The effect of landing zone toricity on scleral lens fitting characteristics and optics.

PURPOSE: The fit and optical performance of a scleral lens is affected by the alignment of the landing zone with the underlying ocular surface. The aim of this research was to quantify the effect of landing zone toricity upon scleral lens fitting characteristics (rotation and decentration) and optics (lens flexure) during short-term wear. METHODS: Scleral lenses with nominal landing zone toricities of 0, 100, 150 and 200 µm were worn in a randomised order by 10 young healthy participants (mean [SD] 24 [7] years) for 30 min, with other lens parameters held constant. Scleral toricity was quantified using a corneo-scleral profilometer, and lens flexure, rotation, and decentration were quantified using over-topography during lens wear. Repeated measures analyses were conducted as a function of landing zone toricity and residual scleral toricity (the difference between scleral and lens toricity) for eyes with 'low' magnitude scleral toricity (mean: 96 µm) and 'high' magnitude scleral toricity (mean: 319 µm). RESULTS: Toric landing zones significantly reduced lens flexure (by 0.37 [0.21] D, p < 0.05) and lens rotation (by 20 [24]°, p < 0.05) compared with a spherical landing zone. Horizontal and vertical lens decentration did not vary significantly with landing zone toricity. These trends for flexure, rotation, and decentration were also observed for eyes with 'low' and 'high' magnitude scleral toricity as a function of residual scleral toricity. CONCLUSION: Landing zones with 100-200 µm toricity significantly reduced lens flexure (by ~62%) and rotation (by ~77%) but not horizontal or vertical lens decentration, compared with a spherical landing zone, when controlling for other confounding variables. The incorporation of a toric landing zone, even for eyes with lower magnitude scleral toricity (~100 µm), may be beneficial, particularly for front surface optical designs.

George K. Smelser (1908-1973): Atmospheric oxygen and the corneal response to contact lens wear.

Professor George Smelser was a scientist who played a crucial role in advancing the understanding of the anatomical and physiological changes within the cornea during contact lens wear. In a series of unique experiments conducted in the early 1950s, using both humans and animal models, his research team provided the first conclusive evidence that contact lenses impaired the delivery of atmospheric oxygen to the cornea, resulting in an excess of lactate within the cornea and a subsequent ingress of water, leading to corneal oedema and disturbed vision (Sattler's veil). This historical note reviews the career of George Smelser, with particular emphasis on his contributions to understanding the importance of atmospheric oxygen in maintaining corneal homeostasis.

Characteristics of corneal microcysts in Hong Kong children wearing orthokeratology.

PURPOSE: To report the characteristics (prevalence, severity, and location) of corneal epithelial microcysts and investigate associated risk factors in children wearing orthokeratology (ortho-k) lenses. METHOD: Ninety-five myopic children wearing ortho-k lenses (examined by one of three independent investigators from March to September 2020) were included in this retrospective cross-sectional study. Pertinent data at baseline before ortho-k treatment and at the aftercare visits (the first visit when the microcysts were observed for children with microcysts, and the last visit before October 2020 for children without microcysts) were retrieved and analysed. RESULTS: A microcystic response was observed in 52.6% of children wearing ortho-k lenses. Children with high myopia (≥ 5.00 D) had a higher prevalence (100.0%, 23/23) and severity (69.5% (16/23) > grade 2 Efron scale) compared to children with low myopia (≤ 4.00 D) (prevalence of 37.5% (27/72) and 7.0% (5/72) > grade 2, p < 0.001). Microcysts were predominantly (86.0%) observed in the region of the inferior pigmented arc, typically originating in the inferior mid-peripheral cornea, and expanding over time into a semi- or whole annulus. Baseline myopia and topographical change at the treatment zone centre were significantly greater (p < 0.05) in low myopic children with microcysts (univariate analyses). CONCLUSIONS: During the COVID-19 pandemic, probably due to lifestyle changes, microcysts were frequently observed in children wearing ortho-k lenses and were associated with higher baseline myopia. Practitioners should examine ortho-k wearers with caution using a slit lamp with high magnification and illumination, especially the mid-peripheral cornea. The use of highly oxygen permeable lenses and frequent aftercare are necessary for ortho-k wearers, especially those with higher myopia.

