Life expectancy of rigid gas permeable and high water content contact lenses

Purpose: The purpose of this study was to evaluate the life expectancy of various rigid gas permeable (RGP) lens materials used on a daily wear basis and to compare these results with the life expectancy of a matched group of soft lens wearers.

Methods: We retrospectively analyzed the records of 600 contact lens wearing patients (300 soft contact lens users and 300 RGP lens users) fit between September 1987 and September 1994. None of the subjects wore lenses on a planned replacement system. For the purposes of the study, RGP lenses were divided into three groups: <40 Dk were considered low-Dk; 41-89 Dk were considered mid-Dk; and >90 Dk were considered high-Dk. All soft lenses were high water content lenses (>60% water content). Lenses were included if they were replaced due to loss, breakage, deposition, or poor wettability but not if replaced because of changes in fit or prescription.

Results; The mean (+SD) life-spans of each lens type in months were 19.9 +/- 17 for low-Dk RGP lenses, 15.9 +/-13.3 for mid-Dk RGP lenses, 9.0+8.2 for high-Dk RGP lenses, and 6.4 +/-5.2 for high water content soft lenses. Statistical analysis using a one-way ANOVA on ranks indicated that these results were statistically significant (P< 0.0001).

Conclusions: Patients should be informed that high-Dk lenses (RGP and soft) provide substantial clinical benefits and that they should expect to replace high-Dk RGP lenses after approximately 6 months. This lends further credence to the use of high-Dk lenses on a planned replacement basis.

Clinical performance of an innovative back surface multifocal contact lens in correcting presbyopia

Purpose: This prospective study was designed to subjectively and objectively evaluate the performance of an aspheric multifocal back surface rigid gas permeable (RGP) contact lens. The multifocal element of this lens design consisted of an aspheric optical zone that varied according to the patient's ametropia, corneal topography, and required reading addition.

Methods: We fit 28 presbyopic subjects with an aspheric multifocal back surface RGP contact lens (age range: 45 to 68 years). Reading additions ranged from +0.75 D to +2.50 D. Subjects were assessed initially and at 2, 6, and 12 weeks for ocular changes, visual performance, and subjective responses.

Results: We required 116 RGP lenses to achieve an acceptable fit and visual acuity in 28 subjects (55 eyes). At the final visit, the distance logMAR acuity with the multifocal contact lens (+0.12 +/-0.10) was not statistically different (t=-0.623, P= 0.5388) from spectacle acuity at the initial visit (+0.10 +/-0.12). The near logMAR acuity with the multifocal contact lens at the final visit (0.36 +/- 0.12) was not statistically different from that for near acuity with spectacles at the initial visit (0.33 +/- 0.13). No slit lamp signs worsened during the study. A reduction in myopia of 0.67 D was noted by the final visit. Spectacle blur was noted if the acuity at the initial refraction was compared to the acuity with the same refraction at the final visit (t= -3.287, P= 0.0028) but not when the refractive changes were incorporated (t= 1.058, P= 0.3127). All subjects rated the performance of the lenses very highly: comfort, 86%; distance acuity, 83%; near acuity, 73%; and stability of vision, 74%. Twenty-four subjects (86%) chose the multifocal contact lens as their preference.

Conclusion: We demonstrated that a multifocal design is able to provide acceptable distance and near correction for presbyopic patients. The aspheric geometry required can be optimized for a given patient by considering his/her degree of ametropia, as well as the corneal topography.

An international survey of contact lens prescribing for presbyopia

Purpose:  The aim was to determine world-wide patterns of fitting contact lenses for the correction of presbyopia.

Methods:  Up to 1,000 survey forms were sent to contact lens fitters in each of 38 countries between January and March every year over five consecutive years (2005 to 2009). Practitioners were asked to record data relating to the first 10 contact lens fittings or refittings performed after receiving the survey form.

