October 2004
Volume 45, Issue 10
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Cornea  |   October 2004
Objective Measurements of Corneal Light-Backscatter during Corneal Swelling, by Optical Coherence Tomography
Author Affiliations
  • Jianhua Wang
    From the Centre for Contact Lens Research, School of Optometry, University of Waterloo, Waterloo, Ontario, Canada.
  • Trefford L. Simpson
    From the Centre for Contact Lens Research, School of Optometry, University of Waterloo, Waterloo, Ontario, Canada.
  • Desmond Fonn
    From the Centre for Contact Lens Research, School of Optometry, University of Waterloo, Waterloo, Ontario, Canada.
Investigative Ophthalmology & Visual Science October 2004, Vol.45, 3493-3498. doi:10.1167/iovs.04-0096
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      Jianhua Wang, Trefford L. Simpson, Desmond Fonn; Objective Measurements of Corneal Light-Backscatter during Corneal Swelling, by Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2004;45(10):3493-3498. doi: 10.1167/iovs.04-0096.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

purpose. To demonstrate that corneal light-backscatter can be measured objectively during corneal swelling by optical coherence tomography (OCT).

methods. One eye (randomly selected) of 20 non–contact-lens wearers (10 men and 10 women; mean age, 35.6 ± 9.6 years) was patched during 3 hours of soft contact lens (SCL) wear. The contralateral eye acted as the control. Central corneal images were captured before and after SCL wear at 20-minute intervals over 100 minutes using optical coherence tomography (OCT) to obtain corneal thickness and light-backscatter profiles. OCT backscattered light of the epithelial layer (decided by the thickness measurements) and 10 equally divided layers of the remaining cornea were analyzed with a custom software program. Two baseline measurements were taken at different visits before lens wear to test the repeatability of light-backscatter measurements.

results. From two baseline measurements, repeated measurements showed good repeatability of normalized backscatter results. Immediately after contact lens removal, total central corneal thickness increased significantly by 13.8% ± 2.3% (mean ± SD) compared with baseline (P = 0.0001, paired t-test) and then decreased during the deswelling course. Corneal backscattered light changed significantly (repeated-measures ANOVA [Re-ANOVA]: F(50, 950) = 2.22, P = 0.0001) after lens wear, and a significant increase in backscatter was found in the epithelial layer (36.4%) and the most posterior corneal layer (35.6%) immediately after lens removal (post hoc test, P = 0.005). There was a strong correlation (r = 0.9375, P < 0.05) between the change in backscatter and corneal swelling during the deswelling period. The backscatter recovery rate was approximately the same for both epithelial and posterior layers after lens removal.

conclusions. Light-backscattering analysis with OCT seems to be a promising and repeatable method of objectively measuring corneal backscatter. This study has demonstrated that corneal backscattered light increased in the anterior and posterior layers of the cornea during corneal swelling induced by contact lens wear and eye closure.

