Journal of Refractive Surgery

Original Article Supplemental Data

Repeatability of Cornea and Sublayer Thickness Measurements Using Optical Coherence Tomography in Corneas of Anomalous Refractive Status

Nan-Ji Lu, MD; Ding Chen, MD; Le-Le Cui, MD, PhD; Lin Wang, MD; Shi-hao Chen, MD, OD; Qin-Mei Wang, MD

Abstract

PURPOSE:

To assess the repeatability of epithelial, stromal, and total corneal thickness measurements with spectral-domain optical coherence tomography (SD-OCT; RTVue-XR; Optovue, Inc., Fremont, CA) in patients with myopia, keratoconus, and corneas after transepithelial photorefractive keratectomy (PRK), small incision lenticule extraction (SMILE), and femtosecond laser–assisted in situ keratomileusis (FS-LASIK).

METHODS:

A total of 352 eyes of 352 patients (75 myopic, 68 post-transepithelial PRK, 61 post-SMILE, 75 post-FS-LASIK, 20 mild keratoconus, and 53 advanced keratoconus eyes) were included. The epithelial, stromal, and total corneal thickness were recorded from the pachymetric map in the following four zones: (1) central 2-mm region, (2) eight paracentral regions within 2- to 5-mm diameter, (3) eight midperipheral regions within 5- to 7-mm diameter, and (4) eight peripheral regions within 7- to 9-mm diameter. Three successive scans were performed to evaluate the repeatability.

RESULTS:

For all zones up to 9-mm diameter, the coefficient of variation (CoV) for epithelial thickness measurements ranged from 1.7% to 3.5% for myopia, 2.6% to 6.2% for post-transepithelial PRK, 2.3% to 4.7% for post-SMILE, 4.0% to 6.3% for post-FS-LASIK, 2.5% to 6.2% for mild keratoconus, and 3.5% to 8.0% for advanced keratoconus. The CoV for stromal and total thickness measurements ranged from 0.2% to 2.0% for myopia, 0.7% to 4.2% for post-transepithelial PRK, 0.3% to 2.4% for post-SMILE, 0.3% to 1.9% for post-FS-LASIK, 0.6% to 3.0% for mild keratoconus, and 1.0% to 5.9% for advanced keratoconus.

CONCLUSIONS:

RTVue-XR SD-OCT showed excellent repeatability when generating the pachymetric map in myopic eyes. Measurements, especially for epithelial thickness, were relatively more variable for corneas with keratoconus and those having undergone keratorefractive surgery.

[J Refract Surg. 2019;35(9):600–605.]

Abstract

PURPOSE:

To assess the repeatability of epithelial, stromal, and total corneal thickness measurements with spectral-domain optical coherence tomography (SD-OCT; RTVue-XR; Optovue, Inc., Fremont, CA) in patients with myopia, keratoconus, and corneas after transepithelial photorefractive keratectomy (PRK), small incision lenticule extraction (SMILE), and femtosecond laser–assisted in situ keratomileusis (FS-LASIK).

METHODS:

A total of 352 eyes of 352 patients (75 myopic, 68 post-transepithelial PRK, 61 post-SMILE, 75 post-FS-LASIK, 20 mild keratoconus, and 53 advanced keratoconus eyes) were included. The epithelial, stromal, and total corneal thickness were recorded from the pachymetric map in the following four zones: (1) central 2-mm region, (2) eight paracentral regions within 2- to 5-mm diameter, (3) eight midperipheral regions within 5- to 7-mm diameter, and (4) eight peripheral regions within 7- to 9-mm diameter. Three successive scans were performed to evaluate the repeatability.

RESULTS:

For all zones up to 9-mm diameter, the coefficient of variation (CoV) for epithelial thickness measurements ranged from 1.7% to 3.5% for myopia, 2.6% to 6.2% for post-transepithelial PRK, 2.3% to 4.7% for post-SMILE, 4.0% to 6.3% for post-FS-LASIK, 2.5% to 6.2% for mild keratoconus, and 3.5% to 8.0% for advanced keratoconus. The CoV for stromal and total thickness measurements ranged from 0.2% to 2.0% for myopia, 0.7% to 4.2% for post-transepithelial PRK, 0.3% to 2.4% for post-SMILE, 0.3% to 1.9% for post-FS-LASIK, 0.6% to 3.0% for mild keratoconus, and 1.0% to 5.9% for advanced keratoconus.

