Limbal Metabolic Support Reduces Peripheral Corneal Edema with Contact-Lens Wear

Central and peripheral scleral lens-induced corneal oedema

PURPOSE

To quantify the magnitude of central and peripheral scleral lens-induced corneal oedema for a range of fluid reservoir thicknesses, and to compare these experimental results with theoretical models of corneal oedema both with and without limbal metabolic support (i.e., the lateral transport of metabolites and the influence of the limbal vasculature).

METHODS

Ten young healthy participants wore scleral lenses (KATT™, Capricornia Contact Lenses) fitted with low (mean 141 μm), medium (482 μm) and high (718 μm) central fluid reservoir thickness values across three separate study visits. The scleral lens thickness, fluid reservoir thickness and stromal corneal oedema were measured using optical coherence tomography. Oedema was quantified across the central (0-2.5 mm from the corneal apex) and peripheral (1.25-3 mm from the scleral spur) cornea. Experimental data were compared with published theoretical models of central to peripheral corneal oedema.

RESULTS

Stromal oedema varied with fluid reservoir thickness (p < 0.001) for both central and peripheral regions. The mean (standard deviation) stromal oedema was greater for the medium (2.08 (1.21)%) and high (2.22 (1.31)%) fluid reservoir thickness conditions compared to the low condition (1.00 (1.01)%) (p ≤ 0.01). Stromal oedema gradually increased from the corneal centre to the periphery by ~0.3% on average (relative increase of 18%), but the change did not reach statistical significance. This trend of increasing, rather than decreasing, oedema towards the limbus is consistent with theoretical modelling of peripheral oedema without metabolic support from the limbus.

CONCLUSIONS

The central and peripheral cornea displayed a similar magnitude of oedema, with increasing levels observed for medium and high fluid reservoir thicknesses. The gradual increase in oedema towards the limbus is consistent with a 'without limbal metabolic support' theoretical model.

A three-dimensional model to describe complete human corneal oxygenation during contact lens wear

We perform a novel 3D study to quantify the corneal oxygen consumption and diffusion in each part of the cornea with different contact lens materials. The oxygen profile is calculated as a function of oxygen tension at the cornea-tear interface and the oxygen transmissibility of the lens, with values used in previous studies. We aim to determine the influence of a detailed geometry of the cornea in their modeling compared to previous low dimensional models used in the literature. To this end, a 3-D study based on an axisymmetric volume element analysis model was applied to different contact lenses currently on the market. We have obtained that the model provides a valuable tool for understanding the flux and cornea oxygen profiles through the epithelium, stroma, and endothelium. The most important results are related to the dependence of the oxygen flux through the cornea-lens system on the contact lens thickness and geometry. Both parameters play an important role in the corneal flux and oxygen tension distribution. The decline in oxygen consumption experienced by the cornea takes place just inside the epithelium, where the oxygen tension falls to between 95 and 16 mmHg under open eye conditions, and 30 to 0.3 mmHg under closed eye conditions, depending on the contact lens worn. This helps to understand the physiological response of the corneal tissue under conditions of daily and overnight contact lens wear, and the importance of detailed geometry of the cornea in the modeling of diffusion for oxygen and other species.

Therapeutic Hyper-CL soft contact lens in Sjögren's syndrome

Purpose

Observations

Conclusions and importance

Quadrant-Specific Changes in Corneal and Tear Fluid Reservoir Thickness for After 2 Hours of Wear

OBJECTIVE

To measure corneal swelling and thickness of the tear fluid reservoir (TFR) after wearing scleral lenses (SLs).

METHODS

Thirty-five participants had 1 eye fitted with each of three SLs (15.0-mm Jupiter, 18.2-mm Jupiter, and 18.0-mm Digiform). Scheimpflug images were obtained before wear, after application, after 2 hr of wear, and after removal. Initial and final TFR thickness and corneal thickness were measured in the central cornea and 3 mm from the center in the superior, inferior, temporal, and nasal quadrants.

RESULTS

Corneal thickness increased with wear, but no between-lens differences were observed in the superior (P=0.09), inferior (P=0.38), or temporal (P=0.53) quadrants. The greatest change in central and nasal cornea thickness was with the 15.0-mm SL (P<0.001). All areas showed settling, with no between-lens differences. Greater final TFR thickness was noted for the superior and nasal quadrants with the 18.0-mm SL (P<0.001), and less final TFR thickness was noted in the inferior (P<0.001) and temporal (P<0.001) quadrants with the 15.0-mm SL. Corneal thickness was not associated with the final TFR thickness.

CONCLUSIONS

The greatest corneal swelling was observed in the inferior quadrant with the 15.0-mm SL, although this lens had the least TFR thickness inferiorly. TFR thickness alone did not account for observed corneal swelling.