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.

Optical changes and association with axial elongation in children wearing orthokeratology lenses of different back optic zone diameter.

PURPOSE: To compare changes in ocular aberrations in children wearing orthokeratology (ortho-k) lenses with a back optic zone diameter (BOZD) of 6 mm (6-MM group) or 5 mm (5-MM group) and their associations with axial elongation (AE) over two years. METHODS: Seventy Chinese children, aged 6 to < 11 years, with myopia between - 4.00 to - 0.75 D, were randomly allocated to 5-MM and 6-MM groups. Ocular aberrations were measured, rescaled to a 4-mm pupil, and fitted with a 6th order Zernike expansion. Measurements, including axial length, were taken prior to commencing ortho-k treatment and then every six months over two years. RESULTS: After two years, the 5-MM group displayed a smaller horizontal treatment zone (TZ) diameter (by 1.14 ± 0.11 mm, P < 0.001) and less AE (by 0.22 ± 0.07 mm, P = 0.002) compared with the 6-MM group. A greater increase in total root mean square (RMS) of higher-order aberrations (HOAs), primary spherical aberration (SA) ([Formula: see text], and coma were also observed in the 5-MM group at all follow-up visits. The horizontal TZ diameter was significantly associated with changes in RMS HOAs, SA (RMS, primary and secondary SA), and RMS coma. After controlling for baseline parameters, RMS HOAs, RMS SA, RMS coma, and primary ([Formula: see text] and secondary ([Formula: see text] SA were significantly associated with AE. CONCLUSIONS: Ortho-k lenses with a smaller BOZD created a smaller horizontal TZ diameter and a significant increase in total HOAs, total SA, total coma, and primary SA and a decrease in secondary SA. Of these ocular aberrations, total HOAs, total SA, and primary SA were negatively correlated with AE over two years. TRIAL REGISTRATION: ClinicalTrial.gov, NCT03191942. Registered 19 June 2017, https://clinicaltrials.gov/ct2/show/NCT03191942 .

Corneal oedema during reverse piggyback scleral lens wear.

PURPOSE: One clinical approach to address poor front surface wettability during scleral lens wear is the use of a "reverse piggyback" system (a soft contact lens applied to the anterior surface of a scleral lens). The aim of this study was to compare the magnitude of corneal oedema induced following short-term reverse piggyback scleral lens wear and standard scleral lens wear. METHODS: Ten young (mean age 22 ± 6 years) healthy participants with normal corneas were recruited. On separate days, central corneal thickness and fluid reservoir thickness were measured using optical coherence tomography before and after 90 min of standard scleral lens wear (Kerectasia Alignment Tangent Torus diagnostic lenses, hexafocon A, Dk 100 × 10-11 (cm2 /s)(ml O2 /ml × mmHg), Capricornia Contact Lenses, capcl.com.au) and reverse piggyback scleral lens wear (the same scleral lens with a Dailies Total 1®, delefilcon A, Dk 140 × 10-11 (cm2 /s)(ml O2 /ml × mmHg), Alcon, alcon.com, applied to the anterior scleral lens surface). RESULTS: After correcting for small variations in the initial central fluid reservoir thickness, central corneal oedema was similar between the reverse piggyback (2.32 ± 1.15%) and standard scleral lens conditions (2.02 ± 0.76%; p = 0.45). CONCLUSIONS: Following 90 min of lens wear, the highly oxygen-permeable reverse piggyback system did not induce a clinically or statistically greater magnitude of central corneal oedema compared with standard scleral lens wear in young adults with healthy corneas. This approach may be suitable to address poor front surface scleral lens wettability or to correct residual refractive error during diagnostic scleral lens fitting.