Corneal transparency and visual performance are currently receiving much attention, particularly after contact lens wear and excimer laser surgery. Corneal transparency is dependent on corneal microstructure and normal metabolism. Any disturbance, such as corneal edema and surgery can compromise corneal transparency, resulting in reduced contrast sensitivity and increasing susceptibility to glare. 1 2 3 The loss of corneal transparency induces increased corneal light-backscatter, which is estimated in many clinical conditions by different approaches. 4 5 6 7 8 9 10 Arbitrary scales have been used as an objective method in most clinics, either by differentiating mild, moderate, or severe haze or by using a scoring scale of 1 to 4. 7 11 Kikkawa and Hirayama 12 used slit lamp photography to assess light scatter in an attempt to establish the relationship between corneal swelling and light-scattering. Recently, high-frequency ultrasound, 13 Scheimpflug photography, 14 confocal microscope through-focusing (CMTF), 4 5 15 and other light-scatter measurements 7 8 9 have been reported; however, none of these is commonly used clinically. 
Optical coherence tomography (OCT) has been used to examine the ocular fundus and anterior segment in a noncontact and noninvasive way. 16 17 Based on light-backscatter measurements detected with an interferometric technique, OCT has been reported to measure corneal and epithelial thickness across the cornea 16 18 19 20 and precorneal tear film thickness. 21 However, there is no report so far that has attempted to quantify OCT light-backscattering of the cornea and its clinical application for objective estimation of corneal transparency. 
This experiment was designed to determine the feasibility of quantifying light-backscatter before and after corneal swelling was induced with soft contact lens wear and eye closure. In addition, a system was designed to segment the cornea into distinct layers from anterior to posterior to determine whether there were regional differences in light-backscattering. 
Methods
Subjects
Twenty subjects (10 men and 10 women; age, 35.6 ± 9.6 years) with no history of contact lens wear or any current ocular or systematic disease were recruited for this study. Informed consent was obtained from each subject after ethics approval was obtained from the Office of Research Ethics, University of Waterloo. All subjects were treated in accordance with the tenets of the Declaration of Helsinki. 
Instrumentation and Lenses
An OCT system (Carl Zeiss Meditec, Dublin, CA) was used in this study. Principles of OCT and measurement of the cornea has been described previously. 17 18 20 22 23 In this study, we measured corneal thickness as the distance between the first and last peaks and epithelial thickness as the distance between the first and second peaks, as described in other studies. 20 22 23 24 To ensure that the OCT scanned the central location, a central fixation target within the OCT was provided, and a TV monitor was used to view the scan area. When the observation and scanning axes were coaxial, the scanning axis was orthogonal to the corneal surface, and a clear reflection was obtained on the monitor, the OCT image was recorded. Using this method, high repeatability of epithelial and corneal thicknesses was obtained. 18 A single-line scan mode was used to measure corneal thickness, with a scan length of 1.13 mm. There were 100 sagittal scan points in each OCT measurement, which meant that the nominal lateral separation was 11.3 μm. OCT calibration was undertaken using the same procedure as that described in a study conducted by Huang et al. 17  
Lathe-cut, 38% water content, hydroxyethyl-methacrylate (HEMA), soft contact lenses with total diameter 14.0 to 14.3 mm with base curve 8.3 to 8.9 mm, central thickness 0.34 to 0.40 mm (total diameter, 9.20–9.80 mm) with parallel back and front surfaces were used in our study to induce corneal edema. These lenses had an average oxygen transmissibility (Dk/t) of 2.1 × 10−9
Procedure
In a prospective experimental study, two study visits were scheduled after 10 AM, to ensure that the corneal edema induced by overnight eye closure had dissipated. All participants were asked to awaken no later than 7 AM. At the initial visit, participants were screened to determine their eligibility for the study. Study procedures were explained and informed consent was obtained. A biomicroscopic examination, automated refraction/keratometry and measurements of both central corneal epithelial thickness and total corneal thickness were conducted at the initial screening visit. At the subsequent visit, these baseline measurements were obtained with OCT, before wearing a contact lens on a randomly selected eye. After lens insertion, the fit was checked to ensure adequate corneal coverage and that no postlens debris was present. The contact-lens–wearing eye was then patched for 3 hours with an ophthalmic eye patch, gauze, and surgical tape to ensure complete eye closure. During the study period, participants were asked to remain at the Centre for Contact Lens Research (CCLR). Normal blinking was allowed for the control eyes, but participants were asked not to close the control eye for longer than 2 minutes. After lens removal, OCT measurements were repeated six times at 20-minute intervals up to 100 minutes. The control eye was measured at approximately the same time as lens removal from the other eye, at 60 and 100 minutes. 
Data Analysis
Custom software was used to process raw data, and multiple sagittal scan points were analyzed to obtain the measurement of epithelial and total corneal thickness. OCT-determined light-backscattering of the epithelial layer (decided by the thickness measurements) and 10 equally divided layers of the remaining layers (whole cornea excluding the epithelium) was analyzed with the custom software. To standardize the light intensity of each OCT measurement for comparison independently on the light intensity of each image, a term called “normalized backscatter” was introduced and calculated by the following equation  
