PRK Safer than LASIK for Retreating Radial Keratotomy

For those who need radial keratotomy (RK) re-treatments, it has been reported by the RK Re-treatment Study that PRK is safer than LASIK.

The RK Re-treatment Study group, led by ophthalmologists, looked at 221 procedures over a 12 year period between 1997 and 2010 from six different US surgical centers. All but three LASIK procedures were done conventionally, while two-thirds of the PRK procedures were conventional. The other one-third were wavefront-guided custom PRK. (Wavefront-treatment did not become popular until around 2005.) Refractive errors between PRK and LASIK patients were roughly the same.

Three to six months after eye surgery, both conventional LASIK and wavefront-guided PRK showed better at keeping best-corrected visual acuity in patients than was conventional PRK. Nearly 80% of all patients showed better than 20/40 vision after eye surgery.

However, for patients who needed to be retreated, there were complications in 12% of the custom LASIK patients, while only 4% of PRK patients had complications. Complications included ectasia in the LASIK group, which required penetrating keratoplasty. Two patients in the PRK group required both eyes needing phototherapeutic keratectomy due to “postoperative haze.” Retreatment gave these patients 20/20 and 20/25 vision respectively.

The RK Re-treatment Study recommends further evaluation in this area of laser vision correction. This may be especially important due to the increasing number of people seeking vision correction surgery.

If you are interested in finding out more about PRK or LASIK, please find a doctor in your area through today.

Deep Sea Eyes Evolved to Protect from Predators

A recent study of the eyes of giant and colossal squid reveals they would likely have only given an advantage for detecting the presence of large predators, such as the sperm whale.

Giant squid have possibly the largest eyes of any creature that ever lived. At a diameter of 10.5 inches, with a pupil size of 3.5 inches and hard lenses as big as human eyes, these eyes are disproportionally sized compared to almost any other creature, which raises the question, “Why?” Any time a creature develops a highly unusual structure such as this type of eye, the typical assumption is that some selection pressure has driven its development. Now researchers believe they have found the answer to what selection pressure drove the development of squids’ huge eyes.

It has long been assumed that the huge eyes of giant squids were in some way an adaptation to living in very dark water. Larger eyes are able to take in more light and so presumably would allow the monstrous squid, which measure up to 49 feet (15 m) in length, to see better in dim light conditions. However, researchers found that for most situations, an eye size greater than 4 inches, the size of swordfish eyes, provided no benefit. See the chart below for a comparison of the relative size of creatures’ eyes.

However, there was one situation in which the very large eyes of the squid would be very helpful: the detection of approaching sperm whales. As sperm whales cut through the deep water, they disturb numerous smaller organisms, which give off bioluminescence. The massive eyes of the giant squid species would allow it to detect and interpret the pattern of disturbed organisms to see sperm whales approaching from a distance of nearly 400 feet, which would allow the squid to potentially avoid approaching whales.

Looking at the chart above, we notice that another creature had eyes about the same size as the giant squid, the Temnodontosaurus platydon. Based on the models provided by researchers, it seems likely that the function of these eyes was the same: to detect the approach of a very large predator.

But what ate a temnodontosaurus? Shown above in comparison with a human, temnodontosaurus was one of the largest known creatures in Jurassic seas.

One possible speculation is the presence of a very large pliosaur. Some estimate that pliosaurs, similar to liopleurodon (image below), may have been up to 50 feet long, about half again the length of temnodontosaurus, which may very well have made it a viable predator. Another possibility, though, is the existence of a kraken, a gigantic cephalopod predator, which would not be well preserved in the fossil record.

What is remarkable about these eyes is their extraordinary ability to function under demanding conditions. If your eyes are not properly functioning, please contact a local ophthalmologist to talk about options for improving your vision.

Electronic IOL May Be the Future of Cataract Surgery

A computer-controlled, fully programmable intraocular lens (IOL) may soon give cataract surgery patients better vision than any time in their lives. One of the persistent problems in cataract surgery is properly calculating the strength of lens to be used for optimal results. Even experienced ophthalmologists find this to be challenging, and subtle, unknown factors can lead to uncertainty in the final results. In about 1-2% of cataract surgeries, the results are so bad that the patients seek reoperation, and most often this is to have a different lens implanted. Many other patients live with less-than-optimal vision, or have secondary refractive procedures (such as LASIK) to improve the results.

