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Epithelial thickness mapping can help determine type of refractive surgery treatment
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Epithelial thickness mapping can help solve diagnostic dilemmas for ophthalmologists considering refractive surgery for patients with mild abnormalities on tomographic or topographic scans.
According to the results of a retrospective review undertaken by Ella Faktorovich, MD, of Pacific Vision Institute, and colleagues, refractive surgery candidates with a single mild topographic or tomographic abnormality and normal epithelial thickness mapping (ETM) may be safe to undergo LASIK. However, if the patient’s prescription is too high for a safe residual stromal bed, PRK may be the more appropriate procedure.
“Regardless of how normal the patient’s imaging studies are, clinical judgement should still be used to decide what type of treatment to recommend to the patient. Nevertheless, it is very helpful to have a third type of technology to help the decision-making process in patients with mild topographic or tomographic abnormalities, such as mild inferior steepening or somewhat thin cornea, for example, where a course of action may bedebatable,” Faktorovich told Ocular Surgery News.
ETM for all candidates
Researchers retrospectively analyzed ETMs, topographies and tomographies of 298 eyes of 149 consecutive myopic and myopic astigmatic soft contact lens wearers who had been out of contacts for 1 week before undergoing scans. Researchers compared ETMs of eyes with normal topography and tomography to those with a single mild topographic or tomographic abnormality, Faktorovich said.
Source: Ella Faktorovich, MD
In group 1, 190 eyes of 95 patients had a normal topography and tomography, and in group 2, 89 eyes of 49 patients had one abnormality. Faktorovich and colleagues compared minimal pachymetry thickness, central epithelial thickness, minimal epithelial thickness, epithelial thickness in the temporal inferior cornea, differences between maximum and minimum epithelial thickness, superior and inferior epithelial thickness, and inferotemporal and superonasal cornea between the two groups.
Previously published literature on ETM reveals a discernible pattern of epithelial thickness distribution in normal corneas vs. corneas with various degrees of severity of keratoconus. In corneas with even mild keratoconus, for example, epithelium overlying the thinnest spot on the cornea is thin and the surrounding epithelium is thickened compared with normal corneas.
In the study by Faktorovich and colleagues, there were no statistically significant differences in measurements between the group with normal eyes and the one with a single mild topographic or tomographic abnormality. Based on these findings, it would be reasonable for patients with thin corneas, for example, providing their prescription is not too high to compromise the residual stromal bed, to undergo LASIK, Faktorovich said.
If the same patient with a slightly thinner cornea needed a higher amount of tissue ablated and had a residual stromal bed of less than 300 µm, PRK may be preferable, she said.
“Any patient with topographic or tomographic abnormalities that pose a diagnostic dilemma, whether to recommend LASIK, PRK or any corneal surgery at all, may benefit from ETM as an additional screening tool. I often find this technology helpful as a tiebreaker when patients come to me for a third or fourth opinion, having gotten different recommendations from different surgeons,” she said.
Identify and review abnormalities
A questionable ETM can prompt an examiner to review a patient’s cornea again to look for any abnormalities or subtle findings that may steer the decision to LASIK or PRK. A large difference between minimum and maximum epithelial thickness values may suggest uneven tear film or subtle epithelial basement membrane dystrophy (EBMD), which may be difficult to detect on a slit lamp exam, Faktorovich said.
“We recently had a patient who at first glance appeared to have normal corneas on slit lamp examination. Their ETM, however, had a pattern of patches of epithelial thickening and thinning at the periphery of the cornea. When we reexamined the patient’s cornea at the slit lamp, we found very subtle fingerprint lines consistent with EBMD. Based on these findings, PRK was recommended rather than LASIK to avoid epithelial loosening and sloughing during flap lift often seen in patients with EBMD,” Faktorovich said. – by Robert Linnehan
- Reference:
- VIDEO: Epithelial thickness mapping a new tool to improve refractive surgery. www.healio.com/ophthalmology/refractive-surgery/news/online/%7B3c03549c-ea02-403d-9fe3-8739958a77e0%7D/video-epithelial-thickness-mapping-a-new-tool-to-improve-refractive-surgery. Published May 14, 2019. Accessed June 18, 2019.
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Ella Faktorovich, MD, can be reached at Pacific Vision Institute, 505 Beach St., San Francisco, CA 94133; email: ella@pacificvision.org.
Disclosure: Faktorovich reports no relevant financial disclosures.