Eye Lessons from Evolution

Many people know that your retina contains two types of photoreceptors, rods and cones, dedicated respectively to low-light vision and color of light discrimination. Many do not know that bird eyes have not two types of photoreceptors, but six: rod cells, four different types of cones, and a special double-cone. The different types of cone cells are dedicated to sensing different colors, giving birds incredible sensitivity to color. The double-cone photoreceptor is thought to be dedicated to enhanced motion sensing.

Why are bird’s eyes so well-developed in terms of color and motion sensitivity? Partly, it is due to the intense selection pressure on birds to adapt to specific ecological niches. The “visual ecology” of birds has been intensely studied and has shown that not only the types of cells, but their distribution is different among the different species of birds, reflecting the specific visual needs of birds in different “visual ecologies.” For example, land birds have a distribution of photoreceptors that is designed to even out the different type of light radiated from the ground as opposed to received by the sky, whereas sea birds have an opposite gradient to counter the intensity of light reflected from the water.

However, the evolution of bird’s eyes is not the only factor, because many of the features of bird’s eyes are thought to be closer to primitive vertebrate eyes than those of human eyes. Instead, we must look at humans’ evolutionary history to get the other part of the answer. The lack of double-cones is common to all placental (that is, non-marsupial) mammals. Another aspect of avian photoreceptors that is lacking in humans and other placental mammals is an oil droplet that helps to filter and reduce light incoming to the receptor. As a result of these two missing adaptations, scientists speculate that all placental mammals developed from a single ancestor or small group of ancestors that lived a nocturnal lifestyle for an extended period of time, losing the double-cone and oil-drop features that give birds such strongly-adapted diurnal vision. This hypothesis is supported by the presence of oil-drops and rudimentary double-cones in marsupials.

From our early nocturnal origins, mammals have adapted to many diurnal niches, but our lack of fully daylight-adapted eyes drives home the importance of several aspects of eye health. Continual exposure to bright daylight and other sources of ultraviolet radiation has been implicated in the incidence of cataracts, and the retinal condition age-related macular degeneration. Therefore, it is crucial that you attempt to protect your eyes from sun during extended or repeated exposure. It is also important to ensure that you are getting the proper nutrition for your eyes.

To learn more about eye safety and vision for life, please contact a local ophthalmologist today.

Refractive Strategies are Increasingly Incorporated in Modern Cataract Surgery Techniques

Chicago, Illinois – Fueled largely by the rapid advances in intraocular lens (IOL) technology and ever increasing patient expectations, many cataract surgeons are beginning to incorporate refractive techniques into their cataract surgery care plan.

“Cataract surgery is not a one-time job,” says Dr. David R. Hardten. “It’s essentially a chess game where we’re trying to anticipate the next move or the next thought process of our patients. So, we have to have a plan if the patient does something that we don’t expect. If they’re unhappy, we need to be able to fix them.”

More and more, these unanticipated alterations to the cataract surgery game plan involve some form of refractive surgery. In fact, a recent poll indicates that approximately 30% of cataract surgeons are also offering corneal refractive surgery procedures to their patients.

The development of presbyopic IOL technology, combined with a sizeable portion of cataract patients exhibiting a willingness to pay for this technology, has spurred this need to incorporate refractive surgery into cataract procedures.

Furthermore, a growing number of cataract patients are looking for an ophthalmologist who can help them manage astigmatism. Approximately 87% of cataract patients have astigmatism of .25D or higher prior to undergoing surgery, and over 30% of patients have .75D astigmatism. Refractive surgery has proven to be highly effective at treating astigmatism.

It is becoming increasingly common for ophthalmologists to use limbal relaxing incisions when inserting presbyopic IOLs in cataract patients in order to allow for future LASIK procedures. By accommodating this growing need, cataract surgeons are developing the skills necessary to compete in an ophthalmology climate dominated by a patient demand for a broader range of treatments.

Researchers Identify Key Nutrient in Preventing Cataracts in Farmed Salmon

(Norwich, UK)–Researchers have identified a key nutrient that prevents the formation of cataracts in farmed salmon. The nutrient, histidine, was supplied to the fish in the pre-1990s through the inclusion of cow blood meal. However the use of blood meal was stopped in the 1990s over fears of bovine spongiform encephalopathy (BSE), commonly called “Mad Cow Disease.” However, once the blood meal was removed from the fish’s diet, the incidence of cataracts increased significantly, leading to significant economic losses, not to mention a degradation of the salmon’s quality of life. The identification of this nutrient has allowed researchers to develop a synthetic dietary supplement that avoids the possibility of contamination while reducing the incidence of cataracts in farmed salmon.

Cataract formation in salmon eyes is different from that in human eyes, but there are some common features. One common factor between the two species in the influence of osmotic pressure on the lens transparency. When a species cannot regulate osmotic pressure, the tightly packed cells of the crystalline lens can be disrupted, causing a loss of transparency. Salmon, unlike humans, develop reversible cataracts first, often shortly after entering seawater, which encourage the formation of permanent cataracts later. Histidine has been shown in studies to perform a regulatory role in the control of water flow through the eye.