The electronic IOL, known as ELENZA, may eliminate that problem, as well as possible problems that may result from future changes in vision. The new IOL is fully programmable, so it can be adjusted not just immediately after cataract surgery, but at a later date in response to eye injury, glaucoma, or other visual changes. The lens is also self-accommodating, so it does not depend on potentially weakening cilia muscles, and it may even be able to surpass the accommodating ability of the eye’s natural lenses. Theoretically, the lens could be used to give its recipients telescopic vision and super visual clarity at all distances.

You may remember the LED contact lens that was announced last year. In talking about that concept, I discussed the possibility of IOLs that replace the natural lens with an LED-array. Essentially, that would involve replacing the transparent lens with an opaque camera-transmitter array, like having a tiny video camera on one side and a tiny TV on the other.

This new electronic lens is different–it still functions like a lens, only it uses liquid crystal as the refractive medium. The arrangement of liquid crystal can be controlled by small electromagnetic fields, which in this case is used to change the refractive index and therefore the focusing power of the lens. The concept has already been applied to prescription glasses, allowing the wearer to change the focus of the glasses, eliminating the need for bifocals.

One problem with electronic lenses is that they need a power source. In the case of ELENZA, developers project the power will be provided by a microscopic rechargeable lithium-ion battery. Although similar to the batteries used on cochlear implants, they will be even smaller. These batteries will need to be recharged every 3-4 days, though developers estimate their lifespan at 50 years. Chargers, they say, can be placed in pillows or in face masks worn while sleeping.

One advantage of the liquid crystal lenses over the LED display is what happens if your batteries fail. In the liquid crystal lens, it simply reverts to a monofocal lens that gives you good distance vision, suitable for driving a car and most other outdoor tasks. The LCD display, on the other hand, would simply go dark, leaving you blind.

It remains to be seen, though, whether these new implantable lenses could be synced with a computer to give you an implanted display.

The developers of ELENZA hope to begin in vivo studies in the near future, possibly as early as 2013, and hopefully FDA approval as early as 2018.

There are still a number of good IOL options for people seeking cataracts today. To learn more about your IOL options, please contact a local ophthalmologist for a consultation today.

Risk Factors for ES Glaucoma Identified

Data from the Nurses’ Health Study (NHS) and Health Professionals Follow-up Study (HPFS) continue to reveal new insights into diseases with complex risk factors, such as glaucoma. In the most recent publication related to NHS-HPFS data, researchers have identified several major risk factors for developing exfoliation syndrome (ES), which can significantly increase a person’s risk for developing glaucoma.

ES occurs when material from the iris rubs off. It can be seen on the lens as a whitish flaky material, but it does not impair vision. The main danger of this material is that it can clog the eye’s drainage angle, leading to elevated intraocular pressure which damages the optic nerve, which is what we call glaucoma. In addition, ES can contribute to your cataract risk, as the flecks may increase crystallization of the lens’ proteins. Now researchers have identified several risk factors that contribute to your likelihood of experiencing this eye disease.

The dominant risk factors seem to be genetics, age, gender, and where you live. The genetics and age connections have long been known. People with a family history of the condition have essentially double the risk for developing it themselves. Risk for the condition also increases with age–the mean age of sufferers seems to be in the early 70s.

Women seem to be at a greater risk for this condition than men, but it is unknown whether this is due to hormonal, environmental, or anatomical variables. perhaps the most striking discovery is that where you live can have a dramatic impact on your risk for developing this condition. Those in the northernmost parts of the US have the highest risk, with those in the middle US have a 47% decreased risk, and those in the southernmost third of the US have a 75% reduced risk. Surprisingly, where you live now is only the second most strongly associated location for your risk of ES. The most strongly associated location was the residence of people at age 15.

The NHS-HPFS data utilizes lifetime data from about 130,000 subjects and can identify some important correlations, though of course it cannot determine whether these are simple correlations or actual causal relationships.

The most important thing to remember about glaucoma is that it can often be subtle with no symptoms before you begin losing vision. To prevent vision loss, you should have regular appointments with your eye doctor for glaucoma screening. If you do not currently have one, you can find an ophthalmologist in your area to help identify glaucoma before vision loss.

Casting about for Profitable Indications

Pharmaceutical companies are in it for the profit, and one of the ways they look to maximize profits from a drug they have patented is to find new indications for a slightly altered and therefore newly-patent-protected variation on an old medication. Sometimes this works. Sometimes it doesn’t.

