Journal of Optometry Journal of Optometry
J Optom 2018;11:57-65 - Vol. 11 Num.1 DOI: 10.1016/j.optom.2017.02.003
Original Article
Relationship between vessel diameter and depth measurements within the limbus using ultra-high resolution optical coherence tomography
Relación entre las mediciones del diámetro y la profundidad de vasos sanguíneos en el limbo obtenidas mediante tomografía de coherencia óptica de ultra-alta resolución
Emmanuel Alabia, , Natalie Hutchingsa, , Kostadinka Bizhevaa,b,c, , Trefford Simpsona,,
a University of Waterloo, School of Optometry and Vision Science, Waterloo, ON, Canada
b University of Waterloo, Department of Physics and Astronomy, Waterloo, ON, Canada
c University of Waterloo, Systems Design Engineering Department, Waterloo, ON, Canada
Received 11 October 2016, Accepted 04 February 2017

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).


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.


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.


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.


Establecer la relación entre el diámetro y la profundidad de los vasos del limbo esclerocorneal superior e inferior mediante tomografía de coherencia óptica de ultra-alta resolución (UHR-OCT).


Se adquirieron 256 conjuntos de imágenes del limbo superior e inferior en 14 sujetos, mediante UHR-OCT. Se analizaron las diferencias en cuanto a diámetro y profundidad del vaso entre el limbo superior e inferior utilizando ANOVA de medidas repetidas en SPSS y R.


Los diámetros medios (± DE) superior e inferior fueron de 29μm±18μm y 24μm±18μm respectivamente, y las profundidades medias (± DE) superior e inferior fueron de 177μm±109μm y 207μm±132μm respectivamente. Los vasos del limbo superior fueron de mayor tamaño que los del limbo inferior (RM-ANOVA, p=0,004), y los vasos del limbo inferior fueron más profundos que los del limbo superior (RM-ANOVA, p=0,041). Se produjo una asociación lineal positiva entre la profundidad y el tamaño del vaso dentro del limbo superior e inferior, con coeficientes de correlación de Pearson de 0,803 y 0,754, respectivamente.


Este estudio demuestra que UHR-OCT fue capaz de obtener imágenes de las características morfométricas tales como tamaño y profundidad de los vasos del limbo. Los resultados de este estudio sugieren una diferencia de tamaño y profundidad de los vasos en las diferentes posiciones del limbo, que puede ser indicativa de adaptaciones a la hipoxia crónica causada por el cubrimiento del limbo superior por parte del párpado superior. UHR-OCT puede ser una herramienta de utilidad para evaluar el efecto de las lentes de contacto sobre las propiedades microvasculares del limbo esclerocorneal.

Limbal vasculature, Optical coherence tomography, Repeatability, Optical imaging, Corneal imaging
Palabras clave
Vasculatura del limbo, Tomografía de coherencia óptica, Córnea, Repetición, Imagen óptica, Imagen de la córnea

The limbus is the zone that separates the opaque sclera (overlaid by transparent conjunctiva) from the transparent cornea. It is a region of interest because it is a site of numerous biological activities ranging from supplying blood to the peripheral cornea, to housing the aqueous outflow apparatus.1 The vascular properties of the limbus is important for many physiological responses such as nutrition, waste removal, and microvascular changes in response to corneal injury, inflammation or contact lens wear.2 For most people, during both awake and asleep conditions, the superior limbus is covered by the upper eyelid; roughly two millimeters of the superior corneal region (the total area of the superior limbus) is obscured while the eye is in the open-eye primary-gaze position.3 The lid is a barrier to atmospheric oxygen within the limbal zone and immediately after the retraction of the upper eyelid, superior corneal oxygen uptake is much higher than other parts of the cornea.4–6 When equilibrated (after longer upper lid retraction) there is no difference in oxygen uptake of the various corneal regions.7 When oxygen delivery to the limbus is reduced, limbal hyperemia occurs as blood flow is increased to the region.8 Since limbal hyperemia is not the norm,3 it can be deduced that anatomical and physiological alterations within the tissue might occur as a response to overcome the possible inadequate exposure to atmospheric oxygen that the superior limbus experiences as a result of it being constantly covered by the upper eyelid. Such adjustments in response to this chronic hypoxia might include but are not limited to, changes in vessel size, density and depth, as well as changes in epithelial thickness.

