Morphological changes in the conjunctiva, episclera and sclera following short-term miniscleral contact lens wear in rigid lens neophytes

Short-term changes in the trabecular iris angle and anterior chamber during wear of scleral lenses with different diameters

CLINICAL RELEVANCE

Scleral lens (SL) compression on the conjunctiva/episclera during wear may alter adjacent structures related to aqueous humour drainage.

BACKGROUND

The aim of this work was to assess short-term changes in the four quadrants of trabecular iris angle (TIA) and anterior chamber parameters during SL wear, using anterior segment optical coherence tomography (AS-OCT).

METHODS

Prospective study was conducted involving 16 healthy subjects with a mean age of 28 ± 5 years. Two SL of diameter 15.80 mm (L1) and 16.80 mm (L2) with the same parameters were used for 2 hours in different days. The central fluid reservoir (FR), the TIA in superior, inferior, nasal, temporal quadrants, and anterior chamber parameters; anterior chamber depth (ACD), anterior chamber width (ACW), anterior chamber area (ACAr) and anterior chamber volume (ACV) were measured with AS-OCT. These measurements were performed immediately after SL application (0 h), one hour (1 h) and two hours (2 h) of SL wear.

RESULTS

TIA decreases significantly in the superior quadrant at 2 hours of L2 wear (-5.19 ± 7.79º) (p = 0.04). In this sector, differences were also observed between the changes induced by both lenses during the 2 hours of wear (p = 0.04) and between first and second hours of wear (p = 0.04). ACD was significantly lower with L1 (-0.09 ± 0.14 mm) relative to L2 (0.00 ± 0.06 mm) between immediately after the application and 2 hours of wear (p = 0.02). A significant reduction in ACAr at 1 hour (-0.65 ± 0.75 mm2) (p = 0.01) and 2 hours of wear (-0.81 ± 1.15 mm2) (p = 0.04), as well as in ACW at 2 hours (-0.11 ± 0.14 mm) (p = 0.02) compared to immediately after application of L1 was found.

CONCLUSION

Small changes in TIA and anterior chamber occur during two hours of SL wear, but these changes are of limited clinical relevance in healthy subjects.

Changes in bulbar conjunctival microcirculation and microvasculature during short-term scleral lens wearing and their associated factors

OBJECTIVE

To explore the changes in microcirculation and microvasculature of the bulbar conjunctiva during the short-term wearing of the scleral lenses (ScCL). And investigate the factors affecting the microcirculation and microvasculature of the bulbar conjunctiva.

METHODS

In this prospective cross-sectional study, functional slit lamp biomicroscopy (FSLB) was used to image the ocular surface microcirculation and microvascular images at two different sites (under the area of ScCL and outside of the area of ScCL) before (baseline) and during the wearing of ScCL at 0 h, 1 h, 2 h and 3 h. Anterior segment optical coherence tomography (AS-OCT) (RTVue, Optovue Inc, USA) was also used to image central post-lens tear film (PoLTF) and the morphology changes of the conjunctiva under the landing zone at the same time period. The semi-automatic quantification of microcirculation and microvasculature including vessel density (Dbox), vessel diameter (D), axial blood flow velocity (Va) and blood flow volume (Q). And the morphological changes of conjunctiva and PoLTF fogging grading were evaluated manually. The changes in the microcirculation and microvasculature of the ocular surface, PoLTF fogging grade and conjunctival morphology were compared before and during the ScCL wearing at different time periods, and the relationship between them was analyzed.

RESULTS

Nineteen eyes (11 right eyes, 8 left eyes) were analyzed in this study. Outside of the area of ScCL, the Dbox before wearing lenses was less than that at 0 h (P = 0.041). The Q at baseline was greater than that after 1 h ScCL wearing (P = 0.026). Under the area of the ScCL, the Q at 1 h was less than that at baseline and 3 h. During the ScCL wearing, statistically significant conjunctival morphology changes were found among different time stages (baseline (0 μm), 0 h (113.18 μm), 2 h (138.97 μm), 3 h (143.83 μm) (all P ＜0.05). Outside the area of the ScCL, the morphology changes of the conjunctiva were negatively correlated with the changes of Va (P＜0.001,r = -0.471) and Q (P = 0.003,r = -0.348),but positively correlated with the Dbox (P = 0.001,r = 0.386). Under the area of ScCL, the morphology changes of the conjunctiva were negatively correlated with the Q (P = 0.012, r = -0.291). The fogging grade was positively correlated with the Q under the area of the ScCL (P = 0.005, r = 0.331).

CONCLUSIONS

The microcirculation and microvasculature of the ocular surface and conjunctival morphology were changed after wearing ScCL in wearers, which indicated that the microvascular responses happened in the ScCL wearers and the severity of microvascular responses of the ocular surface related to the morphology changes of the conjunctiva. The quantification methods and findings in this study provide clues for the safety of ScCL wearing and may supervise the health of the wearer's ocular surface.

The effect of extended periods of mini-scleral lens wear on the conjunctival/episcleral and scleral thickness

PURPOSE

To evaluate the conjunctival/episcleral thickness (CET) and anterior scleral thickness (AST) in patients with keratoconus with an extended duration of mini-scleral contact lens wear by utilizing anterior segment optical coherence tomography (ASOCT).

METHODS

This study included 17 eyes of 17 patients with keratoconus with mini-scleral contact lens wear (Group 1), 20 eyes of 20 patients with keratoconus without any contact lens wear (Group 2), and 20 eyes of 20 healthy controls (Group 3). CET and AST were measured using AS-OCT (Triton, Topcon, Japan) at 1, 2, and 3 mm posterior to the scleral spur in the nasal, temporal, superior, and inferior quadrants.

RESULTS

The median age of the mini-scleral contact lens group was 26, and the number of male patients was 14 (82.4 %). The superior CET values at 1 mm, 2 mm, and 3 mm statistically differed between the groups, with Group 1 having significantly lower values than Group 3 and Group 2 having statistically similar values to the remaining two groups. The inferior CET at 2 mm was lower in Groups 1 and 2 than in Group 3. The inferior CET at 3 mm was lower in Group 1 compared to Groups 2 and 3. AST was similar between the groups at all measured quadrants and distances. The duration of lens wear had a strong, statistically significant, negative correlation with the superior CET at 2 mm (rho: -0.847, p < 0.001) and a moderate, statistically significant, negative correlation with the superior CET at 3 mm (rho: -0.506, p < 0.038).

