discharges” by stimulating only the green cones.

Other people have a quantity-of-light threshold. For these people it is the brightness of the light that ultimately triggers the epileptic response by overexciting all visual cells simultaneously.

What Stimulates Photosensitive Epilepsy?

Other than Breaking Dawn, some of the stimuli that have been shown to cause photosensitive seizures include:

  • Television
  • Video games
  • Computer monitors
  • Sunlight on water
  • Light passing through picket fence posts
  • Strobe lights at a club or theatrical performance
  • Patterns of black and white lines, especially whirling or dartboard patterns

Television is the most common stimulus for photosensitive epilepsy. Half of sufferers in Europe report their first seizure after watching television.

Who Is at Risk

The most common victims of this type of seizure seem to be children, usually appearing between the ages of 8 to 20, with a peak around age 12 or 13, and a link with puberty has been suggested. Girls are more likely to be affected than boys. Overall the condition affects about 1 in 4,000 or 5,000 people, and about 5% of epileptics. There is some evidence to suggest that the condition may pass with age.

How to Avoid Seizures

You don’t have to skip Breaking Dawn to avoid the seizure risk, though if you’re looking for an excuse it’s certainly a good one. Instead, you can just cover your eyes during the scene, which is only a few seconds long, and has enough audio clues to ensure you won’t miss any information. For added safety, you can cover your eyes through the whole movie and you probably also won’t miss anything.

Here are some tips to avoid seizures in other circumstances:

  • Keep your distance from flickering media (about 8 feet from the TV and a foot from your computer monitor). If you have to approach the TV, cover one eye–seizures require stimuli from both eyes.
  • Make sure your monitor’s settings do not have too high a contrast and the refresh rate is at least 60 Hz.
  • Always watch TV, play video games, or work on the computer in a well-lit room
  • Reduce your exposure to fluorescent lights and make sure they get replaced when they begin to flicker at a visible rate
  • Wear polarized blue sunglasses when exposed to flickering light
  • Call ahead if you are attending a venue or performance that may have flashing lights

If you suffer from photosensitive seizures, talk to an eye doctor or neurologist about treatment options.

Increased Astigmatism Risk for Hispanics, African-Americans, and Children of Smokers

Astigmatism is when the cornea is not circular. Instead, it is flattened, more like a section of a football than a section of a soccer ball. Astigmatism is a refractive error that is associated with difficulty seeing at all distances. Astigmatism can also be more difficult to correct with LASIK than other types of refractive errors. Now a new study has shown more light on the risk factors associated with this type of refractive error.

According to results of the Multiethnic Pediatric Eye Disease Study and the Baltimore Eye Disease Study, several factors are associated with an increased risk of astigmatism among preschool-aged children. There was a total of 9970 children involved in the study from Los Angeles, California and Baltimore, Maryland counties. The researchers were looking for connections among clinical, behavioral, and demographic factors with astigmatism.

Researchers found that if you had either myopia or hyperopia, you were at an increased risk of having astigmatism. Hispanic and African-American children were more likely to have astigmatism than non-Hispanic white children. Hispanic children were about 140% more likely to have astigmatism, while African-American children were about 50% more likely to have astigmatism. Researchers also found that a mother who smokes increased the risk her child would have astigmatism by about 50%.

These results largely confirm previous results about astigmatism, but the connection with maternal smoking is relatively new, and important.

Astigmatism is harder to correct than either myopia or hyperopia using laser vision correction techniques such as LASIK. In the past, many patients were turned away because it was impossible to correct astigmatism. With the introduction of wavefront-guided LASIK, however, the treatment of astigmatism has become more commonplace, leading. Even irregular and mixed astigmatism can be corrected with LASIK.

If you or your child is having vision difficulties, please contact a local eye doctor to learn about the best treatment options for your vision.

LED Contact Lenses: Future Computer Display or High-Tech Dead End?

Last week, researchers from the University of Washington and Aalto University reported that they had designed, constructed, and tested in vivo an LED contact lens display. The display was powered wirelessly and consisted of only a single LED light, but it could be controlled by computer. Although the initial test model was only a single pixel, researchers claim that they have already developed a micro-Fresnel lens that would allow multiple-pixel displays to be clearly discernible by a wearer. Although some think that this technology might represent the next phase in the evolution of ever-more personal computing, the visual equivalent to the Bluetooth earpiece that will allow people to use their smartphones without actually looking at the display, I believe that experience with contact lenses has taught us this technology is likely a dead-end that will, at best, have a few years of faddish popularity.

