Scleral Lens Anatomy
- Pp. 48-67 (20)Lynette K. Johns and Melissa Barnett
Scleral lens terminology is vast and can be confusing. Since there are several designs with different parameters, manufacturers have created new terms for various aspects of scleral lenses. Not only do the parameters have a variety of names, but there are different names for large gas permeable lenses themselves. The Scleral Lens Education Society defined large diameter gas permeable lenses by their respective bearing patterns (corneal, corneo-scleral, and scleral) thereby reducing some confusion. The parameters, however, are more difficult to categorize. In this chapter, the anatomy of a scleral lens is described in four separate zones: optic zone, mid-peripheral zone, intermediate zone, and landing zone. The optic zone not only provides the optical correction but also can be manipulated to increase the clearance over the corneal surface. The mid-peripheral zone also can be manipulated to create more even clearance over the peripheral corneal surface. The intermediate zone is a critical junction between the mid-peripheral zone and scleral landing zone that bridges the limbus and can control the overall sagittal height of the lens. Lastly, the landing zone is the fitting zone of the scleral lens that aligns to the ocular surface and conjunctiva overlying the sclera and bears the weight of the entire lens. Due to the unique properties of the ocular surface shape, the landing zone can be rotationally symmetric or asymmetric to accommodate and facilitate proper alignment to the surface. All the terminology of the scleral lens anatomy is described in detail.