\[\mathrm{Normalized\ backscatter\ {=}}\ \frac{\mathrm{mean\ light\ reflectivity\ of\ each\ layer}}{\mathrm{mean\ light\ reflectivity\ of\ the\ whole\ cornea}}\]
Data analysis was conducted on computer (Statistica; StatSoft, Inc., Tulsa, OK). Paired t-tests were used to determine whether there were pair-wise differences (P < 0.05). Repeated-measurement analysis of variance (Re-ANOVA) and paired t-tests were used to determine whether there was a significant change (P < 0.05). Repeatability was calculated as the standard deviation of the differences between the test and retest results at each position before lens wear. 
Results
Normalized corneal backscatter profiles of two baseline visits before lens wear showed good repeatability (standard deviation of the difference of the normalized backscatter between two visits: 0.07) as shown in Figure 1 . The magnitudes of backscattered light were different among corneal sections (slices) from the epithelium to the posterior stroma (ANOVA: F(10,190) = 30.24; P = 0.000). 
Immediately after contact lens removal, central corneal thickness increased significantly (13.8% ± 2.3%; mean ± SD) from baseline (P = 0.0001, paired t-test) then decreased during the deswelling course. The profile of corneal backscattered light changed significantly (Re-ANOVA: F(50, 950) = 2.22, P = 0.0001) after lens wear (Fig. 2) and significant increases were found in the epithelium (EP: 36.4%), anterior (slice [S]1: 19.4%), and posterior stromal layers (S10: 35.6%) immediately after lens removal (post hoc test, P = 0.005), compared with baseline, but returned to baseline by 100 minutes. The anterior (S1: P = 0.005) and posterior (S10: P = 0.003) stromal backscattered light increased significantly compared to the middle layers (S6). Figure 3 shows examples of OCT images of central (1.13 mm) corneal scans before lens insertion and immediately after lens removal. The OCT image shows increased backscattered light depicted in the red and yellow. The quantitative measures of the backscattered light are represented by the reflectivity profiles. The “After” profile shows how the peaks have altered. The graphs of the slice profiles illustrate how the backscattered profile has become bowl shaped, reflecting an increase in light-backscattering in the epithelium, anterior, and posterior stromal layers (lower right graph). There was a strong correlation (r = 0.937, P < 0.05) between the changes in light-backscattering (the integrated area under each profile curve) and corneal swelling during the deswelling period, as indicated in Figure 4
Figure 5 shows the light-backscattering recovery of the anterior and posterior stromal layers during the deswelling period. The Pearson correlation (r) was 0.745 for the anterior layer (S1) and 0.934 for the posterior stromal layer (S10). According to exponential regression, the recovery rate (slope) was −1.08 for the anterior layers and −0.906 for the posterior layers (no significant difference between the two slopes, P > 0.05). The recovery of backscattered light in the epithelium and posterior stromal layer correlated positively with corneal deswelling, as shown in Figure 6 (Pearson correlation: r = 0.938 for the epithelium and r = 0.982 for the posterior stromal layer). 
There was no significant change in light-backscatter in the control eyes (Re-ANOVA: F(20, 380) = 0.72, P >0.05) compared with baseline. However, total corneal thickness in the control eyes changed significantly during the post–lens-wear period (Re-ANOVA: F(4,76) = 5.57, P H-F = 0.003), due to thinning at 60 (−0.6%) and 100 (−0.5%) minutes compared with baseline (post hoc test: P = 0.004). 
Discussion
A novel method was demonstrated in this study to quantify corneal backscattered light in different layers of the cornea by using OCT. After normalization of the OCT data, a repeatable profile was found, as illustrated in Figure 1 . In these slice profiles, each data point represents mean light-backscatter in the slice (EP and S1-10) and the changes within the slice were demonstrated quantitatively. 
Allemann et al. 13 quantified ultrasonic acoustic backscatter in the anterior 150 μm of the stroma in excimer laser-ablated rabbit corneas and found increased acoustic backscatter after surgery. Møller-Pedersen et al. 5 used confocal microscopy through focusing (CMTF), for objective estimation of the haze in the cornea after photorefractive keratectomy (PRK) by digital image analysis based on the light reflectivity of a series of images obtained by confocal microscopy. They found a significant correlation between the objective CMTF haze estimate and clinical haze grading using slit lamp examination. However, the methods used in these studies require direct contact with the cornea. OCT is a noncontact method and has been used to demonstrate an increase in backscattered light at the interface between the corneal flap and the bed after LASIK. 23 Using a slit lamp–adapted OCT system, Wirbelauer et al. 25 demonstrated a localized hyper-reflective area, that was found to correlate with a corneal haze after excimer laser phototherapeutic keratectomy (PTK), but the increase was visualized with OCT and not quantified. The authors admitted the limitation of the quantification of increased light-backscatter amplitude because of the variable height and steepness of the slopes of the reflection spikes. 25  
The cornea transmits approximately 90% of the incident light, but is not homogeneous. 26 Normalized backscattered light profiles of the normal cornea (before lens wear) in our study showed a gradual increase in backscattered light from the anterior to posterior stroma as shown in Figures 1 2 and 3 . In the stromal layer, collagen fibrils in the lamellae lie parallel to each other and are nearly uniform in diameter, but increase in diameter from approximately 19 nm in the anterior stroma to 35 nm near the posterior stroma. 27 A stromal hydration gradient was predicted as early as 1979 28 and measured by others. 29 30 31 32 Komai and Ushiki 29 demonstrated water gradients across the bovine cornea and found that corneal water content was a function of the depth of the cornea from the epithelium. This hydration gradient would be expected to provide a backscattered-light gradient, with the region of greatest hydration (most posterior) inducing the greatest backscatter and the zone of least hydration producing the least. We found a light-scatter gradient across the cornea. 