There are a number of other differences in the structures of the upper limbus: The density of endothelial cells is greater in the superior limbus,9 the diameters and spacing of collagen fibrils10 and stem cell size11 differ, and the superior cornea is thicker.12,13 Because of these structural differences and the coverage of the superior limbus by the upper eyelid, we examined some aspects of the vessel characteristics within the superior limbus and other limbal regions: Our working hypothesis was that there would be morphometric adaptations of the vessels that would provide some physiological accounting for the upper limbus not showing manifestations of chronic hypoxia.

Visualization of the limbus

Many methods exist for the visualization and morphometric analysis of structures within the limbus. Ex vivo technology such as serial histologic sections14,15 and ultrathin sections16,17 have been used to visualize ocular vessels, trabecular meshwork and aqueous outflow in the limbus. Some shortcomings associated with this type of histological sectioning are that the curvature of the eye provides a barrier to the reconstruction of anatomical structures including vasculature, from sectioned materials, and the process cannot be carried out in vivo.18

In vivo methods of visualizing the limbus include but are not limited to slit lamp microscopy (SLB), gonioscopy, confocal microscopy, ultrasound biomicroscopy (UBM) and optical coherence tomography (OCT). In this study, OCT was utilized for visualization of the limbus particularly due to it being non-contact and non-invasive. It also provides high resolution cross-sectional images of optically scattering media and over the past 25 years has found numerous applications in ophthalmology for non-invasive imaging of different ocular tissues such as the retina, cornea, lens, etc. both in human subjects and animal models.19 OCT has previously been used to image the human corneo-scleral limbus. Feng and Simpson,20 utilized OCT to compare epithelial thickness within the central cornea and limbus. Kagemann et al.,21 used OCT to assess the Schlemm's canal in the limbal region of 21 healthy and 3 glaucomatous subjects. Detailed three-dimensional mapping of limbal morphology has been carried out using ultra-high resolution OCT (UHR-OCT)22 and further microstructural and microvascular limbal properties have been observed using a combination of anterior segment OCT and optical microangiography.23 Imaging of both limbal and scleral vasculature has also been performed with swept source OCT.24

Due to the high level of biological activity within the ocular limbus, a repeatable in vivo, non-invasive and non-contact means of monitoring and measuring limbal structures at a high resolution might be beneficial as an aid to diagnosis and evaluation of anterior ocular conditions involving the various components of the limbus. The purpose of this study was to investigate morphometric characteristics of vasculature within the superior and inferior limbal regions using ultra-high resolution optical coherence tomography and compare the relationship between vessel diameter and depth within the human ocular limbus.


We used a research-grade high speed, spectral domain UHR-OCT operating at central wavelength of 1020nm designed for in vivo imaging of the human anterior segment. The UHR-OCT system is based on a fiber-optic Michelson interferometer powered with a broadband superluminescent diode (SLD – Superlum Inc.). The SLD generates a spectrum centered at 1020nm with spectral bandwidth of 110nm. The optic and fiber-optic components of the UHR-OCT system were selected to propagate the SLD spectrum through the entire UHR-OCT system with no significant spectral losses. The detection end of the UHR-OCT system consists of a high resolution custom spectrometer (P&P Optica, Waterloo, Canada) interfaced with a 1024 pixel, line IR camera (LDH, UTC Aerospace Systems, Westford, MA, USA) operating at 47kHz. The UHR-OCT system provided 4.2μm axial resolution in free space, corresponding to ∼3μm in biological tissue assuming an average refractive index of 1.38. The corneal imaging probe used for this study generated lateral resolution of ∼18μm in biological tissue. The UHR-OCT system provided ∼92dB SNR for 1.4mW power of the imaging beam incident on the cornea and conjunctiva, which is in compliance with the safety limits established by the ANSI standard for safe exposure of ocular tissue to laser light. More details about the design of the UHR-OCT system are provided in previous publications from our research group.22,25,26 For imaging the anterior structures of the human eye, an UHR-OCT system operating in the 1060nm spectral range has a major advantage over similar systems operating at 800nm or 1300nm; the dispersion of water has a null at ∼1060nm and provided that the optical dispersion within the UHR-OCT imaging system is balanced, the images acquired do not require post-processing for water dispersion compensation.22 Also, devices operating at the 1060nm range are more suited for the imaging anterior segment structures as they provide greater depth penetration in more scattering biological tissue such as the limbus, sclera, eyelid, etc., as compared to devices operating in the 800nm range.22,27


