September 2009

 

REFRACTIVE SURGERY

 

Pharmaceutical Corner

In-depth look at artificial tears


by Matt Young EyeWorld Contributing Editor

   

Recent scientific literature boasts about the development of a “nutrient ocular lubricant,” which apparently supplies both lubrication and nutrition. These tears don’t just contain vitamins, but also hormones like insulin and recombinant growth factors, and have grown human corneal epithelial cells in the lab. There also is a bevy of research on more versus less viscous tears, and the benefits and drawbacks to each. Some of these studies even are employing aberrometry to study higher-order aberrations after instillation of drops of varying densities. What are we to make of the latest artificial tear claims? H. Dwight Cavanagh, M.D., Ph.D., professor of ophthalmology, University of Texas Southwestern Medical Center, Dallas, suggests clinicians should use a healthy amount of skepticism. “Most of the senior clinicians that have been around 30 years have seen all the ‘new’ trends,” Dr. Cavanagh said. One of the most important factors is preservative-free artificial tears. “Non-preserved tears to me are the only way to go,” Dr. Cavanagh said. Indeed, preservative-free artificial tears have been embraced industry-wide. But even in this regard, opinions are not entirely uniform. Frank J. Holly, Ph.D., president, Dry Eye Institute, Texas, noted in his Harold Stein Lecture at the Contact Lens and Eyecare Symposium meeting in 2003, that “often the use of preservative-free preparations is suggested regardless of the composition of the tear substitute. Harmful preservatives should certainly be excluded. However, the fact is that often a well formulated artificial tear containing a benign preservative proves to be superior to a preservative-free drop if its only advantage of the latter is the lack of preservative. Solely the lack of preservatives per se does not make the formulation efficacious. Unfortunately, the ‘preservative-free label’ is often just a marketing tool.”

Rest assured, however, that marketing is to dry eye what the tip is to the iceberg. Even as new tear formulations may help grow the market, the market itself is unimaginably vast. Recent literature has tried to shed more light on potential dry eye disease factors heretofore only lightly researched. Researchers are now looking beyond LASIK to cataract surgery as a potential cause of dry eye, for instance. Through it all, Dr. Cavanagh and other clinicians have their favorite artificial tear remedies to help with dry eye, whether it has existed for a while or has been induced recently.

The osmolarity factor

Dr. Cavanagh is a big believer in getting the osmolarity of the tear film right. “You’ve got to restore, in the end, the normal tear film osmolarity to get rid of toxicity and what’s driving inflammation,” Dr. Cavanagh said. There are 4 to 5 different artificial tear formulation best-sellers that will do the trick, but Dr. Cavanagh favors TheraTears (Advanced Vision Research, Woburn, Mass.).

“There is some science behind it,” Dr. Cavanagh said. “All the other tear drops restore wetability and the clinging of polymer to the surface. What does that have to do with osmolarity? Nothing.”

TheraTears, indeed, has a compelling story. According to the company’s Web site: an 18-year research program, sponsored by the National Eye Institute, and directed by an eye physician focused on one goal: to develop a profound understanding of dry eye, and effective treatment.

The result: a collection of treatment breakthroughs now available under the TheraTears brand. Dry eye is a result of a loss of water from the tears on the eye surface that makes the tears too salty or “hyper-osmotic.” Hypo-osmotic TheraTears Lubricant Eye Drops help put back the lost water, lowering the high salt concentration, so that they not only wet but also rehydrate dry eyes. We call this “osmo-correction.”

Still, Dr. Cavanagh emphasized that there is “no magic bullet” in restoring normal tear film osmolarity. What he does know is that patients shouldn’t have to use wetting drops more than four times a day if proper osmolarity restoration is taking place. “I have quit wetting every 1 to 2 hours,” Dr. Cavanagh said.

Clinicians also have to pick an appropriate drop viscosity, Dr. Cavanagh said. “I call them ‘regular’ and ‘extra crispy’,” Dr. Cavanagh said, after styles of fried chicken sold at KFC. ‘Extra crispy’ refers to artificial tear gels, while ‘regular’ refers to the less viscous drop formulations. “The gel reduces vision but it does coat the cornea,” Dr. Cavanagh noted. Many brands come in both versions, and Dr. Cavanagh shared some tips about how he advises using these to both maximize healing and visual acuity at the same time: • Put the thick drop in to coat the cornea for a few seconds.

