Evaluation of different OCT systems in quantitative imaging of human Schlemm's canal.

We examined the performance of human Schlemm's canal (SC) imaging using different OCT devices: CIRRUS 5000 (840 nm, spectral-domain (SD)-OCT), PLEX Elite 9000 (1060 nm, swept-source (SS)-OCT) and CASIA SS-1000 (1310 nm, SS-OCT), and analyzed potential impact factors on visualization and the quantitative assessment of SC morphology in a pilot study. Ten healthy subjects were imaged using three OCT devices by a single experienced operator on the same day. Each eye underwent two cubic scans by each device, one on nasal and the other on temporal quadrant. The B-scan showing the largest SC was manually selected for processing. Four quantitative metrics, including one morphological metric as cross-sectional area (CSA), and three performance metrics as contrast, continuity, and coverage, were derived from the datasets. Repeated-measures ANOVA was used to investigate the difference between these parameters from the three devices (P < 0.05). We found the CSA measured from CIRRUS was significantly larger than PLEX, followed by CASIA. The contrast was highest in CIRRUS, followed by PLEX and CASIA. The coverage was also higher in CIRRUS as compared to PLEX and CASIA. No significant difference was seen in the continuity from the three devices. In summary, we showed the measurements from the three devices were not interchangeable.

Objective and Subjective Evaluation of Clinical Performance of Scleral Lens with Varying Limbal Clearance in Keratoconus.

SIGNIFICANCE: This study evaluates how limbal clearance (LC) may impact the clinical performance of scleral lenses based on subjective response on comfort and ocular responses. Limbal zone designs in scleral lenses might affect the integrity of the limbal epithelial tissue as a result of a combined hypoxic and compression-related etiology. PURPOSE: This study aimed to investigate the clinical performance and ocular and subjective responses to the wear of scleral lenses having varying LC. METHODS: Lenses with varying LC with a difference of 50 µm were fitted on and compared among keratoconic participants. The lenses were worn during a 2-week period. Visual analog scales concerning subjective comfort were completed. Ocular surface findings including hyperemia, limbal staining, and corneal swelling were compared. RESULTS: Participants reported greater comfort achieved with high LC. No difference in limbal and bulbar hyperemia was found (P > .05). Corneal response to scleral lens wear with both low and high LCs seems to result in similar perilimbal staining and negative corneal staining. An increase in corneal pachymetric values was noted at the central and peripheral cornea, with no difference between low- and high-LC lenses (all, P < .05). Quadrant-specific analysis indicated that all meridians at both 6 and 8 mm were increased for the low-LC lenses (all, P < .05) and only the temporal region for the high-LC lenses (P = .02). CONCLUSIONS: Limbal clearance may play an important role in subjective performance in scleral lenses but does not impact the degree of hyperemia in either the limbal or bulbar region. Although low LC might result in more compression-related changes to ocular surface, high LC is associated with greater comfort and greater edematous changes. Limbal zone designs in scleral lenses might affect the integrity of the limbal epithelial tissue as a result of a combined hypoxic and compression-related etiology.

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.

The microanatomy of Bowman's layer in the cornea of the pig: Changes in collagen fibril architecture at the corneoscleral limbus

In most animals, Bowman's layer is a feature of the cornea of the eye, and lies between the sur-face epithelium and the stromal extracellular matrix that makes up the bulk of the cornea. It is comprised of a condensation of disorganised collagen fibrils. However, it has been conjectured that not all species possess Bowman’s layer, and pigs are a species that has classically been stated to lack this anatomical structure, although there is disagreement in the published literature. Here, we studied the porcine cornea using transmission and scanning electron microscopy (TEM and SEM) to ascertain whether Bowman’s layer existed. TEM identified a thin band of disorganised collagen fibrils between the epithelial basement membrane and corneal stroma. SEM images of the central and peripheral corneal surfaces, following removal of the corneal epithelium by cell maceration, revealed a disorganised meshwork of collagen fibrils, with a highly aligned annulus of collagen at the limbus. In between the peripheral cornea and limbus, a "transition zone" is observed where collagenfibrils start to align. Quantification of fibril alignment demonstrates a significant increase in collagen alignment from 0.08 ± 0.04 to 0.33 ± 0.07 (p < 0.001; n = 60; 0 = no alignment, 1 = full alignment) with increasing distance from the corneal centre. These data together lead us to conclude that the porcine cornea does include Bowman's layer, though it is thin (contributing roughly 0.2% of corneal thickness), and thus, reaffirms the porcine cornea's similarity to its human counterpart and usefulness as a model system

