April 2020

IN FOCUS

Therapeutic Refractive Corneal Surgery
PTK for corneal pathology


by Ellen Stodola Editorial Co-Director


EBMD

Start with central laser (4–6 µm)

Move reticle toward the limbus and treat the outer cornea, trying to get 4–6 µm to all areas for the cornea.
Source (all): David Hardten, MD

 

For this issue of EyeWorld, we asked world leaders in therapeutic corneal refractive surgery to share their wisdom. This section is packed with pearls on how to treat various corneal issues. It wasn’t that long ago that none of these procedures were available to patients with surgical corneal needs. Please join me in thanking these doctors and the writers at EyeWorld for their hard work. I hope you enjoy this important issue focusing on the pathology side of refractive corneal surgery.
—Vance Thompson, MD
Refractive Editor


PTK can be used for various types of corneal pathologies. Depending on the type of opacity and depth in the cornea, other treatments may also be needed. Experts discussed how they use PTK and the conditions for which they employ it.

Perspectives of Christopher Rapuano, MD

According to Dr. Rapuano, PTK was FDA approved in 1995 for treating corneal pathology. It’s good for treating several types of pathology, he said. One type is elevated opacities, like Salzmann’s nodules, keratoconus nodules, and elevated scars. “Some of those diagnoses don’t need PTK, but some of these opacities don’t come off well with superficial keratectomy, and you have PTK as backup,” Dr. Rapuano said.
For those, Dr. Rapuano will bring the patient to the laser and do superficial keratectomy with a blade under the laser microscope. He said he usually gets a pretty smooth surface and will do a little PTK smoothing after that. “But sometimes it’s not very smooth after I’ve done a mechanical lamellar keratectomy, then I have the laser.”
PTK offers a real advantage, he said, when you’re handling anterior stromal opacities or those in the front 15–20% of the cornea. Patients with superficial scars and many types of anterior and stromal corneal dystrophies can be treated. Most patients with granular corneal dystrophy, some patients with lattice corneal dystrophy, and occasional patients with macular corneal dystrophy can benefit from PTK.
One of the pearls Dr. Rapuano gives when teaching about PTK is if it’s an anterior opacity and if most of the opacity is in the top 15–20% of the cornea, this could be a good candidate. But if it’s much deeper than that, the patient is probably not a good candidate.
A lot of dystrophy patients have 80% of the opacity in the top 10% of the cornea and the other 20% is deep in the cornea, Dr. Rapuano said. When some physicians do PTK they think they have to get all the opacity out, and they take off a lot of the cornea. “That does a good job of getting rid of the opacity, but when you go that deep, you cause significant scarring and flattening of the cornea, and the results are bad,” he said. Even if you get only 80% of the opacity, the patient’s vision will improve dramatically without causing significant scarring or flattening. If you go too deep and there is scarring, the patient may need a corneal transplant. If there is severe irregularity or farsightedness, the patient may need a hard contact lens.
Dr. Rapuano added that insurance coverage may be an issue with PTK. If a physician is doing PTK at a commercial laser center that doesn’t do commercial billing, the patient may have to pay cash for the procedure.

Perspectives of David Hardten, MD

Dr. Hardten said that the most common reason he uses PTK is for epithelial basement membrane dystrophy (EBMD), for either visually significant irregular astigmatism that EBMD causes or associated recurrent erosions. Other treatment options include superficial keratectomy or stromal puncture, but the challenge in these alternatives is you typically don’t get all of the basement membrane dystrophy. “With PTK, you can typically resolve the pathology over a broader area,” Dr. Hardten said.
PTK in patients with significant EBMD deposits with blurry vision can be used to polish deposits off, he said.
Dr. Hardten said PTK can also be useful for treating Salzmann’s nodules. Part of the procedure is the laser component, but it is important to do a careful superficial keratectomy first. Dr. Hardten will use the laser to fine tune the polish after doing the superficial keratectomy and debridement of the larger components.
Dr. Hardten said that it’s difficult when the pathology is very deep. If the pathology is going to require removing cornea more than 75 µm deep, it’s challenging to take the non-involved cornea down enough in order to regularize the corneal curvature.
In patients who have other underlying problems, like neurotrophic keratitis, zoster, or problems where they’ll have difficulty with epithelial healing, there is another set of issues that you’ll have to deal with, Dr. Hardten said. It’s often a big challenge, not from the ability to improve the scar with the laser, but what caused the original scar will also potentially cause you trouble during the healing period of the PTK.

