Ophthalmic Surgery, Lasers and Imaging Retina

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Imaging: Clinical Science 

Serial Measurement of Tear Meniscus by FD-OCT After Instillation of Artificial Tears in Patients With Dry Eyes

Matthew C. Bujak, MD; Samuel Yiu, MD, PhD; Xinbo Zhang, PhD; Yan Li, PhD; David Huang, MD, PhD

Abstract

BACKGROUND AND OBJECTIVE:

To use Fourier-domain optical coherence tomography (FD-OCT) to study the effect of artificial tears on the tear meniscus in patients with dry eyes.

PATIENTS AND METHODS:

The lower tear meniscus of 16 consecutive patients with dry eyes was imaged by an FD-OCT system (RTVue; Optovue, Inc., Fremont, CA). Baseline and five serial pairs of measurements were taken after the instillation of artificial tears (Optive; Allergan, Irvine, CA) at 1, 2, 5, 10, and 15 minutes. The lower meniscus height, depth, and area were measured with a computer caliper.

RESULTS:

Baseline meniscus measurements were 235.5 ± 150.0 μm, 138.1 ± 78.7 μm, and 0.020 ± 0.022 mm2 for height, depth, and area, respectively. After instillation of artificial tears, all lower tear meniscus parameters remained significantly elevated for 5 minutes and returned to baseline by 10 minutes.

CONCLUSION:

FD-OCT is able to quantify a dramatic initial increase in tear meniscus, followed by a decay back to baseline values after approximately 5 minutes. FD-OCT may be useful in objectively quantifying the dynamic efficacy of dry eye treatments.

Abstract

BACKGROUND AND OBJECTIVE:

To use Fourier-domain optical coherence tomography (FD-OCT) to study the effect of artificial tears on the tear meniscus in patients with dry eyes.

PATIENTS AND METHODS:

The lower tear meniscus of 16 consecutive patients with dry eyes was imaged by an FD-OCT system (RTVue; Optovue, Inc., Fremont, CA). Baseline and five serial pairs of measurements were taken after the instillation of artificial tears (Optive; Allergan, Irvine, CA) at 1, 2, 5, 10, and 15 minutes. The lower meniscus height, depth, and area were measured with a computer caliper.

RESULTS:

Baseline meniscus measurements were 235.5 ± 150.0 μm, 138.1 ± 78.7 μm, and 0.020 ± 0.022 mm2 for height, depth, and area, respectively. After instillation of artificial tears, all lower tear meniscus parameters remained significantly elevated for 5 minutes and returned to baseline by 10 minutes.

CONCLUSION:

FD-OCT is able to quantify a dramatic initial increase in tear meniscus, followed by a decay back to baseline values after approximately 5 minutes. FD-OCT may be useful in objectively quantifying the dynamic efficacy of dry eye treatments.

From Doheny Eye Institute, University of Southern California, Los Angeles, California.

Supported by R24EY13015, R01EY018184, research grant from Optovue, Inc., a grant from Research to Prevent Blindness, Charles C. Manger III, MD, Chair in Corneal Laser Surgery endowment.

Dr. Huang received stock options, patent royalty, and travel support from Optovue, Inc. (Fremont, CA). Drs. Huang, Li, and Zhang received research grant support from Optovue, Inc. The remaining authors have no financial or proprietary interest in the materials presented herein.

Address correspondence to Samuel Yiu, MD, PhD, Doheny Eye Institute, 1450 San Pablo St., Suite 5704, Los Angeles, CA 90033. E-mail: samuelyiu@alumni.usc.edu

Received: September 18, 2010
Accepted: March 17, 2011

Introduction

Dry eye is a complex disease that has proven to be difficult to quantify. Traditional methods used to objectively assess both the severity and the efficacy of dry eye treatments have been notoriously inaccurate.1–5 The most commonly used tests, the Schirmer test and cotton thread test, involve placing a wicking material against the eye. Because of their invasive nature, these tests may be more representative of reflex tearing rather than basal secretion. Other tear stability and ocular surface evaluation tests use the introduction of dyes such as rose bengal and fluorescein. Once again, the introduction of both saline and these dyes may alter natural tear film morphology, therefore precluding accurate measurement. Recently, researchers have turned their focus to measuring tear meniscus parameters in a noninvasive manner with optical coherence tomography (OCT). Tear meniscus volume has been positively correlated with lacrimal secretory rate and has been shown to be reduced in a tear-deficient dry eye.2 In a previous study, we have demonstrated the high reproducibility of measuring lower tear meniscus dimensions and area with Fourier-domain OCT (FD-OCT).6 In this study, we aimed to measure tear meniscus dimensions in a dry eye population and to assess the dynamic effect of artificial tear instillation on these tear meniscus parameters.

