PTK on patrol

PTK may help alleviate troublesome striae
Source: Roger Steinert, M.D.

Technique helps to target visually significant striae and improve visual results

For patients with significant striae treatment with PTK can help to safely and reliably alleviate visual symptoms, results from a recent study show. The study published in a recent issue of Ophthalmology considered the impact of PTK on visually significant striae.
While striae after LASIK is relatively common they don’t usually have visual implications, according to Amin Ashrafzadeh, M.D., Northern California Eye Physicians, Modesto; and volunteer assistant clinical professor, University California, Davis. “Striae by themselves are not necessarily a problem,” Dr. Ashrafzadeh said. “But rather when they are high enough that they peak through the sea of epithelium and cause disruption of the tear film—that’s when they’re visually significant.” This probably occurs more frequently than is currently recognized, he believes.
Such striae have also proven very difficult to treat. This difficulty is why the PTK technique was developed, according to Roger F. Steinert, M.D., professor of ophthalmology, professor and vice chair, Clinical Ophthalmology, University of California, Irvine. “We developed the technique of using the PTK approach, because people have tried a number of things over the years,” Dr. Steinert said. “They tried stroking the flaps, hydrating the flaps and even suturing the flaps and none of them had a high success rate.”

Developing PTK maneuvers

In an attempt to develop a reliable technique with a high success rate investigators began exploring PTK’s potential. “It’s a way of evening out irregularities,” Dr. Steinert said. “We’ve been using PTK on rare cases in a similar manner for patients with scars and other types of irregularities since PTK was approved in the mid-nineties, so in a way this is logical evolution.” There was, however, concerns about how the LASIK flap would react to the laser energy. “That’s what the series was designed to explore and see if we were getting reliable good results and not getting complications,” Dr. Steinert said.
This current study was actually a follow up to a more limited previous one. The initial study published in the April 2004 issue of Ophthalmology was limited to a group of 23 patients many with just one month of follow up. In addition to the small group and the short follow up, in this initial study results were inconsistent. “When we looked at the refractive response of these patients to the PTK, the response was very varied from a significant myopic change to a significant hyperopic one,” Dr. Ashrafzadeh said. “All of these put together really made PTK undesirable whereas we felt now that PTK was definitely a worthwhile and desirable procedure.”
Investigators hope that a more standardized PTK protocol would make the difference. In the most recent study investigators used the VISX laser (Advanced Medical Optics, AMO, Santa Ana, Calif.) with a 6.5 mm spot. “We programmed in 300 pulses and we’d run off the first 200 pulses with the tracker working,” Dr. Steinert said. This was enough to allow the laser to cut through the epithelium. “In the process of doing that you eliminate some of the striae,” he said. “The epithelium to some degree acts like a so called masking agent and the elevated areas start to get exposed and to get flat first.”
After the first 200 pulses the tracker was then turned off and investigators started applying the laser in bursts of five or six pulses at a time for a one second period for a maximum of another 100 pulses. In between they would use a merocel sponge to wipe the eye with a thin layer of medium viscosity artificial tear solution. “We’re using the artificial tears as a masking agent so that the deeper valleys are protected by the fluid and the elevated striae are exposed to the light energy,” Dr. Steinert said.
Investigators determined that it was not wise to go over the additional 100 pulses under any circumstances. “When we did more we couldn’t see any evidence that we were getting better results and we were causing some unintended optical shifts,” Dr. Steinert said. “The idea is just to get rid of the most elevated of these striae ridges.”

PTK by the numbers

Although the striae will not completely disappear with the technique, the patient’s symptoms will improve. “As soon as the striae are low enough then when the epithelium regrows it has the ability to cover over the remaining elevation,” Dr. Steinert said. “Then the vision is better.”
This was reflected in the study outcomes. This retrospective consecutive series included 47 eyes of 44 patients with visually significant flap striae. “Results showed that the visual significance of the microstriae became very limited,” Dr. Ashrafzadeh said. “The visual acuity of all patients improved.” Mean uncorrected visual acuity improved from 20/43 to 20/33. Likewise mean best corrected acuity improved from 20/29 to 20/23. “The number of patients that achieved 20/20 best corrected acuity improved from 17% to 54%,” Dr. Ashrafzadeh said. “The number of best corrected vision gains was also significant; 68% of patients gained best corrected visual auity lines.”
That’s not to say that PTK doesn’t have any unwanted consequences, Dr. Ashrafzadeh warns. “There is a hyperopic shift that occurs with PTK which may not be the most desirable,” he said. If a patient is somewhat under corrected on-the-other hand this may neutralize the effect.
It’s also important to bear in mind that these can not be treated using wavefront. “This is a whole different type of optical disruption,” Dr. Steinert said. “These microstriae because they represent fine little linear irregularities are not even detected on wavefront analysis.”
Overall, there are a small number of patients who are unhappy with their LASIK results, Dr. Steinert finds. Some of these are due to issues such as higher-order aberrations, which can be dealt with wavefront. “Another unhappy group are people who have these optically disruptive microstriae,” Dr. Steinert said. “PTK is a method for treating them that is reliable and repeatable and we don’t think that there is any alternative treatment that can give you the same results.”

Editors’ Note: Dr. Ashrafzadeh has no financial interests related to his comments. Dr. Steinert has financial interests with Advanced Medical Optics (Santa Ana, Calif.).

Contact information
Ashrafzadeh: 209-544-2020, DrAsh@mchenrylasik.com
Steinert: 949-824-0327, steinert@uci.edu