14 healthy non-contact lens wearers between the ages of 16–60 years were used in the study. Imaging was done after midday to reduce the influence of diurnal variation.28 There was no dietary exclusion criteria since we were interested in examining the vessels in as unselected a way as possible. Prior to imaging, participants’ ocular health was assessed and informed consent was obtained. This study adhered to the Declaration of Helsinki for research involving human subjects and received ethics approval from the University of Waterloo Office of Research Ethics. Imaging with the UHR-OCT device was carried out on the participants while their upper or lower eyelids were manually retracted and while they fixated on a target inferiorly and superiorly, for upper and lower limbus imaging respectively. Head position remained relatively stable as the subject was comfortably positioned in a chin and forehead rest. Based on a specular reflection, the UHR-OCT imaging probe was approximately orthogonally aligned to the subject's eye to allow for the acquisition of 256 cross-sectional images (1000×1024) of the corneo-scleral limbus.

Data processing and analysis

All UHR-OCT tomograms were processed with Matlab (Mathworks), Amira (Visage Imaging) and Image J.29 8 bit image stacks (1000×1024×256) were acquired of the transition from clear cornea to bulbar conjunctiva at the superior and inferior limbal region. To facilitate definitions of vessels (particularly those with low contrast), sets of images were registered into a stack using a standard translation transformation30 and 3D construction of the aligned stack was done using Amira and ImageJ. Then to define the limbal region, an orthogonal line was drawn on the image, from the termination of the Bowman's-epithelium complex through the termination of the endothelium-Decemet's complex. This denoted the corneo-limbal junction, while a line orthogonal to the ocular surface though the furthermost insertion of the sclera to the anterior chamber denoted the sclera-limbal junction. The area that fell within these two borders was presumed to be the limbal zone (Fig. 1).

Figure 1.

OCT image showing the corneo-scleral limbus. The red arrow shows the termination of the epithelium-Bowman's complex. The blue arrow shows the termination of the Descemet's-endothelial complex. The red dashed line 1 shows the sclero-limbal junction and red dash line 2 shows the corneo-limbal junction. The area between the two lines is the limbal region.

A single 2D image/section of the limbal region was selected as the candidate image for blood vessel evaluation. This was located near the position of orthogonal illumination and was selected on the basis that all layers from ‘front to back’ were in focus. On this 2D section, the diameters of all visible vessels within the limbal region were measured using a circle or ellipse tool, the shorter diameter in the case of an ellipse tool. The vessel depth was quantified as the orthogonal/shortest distance from the ocular surface to the outer vessel boundary.

Pearson correlation coefficients were calculated to investigate the anatomical relationship between vessel diameter and depth. Quantitative differences in vessel size and depth in the limbal region were analyzed using repeated measured ANOVA. R31 and SPSS for Windows32 were used for data analysis procedures. A probability value of 0.05 or less was assumed to be significant.

ResultsMorphometry and quantitative differences

The morphometric characteristics of vessels with the superior and inferior limbus can be found in Tables 1 and 2 respectively. The average vessel size (in microns) for superior and inferior limbus were 29±18 (SD) and 24±18 (SD) respectively. The average vessel depths for superior and inferior limbus were 177±109 (SD) and 206±132 (SD) respectively. Fig. 2 contains information about the vessel diameter and depth found at both the superior and inferior limbus. The vessels within the superior limbus were larger than the vessels found in the inferior limbus (RM-ANOVA, p=0.004) and those within the inferior limbus were on average deeper than the vessels found within the superior limbus (RM-ANOVA, p=0.041).

Table 1.

Morphometric characteristics for the superior limbal region.

Subject  Age (years)/sex (male-M)/(female-F)  Ethnicity  Vessel diameter (μm)Vessel depth (μm)# of vessels 
      Mean value±SD  Min–Max values  Mean value±SD  Min–Max values   
28/M  White  25±17  8–52  230±145  75–519 
30/M  Asian  16±10  6–38  167±105  47–417  10 
42/M  White  25±19  7–70  189±156  57–550  10 
24/M  White  19±14  5–55  200±111  92–464  13 
29/F  Black  22±17  5–55  199±108  117–483  13 
34/M  Black  35±27  9–116  269±136  50–531  15 
34/M  Asian  19±15  6–63  205±166  56–527  18 
32/F  White  20±13  7–64  215±123  57–568  17 
29/F  White  28±17  10–63  219±187  57–591  12 
10  28/F  Black  29±22  7–77  194±89  82–440  15 
11  35/F  White  23±21  6–73  204±126  64–505  13 
12  55/M  Asian  19±13  6–38  173±91  66–374 
13  42/M  White  27±17  6–55  182±129  53–400  12 
14  26/F  White  25±21  9–64  211±182  49–642 
Table 2.