Higher order aberrations and retinal image quality during short-term accommodation in myopic and non-myopic children.

INTRODUCTION: Despite the known associations between near work and myopia, and retinal image quality and eye growth, accommodation-induced changes in higher order aberrations (HOA's) and retinal image quality in children with different refractive errors are poorly understood. METHODS: Ocular HOA's were measured using a Hartmann-Shack wavefront sensor (COAS-HD, Wavefront Sciences) in 18 myopic and 18 age- and sex-matched non-myopic children during short-term accommodation tasks (four demands of 0, 3, 6 and 9 D) presented using a Badal optometer. Eighth order Zernike polynomials were fitted across a 2.3 mm pupil diameter to determine refractive power vectors (M, J180 and J45 ) and the accommodation error, and a 4 mm pupil was used for HOA analyses. Retinal image quality was examined using the visual Strehl ratio based on the optical transfer function (VSOTF) for third to eighth radial orders only. RESULTS: Most refractive error group differences were observed for the 6 and 9 D demands. Myopic children underwent greater changes in with-the-rule astigmatism (J180 ), higher order and third order RMS values, primary vertical ( C 3 - 1 ) and horizontal coma ( C 3 1 ), and several other individual Zernike coefficients compared with non-myopic children (all refractive error group by demand interaction p-values of ≤0.02). Non-myopic children exhibited a greater negative shift in primary ( C 4 0 ) and positive shift in secondary spherical aberration ( C 6 0 ) (both refractive error group by demand interaction p-values of ≤0.002). The VSOTF degraded for the 6 and 9 D demands in both groups, but the myopic children underwent a greater mean (SE) reduction from 0 D of -0.274 (0.048) for the 9 D demand, compared with -0.131 (0.052) for the non-myopic children (p = 0.001). CONCLUSION: These results may have implications for the association between near work, accommodation and myopia development, particularly related to the use of short working distances during near tasks.

Retinal image quality in myopic children undergoing orthokeratology alone or combined with 0.01% atropine.

BACKGROUND: The retinal image quality derived from lower-order (LOA) and higher-order aberrations (HOA) for fixed 3-mm and photopic pupil diameters, in children undergoing combined 0.01% atropine and orthokeratology (AOK) versus those receiving orthokeratology alone (OK) over two years was evaluated. METHODS: The visual Strehl ratio based on the optical transfer function (VSOTF), derived from 2nd- to 4th-order terms (LOA and HOA combined), 2nd-order terms (LOA only), and 3rd- to 4th-order terms (HOA only) for fixed 3-mm and natural photopic pupil diameters, was compared between the two treatment groups. The individual Zernike coefficients for a fixed 3-mm pupil size of 2nd- to 4th-orders, root mean square (RMS) of LOA ([Formula: see text], [Formula: see text], and [Formula: see text] combined), HOA (3rd to 4th orders inclusive), and Coma ([Formula: see text] combined) were also compared between the two groups. RESULTS: Right eye data of 33 AOK and 35 OK participants were analysed. Under photopic conditions, significantly lower VSOTF based on HOA only was observed in the AOK group compared with that in the OK group at all post-treatment visits (all P < 0.05); however, interactions between HOA and LOA resulted in comparable overall retinal image quality (i.e., VSOTF based on LOA and HOA combined) between the two groups at all visits (all P > 0.05). For a fixed 3-mm pupil size, the VSOTF based on HOA only, LOA only, or HOA and LOA combined, were not different between the two groups (all P > 0.05). AOK participants had slower axial elongation (mean ± SD, 0.17 ± 0.19 mm vs. 0.35 ± 0.20 mm, P < 0.001), a larger photopic pupil size (4.05 ± 0.61 mm vs. 3.43 ± 0.41 mm, P < 0.001) than OK participants, over two years. CONCLUSIONS: HOA profile related to an enlarged pupil size may provide visual signal influencing eye growth in the AOK group.

