Contact Lens Design & Materials
Keratoconus Design Options
By Ronald K. Watanabe, OD, FAAO
Corneal GPs made of high-Dk materials are my first choice for new patients with keratoconus because they provide good vision and usually can be fit with minimal corneal insult. In some situations, however, such as corneal insult, inability to adapt or a poor or unstable fitting relationship, other options may be indicated.
Large-diameter GPs Intralimbal corneal GP lenses often improve comfort compared with smaller-diameter lenses because they do not move as much and their edges are tucked under the eyelids. Attaining good alignment with the corneal surface is more difficult with this type of lens, however, especially with an advanced cone.
Soft Lenses Soft keratoconus designs provide the comfort of a soft lens while delivering better vision than conventional soft lenses or eyeglasses. These thick designs can mask some corneal irregularities owing to their relative stiffness. They work well for mild cones but become less effective in more severe cases.
Piggyback Systems These systems provide increased comfort and stability in difficult cases. Although the patient's eyelids still move over the GP edge, the cushioning effect of the underlying soft lens decreases awareness. A high-Dk silicone hydrogel is ideal, although daily disposables are often more practical because of the mechanical effects of the GP on the soft lens during wear.
When an off-the-shelf lens is inadequate, the Flexlens Piggyback (X-Cel Contacts) in Definitive (Contamac) material is an excellent option to center the GP lens. The Pillow Lens (Fusion) can provide a more stable piggyback system where the GP is held within the recess of the Pillow (Figure 1).
Figure 1: Piggyback system with Pillow Lens and high-Dk GP lens.
Hybrid Lenses Hybrid lenses from SynergEyes (A, KC and ClearKone) are more comfortable initially than corneal GPs (Figure 2). These lenses can fit most cones, regardless of severity, with good stability and vision. The fitting philosophy of corneal clearance minimizes corneal insult by the GP part of the lens.
Figure 2: ClearKone lens.
Scleral Lenses Mini-scleral GPs provide significantly improved comfort over corneal GPs. Some patients are reluctant to apply such a large GP lens after having a negative experience with a small one, but all are amazed at how comfortable mini-sclerals are. Because they completely vault the cornea, they do not cause mechanical corneal problems. The key is to rest the lens evenly on the conjunctiva/sclera while avoiding areas of impingement (Figure 3).
When well-fit, these scleral lenses provide stable vision, and lens loss is rare.
Figure 3: Mini-scleral GP contact lens.
Knowing the advantages and disadvantages of fitting options for keratoconus patients can increase your fitting success. CLS
Dr. Watanabe is an associate professor of optometry at the New England College of Optometry. He is a diplomate in the American Academy of Optometry's Section on Cornea and Contact Lenses and Refractive Technologies and is in private practice in Andover, Mass. You can reach him at email@example.com.