Morphometric characteristics for the inferior limbal region.

Subject  Age (years)/sex (male-M)/(female-F)  Ethnicity  Subject  Vessel diameter (μm)Vessel depth (μm)# of vessels 
        Mean value±SD  Min–Max values  Mean value±SD  Min–Max values   
28/M  White  25±17  8–52  230±145  75–519 
30/M  Asian  16±10  6–38  167±105  47–417 
42/M  White  25±19  7–70  189±156  57–550  10 
24/M  White  19±14  5–55  200±111  92–464  12 
29/F  Black  22±17  5–55  199±108  117–483  13 
34/M  Black  35±27  9–116  269±136  50–531  15 
34/M  Asian  19±15  6–63  205±166  56–527  18 
32/F  White  20±13  7–64  215±123  57–568  17 
29/F  White  28±17  10–63  219±187  57–591  12 
10  28/F  Black  10  29±22  7–77  194±89  82–440  15 
11  35/F  White  11  23±21  6–73  204±126  64–505  13 
12  55/M  Asian  12  19±13  6–38  173±91  66–374 
13  42/M  White  13  27±17  6–55  182±129  53–400  12 
14  26/F  White  14  25±21  9–64  211±182  49–642 
Figure 2.

(Above) Superior and inferior limbal mean vessel diameters. (Below) Superior and inferior limbal mean vessel depths. The error bars show the 95% confidence interval of the mean.


There were positive linear relationships between limbal vessel depth and size within the superior and inferior limbus (Fig. 4). The Pearson correlation coefficients for the superior and inferior limbus were 0.803 and 0.754 respectively. The within subject Pearson correlation coefficients are displayed in Fig. 3 for the superior and inferior limbus.

Figure 3.

Subject-wise regressions illustrating the relationships between vessel depth and diameter in the superior limbus (above) and in the inferior limbus (below).

Figure 4.

(A) Representative OCT B-scan of a healthy human corneo-scleral limbus. Black arrow marks the conjunctiva. Red arrows mark limbal blood vessels. Blue arrows mark individual red blood cells in the major scleral blood vessel. (B) Three dimensional reconstruction of a set of UHR-OCT tomograms. This reconstruction can be sliced at different angles and the vessels assessed and measured with the requisite ellipse or circle tool. Red arrows mark cross-sections of scleral blood vessels. (C) Three dimensional reconstruction of the limbus with the epithelium stripped through an oblique slice to reveal the vessel structure within the limbus. In (B) and (C) the images were black/white inverted so that the limbal voids being mapped appear as white against a dark background to allow enhanced viewing for readers.


In this study, we were able to reliably image, obtain and quantify vascular morphometric characteristics in the human corneo-scleral limbus. Our research supports the utility of the UHR-OCT in anterior segment imaging to be beneficial for evaluation of various components of the vascularity of the limbus. Since there is little published work on the test and retest reliability of OCT measurements on vessel characteristics within the limbus, we incorporated a component of repeatability. Initial vessel depth and size measurements were recorded within a 24-h period. The vessel depth and size were re-measured and recorded after a 60-day interval. The UHR-OCT was capable of imaging limbal morphometric characteristics in a repeatable manner (Table 3).

Table 3.

Relationship between replicate measures of vessel diameter and vessel depth of vessels in the image. The table describes the mean difference in repeated measurement, the 95% confidence interval for the mean difference (95% CI Mean), the upper limit of agreement (upper LOA), the lower limit of agreement (lower LOA), and the coefficient of repeatability (CR). Confidence intervals on the LOAs are determined using the method described by Carkeet.33

Measure  Mean diff.  95% CI mean diff.  Upper LOA  95% CI upper LOA  Lower LOA  95% CI lower LOA  CR 
Inferior diameter  +0.17  −1.81 to +2.1  +4.22  +3.85 to +4.72  −3.89  −3.51 to −4.38  2.07 
Superior diameter  +0.05  −1.92 to +2.03  +11.10  +9.97 to +12.63  −11.00  −9.87 to −12.53  5.62 
Inferior depth  −1.28  −3.25 to +0.70  +16.50  +14.85 to +18.66  −19.05  −17.39 to −21.21  9.13 
Superior depth  +0.26  −1.72 to +2.24  +13.08  +11.77 to +14.85  −12.57  −11.25 to −14.34  6.53 

