Until now, we have been talking about patients who have relatively normal eyes. But, what about patients who have what could be termed “difficult-to-fit eyes”? Just because patients have corneal scars, keratoconus or similar ectasias, or are post-laser-assisted in situ keratomileusis (LASIK) or post-radial keratotomy (RK) does not necessarily make them poor multifocal contact lens candidates. Nor does it mean that if you can correct their distance vision beautifully that they won’t want the near vision to be great without glasses also. However, it does mean that we need to think differently in our approach to those particular patients.
Let us look at the example of a keratoconus patient. We know that to maximize vision, we will need to address the irregular astigmatism thatmaximize vision, we will need to address the irregular astigmatism that usually accompanies the thinned and prolate cornea. Depending on how advanced the condition is, it may be possible to use a custom soft toric or a GP lens and add multifocal optics to it. If you choose one of the specialty keratoconic soft lens designs, the multifocal option may not be possible. Most laboratories that produce GP lenses can correct the keratoconic need and the presbyopic need.
Fitting the Proper Lens
First, get a diagnostic GP contact lens on the eye and evaluate the lens-to-cornea fitting relationship. Once a good fluorescein pattern is established so that the eye will maintain good physiology, over-refract for the best distance vision. Next, determine the reading power needed to provide maximum near vision. Last, talk to your lab consultant and order the lens desired in the front-surface multifocal design that the consultant thinks is most appropriate for that case. As with any multifocal contact lens, you may need to make adjustments to arrive at the ultimate outcome.
In some instances, it may be possible to use a corneal GP design to correct the irregular corneal condition. In others, a scleral GP may be required. Both lens types are available as multifocals. The results may be a bit better with the corneal design because these lenses can translate more and help get the lens in the proper position for both distance and near viewing. Corneal lenses also have a wider variety of multifocal design options, such as aspheric, concentric, and annular configurations.
If a scleral lens design is needed, a multifocal lens can still be made, but the options could be more limited because the scleral multifocal lens needs to center for the best near vision. That can be difficult with some of the larger scleral lenses because the toric sclera can push the lens down and out. A laboratory consultant can guide you in making adjustments to the fitting relationship as well as help with the choice of multifocal zone size and whether to utilize a center-near or center-distance design.
Some patients need a GP lens to correct their corneal issue, but also have filtering blebs and/or shunt tunnels for glaucoma management. In such situations, a corneal lens can work if it will center and not rub the bleb.
A scleral lens design could be utilized if it does not collapse the bleb. The shunt tube will usually be deep enough in the sclera that compressing it is not a concern with the scleral lens. However, the shunt tunnel may change the architecture of the superior sclera and force the lens to decenter. In these situations, a custom-molded GP contact lens could be the answer. This custom GP lens can be made to fit around scleral/corneal irregularities and even to protect the bleb. Plus, the molded lenses are available in multifocal designs.
Options for Everyone
There really is no reason to turn away presbyopic patients just because they have some form of corneal abnormality. As with any other patient, use a step-wise approach to determine your final contact lens parameters, and you will find success. CLS