Perspectives of Evan Schoenberg, MD

Dr. Schoenberg said PTK is a laser treatment that’s intended to remove scars from or produce a smoother shape for the anterior cornea. On some laser platforms, PTK and PRK are the same laser procedure performed with different intentions, but other laser platforms have a dedicated PTK mode. “Either way, the target is clearing an anterior stromal opacity, resurfacing an irregular Bowman’s membrane, or decreasing differences in stromal thickness,” he said.
PTK has more recently been supplemented by topography-guided PRK, but it’s not replaced by it, Dr. Schoenberg said. There are some pathologies for which topography-guided PRK is a great solution but others where it wouldn’t be effective at all and PTK is a better approach. “Sometimes you need a sequential plan: PTK first to produce symmetric epithelium and less opacity, then topography-guided to provide focus,” he said.
The indications are varied, Dr. Schoenberg said, and they include previous corneal ulcer, previous trauma, or any other corneal pathology that induces topographic change or scarring.
“The first thing I think about is whether we’re looking at the visual axis directly, or if we are looking at the topographic effect of a peripheral or mid-peripheral change on the visual axis,” he said. You want to know if you are trying to remove a scar that’s blocking vision or trying to reshape the cornea to be a more effective shape for good vision.
When it’s a topographic irregularity, Dr. Schoenberg thinks a hard contact lens over refraction is the most important first assessment tool. If that is effective, you should discuss continuing with a specialty contact lens fitting versus the surgical laser solution, he said. If it’s an opacity in the visual axis, a hard contact lens is less likely to be helpful.
“The next most important diagnostic tools that I use, other than the slit lamp itself, are the topographer and anterior segment OCT,” Dr. Schoenberg said. “Anterior segment OCT is such an important tool for assessing the cornea when considering whether PTK would be helpful or not.” Most modern OCT systems have an anterior segment module, even without a cornea upgrade.
The most at-risk patients are those whose corneal disease comes from previous herpes viral infection or who have some sort of severe dry eye or limbal stem cell deficiency contributing to their issues. “I don’t consider these patients excluded from treatment, but they’re higher risk and need to be counseled more carefully about possible complications,” he said.
In extreme cases, these may be patients who are destined for a corneal transplant and the salvage attempt is PTK.
Dr. Schoenberg shared a case of a patient he treated who previously had severe herpetic stromal keratitis. He got through the infection but ultimately was left with central stromal scar and substantial stromal thinning that was inducing a lot of irregular astigmatism.
“We had him fitted in scleral contact lenses, which managed the astigmatism, but his vision was still very poor because of the dense stromal scar,” Dr. Schoenberg said. “We discussed the risks of laser treatment, including that of viral reactivation.” With pre- and post-treatment valacyclovir (1 gram three times daily starting a week before and continuing for a month after, then 1 gram daily for the next year), Dr. Schoenberg performed a transepithelial PTK via a myopic ablation, normalizing the shape of the cornea and removing much of the scar. This deliberately made him into a +9.00 hyperope, which took him from 20/200 best-corrected to +9.00 20/40. The second step was cataract surgery using a high-power IOL matched to the induced spherical aberration. This took him from +9.00 20/40 to +0.50 sphere for 20/40+.
Dr. Schoenberg also highlighted the possibility of corneal haze. When he performs a substantial ablation, he uses mitomycin-C (MMC) and a longer exposure than he would normally use in a routine refractive case. He uses MMC 0.02% for 30 seconds. He also does an extended steroid taper, typically prednisolone or loteprednol four times a day for a month. He will taper slowly in a 2-week increment, then use a low-potency steroid for a few months after the taper of the steroid. He also recommends that patients take vitamin C supplements for the first few months and use sunglasses when outdoors. Haze remains a risk with large treatments, but these measures tend to minimize that risk, he said.

At a glance

• PTK may work best if most of the opacity is in the anterior of the cornea. Even getting most of the opacity can benefit the patient’s vision.
• PTK can be difficult when the pathology is very deep. If there is pathology more than 75–100 µm deep (depending on the corneal thickness, especially where it is most thinned), it can be challenging.
• Haze could be a possible concern following ablation procedures. Mitomycin-C may help, along with other considerations.

About the doctors

David Hardten, MD
Minnesota Eye Consultants
Minneapolis, Minnesota

Christopher Rapuano, MD
Wills Eye Hospital
Philadelphia, Pennsylvania

Evan Schoenberg, MD
George Eye Partners
Woodstock, Georgia

Relevant disclosures

Hardten
: None
Rapuano: None
Schoenberg: None

Contact

Hardten
: drhardten@mneye.com
Rapuano: cjrapuano@willseye.org
Schoenberg: evan.schoenberg@gaeyepartners.com

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