Dallas — Using a newly designed shallow tip for the Thermage® System in an animal model, researchers effected changes in the eyelid dermis, without causing injury to the epidermis and without causing injury to the eyelid muscle.
In addition, they did not affect a temperature rise in the surface of the eye that was high enough to cause thermal injury or problems, according to Brian S. Biesman, M.D., an assistant clinical professor of ophthalmology at Vanderbilt University Medical Center, Nashville, Tenn.
No injury Dr. Biesman also notes that in a human model the researchers treated human skin and muscle and found that changes also could be effected in dermis without injuring the epidermis or underlying muscle.The radiofrequency (RF) system ThermaCool TC™ (Thermage, Inc., Hayward, Calif.) has been recognized for its ability to deliver RF energy to the facial skin and subcutaneous tissues with favorable clinical results.
"Extrapolating from prior clinical and research experience, we hypothesized that RF energy delivered to the eyelids may result in cosmetically desirable results. However, the center heating zone with the standard Thermage treatment tip is too far beneath the skin's surface to be safely used on an eyelid," Dr. Biesman explains.
"The standard Thermage treatment tip is 1 cm x 1 cm, and a new tip with a dimension of 1.5 cm x 1.5 cm, will also be available soon," he says. "We set out to develop a treatment tip, which would safely heat the tissue less deeply and would not injure the underlying eye or structures of the eyelid.
The shallow tip used for the eyelid treatment is 0.5 cm x 0.5 cm, which results in a treatment area of 0.25 cm2 . "It is a quarter of the size of the standard treatment tip. With capacitive coupled RF energy, the larger the electrode the deeper the energy will be delivered. So, by using a smaller electrode, the treatment will be done more superficially," he says.
Animal model Using animal studies in piglets, Dr. Biesman measured the effect of different energies using the shallow tip.
"We set out to establish the range of responses, starting very low to very high, ranging from no tissue effect to a frank burn on the eyelids. After we determined the extreme upper and lower limits, we selected a zone that we thought would be a safe one to work with," he explains.
But before moving away from the piglet model, Dr. Biesman tested the effect of the temperature on the eye.
A surgical plastic corneal protector was modified with a thermocouple, which was used to sample temperature about a thousand times per second. The studies showed that there was a small elevation in temperature that was well within the safe range and significantly below the temperature that would cause injury to the eye.
In further studies in which the eyelid was unusually and deliberately treated in the same place via pulse stacking, the skin was injured, but the eye did not have a temperature rise that would be significant enough to cause injury, Dr. Biesman explains.
Slitlamp examination showed that there was no injury to the eye itself.
"Temperature did not increase to a level to threaten the eye and upon examination it appeared exactly the same after the treatments as it did before," he says.
Human model A human model was constructed in which eyelid tissue excised during routine blepharoplasty from 10 eyelids was treated with the .05 cm2 electrode specially designed for shallow depth of penetration. An experimental system was designed to closely mimic an in vivo environment. Energies between 16 J and 19 J were delivered to the eyelids. Dr. Biesman says the appropriate dose range was determined from the previous animal studies.
The epidermis remained intact in all specimens. There was no evidence of obvious thermal injury in the underlying orbicularis oculi muscle. Therefore, Dr. Biesman concluded that the ThermaCool TC System with a .05 cm2 treatment tip may be used to treat ex vivo human eyelid tissue without apparent injury.