OCT-detected backscatter (as shown in Fig. 3 ), which includes light that is specularly reflected from keratocyte nuclei, is similar to that detected by a confocal microscope with similar spikes. 5 33 34 35 36 Many studies indicate the keratocyte density is greatest in the anterior stroma in the human cornea. 35 37 38 39 Although keratocyte nuclei cause reflectivity, which dominates backscatter when detected at specular angles, 40 41 the backscatter obtained with the OCT does not appear to depend solely on keratocyte density. If the backscatter is associated solely with keratocyte density, we would have found a decrease (instead of an increase) in backscattering in the posterior stroma during corneal swelling, because the cell density decreased. 42  
The refractive index of the anterior stroma was found to be greater than the posterior stroma in the bovine and human cornea. 43 44 Patel et al. 44 suggested that the corneal refractive index varies along corneal depth and is most likely a function of local hydration. Results from an in vitro study of bovine eyes showed the refractive index decreased from 1.379 to 1.376 in the anterior stroma and from 1.373 to 1.367 in the posterior stroma when corneal swelling was induced (Dennis S, et al. IOVS 2003;44:ARVO E-Abstract 886). Backscattered light has been found to be closely related to corneal swelling, 45 46 47 although Kikkawa and Hirayama 12 have paradoxically shown that the relationship was dependent on layers of the cornea. They found little anterior corneal swelling with intense light-scattering and the opposite effect in the posterior corneal layers. We found a strong correlation between recovery of backscattered light in the epithelium and posterior stroma, and corneal deswelling. This suggests that corneal backscattered light in the epithelium may relate to the distortion of the microstructure (not necessarily thickness changes) and the backscattered light in the stroma may be related to local hydration and refractive index. Further studies are needed to establish a method to predict localized corneal swelling from the changes in backscattered light after contact lens wear. 
In our study, backscattered light was analyzed in each slice of the cornea after 3 hours of contact lens wear and eye closure. A significant increase of backscattered light was found in the epithelium and posterior stromal layer, in agreement with previous observations. 48 49 The changes of corneal transparency from corneal swelling has been well documented, 12 48 50 51 52 53 but reduction of vision was only found if significant swelling was induced. 54 Lambert and Klyce 48 found increased light-scattering in the epithelium during corneal swelling induced by oxygen deprivation and demonstrated how this caused subjective halos. They concluded that the visual halos were due to the change in transparency of the epithelium, although, paradoxically, epithelial thickness did not increase. The absence of epithelial increase from hypoxia has been found by others. 18 20 48 55 Corneal striae and folds (localized light scatter) appear in the posterior stroma accompanying corneal swelling after contact lens wear. 51 56 Korb and Exford 52 described the phenomenon of central corneal clouding due to PMMA lens wear. Farris et al. 57 and Korb and Exford 52 reported that this phenomenon is due to a localized epithelial response to PMMA lens wear, resulting in a focal increase of backscattered light. 
The light-backscattering changes that are demonstrated in Figure 2 support the theory that the stroma has regions with distinctive swelling properties. 12 29 58 59 The anterior and posterior corneal layers prevent excessive imbibition of fluid, and removal of either layer results in corneal swelling. 60 Cristol et al. 59 reported that stromal swelling occurred more rapidly through the posterior corneal surface than the anterior surface in human and rabbit eyes. This is probably due to the anterior stroma having narrower and more interwoven lamellae. 12 29 58 The anterior and posterior corneal layers are more vulnerable to swelling than the central stroma because of the proximity of the aqueous and precorneal tear film. Our results support this, because backscattered light increased in the anterior (S1) and posterior (S10) layers compared and not in the midstroma. 
Our results showed that light-backscattering recovery in the epithelium and posterior stroma occurred simultaneously after lens removal, which supports the theory that active mechanisms are present to maintain corneal thickness and thus corneal transparency. 61  
The normalization used to analyze the OCT data caused an apparent decrease in light-backscatter in the midstroma because of the increase in the epithelium and posterior stroma, which caused a net increase in light-scattering by the cornea. Therefore, the layer without light-scatter changes (or small changes) would be shown as a relative decrease (such as the slice 7 shown in Fig. 2 ) due to the normalization process. The increase of backscattered light of the anterior and posterior layers does not seem to be a random effect, as evidenced by the systematic course of recovery after lens removal. 
In summary, light-backscatter analysis with OCT seems to be a promising method for the objective estimation of corneal light-backscattering. Corneal light-backscattering increases in the epithelium and posterior stromal layer of the cornea during corneal swelling induced by contact lens wear and eye closure. 
 
