If you have keratoconus, Dr. Lenoir may recommend gas permeable or GP lenses. Since GP lenses are made of a non-pliable material, they retain their shape on the eye. Because of this feature, gas permeable contacts replace the irregular surface of a keratoconic cornea with a smooth, uniform, surface to focus light and sharpen vision.
Sometimes an eye with keratoconus is too sensitive and unable to adapt to gas permeable lenses. In these cases, a fitting technique called “piggybacking” may be used. First the cornea is fitted with a soft contact lens, and then a GP lens is fitted over the soft lens. Because the soft lens acts like a cushion, piggybacking can make gas permeable contact lenses more comfortable for people with keratoconus.
Another option for keratoconus is hybrid contact lenses. These advanced lenses have a gas permeable optical center with a soft ring around it. For many wearers, hybrid contacts offer the clarity of GP lenses and wearing comfort that rivals soft lenses. Special hybrid lens designs are available specifically for eyes with keratoconus.
Still another contact lens option for keratoconus is scleral GP lenses. These large gas permeable lenses vault over the irregular surface of the cornea and rest on the white sclera of the eye. The large diameter of scleral lenses provides a more stable fit than regular gas permeable lenses on highly irregular corneas with keratoconus.
Lastly, custom made soft contact lenses for keratoconus is an option. These lenses are tailored for the irregular cornea with soft silicone hydrogel or hydrogel material that will allow comfortable, clear vision. These lenses are a great option for patients who desire a more comfortable fit.
LASIK/ Surgical Procedures
It may seem odd to consider contact lenses after corrective eye surgery. After all, shouldn’t LASIK and other procedures eliminate the need for glasses or contacts?
Theoretically, yes. But LASIK doesn’t always provide perfect vision. And sometimes, a second surgery to sharpen vision is not an option. In these cases, contact lenses may be in order.
For example, if you have very high astigmatism prior to LASIK, you may need toric lenses to correct a lesser degree of astigmatism that may remain after surgery. Soft lenses can work well for this, and specially designed gas permeable and hybrid contact lenses are also an option.
If you’ve had LASIK performed in a monovision fashion — with one eye corrected for distance and the other for near — occasionally you may want to wear a contact lens on the “near eye” so both eyes can see clearly in the distance for sports, driving at night and other activities that require the best possible vision.
Contact lenses can also help address LASIK complications, such as indistinct vision from higher-order aberrations after surgery. Gas permeable or hybrid contact lenses are usually the preferred lenses for this problem. Excessive glare is another potential problem following LASIK. Here, too, GP contact lenses and hybrid contacts usually are your best choice. These lenses often provide sharper night vision than soft contact lenses after surgery.
Keep in mind that fitting contact lenses after LASIK or other corrective surgery may require more trial lenses and a longer period of time than fitting contact lenses on an eye that hasn’t been surgically altered.
Corneal Transplant or PK
A corneal transplant, also known as a corneal graft, or as a penetrating keratoplasty, involves the removal of the central portion (called a button) of the diseased cornea and replacing it with a matched donor button of cornea. Corneal grafts are performed on patients with damaged or scarred corneas that prevent acceptable vision.
Most transplants have significant astigmatism and often some distortion requiring correction with contact lenses made of rigid materials. Many factors make fitting contacts after transplant a challenge. It is common for the edge of the transplant to be slightly raised with respect to the surrounding cornea. The graft is usually steeper than the normal cornea, and may be tilted with respect to the surrounding tissue. To combat high amounts of astigmatism some of the sutures may be removed early. Following healing a relaxing incision or a wedge resection may be done to decrease the astigmatism. In any case there is usually some distortion of the transplant and most patients will obtain better vision with a rigid contact lens. Rigid corneal lenses, scleral (haptic lenses), and the Soft Perm lens are all viable options.
If a contact lens is required following keratoplasty it is customary to wait at least 3 months after the surgery and preferably until after the sutures are removed, which may be up to a year, before fitting contact lenses.
Due to the irregularity of the cornea after transplant, soft contact lenses seldom give satisfactory vision. In addition, hydrogel lenses, scleral lenses, and the SoftPerm lenses may encourage vessel invasion into the graft.
Therefore, rigid gas permeable corneal lenses are usually the lens of choice. Keratometer readings are seldom of any significant value in determining the base curve of the lens, but it may be useful for baseline values to determine if any changes are occurring. Corneal topography with a computerized topographer can be of some value in determining the shape of the transplant and surrounding cornea. However, diagnostic lenses must be used to fit these eyes.
Due to the size and shape of the button and the transition area between the button and the host cornea, it is often best to use a larger diameter lens to maintain lens centration. In the rare instance that a corneal transplant is placed off-center, rigid corneal lenses are nearly impossible to properly fit. In these few cases scleral or SoftPerm lenses may be the only viable option.
Parameters of the lenses are assessed using the flourescein pattern. The power of the final rigid lens is determined by an accurate refraction over the diagnostic lens. A lens material with good oxygen permeability should be used to minimize corneal swelling.
The corneal transplant patient should be followed closely, especially during the first year or two following surgery to be sure corneal integrity is not compromised and that graft rejection is not occurring.