April 2020

IN FOCUS

Therapeutic Refractive Corneal Surgery
Using epithelial mapping for LASIK, PRK, and refractive enhancement


by Vanessa Caceres Contributing Writer


Epithelial thickness map of a normal, healthy cornea

Epithelial thickness map of an eye with keratoconus; the epithelium has thinned over the area of ectasia
Source (all): Jessica Heckman, OD

 

Epithelial thickness mapping is known for its ability to help detect corneal disease, including keratoconus. However, it also can assist with treatment and enhancement decisions for LASIK and PRK, according to ophthalmologists who are using it.
“I think we’re just learning how to use this powerful technology,” said Lance Kugler, MD. “It has taught me how critical the epithelium is to our visual system. The ability to measure it gives us a valuable tool for our treatment decisions.”
Dr. Kugler uses epithelial mapping with the Avanti OCT system (Optovue) with every new patient consultation, be it for LASIK, PRK, or even cataract surgery. After refractive surgery, Dr. Kugler and staff will obtain mapping and also do so on a case-by-case basis with IOL patients. This helps them to track progression of the maps over time.
“Understanding the epithelial distribution can improve clinical decisions, ranging from time of LASIK or PRK enhancement to selecting transepithelial PRK to epithelial debridement in eyes with map dot fingerprint dystrophy,” said Kerry Assil, MD. His work with epithelial mapping with the SPECTRALIS OCT (Heidelberg Engineering) adapted for the anterior segment analyzes epithelial thickness, patterns, and remodeling over time.

What’s considered abnormal

When reviewing epithelial maps, ophthalmologists using them must keep in mind what’s outside of the norm. “A normal epithelial thickness is 50 µm, but what OCT gives us is a pattern and an overview of thickness over a larger area of the cornea,” said Y. Ralph Chu, MD. “This pattern can help determine areas of relative thinner or thicker epithelium, which can be helpful in detecting abnormal curvatures of the cornea.”
Abnormalities that Dr. Assil considers include unusually hypertrophic central epithelium, variably irregular distribution, and insufficient buffering of prior scars. The latter may include apical epithelial hypoplasia coupled with surrounding hypertrophy, he said.
Something additional that Dr. Kugler considers is the bilaterality of the results. “The two eyes should look the same. If you have 60 µm in one eye and 30 in the other, you know one eye is not normal. Fifty microns is the norm, but some people are thicker or thinner,” he said.

Guiding treatment 10 years later

Ophthalmologists interviewed by EyeWorld considered how they would handle a patient who was 10 years post-LASIK and had a normal epithelial thickness. Based on what they saw with epithelial thickness mapping, would they treat with flap relifting and laser or use PRK?
“Since the advent of the femtosecond laser, eyes 10 years post-LASIK are no longer amenable to routine flap relifting, due to firm adherence,” Dr. Assil said. “While nearly all post-myopic PRK and LASIK eyes demonstrate some degree of epithelial hypertrophy, the observation of an unusually large degree of hypertrophy might make a relift more appealing.” This can help avoid “reshuffling the deck,” as Dr. Assil described it.
Both PRK and flap relifting are reasonable, Dr. Kugler thinks. If choosing PRK, make sure to consider how much epithelial thickness there is. “If it doesn’t grow back to the same thickness, you’ll have some residual refractive error. Be cognizant of that, and realize it may take longer than you think to get to the original thickness,” he said.
Dr. Chu prefers PRK and removing the epithelium for that procedure. “I know there are some cases where epithelial hyperplasia results in some slight myopic regression, and a simple debridement can help resolve the small refractive error,” he said. He knows of other surgeons who have used an excimer laser to treat the epithelium to remove hyperplasia, although he has not performed that himself.

Case studies

Dr. Kugler shared several cases where epithelial thickness mapping helped with treatment plans for patients, and he explained the educational role that mapping has with refractive surgery. Mapping gives patients and surgeons an easy, visual tool to explain what happens during the healing process and why it can take some time. “You show patients the maps, and they understand that it needs to reach a certain thickness,” Dr. Kugler said.
One of his patients had a corneal abrasion after cataract surgery. On the first night, the patient’s corneal abrasion caused an area of thinning over the center of the visual axis. The patient’s vision in the affected eye was not as strong at that point and had a hyperopic refraction. The patient went from an epithelium that was 10–20 µm thick to 50 µm as seen with epithelial mapping. “As it filled in, her refraction normalized and approached what it was in the left eye, but that didn’t happen until it was fully thickened,” Dr. Kugler said.
A second patient had LASIK and conjunctivitis with a fair amount of inflammation. The patient’s epithelium became very thin, and vision went from plano to +1.25 D. “It wasn’t until the epithelium had thickened that the refraction turned back to what it was immediately after LASIK, which took about 8 weeks,” Dr. Kugler said. The patient was concerned about vision loss, but Dr. Kugler and staff were able to assure her that there was a physiological reason why she had become hyperopic and that she would heal, as she eventually did.
As a third example, a patient with a PRK enhancement was thrilled with his vision for 3–4 months but then became myopic. Although his eye looked great on exam, the epithelial thickness mapping showed he had gone from 50 µm to more than 80 µm due to hyperplasia. “Had we not had epithelial mapping, it would have been tempting to do an enhancement,” Dr. Kugler said. Instead, they removed the epithelium and let it grow back in a controlled fashion. It did eventually grow back to 50 µm, and the patient’s vision returned to plano.

At a glance

• Epithelial thickness mapping has a role in guiding treatment and enhancement decisions related to LASIK and PRK.
It also helps with patient education.
• Mapping can help surgeons decide what sort of treatment may be used post-refractive surgery, even several years later.
• Understanding of the use of epithelial mapping with refractive surgery patients
will continue to grow.

About the doctors

Kerry Assil, MD

Medical director
The Assil Eye Institute
Beverly Hills, California

Y. Ralph Chu, MD
Founder and medical director
Chu Vision Institute
Bloomington, Minnesota

Lance Kugler, MD
Assistant professor
Truhlsen Eye Institute
University of Nebraska
Medical Center
Omaha, Nebraska

Relevant disclosures

Assil
: None
Chu: None
Kugler: None

Contact

Assil
: kerry@assileye.com
Chu: yrchu@chuvision.com
Kugler: lkugler@kuglervision.com

Using epithelial mapping for LASIK, PRK, and refractive enhancement Using epithelial mapping for LASIK, PRK, and refractive enhancement
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