CONCLUSIONS:

RTVue-XR SD-OCT showed excellent repeatability when generating the pachymetric map in myopic eyes. Measurements, especially for epithelial thickness, were relatively more variable for corneas with keratoconus and those having undergone keratorefractive surgery.

[J Refract Surg. 2019;35(9):600–605.]

Corneal thickness data can give indications of the diagnosis of keratoconus and postoperative ectasia. Both epithelial and stromal thickness data are critical because the corneal thickness may remain constant when stromal thinning takes place due to the mechanism of epithelial remodeling that compensates for the corneal surface irregularity. In keratoconic eyes, the corneal epithelial doughnut pattern—localized epithelial thinning surrounded by its annular thickening—can serve as a warning signal for the presence of an underlying stromal cone.1 Apart from the detection of postoperative ectasia, the epithelial thickness profile is important for the monitoring of epithelial remodeling, which is thought to be a contributing factor to the refractive regression.

Previous studies reported the epithelial and stromal thickness profiles measured using high-frequency ultra-sound biomicroscopy.1–3 The eye needs immersing with a coupling fluid when undergoing the examination. Optical coherence tomography (OCT) is a non-invasive imaging technique.4–7 With the RTVue (Optovue Inc., Fremont, CA) spectral-domain OCT (SD-OCT) system, Li et al.8 innovatively presented the corneal epithelial thickness map algorithm, which generated the pachymetric map of the corneal epithelium with a diameter of 6 mm. Clinically, this technique has been widely used to investigate the epithelial thickness profile in normal eyes, keratoconic eyes, and eyes after keratorefractive surgery.9–22

The latest system (RTVue-XR) is equipped with a “PachymetryWide” scan pattern. It can provide the pachymetric map up to 9 mm in diameter.23 With this mode, the thickness profile for the transition zone of keratorefractive surgery is easy to acquire. Ma et al.23 reported high repeatability for epithelial and corneal thickness measurements using this approach in normal eyes and corneas under different conditions, including dry eyes, keratoconus, previous contact lens wear, and prior laser-assisted in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK). However, there was a lack of keratoconus grading when investigating the reliability of measurement because the severity of corneal sublayer irregularity can potentially challenge the performance of the OCT system. With regard to the measurement of thickness for postoperative corneas, the effect of the type of surgery should also be taken into consideration because the regeneration and remodeling of the corneal epithelium may differ among different surgical procedures.

The aim of this study was to assess the repeatability of pachymetric map measurement using RTVue-XR SDOCT for epithelial, stromal, and total corneal thickness in patients with myopia, keratoconus, and after transepithelial PRK, small incision lenticule extraction (SMILE), or femtosecond laser–assisted LASIK (FS-LASIK).

Patients and Methods

Patients

This prospective study, conducted in the Eye Hospital of Wenzhou Medical University, enrolled patients with myopia, keratoconus, and who underwent transepithelial PRK, SMILE, or FS-LASIK. The research protocol adhered to the tenets of the Declaration of Helsinki and was approved by the Office of Research Ethics, Wenzhou Medical University. All participants had submitted written informed consent.

All participants underwent a detailed ophthalmic examination, including subjective refraction, ophthalmoscopy, non-contact tonometry, slit-lamp microscopy, funduscopy, and corneal keratometric and pachymetric maps. Participants were observed at 3 months postoperatively and those with complications were excluded.

In the current study, patients with mild keratoconus were recruited according to the criteria as follows: (1) a corrected distance visual acuity of 20/20 or better; (2) no slit-lamp findings; (3) a central corneal thickness of greater than 480 µm with maximum keratometry of less than 48.00 diopters (D) obtained with Pentacam HR Scheimpflug imaging system (Oculus Optikgeräte, Wetzlar, Germany); and (4) the presence of asymmetric bow tie with skewed radial axis, central or inferior steep zone, or claw-shaped pattern rendered by Pentacam HR corneal topography. Patients with keratoconus more severe than the above criteria were diagnosed as having advanced keratoconus. No one had previously worn rigid gas permeable contact lenses or undergone surgical treatment.