Figure 1.
 
Baseline 1 and 2 results were obtained at two different visits before wearing contact lenses to test the repeatability of the measurements. Normalized corneal backscattered light (mean ± 2 SE) in each slice from the epithelium to the posterior stroma measured on two different days in 20 eyes. Note that the corneal backscattered light appears to increase gradually from the anterior to the posterior (S1 to S10).
Figure 1.
 
Baseline 1 and 2 results were obtained at two different visits before wearing contact lenses to test the repeatability of the measurements. Normalized corneal backscattered light (mean ± 2 SE) in each slice from the epithelium to the posterior stroma measured on two different days in 20 eyes. Note that the corneal backscattered light appears to increase gradually from the anterior to the posterior (S1 to S10).
Figure 2.
 
The changes of normalized backscattered light after lens removal after 3 hours of lens wear and eye closure showed a bowl-shaped pattern due to an increase in epithelial (EP) and posterior stromal layers immediately after lens removal and returning to a relatively flat pattern at 100 minutes.
Figure 2.
 
The changes of normalized backscattered light after lens removal after 3 hours of lens wear and eye closure showed a bowl-shaped pattern due to an increase in epithelial (EP) and posterior stromal layers immediately after lens removal and returning to a relatively flat pattern at 100 minutes.
Figure 3.
 
Examples of OCT light-backscattering two-dimensional images of the central cornea (1.13 mm) before (top left) and after lens wear (top right). The increase in the red/orange colors is indicative of increased light-backscattering. The magnitude of backscattered light is shown in the reflectivity profiles, higher after lens wear (middle right) in the epithelium, anterior stromal layer (S1), and posterior stromal layer (S10) than that before lens wear (middle left). The graphs illustrate the different normalized backscattered-light profiles before (bottom left) and how light-backscattering increased in the epithelium, anterior (S1) and posterior (S10) stromal layers after lens wear (bottom right).
Figure 3.
 
Examples of OCT light-backscattering two-dimensional images of the central cornea (1.13 mm) before (top left) and after lens wear (top right). The increase in the red/orange colors is indicative of increased light-backscattering. The magnitude of backscattered light is shown in the reflectivity profiles, higher after lens wear (middle right) in the epithelium, anterior stromal layer (S1), and posterior stromal layer (S10) than that before lens wear (middle left). The graphs illustrate the different normalized backscattered-light profiles before (bottom left) and how light-backscattering increased in the epithelium, anterior (S1) and posterior (S10) stromal layers after lens wear (bottom right).
Figure 4.
 
Integrated normalized backscatter (percentage of the cornea) versus corneal swelling during the recovery period after 3 hours of lens wear and eye closure. There was a strong correlation between the changes of the light-backscattering (the integrated area under each profile curve) and corneal swelling during the deswelling period.
Figure 4.
 
Integrated normalized backscatter (percentage of the cornea) versus corneal swelling during the recovery period after 3 hours of lens wear and eye closure. There was a strong correlation between the changes of the light-backscattering (the integrated area under each profile curve) and corneal swelling during the deswelling period.
Figure 5.
 
Light-backscatter recovery in the anterior and posterior stromal layers.
Figure 5.
 
Light-backscatter recovery in the anterior and posterior stromal layers.
Figure 6.
 
The recovery of backscattered light in the epithelium (EP) and posterior stromal layer (S10) correlated positively with corneal deswelling.
Figure 6.
 