• Rinse it out with the regular drop. • Don’t mix brands (for example, use the same brand when applying “extra crispy” tears as well as rinsing out with “regular” tears) “If you don’t wash out the gel, it takes 2 to 3 hours to clear,” Dr. Cavanagh said. “This is not helpful to work. Your eye feels better but gummy.”

The popular group

William B. Trattler, M.D., director, Cornea, Center for Excellence in Eye Care, Miami, meanwhile, has a list of favorite artificial tears he uses. “Optive [Allergan, Irvine, Calif.] has this whole concept of comparable solutes; I was part of the study to get that FDA [Food and Drug Administration] approved,” Dr. Trattler said. The solutes L-Carnitine and erythritol compensate for the osmolarity of the eye fluid, and reportedly their activity is not related to the time they are in contact with the eye. Optive gets absorbed by dehydrated epithelial cells, which then become rehydrated, Dr. Trattler added. “Blink Tears [Abbott Medical Optics, Santa Ana, Calif.], the hyaluronic acid-containing tear, is the most popular tear in Europe,” Dr. Trattler said. “It improves the quality of tears. Patients are really happy because it doesn’t blur vision very much. And it helps stabilize and improve the tear film.”

Dr. Trattler also mentioned Systane Ultra (Alcon, Fort Worth, Texas) as being helpful because it uses guar to improve tears and stabilize the tear film. Just remember, Dr. Cavanagh said: “Wash TheraTears regular out with TheraTears gel. Refresh [Allergan] washing out Refresh Plus is next best. Systane washing out the gummier gel is also good. Cellufresh [Allergan] washing out Celluvisc [Allergan] also is ok. It’s the principal that counts.”

After surgery

Meanwhile, the June 2009 issue of the Korean Journal of Ophthalmology reiterates a fairly new hot topic in eye care: that cataract surgery could impact dry eye. “Cataract surgery may lead to dry eye,” the researchers reported. “A grooved incision can aggravate the symptoms during the early postoperative period in patients without dry eye preoperatively.”

Dr. Trattler added, “Dry eye is one of the biggest issues following cataract surgery that impacts visual results.”

Dr. Cavanagh also agreed with the notion that cataract surgery impacts dry eye. “Any time that you interrupt innervation of the cornea, whether after cataract or LASIK or whatever, you don’t blink,” Dr. Cavanagh said. “Normally we blink 17 times a minute. When we blink, we squish the lacrimal gland, and tears come shooting down the cornea and are drained away. If you don’t blink, you don’t pump tears. You have to blink.”

Because surgery may cause dry eye through some amount of corneal denervation, artificial tears again may come in handy. “You have to get patients to use them before scratchy symptoms, not afterward,” Dr. Cavanagh said. “Prophylactically, they work.” By 12 weeks post-op, the nerves also should be back to normal functioning, he said. Bjorn Johansson, M.D., Linkoping University Hospital, Linkoping, Sweden, however, remains skeptical that cataract surgery causes dry eye. “Frankly, I have not noticed any problems with dryness after cataract surgery,” he said. “When I review my records of patients that were operated 5 to 6 years ago, it is very uncommon if the eye is healthy otherwise that they return complaints of a dry eye problem.”

That said, Dr. Johansson does use artificial tears occasionally for his patients. “I have a couple of preparations that I use in difficult cases where the patient is not helped by simple salt water preparations,” Dr. Johansson said. “One of them is Bion Tears [Alcon]. The company states that the composition is made with the same ions as the natural tear liquids. It’s both lubricating and very physiologically helpful to the eye.”

Editors’ note: Drs. Cavanagh has no financial interests related to his comments. Dr. Holly reported no financial interests related to his presentation. Dr. Trattler has financial interests with Abbott Medical Optics (Santa Ana, Calif.) and Allergan (Irvine, Calif.). Dr. Johansson has no financial interests related to his comments.

Contact information

Cavanagh: 214-648-8074, Dwight.cavanagh@utsouthwestern.edu
Holly: info@dry-eye-institute.org
Johanson: bjorn.johansson@lio.se
Trattler: 305-598-2020, wtrattler@gmail.com

In-depth look at artificial tears In-depth look at artificial tears
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