CONCLUSIONS

In this study, it was found that mini-scleral contact lens usage causes thinning in the conjunctival-episcleral layer, especially in the superior and inferior quadrants, but does not affect scleral thickness. AS-OCT is a non-invasive and clinically applicable technique for assessing the impact of contact lens use on the conjunctiva/episclera and sclera.

Image- and Impression-Based Technology in Scleral Lens Fitting for Keratoconus: Availability and Utilization

OBJECTIVE

Scleral lenses (SLs) can be customized using traditional diagnostic lens fitting or by using image- and/or impression-based technologies. This study describes the availability and usage of SL fitting technology in patients with keratoconus.

METHODS

An online survey queried practitioners on the mode of practice, country of residence, and estimated number of SL fits completed for keratoconus. Practitioners were asked whether they had access to image- and/or impression-based technology and to estimate the percentage of fits completed using diagnostic fitting, image-based technology, and impression-based technology. Access and usage of technology was compared between academic and community practices, United States and non-United States, and high-volume (≥60 SLs) and low-volume fitters.

RESULTS

423 practitioners who fit SL for keratoconus participated. Image- and impression-based technologies were more frequently available in academic practices compared with community practices and high-volume compared with low-volume practitioners ( P <0.005). Practitioners with image-based technology used it for a median [interquartile range] 5 [25]% of SL fittings; those with impression-based technology used it for 8 [9]% of fittings, and those with both types of technology used image-based devices for 12 [23]% of fittings and impression-based for 5 [8]% of fittings.

CONCLUSIONS

In this study, most participants report using diagnostic lenses to fit SLs for patients with keratoconus.

Using clinical optical coherence tomography to characterise contact lens edge shape and base curve radius

CLINICAL RELEVANCE

Clinical optical coherence tomography devices are widely used in optometry and ophthalmology and may be used to measure contact lens base curvature radius and visualise contact lens edge shape.

BACKGROUND

Knowledge of contact lens geometry facilitates fitting, while optical coherence tomography provides a powerful means of measuring geometrical form. This study evaluates the performance of a clinical optical coherence tomography device (3D OCT-1000) in characterising contact lens edge shape and measuring the back optic zone radius of rigid gas-permeable contact lenses in vitro.

METHODS

First, an opto-mechanical optical coherence tomography contact lens adaptor was designed and 3D-printed to facilitate a contact lens being imaged using a commercial optical coherence tomography device. Second, several image-processing algorithms and a simple calibration method were developed to measure the back optic zone radius in optical coherence tomography B-scans. Finally, based on the findings of two experiments, B-scan performance was evaluated in terms of 1) capacity to differentiate between contact lens edge geometries, and 2) capacity to obtain accurate and repeatable back optic zone radius measurements. Statistical and graphical analyses were performed to characterise reliability and reproducibility.

RESULTS

The 3D OCT-1000 and adaptor combination was capable of acquiring images of sufficient quality to discriminate between soft and rigid contact lens edge geometries. Additionally, statistical analysis of the rigid contact lens measurements demonstrated satisfactory back optic zone radius measurement accuracy and reproducibility.

CONCLUSION

This study demonstrates that a 3D OCT-1000 fitted with an opto-mechanical adaptor combination can be used to assess contact lens edges in vitro and that this clinical optical coherence tomography device, combined with image processing and linear calibration of the B-scans, is capable of obtaining back optic zone radius measurements of rigid gas-permeable contact lenses that are close to the ISO 18,369-2:2018 manufacturing tolerance range (±0.05 mm).

Semiscleral Contact Lens Use After Direct Corneal Neurotization for Neurotrophic Keratopathy

PURPOSE

To describe a case of a patient treated for neurotrophic keratopathy (NK) with direct corneal neurotization (CN), where a modification to the CN technique allowed for semiscleral contact lens use postoperatively.

OBSERVATION

Our patient had successful CN with improved corneal sensation. During the procedure, a 1.0 mm gutter was created between the limbus and nerve graft to allow for semiscleral contact lens fitting.

CONCLUSIONS

With the use of preoperative planning and a limbal gutter during CN, a semiscleral contact lens can serve as a well-tolerated postoperative management option to improve visual acuity and protect the corneal surface in patients with NK.

Effect of Scleral Contact Lens Size and Duration of Wear on Intraocular Pressure

OBJECTIVE

To evaluate the effects of scleral lens size and the duration of wear on intraocular pressure (IOP) during lens wear.

METHODS

Healthy adults were recruited for this prospective and randomized study. Intraocular pressure measurements were performed using a pneumotonometer. A block randomization was used to assign the order of scleral lens diameter of either 15.6 mm or 18.0 mm for 5-hr bilateral wear over a course of two visits. Scleral IOP (sIOP) was measured during the predetermined intervals, 1.25 hr apart, during the 5-hr scleral lens wear. Corneal IOP (cIOP) was measured before and after the scleral lens wear. The primary outcome measure was the mean change in sIOP from prelens insertion baseline.

RESULTS

Corneal IOP unchanged after scleral lens removal compared with the baseline measurements ( P =0.878). Smaller and larger lenses introduced significantly higher sIOP at 2.5 hr after lens insertion with the mean (95% CI) increase of 1.16 (0.54, 1.78) mm Hg and 1.37 (0.76, 1.99) mm Hg, respectively. There was no difference in IOP change between the smaller and larger diameter lenses ( P =0.590).

CONCLUSIONS

Well-fitted scleral lenses do not result in clinically significant changes in intraocular pressure during 5-hr lens wear in young and healthy individuals.

Assessment by Optical Coherence Tomography of Short-Term Changes in IOP-Related Structures Caused by Wearing Scleral Lenses

BACKGROUND

The mechanism that could increase intraocular pressure (IOP) during scleral lens (SL) wear is not fully understood, although it may be related to compression of the landing zone on structures involved in aqueous humor drainage.

METHODS

Thirty healthy subjects were fitted with two SLs of different sizes (L1 = 15.8 mm, L2 = 16.8 mm) for 2 h in the right eye and left eye as a control. Central corneal thickness (CCT), parameters of iridocorneal angle (ICA), Schlemm's canal (SC), and optic nerve head were measured before and after wearing both SLs. IOP was measured with a Perkins applanation tonometer before and after lens removal and with a transpalpebral tonometer before, during (0 h, 1 h, and 2 h), and after lens wear.