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[Panorama of limbal alterations (French translation of the article)]. / Panorama des altérations limbiques cornéennes.

The corneal limbus is a privileged region on the border between two quite different microenvironments, where corneal epithelial stem cells, numerous melanocytes, and antigen-presenting cells are all concentrated within a richly vascularized and innervated stroma. This situation within the ocular surface confers on it the key functions of barrier, epithelial renewal and defense of the cornea. As an immunological crossroads and since the corneoscleral limbus is directly exposed to external insults such as caustic agents, ultraviolet radiation, microbial agents, and allergens, it is the potential site of many tumoral, degenerative or inflammatory pathologies and may progress under certain conditions to limbal stem cell deficiency.

Panorama of limbal changes.

The corneal limbus is a privileged region on the border between two quite different microenvironments, where corneal epithelial stem cells, numerous melanocytes, and antigen-presenting cells are all concentrated within a richly vascularized and innervated stroma. This situation within the ocular surface confers on it the key functions of barrier, epithelial renewal and defense of the cornea. As an immunological crossroads and since the corneoscleral limbus is directly exposed to external insults such as caustic agents, ultraviolet radiation, microbial agents, and allergens, it is the potential site of many tumoral, degenerative or inflammatory pathologies and may progress under certain conditions to limbal stem cell deficiency.

Effect of Air Injection Depth on Big-bubble Formation in Lamellar Keratoplasty: an Ex Vivo Study.

This study evaluated the effect of air injection depth in the big-bubble (BB) technique, which is used for corneal tissue preparation in lamellar keratoplasty. The BB technique was performed on ex vivo human corneoscleral buttons using a depth-sensing needle, based on optical coherence tomography (OCT) imaging technology. The needle tip, equipped with a miniaturized OCT depth-sensing probe, was inserted for air injection at a specified depth. Inside the corneal tissue, our needle obtained OCT line profiles, from which residual thickness below the needle tip was measured. Subjects were classified into Groups I, II, III, and IV based on injection depths of 75-80%, 80-85%, 85-90%, and >90% of the full corneal thickness, respectively. Both Type I and II BBs were produced when the mean residual thicknesses of air injection were 109.7 ± 38.0 µm and 52.4 ± 19.2 µm, respectively. Type II BB (4/5) was dominant in group IV. Bubble burst occurred in 1/16 cases of type I BB and 3/16 cases of type II BB, respectively. Injection depth was an important factor in determining the types of BBs produced. Deeper air injection could facilitate formation of Type II BBs, with an increased risk of bubble bursts.

Lipid Emulsion-Based OCT Angiography for Ex Vivo Imaging of the Aqueous Outflow Tract.