Consider the case of ISTA Pharmaceuticals, a manufacturer of eye medications, and their flagship product to date had been Xibrom, a twice-daily non-steroidal anti-inflammatory drug (NSAID) solution that is used by cataract surgery patients to reduce inflammation and speed healing. Xibrom’s patent expired in January 2009. However, the company recently capitalized on a reformulated version, Bromday, designed for once-a-day use and capable of providing similarly good results. However, the patent for Bromday expires in 2013, at which point ISTA seems to be out of tricks for this drug.

Or are they? ISTA is trying to find a new indication for a slightly reformulated version to treat the profitable condition du jour, dry eyes. Everyone is trying to get into the dry eyes market, one of the most common eye conditions for which there is not a standard treatment available. The market for dry eye treatments is already $1.7 billion and is expected to grow at least 10% per year until at least 2014, with a potential for reaching $2.4 billion, according to some estimates. That’s some serious scratch, so of course any sensible drug company is going to jump on the opportunity if it has some potentially effective drug under patent.

ISTA moved to third phase clinical trials of its new dry eyes medication Remura in 2010. Positive results from the phase II trials made them hopeful, but when the results came back from the phase III clinical trials, it was found that the drug did not perform better than placebo. Sophisticated statistical analysis showed that the drug actually did give some level of response for “conjunctival staining” (red eyes) when used at the highest dose for women aged 51-70. In other words, the trial is viewed as a total failure.

So ISTA’s stock prices took a dramatic dip (28%), despite a press release that blamed the failure of the study on a “dramatic” placebo response. And the company is looking for some other way to use this drug to make money.

The profit-driven nature of the pharmaceutical industry is another good reason to consult with a doctor about your medications rather than trusting claims or marketing material by the company itself. If you are looking to find the best treatment for your eye condition, please contact a local ophthalmologist today.

Will Phakic IOLs Be Approved for Hyperopia?

Phakic IOLs are a type of intraocular lens that is used to help your eye attain the proper focus. Unlike the lenses used in cataract surgery, which are sometimes called aphakic IOLs, these lenses do not replace your eye’s natural crystalline lens. Instead, they are helper lenses, sometimes described as “implantable contact lenses.”

Phakic IOLs have been approved for the treatment of myopia by the US Food and Drug Administration (FDA) since 2003. However, they have not been approved for the treatment of hyperopia. According to industry representatives, studies of phakic IOLs for treatment of hyperopia are ongoing, but will they ever be approved?

Concerns with Phakic IOLs for Hyperopia

There are two significant concerns that have delayed the approval of phakic IOLs for hyperopia. Both relate to the narrow anterior chamber of hyperopes, the part of the eye between the iris and the cornea, where some phakic IOLs are placed. First, there is concern that the IOL will abrade the endothelium, the innermost layer of the cornea, which could result in a condition similar to Fuchs’ Dystrophy. Second, there is concern that implantation of a phakic IOL in an already crowded anterior chamber could increase the risk of closed angle, or acute glaucoma.

Both of these risks are likely very rare, but because of the seriousness of the conditions, even a small risk merits significant study before approval.

Some Study Results

In the early clinical trials, phakic IOLs were being studied equally for both myopia and hyperopia. It was concluded that phakic IOLs should only be placed in the posterior chamber, behind the iris. These early studies confirmed that risks associated with phakic IOLs were small, but also showed that the results were not highly predictable.

However, a recent Italian study of 59 eyes with posterior chamber placement of phakic IOLs showed significant results. The study looked at the patients’ results at several points up to ten years after implantation. It showed that people received the phakic IOLs achieved, on average, a spherical equivalent of +0.07 diopters, essentially 20/20, though one eye did lose one line of best corrected visual acuity. Visual acuity was stable over the ten-year period. Endothelial loss was slight, and did not increase. Intraocular pressure increased by about 5.3%, and there was one incident of closed angle glaucoma.

Overall, though, this more recent study suggests that the path should be clear for approval of phakic IOLs.

Market Concerns

The main barrier to approval of phakic IOLs for hyperopia is likely market-based. In addition to potentially increasing risks, the narrow anterior chamber of hyperopes makes implantation of the IOLs more difficult for surgeons. This makes them less popular among surgeons. With other treatment options like LASIK and PRK available, surgeons do not seem to be crowing for phakic IOLs for hyperopia treatment. With no extant market, it seems unlikely that companies will be making the big push for approval of phakic IOLs for hyperopia any time soon.