RESULTS

CCT increased after wearing L1 (8.10 ± 4.21 µm; p < 0.01) and L2 (9.17 ± 4.41 µm; p < 0.01). After L1 removal, the ICA parameters decreased significantly (p < 0.05). With L2 removal, nasal and temporal SC area and length were reduced (p < 0.05). An increased IOP with transpalpebral tonometry was observed at 2 h of wearing L1 (2.55 ± 2.04 mmHg; p < 0.01) and L2 (2.53 ± 2.22 mmHg; p < 0.01), as well as an increased IOP with Perkins applanation tonometry after wearing L1 (0.43 ± 1.07 mmHg; p = 0.02).

CONCLUSIONS

In the short term, SL resulted in a slight increase in IOP in addition to small changes in ICA and SC parameters, although it did not seem to be clinically relevant in healthy subjects.

Anatomical and physiological considerations in scleral lens wear: Intraocular pressure

Intraocular pressure (IOP) is maintained through complex and interrelated systems which control aqueous production and drainage, and it has been suggested that scleral lens (SL) wear may disrupt these vital homeostatic processes. This review provides an overview of anatomical and physiological processes that control IOP, identifies potential effects of SLs on these regulatory mechanisms, and examines studies that have attempted to quantify the effect of SLs on IOP. Lack of access to the cornea during SL wear makes accurate assessment of IOP challenging; therefore, a range of different assessment techniques and instruments have been employed to quantify IOP during and following SL wear. Some studies have evaluated IOP using standard techniques prior to lens application and following lens removal, or through a large central fenestration. Other studies have utilised instruments that facilitate assessment of IOP on the peripheral cornea or conjunctiva overlying the sclera (e.g. Schiotz, transpalpebral, and pneumatonometry). Two studies have recently evaluated changes in optic nerve structure during SL wear. Conflicting results have been reported on this topic, much of which examines changes in IOP in healthy subjects over limited periods of time. Currently, only a few studies have reported on long-term effects of SL wear on IOP in habitual SL wearers (after lens removal). Future research in this area must not only consider the fact that ocular conditions treated with SLs may potentially alter corneal biomechanical properties which can influence IOP, but also that these properties may be further altered by SL wear. Monitoring other risk factors for glaucoma (permanent alterations in optic nerve physiology, visual field defects) could provide a more comprehensive assessment of potentially increased risk of glaucomatous optic neuropathy due to SL wear. Ongoing clinical assessment of optic nerve structure and function is advisable in patients at risk for glaucoma who require SLs.

Tear Exchange, Intraocular Pressure, and Wear Characteristics of Quadrant-specific Versus Spherical Haptic Scleral Lenses

OBJECTIVES

To compare scleral lenses (SLs) with a quadrant-specific (study lens) or a spherical (habitual lens) landing zone in a crossover study.

METHODS

Seven participants (eight eyes) wore each of two lenses for 2 weeks before measurements. We measured visual acuity, contrast sensitivity, intraocular pressure (IOP), fluid reservoir clearance, corneal thickness, tear exchange, and lens experience. Variables were compared between lenses and before and after 2 hr of wear.

RESULTS

The visual acuity was not different between the study lens, 0.12 logarithm of the minimum angle of resolution (logMAR), and habitual lens, 0.18 logMAR (median, P = 1.0). Contrast sensitivity was 1.3% under the study lens and 1.6% under the habitual lens ( P = 0.94). IOP did not change after 2 hr of wear for either lens (study lens, P = 0.33 and habitual lens, P = 0.74), and corneal thickness did not change during wear of either lens ( P = 0.44). The fluorescein concentration under the study lens did not change after 2 hr (99% of initial concentration; P = 0.84) but decreased to 46% of initial concentration under the habitual lens ( P = 0.008). Lens comfort was slightly better with the study lens (5.0 vs. 4.0, respectively; P = 0.05).

CONCLUSIONS

SLs with spherical or quadrant-specific landing zones provide good vision and do not affect IOP or corneal thickness. However, tear exchange is greater under spherical lenses than under quadrant-specific lenses. The quadrant-specific lens provides greater patient comfort.

Corneal Biomechanics and Intraocular Pressure Following Scleral Lens Wear in Penetrating Keratoplasty and Keratoconus

OBJECTIVE

To compare corneal biomechanics and intraocular pressure (IOP) in keratoconus and penetrating keratoplasty eyes before and after nonfenestrated scleral lens wear.

METHODS

Twenty-three participants were enrolled, and 37 eyes were included in the analysis (11 penetrating keratoplasty and 26 keratoconus). A range of corneal biomechanical parameters and IOP were measured using the CORVIS ST before and after 8 hr of nonfenestrated scleral lens wear (Keracare, Acculens, Denver, CO).

RESULTS

Before lens wear, penetrating keratoplasty eyes displayed significantly greater median values for central corneal thickness (97 μm thicker, P=0.02), IOP (3.89 mm Hg higher, P=0.01), and biomechanical parameter A2 length (0.48 mm longer, P=0.003) compared with keratoconic eyes. No significant changes in corneal biomechanical parameters or IOP were observed after scleral lens wear in either group (all P>0.05).

CONCLUSION

Although nonfenestrated scleral contact lenses can induce a subatmospheric pressure after lens settling and compress tissue surrounding the limbus, no significant changes were detected in the corneal biomechanical parameters studied using CORVIS ST after scleral lens wear in eyes with penetrating keratoplasty and keratoconus.

How Can We Best Measure the Performance of Scleral Lenses? Current Insights

Scleral lenses (SLs) present several unique advantageous characteristics for patients. As these lenses are mainly fitted in severely diseased eyes, a thorough evaluation of the ocular surface before and after SL fitting and the on-eye SL fitting evaluation are essential and help minimize potential physiological complications. This review will explore the current and emerging techniques and instrumentation to best measure SL performance ensuring optimal lens fitting, visual quality, comfort and physiological responses, highlighting some potential complications and follow-up recommendations. A single physician could perform the great majority of evaluations. Still, the authors consider that the assessment of SL fitting should be a collaborative and multidisciplinary job, involving contact lens practitioners, ophthalmologists and the industry. This publication has reviewed the most up-to-date work and listed the most used techniques; however, the authors encourage the development of more evidence-based recommendations for SL clinical practice.