Patients and Methods

Nineteen patients with significantly dry eyes were recruited in a consecutive manner from a tertiary cornea practice for the current prospective study. The lower tear meniscus of the right eye in each subject was imaged by vertical scans centered on the inferior cornea and the lower eyelid using an FD-OCT system (RT-Vue software version 4.7; Optovue, Inc., Fremont, CA) with a corneal adaptor. Patients were asked to refrain from placing any lubricating drops or medications for 2 hours prior to their measurements. All of the measurements were performed by one technician. This study was in accordance with the Health Insurance Portability and Accountability Act of 1996. The lower meniscus height and depth were measured with a computer caliper. The cross-sectional area was calculated using a two-triangle approximation. All of the computer caliper measurements were made by the first author.

Imaging Procedure

An FD-OCT system (RTVue) with a corneal adaptor module was used. The system operated at an 830-nm wavelength and had an axial resolution in the tissue of 5 μm. The corneal adaptor module produced telecentric scanning for anterior segment imaging using either a wide-angle or high-magnification adaptor lens. We used the wide-angle lens, which provided a transverse resolution of 15 μm. The room temperature was set at 70°F and humidity was at 40%. Patients were asked to look straight ahead at the fixating target within the OCT system. The OCT pattern used to scan the lower tear meniscus was a 6-mm vertical line centered on the middle of the inferior corneal limbus (Fig. 1). Subjects were instructed to blink and then keep the eyes open for the duration of a 3-second count. Images were taken at 2 seconds after blink.

Video image illustrating the 6-mm vertical scan path (arrow) of the optical coherence tomography beam used to image the lower tear meniscus.

Figure 1. Video image illustrating the 6-mm vertical scan path (arrow) of the optical coherence tomography beam used to image the lower tear meniscus.

Two baseline measurements were taken for each subject prior to administration of a drop of artificial tears (carboxymethylcellulose sodium 0.5%, Optive; Allergan, Inc., Irvine, CA). Five serial pairs of measurements were then taken at 1, 2, 5, 10, and 15 minutes after the instillation of artificial tears. Only right-eye images were used for the current study. The OCT images were exported for computer caliper measurements of lower tear meniscus height, depth, and cross-sectional area (Fig. 2). The height was measured from the cornea–meniscus junction to the lower eyelid–meniscus junction. The depth was measured from the midpoint of the air–meniscus interface to the cornea–lower eyelid junction. The area was approximated by two triangles (Fig. 2). The saline group index of 1.342 at 830-nm wavelength was used to correct the refraction at the air–meniscus interface.

The tear meniscus height and depth on a vertical optical coherence tomography section centered on the inferior corneal–eyelid junction. The cross-sectional area was calculated using a dual triangle approximation.

Figure 2. The tear meniscus height and depth on a vertical optical coherence tomography section centered on the inferior corneal–eyelid junction. The cross-sectional area was calculated using a dual triangle approximation.

Statistical Analysis

The Wilcoxon signed rank test was used to compare tear meniscus height, depth, and area at baseline to each subsequent interval after instillation of artificial tears (1, 2, 5, 10, and 15 minutes). The Wilcoxon signed rank test was specifically used because of our small population size of 16 subjects and the non-normal distribution of our measurements.

Results

The study included the right eye of 19 subjects with dry eye from a tertiary corneal practice. Three subjects were excluded from the data analysis because they had significant conjunctivochalasis precluding accurate measurement of the lower tear meniscus (Fig. 3). The remaining 16 subjects with dry eye reflected the normal predominance of dry eye among the female population, with 10 women and 6 men (age: 52.3 ± 16.1 years).

Lax conjunctival folds prevent accurate measurement of tear meniscus.

Figure 3. Lax conjunctival folds prevent accurate measurement of tear meniscus.

