A higher reverse zone depth 2 (RZD2), smaller landing zone angle 1 (LZA1), and larger lens diameter can lead to a smaller treatment zone for patients treated with corneal refractive therapy (CRT), according to research published in Contact Lens and Anterior Eye.

Researchers retrospectively analyzed data from 309 eyes of 309 orthokeratology (OK) lens wearers (mean age 9.81±1.79 years, 160 girls) presenting to a single center between January 2019 and February 2021. They obtained baseline data including refraction, horizontal visible iris diameter (HVID), pupil diameter, central corneal thickness (CCT), anterior chamber depth (ACD), flat (K1) and steep (K2) keratometry (K) readings, mean K reading, eccentricity vale, and initial axial length (AL).

The team included patients with spherical refraction values from -0.75 to -6.00 D,  astigmatism values less than or equal to -2.50 D, and best corrected visual acuity (BCVA) of 20/20 or better. They excluded patients with a history of eye disease, poor corneal topography assessment, or poor adherence to lens wearing during follow-up from the analysis.


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The investigators noted that spherical refraction and K1 were positively correlated with treatment zone diameter for baseline patient parameters (P =0.00 and P =.003, respectively). After controlling for spherical refraction and K1, they no longer observed statistically significant differences with respect to other parameters. With the exception of RZD1, the fitting parameters of CRT were related to treatment area.  

The researchers used a multiple linear regression model to clarify the impact of adjusting each parameter on the treatment area. They determined that LZA1 was positively correlated with treatment area size, while RZD2 and lens diameter were negatively correlated with treatment area size (P =0.00 for all). The accuracy of logistic regression in predicting treatment zone size was 71.5%. 

“Our results indicated that when patients were fitted with ortho-K lenses, CRT lenses should be selected with large diameters within the appropriate range whenever possible, and lenses with a high RZD2 and small LZA1 should be selected as long as the overall lens fit is clinically acceptable,” according to the investigators.

Study limitations include its retroscopic nature and single center design.  

Reference

Sun L, Li X, Zhao H, et al. Biometric factors and orthokeratology lens parameters can influence the treatment zone diameter on corneal topography in corneal refractive therapy lens wearers. Cont Lens Anterior Eye. Published online April 29, 2022. doi:10.1016/j.clae.2022.101700