Keratoconus: An updated review

Keratoconus is a bilateral and asymmetric disease which results in progressive thinning and steeping of the cornea leading to irregular astigmatism and decreased visual acuity. Traditionally, the condition has been described as a noninflammatory disease; however, more recently it has been associated with ocular inflammation. Keratoconus normally develops in the second and third decades of life and progresses until the fourth decade. The condition affects all ethnicities and both sexes. The prevalence and incidence rates of keratoconus have been estimated to be between 0.2 and 4,790 per 100,000 persons and 1.5 and 25 cases per 100,000 persons/year, respectively, with highest rates typically occurring in 20- to 30-year-olds and Middle Eastern and Asian ethnicities. Progressive stromal thinning, rupture of the anterior limiting membrane, and subsequent ectasia of the central/paracentral cornea are the most commonly observed histopathological findings. A family history of keratoconus, eye rubbing, eczema, asthma, and allergy are risk factors for developing keratoconus. Detecting keratoconus in its earliest stages remains a challenge. Corneal topography is the primary diagnostic tool for keratoconus detection. In incipient cases, however, the use of a single parameter to diagnose keratoconus is insufficient, and in addition to corneal topography, corneal pachymetry and higher order aberration data are now commonly used. Keratoconus severity and progression may be classified based on morphological features and disease evolution, ocular signs, and index-based systems. Keratoconus treatment varies depending on disease severity and progression. Mild cases are typically treated with spectacles, moderate cases with contact lenses, while severe cases that cannot be managed with scleral contact lenses may require corneal surgery. Mild to moderate cases of progressive keratoconus may also be treated surgically, most commonly with corneal cross-linking. This article provides an updated review on the definition, epidemiology, histopathology, aetiology and pathogenesis, clinical features, detection, classification, and management and treatment strategies for keratoconus.

OCT applications in contact lens fitting

Optical Coherence Tomography (OCT) is a noninvasive, high-speed, high-resolution imaging technology based in the Michaelson interferometry. A near-infrared light beam is used to register the intensity variations for the light backscattered on each sample layer. Due to the high repeatability on corneal measurements, spectral domain OCT (SD-OCT) is the gold standard when talking about in vivo, non-invasive anterior segment imaging. Changes in the morphology of various ocular surfaces such as the cornea, conjunctiva, limbus or tear film with soft (SCL), rigid, corneal or scleral lens (SL) wear can be described by OCT measurements. For instance, evaluation of the corneoscleral region is essential on SL fitting. For orthokeratology lenses central epithelial thinning and peripheral thickening and their regression could be quantified with OCT after Ortho-K lens wear. Blood vessel compression on the landing zone as well as vault thickness and fluid reservoir (FR) turbidity could be imaged with OCT. Tear film evaluation on contact lens wearers is essential because its use could lead to variations on the biochemical components in tears. Changes in tear meniscus dynamics and several parameters such as volume (TMV), tear meniscus height (HMT) and turbidity could be determined with OCT and positively correlated with the instillation of different ophthalmic solutions with Non-Invasive Break Up Time (NIBUT) and Schirmer test values. This manuscript shows the increasing applicability of OCT technology for the in vivo characterization of contact lens fitting and interaction with the ocular surface in a faster, safer and non-invasive way. Future research will still allow exploring OCT imaging to its full potential in contact lens practice, as there is still a significant amount of information contained in the images that are not yet easy to extract, analyze and give clinical value.

Comparison of Pneumatonometry and Transpalpebral Tonometry Measurements of Intraocular Pressure during Scleral Lens Wear

SIGNIFICANCE

As scleral lens wear becomes more common, understanding the impact of these lenses upon ocular physiology is critically important. Studies on the effect of scleral lens wear upon intraocular pressure (IOP) have used different instruments and have reported conflicting results.

PURPOSE

The purpose of this study was to compare assessment of IOP during scleral lens wear using pneumatonometry and transpalpebral tonometry.

METHODS

Twenty healthy subjects wore a small-diameter (15.2 mm) and a large-diameter (18.0 mm) scleral lens on the right eye, each for 1 hour in randomized order. IOP was assessed with pneumatonometry and transpalpebral tonometry on both eyes before lens application, immediately after lens application, after 1 hour of lens wear, and immediately after lens removal. Paired t test compared mean IOP in the study eye to the control eye. Repeated-measures ANOVA was performed to take instrumentation, lens diameter, and their interaction into account in an analysis of the change in IOP in the study eye.

RESULTS

Mean peripheral IOP measured with pneumatonometry was not significantly different from baseline at any subsequent measurement. Measurements with transpalpebral tonometry, however, were significantly different during scleral lens wear immediately after application and after 1 hour of wear with both diameter lenses (P < .005), but were not significantly different after either sized lens was removed. Repeated-measures ANOVA revealed that the instrument used to measure IOP was a significant factor in IOP changes found during lens wear (P ≤ .001).

CONCLUSIONS

Assessment of IOP during scleral lens wear varies based upon the instrument that is used. Although further studies are clearly needed to further elucidate this issue, clinicians should continue to monitor optic nerve structure and function in scleral lens wearers, as they do in all patients.

Fluid Reservoir Thickness and Corneal Edema during Open-eye Scleral Lens Wear

SIGNIFICANCE

There is debate concerning corneal oxygenation during scleral lens wear due to the potential additive hypoxic effect of a lens plus a fluid reservoir. This study investigated the agreement between theoretical models and empirical measurements of scleral lens-induced corneal edema with respect to central fluid reservoir thickness.

PURPOSE

The purpose of this study was to examine the effect of altering the fluid reservoir thickness on central corneal edema during short-term open-eye scleral lens wear and to compare these empirical measurements with predictive theoretical models.

METHODS

Ten participants (age, 30 ± 4 years) with normal corneas wore highly oxygen-permeable scleral lenses (141 Dk ×10 cm O2 (cm)/[(s) (cm) (mmHg)]) on separate days with either a low (mean, 144; 95% confidence interval [CI], 127 to 160 μm), medium (mean, 487; 95% CI, 443 to 532 μm), or high (mean, 726; 95% CI, 687 to 766 μm) initial fluid reservoir thickness. Epithelial, stromal, and total corneal edema were measured using high-resolution optical coherence tomography after 90 minutes of wear, before lens removal. Data were calculated or extracted from published theoretical models of scleral lens-induced corneal edema for comparison.

RESULTS

Scleral lens-induced central corneal edema was stromal in nature and increased with increasing fluid reservoir thickness; mean total corneal edema was 0.69% (95% CI, 0.34 to 1.04%), 1.81% (95% CI, 1.22 to 2.40%), and 2.11% (95% CI, 1.58 to 2.65%) for the low, medium, and high thickness groups, respectively. No significant difference in corneal edema was observed between the medium and high fluid reservoir thickness groups (P = .37). "Resistance in series" oxygen modeling overestimated the corneal edema observed for fluid reservoir thickness values greater than 400 μm.

