- Email: [email protected]
Assessment of the wettability of different silicone hydrogel contact lenses using a novel in vitro method
Poster abstracts / Contact Lens & Anterior Eye 36 (2013) e16–e46
39 Assessment of the wettability of different silicone hydrogel contact lenses using a novel in vitro method S. Marx (Dipl.-Ing. (FH) AO, FIACLE), M. Sinnig (M.Sc.), W. Sickenberger (Prof. M.S. Optom. (USA), Dipl.-Ing. (FH) AO) Purpose: The aim of the study was to determine differences between the surface wettability of various lens/solution combinations in terms of the drying-up time measured in vitro using a modified corneal topographer (Non-Invasive Keratograph–DryingUp Time (NIK-DUT)). Methods: Five market-leading silicone hydrogel SCLs underwent a washing procedure and were soaked subsequently in OPTI-FREE® PureMoist® MPDS (OFPM) whereas saline served as reference (10 combinations in total). The NIK-DUT was measured ten times for every combination by evaluating the reflected placidoring image objectively. The focus was on the measurement of the NIK- DUT value derived when 25% of the entire measurement segments showed dry-up during the measuring time (NIK- DUT S25). Based on an asymptotic, normally distributed mean value an analysis of variance (ANOVA, alpha = 0.05) and subsequently a post-hoc analysis (Duncan) was conducted to determine inter-group comparisons. Results: Within and between the 10 combinations the differences were statistically significant (p < 0.001). The following NIK-DUT S25 values were achieved in combination with saline and OFPM respectively: Lotrafilcon B with Aqua Technology (129.0 ± 15.1s and 154.1 ± 5.5s); Lotrafilcon A (120.8 ± 20.5s and 140.9 ± 12.8s); Comfilcon A (123.5 ± 7.9s and 149.5 ± 7.6s); Balafilcon A (128.3 ± 16.3s and 131.4 ± 8.0s); Senofilcon A (123.2 ± 5.1s and 191.6 ± 23.4s). Conclusion: There are significant differences between the tested SCL materials and test solutions regarding the wettability. The wettability values were higher for all lenses when they were pre-soaked in OFPM. Increasing lens wettability through use of a lens care solution with a wetting agent designed to interact with silicone material may have a positive impact on the patient’s lens wearing experience. http://dx.doi.org/10.1016/j.clae.2013.08.102 40 50 years of contact lenses: How has the modulus changed? Tarnveer S Bhamra (MChem in Applied Chemistry), Brian Tighe (Professor) ∗ E-mail address: [email protected] (B. Tighe). Purpose: As contact lens materials have developed, the relevance of mechanical properties and particularly the modulus (stiffness) has been a matter of considerable debate. As poly(methyl methacrylate) (PMMA) began to be replaced by more oxygen permeable materials, dimensional stability and lens durability were key concerns. The spectrum of materials used for manufacture has since expanded to encompass much softer hydrogels. Although modulus was initially used as a comparative factor for specific aspects of materials performance, is now understood to influence factors such as initial comfort. The aim of this poster is to explore modulus changes over the last 50 years. Method: An extensive range of SiHy and conventional hydrogels, some of which are no longer available to the practitioner has been characterised using static and dynamic mechanical techniques. Tensile tests were conducted with a Hounsfield Ten-
e29
someter using a 10 N load cell. Shear-dependent behaviour was assessed using the Bohlin CVO Rheometer at 34oC, with a range of shear rates -10 Hz) reflecting deformation during handling and wear. Results: Traditional conventional hydrogels show tensile moduli in the range of 0.14 to 0.90 MPa. Comparable moduli of Silicone hydrogels (SiHy) at initial launch were in excess of 1.0 MPa but the trend is now to have moduli around 0.5 MPa. Dynamic moduli of early materials over the frequency range 0.5 Hz to 10 Hz typically rose by 25 kPa (balafilcon A) whereas more recently developed materials typically rise by only 11 kPa (senofilcon A). Conclusions: Measurement techniques and practitioner feedback have combined over a long period to aid the development of materials and lenses with optimised lens handling and “ineye” behaviour. This comprehensive assessment of the mechanical properties of lenses past and present shows: (a) how mechanical properties have evolved, over time and (b) the cumulative frequency distribution