First, let’s consider what researchers have accomplished. They created an LED display on a contact lens. To accomplish this, they put wiring to serve as an antenna that can receive signals and channel power to the LED. When the lens was sitting in free space, it could be powered from up to three feet away, but when it was on the eye, its effective range dropped to less than an inch.

The lens itself is made of polyethylene terephthalate (PET to you and me), because it is chemically resistant, thermally stable, and transparent. However, PET is a terrible material to make contact lenses out of because it is hard and doesn’t allow airflow to the eye, so you’d only be able to use the lens for a few minutes at a time. And since the surface of your eye is actually too close to allow you to focus on the display, it would require a series of micro-Fresnel lenses to focus light from the display. Invented in 1822 by French physicist Augustin Fresnel, Fresnel lenses use concentric prismatic structures to capture and refract light in the intended direction. Testing of the micro-Fresnel setup showed that it could be used to separate the incoming light into a tiny 3×5 array on the rabbit’s retina.

But despite the apparent promise of this technology, I personally do not think it will have much success. Let us assume that many of the limitations of the initial research model will be overcome, that the contact lens will be able to be made as comfortable and effective as regular contact lenses–their popularity will still be limited. Why? Because contact lenses are so inconvenient and uncomfortable that they have driven hundreds of thousands of people to LASIK.

If you are a contact lens wearer, you know about the limitations of contact lenses, the irritation of the eye, and the necessity of cleaning the lenses. Even with regular cleaning, contact lenses are prone to develop bacterial films, which can in turn lead to vision-threatening eye infections. Disposable contact lenses are for that reason the norm, but if your contact lens was printed with possibly hundreds of dollars worth of circuitry, would you really want to get rid of it, or would you be more likely to cheat and take the risk of eye infection?

And what if you lost one of these contact lenses at a party or when walking down the street? How often do you actually find the lens, and how often does it end up lost? Now, again, imagine that that lens has several hundred dollars of circuitry printed on it.

Better solutions for integrated visual displays already exist. For example, researchers in 2005 reported a method that involves replacing the eye’s natural lens with an LED-array that is capable of projecting visual data onto the retina. The implanted array could be designed to switch between rebroadcasting visual data received on the back of the lens and a computer display.

An even more promising option, I believe, is to bypass the eye altogether. Subretinal implants have been shown to be able to stimulate the central visual system directly. Although these are currently being studied to restore sight to the blind, once perfected they can be used to transmit any kind of visual data to the optic nerve, including a computer display.

However, any of these techniques is likely a decade or more from implementation, and time will tell which approach proves most practical.

Corneal and Conjunctival Impact of Pepper Spray

With the increased use of pepper spray to subdue protestors from coast to coast, the nonlethal weapon is receiving extensive media attention from pundits, and it is worthwhile to take some time to analyze the health effects of pepper spray. Elsewhere people may consider the impact of the spray on respiratory health, permanent alteration of pain response, and possible death. Here we will consider what we know about the impact of pepper spray on the human cornea as well as the conjunctiva.

What we know about possible eye injury from pepper spray seems to be surprisingly limited. The product has never been evaluated by a regulatory body for human health and safety, so accounts of its eye safety remain largely anecdotal, based on very few limited studies on humans and animals. How few studies? Probably less than a dozen looking at eye safety. How limited? The total number of human subjects is probably less than 100, not enough for a single decent study, let alone the basis for declaring any substance “safe.” I say “probably” because I am allowing that my limited research on the NCBI database may have missed some studies, but I only found four studies looking at human corneal exposure, with a total of 62 subjects.

Two studies report the impact of pepper spray on 57 volunteers. According to one study, which used pre- and post-exposure visual exams at 10 minutes, 1 hour, and 1 week. This study found that among its 47 subjects visual acuity was unaffected by pepper spray exposure. Although corneal sensitivity was reduced at 10 minutes and 1 hour, it had returned to baseline by 1 week after exposure.

A second study looked at the impact of pepper spray on 10 volunteers. It also reported that the corneal response to a first exposure to pepper spray is primarily temporary swelling of the cornea’s outer layer, with no impact on the cornea or its nerves, though tear fluid showed increased levels of nerve growth factor, showing that nerves were responding to the stress, though sprouting of nerves was not observed. However, one volunteer did lose one line of best corrected visual acuity. This study concluded, however, that a volunteer who had been exposed to pepper spray before showed an unusual arrangement of nerve fibers.