Morphometric characteristics of limbal vessel diameter and depth are important. First, they provide information about the function of the vessels34 and give further insight into the anatomical/physiological properties within the limbus.1 An understanding of the morphometry in the limbal region is of further importance in ocular pathophysiology, for example, the microvascular changes that occur during and after contact lens wear.35,36 While the changes that occur in the cornea after contact lens wear have been very well documented, there is little knowledge about the effect of contact lens wear on morphometric microvascular properties within the limbus. Studies have shown increase in limbal redness35 and significant neovascularization within the limbus after extended contact lens wear,36 our imaging technique would thus provide a quantitative means of assessing these limbal morphometric changes. Other applications where quantitative characterization of the vessels in the limbus would be beneficial include vessel changes (size, tortuosity, neovascularization, etc.) in response to ocular surface injury, infection and inflammation.

The morphometric findings of this study suggest that the vessels found in the superior limbus are on average larger (have greater diameter) and are closer to the ocular surface than the vessels located within the inferior limbus. In support of this finding, there appears to be greater demand for oxygen in the region around the superior limbus,4,5,7 and this could be a reason for the difference in vessel sizes within the two limbal regions. The difference in vessel size between the superior and inferior limbus may very well be an adaptation to the chronic hypoxia caused by the upper eyelid's constant coverage of the superior limbus.37

It is important to mention that though we have focused on hypoxia as being a primary difference between the upper limbus and other corneal areas not covered by the lid, there are other putative differences that alone or in combination with any of the others might contribute to structural and/or physiological differences that might impact vascularity under the lid. These would include mechanical effects of the lid on the tissue, the effect of the lid in occluding illumination (in particular, perhaps, UV), differences in the chemistry of the tear film, and thermal effects. Since, unfortunately, we are not able to systematically assess the contributions of these variables, at least for the time being, we can only speculate that they might play a role in regional corneal, conjunctival and scleral tissue differences: This is not any different than our speculation about the effect of the lid inducing relative hypoxia.

There were some limitations to our study. For our experiment, a refractive index of 1.376 was assumed for the entire corneo-limbal region. It is important to note that a variation in refractive index both axially and across the cornea has previously been reported.38 Since we did not adopt these variations to adjust the images from which measurements were made there might be minor variations of our measurements compared to, say, histological measurements. In addition to this challenge, vessel contents do not have the same refractive index; this might also contribute minor errors in the transitioning from optical thickness measures to physical thickness. Since we were relatively unselective in our sampling as far as controlling potential covariates that might have influenced vessel diameter is concerned (e.g. stimulants in the diet), it is possible that vessel diameter (but presumably not vessel depth) might have been influenced by these sorts of factors. Nevertheless, within participants and on average, the relationship between diameter and depth was similarly linear, and although the slopes of the functions illustrated in Fig. 3 might have been different because of, say, a dietary vaso-constrictor or vaso-dilator, the linearity of the relationships would not have been expected to be altered (although the regression intercept but not the regression slopes might have been expected to be different).

The sample size was not large and one might argue that the differences between participants was large (or one might also argue that the difference between participants was small). Unfortunately, with a new metric, there is little to go on in making judgements about variability. What we were able to determine, however, was that despite the between subject variability, the difference in mean vessel size and depth statistically differed with location (a calculation based both on the mean difference as well as the variability between participants). A larger sample size or less variability between participants would not theoretically alter this, other than making it less likely that we would be rejecting the null hypothesis in error (i.e., making a type I error).

Finally, the vasculature of the corneo-scleral limbus consists of both blood and lymph vessels. Because the ranges of blood and lymph vessels diameters overlap and the fact that our study employed only morphological OCT imaging, it was not possible to distinguish between blood and lymph vasculature in from the OCT data. Because blood and lymph flow have different velocities, it may be possible to identify blood and lymph vessels in OCT images by employing a Doppler OCT protocol. The OCT instrument used in our study is capable of executing a Doppler OCT imaging protocol. However, there are several potential challenges: first, lymph is far less scattering than red blood cells in the 1060nm spectral range (the operation wavelength of OCT instrument used in our study), which means that the Doppler signal from lymph vessels will be close to the noise level. Second, lymph and blood flow velocities in vessels are dependent on the vessel size and viscosity of the flowing fluid. Blood flow in capillaries has rates similar to that of large lymph vessels, therefore identifying blood and lymph vessels based purely on frequency Doppler shift would generate unreliable data and can lead to incorrect conclusions.