of moduli over the history of the hydrogel contact lens. http://dx.doi.org/10.1016/j.clae.2013.08.103 41 In-vitro wettability of four silicone hydrogel lenses with differing surface properties Jill Woods (BSc(Hons) MCOptom FBCLA) ∗ , Lakshman Subbaraman (PhD BSOptom FAAO), Lyndon Jones (PhD FCOptom FAAO) E-mail address: [email protected] (J. Woods). Purpose: To determine and compare the advancing sessile drop water contact angles (CAs) of four silicone hydrogel (SH) materials which utilise differing approaches to enhance wettability. These included a material that is plasma oxidized (balafilcon A), one with a plasma coating (lotrafilcon B), one with an internal wetting agent (senofilcon and also an untreated/unmodified material (comfilcon A). Method: The CAs of all the contact lenses (n = 5 for each lens type) were initially measured when taken immediately out of their blister packaging solution (BPS). The CAs were then measured again after the lenses were soaked thoroughly in a phosphate-buffered saline (PBS), in order to remove the BPS from the materials. On each occasion, excess solution was wicked off with lint-free lens paper and the lenses were then placed on an optical contact angle (OCA) analyser and the CAs were measured using the sessile drop technique. Results: The lowest CAs were displayed by comfilcon A and lotrafilcon B and the highest by balafilcon A. Directly out of the BPS, the CA (mean ± SD) of comfilcon A and lotrafilcon B were 28◦ ±3 and 30◦ ±3 respectively, and these were statistically significantly lower than those of both balafilcon A and senofilcon A (both p < 0.05). Following rinsing in PBS, the CAs of comfilcon A and lotrafilcon B increased to 39◦ ±4 and 40◦ ± 5 respectively, though they still remained statistically significantly lower than those of both balafilcon A and senofilcon A (both p < 0.05). Conclusions: Among the four contact lenses tested, the untreated (comfilcon A) and the plasma coated (lotrafilcon SH materials displayed the lowest CAs, both directly from the packaging solution and also after rinsing in PBS. The material that underwent a plasma oxidation process displayed the highest CA. Further work is needed to determine the correlation between contact angles and subjective comfort. http://dx.doi.org/10.1016/j.clae.2013.08.104
39 Assessment of the wettability of different silicone hydrogel contact lenses using a novel in vitro method S. Marx (Dipl.-Ing. (FH) AO, FIACLE), M. Sinnig (M.Sc.), W. Sickenberger (Prof. M.S. Optom. (USA), Dipl.-Ing. (FH) AO) Purpose: The aim of the study was to determine differences between the surface wettability of various lens/solution combinations in terms of the drying-up time measured in vitro using a modified corneal topographer (Non-Invasive Keratograph–DryingUp Time (NIK-DUT)). Methods: Five market-leading silicone hydrogel SCLs underwent a washing procedure and were soaked subsequently in OPTI-FREE® PureMoist® MPDS (OFPM) whereas saline served as reference (10 combinations in total). The NIK-DUT was measured ten times for every combination by evaluating the reflected placidoring image objectively. The focus was on the measurement of the NIK- DUT value derived when 25% of the entire measurement segments showed dry-up during the measuring time (NIK- DUT S25). Based on an asymptotic, normally distributed mean value an analysis of variance (ANOVA, alpha = 0.05) and subsequently a post-hoc analysis (Duncan) was conducted to determine inter-group comparisons. Results: Within and between the 10 combinations the differences were statistically significant (p < 0.001). The following NIK-DUT S25 values were achieved in combination with saline and OFPM respectively: Lotrafilcon B with Aqua Technology (129.0 ± 15.1s and 154.1 ± 5.5s); Lotrafilcon A (120.8 ± 20.5s and 140.9 ± 12.8s); Comfilcon A (123.5 ± 7.9s and 149.5 ± 7.6s); Balafilcon A (128.3 ± 16.3s and 131.4 ± 8.0s); Senofilcon A (123.2 ± 5.1s and 191.6 ± 23.4s). Conclusion: There are significant differences between the tested SCL materials and test solutions regarding the wettability. The wettability values were higher for all lenses when they were pre-soaked in OFPM. Increasing lens wettability through use of a lens care solution with a wetting agent designed to interact with silicone material may have a positive impact on the patient’s lens wearing experience. http://dx.doi.org/10.1016/j.clae.2013.08.102 40 50 years of