The baseline meniscus measurements were 235.5 ± 150.0 μm, 138.1 ± 78.7 μm, and 0.020 ± 0.022 mm2 for height, depth, and area, respectively (Table). At 1 minute after instillation of artificial tears, there was a more than three-fold increase in all lower tear meniscus parameters. Specifically, the increases were 374%, 346%, and 950% for height, depth, and cross-sectional area, respectively. At 5 minutes, there continued to be a statistically significant elevation of all parameters including height (163%), depth (163%), and area (225%) (Table; Fig. 4). By 10 minutes, all of the parameters, had returned to just slightly higher values than baseline. Although there was a trend, there was no statistical difference between baseline and 10 minute values (P > .05).

Serial Tear Meniscus Parameters After Artificial Tear Instillation

Table 1: Serial Tear Meniscus Parameters After Artificial Tear Instillation

Lower tear meniscus dynamics after artificial tear instillation.

Figure 4. Lower tear meniscus dynamics after artificial tear instillation.

Discussion

Dry eye evaluation has traditionally been performed by a series of invasive tests such as Schirmer test, cotton thread test, rose bengal staining, fluorescein staining, and tear break-up time. These tests are considered invasive because they involve contact with the ocular surface or the instillation of a dye. By introducing an irritant, they induce reflex tearing and thus may not accurately reflect basal tear secretion in the dry eye state.1–5

Some authors have switched to using lower tear meniscus measurements to quantify dry eye. Lower tear meniscus parameters have been shown to correlate well with dry eye. Mainstone et al.2 measured height and radius of tear meniscus with a slit-lamp–equipped micrometer. Their findings demonstrated a significant difference between normal subjects and patients with dry eye with lower tear meniscus height having a greater than 90% sensitivity for identifying tear-deficient dry eye.2 Similarly, Kawai et al.7 used a slit-lamp photograph to measure tear meniscus height after instillation of fluorescein and found significantly lower tear meniscus in subjects with dry eye as compared with the normal population. However, the findings of both of these studies may be confounded by the addition of fluorescein required for photographic evaluation.

Reflective meniscometry is a tear meniscus assessment tool that has been developed as an attempt to quantify meniscus volume in a non-invasive manner.8–10 It has been used to study tear dynamics in both normal patients and the population with dry eye.8–10 Although it has been useful in documenting changes in tear meniscus curvature, it does not directly measure tear meniscus height or area. Instead, it requires mathematical models and several assumptions to estimate meniscus volume and cross-sectional area.

With the refinement of OCT, researchers have been able to directly quantify tear meniscus parameters. Shen et al.11 used real-time OCT to measure upper and lower tear menisci in patients with dry eye. They found that lower tear meniscus height was a good predictor of dry eye and had improved sensitivity and specificity as compared to the superior meniscus.11 Quantification of the upper meniscus has been limited by several factors, including eyelashes that block the view of the tear meniscus, rapid movement and twitches of the upper eyelid, and smaller meniscus volumes as compared with the lower meniscus.11,12

In review of the literature, baseline lower tear meniscus measurements have varied depending on both the method used to evaluate the meniscus and the population studied. Slit-lamp video photography has been used to measure tear meniscus height as low as 171 μm in the elderly population.13 Oguz et al.14 used a slit-lamp micrometer to measure tear meniscus height of 190 μm in a population with dry eye. In contrast, Mainstone et al.2 measured elevated tear meniscus heights of 461 μm with a slit-lamp micrometer in the normal population. There has been significant variability between different populations in different studies. However, Johnson and Murphy12 found good agreement between OCT and video measurements of tear meniscus height in their normal population. Lower tear meniscus cross-sectional area has not been given much attention in the past because, prior to the development OCT, there was not a reliable way of directly measuring cross-sectional area.