CONCLUSIONS

Scleral lens-induced central corneal edema increases with increasing reservoir thickness, but plateaus at a thickness of around 600 μm, in agreement with recent theoretical modeling that incorporates factors related to corneal metabolism.

Corneoscleral Topography Measured with Fourier-based Profilometry and Scheimpflug Imaging

SIGNIFICANCE

Precise measurement of corneoscleral topography makes a valuable contribution to the understanding of anterior eye anatomy and supports the fitting process of contact lenses. Sagittal height data, determined by newer noninvasive techniques, are particularly useful for initial scleral lens selection.

PURPOSE

The purpose of this study was to investigate the agreement and repeatability of Fourier-based profilometry and Scheimpflug imaging, in the measurement of sagittal height and toricity of the corneoscleral region.

METHODS

Minimal (Minsag), maximal (Maxsag) sagittal height, toricity (Maxsag - Minsag), and the maximum possible measurement zone diameter of 38 subjects were compared using the Eye Surface Profiler (ESP; Eagle Eye, Houten, the Netherlands) and the corneoscleral profile module of the Pentacam (Oculus, Wetzlar, Germany) at two different sessions. Correlations between the instruments were analyzed using the Pearson coefficient. Differences between sessions and instruments were analyzed using Bland-Altman and paired t tests.

RESULTS

For an equal chord length, the measurement with Pentacam was significantly greater for Minsag (344 μm; 95% confidence interval [CI], 322 to 364 μm; P < .001) and significantly greater for Maxsag (280 μm; 95% CI, 256 to 305 μm; P < .001), but significantly smaller for toricity (-63 μm; 95% CI, -95 to -31 μm; P < .001). Maximum possible measurement zone diameter with ESP (16.4 ± 1.3 mm) was significantly greater than with Pentacam (14.8 ± 1.1 mm) (P < .001). Repeated measurements from session 1 and session 2 were not significantly different for Pentacam and ESP (P = .74 and P = .64, respectively). The 95% CIs around differences indicate good repeatability for Pentacam (mean difference, -0.9 μm; 95% CI, -6.7 to 4.8 μm) and ESP (4.6 μm; -22.4 to 31.6).

CONCLUSIONS

Although both instruments deliver useful data especially for the fitting of scleral and soft contact lenses, the sagittal height and the toricity measurements cannot be considered as interchangeable.

IOP and Optic Nerve Head Morphology during Scleral Lens Wear

SIGNIFICANCE

Scleral lenses (SLs) are increasing in scope, and understanding their ocular health impact is imperative. The unique fit of an SL raises concern that the landing zone causes compression of conjunctival tissue that can lead to resistance of aqueous humor outflow and increased intraocular pressure (IOP).

PURPOSE

This study aimed to assess changes in optic nerve head morphology as an indirect assessment of IOP and evaluate other IOP assessment methods during SL wear.

METHODS

Twenty-six healthy adults wore SL on one randomly selected eye for 6 hours, whereas the fellow eye served as a control. Global minimum rim width (optical coherence tomography) and IOP (Icare, Diaton) were measured at baseline, 2 and 6 hours after SL application, and again after SL removal. Central corneal thickness, anterior chamber depth, and fluid reservoir depth were monitored.

RESULTS

Minimum rim width thinning was observed in the test (-8 μm; 95% confidence interval [CI], -11 to -6 μm) and control (-6 μm; 95% CI, -9 to -3 μm) eyes after 6 hours of SL wear (P < .01), although the magnitude of thinning was not significantly greater in the lens-wearing eyes (P = .09). Mean IOP (Icare) significantly increased +2 mmHg (95% CI, +1 to +3 mmHg) in the test eyes (P = .002), with no change in the control eyes. Mean IOP changes with Diaton were +0.3 mmHg (95% CI, -0.9 to +3.2 mmHg) in the test eyes and +0.4 mmHg (95% CI, -0.8 to +1.7 mmHg) in the control eyes. However, Diaton tonometry showed poor within-subject variation and poor correlation with Icare. No clinically significant changes were observed in central corneal thickness or anterior chamber depth.

CONCLUSIONS

This study suggests that SLs have a minimal effect on IOP homeostasis in the normal eye during SL wear and an insignificant impact on the optic nerve head morphology in healthy adult eyes.

CLEAR - Scleral lenses

Scleral lenses were the first type of contact lens, developed in the late nineteenth century to restore vision and protect the ocular surface. With the advent of rigid corneal lenses in the middle of the twentieth century and soft lenses in the 1970's, the use of scleral lenses diminished; in recent times there has been a resurgence in their use driven by advances in manufacturing and ocular imaging technology. Scleral lenses are often the only viable form of contact lens wear across a range of clinical indications and can potentially delay the need for corneal surgery. This report provides a brief historical review of scleral lenses and a detailed account of contemporary scleral lens practice including common indications and recommended terminology. Recent research on ocular surface shape is presented, in addition to a comprehensive account of modern scleral lens fitting and on-eye evaluation. A range of optical and physiological challenges associated with scleral lenses are presented, including options for the clinical management of a range of ocular conditions. Future applications which take advantage of the stability of scleral lenses are also discussed. In summary, this report presents evidence-based recommendations to optimise patient outcomes in modern scleral lens practice.

Anatomical and physiological considerations in scleral lens wear: Eyelids and tear film

Scleral lenses can affect a range of anterior segment structures including the eyelids and the tears. The eyelids, consisting of the outer skin layer, the middle tarsal plate, and the posterior palpebral conjunctiva, provide physical protection and house the meibomian glands and cilia which have important and unique functions. Tears consist of a mix of aqueous, mucus, and lipidomic components that serve vital functions of lubricity, protection, and nourishment to the ocular surface. Both the eyelids and the tear film interact directly with scleral lenses on the eye and can affect but also be impacted by scleral lens wear. The purpose of this paper is to review the anatomy and physiology of the eyelids and tear film, discuss the effects and impacts of the scleral lenses on these structures, and identify areas that require further research.

[Intraocular pressure with miniscleral contact lenses]

According to literature data, some experts do not exclude the possibility that scleral lens wear could influence intraocular pressure.