contact lenses: How has the modulus changed? Tarnveer S Bhamra (MChem in Applied Chemistry), Brian Tighe (Professor) ∗ E-mail address: [email protected] (B. Tighe). Purpose: As contact lens materials have developed, the relevance of mechanical properties and particularly the modulus (stiffness) has been a matter of considerable debate. As poly(methyl methacrylate) (PMMA) began to be replaced by more oxygen permeable materials, dimensional stability and lens durability were key concerns. The spectrum of materials used for manufacture has since expanded to encompass much softer hydrogels. Although modulus was initially used as a comparative factor for specific aspects of materials performance, is now understood to influence factors such as initial comfort. The aim of this poster is to explore modulus changes over the last 50 years. Method: An extensive range of SiHy and conventional hydrogels, some of which are no longer available to the practitioner has been characterised using static and dynamic mechanical techniques. Tensile tests were conducted with a Hounsfield Ten-
e29
someter using a 10 N load cell. Shear-dependent behaviour was assessed using the Bohlin CVO Rheometer at 34oC, with a range of shear rates -10 Hz) reflecting deformation during handling and wear. Results: Traditional conventional hydrogels show tensile moduli in the range of 0.14 to 0.90 MPa. Comparable moduli of Silicone hydrogels (SiHy) at initial launch were in excess of 1.0 MPa but the trend is now to have moduli around 0.5 MPa. Dynamic moduli of early materials over the frequency range 0.5 Hz to 10 Hz typically rose by 25 kPa (balafilcon A) whereas more recently developed materials typically rise by only 11 kPa (senofilcon A). Conclusions: Measurement techniques and practitioner feedback have combined over a long period to aid the development of materials and lenses with optimised lens handling and “ineye” behaviour. This comprehensive assessment of the mechanical properties of lenses past and present shows: (a) how mechanical properties have evolved, over time and (b) the cumulative frequency distribution of moduli over the history of the hydrogel contact lens. http://dx.doi.org/10.1016/j.clae.2013.08.103 41 In-vitro wettability of four silicone hydrogel lenses with differing surface properties Jill Woods (BSc(Hons) MCOptom FBCLA) ∗ , Lakshman Subbaraman (PhD BSOptom FAAO), Lyndon Jones (PhD FCOptom FAAO) E-mail address: [email protected] (J. Woods). Purpose: To determine and compare the advancing sessile drop water contact angles (CAs) of four silicone hydrogel (SH) materials which utilise differing approaches to enhance wettability. These included a material that is plasma oxidized (balafilcon A), one with a plasma coating (lotrafilcon B), one with an internal wetting agent (senofilcon and also an untreated/unmodified material (comfilcon A). Method: The CAs of all the contact lenses (n = 5 for each lens type) were initially measured when taken immediately out of their blister packaging solution (BPS). The CAs were then measured again after the lenses were soaked thoroughly in a phosphate-buffered saline (PBS), in order to remove the BPS from the materials. On each occasion, excess solution was wicked off with lint-free lens paper and the lenses were then placed on an optical contact angle (OCA) analyser and the CAs were measured using the sessile drop technique. Results: The lowest CAs were displayed by comfilcon A and lotrafilcon B and the highest by balafilcon A. Directly out of the BPS, the CA (mean ± SD) of comfilcon A and lotrafilcon B were 28◦ ±3 and 30◦ ±3 respectively, and these were statistically significantly lower than those of both balafilcon A and senofilcon A (both p < 0.05). Following rinsing in PBS, the CAs of comfilcon A and lotrafilcon B increased to 39◦ ±4 and 40◦ ± 5 respectively, though they still remained statistically significantly lower than those of both balafilcon A and senofilcon A (both p < 0.05). Conclusions: Among the four contact lenses tested, the untreated (comfilcon A) and the plasma coated (lotrafilcon SH materials displayed the lowest CAs, both directly from the packaging solution and also after rinsing in PBS. The material that underwent a plasma oxidation process displayed the highest CA. Further work is needed to determine the correlation between contact angles and subjective comfort. http://dx.doi.org/10.1016/j.clae.2013.08.104