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TOPIC: point The Prognosis of GP Lenses
What GP Decline?
BY EEF VAN DER WORP, BOPTOM, PHD, FAAO, FIACLE, FBCLA
Experts have previously predicted that GP lenses would be obsolete by 2010, even publishing on 'the desperate last gasps of rigid contact lenses.' But here on the brink of 2010 and with actual fitting data in hand, there are no signs of this being true.
Approximately 10 percent of all lens fits in the United States are with GPs, which is similar to the average worldwide. But this does not do justice to large local variability. For instance, in the Netherlands 33 percent of lens wearers and 24 percent of lens fits are with GPs, and these numbers have remained stable over the last few years. GP lens wear also remains high in the Germanic countries, Israel, and Japan.
GPs are the Safest Lenses
Globally, the number-one consideration in contact lens patient management is safety. For years studies have repeatedly shown that GPs are the safest contact lens option available. A recent study presented at ARVO by Stapleton (2009) evaluating the safety of contact lens wear versus refractive surgery could not even include risk with GP lens wear because there were simply no incidences of corneal infection with GPs. Studies by industry experts such as Efron et al (2005) also show that inflammatory responses are very low in GP lens wear in hospital-based studies.
Better Quality Vision
GPs provide the best acuity of all vision correction methods, even correcting some higher-order aberrations. In some cases, only GPs can provide acceptable vision for patients who have irregular corneas from keratoconus, post corneal graft, high astigmatism, and post refractive surgery.
There is no reason to believe that the number of irregular corneas is decreasing. In fact, corneal topography demonstrates that an increasing number of corneas are irregular, with the popularity of laser refractive surgery playing a role in the increase.
GP vision advantages also extend to presbyopia. Hydrogel lenses (and refractive surgery for that matter) do not provide the same visual quality that GPs can for presbyopes. While it appears that the average age of GP wearers is increasing (potentially a negative), this same data demonstrates that GPs may be the best alternative for aging lens wearers who have critical vision needs.
GP Technology is Advancing
It's expected that new technologies will help (re)build the GP lens market. Initial comfort is an obstacle when fitting GP lenses. But after adaptation, GP lens wearers are successful, loyal lens wearers with low dropout rates. Topography-based custom lenses are proving to increase GP comfort, decrease corneal warpage, and further support corneal health. Plus, younger practitioners appear to embrace designing custom lenses with today's more sophisticated fitting software.
Recently, optical coherence tomography has proven very helpful in fitting larger GPs such as (semi-)scleral designs. Going forward, improvements in wavefront technology should help to reinforce the superior quality of vision with GP lenses.
I believe the new millennium for GP lenses has yet to start. Rather than a decline, we seem to be experiencing a GP revival, illustrated, for instance, by the success of the Global Specialty Lens Symposium. In fact, data presented at the recent BCLA meeting show a slight increase in new GP lens fits in the United Kingdom for the first time in years. New modalities such as orthokeratology for myopia control and large-diameter lenses along with improvements in presbyopic designs will further drive the GP market. We should be proud and thankful that GPs are available to us. CLS
Of course, a main reason why patients seek soft lenses is the common knowledge that these lenses can hardly be felt on the eye, whereas GP lenses are uncomfortable. Although patients can adapt to this initial discomfort, it is self-evident that they will seek something that is instantly comfortable in the absence of a good reason to the contrary. Modern active lifestyles involving sports and other recreational pursuits necessitate lenses that are comfortable and secure in the eye and that do not require constant readaptation due to diurnal changes in wearing patterns. Soft lenses meet this challenge. GPs do not.
There are compelling commercial reasons why most practitioners prefer soft lenses. Large stocks of soft lenses can be maintained, which facilitates rapid and accurate lens fitting. Patients can immediately take away an initial supply, and subsequent supplies are easy to obtain and dispense.
The notion that GP lenses afford better ocular physiology may have been valid 25 years ago when the alternative was early generation, thick, low-Dk hydrogel lenses that were worn for up to three years. Almost all soft lenses today are replaced monthly or more frequently, largely eliminating deposit-related adverse events. Problems related to hypoxia have also been nearly eradicated by silicone hydrogels, which now represent about half of all lenses prescribed globally.
When contrasting this against the intractable problems with GP lenses of upper lid ptosis, 3 o'clock and 9 o'clock staining, corneal warpage, and lens binding, it is clear that modern soft lenses have a distinct pathophysiological advantage over GPs.
The idea that GP lenses are suitable for specialist applications has recently been called into question. It is now clear that spherical GPs do not retard myopia progression. The renewed interest in orthokeratology over the past decade is tempered by the fact that the procedure has limited efficacy, is time consuming and expensive, and lens delivery times are protracted. For these reasons, ortho-k is practiced only by a very small number of enthusiasts. Therefore, this procedure cannot be advanced as a rationale for the long-term preservation of GP lenses.
Impact of Wavefront Optics
A number of reports have recently appeared demonstrating the utility of custom-designed soft lenses that incorporate wavefront-correcting optics and can provide good vision for patients who have keratoconus and other forms of corneal distortion. So the last bastion of GP lenses — the optical correction of irregular corneas — is also under threat. In view of the above, the prognosis for GPs is very poor indeed! CLS