To the editor
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We read the article “Topography-guided ablation may offer benefits after laser vision correction” published on Healio and share Dr. Pineda’s enthusiasm for the benefits of this technology.
The article states with “increased higher-order aberrations, there is typically a larger discrepancy between manifest and topographic cylinder.” This statement contradicts the current literature and is not well supported by data. Our Journal of Cataract & Refractive Surgery study of more than 37,000 eyes, as well as other independent studies, have shown no meaningful correlation between anterior corneal higher-order aberrations and the discrepancy between manifest and topographic astigmatism. The difference between these two measures is termed ocular residual astigmatism (ORA). We have written several letters to the editor on this topic and have discussed these concepts in publications.
The term “TGA-recommended astigmatism” used in the article can be misleading and is not widely used in the field. The customary nomenclature for this value is “Contoura-measured anterior corneal astigmatism,” “Vario-measured astigmatism” or “topography-measured astigmatism.” These terms accurately reflect that the value is objectively obtained from instrument measurements, specifically the Vario high-resolution Placido-disc topographer (Alcon), which directly images the cornea. Describing it as a recommendation may cause confusion.
The article states, “Ocular residual astigmatism can be significant in magnitude and axis between manifest astigmatism and TGA-recommended astigmatism,” and Dr. Pineda suggests that this parameter needs to be considered when treating. In a separate ORA study in 21,581 eyes, we demonstrated that the contribution of ORA to topography-guided clinical outcomes in virgin healthy eyes is negligible, with similar findings in the laser vision correction literature. These findings are analogous to our previous study showing no outcome effect between eyes with small vs. very large discrepancy between manifest axis and topographical axis. TGA treatment planning does not need to account for ORA as even eyes with greater ORA or axis discrepancy do well when treated on the clinically measured refractive astigmatism and should not be excluded from topography-guided surgery.
The article says that “there are several approaches for presurgical planning for TGA but no standardized method.” With data from more than 150,000 eyes, our research on topography-guided ablation has led to strong scientific validity of inputting and targeting the manifest refractive cylinder for excimer treatment. Algorithms or software that consider corneal higher-order aberrations into LASIK planning (like Phorcides) or that treat on the Contoura-measured corneal astigmatism are all based on the false premise that corneal higher-order aberrations affect the manifest refraction in healthy virgin eyes and do so in a predictive fashion. We have demonstrated that this is not the case, and others have independently replicated our studies. Using accurate manifest refractions with a calibrated and continually improved nomogram is what is paramount to obtaining good results with topography-guided technology. There is no evidence-based reason to move away from manifest refraction, the input standard that has been used for excimer refractive correction since the advent of the technology.
- References:
- Wallerstein A, et al. Graefes Arch Clin Exp Ophthalmol. 2023;doi:10.1007/s00417-022-05859-4.
- Wallerstein A, et al. J Cataract Refract Surg. 2019;doi:10.1016/j.jcrs.2019.02.041.
- Wallerstein A, et al. J Cataract Refract Surg. 2022;doi:10.1097/j.jcrs.0000000000001068.
- Wallerstein A, et al. J Refract Surg. 2019;doi:10.3928/1081597X-20181113-01.
- Wallerstein A, et al. J Refract Surg. 2020;doi:10.3928/1081597X-20200609-01.
- Wallerstein A, et al. J Refract Surg. 2021;doi:10.3928/1081597X-20210716-01.
Avi Wallerstein, MD, FRCSC
and Mathieu Gauvin, BEng, PhD
Department of ophthalmology and visual sciences
McGill University, Montreal
LASIK MD, Montreal
The presenter responds:
The comments from Drs. Wallerstein and Gauvin are welcomed and highlight the evolving use of terminology and current research in this field.
The purpose of the article and talk, specifically aimed at practicing refractive surgeons, was to provide a high view for using topography-guided excimer treatments after previous laser vision correction (LVC) and to review some of the past and current approaches being utilized. The short talk and article did not endorse any specific approach in treating such patients, even if the authors felt based on their research that their approach was superior to other techniques, software or algorithms regarding manifest refraction. Their responses, while appropriate, focus principally on virgin eyes undergoing LVC and not eyes with prior laser vision correction. Research in this area is still limited. Their comments underscore the continuing progress and debates in this field. I look forward to more published research in this critical area so our patients may benefit from this emerging and transformative technology.
Roberto Pineda, MD
Associate professor of ophthalmology
Harvard Medical School
Massachusetts Eye and Ear
Boston