Intraocular composition of higher order aberrations in non-myopic children.

This study examined anterior corneal, internal ocular, and total ocular higher order aberrations (HOA's), and retinal image quality in a non-myopic, paediatric cohort. Anterior corneal aberrations were derived from corneal topography data captured using a Placido disk videokeratoscope (E300, Medmont International), and whole eye HOA's were measured using a Hartmann-Shack wavefront sensor (COAS-HD, Wavefront Sciences). The associations between HOA's and age, sex, refractive error, and axial length were explored using correlation analyses. Data for 84 children aged between 5 and 12 years (mean ± standard deviation spherical equivalent refraction (SER), +0.63 ± 0.35 D; range 0.00 to +1.75 D) were included, and an eighth order Zernike polynomial was fit for 4 and 6 mm pupil diameters for both the anterior corneal and total ocular HOA's, from which internal ocular HOA's were calculated via subtraction following alignment to a common reference axis (pupil centre). Internal ocular HOA's were of greater magnitude than previous studies of adolescents and adults, however partial internal "compensation" of HOA's was observed, which resulted in reduced levels of HOA's and excellent retinal image quality. Few significant associations were observed between HOA's and age, SER, and axial length (all correlations, p > 0.001), and there were minimal sex-based differences (all comparisons, p > 0.005). Coefficients for vertical coma ( C 3 - 1 and C 5 - 1 ) and spherical aberration ( C 4 0 and C 6 0 ), were most strongly associated with the visual Strehl ratio based on the optical transfer function (VSOTF), which indicated that the absolute magnitudes of these Zernike coefficients have the greatest impact on retinal image quality in this paediatric cohort. These findings provide an improved understanding of the optics and retinal image quality of children's eyes.

Long-term limitations and complications of trans-scleral diode laser cycloablation for refractory glaucoma.

BACKGROUND: Trans-scleral diode laser cycloablation (cyclodiode) is effective in the short-term management of refractory glaucoma where alternative treatments are not feasible. Long-term outcomes of 5-years or more are not well-documented, particularly in relation to intraocular pressure (IOP) control, need for further procedures and complications such as hypotony and phthisis. METHODS: A review was undertaken of patient medical records with refractory glaucoma who underwent cyclodiode at City Eye Centre in Brisbane from 2012 to 2016. Data included sex, age, laterality, type of glaucoma, cyclodiode parameters, number of glaucoma medications, visual acuity and treatment with acetazolamide. Data were analysed using generalised linear modelling and Kaplan-Meier analysis. RESULTS: A total of 54 eyes in 54 patients (29 M:25F) with a mean age of 66 years (range 15-85 years) with a minimum of 5 years follow up were included. The mean number of burns was 23.3 (range 12-40) over 180-270 degrees, mean power per burn was 1967 mW (range 1500-2000 mW), with a mean duration of 1981 ms (1500-2000 ms). The mean pre-treatment IOP was 31.5 mmHg (range 17-56 mmHg) and mean IOP 5 years post-treatment was 16.1 mmHg (2-42 mmHg). The mean number of pre-treatment medications was 3.6 (range 1-6) and 2.7 (range 0-5) 5 years post treatment, including 5 (8.3%) on oral acetazolamide. Complications of cyclodiode were seen in 6 (11.1%) patients, including 3 (5.0%) cases of hypotony, and 2 (3.3%) phthisis. CONCLUSION: Cyclodiode is often utilised for end-stage glaucoma when the IOP is uncontrolled on medical treatment and drainage surgery is not indicated, resulting in long-term reduction of IOP and the number of medications, including acetazolamide. Hypotony and phthisis can be significant complications.

Patch-based CNN for corneal segmentation of AS-OCT images: Effect of the number of classes and image quality upon performance.