Because the study involved a detailed examination of the responses of the fish’s lens to changing conditions, it helps to better understand how the eye responds to changing conditions and how these changing conditions can lead to cataract formation, although it is unlikely to lead to significant insight into the causes of cataracts in human eyes.

Caffeine May Help Prevent Cataracts

Dr. Shambhu D. Varma of the University of Maryland School of Medicine has found that caffeine can prevent cataracts in rats. Dr. Varma treated rat pups with sodium seramide, a chemical that causes cataracts in the pups. While the control group all developed cataracts, the rat pups that were also given caffeine did not.

Cataracts are responsible for about half of all cases of blindness and while they can be treated with cataract surgery, no strategy for cataract prevention has yet been proven safe and effective. Caffeine, a bioflavonoid present in coffee and tea, prevents cataracts by inhibiting oxidative stress caused by oxygen radicals and by inhibiting the cataract-causing enzyme aldose reductase.

However, caffeine treatment for cataract prevention is not yet viable for humans as the dosage administered to Dr. Varma’s rat pups was quite high. Dr. Varma estimates that a human would need to consume about half a gram of pure caffeine (equivalent to 6.25 cups of coffee) daily to achieve the same effect. Dr. Varma is currently working on a more direct delivery system that works with a smaller dosage for use in humans. Caffeinated eye drops seem to be the most likely to work in people.

For more information on cataracts, find a qualified ophthalmologist in your area.

Smoking, Socioeconomic Status Linked to Cataracts

SINGAPORE – A survey done by researchers from Singapore and Australia has found that smokers and people of low socioeconomic status had a higher prevalence of certain types of cataracts. In this survey, researchers administered thorough eye exams designed to diagnose cataracts and interview questionnaires to more than three thousand Malay adults in Singapore.

After the researchers adjusted for age, sex, BMI, high blood pressure, and diabetes, they found that the subjects who currently smoke tobacco were more likely to have cataracts. In addition, individuals lacking secondary education or having low monthly income were more likely to have nuclear cataract and those living in small public housing units were more likely to have posterior subcapsular cataract.

The researchers also concluded that smoking could be blamed for about one in every six nuclear cataract cases in the survey. Previous studies of (mostly white) American, European, and Australian populations have already linked smoking to the prevalence and progression of cataracts. However, the Singapore survey raises serious concerns because smoking has increased significantly in Asia in the past few decades.

In fact, the 14% of Singapore’s 4.1 million people who smoke represent the smallest smoker percentage in Asia. In comparison, about 60% of men across Asia are smokers and sales figures suggest this number is on the rise. Singapore’s low incidence of smoking is likely due to a total ban on cigarette advertising that began in 1971.

To learn more about cataracts and smoking, consult an ophthalmologist near you.

Possible Increased Risk of Cataracts with Elderly Use of SSRIs and SNRIs

Researchers from the Center for Clinical Epidemiology and Evaluation, Vancouver Coastal Health Research Institute, Vancouver, Canada have reported that people 65-years-old and older may be at increased risk for cataracts if they are receiving selective serotonin reuptake inhibitors (SSRI) or serotonin and norepinephrine reuptake inhibitors (SNRI).

Both SSRIs and SNRIs are classes of chemicals used as antidepressants to treat depression, personality disorders, and other issues. The authors of the study say this is the first time that SSRIs may be associated with an increased risk of cataracts. However, it is known that serotonin plays an important part in lens transparency, and therefore in the development of cataracts.

The Study

The case-control study focused on residents 65 years old and older from Quebec who had undergone coronary revascularization between 1995 and 2004. Almost 19,000 of these patients (cases) were diagnosed with cataracts. Almost 190,000 patients (controls) were not diagnosed by an ophthalmologist. Nearly six percent of the cases and four and a half percent of the controls were receiving an SSRI or an SNRI.

The SSRIs and SNRIs the patients were receiving include venlafaxine (brand name Effexor) and fluvoxamine (brand name Luvox). According to researchers, when the cases were restricted to outpatient surgical treatment, the same results were found, but paroxetine (brand name Paxil)was an independent predictor for the need for cataract surgery.

A statistically significant increase in the risk of cataracts was not found in:

  • Citalopram (Celexa)
  • Fluoxetine (Prozac, Prozac Weekly, Sarafem)
  • Sertraline (Zoloft)

The risk to patients seems to be confined to current users of SSRIs and SNRIs. The researchers estimate that about ten percent of Americans are currently taking an antidepressant that is an SSRI or an SNRI. Based on these estimates and the results of the study, the researchers suggest that around 22,000 cases of cataracts caused by SSRIs may be avoided each year.

To learn more about the risks of developing cataracts, or to find a cataract surgeon near you, please visit www.eyes.com today.

Study Links Antidepressant Use and Cataract Risk

A study by the University of Pennsylvania School of Medicine, published in June of 2010, links antidepressants to the formation of cataracts. A cataract is the clouding of your eye’s natural lens that makes it seem as if you are looking through misty glass.

