Back Optic Zone Diameter in Orthokeratology: Why Lens Design Affects Myopia Control

The role of back optic zone diameter in myopia control

A study published in 2021 compared the efficacy of controlling annual axial length (AL) increase in myopic Caucasian children based on two parameters of orthokeratology (OK) lens design: the back optic zone diameter (BOZD) and the plus power ring diameter (PPRD), the mid-peripheral annular ring of corneal steepening.

The research involved 71 myopic patients, mostly young and male, treated with different orthokeratology lens designs from a Spanish optometry clinic.

What the study found

Subjects were divided into groups with BOZDs above or below 5.00 mm, and the induced PPRD above or below 4.5 mm. The relationship to axial length and refractive progression at 12 months was then analysed.

Subjects with smaller BOZDs, and a PPRD that fell within the pupil, performed the best at reducing myopia progression.

The result: 76% less axial length growth, or a 0.13 mm/year absolute reduction. Smaller BOZD induces a reduced PPRD that slows axial elongation better than standard OK lenses.

What this means at Carina Eye Care

The BOZD is a parameter that is looked at carefully at Carina Eye Care to customise orthokeratology for patients requiring an aggressive myopia management strategy.

However, the outcome of orthokeratology is not entirely predictable, as it depends on multiple corneal factors including corneal topography, eccentricity, and how the individual cornea responds to the lens. This is why regular follow-up appointments are essential, they allow us to monitor axial length progression and adjust the lens design if needed.

If your child is in orthokeratology or you’re considering it, book a consultation and we can discuss whether optimising the BOZD is appropriate for their specific corneal profile and progression rate.