If you want to learn more about phakic IOLs or other types of refractive eye surgery, please contact a local eye doctor today.

Study Reveals Improper Contact Lens Care is Common

According to a recent study appearing in the journal Optometry and Vision Science, only 2 percent of contact lens users are compliant in contact lens hygiene, while more than 80 percent of contact users believe they are compliant.

Poor Care of Contact Lenses

There are actually quite a few guidelines for proper contact lens use and care. Some of the most common ways people deviate from these guidelines include:

  • Not removing your contact lenses before going to bed.
  • Wearing your contact lenses while you are swimming.
  • Showering while wearing your contact lenses.
  • Using your contact lenses longer than you should before switching to a new pair.
  • Failing to use fresh cleaning solution every day.

In some cases, failing to care for contact lenses properly can lead to serious ocular consequences. Improper care can cause harmful debris, bacteria and other things to come into contact with your eye.

Consequences of Improper Contact Lens Care

In the study, 72 percent of contact lens wearers reported they had experienced discomfort while wearing their lenses. Forty-seven percent said they had gotten an infection from their contact lenses.

Improper contact lens hygiene can cause a number of eye infections, including pink eye and E. coli infections. The most serious cases of eye infection can lead to blindness or even damage the eye itself.

Proper care and hygiene for contact lenses includes:

  • Always wash your hands before handling your contact lenses.
  • Throw away old lenses and switch to a new pair as instructed.
  • Use your lens solution to rinse your contact lenses, not water.
  • Do not store your lenses in water only.
  • Replace the case you keep your contacts in every three months.
  • Follow cleaning and storing directions for your contact lenses.

You should also discuss additional care instructions with your eye doctor. Your eye doctor can provide you with detailed instructions regarding how to care for your specific contact lenses.

For more information about contact lenses and contact lens alternatives, please find an experienced eye doctor in your area.

Giant Cambrian Predator Had Excellent Vision

Recent analysis of fossils of an ancient predator reveal that the creature had excellent vision. The predator, Anomalocaris, had a worldwide distribution and is though to have been the top predator in the Cambrian seas. The existence of the predator was postulated before the creature was known. In 1979, a paleontologist studying trilobites explained that wounds on the bodies of certain trilobites might be caused by a large predator. At the same time, another paleontologist realized that what had previously been identified as a shrimp body was actually an appendage on a larger creature, which might be responsible for trilobite injuries. When the full body of the creature was described in 1985, it was characterized as “a formidable predator.”

Now we know that vision was an essential tool for this predator. 515 million year old fossils attributed to the creature show extremely complicated compound eyes. The eyes are speculated to have had as many as 16,0000 individual lenses, which is comparable to modern dragonflies, which may have as many as 30,000 lenses per eye. By contrast, triDragonflies use their excellent vision for hunting prey in a three-dimensional space, much like the Anomalocaris, which, with its newly-discovered vision could locate prey more effectively than competitors. In response, it is likely that prey developed anti-vision defenses, such as camouflage.

But what did Anomalocaris eat? Some researcher claim its teeth were too soft to eat trilobites, but fossil feces too large to be from any other known animal contain trilobite pieces. So, until another candidate is discovered, Anomalocaris is the prime culprit.

Because the fossils in question are not directly attached to Anomalocaris, some dispute that the eyes actually belonged to the predator. However, it is unknown what other creature they might belong to. Again, Anomalocaris is the only creature large enough to have owned them. However, because preservation of lenses is rare in fossils of this age, there may be many creatures with similarly sharp eyesight, which had been unknown before this discovery. It also likely means that arthropods likely developed eyes before they developed their characteristic jointed skeletons. For more information on this predator and its vision, see the Discover blog Not Exactly Rocket Science.

This type of eye is very different from human eyes. Instead of having a pair of lenses (the cornea and the crystalline lens) that focuses light onto a bank of nerve endings (the retina), compound eyes have many separate lenses that each focus light onto a separate photoreceptor. Thus, each separate lens represents a pixel in the creature’s vision, creating an arrangement that is ideally suited for capturing movement, but less well suited to capturing detail. An evolutionary arms race between camouflage and vision would drive increasing numbers of pixels that could resolve detail to allow predators to spot hiding prey, even when static.

