Orthokeratology Treatment Zone Influenced By Myopia, Contact Lens Parameters

Orthokeratology treatment zone area and peripheral plus ring (PPR) diameters may be affected by myopia degree, corneal topography, and contact lens parameters, according to a study published in Contact Lens and Anterior Eye. Since the back optic zone diameter demonstrates the highest correlation with the treatment zone and PPR diameter, differences in length between the short and long diameter measurements for both indicate elliptical shapes — a finding that suggest using an elliptical area may better for measuring treatment zone area compared with horizontal and vertical diameters alone.

Researchers performed a retrospective assessment of 106 patients (mean age, 22.16 years; 73 women) who underwent topographical measurements for orthokeratology lenses between 2014 and 2022.

Prior to the investigation, the team performed a pre study using a subset of 12 patients (mean age, 19.17 years; 7 women and girls) to evaluate treatment zone changes during a 2-year period. This initial assessment revealed that orthokeratology treatment zone size does not change significantly after a period of 3 months from the baseline fitting. Once the team established this finding, investigators examined correlations between myopia degree, corneal topography, and contact lens parameters and orthokeratology treatment zone and PPR diameter for 3 back optic zone (BOZD) diameters (5.5, 6.0, and 6.6 mm).

According to the report, the BOZD demonstrated a positive correlation with all zone sizes (all P <.005). Stratified by BOZD, individuals with 6.0 mm BOZD had a 16% greater orthokeratology treatment zone area compared with participants with a 5.5 mm BOZD. Similarly, those with 6.6 mm BOZD showed a 20% increase in orthokeratology treatment zone area compared with individuals with a 6.0 mm BOZD.

Among individuals using a BOZD of 6.0, myopia level correlated with shortest treatment zone diameter (r, −0.25; P =.025), steepest corneal radius and vertical diameter (r, –0.244; P =.029), longest diameter (r, −0.254; P =.023) treatment zone area (r, −0.228; P =.042), the amount of astigmatism and PPR width (r, 0.266; P =.017), and eccentricity of the steep corneal meridian and PPR width (r, –0.222, P =.047).

“Considering only horizontal or vertical diameters may not provide a complete representation of the [treatment zone] size and might underestimate the [treatment zone] area,” according to the researchers. “Thus, by describing the [treatment zone] size based on the area of an elliptic shape, the present study provides an approach for a more comprehensive sketch of its shape and size.”

An inability to measure contact lens wearing time is an acknowledged limitation to the research.