Anterior segment optical coherence tomography (AS-OCT) is a fundamental ophthalmic imaging technique. AS-OCT images can be examined by experts and segmented to provide quantitative metrics that inform clinical decision making. Manual segmentation of these images is time-consuming and subjective, encouraging software developers in the field to automate segmentation procedures. Traditional programing segmentation approaches are being replaced by deep learning methods, which have shown state-of-the-art performance in AS-OCT image analysis. In this study, a method based on patch-based convolutional neural networks (CNN) was used to segment the three main boundaries of the cornea: the epithelium, Bowman's layer, and the endothelium. To assess the effect of the number of classes on performance, the model was designed as a patch-based boundary classifier using 4 and 8 classes. The effect of image quality was also assessed using different data distributions during the training process. While the Dice coefficient and probability revealed greater precision for the 8 class models, the boundary error metric indicated comparable performance. Additionally, for 8 class models, the image quality test had only a small negative effect on performance, which may be an indication of the robustness of the model and could also suggest that the data augmentation methods did not show significant improvement. These findings contribute to the development of automatic segmentation techniques for AS-OCT images, since patch-based methods have been largely unexplored in favor of other deep learning techniques. The overall performance of the proposed method is comparable to other well-established segmentation methods.

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.

A comparison of deep learning U-Net architectures for posterior segment OCT retinal layer segmentation.

Deep learning methods have enabled a fast, accurate and automated approach for retinal layer segmentation in posterior segment OCT images. Due to the success of semantic segmentation methods adopting the U-Net, a wide range of variants and improvements have been developed and applied to OCT segmentation. Unfortunately, the relative performance of these methods is difficult to ascertain for OCT retinal layer segmentation due to a lack of comprehensive comparative studies, and a lack of proper matching between networks in previous comparisons, as well as the use of different OCT datasets between studies. In this paper, a detailed and unbiased comparison is performed between eight U-Net architecture variants across four different OCT datasets from a range of different populations, ocular pathologies, acquisition parameters, instruments and segmentation tasks. The U-Net architecture variants evaluated include some which have not been previously explored for OCT segmentation. Using the Dice coefficient to evaluate segmentation performance, minimal differences were noted between most of the tested architectures across the four datasets. Using an extra convolutional layer per pooling block gave a small improvement in segmentation performance for all architectures across all four datasets. This finding highlights the importance of careful architecture comparison (e.g. ensuring networks are matched using an equivalent number of layers) to obtain a true and unbiased performance assessment of fully semantic models. Overall, this study demonstrates that the vanilla U-Net is sufficient for OCT retinal layer segmentation and that state-of-the-art methods and other architectural changes are potentially unnecessary for this particular task, especially given the associated increased complexity and slower speed for the marginal performance gains observed. Given the U-Net model and its variants represent one of the most commonly applied image segmentation methods, the consistent findings across several datasets here are likely to translate to many other OCT datasets and studies. This will provide significant value by saving time and cost in experimentation and model development as well as reduced inference time in practice by selecting simpler models.

Mediastinal melioidosis: A case series from far North Queensland.

Melioidosis is the clinical disease caused by the Gram-negative bacillus Burkholderia pseudomallei and is endemic to Northern Australia and Southeast Asia. It is commonly referred to as the 'great mimicker' because of its wide range of clinical presentations, often making diagnosis challenging. Isolated mediastinal lymphadenopathy as the presenting feature of melioidosis is rare and can be indistinguishable from tuberculosis or malignancy. Endobronchial ultrasound (EBUS) is the preferred technique for evaluating undifferentiated mediastinal lymphadenopathy but its role in the diagnosis of mediastinal melioidosis remains sparsely reported in the literature. In this case series, we present four cases of mediastinal melioidosis, and the role that EBUS guided fine needle aspiration (FNA) played in the diagnosis and management.

Anterior segment optical coherence tomography (AS-OCT) image analysis methods and applications: A systematic review.