In both of these studies, one week follow-up time is too short to evaluate the impact of pepper spray on the cornea. In many circumstances, such as coronary nerve recovery following myocardial infarction, nerve recovery may begin almost immediately, but studies of corneal healing after LASIK indicate that corneal nerves may not begin to recover until six months after injury.

The other two studies looking at the corneal impacts of pepper spray are evaluations of exposure victims who suffered serious adverse consequences of exposure. One study evaluated four individuals who suffered corneal erosion due to pepper spray exposure. The primary culprit in all four cases was not the oleoresin capsicum, the so-called “pepper,” but the carrier agents. In fact, one victim was exposed to a mock pepper spray with only carrier and no actual oleoresin capsicum. In this study, all four patients showed “a long-lasting, deep corneal and conjunctival erosion,” which resolved partially, but full healing of the cornea’s deeper layers does not generally restore the cornea to its original form (which is what makes LASIK treatment generally permanent). In this study, researchers also used pepper spray on a soft contact lens and plastic cup to demonstrate the erosive effects of the carrier.

The fourth study looked at a 2.5 year old boy who suffered conjunctival proliferation after accidental exposure to pepper spray. Conjunctival proliferation is when the outer layer of the eye sprouts additional growth, such as a pterygium. This growth began three weeks after exposure, and had to be surgically removed. Once removed, the growth did not recur during three months of follow-up.

Although conventional wisdom suggests that pepper spray is largely safe for use in subduing arrest subjects, there is actually little evidence to support this supposition, and certainly enough evidence to suggest that it should be evaluated clinically in larger populations with longer follow-ups to ensure it is actually reasonably safe.

In the meantime, if you have suffered pepper spray in the eyes, you should be evaluated by your eye doctor, even if you do not believe you have suffered any lasting effects.

Eliminating Cells in Mice Found to Prevent Cataracts, other Signs of Aging

The targeted elimination of certain cells may prevent and slow the physical signs of aging, according to a recent study from researchers at the Mayo Clinic.

A certain drug treatment in mice prevented the onset of cataracts. The drug also slowed the progression of muscle wasting, as well as preventing the thinning of fat that leads to wrinkles.

The drug eliminated “senescent cells,” cells that are no longer viable and have stopped dividing. Our bodies use cellular senescence to halt the progression of malignant tumor cells.

Cataract-Inducing Cells

Prior to the study, the link between senescent cells and aging signs was unclear. Now, researchers know that cellular senescence causes tissue aging. There is a buildup of these cells in aging tissues, such as the tissue of cataracts and arthritic joints. Not only do the cells accumulate in these tissues, they accelerate the aging of the tissues.

The researchers used genetically engineered mice that aged rapidly. Young mice that were treated with the drug did not develop signs of cataracts and other signs of aging. Mice that were not treated with the drug until middle age already had cataracts that could not be reversed.

Implications for Healthspan

The gene-flushing of the mice cannot be performed in humans, but the findings of the study hold important implications for preventing cataracts and other signs of aging.

The study did not look at whether removing senescent cells extends lifespan. Instead, the removal of the cells extends what can be called “healthspan” as we age. After all, living longer than ever before loses much of its appeal if those years are spent living with age-related diseases and maladies. The researchers plan to undertake another study in which the mice will not be engineered to age rapidly. In that study, they aim to discover if removing senescent cells will also extend lifespan.

Throughout our lives, our immune systems remove some of our senescent cells. As we age, our bodies remove these cells less efficiently and senescent cells begin to accumulate more rapidly.

While cells cannot be removed from humans like they were in the mice, the finding of the link between senescent cells and tissue degeneration may provide scientists with a new direction for combating cataracts and other signs of aging. Drugs or therapies could be developed to boost the immune system so that it continues to remove senescent cells in old age. There is also the possibility that drugs could be developed that would target and remove senescent cells in humans.

To learn more about cataracts and cataract treatment, please contact an experienced eye doctor in your area.

Dinovision: How We Know What We Know about Dinosaur Vision

Studying the vision of current and prehistoric animals can help us understand the origins of our vision and track down causes for visual defects or shortcomings. Studying the vision of current animals is relatively easy. Researchers have devised a number of vision tests that allow us to test the functional vision of animals. We can also look at the structure of their eyes to determine their vision on the basis of the optical structures they possess.