PURPOSE

To evaluate the influence of rigid gas permeable miniscleral contact lenses on intraocular pressure (IOP), keratometry readings and corneal thickness, and to study the correlation between scleral (IOPs) and corneal (IOPc) intraocular pressure using the Icare ic100 tonometer (model TAO11, Icare Finland Oy).

MATERIAL AND METHODS

The study included 99 volunteers without history of ocular diseases. The first group consisted of 66 participants (122 eyes) aged 22.3±2.2 years - IOPc and IOPs were measured by the Icare ic100 tonometer in order to determine the correlation. The second group (33 participants, aged 22.7±1.7 years) - day 1, diurnal IOPc and IOPs fluctuations were measured; on day 2, a miniscleral lens (diameter 14.9 mm) was placed on the study eye and was worn for 6 hours, the paired eye served as control. IOP was measured before, after lens placement, after 2 hours of lens wear, and before and after lens removal. Corneal topography was evaluated before and after lens removal.

RESULTS

In the first group, there was a weak but significant correlation between IOPc and IOPs (Spearman correlation coefficient 0.285, p=0.001). In the second group, IOPc in the study eye before lens placement (14.8±3.8 mm Hg) and IOPc after its removal (13.6±3.9 mm Hg) were not different from those in the control eye. There were also no statistically significant changes in IOPs before, during lens wear, and after lens removal. The central corneal thickness increased by 2.9% (p<0.001) after 6 hours of lens wear.

CONCLUSION

In young individuals without history of ocular diseases, wearing the miniscleral lens for 6 hours does not have significant influence on IOP and does not cause clinically significant corneal edema.

Multicenter review of impression-based scleral devices

OBJECTIVE

To describe outcomes using impression based-scleral devices for the management of anterior segment disease.

METHODS

Retrospective chart review identified all patients who were fitted with impression-based scleral devices between January 1, 2013 and June 30, 2019 at three specialty contact lens practices. Patient demographic data, indication for device use, visual and physiological outcomes, as well as details of the fitting process and survival of device use were determined.

RESULTS

Forty-four patients (70 eyes) were included in the study. Primary indications for device use included corneal irregularity (28 patients, 44 eyes) and ocular surface disease (16 patients, 26 eyes). Fifty-four percent of patients had more than one ocular surface condition, and 39 % of patients had undergone at least one anterior segment surgical procedure. Twenty-nine patients had unsuccessfully attempted to wear standard scleral lenses prior to being fit with impression-based devices. Visual acuity improved significantly with impression-based devices compared to habitual correction (p < 0.001). Completion of the fitting process (including visit to acquire the impression and post-fitting assessments) required an average of 4 [1.5] visits.Ideal haptic alignment was achieved with 74 % and complete limbal clearance was achieved in 83 % of fits. Device use was discontinued due to complications in two eyes.

CONCLUSION

Patients with complex eye disease who are unable to successfully wear standard scleral lenses successfully may achieve visual and therapeutic success with impression-based devices.

Anterior Scleral Regional Variation between Asian and Caucasian Populations

Purpose: To evaluate the anterior scleral shape regional differences between Asian and Caucasian populations. Methods: The study included 250 Asian eyes and 235 Caucasian eyes from participants aged 22 to 67 years (38.5 ± 7.6). Three-dimensional (3D) corneo-scleral maps were acquired using a corneo-scleral topographer (Eye Surface Profiler, Eaglet Eye BV) and used to calculate sagittal height. For each 3D map, the sclera (maximum diameter of 18 mm) and cornea were separated at the limbus using an automated technique. Advanced data processing steps were applied to ensure levelled artefact-free datasets to build an average scleral shape map for each population. Results: Statistically, Asian and Caucasian sclerae are significantly different from each other in sagittal height (overall sclera, p = 0.001). The largest difference in sagittal height between groups was found in the inferior-temporal region (271 ± 203 µm, p = 0.03), whereas the smallest difference was found in the superior-temporal region (84 ± 105 µm, p = 0.17). The difference in sagittal height between Caucasian and Asian sclera increases with the distance from the limbus. Conclusions: Asian anterior sclera was found to be less elevated than Caucasian anterior sclera. However, the nasal area of the sclera is less elevated than the temporal area, independently of race. Gaining knowledge in race-related scleral topography differences could assist contact lens manufacturers in the process of lens design and practitioners during the process of contact lens fitting.

Corneal tissue properties following scleral lens wear using Scheimpflug imaging

Purpose

To investigate the effect of short‐term scleral lens wear on the corneal stroma at a macroscopic (thickness) and microscopic (within tissue) level, including regional variations.

Methods

Fourteen young, healthy participants wore a rotationally symmetric, 16.5 mm diameter, scleral lens for 8 h. Scheimpflug images were captured before, and immediately after, lens wear, and also on a second day (without lens wear) to quantify natural corneal diurnal variations. After corneal segmentation, pixel intensities of the stromal tissue were statistically modelled using a Weibull probability density function from which parameters α and β were derived.

Results

Both α and β parameters increased significantly following scleral lens wear (by 5.7 ± 10% and 6.5 ± 6.5%, respectively, both p < 0.01). Corneal thickness also increased slightly following lens wear (mean increase 0.49 ± 1.77%, p = 0.01); however, the change in α and β parameters did not correlate with the magnitude of corneal swelling. On the control day, small but significant corneal thinning was observed (−0.82 ± 1.1%, p = 0.03), while α and β parameters remained stable. Both microparameters varied significantly across the cornea, with α decreasing (−15.4 ± 0.7%) and β increasing towards the periphery (+4.4 ± 2.6%) (both p < 0.001).

Conclusion

Corneal microparameters α and β varied regionally across the cornea and displayed a statistically significant increase following short‐term scleral lens wear, but remained stable between morning and evening measurements taken during a control day without lens wear. These corneal microparameters may be a useful metric to quantify subclinical corneal changes associated with low level hypoxia.

Anatomical and physiological considerations in scleral lens wear: Conjunctiva and sclera

While scleral lenses have been fitted using diagnostic lenses or impression moulding techniques for over a century, recent advances in anterior segment imaging such as optical coherence tomography and corneo-scleral profilometry have significantly improved the current understanding of the anatomy of the anterior eye including the morphometry of the conjunctiva, sclera, and corneo-scleral junction, as well as the ocular surface shape and elevation. These technological advances in ocular imaging along with continual improvements and innovations in scleral lens design and manufacturing have led to a global increase in scleral lens prescribing. This review provides a comprehensive overview of the conjunctiva and sclera in the context of modern scleral lens practice, including anatomical variations in healthy and diseased eyes, the physiological impact of scleral lens wear, potential fitting challenges, and current approaches to lens modifications in order to minimise lens-induced complications and adverse ocular effects. Specific topics requiring further research are also discussed.