Results:  Data were received relating to 16,680 presbyopic (age 45 years or older) and 84,202 pre-presbyopic (15 to 44 years) contact lens wearers. Females are over-represented in presbyopic versus pre-presbyopic groups, possibly reflecting a stronger desire for the cosmetic benefits of contact lenses among older women. The extent to which multifocal and monovision lenses are prescribed for presbyopes varies considerably among nations, ranging from 79 per cent of all soft lenses in Portugal to zero in Singapore. There appears to be significant under-prescribing of contact lenses for the correction of presbyopia, although for those who do receive such corrections, three times more multifocal lenses are fitted compared with monovision fittings. Presbyopic corrections are most frequently prescribed for full-time wear and monthly replacement.

Conclusions:  Despite apparent improvements in multifocal design and an increase in available multifocal options in recent years, practitioners are still under-prescribing with respect to the provision of appropriate contact lenses for the correction of presbyopia. Training of contact lens practitioners in presbyopic contact lens fitting should be accelerated and clinical and laboratory research in this field should be intensified to enhance the prospects of meeting the needs of presbyopic contact lens wearers more fully.

Trends in Australian contact lens prescribing during the first decade of the 21st century (2000–2009)

Purpose:  The aim was to document contact lens prescribing trends in Australia between 2000 and 2009.

Methods:  A survey of contact lens prescribing trends was conducted each year between 2000 and 2009. Australian optometrists were asked to provide information relating to 10 consecutive contact lens fittings between January and March each year.

Results:  Over the 10-year survey period, 1,462 practitioners returned survey forms representing a total of 13,721 contact lens fittings. The mean age (± SD) of lens wearers was 33.2 ± 13.6 years and 65 per cent were female. Between 2006 and 2009, rigid lens new fittings decreased from 18 to one per cent. Low water content lenses reduced from 11.5 to 3.2 per cent of soft lens fittings between 2000 and 2008. Between 2005 and 2009, toric lenses and multifocal lenses represented 26 and eight per cent, respectively, of all soft lenses fitted. Daily disposable, one- to two-week replacement and monthly replacement lenses accounted for 11.6, 30.0 and 46.5 per cent of all soft lens fittings over the survey period, respectively. The proportion of new soft fittings and refittings prescribed as extended wear has generally declined throughout the past decade. Multi-purpose lens care solutions dominate the market. Rigid lenses and monthly replacement soft lenses are predominantly worn on a full-time basis, whereas daily disposable soft lenses are mainly worn part-time.

Conclusions:  This survey indicates that technological advances, such as the development of new lens materials, manufacturing methods and lens designs, and the availability of various lens replacement options, have had a significant impact on the contact lens market during the first decade of the 21st Century.

Use of silicone hydrogel contact lenses by Australian optometrists

Background: Prior to the launch of silcone hydrogel (Si-H) materials in Australia in 1999, only 1.6 per cent of lenses were prescribed on a continuous wear basis.

Methods: One thousand surveys were distributed randomly to practitioners in Australia during January 2000, 2001 and 2002 (total surveys 3,000). Each anonymous survey requested data about the next 10 patients fitted with contact lenses, including date, age, gender, new fitting or refitting, lens material type, lens design, frequency of replacement, modality of wear, uses per week and care regimen.

Results: Twenty per cent (599) were returned, reporting data on 5,976 fittings. A total of 710 fittings used Si-H contact lenses (11.9 per cent), which represented 18.6 per cent of all soft lens fittings. During the three years, the proportion of practitioners prescribing Si-H lenses increased from 42.2 to 52.5 per cent. In 2000, 43.8 per cent were daily wear, which decreased to 32.2 per cent by 2002. The solution system of choice for daily wear lenses was multipurpose solutions (98.4 per cent); the only alternative was hydrogen peroxide systems. Continuous wear represented 11.7 per cent of all fittings, ofwhich 85.7 per cent were Si-H, 3.0 per cent RGP lenses and 11.3 per cent conventional hydrogels. For continuous wear, 79.0 per cent of fittings were to existing wearers, whereas for daily wear, 59.4 per cent were existing wearers. More males were prescribed Si-H continuous wear contact lenses, while females were more likely to be prescribed Si-H on a daily wear basis.