Protection against corneal hyperosmolarity with soft-contact-lens wear

Hyperosmotic tear stimulates human corneal nerve endings, activates ocular immune response, and elicits dry-eye symptoms. A soft contact lens (SCL) covers the cornea preventing it from experiencing direct tear evaporation and the resulting blink-periodic salinity increases. For the cornea to experience hyperosmolarity due to tear evaporation, salt must transport across the SCL to the post-lens tear film (PoLTF) bathing the cornea. Consequently, limited salt transport across a SCL potentially protects the ocular surface from hyperosmotic tear. In addition, despite lens-wear discomfort sharing common sensations to dry eye, no correlation is available between measured tear hyperosmolarity and SCL-wear discomfort. Lack of documentation is likely because clinical measurements of tear osmolarity during lens wear do not interrogate the tear osmolarity of the PoLTF that actually overlays the cornea. Rather, tear osmolarity is clinically measured in the tear meniscus. For the first time, we mathematically quantify tear osmolarity in the PoLTF and show that it differs significantly from the clinically measured tear-meniscus osmolarity. We show further that aqueous-deficient dry eye and evaporative dry eye both exacerbate the hyperosmolarity of the PoLTF. Nevertheless, depending on lens salt-transport properties (i.e., diffusivity, partition coefficient, and thickness), a SCL can indeed protect against corneal hyperosmolarity by reducing PoLTF salinity to below that of the ocular surface during no-lens wear. Importantly, PoLTF osmolarity for dry-eye patients can be reduced to that of normal eyes with no-lens wear provided that the lens exhibits a low lens-salt diffusivity. Infrequent blinking increases PoLTF osmolarity consistent with lens-wear discomfort. Judicious design of SCL material salt-transport properties can ameliorate corneal hyperosmolarity. Our results confirm the importance of PoLTF osmolarity during SCL wear and indicate a possible relation between PoLTF osmolarity and contact-lens discomfort.

Case Report: Modified Piggyback System to Treat Peripheral Iridotomies and Degenerative Myopia

SIGNIFICANCE

This report details how a case with degenerative myopia and symptoms secondary to laser peripheral iridotomies is managed with a modified piggyback contact lens system. The benefits of using a system with tinted and gas-permeable (GP) lenses are discussed.

PURPOSE

This study aimed to report the positive outcome of a modified piggyback system in the treatment of degenerative myopia and iris abnormalities.

CASE REPORT

A patient with degenerative myopia presented with visual disturbances secondary to laser peripheral iridotomies in both eyes. A modified piggyback system was trialed using a corneal GP lens overlaying a tinted soft contact lens to provide optimal vision and visual comfort in both eyes. After optimizing the fit, there was a reduction in glare and improved vision.

CONCLUSIONS

Hard contact lenses often provide superior optics and vision compared with soft lenses, especially to patients with high refractive errors. Patients who require hard lenses and also have visual disturbances secondary to iris abnormalities could be managed with a modified piggyback contact lens systems using a corneal GP lens and tinted soft lens.

Profiling of non-polar lipids in tears of contact lens wearers during the day

PURPOSE

This study explored whether the non-polar lipids in the human tear fluid lipidome show diurnal variation with and without contact lens wear. It also addressed the relationship between changes in ocular comfort during the day with the level of non-polar lipids.

METHODS

Tear samples were collected in the morning and evening with and without contact lenses using fine glass capillary tubes and were analysed by chip-based nano-electrospray ionization tandem mass spectrometric techniques. Tear levels of cholesteryl esters (CE), wax esters (WE) and triacylglycerides (TAG) were quantified.

RESULTS

TAG 48:0, 52:0 and WE 26:0/16:0, and 27:0/17:0 increased from morning to evening. TAG 52:2, WE 21:0/16:0, 21:0/18:1 and 28:0/18:1 decreased during the day when no lenses were worn. CE 21:0 was the only non-polar lipid that increased from morning to evening in contact lens wear. WE 21:0/16:0 and 27:0/17:0 were lower in the morning in contact lens wear compared to no lens wear (p ≤ 0.05). The level of non-polar lipids did not correlate with ocular comfort at the end of the day.

CONCLUSION

Even though the level of some of non-polar lipid species changed from morning to evening the total level of major tear non-polar lipids remained unchanged during the day with and without contact lens wear. The effect of change in the quantity and structure of lipid species on tear stability and ocular comfort warrants more investigation.

Central-to-peripheral corneal edema during wear of embedded-component contact lenses

PURPOSE

With active investigation underway for embedded-circuit contact lenses, safe oxygen supply of these novel lenses remains a question. Central-to-peripheral corneal edema for healthy eyes during wear of soft contact (SCL) and scleral lenses (SL) with embedding components is assessed.

METHODS

Various 2-dimensional (2D) designs of SL and SCL with embedded components are constructed on Comsol Multiphysics 5.5. Local corneal swelling associated with the designed lenses is determined by a recently developed 2D metabolic-swelling model. Settled central post-lens tear-film thicknesses (PoLTFs) are set at 400 μm and 3 μm for SL and SCL designs, respectively. Each lens design has an axisymmetric central and an axisymmetric peripheral embedment. Oxygen permeability (Dk) of the lens and the embedments ranges from 0 to 200 Barrer. Dimensions and location of the embedments are varied to assess optimal-design configurations to minimize central-to-peripheral corneal edema.