SD-OCT Epithelial Thickness Mapping

The RTVue-XR is an SD-OCT system using a near-infrared light source at a wavelength of 830 nm. It achieves a depth resolution of 5 µm (full-width-half-maximum) in tissue at a speed of 26,000 A-scans per second. Equipped with an add-on lens (CAM-L mode), this system is called the corneal adaptor module, which is capable of conducting corneal measurements with the “PachymetryWide” scan mode, consisting of B-scans evenly in eight radial directions at a length of 9 mm centered at the pupil center.

Measurement Protocol

The device was used according to the user's manual. The scans were triggered manually after the alignment procedure was completed. To ensure the measurement independence, participants were asked to sit back and the scan unit was thoroughly reset before each subsequent scan. The data were valid if the measurement outcomes showed sufficient image signals and good quality. The epithelial, stromal, and total corneal thickness data were recorded for the following four zones: (1) the central region within a 2-mm diameter; (2) eight paracentral regions within 2 to 5 mm; (3) eight midperipheral regions within 5 to 7 mm; and (4) eight peripheral regions within 7 to 9 mm. The eight regions for paracentral, mid-peripheral, and peripheral zones were located on temporal, superior-temporal, superior, superior-nasal, nasal, inferior-nasal, inferior, and inferior-temporal positions. Three consecutive measurements were performed by an experienced operator (N-JL) between 9 AM and 5 PM.

Statistical Analysis

StatsModels (version 0.9.0) and SciPy (version 1.2.0) software, based on Python (version 3.7.0) were used for statistical analysis. The normality of data distribution was verified using the Shapiro–Wilk test. To assess the repeatability, within-subject standard deviation (Sw), test–retest repeatability (TRT), within-subject coefficient of variation (CoV), and intraclass correlation coefficient (ICC) were calculated. The TRT was equal to 2.77 × Sw, which indicated the expected upper limit for the 95% of the difference between measurements.24 The CoV was calculated as Sw divided by the arithmetic average × 100%. ICC values greater than 0.9, between 0.75 and 0.9, between 0.5 and 0.75, and less than 0.5 are considered as excellent, good, moderate, and poor reliability, respectively.25

Results

A total of 352 eyes of 352 patients (29 right eyes and 323 left eyes) were recruited in this study. They were divided into six groups: (1) 75 left eyes for myopia; (2) 68 left eyes for post-transepithelial PRK; (3) 61 left eyes for post-SMILE; (4) 75 left eyes for post-FS-LASIK; (5) 7 right eyes and 13 left eyes for mild keratoconus; and (6) 22 right eyes and 31 left eyes for advanced keratoconus. The mean age for the six groups was 25.04 ± 6.30 years (range: 16 to 41 years), 27.85 ± 5.43 years (range: 17 to 40 years), 26.33 ± 6.50 years (range: 17 to 42 years), and 26.79 ± 5.36 years (range: 17 to 39 years), 20.50 ± 4.64 years (range: 13 to 32 years), and 21.36 ± 6.38 years (range: 9 to 36 years), respectively. The mean spherical equivalent was −5.61 ± 1.48 D (range: −9.88 to −2.75 D), −5.66 ± 1.80 D (range: −9.88 to −1.88 D), −4.95 ± 1.72 D (range: −8.75 to −1.88 D), −6.08 ± 2.03 D (range: −10.75 to −2.00 D), −3.53 ± 2.16 D (range: −8.00 to +0.13 D), and −5.19 ± 3.12 D (range: −13.38 to +3.00 D), respectively.

The CoV values are shown in Figure 1.

Coefficient of variation for repeatability of epithelial thickness (left), stromal thickness (middle). and total corneal thickness (right) measurement in (A) myopic eyes, (B) corneas after transepithelial photorefractive keratectomy, (C) corneas after small incision lenticule extraction, (D) corneas after femtosecond laser–assisted in situ keratomileusis, (E) eyes with mild keratoconus, and (F) eyes with advanced keratoconus. Temporal, superior, nasal, and inferior locations are marked as ‘T’, ‘S’, ‘N’, and ‘I’, respectively.

Figure 1.

Coefficient of variation for repeatability of epithelial thickness (left), stromal thickness (middle). and total corneal thickness (right) measurement in (A) myopic eyes, (B) corneas after transepithelial photorefractive keratectomy, (C) corneas after small incision lenticule extraction, (D) corneas after femtosecond laser–assisted in situ keratomileusis, (E) eyes with mild keratoconus, and (F) eyes with advanced keratoconus. Temporal, superior, nasal, and inferior locations are marked as ‘T’, ‘S’, ‘N’, and ‘I’, respectively.