When compared with normative OCT tear meniscus studies, our baseline dry eye tear meniscus measurements of 236 μm height and 0.020 mm2 area fell within accepted ranges.6,11,12,15–22 Previous OCT studies of normal patients have reported mean tear meniscus heights ranging from 190 to 310 μm, whereas cross-sectional area has ranged from .0150 to .0307 mm.2,6,11,12,15–22 However, our baseline meniscus measurements were higher than previous OCT studies in the population with dry eye. Shen et al.’s11 OCT study on patients with aqueous tear deficiency reported a lower tear meniscus height of 196 μm and a much lower cross-sectional area of .0095 mm2. Similarly, Wang et al.22 reported dry eye values of 179 μm and .01 mm2 for tear meniscus height and area, respectively, in their FD-OCT study. Although slit-lamp photography of the tear meniscus cannot comment on cross-sectional area, it was the primary tool used to measure tear meniscus prior to the development of OCT. When considering the population with dry eye, both our current study results, as well as those of Shen et al. and Wang et al., compare well with the previous slit-lamp studies that reported lower tear meniscus heights ranging from 170 to 290 μm.1,2,7,14 The differences between our current study and Shen et al.’s and Wang et al.’s studies can likely be explained by our different patient populations. Both of these studies11,22 defined their dry eye population by a Schirmer test of less than 5 mm, and thus limited their population to dry eye secondary to severe aqueous tear deficiency. Our dry eye population was a more heterogenous population that included some patients with reflex tearing and Schirmer scores of greater than 20 mm. The reflex tearing in our dry eye population likely accounted for higher baseline meniscus measurements.

In the current study, we aimed not only to examine baseline tear meniscus values, but also to describe tear film dynamics. After instillation of artificial tears, there was a more than threefold initial increase in all lower meniscus parameters that remained significantly elevated for 5 minutes and returned to baseline by 10 minutes. Our study found longer dwell time of artifical tears when compared with most previous studies.

Yokoi et al.8 used reflective meniscometry to demonstrate a marked increase in lower tear meniscus curvature with the instillation of 1% carboxymethylcellulose. This marked increase in curvature quickly returned to baseline and seemed to stabilize at 5 minutes after instillation. Wang et al.17 also used real-time OCT to study the dynamic tear distribution of 1% carboxymethylcellulose artificial tears. They found that although lower tear meniscus height stayed elevated for 5 minutes, the area had returned to baseline.17 In a follow-up OCT study using the same midviscosity 1% carboxymethylcellulose artificial tears, Palakuru et al.19 found that there was a similar large increase in lower tear meniscus values that returned to baseline by 5 minutes with normal blinking. They hypothesized that the increase in tear meniscus volume was compensated by an increase in output resulting from blinking.19

In a subsequent study, Wang et al.22 used FD-OCT to assess the effect of both 0.5% and 1% carboxymethylcellulose artificial tears. They found that 0.5% carboxymethylcellulose drops elevated both tear meniscus height and area for 5 minutes, whereas 1% carboxymethylcellulose elevated these parameters for 30 minutes. In our study, we used a lower viscosity 0.5% carboxymethylcellulose artificial tear. The instillation of this tear substitute resulted in a similar large increase in lower tear meniscus followed by a rapid decrease over the next 5 minutes. Both our current study and the latest study by Wang et al.22 used FD-OCT to assess tear meniscus dynamics. Both FD-OCT studies found significant elevation of the tear meniscus at 5 minutes. This longer artificial tear-dwell time may reflect the improved sensitivity of higher resolution FD-OCT. With an axial resolution of 5 μm, FD-OCT may provide better visualization of tear meniscus tails and thus allow more accurate and sensitive documentation of tear dynamics. Although artificial tear instillation significantly increased tear meniscus parameters for only 5 minutes, the patients reported improvement in symptoms for much longer.

It is likely that the beneficial effects of artificial tear instillation cannot be solely quantified by changes in tear meniscus dimensions. Other beneficial effects, such as reduction in tear film osmolarity and dilution of inflammatory mediators, may also account for the improvement in symptoms.23–26 Laboratory tests have confirmed that tear hyperosmolarity leads to a cycle of inflammation and damage to the ocular surface. By diluting the osmolarity, artificial tears may decrease epithelial stress, inflammation, and symptoms of irritation.27,28

There are several limitations to our study. Our dry eye population was a heterogenous group of patients, some of whom had severe aqueous tear deficiency as evidenced by a Schirmer test of less than 5 seconds, whereas others had poor quality tears and reflexive tearing. This inclusive population is reflective of the heterogenous nature of a tertiary population of patients with dry eye and thus may show variability in tear meniscus parameters. Two patients had lower punctal plugs, one patient had the lower puncta cauterized, and a fourth patient had the upper puncta cauterized. These confounding variables may have affected the tear meniscus dynamics. A future study with larger numbers could assess the effect of punctal occlusion on tear meniscus parameters. Three patients were excluded due to significant conjunctivochalasis. This is a relatively common finding in the older dry eye population. Mainstone et al.2 found that 7 of 30 subjects had folds of the inferior conjunctiva with irregular tear menisci. Although our images were of sufficient resolution to measure a cross-sectional area in these patients, our triangle approximation computer caliper measurement would not have been accurate.

