High myopia control is comparable between multifocal rigid gas-permeable lenses and spectacles.

Purpose: Ocular pathology may be reduced by slowing myopia progression. The purpose of this study was to evaluate the potential of a novel custom-designed rigid gas permeable (RGP) contact lens to control high myopia by comparing the efficacy of multifocal RGP lenses and single-vision spectacles for high myopia control. Methods: The medical records of children fitted with spectacles or multifocal rigid gas-permeable lenses between January 2018 and May 2020 were retrospectively reviewed. Children (5-17 years) with non-cycloplegic spherical equivalent refraction of ≤ -6.00 D or spherical equivalent refraction > - 6.00 D with baseline axial length ≥ 26.5 mm, and astigmatism of ≥ -2.00 D were included. Axial length and refraction were measured at baseline, before fitting the participants with multifocal rigid gas-permeable lenses or spectacles, and at 1- and 2-year follow-up visits. Changes in axial length were compared between the groups. Results: Among the 77 children with 1-year follow-up data, the mean axial elongation was 0.20 ± 0.17 mm and 0.21 ± 0.14 mm in the multifocal rigid gas-permeable and control groups, respectively, without significant differences between groups (F = 0.004, p = 0.835). Among the 41 patients who completed 2 years of follow-up, the mean axial elongation values in the multifocal rigid gas-permeable and control groups were 0.21 ± 0.15 mm and 0.24 ± 0.13 mm, respectively, at the 1-year follow-up, and 0.37 ± 0.27 mm and 0.43 ± 0.23 mm, respectively, at the 2-year follow-up, without significant between-group differences at either time point (p = 0.224). Conclusion: Axial length increased at a similar rate in both the control (spectacles) and multifocal rigid gas-permeable lens groups, suggesting that multifocal rigid gas-permeable lenses have no significant impact on controlling high myopia progression compared with spectacles.

To rub or not to rub? - effective rigid contact lens cleaning.

PURPOSE: To compare the efficacy of cleaning of rigid contact lenses using two care solutions with and without rubbing. METHODS: A masked randomised trial was conducted. The cleaning efficacy of two solutions recommended for rigid contact lenses, a one-step hydrogen peroxide solution (HP) and a povidone iodine-based solution (PI), were evaluated on 64 unworn orthokeratology (ortho-k) lenses subsequent to cleaning with rubbing (R) with a surfactant cleaner or without rubbing (NR). Either mascara or hand cream was applied as a contaminant to the lenses to simulate stubborn and loosely bounded deposits, respectively. For each type of deposit, the lenses were randomly assigned to four cleaning treatments: R with HP, NR with HP, R with PI, and NR with PI (n = 8 for each group). Each lens surface was assessed on site by a masked examiner under a low-magnification slit-lamp and with photo-documentation. Lenses were graded according to the deposit coverage area using a pre-set five-point scale [0 (<20% coverage) - 4 (>80% coverage)]. RESULTS: For stubborn deposits (mascara), NR failed to remove deposits from 94% of lenses, whilst R removed more than 80% of deposits from 63% of the lenses. For oily deposits, 25% of NR lenses had >80% coverage, whilst only one R lens had 60-80% coverage, with 19% having 40-60% coverage, and 38% with either 20-40% or <20%. Rubbing improved lens cleanliness for both types of deposits, but only reached statistical significance for the stubborn deposit group. There were no significant differences between the solutions. CONCLUSION: Not Rubbing and using either HP or PI solutions, is not effective in removing stubborn deposits from ortho-k lenses. It is essential to rub lenses when cleaning rigid lenses to ensure optimal lens hygiene for ocular health, especially as rigid gas permeable (RGP) lenses are intended to be reused for at least a year before replacement. Rubbing with a daily cleaner should be included in the instructions for use of the solutions tested for rigid lenses and practitioners should be encouraged to emphasise the importance of rubbing in lens care.

An approach for simulating the fitting of rigid gas-permeable contact lenses using 3D printing technology.

OBJECTIVE: To introduce a new approach to simulatethe fitting process of rigid gas-permeable (RGP) contact lenses using 3D printing technology. METHODS: A hemispherical or parabolic 3D model was created using 3D Builder or Tinkercad software. The horizontal and vertical diameters and the hemispherical or ellipsoid height were adjusted to simulate different morphologies of the corneal anterior surface. After exporting the file in stereo lithography (STL) format, a solid model was printed using a 3D printer and was used to simulate RGP contact lens fitting. RESULTS: Limited by the precision of the entry-level 3D printer which was used in this study, the print-outs of the corneal models were crude, but the models were tested for their ability to simulate common corneal morphologies with no corneal astigmatism and different axial corneal astigmatism. Compared with some built-in simulation programs for corneal topography, the solid models generated by 3D printing could well simulate the positioning of the lens under the influence of gravity and the eyelid, as well as lens eccentricity or the bubbles under lenses caused by an improper wearing method. CONCLUSION: 3D printing technology can be well applied in the simulation of RGP contact lens fitting, which may become a new teaching method in optometry.

