All things considered, there is no right or wrong design. Each has its advantages and disadvantages as just described. Empirical lens fitting offers a low-cost entry point into OrthoK lens fitting. Recent improvements to computer modeling have also led to ever-increasing first-time success rates with these designs, which offsets their potential inconvenience for the delay in organizing a replacement if needed at follow up – if it is right the first time there is no need to order a replacement lens. This accuracy for first lens fit success, however, diminishes as higher refractive corrections are targeted, or for corneal shapes outside the average range. Equally, some may not like the lack of control over the empirical fit process.
Trial lens sets give greater control over determining the best fit but at the cost of not being able to specifically target refractive correction. Having alternative trial lenses to choose from when responding to lens overnight wear outcomes offers the benefit of reduced chair time compared to the empirical lens fitting approach. But, there is no capacity to control refractive effect, meaning that the patient is likely to end up under or over corrected from the overnight lens wearing trial. Inventory lens sets overcome this shortfall by offering more flexibility as you become more experienced, however, this flexibility comes at the cost of needing to stock more lenses.
Both trial and inventory systems follow a pigeonhole approach, in that lenses are arranged in steps with the closest lens selected at first fit, and a neighboring lens step subsequently selected if overnight wear reveals the fit is not quite right. This brings us back to empirical designs, which by following a ‘tailor-made’ approach should at least in theory offer greater refinement for both the initial fit and any subsequent lens changes that are required. That said, most inventory designs can be modified outside of their normal range to provide half, quarter, or some other denomination step difference in design parameters.
The one option that I haven’t mentioned is to fully design your own OrthoK lens for each patient. OrthoK lenses are no different in basic design to standard rigid lenses that can be ordered by specifying the individual radii, back optic diameter, and width of each peripheral curve. The math is a bit more complex through calculating sag clearances from the cornea instead of curvature alignment, but not insurmountable.