Fig. 4 displays the proportion of rigid lens fits according to material type and overall lens form. For the purposes of this survey, contact lens oxygen permeability (Dk) values were categorized as low Dk (<40 × 10-9 cm mL O2/s mL mm Hg), mid-Dk (40 to 90 × 10-9 cm mL O2/s mL mm Hg), and high Dk (>90 × 10-9 cm mL O2/s mL mm Hg). Fig. 4 reveals that most rigid lenses were fabricated from high-Dk (36%) or mid-Dk (42%) materials. Scleral and PMMA lenses represented only a small minority of rigid lens fits (1.6% and 1.2%, respectively).
Whereas 85% of soft lenses were replaced regularly (daily, 1 to 2 weekly, or monthly), only 7% of rigid lenses were regularly replaced (lenses replaced on a planned basis of any frequency) (χ2 = 8115.3, p < 0.0001). There was no difference between rigid and soft lenses with respect to the extent of extended wear prescribing (χ2 = 0.26, p = 0.61), with extended wear representing 8% of both rigid and soft lens fits. Most rigid lens extended wear fits (51%) were for orthokeratology.
We arbitrarily define “part time” and “full time” as wearing lenses one to three times per week and four to seven times per week, respectively. Four percent of rigid lenses were fitted for part time wear versus 10% of soft lenses (χ2 = 206.3, p < 0.0001).
The trend in rigid lens fitting in all countries surveyed between 1996 and 2011 is displayed in Fig. 5. As is clear from inspection of this figure, there was a general decline in rigid lens fitting during the course of this survey period.
Differences in the extent of rigid lens prescribing between nations may be attributed to international differences in the training, attitudes, and collective confidence of the predominant practitioner groups—opticians, optometrists, and ophthalmologists. For example, ophthalmologists, who largely or exclusively manage serious contact lens–related eye infections in many regions of the world, may harbor more conservative attitudes and concerns relating to the ocular health risks of soft lenses in general and for this reason may prefer to prescribe rigid lenses, which are known to be associated with a lower rate of vision-threatening microbial keratitis.5–8
The much higher age at which people are fitted with rigid lenses is perhaps a reflection of the overall trend of a reduction in rigid lens fitting over time (see below for discussion of rigid lens fitting trends). That is, those being fitted with rigid lenses are largely existing (and thus older) wearers who have happily adapted to this lens type and see no reason to change to soft lenses.
The analysis of rigid lens fits according to lens design highlights the trend toward rigid lenses being fitted for specialist applications. This is evidenced by the higher rate of fittings for presbyopia with rigid lenses; certain presbyopic fitting strategies, such as translating bifocal designs, can only be achieved with rigid lenses.9 As well, only rigid lenses can induce sufficient changes in corneal topography to induce a meaningful shift in refraction, which is the essential requirement of orthokeratology.10 International differences in the extent of orthokeratology fitting are probably impacted to a large extent by the enthusiastic endorsement of local practitioners or societies and access of local laboratories prepared to supply this highly specialized form of lens.
A significant proportion of rigid lens designs (7.3%) were designated as “other”; however, there was no facility on the survey form to indicate the specific type of “other” lens design fitted. These may have been one of a growing variety of innovative specialized rigid lens designs that have become available in recent years, such as intralimbal lenses, piggyback, and hybrid lenses.11
The proven ocular health benefits of higher Dk materials in both soft and rigid lens domains12,13 explain the predominance of mid- to high-Dk rigid lens prescribing. Rigid lenses are now rarely made from oxygen-impermeable PMMA.
Scleral lenses, which today are mainly used for advanced keratoconus and medical and cosmetic restoration reasons,14 still represent only a small proportion (1.6%) of rigid lens fits. Although our survey form did not distinguish between scleral lens types, it is likely that these scleral lens fits were of a variety of forms, including corneo-scleral, semi-scleral, mini-scleral, and conventional scleral designs.15 The wide variety of scleral lens types now available offers more scope for specialist contact lens fitting and may lead to increased prescribing within this niche sector.
Rigid contact lenses, by definition, have a high modulus of elasticity and are thus more durable and resistant to physical damage and deformation. Indeed, such lenses have been shown to have a longer natural “life expectancy” than soft lenses.16 Therefore, from a material integrity standpoint, rigid lenses do not need to be replaced as regularly as soft lenses. However, deposits may build up on the surface of rigid lenses,17 and for this reason, regular replacement is advisable.18 Because of the relatively high cost involved in the manual manufacture (lathing and polishing) of rigid contact lenses,19 the unit cost of rigid lenses is considerably higher than that of soft lenses, making regular rigid lens replacement prohibitive. This largely explains why only 7% of rigid lenses are regularly replaced compared with 85% of soft lenses.
