Topography-modified refraction (TMR): adjustment of treated cylinder amount and axis to the topography versus standard clinical refraction in myopic topography-guided LASIK

Anastasios John Kanellopoulos, Anastasios John Kanellopoulos

Abstract

Purpose: To evaluate the safety, efficacy, and contralateral eye comparison of topography-guided myopic LASIK with two different refraction treatment strategies.

Setting: Private clinical ophthalmology practice.

Patients and methods: A total of 100 eyes (50 patients) in consecutive cases of myopic topography-guided LASIK procedures with the same refractive platform (FS200 femtosecond and EX500 excimer lasers) were randomized for treatment as follows: one eye with the standard clinical refraction (group A) and the contralateral eye with the topographic astigmatic power and axis (topography-modified treatment refraction; group B). All cases were evaluated pre- and post-operatively for the following parameters: refractive error, best corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA), topography (Placido-disk based) and tomography (Scheimpflug-image based), wavefront analysis, pupillometry, and contrast sensitivity. Follow-up visits were conducted for at least 12 months.

Results: Mean refractive error was -5.5 D of myopia and -1.75 D of astigmatism. In group A versus group B, respectively, the average UDVA improved from 20/200 to 20/20 versus 20/16; post-operative CDVA was 20/20 and 20/13.5; 1 line of vision gained was 27.8% and 55.6%; and 2 lines of vision gained was 5.6% and 11.1%. In group A, 27.8% of eyes had over -0.50 diopters of residual refractive astigmatism, in comparison to 11.7% in group B (P<0.01). The residual percentages in both groups were measured with refractive astigmatism of more than -0.5 diopters.

Conclusion: Topography-modified refraction (TMR): topographic adjustment of the amount and axis of astigmatism treated, when different from the clinical refraction, may offer superior outcomes in topography-guided myopic LASIK. These findings may change the current clinical paradigm of the optimal subjective refraction utilized in laser vision correction.

Keywords: EX500 excimer laser; FS200; TMR; astigmatism correction; femtosecond laser; long-term stability; myopic LASIK; post-LASIK refraction; regression; topography-modified refraction.

Conflict of interest statement

The author reports no conflicts of interest in this work.

Figures

Figure 1
Figure 1
Image A shows the topography-guided treatment when refractive error is adjusted by the user to zero sphere and zero cylinder. This image allows the user to visualize the corrections made by the software and added to the excimer correction in order to normalize the anterior cornea curvature to the cornea vertex. Image B illustrates the topography treatment pattern after the refraction has been adjusted by the user to the desired sphere and cylinder and includes the changes noted in image A. Notes: “Clinical” is the clinical refraction dialed by the user into the system; the “measured” refraction is the cylindrical amount and axis calculated by the topography software, to be corrected so the anterior cornea can me maximally normalized in regard to the cornea vertex; “modified” represents the surgeon/user adjusted data. Abbreviations: 3D, three-dimensional; max, maximum, cen, center; trans, transition zone; res, residual; VD, vertex distance.
Figure 2
Figure 2
Corrected distance visual acuity at 3 months: (A) group A and (B) group B. Notes: Group A: one eye with the standard clinical refraction; Group B: the contralateral eye with the topographic astigmatic power and axis (topography-modified treatment refraction).
Figure 3
Figure 3
Post-operative uncorrected distance visual acuity at 3-month visit: (A) group A and (B) group B. Notes: Group A: one eye with the standard clinical refraction; Group B: the contralateral eye with the topographic astigmatic power and axis (topography-modified treatment refraction).
Figure 4
Figure 4
Safety distance visual acuity graph (percentage of eyes with gain/loss in Snellen lines), at 3-month visit: (A) group A and (B) group B. Notes: Group A: one eye with the standard clinical refraction; Group B: the contralateral eye with the topographic astigmatic power and axis (topography-modified treatment refraction).
Figure 5
Figure 5
Defocus equivalent results at 3-month visit: (A) group A and (B) group B. Notes: Group A: one eye with the standard clinical refraction; Group B: the contralateral eye with the topographic astigmatic power and axis (topography-modified treatment refraction).
Figure 6
Figure 6
Predictability of spherical equivalent (SE) correction, showing achieved SE versus attempted SE: (A) group A and (B) group B. Notes: Group A: one eye with the standard clinical refraction; Group B: the contralateral eye with the topographic astigmatic power and axis (topography-modified treatment refraction). Green marks show outcomes within 0.25 diopters of attempted vs achieved; blue marks show attempted vs achieved of under 0.25 diopters (under-corrections); red marks show attempted vs achieved of over 0.25 diopters (over-corrections).
Figure 7
Figure 7
Refractive astigmatism, pre-operatively and at 3-month post-operative visits. Notes: Percentage of eyes (vertical axis) versus refractive astigmatism (D), horizontal axis: (A) group A and (B) group B. Group A: one eye with the standard clinical refraction; Group B: the contralateral eye with the topographic astigmatic power and axis (topography-modified treatment refraction).
Figure 8
Figure 8
Contrast sensitivity comparison at 3-month visit. Notes: As pre-operative data were not statistically significant in groups A and B, they are noted together as “Pre-op ALL”. The average contrast sensitivity data is indicated with the green, red, and blue lines. Group A: one eye with the standard clinical refraction; Group B: the contralateral eye with the topographic astigmatic power and axis (topography-modified treatment refraction).

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