Purpose: Contrast agents applicable for optical coherence tomography (OCT) imaging are rare. The intrascleral aqueous drainage system would be a potential application for a contrast agent, because the aqueous veins are of small diameter and located deep inside the highly scattering sclera. We tested lipid emulsions (LEs) as candidate OCT contrast agents in vitro and ex vivo, including milk and the anesthetic substance Propofol. Methods: Commercial OCT and OCT angiography (OCTA) devices were used. Maximum reflectivity and signal transmission of LE were determined in tube phantoms. Absorption spectra and light scattering was analyzed. The anterior chamber of enucleated porcine eyes was perfused with LEs, and OCTA imaging of the LEs drained via the aqueous outflow tract was performed. Results: All LEs showed a significantly higher reflectivity than water (P < 0.001). Higher milk lipid content was positively correlated with maximum reflectivity and negatively with signal transmission. Propofol exhibited the best overall performance. Due to a high degree of signal fluctuation, OCTA could be applied for detection of LE. Compared with blood, the OCTA signal of Propofol was significantly stronger (P = 0.001). As a proof of concept, time-resolved aqueous angiography of porcine eyes was performed. The three-dimensional (3D) structure and dynamics of the aqueous outflow were significantly different from humans. Conclusions: LEs induced a strong signal in OCT and OCTA. LE-based OCTA allowed the ability to obtain time-resolved 3D datasets of aqueous outflow. Possible interactions of LE with inner eye's structures need to be further investigated before in vivo application.

Characterization of Corneoscleral Geometry Using Fourier Transform Profilometry in the Healthy Eye.

OBJECTIVE: To characterize peculiarities of the corneoscleral geometry in healthy eyes. METHODS: This is a prospective case series including 88 healthy eyes of 88 patients with an age ranging from 21 to 73 years. A complete ocular examination was performed with emphasis on the analysis of the corneoscleral topographic profile with the Fourier transform profilometer Eye Surface Profiler (Eaglet-Eye BV, Houten, the Netherlands). The distribution of different topographic parameters was evaluated, as well as the correlations between corneal and scleroconjunctival parameters. RESULTS: Mean values of 8.64±0.37 (range, 7.81-9.50 mm), 6.06±0.52 (4.88-7.63 mm) and 11.93±1.32 mm (8.17-15.89 mm) were obtained for inner, limbal, and outer best-fit sphere, respectively. Mean values of 8.54±0.38 (7.86-9.66 mm) and 13.35±1.29 mm (11.05-17.31 mm) were obtained for mean corneal and scleral radius, respectively. Regarding tangent angles at limbus, mean values of 35.31±6.55°, 38.76±5.90°, 32.75±7.04°, and 25.91±8.99° were obtained for nasal, temporal, superior, and inferior angles, respectively. Mean difference between temporal and nasal sagittal heights increased from -1.48±120.70 µm for a chord of 11 mm to 73.53±236.55 µm for a chord of 14 mm. A weak but statistically significant correlation was found between corneal and scleral radii (r=0.325, P=0.004). The maximum sagittal height for a diameter of 12 mm was significantly correlated with flattest keratometry, astigmatism, corneal diameter, and corneal eccentricity (R: 0.77, P<0.001). CONCLUSIONS: The scleroconjunctival surface in the healthy eye presents some level of nasotemporal asymmetry that is higher with increasing diameters of analysis.

Dynamic Changes in Schlemm Canal and Iridocorneal Angle Morphology During Accommodation in Children With Healthy Eyes: A Cross-Sectional Cohort Study.

Purpose: The purpose of this study was to explore changes in Schlemm canal (SC), trabecular meshwork (TM), and iridocorneal angle (ICA) morphology during accommodative effort in children and young adults. Methods: We acquired anterior segment optical coherence tomography images (AS-OCT) of the ICA and ciliary muscle (CM) of both eyes of 50 children age 4 to 16 years with healthy eyes, at two levels of accommodation: 2.5 and 15 diopters (D). Semiautomated nasal ICA measurements were as follows: angle opening distance at 500/750 µm (AOD-500, -750), trabecular iris space area at 500/750 µm (TISA-500, -750), and trabecular iris angle at 500/750 µm (TIA-500, -750). Manual measurements were as follows: anteroposterior and radial SC diameter (SC-APD, SC-RD), cross-sectional area of SC (SC-CSA) and TM height (TMH), TM length (TML), and TM density (TMD). CM width was measured at 1, 2, and 3 mm from the scleral spur (CM-1, CM-2, CM-3). For each parameter, a three-level random-effects model was fitted to estimate differences between the two levels of accommodation. Results: With accommodative effort, SC diameters and CSA increase significantly, as do TM length and iridocorneal angle parameters. With increasing age, SC dimensions reduce. Angle parameters are smaller in eyes with greater spherical equivalent (hypermetropia). Conclusions: AS-OCT can be used to visualize dynamic morphologic changes in outflow structures with physiologic accommodation. The increase in SC dimensions with accommodative effort may contribute to the regulation of IOP in children.