Estimation of the hybrid lens parameters through rigid gas permeable lens fitting.

PURPOSE: To estimate the fitting parameters of the hybrid contact lens in patients with corneal ectasia using the rigid gas permeable (RGP) lens. METHODS: Thirty-four eyes with corneal ectasia were evaluated in this study. The patients were examined once with the RGP lens and once with the hybrid contact lens. The relationship between the base curvature of the RGP and the vault of the hybrid lens and the correlation between their powers were analyzed. RESULTS: We found a linear relationship between the base curvature of the RGP lens and the vault of the hybrid lens (P < 0.001) (R(2) = 0.45). Moreover, we found a correlation between the power of the RGP and hybrid lens (P < 0.001) (R(2) = 0.4). However, a 0.5 mm decrease in the base curvature radius of the RGP lens increased the vault of the hybrid lens by 72 µ. CONCLUSION: The results of this study could be used for better and faster selection of the first hybrid contact lens.

Comparison of Changes in Ocular Surface Status after Wearing Orthokeratologic and Rigid Gas Permeable Lens

PURPOSE: To evaluate the differences in dry eye and meibomian gland dysfunction (MGD) by comparing ocular surface status before and after wearing an orthokeratologic (OK) lens and rigid gas permeable (RGP) lens made of the same material. METHODS: The ocular surface and meibomian gland statuses of 12 eyes of 12 OK lens wearers (OK lens group) and 16 eyes of 16 RGP wearers (RGP lens group) were evaluated before and 1 and 3 months after lens wearing. Ocular surface disease index (OSDI), tear film break-up time (TBUT), Schirmer's test I, and ocular surface staining score were evaluated for ocular surface parameters. Meibomian gland function was evaluated by assessing lid margin abnormality, meibomian gland expressibility, and meibum quality. RESULTS: TBUT and ocular surface staining score after 1 and 3 months of wearing an OK lens were significantly aggravated (p= 0.004, p < 0.001). The MGD grade, lid margin abnormality, meibomian gland expressibility, and meibum quality were aggravated after 1 and 3 months of wearing an OK lens (p < 0.001, p < 0.001, p < 0.001, p= 0.002). After 1 and 3 months of wearing an RGP lens, OSDI, TBUT, and ocular surface staining score were aggravated (all p < 0.001). The MGD grade, lid margin abnormality, meibomian gland expressibility, and meibum quality were aggravated after 1 and 3 months of wearing an RGP lens (all p < 0.001). MGD grade, lid margin abnormality, meibomian gland expressibility, and meibum quality were significantly more aggravated in the RGP lens group than in the OK lens group after 3 months (p < 0.001, p < 0.001, p= 0.001, p < 0.001). CONCLUSIONS: Use of OK and RGP lenses affects ocular surface status. Especially, meibomian gland parameters and OSDI showed greater changes in RGP lens wearers than OK lens wearers.

Comparison of Changes in Ocular Surface Status after Wearing Orthokeratologic and Rigid Gas Permeable Lens

PURPOSE: To evaluate the differences in dry eye and meibomian gland dysfunction (MGD) by comparing ocular surface status before and after wearing an orthokeratologic (OK) lens and rigid gas permeable (RGP) lens made of the same material. METHODS: The ocular surface and meibomian gland statuses of 12 eyes of 12 OK lens wearers (OK lens group) and 16 eyes of 16 RGP wearers (RGP lens group) were evaluated before and 1 and 3 months after lens wearing. Ocular surface disease index (OSDI), tear film break-up time (TBUT), Schirmer's test I, and ocular surface staining score were evaluated for ocular surface parameters. Meibomian gland function was evaluated by assessing lid margin abnormality, meibomian gland expressibility, and meibum quality. RESULTS: TBUT and ocular surface staining score after 1 and 3 months of wearing an OK lens were significantly aggravated (p= 0.004, p < 0.001). The MGD grade, lid margin abnormality, meibomian gland expressibility, and meibum quality were aggravated after 1 and 3 months of wearing an OK lens (p < 0.001, p < 0.001, p < 0.001, p= 0.002). After 1 and 3 months of wearing an RGP lens, OSDI, TBUT, and ocular surface staining score were aggravated (all p < 0.001). The MGD grade, lid margin abnormality, meibomian gland expressibility, and meibum quality were aggravated after 1 and 3 months of wearing an RGP lens (all p < 0.001). MGD grade, lid margin abnormality, meibomian gland expressibility, and meibum quality were significantly more aggravated in the RGP lens group than in the OK lens group after 3 months (p < 0.001, p < 0.001, p= 0.001, p < 0.001). CONCLUSIONS: Use of OK and RGP lenses affects ocular surface status. Especially, meibomian gland parameters and OSDI showed greater changes in RGP lens wearers than OK lens wearers.

