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Now that the 'prediction year' of 2010 has ended, I can reflect upon my prediction in the context of having collected - together with Dr Philip Morgan and an international team of colleagues - 15 years of contact lens prescribing data in the UK and 40 other nations. Figure 2 demonstrates the dramatic decline in rigid lens fitting in the UK from 1965 to the present time. International rigid lens fitting data gathered in 2010 is equally as bleak.2 In 14 of the 28 countries surveyed, new rigid lens fits amounted to 5 per cent or less of all lens fits.
There are many reasons for the dramatic decline in rigid lens fitting across the world. Here I shall review - in approximate rank order from most to least pertinent - 10 key reasons why I believe that rigid lenses have dropped to such a low level of prescribing.
1) Initial discomfort with rigid lenses
One of the main reasons that patients seek soft lenses is the common knowledge that, in the first instance, they can hardly be felt in the eye, compared with rigid lenses which are initially uncomfortable.3,4 Over the years, rigid lens fitters have attempted to employ strategies to overcome the discomfort problem, such as:
? Masking rigid lens comfort using corneal anaesthetic
? Using plasma or hydrophilic surface coatings
? Creating a thinner edge profile
? Changing terminology - such as referring to 'GP' rather than 'rigid' lenses.
These strategies have largely failed. Rigid lenses always have been, and always will be, uncomfortable.
2) Intractable rigid lens-induced corneal and lid pathology
The only severe complication of contact lens wear is microbial keratitis (MK). Although the incidence of MK is numerically lower with rigid versus soft lenses, this small difference pales into insignificance when considered against other life risks.5 Virtually all soft lens complications are transient and resolve completely upon cessation of lens wear. There are, however, two intractable complications that occur in virtually all rigid lens wearers - blepharoptosis (Figure 3) and 3 & 9 o'clock staining (Figure 4). Successful treatment options for alleviating these conditions remain elusive.6
3) Soft lens advertising
The total amount of advertising on soft contact lenses each year to practitioners and the public is estimated to be over £450m. The impact of such advertising is self evident practitioners are seeking to prescribe, and patients are demanding, comfortable and convenient soft lenses. Rigid lens advertising is only about £6.4m globally and is almost exclusively directed at practitioners rather than the public.
4) Superior soft lens fitting logistics
There are compelling logistical reasons why practitioners generally prefer to fit soft lenses. Modern manufacturing technology and sophisticated lens supply arrangements have resulted in the facility for practitioners to hold a selection of lenses in a near-complete range of parameters and powers. Consequently, lenses can be fitted quickly and accurately, an initial supply can be given to the patient to take away immediately, and subsequent lens supplies are quick and easy to obtain and dispense.7 Conversely, rigid lenses take longer to fit and must be ordered from a custom laboratory. The patient cannot be issued with an initial set of lenses and typically must wait many days or weeks for the lenses to be fabricated.
5) Lack of rigid lens clinical training opportunities
The reason why optometrists entering practice have little confidence in rigid lens fitting is because of a lack of experience in the public-access clinics of our optometry schools. These clinics mimic the real world, in which patients are demanding and expecting to be fitted with soft lenses. Although skills can be learned by practising to fit lenses to each other during clinical training sessions, optometry students graduating today from many optometry schools would be fortunate to have fitted one 'real patient' with rigid lenses prior to graduating.
6) Rigid lens 'problem-solver' function redundant
Even by the mid-1980s - 20 years after soft lenses first became available in the UK - mechanical and hypoxic complications were common, and the crude care solutions available at the time frequently resulted in toxic epithelial reactions. In that context, rigid lenses often provided a viable alternate as a 'problem solver'.
However, time has moved on. A majority of soft lenses today are manufactured from silicone hydrogel materials, which typically have Dk/t values in excess of 100,8 and there are numerous lens designs and material types from which to choose.9 Contact lens solutions are manufactured from sophisticated chemical formulations that are inert and safe in the eye. The argument that 'a patient is not suited to soft lenses' - which may have been valid up until the mid-1980s - cannot be advanced today.
7) Improved soft toric and bifocal/varifocal lenses
In the early days of soft lenses, when toric designs were crude, spherical rigid lenses offered a viable alternative for the correction of astigmatism by masking corneal toricity. However, current soft toric lenses are easy to fit, they are available in a wide variety of powers, axes, and stabilisation designs,9 and the vast majority of astigmatic corrections can be fitted from stock lenses. There have been significant advances in the optical design of soft lens bifocal designs in recent years, such that over the past decade there has been a reversal of the preferred mode of presbyopic soft lens correction from monovision to bifocal lenses.
In view of the significant developments in soft lens toric and bifocal designs for the correction of astigmatism and presbyopia, rigid lenses now only have a very minor role in these domains, except in the most extenuating of circumstances.
8) Limited uptake of orthokeratology
The impetus behind the current interest in orthokeratology among a small number of enthusiasts worldwide appears to be that a 'specialist' niche market can be created based upon often exaggerated claims of temporarily or permanently curing myopia. Another driving force is the natural academic curiosity of researchers. However, overnight orthokeratology is still only capable of reducing myopia by about 2.00D, no matter what approach to fitting is adopted,10 the magnitude of the effect is unpredictable, and vision regresses during the waking hours.10
No orthokeratology lens fits were recorded in 21 of the 28 countries surveyed by Morgan et al2 in 2010 and, of the remaining countries, orthokeratology represented 1 per cent or less of new fits in all but three nations (The Netherlands, New Zealand and Portugal). Clearly, orthokeratology has failed to capture the attention of contact lens fitters around the world, and those who have claimed that this approach to vision correction could be the saviour of rigid lenses have been proven wrong.
9) Lack of investment in rigid lenses
There have only been minor improvements in rigid lens material developments since silicone acrylates and fluoro-silicone acrylates were introduced over a quarter of a century ago. Although there have been enhancements in mechanical lathing technology in the rigid lens field - primarily as a result of developments in computer-controlled systems - rigid lenses are still manufactured using labour-intensive lathing processes, which is why the lens unit cost remains much higher than for disposable soft lenses. This high unit cost appears to be the primary reason for dispensing rigid lenses on an unplanned replacement basis, despite convincing evidence of the ocular health benefits of regular rigid lens replacement.11
10) Emergence of aberration-control soft lenses
A hitherto important application of rigid lenses has been to mask irregular corneal shapes, such as in keratoconus, irregular astigmatism, post-trauma and following refractive surgery and other forms of ocular surgery (eg cataract extraction and penetrating keratoplasty). Over the past decade, important advances in ocular aberrometry have resulted in the development of soft contact lenses capable of significantly reducing the optical aberrations inherent in keratoconus.12,13 Thus, the role of rigid lenses as the last bastion of optically correcting corneal distortion is about to fall.
Future rigid lens fitting
It is time to bid farewell to rigid lenses as a mainstream form of contact lens correction. Rigid lens fitting has essentially now been elevated to the status of a speciality that is only practised by a small number of clinicians with an interest and requisite skills in this field. We should all mourn the passing of rigid lenses as a once-glorious form of vision correction, which - following the invention in their antecedent, glass scleral lenses, in 1888 - provided the only alternative to spectacles for thousands of visually challenged patients for around 75 years. ?
Acknowldgement
This article is published with permission of the British Contact Lens Association and Elsevier, as an abbreviated version of a paper by Professor Efron which appeared in Contact Lens and Anterior Eye.14
References
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? Nathan Efron is Research Professor at Queensland University of Technology, Australia