Relationship between vessel diameter and depth measurements within the limbus using ultra-high resolution optical coherence tomography.

PURPOSE: To establish a relationship between the diameter and depth position of vessels in the superior and inferior corneo-scleral limbus using ultra-high resolution optical coherence tomography (UHR-OCT). METHODS: Volumetric OCT images of the superior and inferior limbus were acquired from 14 healthy subjects with a research-grade UHR-OCT system. Differences in vessel diameter and depth between superior and inferior limbus were analyzed using repeated measured ANOVA in SPSS and R. RESULTS: The mean (± SD) superior and inferior diameters were 29±18µm and 24±18µm respectively, and the mean (± SD) superior and inferior depths were 177±109µm and 207±132µm respectively. The superior limbal vessels were larger than the inferior ones (RM-ANOVA, p=0.004), and the inferior limbal vessels were deeper than the superior vessels (RM-ANOVA, p=0.041). There was a positive linear association between limbal vessel depth and size within the superior and inferior limbus with Pearson correlation coefficients of 0.803 and 0.754, respectively. CONCLUSION: This study demonstrated that the UHR-OCT was capable of imaging morphometric characteristics such as the size and depth of vessels in the limbus. The results of this study suggest a difference in the size and depth of vessels across different positions of the limbus, which may be indicative of adaptations to chronic hypoxia caused by the covering of the superior limbus by the upper eyelid. UHR-OCT may be a useful tool to evaluate the effect of contact lenses on the microvascular properties within the limbus.

Size does matter: what is the corneo-limbal diameter?

This review surveys available literature for corneal and limbal dimensions. With modern scleral lenses, these measures have become central to determining the overall size of a lens for satisfactory fitting. In general, published values are not based on a definition of what is being measured. In addition, the most widely accepted average corneal diameter measurement, 11.7 × 10.6 mm, emanates from one source published more than 50 years ago. This value was not based on a measurement but appears to be the cumulative impression of measurements from seven studies conducted between 67 and 127 years ago. Furthermore, in most instances, if at all stated, quoted measures are based on horizontal visible iris diameter, providing limited acknowledgement of limbal width and its inclusion as part of the corneal diameter. The corneo-scleral sulcus from one side to the other has been measured, giving a larger diameter, but may include at least part of the limbus. More objective measurements are possible with modern ophthalmic instrumentation but the lack of structural definition and low magnification resolution with these techniques raises concerns with the accuracy of the results. Measurement of the horizontal visible iris diameter does not include the limbal width, which means that the horizontal visible iris diameter is an underestimate of the true corneo-limbal diameter. This review concludes that the width of the limbus has been neither structurally defined nor accurately measured and that there is a need for the development of new protocols for determining the dimensions of the average cornea and limbus. It is predicted that more accurate measures will indicate that to vault across cornea with limbus and provide excellent comfort, the average cornea will need a lens to have a diameter of 16.0 mm or larger.

On the Methods for Estimating the Corneoscleral Limbus.