As with these early predators, your vision is a great tool, and visual acuity can make the difference in facing your competition. To make sure your vision is at its peak, please contact a local ophthalmologist today.

The Eye Knows Better Than the Brain What It Has Seen

As the US Supreme Court is hearing arguments that eyewitness testimony is not a reliable category of evidence, researchers are proving that eye witness testimony might actually be the answer.

Police and lawyers have long struggled with the reliability of eyewitness testimony. In 12 Angry Men, the eyewitness testimony that may have served to convict a young man of murder is famously dismissed because of the eyewitness’ myopia, but even without refractive error, eyewitness testimony is unreliable. According to recently released research, about 75% of DNA exonerations come in cases where an eyewitness misidentified the perpetrator.

This is due, in part, to the pliability of memory, which can be altered by an act as simple as retelling what happened. By the time a witness is asked to identify a perpetrator from a line-up, he or she may have been asked to retell the events several times, and each time the memory is accessed, it is also resculpted, and the actual visual memory is lost and replaced more or less with a set of descriptors.

However, it turns out the eyes themselves also have a memory, distinct from the one in the brain, that might be a better way to make eyewitness identifications. According to research to be published in Psychological Science, eye movements more accurately identified a remembered face than conscious identification.

The researchers gave students a set of 36 faces to study. These faces were also subtly morphed to create slightly different faces that were not seen by the students. Then students were shown 36 3-face displays and identify a face they had seen, if there was one. If there was not a face they had seen before in the display, they were to pick any face and verbally say whether the face they were looking for was there or not. Eye tracking was used to look at the movement of their eyes as they were making their identifications.

The research showed that eye movements disproportionally moved to the previously seen face even before an identification was made. However, this memory is not immune to rewriting. Once the person had identified a face as having been seen before, the eyes kept moving to the “known” face as if it had been seen before, whether it had or not. In the words of researchers, “pre-response viewing seems to reflect actual experience, and post-response viewing seems to reflect the decision making process,” which leads the eye to “endorse” the face the brain has decided is the right one.

This research is in its early stages, but perhaps it will in the future allow for more reliable eyewitness reports and fewer wrongful convictions.

Also helpful in being a reliable eyewitness is having your refractive error corrected. To learn more about LASIK, please talk to a local ophthalmologist today.

Study Reveals the Effect of Long-Term Space Travel on the Eyes

Results from a NASA study show that long-term spaceflight could have a significant impact on the eyes. The study looked at seven astronauts who had spent six continuous months or more in space, on the international space station. All the astronauts were about age 50.

The astronauts all reported some degree of visual symptoms, including blurriness, which was reported by all subjects. The visual symptoms typically began around six weeks into the mission. An in-depth examination of the astronauts’ eyes showed that all had one or more of the following symptoms:

  • Flattening of the back of the eyeball (five subjects)
  • Folds in the vascular tissue (choroid) behind the retina (five subjects)
  • Excess fluid around and presumed swelling of the optic nerve (five subjects)

Researchers speculate that the changes might have been caused by increased intracranial pressure, abnormal flow of spinal fluid around the optic nerve, changes in blood flow, low intraocular pressure, or a combination of factors. In orbit, astronauts experience what is known as microgravity, which can change the distribution and flow of fluids in the body.

Most of the astronauts reported that visual symptoms went away about 6 weeks after returning to earth, while others report symptoms lasting months or years.

Overall, visual changes are seen in about 23% of astronauts on short missions and 48% of astronauts on longer missions. However, it is unknown which changes resulted in visual changes. Although choroidal folds can sometimes be associated with visual symptoms, it is more likely that visual changes were caused by flattening of the eye, which could result in hyperopia, since the lens might be focusing light behind the retina. Researchers also propose that the astronauts may be experiencing presbyopia, which would be more common in astronauts now that their average age has increased.

Visual changes associated with space travel have been speculated since the earliest days. “space anticipation glasses” for improved visual acuity were made for early astronauts. John Glenn and others had them in their space capsule.

These findings are significant for longer trips to Mars or other planets that are being planned for this century. Perhaps these findings will encourage the use of faster continuous-acceleration voyages rather than lower-energy but cheaper “coasting” missions.

If your vision is not as clear as it used to be, you should visit a local ophthalmologist for a comprehensive vision exam.