BACKGROUND: Anterior segment optical coherence tomography (AS-OCT) constitutes an important imaging modality to examine the anterior eye, which is commonly used in research and clinical practice. Since its introduction, a range of image analysis methods have been developed to quantify these images using different analysis techniques for various applications. This systematic review aims to provide an in-depth summary and to classify image analysis techniques found in the literature applied to AS-OCT images. METHODS: Scopus and Engineering Village databases were searched to retrieve relevant studies up to and including January 2022. Customized search statements were used along with cross reference and hand search techniques to ensure a complete coverage. Performance metrics were extracted, analyzed, and compared (when possible). RESULTS: Three main application categories were identified: glaucoma assessment, corneal segmentation, and anterior segment biometry. These three categories constitute 66% of the total studies reported in this review. Studies were also analyzed by year of publication, and since 2019 deep learning methods were favored over traditional programming or machine learning methodologies. Overall, the AS-OCT image analysis field is less developed compared to posterior segment OCT imaging. CONCLUSION: This review presents the state of the art in the field of AS-OCT image analysis. It highlights the opportunities for future areas of research, such as the expansion of DL methods and the extension to specific clinical areas that have received limited attention including surgical monitoring, contact lenses, and specific clinical conditions such as keratoconus and corneal lesions.

Scleral Lens Thickness and Corneal Edema Under Closed Eye Conditions.

OBJECTIVES: To examine the relationship between central lens thickness and central corneal edema during short-term closed eye scleral lens wear. METHODS: Nine participants (mean age 30 years) with normal corneas wore scleral lenses (Dk 141) under closed eye conditions on separate days with nominal center thicknesses of 150, 300, 600, and 1,200 µm. Epithelial, stromal, and total corneal edema were measured using high-resolution optical coherence tomography immediately after lens application and after 90 min of wear, before lens removal. Data were corrected for variations in initial fluid reservoir thickness and compared with predictions from theoretical modeling of overnight scleral lens wear. RESULTS: Scleral lens-induced central corneal edema was primarily stromal in nature. The mean±standard error of corrected total corneal edema was 4.31%±0.32%, 4.55%±0.42%, 4.92%±0.50%, and 4.83%±0.22% for the 150-, 300-, 600-, and 1,200-µm lenses, respectively. No significant differences in the corrected total corneal edema were observed across all thickness groups (P=0.20). Theoretical modeling of overnight scleral lens wear seemed to overestimate the relative increase in central corneal edema as a function of decreasing lens Dk/t for values lower than 25. CONCLUSION: The magnitude of scleral lens-induced central corneal edema during short-term closed eye lens wear did not vary significantly with increasing central lens thickness. Theoretical modeling of overnight closed eye scleral lens wear seems to overestimate the effect of increasing lens thickness.

Corneal oedema during open-eye fenestrated scleral lens wear.

INTRODUCTION: Studies examining the effect of fenestrating soft and corneal rigid contact lenses upon corneal oedema have yielded conflicting results. Although often utilised in clinical practice, no studies have quantified the effect of fenestrating a scleral contact lens upon corneal oedema. Therefore, the aim of this experiment was to examine the effect of incorporating a single peripheral fenestration on central corneal oedema during short-term open-eye scleral lens wear, while controlling for potential confounding variables. METHODS: Nine participants (mean age 30 years) with normal corneas wore a fenestrated (1 × 0.3 mm limbal fenestration) and non-fenestrated scleral lens (both lenses manufactured using a material Dk of 141 × 10-11  cm3 O2 (cm)/[(sec.)(cm2 )(mmHg)]) under open-eye conditions on separate days. Scleral lens thickness profiles were measured using a high-resolution optical coherence tomographer (OCT). Epithelial, stromal and total central corneal oedema were also measured using the OCT immediately after lens application and following 90 min of wear, prior to lens removal. RESULTS: After adjusting for differences in initial central fluid reservoir thickness and scleral lens thickness between the two lens conditions, the mean (standard error) total corrected central corneal oedema was 0.50 (0.36)% for the fenestrated lens and 0.62 (0.16)% for the non-fenestrated lens. This small difference was not statistically significant (t8  = 2.31, p = 0.81) and represents a 19% relative reduction in central corneal oedema. Similarly, epithelial (t8  = 2.31, p = 0.82) and stromal (t8  = 2.31, p = 0.92) corneal oedema were not significantly different following the fenestrated and non-fenestrated wearing conditions. CONCLUSION: Central corneal oedema in healthy corneas was comparable between fenestrated and non-fenestrated high Dk scleral lenses under short-term open-eye conditions when controlling for lens oxygen transmissibility and initial central fluid reservoir thickness.