OBJECTIVE: The aim of this study was to develop computational methods for estimating limbus position based on the measurements of three-dimensional (3-D) corneoscleral topography and ascertain whether corneoscleral limbus routinely estimated from the frontal image corresponds to that derived from topographical information. METHODS: Two new computational methods for estimating the limbus position are proposed: One based on approximating the raw anterior eye height data by series of Zernike polynomials and one that combines the 3-D corneoscleral topography with the frontal grayscale image acquired with the digital camera in-built in the profilometer. The proposed methods are contrasted against a previously described image-only-based procedure and to a technique of manual image annotation. RESULTS: The estimates of corneoscleral limbus radius were characterized with a high precision. The group average (mean ± standard deviation) of the maximum difference between estimates derived from all considered methods was 0.27 ± 0.14 mm and reached up to 0.55 mm. The four estimating methods lead to statistically significant differences (nonparametric ANOVA (the Analysis of Variance) test, p 0.05). CONCLUSION: Precise topographical limbus demarcation is possible either from the frontal digital images of the eye or from the 3-D topographical information of corneoscleral region. However, the results demonstrated that the corneoscleral limbus estimated from the anterior eye topography does not always correspond to that obtained through image-only based techniques. SIGNIFICANCE: The experimental findings have shown that 3-D topography of anterior eye, in the absence of a gold standard, has the potential to become a new computational methodology for estimating the corneoscleral limbus.

Effect of Cyclopentolate on In Vivo Schlemm Canal Microarchitecture in Healthy Subjects.

PURPOSE: To characterize the in vivo effect of cyclopentolate on the microstructure of Schlemm canal (SC) in healthy eyes. METHODS: For healthy subjects, 81 serial horizontal enhanced depth imaging optical coherence tomography B-scans (interval between scans, ∼35 µm) of the nasal corneoscleral limbal area were obtained before and 1 hour after cyclopentolate 1% administration in 1 eye. The structures of aqueous and blood vessels in each scan were used as landmarks to select 50 overlapping scans between the 2 sets of 81 serial scans (before and after cyclopentolate administration). The SC cross-sectional area was measured in each of the 50 selected scans. After 3-dimensional reconstruction, SC volume was determined. RESULTS: Twelve eyes (12 healthy subjects) were imaged successfully before and after cyclopentolate administration. Mean age was 27.8±4.9 years (range, 25 to 38 y). Following cyclopentolate administration, mean intraocular pressure did not change significantly (13.9±1.5 to 14.2±1.5 mm Hg; P=0.19). Mean SC cross-sectional area decreased by 17%, from 3563±706 to 2959±460 µm (P<0.001). Mean SC volume in the overlapping area (approximately 1.7 mm of circumferential length of SC) decreased from 6,164,061±1,220,787 to 5,119,462±794,763 µm (P<0.001). The decrease in the mean SC cross-sectional area after cyclopentolate administration was greater in eyes with larger baseline SC cross-sectional area (P<0.001, R=0.873). CONCLUSIONS: Cyclopentolate causes a reduction in SC dimensions in healthy eyes. Future studies are warranted to determine the exact mechanism(s) of this change.

Variaciones en la técnica del trasplante limbar autólogo / Variations in the technique for autologous limbal transplantation

OBJETIVO: Presentar los resultados del uso de un único segmento de autoinjerto limbar combinado con trasplante de membrana amniótica y epiteliectomías conjuntivales sectoriales secuenciales postoperatorias en 2 pacientes con insuficiencia límbica unilateral total. CONCLUSIONES: Un solo segmento de autoinjerto limbal junto con el trasplante de membrana amniótica puede ser suficiente para restaurar una superficie corneal estable, siendo en ocasiones necesario realizar en el postoperatorio epiteliectomías conjuntivales secuenciales en zonas remanentes de epitelio anómalo

OBJECTIVE: To present the results on the use of a single block limbal autograft, combined with amniotic membrane transplantation and sectoral sequential postoperative epitheliectomy of the conjunctiva in 2 patients with unilateral total limbal stem cell deficiency. CONCLUSIONS: A single block limbal autograft combined with amniotic membrane transplantation may be sufficient to restore a stable corneal surface, but sometimes sequential sectoral conjunctival epitheliectomy may be required to treat anomalous epithelial remnants

Measurement of corneal and limbal epithelial thickness by anterior segment optical coherence tomography and in vivo confocal microscopy.