Repeatability in Myopia

As shown in Tables AC (available in the online version of this article), the TRT ranged from 2.47 to 4.49 µm for epithelial thickness measurement, from 2.35 to 32.58 µm for stromal thickness measurement, and from 3.05 to 32.33 µm for total corneal thickness measurement. The CoV was on a scale of 1.7% to 3.5% for epithelial thickness measurement, 0.2% to 2.0% for stromal thickness measurement, and 0.2% to 1.9% for total corneal thickness measurement.

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in myopic patients (n = 75)

Table A:

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in myopic patients (n = 75)

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in myopic patients (n = 75)

Table B:

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in myopic patients (n = 75)

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in myopic patients (n = 75)

Table C:

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in myopic patients (n = 75)

Repeatability in Post-Transepithelial PRK

As shown in Tables DF (available in the online version of this article), the TRT ranged from 3.74 to 7.48 µm for epithelial thickness measurement, from 7.12 to 64.24 µm for stromal thickness measurement, and from 8.03 to 61.72 µm for total corneal thickness measurement. The CoV was on a scale of 2.6% to 6.2% for epithelial thickness measurement, 0.7% to 4.2% for stromal thickness measurement, and 0.7% to 3.7% for total corneal thickness measurement.

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-TPRK patients (n = 68)

Table D:

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-TPRK patients (n = 68)

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-TPRK patients (n = 68)

Table E:

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-TPRK patients (n = 68)

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-TPRK patients (n = 68)

Table F:

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-TPRK patients (n = 68)

Repeatability in Post-SMILE

As shown in Tables GI (available in the online version of this article), the TRT ranged from 3.49 to 6.01 µm for epithelial thickness measurement, from 2.77 to 40.39 µm for stromal thickness measurement, and from 3.99 to 38.89 µm for total corneal thickness measurement. The CoV was on a scale of 2.3% to 4.7% for epithelial thickness measurement, 0.3% to 2.4% for stromal thickness measurement, and 0.3% to 2.1% for total corneal thickness measurement.

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-SMILE patients (n = 61)

Table G:

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-SMILE patients (n = 61)

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-SMILE patients (n = 61)

Table H:

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-SMILE patients (n = 61)

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-SMILE patients (n = 61)

Table I:

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-SMILE patients (n = 61)

Repeatability in Post-FS-LASIK

As shown in Tables JL (available in the online version of this article), the TRT ranged from 6.48 to 8.14 µm for epithelial thickness measurement, from 7.15 to 32.44 µm for stromal thickness measurement, and from 3.52 to 31.36 µm for total corneal thickness measurement. The CoV was on a scale of 4.0% to 6.3% for epithelial thickness measurement, 0.7% to 1.9% for stromal thickness measurement, and 0.3% to 1.8% for total corneal thickness measurement.

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-FS-LASIK patients (n = 75)

Table J:

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-FS-LASIK patients (n = 75)

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-FS-LASIK patients (n = 75)

Table K:

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-FS-LASIK patients (n = 75)

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-FS-LASIK patients (n = 75)

Table L:

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-FS-LASIK patients (n = 75)

Repeatability in Mild Keratoconus

As shown in Tables MO (available in the online version of this article), the TRT ranged from 3.77 to 7.98 µm for epithelial thickness measurement, from 8.14 to 50.14 µm for stromal thickness measurement, and from 8.73 to 46.87 µm for total corneal thickness measurement. The CoV was on a scale of 2.5% to 6.2% for epithelial thickness measurement, 0.6% to 3.0% for stromal thickness measurement, and 0.6% to 2.6% for total corneal thickness measurement.

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in mild keratoconic patients (n = 20)

Table M:

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in mild keratoconic patients (n = 20)

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in mild keratoconic patients (n = 20)

Table N:

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in mild keratoconic patients (n = 20)

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in mild keratoconic patients (n = 20)

Table O:

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in mild keratoconic patients (n = 20)

Repeatability in Advanced Keratoconus

As shown in Tables PR (available in the online version of this article), the TRT ranged from 5.32 to 11.11 µm for epithelial thickness measurement, from 11.91 to 89.06 µm for stromal thickness measurement, and from 13.55 to 88.81 µm for total corneal thickness measurement. The CoV was on a scale of 3.5% to 8.0% for epithelial thickness measurement, 1.0% to 5.9% for stromal thickness measurement, and 1.0% to 5.4% for total corneal thickness measurement.