RESULTS

By adjusting oxygen Dk of the central embedment, the peripheral embedment, or the lens matrix polymer, corneal swelling is reduced by up to 2.5 %, 1.5 %, or 1.4 % of the baseline corneal thickness, respectively, while keeping all other parameters constant. A decrease in PoLTF thickness from 400 μm to 3 μm decreases corneal edema by up to 1.8 % of the baseline corneal thickness. Shifting the peripheral embedment farther out towards the periphery and towards the anterior lens surface reduces peak edema by up to 1.3 % and 0.6 % of the baseline corneal thickness, respectively.

CONCLUSIONS

To minimize central-to-peripheral corneal edema, embedments should be placed anteriorly and far into the periphery to allow maximal limbal metabolic support and oxygen transport in the polar direction (i.e., the θ-direction in spherical coordinates). High-oxygen transmissibility for all components and thinner PoLTF thickness are recommended to minimize corneal edema. Depending on design specifications, less than 1 % swelling over the entire cornea is achievable even with oxygen-impermeable embedments.

Therapeutic HL-Contact Lens versus Standard Bandage Contact Lens for Corneal Edema: A Prospective, Multicenter, Randomized, Crossover Study

Introduction

To compare the safety and efficacy of the Therapeutic Hyper-CL™ lens versus a standard bandage contact lens (PureVision B&L) for chronic corneal edema.

Methods

Prospective, multicenter, randomized, crossover study. Chronic corneal edema patients were randomized to one of two arms. The first arm was fitted with the Therapeutic Hyper-CL™ lens while the second arm was fitted with a standard soft bandage contact lens. Both arms were treated with 5% sodium chloride 6 times a day. After a 7-day treatment period, there was a 7-day washout period, after which the arms were crossed over. Patients were evaluated at days 0 (baseline), 7 (following first treatment allocation), 14 (following washout), and 21 (following second treatment allocation). The primary outcomes were 3 lines of BCVA (best corrected visual acuity) improvement.

Results

In total, 49 patients were enrolled. There was significantly greater BCVA improvement rate >3 lines (30.4% versus 17.4%, P=0.04) in the Therapeutic Hyper-CL™ lens group. The mean change in BCVA lines was significantly greater for the Therapeutic Hyper-CL™ lens (3.4 ± 6.7 versus 0.9 ± 2.3, P=0.02).

Conclusions

The Therapeutic Hyper-CL™ lens was associated with a higher chance for significant visual acuity improvement when compared to a standard bandage contact lens combined with 5% sodium chloride. This trial is registered with NCT02660151.

Corneal Health during Three Months of Scleral Lens Wear

SIGNIFICANCE

This study evaluated the effects scleral lens wear has on corneal health using fluorometry and in vivo confocal microscopy. No subclinical changes on healthy corneas of young subjects were observed during 3 months of scleral lens wear.

PURPOSE

This study aimed to evaluate the effects 3 months of scleral lens wear has on the corneal epithelial barrier function, dendritic cell density, and nerve fiber morphology.

METHODS

Twenty-seven neophytes (mean [standard deviation] age, 21.4 [3.9] years) wore scleral lenses of a fluorosilicone acrylate material bilaterally (97 Dk, 15.6 to 16.0-mm diameter) for 3 months without overnight wear. Subjects were randomized to use either Addipak (n = 12) or PuriLens Plus (n = 15) during lens insertion. Measurements of corneal epithelial permeability to fluorescein were performed with automated scanning fluorophotometer (Fluorotron Master; Ocumetrics, Mountain View, CA) on the central cornea of the right eye and the temporal corneal periphery of the left eye. Images of the distributions of corneal nerve fibers and dendritic cells and nerve fibers were captured in vivo with a confocal laser scanning microscope (Heidelberg Retina Tomograph, Rostock Cornea Module; Heidelberg Engineering, Heidelberg, Germany) on the central and inferior peripheral cornea of the left eye. Corneal measurements and imaging were performed at baseline and after 1 and 3 months of lens wear.

RESULTS

The corneal permeability values in natural log, dendritic cell densities, and nerve fiber morphology did not significantly change from baseline to 1 and 3 months of lens wear, for both central and peripheral corneal regions (P > .05). Dendritic cell density at the inferior cornea was higher than the central cornea throughout the study (P < .001). No relationships were observed between each outcome measurements and the saline solution groups (P > .05).

CONCLUSIONS

Scleral lens wear for 3 months on healthy cornea of young subjects did not affect corneal epithelial barrier function, nerve fiber, and dendritic cell densities. Buffered and nonbuffered saline solutions impacted the corneal health in similar ways.