BACKGROUND: To compare corneal epithelial thickness (CET) and limbal epithelial thickness (LET) measured by anterior segment optical coherence tomography (AS-OCT) and in vivo confocal microscope (IVCM) in normal subjects, and evaluate the consistency between them. METHODS: Thirty-eight normal subjects (17 men and 21 women) were enrolled in this study. AS-OCT was performed at central cornea and the superior, inferior, nasal and temporal limbus. Then followed by IVCM examination performed at the same location. Agreement was analyzed by mean difference (AS-OCT minus IVCM), 95 % limits of agreement (LoA) (1.96 standard deviation of the difference), and Bland-Altman analysis. RESULTS: The average CET measured by AS-OCT and IVCM was 55.6 ± 4.0 µm and 51.9 ± 4.9 µm respectively. The value measured by IVCM was significantly lower than that measured by AS-OCT (P = 0.015). The average LET values tested by AS-OCT were 10.3 and 10.9 % less at nasal and temporal quadrant (nasal: P = 0.019, temporal: P = 0.003), and were similar as those measured by IVCM at superior and inferior quadrant. In subjects older than 40 years, CET and LET values measured by AS-OCT were significantly higher than those by IVCM. Such differences were not found in subjects ≤ 40 years old. CONCLUSIONS: CET values measured by IVCM are lower than those by AS-OCT, while LET values measured by two devices have good agreement. These two techniques have their own advantages in measuring epithelial thickness and are mutually complementary.

Using optical coherence tomography to assess the role of age and region in corneal epithelium and palisades of vogt.

Using spectral-domain optical coherence tomography (OCT) to observe the morphology and epithelial thickness (ET) of the palisades of Vogt (POV), and to evaluate the role of age and region on these structures.One hundred twelve eyes of 112 healthy subjects were enrolled and divided into 4 groups: A (0-19), B (20-39), C (40-59), and D (≥60 years old). RTvue-100 OCT was applied on the cornea and the limbus. The morphology of the subepithelial stroma underneath the epithelium of POV was classified into typical and atypical types. Maximum ET of POV was measured manually from OCT images.The positive rate of typical POV in superior, nasal, temporal, and inferior limbus was: Group A: 100%, 69.2%, 65.4%, 100%; Group B: 100%, 73.5%, 61.8%, 94.1%; Group C: 95.8%, 41.7%, 37.5%, 83.3%; Group D: 67.9%, 0%, 3.6%, 25%, showing a significant decreasing tendency with age. The maximum ET of POV in superior, nasal, temporal, and inferior limbus was: Group A: 103.5 ±â€Š10.1 um, 89.2 ±â€Š9.7 um, 87.9 ±â€Š13.6 um, 104.7 ±â€Š14.1 um; Group B: 111.4 ±â€Š15.8 um, 85.3 ±â€Š9.9 um, 88.2 ±â€Š8.6 um, 112.6 ±â€Š19.7 um; Group C: 116.4 ±â€Š16.4 um, 82.8 ±â€Š11.6 um, 87.0 ±â€Š11.6 um, 120.0 ±â€Š25.6 um; Group D: 96.3 ±â€Š17.9 um, 73.8 ±â€Š15.9 um, 79.2 ±â€Š16.7 um, 87.4 ±â€Š18.5 um. Age-dependent change was observed. In general, the maximum ET of POV in superior/inferior quadrants was thicker than the other 2 quadrants.Spectral-domain OCT is a useful tool to observe the limbal microstructure and provide invaluable information. Aging and anatomic regions had significant effects on the microstructure of these areas.

Identifying the Palisades of Vogt in Human Ex Vivo Tissue.