For these reasons, we chose to adopt the term “vasculature” throughout our manuscript without specifying blood or lymph vessels. It is evident that this limits the findings of this study to its utility in aqueous related applications such as glaucoma pathophysiology. However, in relation to the earlier mentioned applications (tracking limbal vessel changes in response to contact lens wear corneal injury or infection, and identifying and quantifying neovascularization in limbus) our technique is a valid and useful tool.


The results from this study primarily indicate that vessel depth and diameter within the human limbus can effectively be imaged and measured in vivo using UHR-OCT, even under the lid where details might be obscured with conventional methods (e.g., a slit lamp biomicroscope). In addition, with protocols controlling imaging procedures (e.g., optical and structural alignment) and automated measurement tools, these measurements are repeatable. There are linear associations between vessel diameter and depth in both the upper and lower limbus and together with their quantitative differences it can be suggested that the relatively hypoxic environment under the upper lid contributes to vessels in the superior limbus being relatively larger and closer to the ocular surface than those within the inferior limbus. UHR-OCT can be a useful tool in evaluating changes to the microvascular properties that may occur within the limbus after contact lens wear.

Conflicts of interest

The authors have no conflicts of interest to declare.


This work was supported by NSERC Canada (grant numbers 183965 (TS), 290565 (KB)).

E.L. van der Merwe,S.H. Kidson
Advances in imaging the blood and aqueous vessels of the ocular limbus
Exp Eye Res, 91 (2010), pp. 118-126
N. Efron,L. Jones,A.J. Bron
The TFOS International Workshop on Contact Lens Discomfort: report of the contact lens interactions with the ocular surface and adnexa subcommittee
Investig Ophthalmol Vis Sci, 54 (2013),
C.W. Oyster
The Human Eye: Structure and Function
Sinauer Associates, (1999)
W.J. Benjamin,R.M. Hill
Human cornea: superior and central oxygen demands
Graefe's Arch Clin Exp Ophthalmol, 226 (1988), pp. 41-44
W.J. Benjamin,M.A. Rasmussen
Oxygen consumption of the superior cornea following eyelid closure
Acta Ophthalmol, 66 (1988), pp. 309-312
J. Fitzgerald,N. Efron
Oxygen uptake profile of the human cornea
Clin Exp Optom, 69 (1986), pp. 149-152
W.J. Benjamin,C.M. Ruben
Human corneal oxygen demands at superior, central, and inferior sites
J Am Optom Assoc, 66 (1995), pp. 423-428
E. Papas
The role of hypoxia in the limbal vascular response to soft contact lens wear
Eye Contact Lens: Sci Clin Pract, 29 (2003),
S72-4; discussion S83-4, S192-4.
J. Amann,G. Holley,S. Lee,H. Edelhauser
Increased endothelial cell density in the paracentral and peripheral regions of the human cornea
Am J Ophthalmol, 135 (2003), pp. 584-590
C. Boote,S. Dennis,R. Newton,H. Puri,K. Meek
Collagen fibrils appear more closely packed in the prepupillary cornea: optical and biomechanical implications
Investig Ophthalmol Vis Sci, 44 (2003), pp. 2941-2948
A.C. Romano,E.M. Espana,S.H. Yoo,M.T. Budak,J.M. Wolosin,S.C. Tseng
Different cell sizes in human limbal and central corneal basal epithelia measured by confocal microscopy and flow cytometry
Investig Ophthalmol Vis Sci, 44 (2003), pp. 5125-5129
Z. Liu,A. Huang,S. Pflugfelder
Evaluation of corneal thickness and topography in normal eyes using the Orbscan corneal topography system
Br J Ophthalmol, 83 (1999), pp. 774-778
Z. Liu,Y. Xie,M. Zhang
Corneal topography and pachymetry in normal eyes
Zhonghua Yan Ke Za Zhi, 37 (2001), pp. 125-128