It is much harder to understand the visual systems of extinct animals, since the eyes, as soft tissue, are rarely preserved, and then only in hard-bodied animals whose eyes were part of their exoskeleton, such as insects or arthropods.

In the case of something like dinosaurs, the problem is much more complicated. We can get a lot of answers from the morphology of the skull. The skull tells us a lot about the structure of the eyes, including whether they had a scleral ring to support their large eyes. A scleral ring is a bone that sits inside the sclera of the eye to give it support and tells us the size of the iris of an animal and therefore how much light it could admit

The shape of the skull also tells us the size and shape of the animal’s brain. We know that the brain performs numerous tricks in helping us to see, including selecting between different images, which is helpful in the case of people receiving multifocal intraocular lenses after cataract surgery.

Another important tool for determining the way extinct animals see is looking at their evolutionary relatives. We know, for example, that dinosaurs are closely related to crocodiles and birds. By looking at the vision of an animal’s living relatives, we can extrapolate how they may have been able to see.

Based on all this evidence, we have actually learned a lot about what and how well dinosaurs see, something we will explore periodically.

To learn more about your own vision, please contact a local eye doctor for a consultation.

Time Spent Outdoors may Prevent Myopia in Children

Children who spend more time in natural light and looking at distant objects may be less likely to develop myopia, according to recent studies.

Myopia is nearsightedness, a condition in which the eyeball is elongated from front to back. Myopic eyes focus light in front of the retina, causing distant objects to appear blurry.

The conclusion about natural light exposure came from a review of several studies from the University of Cambridge. For the 10,400 children and adolescents in the study, each additional hour spent outside decreased the risk of myopia by 2 percent, according to Anthony Khawaja, MD. Dr. Khawaja presented these results at the American Academy of Ophthalmology’s annual meeting in Florida.

Additionally, nearsighted children in the study spent 3.7 fewer hours per week outside, compared to children with normal or farsighted vision.

The reasons behind the findings are not clear. Dr. Khawaja said that further studies are needed before any well-founded recommendations can be made. Possible explanations of the findings include:

  • Children who play outside focus on distant objects more frequently
  • Children who play outside look at objects up-close less frequently
  • Natural ultraviolet light exposure prevents myopia
  • Increased physical activity prevents myopia

Among ophthalmologists, it has traditionally been somewhat controversial to suggest prevention of myopia in children. Many nearsighted children have parents with the same vision disorder, suggesting that myopia is in some cases genetic. Hereditary causes of nearsightedness cannot be changed, but this new study seems to suggest that the environmental causes of myopia can be prevented.

Progressive myopia causes a child’s vision to change until it stabilizes around age 20. The conclusions from these studies provide some insight into how environmental factors can be manipulated to decrease the risk of nearsightedness or slow the progression of the vision disorder.

Judging from the current prevalence of myopia (about 41 percent of Americans are nearsighted, according to the National Eye Institute), it seems that certain modern behaviors have put us at risk for nearsightedness. Nearsightedness is much more common today than in decades past, and this could be because of the rampant need to view objects – such as computer screens – up close in today’s educational and business spheres. Further research is needed to determine if balancing today’s up-close tasks with outdoors activity can prevent or decrease myopia progression.

To find out more about treating myopia in children, please contact an experienced ophthalmologist in your area today.

Lasers May Make Cataract Surgery Safer

According to data presented at the annual American Academy of Ophthalmology meeting, pretreatment of cataracts with a laser could make the procedure safer. Two studies considered the use of lasers to soften cataracts before cataract surgery and suggest that this could make cataract surgery safer.

In the past, cataract patients were asked to let their cataracts “ripen,” meaning the proteins would congeal to the point that the crystalline lens was firmer and easier to remove. Now, though, in most cases the lens in broken up in ultrasonic phacoemulsification and then suctioned out, which does not require the lens to be firm. In fact, it is easier to emulsify the lens if it is less firm.

To accomplish a less firm lens, a femtosecond laser (the same one used to create a flap in some LASIK procedures) is used to deliver near-infrared light that fragments the lens so ultrasound is less necessary or even unnecessary. The femtosecond laser procedure has been FDA-approved, but is not widely used because its benefits are not well understood.