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in advanced keratoconus patients (n = 53)

Table P:

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in advanced keratoconus patients (n = 53)

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in advanced keratoconus patients (n = 53)

Table Q:

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in advanced keratoconus patients (n = 53)

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in advanced keratoconus patients (n = 53)

Table R:

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in advanced keratoconus patients (n = 53)

Discussion

The precise measurement of corneal thickness is helpful for ophthalmologists to determine the corneal status. This also provides surgeons with data to make better surgical decisions when performing keratoconus therapy (corneal cross-linking or keratoplasty), myopia correction (keratorefractive surgery or phakic intraocular lens implantation), and even a second corneal refractive surgery scheme. The RTVue-XR SD-OCT is a convenient technique for acquiring thickness data for the epithelium, stroma, and total cornea over a wide area. Ma et al.23 assessed the precision of the RTVue-XR in epithelial and total corneal thickness measurement in normal individuals, contact lens wearers, dry eyes, and post-LASIK/PRK eyes, and found Sw of 2.6 µm or less for all corneas in a 9-mm diameter. With the older version of the RTVue, Li et al.8 found Sw values for repeatability of epithelial thickness measurement ranged from 0.7 to 1.9 µm in normal and keratoconic corneas up to a 6-mm diameter. Kanellopoulos and Asimellis17 investigated the epithelial thickness distribution in a healthy population and reported repeatability Sw of 0.88, 1.01, and 0.83 µm, respectively, for central 2-mm, superior, and inferior epithelial thickness measurement. Ma et al.26 reported Sw of 2.2 µm or less in normal and post-LASIK eyes over a 6-mm diameter area. Ryu et al.12 evaluated epithelial thickness measurement in corneas having undergone SMILE 1 to 6 months previously and observed a CoV of 1.44% for central 2-mm, 1.68% to 1.97% for paracentral 2- to 5-mm, and 2.23% to 2.93% for midperipheral 5- to 6-mm regions. These outcomes are similar to our results observed in myopic patients.

We found that the repeatability for epithelial, stromal, and total corneal thickness measurement with the RTVue-XR was excellent in myopic eyes. Ma et al.23 reported similar repeatability of epithelial thickness measurements between myopic eyes and post-LASIK/PRK eyes (Sw from 0.7 to 2.5), although the results were not explicitly shown in their study. This was in agreement with our finding in the myopic group (Sw from 0.88 to 1.63). However, it was less consistent with the outcomes of the post-keratorefractive surgery groups in our study. We observed lower repeatability for postoperative eyes compared with myopic eyes. This disparity may be caused by the different corneal epithelial status of the patients. Most of the patients (10 of 12) they included underwent surgeries 1 year ago or earlier, whereas in the current study all patients were examined at 3 months postoperatively. Kanellopoulos22 found that the epithelial thickening ceased at 6 months after LASIK. The later the period after surgery the cornea was in, the “quieter” the epithelial remodeling became. Hence, it is conceivable that the repeatability might seem better when recruiting patients at this stage. Our investigation revealed the measurement repeatability in the early postoperative course, which is more important for the assessment of epithelial remodeling and monitoring of corneal ectasia.

Among the three postoperative groups, we found the highest repeatability for epithelial thickness measurement in post-SMILE eyes, followed by post-transepithelial PRK eyes, and the poorest outcome in post-FS-LASIK eyes. The likely reason for this may be the different postoperative epithelial remodeling processes among these surgical methods. Ryu et al.12 compared this process at postoperative 1 and 3 months between the post-SMILE and post-FS-LASIK groups and found a higher epithelial thickening in corneas after FS-LASIK. Although the epithelial remodeling after transepithelial PRK has not yet been reported, it is actually observable in another study we are now conducting. Regarding stromal and total corneal thickness measurements, excellent outcomes were observed for all of the surgical methods, except for the peripheral inferior region in the post-transepithelial PRK group.

Luft et al.27 developed a semi-automated segmentation algorithm for the RS 3000 Advance (Nidek Co., Ltd., Gamagori, Japan). They assessed the repeatability of epithelial thickness and stromal thickness measurements in a 5-mm diameter along the horizontal direction (temporal to nasal, vertex included). For corneas 6 months after SMILE, they reported excellent results for stromal thickness measurement (CoV: 0.6% to 0.7%), which was comparable to our results (CoV: 0.3% to 1.1%). However, they generated slightly higher CoVs (2.4% to 3.1%) for epithelial thickness measurement compared with ours (CoV: 2.0% to 2.5%). To the best of our knowledge, to date there has been no investigation of the measurement repeatability of the corneal sublayer thickness in post-transepithelial PRK or post-FS-LASIK corneas.