At Eyes.com, we want you to be fully aware of any medications that may increase your chance of developing cataracts.

SSRIs and Cataracts

Selective serotonin reuptake inhibitors (SSRI) antidepressants may cause cataracts among older adults, based on a large population study involving more than 200,000 residents of Quebec. The study revealed that SSRI users ages 65 and older had a 15 percent increased risk of developing cataracts compared to those who do not use SSRIs.

Background information for the study reveals that about 10 percent of Americans currently take antidepressants, mostly SSRIs and a newer selective serotonin-norepinephrine reuptake inhibitor (SNRI).

Because serotonin receptors exist in the lens of your eye, serotonin has been shown to play a role in opacification of the lens and formation of cortical cataracts, the researchers revealed. They also found that older-generation antidepressants (such as amitriptyline, also known as Elavil) may increase your chance of developing cataracts.

If you would like more information on cataract surgery or are interested in scheduling a consultation, please visit our Eye Doctor Directory to find an experienced eye surgeon in your area.

Medications and Cataracts

A cataract is the clouding of your eye’s natural lens. They may occur for various reasons, one of them being the use of certain medications.

At Eyes.com, we are committed to providing accurate information about cataract surgery and can help you find the best eye surgeon to meet your refractive goals.

Photosensitizing Drugs

Photosensitizing drugs (drugs that make you more sensitive to the sun) are drugs that absorb light energy and undergo a reaction that chemically modifies your tissue. This classification of drugs also makes you more susceptible to developing cataracts.

Some of these drugs include:

  • Birth control pills
  • Eretinate, isoretinoin
  • Tranquilizers
  • Sulfa drugs
  • Antihistamines
  • Oral anti-diabetic drugs
  • Antidepressants
  • NSAIDS (for example aspirin, ibuprofen, advil, meclofen)
  • Fluroquinone, terbinafine, mefloquine type antibiotics
  • Glucocorticoids (Prednisone)

Dangers of Taking Flomax® Prior to Cataract Surgery

The prostate drug Flomax® is especially dangerous if taken before cataract surgery. This drug has been proven to block your iris dilator muscle and prevent the pupil dilation that is needed for safe and successful cataract surgery.

Flomax® has also been shown to cause your iris to flop around during surgery, which can lead to surgical complications and a less-than-optimal outcome. If you are taking Flomax®, be sure to discuss the risks with your ophthalmologist.

If you are looking for an experienced and talented ophthalmologist in your area, please visit www.eyes.com today.

Correcting Less-Than-Optimal Results From Cataract Surgery

While cataract surgery is highly successful, it is not faultless. Following this procedure, there are some common side effects that you may experience, such as dry eyes, astigmatism or cystoid macular edema.

Because no surgery is perfect, Eyes.com is committed to providing you with information on how to address less-than-optimal results. We can also help you find the right ophthalmologist to correct your vision.

Here are ways these common conditions may be resolved:

  • Dry eyes: This side effect can delay healing and expose your eyes to environmental factors. Ointments and artificial tears can help moisten and alleviate this condition. Polymer inserts that slowly dissolve in your eyes can also be used to provide additional moisture.
  • Cystoid macular edema: This outcome is occurs when the macula, the visual center of your retina, becomes swollen and causes blurry vision. Cystoid macular edema can be treated with anti-inflammatory eye drops or oral medication. If this does not help, a vitrectomy can be performed to surgically remove your eye’s inner gel-like substance and restore your vision.
  • Astigmatism: Post-operative astigmatism (blurred vision) may be corrected by wearing glasses or contacts. If your astigmatism is more severe, you may need to undergo refractive surgery such as LASIK or Limbal Relaxing Incisions (LRI) to alter the shape of your cornea.

To learn more about how to correct cornea surgery, or to find a reputable eye surgeon near you, please visit www.eyes.com today.

Pupil Size and Cataract Surgery

A well-dilated pupil is essential for safe and successful cataract surgery. If your pupil does not dilate as it’s supposed to, you are at a higher risk for complications.

Eyes.com is dedicated to providing thorough information about cataract surgery and pupil dilation so that you are well-educated before undergoing surgery.

Pupil Dilation

In preparation for cataract surgery, your pupil will be dilated with eye drops so that your eye surgeon can see your eye in full detail. Lighter colored eyes are more sensitive to dilating drops and will dilate faster than darker colored eyes.

There are two main types of dilating drops that work in different ways. Parasympatholytic eye drops work by temporarily paralyzing your iris sphincter muscle, which makes your pupil smaller. These drops will keep your pupils dilated anywhere from 24 hours to two weeks. Sympathomimetic eye drops stimulate your iris dilator muscle and last between three to six hours.

Once your cataract is removed, your pupils will be constricted with another type of eye drop so that an intraocular lens (IOL) can be implanted. If you have an accommodating IOL such as Crystalens™, your pupil will likely will remain dilated for a longer period than if you have a multifocal IOL implanted.

If you would like to schedule a consultation, please visit our Eye Doctor Directory to find an experienced eye surgeon in your area.