Traditionally, irregular cornea patients have been fitted with GP lens designs to provide visual improvement. In most cases, these patients truly appreciate the significant increase in clarity that they attain with a lens that maintains its shape and neutralizes much of the corneal distortion. But, GP lenses are not for everyone, and there are many other good options for irregular corneas that may prove to be better solutions for some patients.
Corneal GP lenses have been the go-to option for many practitioners when presented with an irregular cornea. Some conditions, such as keratoconus with smaller central cones, are best fitted with small-diameter designs. They have the advantages of easier application and removal, better tear exchange and oxygen delivery to the cornea, and relative value considering unit cost and durability. On the downside, they are more difficult to adapt to, can cause significant corneal changes when they don’t align well with the cornea, and they may cause visual compromise due to the small optic zone, especially if they decenter.
Larger intralimbal corneal GP designs can provide improved comfort and vision compared to their smaller cousins, but they are more difficult to align with irregular corneas. They are also more difficult to apply and remove, and they may have a tendency to adhere to the cornea due to larger areas of corneal clearance and less movement.
Scleral GP lenses are still growing in popularity due to their significant increase in comfort compared to corneal GP lenses. When well-fitted, they can be as comfortable as soft lenses, and for some, they can be more comfortable than soft lenses due to the fluid reservoir under the lens and the lack of lens surface dehydration. This is particularly true for patients who have desiccative ocular surface conditions. Plus, the vision with scleral lenses is superior due to the rigid surface, large optic zone, and good centration.
Nevertheless, scleral lenses are not without compromises. In addition to being quite expensive compared to corneal lenses, they are more difficult to apply and remove. Patients also have to be more careful with lens care products, making sure to fill the lens with unpreserved saline before application. Also, scleral lenses do have potential complications, including corneal and limbal edema, conjunctival prolapse and impingement, and post-lens clouding. With more experience and research, fitting and management of scleral lenses will continue to improve.
Specialty Soft Lenses
Several specialty soft lens designs for irregular corneas are available. Compared to standard soft lenses, they can better correct for those corneal irregularities and deliver much improved visual acuity. They have the advantages of good comfort, familiar soft lens handling and care, and more frequent replacement. Their main drawback is the complexity of the fitting processes to achieve clear, stable vision; even in the best cases, vision is typically less clear than with GP lenses.
Hybrids combine both GP and soft materials. Their GP optics can rival those of corneal and scleral GP lenses, and comfort can be as good as that of soft lenses. However, there are more parameter limitations for both fitting curves and lens powers, so there may be patients for whom this option does not work. For example, there are no toric options, so patients who have highly toric peripheral corneas or large amounts of lenticular astigmatism will not do well with this option.
Ultimately, practitioners must determine what is best for each patient’s vision, comfort, ocular surface health, lifestyle, and comfort level. Having so many options can make fitting decisions more difficult, but in the end, it is an enormous benefit for patients who have compromised corneas. CLS