ORTHOKERATOLOGY (ortho-k) retainers utilize curves to achieve target correction and induce peripheral plus power onto the retina for myopia control. Each curve is unique and important in ortho-k design and in overall treatment on the cornea.

Let’s look at lens design from the outside in and discuss the peripheral curve (PC) in ortho-k design in depth.

GENERAL CONSIDERATIONS

The PC refers to the outermost edge of the ortho-k retainer. It interacts completely with the peripheral cornea and ideally should be anterior to the limbus in corneal ortho-k designs. In my clinical experience, the interaction of the PC with the peripheral cornea is important for proper alignment, comfort, and health of the cornea during treatment.

Proper alignment of the ortho-k retainer is crucial for success. While other curves, such as the alignment curve (AC), play a large role in proper alignment and centration, the PC is also a contributor. The peripheral cornea will vary from the central Ks that many instruments measure and eccentricity becomes a big factor in proper alignment. While toric and aspheric curves in the alignment zone are utilized to properly align with the patient’s cornea, the outermost PC needs to be designed to properly match the corneal architecture as well.

COMFORT AND HEALTH

Patient comfort is also an element that needs to be considered for ortho-k success. Often, we are very focused as clinicians to hit refractive targets and carefully monitor the ocular surface; however, we must remember to treat the patient as a person and monitor their symptoms.

Patient comfort will highly correlate with compliance with treatments, and ortho-k is no exception. While patients are only wearing ortho-k retainers while they sleep, a poorly designed retainer can still cause comfort issues.

The main culprit of discomfort in ortho-k is the PC. If the peripheral edge of the retainer is too flat, lens awareness will be reported by the patient. While edge clearance is needed for proper tear exchange, excessive edge clearance will cause the patient discomfort. Steepening the PC in this instance will typically solve any comfort issues.

The PC is an important part of ortho-k architecture. It plays an important role in centration and alignment. Its proper design is also crucial for patient comfort, which will lead to better treatment compliance.

Corneal health is also dictated by proper PC design to ensure oxygen permeability and proper tear exchange to prevent any ocular surface compromise. While the curve may be in the periphery, it’s important to keep it in the front of your thoughts when designing.