T. Hamanaka,A. Bill,R. Ichinohasama,T. Ishida
Aspects of the development of Schlemm's canal
Exp Eye Res, 55 (1992), pp. 479-488
J. Krohn,T. Bertelsen
Light microscopy of uveoscleral drainage routes after gelatine injections into the suprachoroidal space
Acta Ophthalmol Scand, 76 (1998), pp. 521-527
A. Bron,R. Tripathi,B. Tripathi,E. Wolff
Wolff's Anatomy of the Eye and Orbit
Chapman & Hall Medical, (1997)
R. Smith
Haploinsufficiency of the transcription factors FOXC1 and FOXC2 results in aberrant ocular development
Hum Mol Genet, 9 (2000), pp. 1021-1032
P.C. Burger,D.B. Chandler,A.W. Fryczkowski,G.K. Klintworth
Scanning electron microscopy of microcorrosion casts: applications in ophthalmologic research
Scan Microsc, 1 (1987), pp. 223-231
W. Drexler,J. Fujimoto
Optical Coherence Tomography
Springer, (2008)
Y. Feng,T. Simpson
Comparison of human central cornea and limbus in vivo using optical coherence tomography
Optom Vis Sci, 82 (2005), pp. 416-419
L. Kagemann,G. Wollstein,H. Ishikawa
Identification and assessment of Schlemm's canal by spectral-domain optical coherence tomography
Investig Ophthalmol Vis Sci, 51 (2010), pp. 4054-4059
K. Bizheva,N. Hutchings,L. Sorbara,A. Moayed,T. Simpson
In vivo volumetric imaging of the human corneo-scleral limbus with spectral domain OCT
Biomed Opt Exp, 2 (2011), pp. 1702-1794
P. Li,L. An,R. Reif,T. Shen,M. Johnstone,R. Wang
In vivo microstructural and microvascular imaging of the human corneo-scleral limbus using optical coherence tomography
Biomed Opt Express, 2 (2011), pp. 3109-3118
I. Grulkowski,J.J. Liu,B. Baumann,B. Potsaid,C. Lu,J.G. Fujimoto
Imaging limbal and scleral vasculature using swept source optical coherence tomography
Photonics Lett Pol, 3 (2011), pp. 132-134
L. Sorbara,T. Simpson,J. Maram,E. Song,K. Bizheva,N. Hutchings
Optical edge effects create conjunctival indentation thickness artefacts
Ophthalmic Physiol Opt, 35 (2015), pp. 283-292
K. Bizheva,P. Lee,L. Sorbara,N. Hutchings,T. Simpson
In vivo volumetric imaging of the human upper eyelid with ultrahigh-resolution optical coherence tomography
J Biomed Opt, 15 (2010), pp. 0405-408
R. Steinert,D. Huang
Anterior Segment Optical Coherence Tomography
SLACK, (2008)
B. Thompson,S.A. Read,S.O. Dumoulin
Imaging the visual system: from the eye to the brain
Ophthalmic Physiol Opt, 36 (2016), pp. 213-217
W. Rasband,J.U. Image
National Institutes of Health
Bethesda, (2014)
P. Thevenaz,U. Ruttimann,M. Unser
A pyramid approach to subpixel registration based on intensity
IEEE Trans Image Process, 7 (1998), pp. 27-41
R Core Team
R: A Language and Environment for Statistical Computing
R Foundation for Statistical Computing, (2012)
SPSS Inc. Released 2007. SPSS for Windows, Version 16.0. Chicago, SPSS Inc.
A. Carkeet
Exact parametric confidence intervals for Bland–Altman limits of agreement
Optom Vis Sci, 92 (2015), pp. 71-80
E.B. Papas
The limbal vasculature
Contact Lens Anterior Eye, 26 (2003), pp. 71-76
C.W. McMonnies,A. Chapman-Davies,B.A. Holden
The vascular response to contact lens wear
Optom Vis Sci, 59 (1982), pp. 795-799
K.A. Dumbleton,R.L. Chalmers,D.B. Richter,D. Fonn
Vascular response to extended wear of hydrogel lenses with high and low oxygen permeability
Optom Vis Sci, 78 (2001), pp. 147-151
J.L. Baum
Prolonged eyelid closure is a risk to the cornea
Cornea, 16 (1997), pp. 602-611
B. Vasudevan,T.L. Simpson,J.G. Sivak
Regional variation in the refractive-index of the bovine and human cornea
Optom Vis Sci, 85 (2008), pp. 977-981
Corresponding author. (Trefford Simpson
Copyright © 2017. Spanish General Council of Optometry
J Optom 2018;11:57-65 - Vol. 11 Num.1 DOI: 10.1016/j.optom.2017.02.003