MYOPIA MANAGEMENT: Lens Design and Fitting – Empirical vs. Diagnostic Fitting
Jessica Liaw OD, FAAO
Empirical Fitting
- Share aforementioned diagnostic testing data with the laboratory for lens design
Diagnostic Fitting: Selecting an Initial Lens
- Base Curve: Flat K – Rx – Jessen Factor (+0.50 to +1.00D for overcorrection)
- Diameter: Horizontal visible iris diameter (HVID) – 1.0mm (occupies ~90% of cornea)
- Considerations for choosing toric lens design
- Limbus-to-limbus astigmatism on axial map
- Elevation differential > 30 microns
- Corneal toricity > 0.75D
Optimizing Myopia Control Effect
- Larger pupils have demonstrated greater myopia control by directing more of the pupil to the peripheral defocus area
- Larger-than-average pupil size in the Ortho-K wearers was associated with less axial elongation, while pupil size had no significant effect in the spectacle wearers. Additionally, cycloplegic agent use accompanying Ortho-K lens wear might further reduce myopic shift.1
- Consider a smaller treatment zone for enhanced myopia control
Fit Evaluation
- Apply lenses to evaluate fluorescein pattern
- Good centration, minimal movement (1mm or less)
- Bullseye central pattern: 4mm zone of bearing, 0.5mm edge lift
- Maintain ~0.5mm edge lift, ensure no binding, and allow tear exchange.
Topography
- Bullseye pattern: central flattening, paracentral steepening
- Analyze treatment zone size and centration
Sources
- Chen Z, Niu L, Feng X, et al. Impact of pupil diameter on axial growth in orthokeratology. Optom Vis Sci 2012; 1636-1640.