FD-OCT is able to capture tear meniscus baseline values and tear dynamics after instillation of artificial tears. Artificial tear (0.5% carboxymethylcellulose) instillation dramatically increases tear meniscus initially, and then decays back to baseline values after approximately 5 minutes. FD-OCT may be useful in objectively quantifying the dynamic efficacy of various dry eye treatments ranging from tear supplementation to anti-inflammatories to punctal plugs.

References

  1. Nichols KK, Mitchell GL, Zadnik K. The repeatability of clinical measurements of dry eye. Cornea. 2004;23:272–285. doi:10.1097/00003226-200404000-00010 [CrossRef]
  2. Mainstone JC, Bruce AS, Golding TR. Tear meniscus measurement in the diagnosis of dry eye. Curr Eye Res. 1996;15:653–661. doi:10.3109/02713689609008906 [CrossRef]
  3. Tsubota K. The importance of the Schirmer test with nasal stimulation. Am J Ophthalmol. 1991;111:106–108.
  4. Lemp MA, Hamill JR Jr, . Factors affecting tear film breakup in normal eyes. Arch Ophthalmol. 1973;89:103–105.
  5. Cho P, Yap M. Schirmer test. II: a clinical study of its repeatability. Optom Vis Sci. 1993;70:157–159. doi:10.1097/00006324-199302000-00012 [CrossRef]
  6. Zhou S, Li Y, Lu AT, et al. Reproducibility of tear meniscus measurement by Fourier-domain optical coherence tomography: a pilot study. Ophthal Surg Lasers Imaging. 2009;40:442–447. doi:10.3928/15428877-20090901-01 [CrossRef]
  7. Kawai M, Yamada M, Kwashima M, et al. Quantitative evaluation of tear meniscus height from fluorescein photographs. Cornea. 2007;26:403–406. doi:10.1097/ICO.0b013e318033c242 [CrossRef]
  8. Yokoi N, Bron A, Tiffany J, et al. Reflective meniscometry: a non-invasive method to measure tear meniscus curvature. Br J Ophthalmol. 1999;83:92–97. doi:10.1136/bjo.83.1.92 [CrossRef]
  9. Yokoi N, Kinoshita S, Bron AJ, et al. Tear meniscus changes during cotton thread and Schirmer testing. Invest Ophthalmol Vis Sci. 2000;41:3748–3753.
  10. Yokoi N, Bron AJ, Tiffany JM, et al. Relationship between tear volume and tear meniscus curvature. Arch Ophthalmol. 2004;122:1265–1269. doi:10.1001/archopht.122.9.1265 [CrossRef]
  11. Shen M, Li J, Wang J, et al. Upper and lower tear menisci in the diagnosis of dry eye. Invest Ophthalmol Vis Sci. 2009;50:2722–2726. doi:10.1167/iovs.08-2704 [CrossRef]
  12. Johnson ME, Murphy PJ. The agreement and repeatability of tear meniscus height measurement methods. Optom Vis Sci. 2005;82:1030–1037. doi:10.1097/01.opx.0000192352.78935.e0 [CrossRef]
  13. Doughty MJ, Laiquzzaman M, Button NF. Video-assessment of tear meniscus height in elderly Caucasians and its relationship to the exposed ocular surface. Curr Eye Res. 2001;22:420–426. doi:10.1076/ceyr.22.6.420.5487 [CrossRef]
  14. Oguz H, Yokoi N, Kinoshita S. The height and radius of the tear meniscus and methods for examining these parameters. Cornea. 2000;19:497–500. doi:10.1097/00003226-200007000-00019 [CrossRef]
  15. Bitton E, Keech A, Simpson T, et al. Variability of the analysis of the tear meniscus height by optical coherence tomography. Optom Vis Sci. 2007;84:903–908. doi:10.1097/OPX.0b013e3181560ba8 [CrossRef]
  16. Wang J, Aquavella J, Palakuru J, et al. Relationships between central tear film thickness and tear menisci of the upper and lower eyelids. Invest Ophthalmol Vis Sci. 2006;47:4349–4355. doi:10.1167/iovs.05-1654 [CrossRef]
  17. Wang J, Aquavella J, Palakuru J, et al. Repeated measurements of dynamic tear distribution on the ocular surface after instillation of artificial tears. Inv Ophthal Vis Sci. 2006;47:3325–3329. doi:10.1167/iovs.06-0055 [CrossRef]
  18. Palakuru JR, Wang J, Aquavella JV. Effect of blinking on tear dynamics. Invest Ophthalmol Vis Sci. 2007;48:3032–3037. doi:10.1167/iovs.06-1507 [CrossRef]
  19. Palakuru JR, Wang J, Aquavella JV. Effect of blinking on tear volume after instillation of midviscosity artificial tears. Am J Ophthalmol. 2008;146:920–924. doi:10.1016/j.ajo.2008.06.020 [CrossRef]
  20. Savini G, Barboni P, Zanini M. Tear meniscus evaluation by optical cohenrence tomography. Ophthalmic surg Lasers Imaging. 2006;37:112–118.
  21. Savini G, Goto E, Carbonelli M, et al. Agreement between Stratus and Visante optical coherence tomography systems in tear meniscus measurements. Cornea. 2009;28:148–151. doi:10.1097/ICO.0b013e31818526d0 [CrossRef]
  22. Wang Y, Zhuang H, Xu J, Wang X, Jiang C, Sun X. Dynamic changes in the lower tear meniscus after instillation of artificial tears. Cornea. 2010;29:404–408.
  23. Lester M, Orsoni GJ, Gamba G, et al. Improvement of the ocular surface using hypotonic 0.4% hyaluronic acid drops in keratoconjunctivitis sicca. Eye. 2000;14:892–898. doi:10.1038/eye.2000.244 [CrossRef]
  24. Sobrin L, Liu Z, Monroy DC, et al. Regulation of MMP-9 activity in human tear fluid and corneal epithelial culture supernatant. Invest Ophthalmol Vis Sci. 2000;41:1703–1709.
  25. Solomon A, Dursun D, Liu Z, et al. Pro- and anti-inflammatory forms of interleukin-1 in the tear fluid and conjunctiva of patients with dry-eye disease. Int Ophthalmol Vis Sci. 2001;42:2283–2292.
  26. Gilbard JP. Human tear film electrolyte concentrations in health and dry-eye disease. Int Ophthalmol Clin. 1994;34:27–36. doi:10.1097/00004397-199403410-00005 [CrossRef]
  27. Li DQ, Chen Z, Song XJ, et al. Stimulation of matrix metalloproteinase’s by hyperosmolarity via a JNK pathway in human corneal epithelial cells. Invest Ophthalmol Vis Sci. 2004;45:4302–4311. doi:10.1167/iovs.04-0299 [CrossRef]
  28. Luo L, Li DQ, Pflugfelder SC. Hyperosmolarity-induced apoptosis in human corneal epithelial cells is mediated by cytochrome c and MAPK pathways. Cornea. 2007;26:452–460. doi:10.1097/ICO.0b013e318030d259 [CrossRef]