Cytotoxicity of rigid gas-permeable lens care solutions.

PURPOSE: Reports on cytotoxic effects of rigid gas-permeable lens multipurpose solutions, which remain important because of increasing popularity of orthokeratology, are limited. This study determined cytotoxic effects of rigid gas-permeable lens multipurpose solutions on human corneal epithelial cells and assessed the proliferation rate at different levels of cell membrane damage. METHODS: The human corneal epithelial cells were exposed to multipurpose solutions containing chlorhexidine gluconate (0.003%) and polyaminopropyl biguanide (PHMB) (0.0005%) (MPS-A), PHMB (0.0005%) (MPS-B) and PHMB (0.0001%) (MPS-C) for one, five and 10 minutes. Following staining with Annexin V-FITC/7-AAD, cell viability and membrane integrity were assessed by flow cytometry. Effects of exposure to concentrations of 10 to 40 per cent multipurpose solutions for 12 hours on the metabolic rate of human corneal epithelial cells were assessed by 3-(4-,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell proliferation assay. Recovery rates were assessed after re-culture for 96 hours at 37°C. RESULTS: MPS-A exposure caused the highest percentage of early and late necrotic cells for all exposure times and was significantly higher than other multipurpose solutions (p < 0.0001). After 10 minutes exposure, almost 40 per cent of cells in MPS-A but less than five per cent in MPS-B or MPS-C, were in late necrotic stage. After 12 hours of exposure, cell activity was significantly reduced in a dose-response manner for MPS-A treated cells only (p > 0.05). After 96 hours of re-culture, all exposed cells showed some reduction in viability but the effects of exposure to 30 and 40 per cent MPS-A resulted in loss of viability. CONCLUSION: The presence of chlorhexidine appeared to increase cytotoxicity of multipurpose solutions for rigid gas-permeable lenses. This was apparent in both increased levels of necrotic cells on initial exposure and reductions in viability after prolonged exposures at lower dilutions. Multipurpose solutions containing PHMB as a preservative, while not causing acute cytotoxicity, did affect cell viability following exposure to diluted solutions. This indicated it is inadvisable to expose the cornea to multipurpose solutions but rather to rinse lenses with saline before insertion and use artificial tears for rewetting.

The Effect of RGP Lens and Reverse Geometry Lens on Apoptosis in Rabbit Cornea

PURPOSE: To investigate the cytotoxic effect of rigid gas permeable(RGP) and reverse geometry lens(RGL) on rabbit corneal cells. METHODS: In 36 white rabbits, right eyes were worn with either RGP or RGL. Left eyes were served as control. The rabbits were sacrificed at 1, 3, 7, 14 days after fitting and 7, 14 days after removal. Morphological changes of the basal epithelial cells and stromal keratocytes were observed using the light and transmission electron microscopy. The samples were examined after TUNEL staining in 3 high power fields (x400). RESULTS: In control eyes, 2.26% of central corneal epithelial cells showed apoptosis. After RGP wearing, the epithelial apoptosis decreased by 0.32% compared to control eyes(2.17%) at 14 days(p<0.001), and returned to 1.55% at 14 days after lens removal(2.04% in control, p=0.161). After RGL wearing, the degree of apoptosis was also lower than control(3.22%) by 0.30% at 14 days(p=0.003). However, it increased to 0.75% at 14 days after lens removal(1.67% in control, p=0.077). A few TUNEL positive fibroblasts were found in superficial stroma in both RGP and RGL group, but not in control eyes. CONCLUSIONS: Both RGP and RGL wearing may decrease the degree of apoptosis in corneal epithelium and lead the apoptosis in corneal stroma. The degree of apoptosis was recovered after lens removal, suggesting the process might to be reversible. The fitting with RGL induced apoptosis of keratocyte more than the fitting with RGP did. It suggests that the RGL wearing may be less physiologic than RGP wearing.