Influence of Corneal Topographic Parameters in the Decentration of Orthokeratology

Abstract

Objective: To investigate the lens decentration (LD) of orthokeratology (ortho-k) and the association between pretreatment corneal topographic parameters and LD of the ortho-k. Methods: Fifty right eyes of 50 myopes wearing ortho-k lenses were included in the prospective study. Corneal topography was conducted pretreatment to get topographic corneal parameters, including flat-K (K1); steep-K (K2); corneal astigmatism (CA), CA at 0 to 3 mm (3 mm-CA), 3 to 5 mm (5 mm-CA), 5 to 7 mm (7 mm-CA); surface asymmetry index (SAI); surface regularity index; the curvature of best-fit sphere; the diameter of cornea (DC); the distance from the corneal center to the corneal vertex (CCCV); flat eccentricity (E1), steep eccentricity (E2), and E1/E2 (E ratio); and the corneal curvature differences between the nasal and temporal quadrants at 0 to 3 mm (3 mm-Knt), and the corneal curvature differences between the superior and inferior quadrants at 0 to 3 mm (3 mm-Ksi), 5 mm-Knt (at 3–5 mm), 5 mm-Ksi (at 3–5 mm), 7 mm-Knt (at 5–7 mm), and 7 mm-Ksi (at 5–7 mm). The relationship between these cornea topographic parameters and LD of the ortho-k was tested using stepwise multiple linear regression models. Results: The mean magnitude of LD was 0.51±0.23 mm (0.06–1.03 mm). According to the stepwise analysis, 4 factors were associated with the overall LD (P<0.01): SAI (β=0.252), CCCV (β=0.539), 5 mm-CA (β=−0.268), and 3 mm-Ksi (β=−0.374); 5 factors were associated with the horizontal LD (P<0.01): DC (β=0.205), CCCV (β=0.881), 3 mm-CA (β=−0.217), 5 mm-Knt (β=0.15), and 3 mm-Ksi (β=−0.18); and 3 factors were associated with the vertical LD (P<0.01): SAI (β=0.542), 5 mm-CA (β=−0.188), and 3 mm-Ksi (β=−0.213). Conclusion: Lens decentration is most common, but in most cases, the amount of LD is moderate and acceptable. The magnitude of LD can be predetermined by topographic corneal parameters. Surface asymmetry index, CCCV, 5 mm-Knt, and 3 mm-Ksi may be more preferable parameters in terms of the assessment of LD of ortho-k.

The effect of orthokeratology treatment zone decentration on myopia progression

“…In addition, the unequal alignment of the Ortho-K lens along the main meridian could affect the stability of the Ortho-K lens, and therefore, might increase the possibility of Ortho-K lens decentration [ 37 ]. In addition, external forces, such as the eyelid force, which are due to large differences in the cornea central curvature in the inferior and superior meridian, might push the Ortho-K lens down, resulting in inferior decentration [ 38 ].…”

The Effect of Corneal Refractive Power Area Changes on Myopia Progression during Orthokeratology

“…Modern orthokeratology is a process that uses reverse-geometry-designed rigid contact lenses to reshape the eye over time. Each lens had a back optical zone diameter of 6.0 mm, a reverse curve of 0.6 mm in width, an alignment curve of 1.25 mm in width, and a peripheral curve of 0.4 mm in width [ 14 , 25 , 28 ]. After the base curve flattens the cornea, ideally, a flat zone is formed to correct the refractive error.…”

“…Based on the recorded power areas of the pupillary area obtained from axial difference topography, the following measurements were made: positive-power area (positive D value), corrected area (D value = baseline SER ± 0.25 D), overcorrected area (D value > baseline SER − 0.25 D), and undercorrected area (D value < baseline SER + 0.25 D). To calculate the different refractive powers in the central 4 mm pupillary area, axial difference topography was performed, based on the axial topography [ 25 ], at the baseline and after three months of continuous orthokeratology lens wear. According to the axial difference topography, the refractive power parameter was set as the individual baseline SER power ( Figure 1 ).…”

Effect of treatment zone decentration on axial length growth after orthokeratology

“…Only when the defocus exceeds this threshold will the “stop” signal start to delay the ALG ( Kang and Swarbrick, 2016 ). For the same average RCRP, the greater the variation in all directions, the more uneven the distribution and the slower the ALG ( Gu et al, 2019 ). The current study did not find any association between decentration direction and 12-month ALG.…”