The recovery of backscattered light in the epithelium (EP) and posterior stromal layer (S10) correlated positively with corneal deswelling.
The authors thank Trevor German for development of the software for this study. 
Lohmann CP, Fitzke F, O’Brart D, Muir MK, Timberlake G, Marshall J. Corneal light scattering and visual performance in myopic individuals with spectacles, contact lenses, or excimer laser photorefractive keratectomy. Am J Ophthalmol. 1993;115:444–453. [CrossRef] [PubMed]
Holden R, Shun-Shin GA, Brown NA. Central corneal light scatter in long-term diabetics. Am J Optom Physiol Opt. 1994;8:44–45.
Griffiths SN, Drasdo N, Barnes DA, Sabell AG. Effect of epithelial and stromal edema on the light scattering properties of the cornea. Am J Optom Physiol Opt. 1986;63:888–894. [CrossRef] [PubMed]
Møller-Pedersen T, Cavanagh HD, Petroll WM, Jester JV. Stromal wound healing explains refractive instability and haze development after photorefractive keratectomy: a 1-year confocal microscopic study. Ophthalmology. 2000;107:1235–1245. [CrossRef] [PubMed]
Møller-Pedersen T, Vogel M, Li HF, Petroll WM, Cavanagh HD, Jester JV. Quantification of stromal thinning, epithelial thickness, and corneal haze after photorefractive keratectomy using in vivo confocal microscopy. Ophthalmology. 1997;104:360–368. [CrossRef] [PubMed]
Olsen T. Light scattering from the human cornea. Invest Ophthalmol Vis Sci. 1982;23:81–86. [PubMed]
Braunstein RE, Jain S, McCally RL, Stark WJ, Connolly PJ, Azar DT. Objective measurement of corneal light scattering after excimer laser keratectomy. Ophthalmology. 1996;103:439–443. [CrossRef] [PubMed]
Maldonado M, Arnau V, Martinez-Costa R, et al. Reproducibility of digital image analysis for measuring corneal haze after myopic PRK. Am J Ophthalmol. 1997;123:31–41. [CrossRef] [PubMed]
Maldonado MJ, Arnau V, Navea A, et al. Direct objective quantification of corneal haze after excimer laser photorefractive keratectomy for high myopia. Ophthalmology. 1996;103:1970–1978. [CrossRef] [PubMed]
Lohmann C, Timberlake GT, Fitzke F, Gartry D, Muir MK, Marshall J. Corneal light scattering after excimer laser photorefractive keratectomy: the objective measurement of haze. Refract Corneal Surg. 1992;8:114–121. [PubMed]
Fantes FE, Hanna KD, Waring GO, Pouliquen Y, Thompson KP, Savoldelli M. Wound healing after excimer laser keratomileusis (photorefractive keratectomy) in monkeys. Arch Ophthalmol. 1990;108:665–675. [CrossRef] [PubMed]
Kikkawa Y, Hirayama K. Uneven swelling of the corneal stroma. Invest Ophthalmol. 1970;9:735–741. [PubMed]
Allemann N, Chamon W, Silverman RH, et al. High-frequency ultrasound quantitative analyses of corneal scarring following excimer laser keratectomy. Arch Ophthalmol. 1993;111:968–973. [CrossRef] [PubMed]
Binder PS, Bosem M, Weinreb RN. Scheimpflug anterior segment photography assessment of wound healing after myopic excimer laser photorefractive keratectomy. J Cataract Refract Surg. 1996;22:205–212. [CrossRef] [PubMed]
Møller-Pedersen T, Cavanagh HD, Petroll WM, Jester JV. Corneal haze development after PRK is regulated by volume of stromal tissue removal. Cornea. 1998;17:627–639. [CrossRef] [PubMed]
Izatt JA, Hee MR, Swanson EA, et al. Micrometer-scale resolution imaging of the anterior eye in vivo with optical coherence tomography. Arch Ophthalmol. 1994;112:1584–1589. [CrossRef] [PubMed]
Huang Y, Cideciyan AV, Papastergiou GI, et al. Relation of optical coherence tomography to microanatomy in normal and rd chickens. Invest Ophthalmol Vis Sci. 1998;39:2405–2416. [PubMed]
Wang J, Fonn D, Simpson TL, Jones L. The measurement of corneal epithelial thickness in response to hypoxia using optical coherence tomography. Am J Ophthalmol. 2002;133:315–319. [CrossRef] [PubMed]
Wang J, Fonn D, Simpson TL, Sorbara L, Kort R, Jones L. Topographical thickness of the epithelium and total cornea after overnight wear of reverse-geometry rigid contact lenses for myopia reduction. Invest Ophthalmol Vis Sci. 2003;44:4742–4746. [CrossRef] [PubMed]
Wang J, Fonn D, Simpson TL. Topographical thickness of the epithelium and total cornea after hydrogel and PMMA contact lens wear with eye closure. Invest Ophthalmol Vis Sci. 2003;44:1070–1074. [CrossRef] [PubMed]
Wang J, Fonn D, Simpson TL, Jones L. Precorneal and pre- and postlens tear film thickness measured indirectly with optical coherence tomography. Invest Ophthalmol Vis Sci. 2003;44:2524–2528. [CrossRef] [PubMed]
Wang J, Fonn D, Simpson TL, Jones L. Relation between optical coherence tomography and optical pachymetry measurements of corneal swelling induced by hypoxia. Am J Ophthalmol. 2002;134:93–98. [CrossRef] [PubMed]
Maldonado MJ, Ruiz-Oblitas L, Munuera JM, Aliseda D, Garcia-Layana A, Moreno-Montanes J. Optical coherence tomography evaluation of the corneal cap and stromal bed features after laser in situ keratomileusis for high myopia and astigmatism. Ophthalmology. 2000;107:81–87. [CrossRef] [PubMed]
Feng Y, Varikooty J, Simpson TL. Diurnal variation of corneal and corneal epithelial thickness measured using optical coherence tomography. Cornea. 2001;20:480–483. [CrossRef] [PubMed]
Wirbelauer C, Scholz C, Haberle H, Laqua H, Pham DT. Corneal optical coherence tomography before and after phototherapeutic keratectomy for recurrent epithelial erosions. J Cataract Refract Surg. 2002;28:1629–1635. [CrossRef] [PubMed]
Beems E, van Best JA. Light transmission of the cornea in whole human eyes. Exp Eye Res. 1990;50:393–396. [CrossRef] [PubMed]