Axial Elongation During Short-Term Accommodation in Myopic and Nonmyopic Children.

Purpose: Axial length increases during accommodation in adults and children; however, refractive error group differences are conflicting and have not been explored in pediatric populations. This study aimed to evaluate differences in accommodation-induced axial elongation between myopic and nonmyopic children. Methods: A range of ocular biometric measurements were captured during brief accommodation tasks (0, 3, 6, and 9 D) using a Badal optometer mounted to a noncontact optical biometer (Zeiss IOLMaster 700). Reliable measurements were captured for 15 myopic and 15 age- and sex-matched nonmyopic children. The average central corneal thickness (CCT), anterior chamber depth (ACD), crystalline lens thickness (LT), anterior segment length (ASL), vitreous chamber depth (VCD), and axial length (AL) were determined for each accommodation stimulus. Raw measurements of AL and VCD were corrected for the estimated error associated with LT increases during accommodation. Results: All biometric parameters, except CCT, changed significantly during accommodation (all P < 0.001). Myopic children exhibited significantly greater accommodation-induced axial elongation than nonmyopic children (P = 0.002) at the 3, 6, and 9 D accommodation stimuli, with a mean difference of 7, 10, and 16 µm, respectively (all pairwise comparisons, P ≤ 0.03). The changes in all other biometric parameters were not different between the refractive error groups (P ≥ 0.23). Conclusions: Accommodation-induced axial elongation was greater in myopic than nonmyopic children. This finding could support a potential mechanism linking near work, axial elongation, and myopia development in children or may reflect greater susceptibility to accommodation-induced axial elongation in children with established myopia.

Scleral Lens Thickness and Corneal Edema Under Open Eye Conditions.

PURPOSE: To examine the relationship between lens thickness and central corneal edema during short-term open-eye scleral lens wear, and to compare these empirical edema measurements with theoretical modelling. METHODS: Nine participants (mean age 30 years) with normal corneas wore scleral lenses {Dk 141×10-11 cm3 O2 [cm]/([sec] [cm2] [mm Hg])} under open-eye conditions on separate days with nominal center thicknesses of 150, 300, 600, and 1,200 µm. Epithelial, stromal, and total corneal edema were measured using high-resolution optical coherence tomography immediately after lens application and after 90 min of wear, before lens removal. RESULTS: Central corneal edema was primarily stromal in nature and increased with increasing central lens thickness. The mean±standard error total corneal edema was 1.14±0.22%, 1.36±0.26%, 1.74±0.30%, and 2.13±0.24% for the 150, 300, 600, and 1,200 µm lenses, respectively. A significant difference in stromal and total corneal edema was observed between the 1,200 and 150 µm thickness lenses only (both P<0.05). Theoretical modelling overestimated the magnitude of central corneal edema and the influence of central lens thickness when the scleral lens Dk/t was less than 20. CONCLUSION: Scleral lens-induced central corneal edema during short-term open-eye lens wear increases with increasing central lens thickness. Theoretical models overestimated the effect of increasing scleral lens thickness upon central corneal edema for higher lens thickness values (lens Dk/t<20) when controlling for initial central fluid reservoir thickness.