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J Curr Ophthalmol
J Curr Ophthalmol
JCO
J Curr Ophthalmol
Journal of Current Ophthalmology
2452-2325
Wolters Kluwer - Medknow India

JCO-35-415
10.4103/joco.joco_162_23
Letter to Editor
Mitigated Residual Error in Inaccurate Myopic Keratorefractive Surgery
Peyman Alireza 1
Pourazizi Mohsen 1
Peyman Mohammadreza 2
1 Isfahan Eye Research Center, Department of Ophthalmology, Isfahan University of Medical Sciences, Isfahan, Iran
2 Parsian Vision Science Research Institute, Isfahan, Iran
Address for correspondence: Mohammadreza Peyman, Department of Ophthalmology, Feiz Hospital, Modares St., Isfahan, Iran. E-mail: drmpeyman@yahoo.com
Oct-Dec 2023
10 8 2024
35 4 415415
11 8 2023
25 9 2023
29 9 2023
Copyright: © 2024 Journal of Current Ophthalmology
2024
https://creativecommons.org/licenses/by-nc-sa/4.0/ This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given and the new creations are licensed under the identical terms.
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pmcDear Editor,

As refractive surgeons, we try to have the most precise results. There are doubts about the best nomogram for estimated overcorrection according to age and other factors.1 It is not possible to determine the exact refractive error of all candidates. There is some difference between manifest, subjective, and cyclorefraction dioptric results. Even so, many patients look contented after any myopic keratorefractive surgery in actual practice. The cornea appears to be quite forgiving in this regard. Variations in laser system settings and surgical techniques, the healing process among different age groups, environmental variables, and postoperative drug regimens influence the outcome. However, the focus of this letter is to look into the effect of calculation and optics in myopic keratorefractive surgery.

Refractive surgeons usually measure the refractive error and think out for treatment plan at the plane of the glasses, a vertex distance of 12 mm for most. The actual treatment, however, is applied at the cornea plane. In the case of a refractive error, it takes place at the cornea plane, and the ophthalmologist will measure it at the plane of the glasses later on. For instance, if the actual refraction was −6.0 diopters and the surgeon had treated the cornea for −7.0 by error, the remaining refraction is expected to be one diopter of hyperopia. By converting the values to the cornea plane, the actual refraction is about −5.59 diopters, the treatment at the cornea plane is −6.45 diopters, and the estimated residue at the plane of the cornea will be +0.86 diopter, which is equal to +0.85 diopter at glasses plane. While we ordinarily expect the remaining residual error to be one diopter of hyperopia, the calculations reveal a lower number, +0.85 diopter. Presuming that the actual refraction was −6.0 diopters and the surgeon had treated the cornea for −5.0 by error, the calculated residue is −0.88 diopter and −0.89 diopters at the cornea and glasses’ plane, respectively, instead of one diopter of myopia. The consequence of an error in a myopic treatment is calculated to be lower than anticipation in both directions. The theoretical calculation reveals a reverse situation for hyperopia. Namely, the mistake will be magnified in a hyperopic keratorefractive procedure. Reckoning of this kind may help the cornea surgeon amend the error with more precision after discovering the mistake.

Another utilization could be calculating the necessary treatment to achieve the postoperative target. For example, in a subject with a preoperative refraction of −6.0, if the surgeon intends for a +0.5 diopter postoperative refraction target, the attempted refraction should be −6.58 instead of −6.5 diopter. With −6.5 treatment, postoperative refraction of +0.43 is anticipated.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.
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REFERENCE

1 Shapira Y Vainer I Mimouni M Sela T Munzer G Kaiserman I Myopia and myopic astigmatism photorefractive keratectomy: Applying an advanced multiple regression-derived nomogram Graefes Arch Clin Exp Ophthalmol 2019 257 225 32 30121713
