Monthly Archives: November 2006

Refractive Surgery

LASIK and PRK, the most commonly performed refractive procedures, are great for a lot of people, but there are many newer procedures now that can help minimize the risk of complications. With regards to Asian patients in particular, there is fairly recent evidence that Asians are much more likely to develop dry eye problems than non-Asians after LASIK, even after factoring out the amount of myopia. It has also been shown that the corneal nerves do not seem to completely grow back to normal like we had once believed. Even if the nerves appear to grow back morphologically, their function is ultimately what must return to equilibrium.

What causes post LASIK dry eyes?

A sophisticated feed-back-loop links the corneal epithelium, stroma, nerves to the central nervous system, then back out through the facial nerve to the lacrimal gland and orbicularis fibers. When corneal nerves are damaged, the feed-back-loop is disrupted. As the sensation of dryness deminishes, the blink rates decrease and tear secretion is slowed.

LASIK induced neurotrophic epitheliopathy (LINE) initially described by Wilson, was found to correlate with blink rate. Because LASIK first requires the creation of a large corneal flap, a larger area of sub epithelial corneal nerves are damaged in LASIK than by PRK. This is believed to be part of the reason why PRK seems to have fewer problems with post operative dry eyes.

For patients especially at risk of developing dry eyes, nasal flap orientation was believed to help save a portion of the nerves (that enter the cornea from 3 and 9 o’clock) and reduce the incidence of dry eye symptoms. A recent prospective randomized clinical trial however found no significant difference in symptoms between the superior or nasal flapped patients, but did however find a correlation with the amount of preoperative myopia and ablative depth.

With this evidence, I believe that it is the deeper stromal corneal nerves that play a greater role in the development of dry eyes. Because LASIK begins ablation deeper within the stroma than PRK, this may also help explain why PRK patients suffer less from dry eyes. I will further discuss how each of the three different types of corneal nerves (cold sensors, nociceptors, and propriocepts) impact the blink rate on my Dry Eye page.

Phakic IOL’s

For people with higher degrees of myopia that require deeper ablations there are now more options that avoid corneal ablation. Phakic intra ocular lenses (P-IOLs) have been used for years in Europe but are starting to be used here in the US. Two types of lenses are currently FDA approved for use in myopic eyes. The Verisyse PIOL by Ophtec BV was approved 9/2004 for implantation infront of the iris. The Visian ICL (Implantable Collamer Lens) by STAAR surgical was approved 12/2005 for implantation behind the iris.

For highly myopic Asian patients who are particularly at risk of dry eyes, I believe this will become the best choice refractive procedure.

Botulinum Toxin

Before jumping into getting botulinum toxin for the face, we really need to understand what we’re messing with.  I believe that the facial muscles and their connection to the brain, are the most highly evolved of all human bodily functions.  Firstly, what are the functions of the face?Most practitioners of botulinum toxin approach the face as two halves.  The upper half that is more forgiving, and the lower half that requires more caution.  Mobility of the lower face is essential to clear speech and enunciation. The muscles around the mouth and cheeks keep a tight seal at the lips to prevent drooling and are major components in the process of eating and drinking.

What is under appreciated however is that there are similarly important autonomic functions for the upper half of the face as well.  The eyelids move to protect our precious eyes from the environment, and automatically adjust their positions in response to what the eyes sense.  In dry and windy conditions, the orbicularis muscles tighten the aperture to minimize mucus membrane exposure. Sudden bursts of light similarly cause an immediate reflexive closing of the eyes to shield the retina from photo-toxicity.  Although complications from botulinum toxin injections in the upper face are relatively mild and rare, they nearly always involve eyes.

I believe however that the most sophisticated function of our faces is in communication. The face is the single most visible portion of our bodies, especially for this Seattle’s winter.  As an ophthalmologist, I am acutely aware that our eyes are our windows to the world. But as an oculoplastic surgeon, I have learned to appreciate how the muscles and skin around the eyes serve as the window into our souls. They are the focus of gaze during conversations with other people and even animals. We have evolved to “read” eyes and are surprisingly good at it. Everyone knows that the difference between a true smile and a fake one is in the eyes.

Botulim toxin injections were first approved by the FDA for human use by an ophthalmologist who injected the substance into the muscles on the eyes to straighten strabismus.  It was first approved for cosmetic purposes in the muscles around the eyes at the glabellar folds. Since then use of the chemical has spread to all areas of the face. In Shanghai, we even injected it into the masseter muscles of the jaw for aesthetically pronounced jowls. The technique however to apply it to the facial muscles truly requires some appreciation for not just the anatomy, but also for how they work in dynamic facial expression. Although commonly used to reduce the visibility of dynamic wrinkles, there is growing use of botulinum toxin to aesthetically alter the balance of facial expressions. By minimizing the contractions of typically negative expressing muscles, the face at rest develops a more positive and confident pose. The downside however is that when the “negative” expressions are attempted, the balance can be some what abnormal appearing. Unfortunately there is give and take in everything, even for botulinum toxin.

I have helped to write a review article with my Cleveland Clinic colleague and mentor regarding the medical and aesthetic uses for botulinum toxin injections around the eyes and face. Further details to come upon publication.