Freegard T. The physical basis of transparency of the normal cornea. Am J Optom Physiol Opt. 1997;11:465–471.
Klyce SD, Russell SR. Numerical solution of coupled transport equations applied to corneal hydration dynamics. J Physiol. 1979;292:107–134. [CrossRef] [PubMed]
Komai Y, Ushiki T. The three-dimensional organization of collagen fibrils in the human cornea and sclera. Invest Ophthalmol Vis Sci. 1991;32:2244–2258. [PubMed]
Castoro JA, Bettelheim AA, Bettelheim FA. Water gradients across bovine cornea. Invest Ophthalmol Vis Sci. 1988;29:963–968. [PubMed]
Fisher BT, Masiello KA, Goldstein MH, Hahn DW. Assessment of transient changes in corneal hydration using confocal Raman spectroscopy. Cornea. 2003;22:363–370. [CrossRef] [PubMed]
Ansari RR. Ocular static and dynamic light scattering: a noninvasive diagnostic tool for eye research and clinical practice. J Biomed Opt. 2004;9:22–37. [CrossRef] [PubMed]
Erie JC, Patel SV, McLaren JW, et al. Effect of myopic laser in situ keratomileusis on epithelial and stromal thickness: a confocal microscopy study. Ophthalmology. 2002;109:1447–1452. [CrossRef] [PubMed]
Patel S, McLaren J, Hodge D, Bourne W. Normal human keratocyte density and corneal thickness measurement by using confocal microscopy in vivo. Invest Ophthalmol Vis Sci. 2001;42:333–339. [PubMed]
Hahnel C, Somodi S, Weiss DG, Guthoff RF. The keratocyte network of human cornea: a three-dimensional study using confocal laser scanning fluorescence microscopy. Cornea. 2000;19:185–193. [CrossRef] [PubMed]
Li HF, Petroll WM, Møller-Pedersen T, Maurer JK, Cavanagh HD, Jester JV. Epithelial and corneal thickness measurements by in vivo confocal microscopy through focusing (CMTF). Curr Eye Res. 1997;16:214–221. [CrossRef] [PubMed]
Mustonen RK, McDonald MB, Srivannaboon S, Tan AL, Doubrava MW, Kim CK. Normal human corneal cell populations evaluated by in vivo scanning slit confocal microscopy. Cornea. 1998;17:485–492. [CrossRef] [PubMed]
Prydal JI, Franc F, Dilly PN, Kerr Muir MG, Corbett MC, Marshall J. Keratocyte density and size in conscious humans by digital image analysis of confocal images. Am J Optom Physiol Opt. 1998;12:337–342.
Petroll W, Boettcher K, Barry P, Cavanagh H, Jester J. Quantitative assessment of anteroposterior keratocyte density in the normal rabbit cornea. Cornea. 1995;14:3–9. [PubMed]
McCally RL, Farrell RA. The depth dependence of light scattering from the normal rabbit cornea. Exp Eye Res. 1976;23:69–81. [CrossRef] [PubMed]
Farrell RA, McCally RL. On the interpretation of depth dependent light scattering measurements in normal corneas. Acta Ophthalmol (Copenh). 1976;54:261–270. [PubMed]
Efron N, Mutalib HA, Perez-Gomez I, Koh HH. Confocal microscopic observations of the human cornea following overnight contact lens wear. Clin Exp Optom. 2002;85:149–155. [CrossRef] [PubMed]
Patel S. Refractive index of the mammalian cornea and its influence during pachometry. Ophthalmic Physiol Opt. 1987;7:503–506. [CrossRef] [PubMed]
Patel S, Marshall J, Fitzke FW, III. Refractive index of the human corneal epithelium and stroma. J Refract Surg. 1995;11:100–105. [PubMed]
Wallis NE. Recovery time course of corneal edema as determined by light scatter. J Am Optom Assoc. 1969;40:276–279. [PubMed]
Stevenson R, Vaja N, Jackson J. Corneal transparency changes resulting from osmotic stress. Ophthalmic Physiol Opt. 1983;3:33–39. [CrossRef] [PubMed]
Kikkawa Y. Light scattering studies of the rabbit cornea. Jpn J Physiol. 1960;10:292–302. [CrossRef] [PubMed]
Lambert S, Klyce S. The origins of Sattler’s veil. Am J Ophthalmol. 1981;91:51–56. [CrossRef] [PubMed]
Polse K, Sarver MD, Harris M. Corneal edema and vertical striae accompanying the wearing of hydrogel lenses. Am J Optom Physiol Optics. 1975;52:185–191. [CrossRef]
Maurice D. The structure and transparency of the cornea. J Physiol. 1957;136:263–286. [CrossRef] [PubMed]
Polse KA, Mandell RB. Etiology of corneal striae accompanying hydrogel lens wear. Invest Ophthalmol. 1976;15:553–556. [PubMed]
Korb DR, Exford JM. The phenomenon of central circular clouding. J Am Optom Assoc. 1968;39:223–230. [PubMed]
Fonn D, du Toit R, Simpson TL, Vega JA, Situ P, Chalmers RL. Sympathetic swelling response of the control eye to soft lenses in the other eye. Invest Ophthalmol Vis Sci. 1999;40:3116–3121. [PubMed]
Cox I, Holden BA. Can vision loss be used as a quantitative assessment of corneal edema?. Int Contact Lens Clin. 1990;17:176–180. [CrossRef]
O’Leary DJ, Wilson G, Henson DB. The effect of anoxia on the human corneal epithelium. Am J Optom Physiol Opt. 1981;58:472–476. [PubMed]
Johnson M, Ruben CM, Perrigin D. Entoptic phenomena and reproducibility of corneal striae following contact lens wear. Br J Ophthalmol. 1987;71:737–741. [CrossRef] [PubMed]
Farris RL, Kubota Z, Mishima S. Epithelial decompensation with corneal contact lens wear. Arch Ophthalmol. 1971;85:651–660. [CrossRef] [PubMed]
Lee D, Wilson G. Non-uniform swelling properties of the corneal stroma. Curr Eye Res. 1981;1:457–461. [CrossRef] [PubMed]
Cristol SM, Edelhauser HF, Lynn MJ. A comparison of corneal stromal edema induced from the anterior or the posterior surface. Refract Corneal Surg. 1992;8:224–229. [PubMed]
Maurice D, Giardini A. Swelling of the cornea in vivo after the destruction of its limiting layers. Br J Ophthalmol. 1951;35:791–797. [CrossRef] [PubMed]
O’Neal MR, Polse KA. In vivo assessment of mechanisms controlling corneal hydration. Invest Ophthalmol Vis Sci. 1985;26:849–856. [PubMed]
Figure 1.
 