For the keratoconic corneas, repeatability varied with the severity of disease. For the mild keratoconus group, the outcomes indicated a good repeatability of measurement for central and paracentral epithelial thickness, with a decrease of repeatability toward the midperipheral and peripheral zones. The stromal and total corneal thickness measurements exhibited high repeatability in this group. With regard to the eyes with advanced keratoconus, we found a moderate to good repeatability of epithelial thickness measurement. For stromal and total corneal thickness measurement, excellent repeatability was generated for the central, paracentral, and midperipheral zones, with moderate to good results for the peripheral zone. Ma et al.23 reported that Sw was on a scale of 1.6 to 2.2 for epithelial thickness. Li et al.8 observed the repeatability of Sw for epithelial thickness measurement ranged from 0.7 to 1.9 in normal and keratoconic eyes. These outcomes are consistent with our findings in the mild keratoconus group. In addition, we noticed that, in regard to both stromal and corneal thickness measurements in the midperipheral and peripheral zones, the logically poorest repeatability outcomes were generated in the inferior-temporal region. It suggested an unavoidable effect on thickness measurement was posed by the disease, because most of the time the cone of the keratoconic cornea was observed in this area. This trend failed to be observed by previous studies, which may be because the patients they recruited had less severe keratoconus.

Consistently in all eyes, the pachymetric map of the epithelium showed the greatest CoV when measuring peripheral superior thickness, as compared with other regions. This was contrary to the finding by Ma et al.,23 who found the highest variation of epithelial thickness measurement in the inferior peripheral zones. A possible explanation for the relatively higher CoV peripherally and superiorly may be the interference of the upper eyelashes, which tended to cover the cornea and thus had a detrimental effect on measurement.

There are limitations in our work. We merely incorporated the metrics directly rendered by the pachymetric map. The indices that were critical for diagnosis of keratoconus, such as minimum, maximum, and median thickness and the difference between superior and inferior regions, were not investigated. The epithelial, stromal, and total corneal thickness profiles are also important for other corneal conditions, such as keratoplasty and Terrien's marginal degeneration, which were not taken into consideration in this study. Further studies are warranted to include more metrics and a wider spectrum of corneal pathologies.

Our study demonstrated that the RTVue-XR SDOCT showed excellent repeatability in measuring epithelial, stromal, and total corneal thickness in myopic corneas. For eyes with previous keratorefractive surgery, the epithelial thickness measurement was more variable for post-FS-LASIK corneas compared with post-SMILE and post-transepithelial PRK corneas. The stromal and corneal thickness measurements had high repeatability in eyes after all three surgical methods. For keratoconic corneas, the severity of disease seemed to have an impact on measurement. We advise caution when using SD-OCT to measure epithelial, peripheral stromal, and total corneal thickness in corneas for the purpose of screening the development of corneal ectasia or monitoring the progression of keratoconus.

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Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in myopic patients (n = 75)