Discussion: Si-H contact lenses were introduced to the Australian market as a continuous wear contact lens, yet many practitioners use this product for daily wear with multipurpose solutions. By 2002, more practitioners were prescribing Si-H contact lenses for continuous wear than in 2000, suggesting a growing confidence in that product for that mode of wear. A comparison with an earlier survey shows there is an increase in continuous wear from 1.6 per cent to 11.7 per cent over a five-year period.

Contact lens prescribing in the Australian states and territories 2001

Background: This study was conducted to ascertain current preferences for contact lens prescribing in the Australian states and territories.

Methods: One thousand questionnaires were randomly distributed to proportionate samples of optometrists in each state of Australia. We requested details of the first 10 patients fitted with contact lenses after receipt of the questionnaire.

Results: One hundred and seventy-eight completed questionnaires were returned, detailing contact lens fits to 1,611 patients. The mean age of the patient group was 32.1 $pL 13.0 yrs (65 per cent female). For Australia as a whole: 53 per cent of patients were existing wearers, the remainder were new fits; 93 per cent of new fits were with soft lenses, of which seven per cent were for extended wear. Of the refits, 89 per cent were soft lenses and 18 per cent for extended wear. The lens material of first choice was mid-water-content (62 per cent of all soft lens fits). Only eight per cent of all soft fits were for lenses that were not replaced on a planned basis, with two weeks being the replacement interval of choice in all states and territories. The majority of rigid lenses were prescribed using mid-Dk materials (50 per cent). Analysis of solution prescribing indicates that multi-purpose products were the most common regimens for planned replacement soft lenses. The percentage of hydrogen peroxide prescribed increased as lens replacement became less frequent. By state or territory: practitioners in Tasmania prescribed more extended wear than those in any other state (p = 0.007) and practitioners in Queensland prescribed more daily disposable contact lenses than those in any other state (p = 0.009).

Conclusions: Non-planned replacement lenses are now rarely prescribed to patients. Extended-wear lenses and rigid lenses continue to be prescribed more to existing contact lens wearers than to new patients. The impact of soft multifocal lens designs on contact lens prescribing is very small, ranging from 2.6 per cent in Queensland to 4.7 per cent in Victoria, despite 20 per cent of patients being more than 45 years of age.

Trends in Australian contact lenses prescribing 2000

Background:This study was conducted to ascertain current modes of contact lens prescribing in Australia.

Methods:One thousand questionnaires were randomly distributed to proportionate samples of optometrists in each state of Australia. The profession fits the majority of contact lenses in Australia and the sample represents 55 per cent of all optometrists. We requested details of the first 10 patients fitted with contact lenses after receipt of the questionnaire.

Results:We received 224 completed questionnaires, detailing contact lens fits to 2,230 patients. The mean age of the patient group was 32.3 ± 12.9 years and 65 per cent of these were female. Sixty per cent of patients were existing wearers, the remainder being new fits. The data indicated that 94 per cent of new fits were with soft lenses, of which six per cent were for extended wear. For refits 83 per cent were soft lenses and 24 per cent were extended wear. It was clear that the lens of first choice was mid-water-content (52 per cent of all soft lens fits). Only nine per cent of all soft fits were for lenses which were not replaced on a planned basis. The majority of rigid lenses were prescribed using mid-Dk materials (71 per cent). Analysis of solution prescribing indicates that multipurpose products were the most common regimens for planned replacement soft lenses. The percentage of hydrogen peroxide prescribed increased as lens replacement became less frequent.

Conclusions:Non-planned replacement lenses are now rarely prescribed to patients. Extended wear lenses and rigid lenses are prescribed more to existing contact lens wearers. The impact of multifocal lens designs on contact lens prescribing is very small, namely, five per cent of soft contact lenses and eight per cent of rigid lenses, despite 20 per cent of patients being over 45 years of age.