Baseline 1 and 2 results were obtained at two different visits before wearing contact lenses to test the repeatability of the measurements. Normalized corneal backscattered light (mean ± 2 SE) in each slice from the epithelium to the posterior stroma measured on two different days in 20 eyes. Note that the corneal backscattered light appears to increase gradually from the anterior to the posterior (S1 to S10).
Figure 1.
 
Baseline 1 and 2 results were obtained at two different visits before wearing contact lenses to test the repeatability of the measurements. Normalized corneal backscattered light (mean ± 2 SE) in each slice from the epithelium to the posterior stroma measured on two different days in 20 eyes. Note that the corneal backscattered light appears to increase gradually from the anterior to the posterior (S1 to S10).
Figure 2.
 
The changes of normalized backscattered light after lens removal after 3 hours of lens wear and eye closure showed a bowl-shaped pattern due to an increase in epithelial (EP) and posterior stromal layers immediately after lens removal and returning to a relatively flat pattern at 100 minutes.
Figure 2.
 
The changes of normalized backscattered light after lens removal after 3 hours of lens wear and eye closure showed a bowl-shaped pattern due to an increase in epithelial (EP) and posterior stromal layers immediately after lens removal and returning to a relatively flat pattern at 100 minutes.
Figure 3.
 
Examples of OCT light-backscattering two-dimensional images of the central cornea (1.13 mm) before (top left) and after lens wear (top right). The increase in the red/orange colors is indicative of increased light-backscattering. The magnitude of backscattered light is shown in the reflectivity profiles, higher after lens wear (middle right) in the epithelium, anterior stromal layer (S1), and posterior stromal layer (S10) than that before lens wear (middle left). The graphs illustrate the different normalized backscattered-light profiles before (bottom left) and how light-backscattering increased in the epithelium, anterior (S1) and posterior (S10) stromal layers after lens wear (bottom right).
Figure 3.
 
Examples of OCT light-backscattering two-dimensional images of the central cornea (1.13 mm) before (top left) and after lens wear (top right). The increase in the red/orange colors is indicative of increased light-backscattering. The magnitude of backscattered light is shown in the reflectivity profiles, higher after lens wear (middle right) in the epithelium, anterior stromal layer (S1), and posterior stromal layer (S10) than that before lens wear (middle left). The graphs illustrate the different normalized backscattered-light profiles before (bottom left) and how light-backscattering increased in the epithelium, anterior (S1) and posterior (S10) stromal layers after lens wear (bottom right).
Figure 4.
 
Integrated normalized backscatter (percentage of the cornea) versus corneal swelling during the recovery period after 3 hours of lens wear and eye closure. There was a strong correlation between the changes of the light-backscattering (the integrated area under each profile curve) and corneal swelling during the deswelling period.
Figure 4.
 
Integrated normalized backscatter (percentage of the cornea) versus corneal swelling during the recovery period after 3 hours of lens wear and eye closure. There was a strong correlation between the changes of the light-backscattering (the integrated area under each profile curve) and corneal swelling during the deswelling period.
Figure 5.
 
Light-backscatter recovery in the anterior and posterior stromal layers.
Figure 5.
 
Light-backscatter recovery in the anterior and posterior stromal layers.
Figure 6.
 
The recovery of backscattered light in the epithelium (EP) and posterior stromal layer (S10) correlated positively with corneal deswelling.
Figure 6.
 
The recovery of backscattered light in the epithelium (EP) and posterior stromal layer (S10) correlated positively with corneal deswelling.
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