A few years ago, my esteemed colleague Nathan Efron, Ph.D., D.Sc., made a strong statement about the imminent death of rigid gas-permeable (RGP) contact lenses, which were supposed to be eradicated in the subsequent years. His words created a shockwave. However, obviously this scenario never became a reality. In fact, the marketplace is now saturated with RGP lenses to better serve our patients’ needs.
Based on today’s technology and a better understanding of the dynamics between the new lens designs and the cornea, modern large-diameter RGPs are the lenses of the future. In fact, I estimate that they will double their presence in the market within the next five years, competing to replace soft lenses as the go-to option in manycases. This will happen simultaneously with the launch and development of a new generation of lenses—with large diameters and made from very high-permeable materials.
They will be as comfortable as soft lenses, as easy to fit as soft toric lenses, but with all the benefits of rigid materials, including better visual acuity and less infections or inflammatory events.
Evolution or Revolution?
In the last five years, manufacturers have developed interesting RGP lens designs featuring large diameters that exceed the corneal border. The increased availability of material to produce such large lenses, improved manufacturing processes to customize their design and a better understanding of the conjunctival anatomy helped establish new standards in RGP lens fitting.
Nowadays, large-diameter lenses are available from 14mm to 24mm in spherical, toric, reverse geometry and even multifocal designs. In addition, we now have two new types of lenses: corneo-scleral (<15mm diameter lenses partially supported by the cornea) and mini/true scleral (14.3mm to 16mm diameter lenses supported only by the conjunctiva aimed to vault the cornea). The latter offers better options to restore and protect the ocular surface.
Clinical applications for large-diameter lenses are numerous and exceed the natural niche for RGP lenses (corneal ectasia, irregular corneas, post-surgical correction of ametropia). Modern large-diameter lenses offer a valid option for correcting moderate to high spherical refractive errors, moderate to high astigmatism and presbyopia. This represents not only a true evolution in this category of contact lenses, but a real revolution for the entire profession.
Benefits of Large RGPs
Large-diameter (14.3mm to 18mm) RGP lenses offer many advantages over their small-diameter counterparts. For starters, initial discomfort—the primary reason practitioners are not fitting small RGP lenses—is no longer an issue because the lenses lie on conjunctiva, a less sensitive tissue. Most of the large-diameter lenses vault the cornea, without touching it. This not only preserves the tissue integrity but alleviates any intolerance or corneal sensation associated with contact lens wear. Once properly fitted, large-diameter lenses are as comfortable as a soft lens.
Also consider that there is no invasion of dust and particulates under the surface of a large-diameter lens. Many RGP wearers complain that, especially in the wind, some debris can remain trapped under their lenses, which creates immediate discomfort that ultimately leads to the lens removal. This cannot happen with large-diameter RGP lenses—once again, offering the same comfort as soft lens wear.
Ocular dryness is the leading cause of contact lens dropout. With large-diameter RGP lenses, the cornea is bathing in fluid during all the wearing hours. Primary ocular dryness can be reduced, and contact lens-induced dryness at the end of the day is eliminated. Therefore, large-diameter lenses can provide a solution to address these issues, which is the reason why many corneal specialists look at large-diameter RGP lenses to treat even the most severe dryness conditions.
Keep in mind that RGP lenses provide a crisp and sharp visual acuity that cannot be compared to soft lenses. This is especially true when moderate to significant astigmatism is involved. Because RGP materials do not dehydrate over time, and large lenses do not move a lot and do not rotate, these lenses are the optimal choice to correct astigmatism (up to 4D). They also are preferred for the correction of presbyopia and emerging designs of large-diameter lenses are showing promising results.
As an added bonus, large RGP lenses currently are unavailable for purchase on the Internet. This can give practitioners an upper hand in practice sales, as well as in their ability to effectively control the patient’s eye health.
The future success of large-diameter RGPs will become a reality if a significant number of practitioners prescribe and fit these lenses. This evolution is not instantaneous.
We need to begin considering large-diameter lenses as our first option. The potential market for these RGP lenses include toric lens patients who are not completely satisfied with their vision, patients who report end-of-the-day ocular dryness or RGP lens wearers complaining of periodic discomfort.
Learning how to fit large-diameter RGP lenses is relatively easy. The exact learning time will vary, of course, based on experience. Fortunately, the newest lenses in today’s market are user-friendly; the smallest of the large-diameter lenses (14.2mm to 15mm) are as easy to fit as soft lenses. Outside of this range, true scleral lenses remain a challenge due to conjunctival toricity.
The key is to devote enough time initially to learn the fitting process and to be able to troubleshoot the problems as they occur. You can build your expertise by familiarizing yourself with the lenses through regularly fittings.
Learn to Troubleshoot
Difficulty handling large-diameter lenses is the number one reason why many patients cannot wear this modality. For some, such as our arthritic patients, insertion and removal of the lenses can be a challenging task, especially without help.
Another common complaint is tight lenses, a syndrome that is characterized by the sudden occurrence of a red and painful eye after only a few hours of wear. This happens when the lens becomes tight on the ocular surface and seals off the corneal periphery. The absence of tear exchange (habitually limited, but present) contributes to trapped debris and toxins under the lens surface, which triggers a severe inflammatory reaction. At that time, the fit has to be revisited, allowing for more tear exchange and increased movement of the lens.
Discomfort with the large-diameter lenses is a sign of a bad fit. In theory, lens awareness can be present in the first minutes of wear, but true discomfort is certainly not expected.
Keep in mind that large-diameter lenses take time to be fitted. At minimum, it takes 20 to 30 minutes for the lens to settle. In some conditions, once the optimal lens is found, a practitioner may first prefer to reassess the fit after a few hours of wear before deciding on the modality.
Once stabilized on the eye, a clearance of 125µm to 150µm at the thinnest point is considered optimal for lenses under 15mm. For large lenses, a 200µm clearance is acceptable; although, some practitioners prefer a clearance of 300µm to 400µm. Optical coherence tomography (OCT) can help to evaluate the lens-to-ocular surface relationship, and to accurately define the appropriate modifications needed. Some labs offer custom designs based on the OCT measurements.
Large-diameter RGPs represent a true, modern alternative to other modalities. They can compete with soft lenses in both comfort and convenience. They outperform other lenses for visual acuity and in the treatment of ocular dryness. Contrary to all predictions, RGP lenses are not dead—in fact, I believe they are taking on a whole new life.
Dr. Michaud graduated from the University of Montreal with a degree in optometry in 1986 and a masters degree in science in 1998. After 15 years in practice, he returned to the University of Montreal, where he now serves as an associate professor and chief of the contact lens department. He is a diplomate for the Section on Cornea and Contact Lenses of the American Academy of Optomety, a well-known clinical investigator and a worldwide lecturer on contact lenses and anterior segment disease.