Analysis of Two Orthokeratology Lens Designs and Comparison of Their Optical Effects on the Cornea
Authors: Marcotte-Collard, Rémy O.D.; Simard, Patrick O.D., M.Sc., M.B.A.; Michaud, Langis O.D., M.Sc.
Purpose: This study aims to analyze two commercial orthokeratology lens designs and compare their optical effects at the corneal level.
Methods: This is a retrospective study on subjects seeking an orthokeratology fitting for myopia management at the Université de Montréal clinic between January 2013 and August 2015. Group A included the first 64 subjects fitted with a 4-curve lens design (Paragon CRT; Paragon) who met the inclusion criteria, whereas group B included the same number of subjects fitted with a 5-curve lens design (Dreamlens; Polymer Technology, Rochester, NY). Topographic tangential maps were collected at baseline and 3 months after fitting. The differential map was generated for each patient and analyzed, which involved determining the radius of the central distance zone (CDZ) and the power and width of the high convex zone (HCZ). Results were compared between the two groups, taking baseline refraction into account. Finally, a correlation was estimated between topographic data and corneal parameters (flat and steep K, the corneal eccentricity of each principal meridian).
Results: The CDZ for group A is significantly larger than the one generated for group B both horizontally (t(126)=12.12, P<0.01) and vertically (t(126)=15.690, P<0.01). However, there was no significant difference regarding the HCZ power generated. The only correlations found were a strong positive association between CDZ radius and HCZ power generated by lens A nasally (r=0.450; P=0.000) and temporally (r=0.558; P=0.000), and a weaker association between the baseline refractive error, along with the nasal (r=0.237; P=0.033) and temporal (r=0.288; P=0.028) HCZ power for lens B.
Conclusion: The four- and five-curve orthokeratology lens designs generate significantly different optical modifications on the cornea. This can affect reports on orthokeratology efficacy for myopia management as well as the lens selection when used for myopia correction.
OSO comment: This is a really good paper in that it highlights the fact that not all designs are equal in their treatment effect and potentially management of the myopia control effect. It suggests that customised lens designs may be more favourable in lower amounts of Myopia control. It also describes a potential reason for the variability of controlling effect across the research.