In one study, 29 patients all had the femtosecond laser procedure in one eye and standard cataract surgery in the other eye. The femtosecond laser was used to etch cross-hatch patterns in the surface, essentially scoring the lens for fragmentation. These lenses required 45% less ultrasound energy to fragment, and surgeons made 45% fewer movements.

The second study looked at the incidence of cell damage caused by laser cataract surgery vs. conventional surgery. In 225 eyes where laser lens fragmentation was preserved, no endothelial cells were lost from the cornea. In eyes receiving standard cataract surgery treatment, 1-7% of endothelial cells were lost. Endothelial cells represent the innermost layer of the cornea and are a useful gauge of eye health because they do not regenerate.

Lasers can also be used to perform precise, accurate, and repeatable incisions for cataract surgery, unlike manual surgery, which is more variable.

It is unknown whether laser cataract surgery will take off in the future, but it does seem to have significant advantages. To learn which procedure is right for you, please contact a local ophthalmologist.

What Is the Cornea?

The cornea is the clear outer window at the front of the eye. You can see the cornea when looking at the eye from the side, it bulges out visibly from the eye’s spherical shape.

Directly behind the cornea is the eye’s anterior chamber, filled with aqueous humor, one of the eye’s intraocular fluids. This fluid is essential for nourishing the cornea, which does not have blood vessels.

In terrestrial animals, the cornea is the first of the eye’s two refractive lenses. The second is the crystalline lens, which sits behind the iris. Although the crystalline lens can change focus, the cornea’s focal power is essentially fixed for life. In aquatic animals, such as fish and whales, the cornea is actually not a focal lens because its density is too close to that of water to perform any significant refraction of light. In whales, it is unknown how they focus, because the lens does not change shape.

The cornea has five layers:

  • Epithelium
  • Bowman’s layer
  • Stroma–about 90% of the cornea’s thickness
  • Descemet’s membrane
  • Endothelium

As the eye’s primary focal lens, problems with the cornea have the potential to impair or completely disable a person’s vision. The most common defect with the cornea is simple refractive errors, whether myopia, hyperopia, or astigmatism. The most common correction methods for treating this type of problem with the cornea are glasses, contacts, and LASIK or other laser vision correction procedures.

Keratoconus and Fuchs’ dystrophy are two other types of corneal conditions that may threaten your vision. Sometimes keratoconus can be treated with a special contact lens. Other times, it requires a cornea transplant. Fuchs’ dystrophy always requires a cornea transplant.

Unlike the eye’s crystalline lens, there is no artificial substitute for the cornea. Also, corneas from other animals cannot be used for cornea transplants. The only source of cornea transplants is corneas donated by people.

Remember to donate your corneas if you can. Even if you have refractive errors, you can still be a good cornea donor.

To learn more about your cornea or other parts of your eye anatomy, please contact a local eye doctor for a consultation.

Cataract Surgery Improves Mood, Sleep in Alzheimer’s Patients

According to findings presented at the annual meeting of the American Academy of Ophthalmology, cataract surgery can improve the mood and sleep patterns of Alzheimer’s patients. Although some advocates had feared that cataract surgery may worsen dementia and other mental health symptoms, cataract surgery actually created a marked improvement in two key indicators for patients.

The relatively small study looked at 38 Alzheimer’s patients with an average age of 86, the majority of whom were women. They were evaluated before surgery and three months after surgery. By three months, most patients have stable vision and are considered to have achieved final results from cataract surgery.

Seven of these patients had been rated as “depressed” before surgery. Six of them showed improvement, while the other remained about the same. Three out of four patients showed improved or unchanged scores in mood, memory, and their ability to function independently. Researchers pointed out that cataract surgery might help improve “sun-downing” behavior in which Alzheimer’s patients experience decreased memory and depression when the sun goes down. By improving night vision, cataract surgery might help Alzheimer’s patients to use visual clues to context themselves.

The survey also evaluated the benefits for caregivers. Although fewer experienced significant benefits, one in four caregivers reported that caring for their loved one was easier. Unfortunately, about the same amount reported that it was harder, most commonly because of increased agitation.

One of the main limitations of the study was that there was no control group. However, this is a worthwhile study because it dispels the myth that Alzheimer’s patients will not benefit from cataract surgery. This paves the way for more Alzheimer’s patients to get cataract surgery in the future as well as future studies that will demonstrate the benefits of the surgery for this demographic.

To learn more about the benefits of cataract surgery or to schedule a cataract surgery for yourself or a loved one, please contact a local ophthalmologist today.