PURPOSE: The Palisades of Vogt (POV) constitute the corneal epithelial stem cell niche, but identification of this region in ex vivo tissue is difficult. Here we introduce a simple, direct method of identifying the POV in unsectioned, ex vivo human tissue. METHODS: Twenty-two eyes were studied, four whole and eighteen rims. Orientation of whole eyes was determined and the eyes were marked to maintain their cardinal orientation prior to dissection. Samples were imaged with brightfield, linearly polarized light and transmitted circularly polarized light (CPL), and optical coherence tomography (OCT) volumes were acquired in all twelve clock hrs around the limbus. Five samples were also fluorescently labeled to identify the epithelial basement membrane, and whole mounts were imaged with laser scanning confocal microscopy. Images were compared to confirm that the structures visible with polarized light were POV. RESULTS: Under CPL the POV presented as amber radial ridges visible in the superior and inferior regions of the tissue. Identification of POV was confirmed by correlating the structures seen under CPL, OCT and laser-scanning confocal microscopy. CONCLUSIONS: CPL can be used to quickly identify POV regions in donor tissue. This technique can assist in targeted harvesting of stem cell regions for research and tissue for limbal transplant.

Assessing Efficacy of Canaloplasty Using Continuous 24-Hour Monitoring of Ocular Dimensional Changes.

PURPOSE: We investigated whether 24-hour monitoring of corneoscleral limbus area (CSLA) with the Sensimed Triggerfish contact lens sensor (CLS) can be used clinically to assess midterm efficacy of canaloplasty and to assess the relationships of CSLA changes with the heart rhythm. METHODS: Ten eyes of 10 patients, with POAG, which were qualified either to canaloplasty or canaloplasty and phacoemulsification, were included in this study. Eyes were washed out before the surgery and control visits were done at days 1, 7, and 3, 6, 12 months postoperatively, at which subjects were examined. We performed 24-hour monitoring of CSLA changes and Holter ECG at washout, and at 3- and 12-month postop visits. Raw CLS signals were processed to lead two parameters describing short-term 24-hour variability of CSLA (VAR, â). Heart activity parameters from CLS were compared to those acquired from Holter ECG. RESULTS: Mean post washout IOP was 20.6 ± 4.7 and decreased to 14.2 ± 3.0 mm Hg 1 year after surgery (P < 0.01). A decreasing trend in VAR and â parameters were noted. Statistically significant differences were found between the washout and 3-month postop visit for VAR and â (P = 0.014 and P = 0.027, respectively) as well as between the washout and 12-month postop result for the parameter â (P = 0.031). No statistically significant differences were found between the 3- and 12-month postop results for both considered parameters. CONCLUSIONS: Canaloplasty alone or combined with cataract surgery is a successful surgical method of lowering IOP in glaucoma patients. Canaloplasty decreases 24-hour CSLA fluctuation pattern measured with CLS.

Corneo-scleral limbus demarcation from 3D height data.

PURPOSE: To accurately and precisely demarcate the transition points in the anterior limbal surface from 3D anterior eye height data. METHODS: Data of anterior eye surface was acquired using a corneo-scleral profilometer. Two methods for automatic limbal radius estimation were proposed. One is based on the residual error between the original data and low order fit data while the other method takes a step further, calculating the cumulative root mean square (RMS) of the residual error. Data of a simulated example, collected from an artificial bi-sphere test surface and four real eyes is used to validate the methodology. RESULTS: Both methods of limbal radius estimation were found to be equivalent in a low noise regime while the residual RMS method performs better in higher noise regimes. The relative error for the proposed methods was below 0.05% and below 1.1% for the simulated test surface and the artificial bi-sphere, respectively. For the four considered subjects, the variability of the methods was less than 10µm. There was no statistically significant difference between methods nor between method and subject but there was statistically significant difference between the subjects (two-way ANOVA, p<0.001). Asymmetry in limbal shape between nasal and temporal side was observed. CONCLUSIONS: Determining the anterior limbus position in a non-invasive, automatic, accurate and precise manner is possible using 3D anterior eye height data. The topographical information of limbus does not necessarily coincide with the maximum rate of change in colour from the iris to sclera observable with en-face imaging.