Serial Tear Meniscus Parameters After Artificial Tear Instillation

Time (Min)Height (μm)Depth (μm)Area (mm2)
Baseline235 ± 150138 ± 790.0200 ± 0.0222
1881 ± 510a478 ± 239a0.1896 ± 0.1947a
2703 ± 504a400 ± 237a0.1553 ± 0.1913a
5384 ± 216a225 ± 106a0.0449 ± 0.0494a
10282 ± 197168 ± 900.0298 ± 0.0406
15264 ± 115158 ± 610.0222 ± 0.0127
Authors

From Doheny Eye Institute, University of Southern California, Los Angeles, California.

Supported by R24EY13015, R01EY018184, research grant from Optovue, Inc., a grant from Research to Prevent Blindness, Charles C. Manger III, MD, Chair in Corneal Laser Surgery endowment.

Dr. Huang received stock options, patent royalty, and travel support from Optovue, Inc. (Fremont, CA). Drs. Huang, Li, and Zhang received research grant support from Optovue, Inc. The remaining authors have no financial or proprietary interest in the materials presented herein.

Address correspondence to Samuel Yiu, MD, PhD, Doheny Eye Institute, 1450 San Pablo St., Suite 5704, Los Angeles, CA 90033. E-mail: samuelyiu@alumni.usc.edu

10.3928/15428877-20110603-02

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