Rigid lenses are fitted for extended wear to the same extent as soft lenses but apparently for different reasons. The primary reason for extended wear rigid lens fitting is overnight orthokeratology,10 whereas with soft lenses, extended wear is fitted as a modality that confers increased wearer convenience.
The staged physiological adaptation required for comfortable rigid lens wear20 largely precludes the fitting of this lens type on a part-time basis. Conversely, current-generation soft lenses essentially require no adaptation and can be worn all day from the first wearing occasion.21 This explains why only 4% of rigid lenses were fitted for part-time wear compared with 10% of soft lenses.
Decline in Rigid Lens Fitting Over Time
The extent of rigid lens fitting seems to have been in decline during the past 16 years of this survey. The reasons for this decline are complex, and a full discussion of the various factors involved is beyond the scope of this article. By way of summarizing these issues, Efron22 has cited 10 reasons for the gradual decline in rigid lens fitting: initial rigid lens discomfort; intractable rigid lens–induced corneal pathology (3 and 9 o’clock staining) and lid pathology (ptosis); extensive soft lens advertising; superior soft lens fitting logistics; lack of rigid lens training opportunities; redundancy of the rigid lens “problem solver” function; improved soft toric and bifocal/varifocal lenses; limited uptake of orthokeratology; lack of investment in rigid lenses; and the emergence of aberration control soft lenses.
Although rigid lenses are generally no longer considered as the “first choice” option when fitting contact lenses for cosmetic reasons, the results of this survey confirm that this lens category still has a limited specialist role in refractive correction. Notwithstanding the considerable variance across nations, rigid lenses overall currently represent 10.8% of all contact lenses fitted. Some practitioners still prefer fitting, and patients prefer wearing, rigid lenses because of their physical resilience and stable surface characteristics. As well, the unique optical and physical requirements of contact lenses to achieve good vision in challenging situations such as keratoconus and adequate refractive change with orthokeratology necessitate the fitting of rigid lenses. For these reasons, it is likely that the decline in rigid lens fitting will asymptote toward, but not reach, the “zero fitting” baseline and will remain as a viable, albeit increasingly specialized, form of vision correction.
Institute of Health and Biomedical Innovation
and School of Optometry
Queensland University of Technology
Kelvin Grove Queensland 4059
Members of the International Contact Lens Prescribing Survey Consortium
Philip B. Morgan, United Kingdom; Nathan Efron, Australia; Craig A. Woods, Australia; Suresh Awasthi, Nepal; Vadim Belousov, Russia; Jolanta Bendoriene, Lithuania; Aris Chandrinos, Greece; Prema Chane, India; Byoung Sun Chu, South Korea; Edgar Davila-Garcia, Puerto Rico; Nir Erdinest, Israel; Philip Fine, Israel; José Manuel González-Méijome, Portugal; Hans-Jürgen Grein, Germany; Christina N. Grupcheva, Bulgaria; Jorgen Gustafsson, Sweden; Magne Helland, Norway; Hreinn Ingi Hreinsson, Iceland; John Hsiao, Taiwan; Motozumi Itoi, Japan; Oskar Johansson, Sweden; Deborah Jones, Canada; Razmig Knajian, United Arab Emirates; Wanda Lam, New Zealand; Carla J. Mack, United States of America; Florence Malet, France; Edoardo Marani, Italy; Sebastian Marx, Germany; Giancarlo Montani, Italy; Jason J. Nichols, United States of America; Alice Pesinova, The Czech Republic; Geraint Phillips, New Zealand; Simona Radu, Romania; Ole Ravn, Denmark; Svend-Erik Runberg, Denmark; Jacinto Santodomingo, Spain; Mirna S. Silih, Slovenia; Kah-Ooi Tan, China; Ioannis G. Tranoudis, Greece; Eef van der Worp, The Netherlands; Mihály Végh, Hungary; Edit Vodnyanszky, Hungary
Received July 27, 2012; accepted October 10, 2012.
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Keywords:© 2013 American Academy of Optometry
contact lenses; fitting; survey; rigid lenses; orthokeratology