Scleral lens wear following penetrating keratoplasty: changes in corneal curvature and optics

PURPOSE

Visual rehabilitation following penetrating keratoplasty is the primary indication for approximately 15% of all scleral lens fittings. Since corneal biomechanics are altered following penetrating keratoplasty, the aim of this study was to quantify changes in anterior corneal optics following short-term scleral lens wear in eyes with corneal grafts.

METHODS

Scheimpflug images were obtained before and after a period of scleral lens wear (mean 6.3 ± 1.4 h), from eyes that had previously undergone penetrating keratoplasty (10 eyes of nine participants, mean age 31 ± 9 years). Corneal power and thickness data were examined over the central 6 mm, including regional analyses of the central (0-3 mm) and the mid-peripheral cornea (3-6 mm annulus) using customised software to deterime corneal power vectors M (best fit sphere), J₀ (90/180 astigmatism) and J₄₅ (45/135 astigmatism). Anterior corneal aberrations were extracted using corneal elevation data.

RESULTS

Corneal power vector J₄₅ increased following lens wear (by 0.22 ± 0.05 D, p = 0.003) across the central 6 mm, while M displayed regional variations following lens wear indicating larger changes further from the corneal centre (p = 0.004). The change in corneal power vector M was also correlated with the magnitude of central corneal swelling (r = 0.65, p = 0.04). The anterior corneal aberration terms of oblique astigmatism, hoirzontal coma, and spherical aberration also varied following lens wear (all p ≤ 0.01). The mean change in the corneal spherocylinder derived from the elevation data following lens wear was +0.14/-0.54 × 44 for a 6 mm corneal diameter.

CONCLUSIONS

Clinically significant alterations in anterior corneal topography and higher order aberrations were observed following short-term scleral lens wear in eyes that had undergone penetrating keratoplasty. Spherocylindrical changes were approximately double the magnitude and more oblique in orientation compared to previous reports of healthy eyes. Changes in corneal power vector M may be related to epithelial corneal oedema.

The impact of short-term fenestrated scleral lens wear on intraocular pressure

PURPOSE

To examine the influence of short-term fenestrated scleral lens wear on intraocular pressure (IOP) in healthy eyes.

METHODS

IOP was measured before, during, and after a brief period (1-2 min) of fenestrated, scleral lens wear, using a rebound tonometer, in fifty, young healthy adults (mean age 23 ± 4 years) with normal corneas.

RESULTS

Immediately following lens insertion, 48 of the 50 (96 %) of participants displayed an increase in IOP (mean ± SD increase in these participants of 3.8 ± 2.0 mmHg). Immediately following lens removal, 50 % of participants displayed a reduction in IOP, equal to or lower than, the pre-insertion IOP (-1.0 ± 0.8 mmHg lower than baseline). The remaining 50 % of participants displayed an IOP slightly greater than the pre-insertion IOP (1.6 ± 1.0 mmHg greater) after lens removal.

CONCLUSIONS

Short-term fenestrated scleral lens wear resulted in a small, but statistically significant, increase in IOP in 96 % of young healthy participants (< 4 mmHg on average), which decreased to a level similar to pre-lens insertion IOP levels immediately following lens removal. Further research is required to determine if this measured change in IOP during scleral lens wear is artefactual, or an elevation in the true IOP.

Anterior segment optical coherence tomography scanning protocols and corneal thickness repeatability

PURPOSE

To examine the influence of anterior segment optical coherence tomography imaging protocols on the intraobserver and intrasession repeatability of epithelial, stromal, and total corneal thickness measurements.

METHODS

Repeated anterior segment optical coherence tomography (AS-OCT) images (Spectralis, Heidelberg) were obtained from 15 adults using single 8.3 mm wide horizontal line scans with an average of 2, 10, 20, 30, 50 and 100 B-scans. Volumetric scans consisting of nine 8.3 mm horizontal line scans encompassing a 1.3 mm vertical region were also captured (with 20 B-scans per line scan). Single point thickness measures (at the normal to the tangent of the anterior corneal surface) were compared with thickness measures averaged over the central 6 mm. The impact of B-scan averaging and intraobserver variability were examined for single line scans. For volumetric scans, the impact of the number of line scans upon intraobserver and intrasession variability were calculated.

RESULTS

Intraobserver repeatability did not vary significantly as a function of the number of averaged B-scans per line scan, but was lowest for 20-30 averaged B scans. For volumetric scans, increasing the number of line scans did increase scan duration (p < 0.001), with minimal impact upon the average scan quality index (p = 0.06). Averaging more than 3 line scans did not significantly improve intraobserver or intrasession repeatability for either single point or average thickness measurements.

CONCLUSION

AS-OCT volumetric scans with 3 lines each consisting of 20 B-scans with measurements averaged over a central 6 mm of the cornea provide highly repeatable measures of epithelial, stromal and total corneal thickness (95 % LoA ≤ ±3.2 μm for intraobserver repeatability and ≤ ±3.7 μm for intrasession repeatability). This scanning protocol can provide reliable information when monitoring subtle changes in corneal thickness.

In vivo assessment of the anterior scleral contour assisted by automatic profilometry and changes in conjunctival shape after miniscleral contact lens fitting

PURPOSE

To compare the shape of the anterior sclera of candidates to scleral lens (ScCL) fitting with regular and irregular corneas and analyze the changes induced in the shape of the sclero-conjunctiva after ScCL wear.

METHODS

Thirty-five eyes of 18 subjects (19 eyes with irregular corneas and 16 with regular corneas) were consecutively recruited. Three measures of sclero-conjunctival shape were taken with Eye Surface Profiler (ESP, Eaglet Eye, Houten, The Netherlands). Tangent angles and ocular sagittal heights (OC-SAG) were analyzed at different chords from 13 to 17mm in the nasal, temporal, superior and inferior regions. The 19 eyes with irregular cornea were selected to wear ScCL and the changes in their sclero-conjunctival surface parameters were compared before and after 3h of lens wear.

RESULTS

Irregular corneas showed higher OC-SAG values than regular corneas in all the chords analyzed, with statistical significant differences in the temporal region. Regarding tangent angles, regular corneas showed lower values (flatter surface), with statistical significant differences at 8 and 8.50mm on the nasal and 8.50mm on the temporal region. Some changes were seen in sclero-conjuctival shape after short-term ScCL wear. There was an augment in OC-SAG after 3h of scleral lens wear and a reduction on tangent angles, namely on the nasal region at 7.5mm and 8.00mm chord lengths, which is coincidental with the landing zone of ScCL.

CONCLUSIONS

ESP shows mild differences in scleral shape between eyes with regular and irregular corneas. ESP might be valuable in quantifying the mechanical impact of the ScCL on the anterior eye surface.

Optical coherence tomography and scleral contact lenses: clinical and research applications

Anterior segment optical coherence tomography (OCT) provides a wealth of opportunities for modern contact lens practice. OCT imaging has numerous clinical and research applications related to the tear film, cornea, conjunctiva, sclera and ocular adnexae, in addition to soft, rigid, and hybrid contact lenses. This review summarises the potential use of OCT imaging in modern scleral contact lens practice including initial lens selection, assessing the scleral contact lens fit with respect to the cornea and sclera, and accurately quantifying the ocular response to lens wear. Recent advances in the understanding of anterior segment metrics including scleral thickness, curvature, toricity, and the anatomy of the corneoscleral limbal junction are also discussed.

Intra-ocular pressure variation associated with the wear of scleral lenses of different diameters

PURPOSE

To evaluate the variation of intra-ocular pressure during scleral lens wear, and the influence of the lens diameter on the results.

METHODS

This is a prospective, randomized study performed on Caucasian subjects (16 F; 5 M), aged 24.7 + 4.1 y.o. A diurnal variation pattern (IOPg) was established, then, transpalpebral IOP (IOPt) was taken before and during SL wear. One eye, randomly fitted with a 15.8 diameter SL (L1), was compared to the fellow eye, fitted with an 18 mm SL of the same design, thickness and material (L2). Anterior segment tomography was taken pre-and after lens removal.

RESULTS

Baseline IOPg (L1:15.2 + 3.1 mm HG; L2: 15.1 +/- 2.8 mm) did not reveal significant diurnal variations. Wearing L1, IOPt rose from 10.1 + 1.9 mm HG to 14.4 + 5.5 mm HG after 4.5 + 0.3 hrs, while with L2, it rose from 9.2 + 2.1 mm HG to 14.4 + 4.8 mm Hg. This difference is statistically significant based on time but not on lenses. Anterior segment parameters did not vary except for the anterior chamber volume (L1: -1.53 + 7.61 mm³; L2: -3.47 + 6.4 mm³), and for the corneal thickness (+2.1% with L1 and L2).

CONCLUSION

These results suggest that, as evaluated with a non-standard transpalpebral methodology, IOP during scleral lens wear may be increased in average by 5 mm Hg, regardless of the lens diameter. More work is needed to confirm if practitioners should be warned when using SL on populations at risk for glaucoma.

The time course and nature of corneal oedema during sealed miniscleral contact lens wear

PURPOSE

To examine the magnitude and time course of central epithelial, stromal and total corneal thickness changes during sealed miniscleral contact lens wear and the influence of initial central corneal clearance upon these thickness changes.

METHODS

High-resolution OCT images were captured over an 8 h period of miniscleral contact lens wear (using a rotationally symmetric 16.5 mm diameter lens) in 15 young, healthy participants with normal corneae. Corneal thickness data were derived from OCT images using semi-automated image processing techniques over the central 4 mm.

RESULTS

Changes in stromal and total corneal thickness followed a similar pattern throughout lens wear with oedema first detected 15 min after lens insertion (0.47 ± 0.09% increase in stromal and total corneal thickness, both p < 0.01) which peaked after 90 min of lens wear (1.36 ± 0.24% increase in stromal and 1.18 ± 0.20% increase in total corneal thickness, both p < 0.01) and gradually decreased thereafter. Epithelial thickness increased slightly during the first 30 min of lens wear (0.56 ± 0.30% increase, p > 0.05), then rapidly decreased reaching a minimum thickness 480 min after lens insertion (2.38 ± 0.70% decrease, p < 0.05). The maximum total corneal oedema, maximum stromal oedema, and maximum epithelial thinning were not associated with the initial central corneal clearance or the extent of lens settling over the 8 h period (all p > 0.05). Greater initial central corneal clearance resulted in less oxygen concentration reaching the cornea (∼2% less) based on previously published data, which manifested as ∼0.5% more central corneal oedema.

CONCLUSIONS

Scleral lens induced corneal oedema is stromal in nature. On average, central stromal and total corneal thickness increased rapidly following lens insertion and peaked after 90 min, while central epithelial thickness gradually decreased throughout lens wear consistent with natural diurnal variation. A greater initial central corneal clearance resulted in reduced oxygen delivery to the cornea, which had minimal short-term impact upon healthy eyes, however, minimising central corneal clearance may be important in eyes with reduced endothelial cell function to minimise hypoxic stress.

Comparison of the influence of corneo-scleral and scleral lenses on ocular surface and tear film metrics in a presbyopic population

PURPOSE

To assess and compare the effect of the corneo-scleral lenses (C-ScL) and scleral lenses (ScL) on tear film parameters and central corneal thickness (CCT) in healthy presbyopic subjects.

METHODS

Thirty subjects wore two contact lenses (CLs), randomly assigned, of neutral power, but of different diameters, 12.7mm (C-ScL) and 18mm (ScL) and being equal in the others parameters: material (HS100) and centre thickness (0.29mm). At baseline, 20min after insertion and at 8h, the tear meniscus area (TMA) and CCT was measured (with optical coherence tomography) as well as tear osmolarity.

RESULTS

TMA revealed statistical differences for both lenses at 20min (p<0.001), and also at 8h (p=0.003), being greater for the C-ScL. CCT showed statistical differences for both lenses at 20min (p=0.002), and also at 8h (p=0.001), being lower for the C-ScL. Osmolarity did not reveal statistical differences at 20min (p=0.29), while it was statistically different at 8h (p=0.03), being lower for the C-ScL.

CONCLUSIONS

C-ScL lead to a lesser reduction in the TMA and a lower induced hypoxic stress than the ScL. Osmolarity levels remained within normal values across the day with no clinical difference between lenses. Both designs can represent a good optical platform for correcting presbyopia as well as protecting the ocular surface by vaulting the cornea.