Diameter (mm)RegionMEAN ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center53.41 ± 3.030.892.471.70.97 (0.957 to 0.98)
2 – 5Temporal53.36 ± 2.991.042.881.90.957 (0.939 to 0.971)
Superior-Temporal52.9 ± 2.781.193.32.20.931 (0.902 to 0.953)
Superior52.43 ± 2.851.153.192.20.94 (0.915 to 0.96)
Superior-Nasal52.86 ± 2.791.23.322.30.931 (0.902 to 0.953)
Nasal53.74 ± 2.810.992.741.80.955 (0.936 to 0.97)
Inferior-Nasal54.37 ± 2.981.093.0220.952 (0.931 to 0.967)
Inferior54.41 ± 3.241.173.242.20.953 (0.932 to 0.968)
Inferior-Temporal53.91 ± 3.241.243.432.30.947 (0.924 to 0.964)
5 – 7Temporal53.14 ± 2.861.163.212.20.94 (0.914 to 0.959)
Superior-Temporal52.07 ± 2.891.263.492.40.928 (0.898 to 0.951)
Superior50.79 ± 3.21.143.162.20.955 (0.935 to 0.969)
Superior-Nasal52.61 ± 2.951.143.162.20.945 (0.922 to 0.963)
Nasal54.04 ± 2.6512.771.90.948 (0.926 to 0.965)
Inferior-Nasal54.66 ± 3.021.072.9620.955 (0.936 to 0.97)
Inferior54.46 ± 3.351.093.0220.963 (0.947 to 0.975)
Inferior-Temporal53.88 ± 3.141.233.412.30.943 (0.919 to 0.962)
7 – 9Temporal52.44 ± 2.91.032.8520.955 (0.936 to 0.97)
Superior-Temporal49.11 ± 3.491.413.912.90.939 (0.914 to 0.959)
Superior45.76 ± 3.811.624.493.50.932 (0.903 to 0.954)
Superior-Nasal49.87 ± 3.881.383.822.80.954 (0.934 to 0.969)
Nasal54.42 ± 2.881.123.12.10.944 (0.921 to 0.962)
Inferior-Nasal53.98 ± 3.390.922.551.70.974 (0.963 to 0.983)
Inferior52.88 ± 3.911.113.072.10.972 (0.96 to 0.981)
Inferior-Temporal53.24 ± 3.351.313.632.50.944 (0.92 to 0.962)

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in myopic patients (n = 75)

Diameter (mm)RegionMEAN ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center477.44 ± 34.280.852.350.21.0 (1.0 to 1.0)
2 – 5Temporal494.73 ± 33.672.436.730.50.998 (0.998 to 0.999)
Superior-Temporal508.09 ± 34.322.988.250.60.997 (0.996 to 0.998)
Superior518.95 ± 34.473.399.390.70.997 (0.995 to 0.998)
Superior-Nasal514.85 ± 34.483.8310.610.70.996 (0.994 to 0.997)
Nasal506.5 ± 34.053.499.670.70.997 (0.995 to 0.998)
Inferior-Nasal500.28 ± 33.672.797.730.60.998 (0.997 to 0.998)
Inferior495.87 ± 33.532.296.340.50.998 (0.998 to 0.999)
Inferior-Temporal492.18 ± 33.522.496.90.50.998 (0.997 to 0.999)
5 – 7Temporal528.0 ± 33.944.3812.130.80.994 (0.992 to 0.996)
Superior-Temporal551.84 ± 35.565.3914.9310.992 (0.989 to 0.995)
Superior568.48 ± 34.565.1614.290.90.993 (0.989 to 0.995)
Superior-Nasal560.85 ± 34.936.2617.341.10.989 (0.985 to 0.993)
Nasal546.86 ± 34.935.414.9610.992 (0.989 to 0.995)
Inferior-Nasal540.04 ± 35.115.214.410.993 (0.989 to 0.995)
Inferior534.64 ± 34.224.1311.440.80.995 (0.993 to 0.997)
Inferior-Temporal526.25 ± 33.535.6915.761.10.99 (0.986 to 0.993)
7 – 9Temporal569.44 ± 37.16.5918.251.20.989 (0.985 to 0.993)
Superior-Temporal601.84 ± 39.0311.0630.641.80.972 (0.96 to 0.981)
Superior619.44 ± 35.7811.7632.581.90.962 (0.945 to 0.974)
Superior-Nasal614.16 ± 37.2910.930.191.80.97 (0.957 to 0.98)
Nasal596.86 ± 38.237.1119.691.20.988 (0.983 to 0.992)
Inferior-Nasal589.44 ± 39.649.9327.511.70.978 (0.969 to 0.985)
Inferior579.68 ± 37.5310.9730.391.90.97 (0.957 to 0.98)
Inferior-Temporal568.11 ± 36.0311.6432.2420.963 (0.947 to 0.975)

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in myopic patients (n = 75)

Diameter (mm)RegionMEAN ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center530.85 ± 35.541.13.050.21.0 (1.0 to 1.0)
2 – 5Temporal548.09 ± 34.792.647.310.50.998 (0.997 to 0.999)
Superior-Temporal560.99 ± 35.162.988.250.50.998 (0.997 to 0.998)
Superior571.39 ± 35.083.399.390.60.997 (0.996 to 0.998)
Superior-Nasal567.71 ± 35.23.9210.860.70.996 (0.994 to 0.997)
Nasal560.24 ± 35.03.579.890.60.997 (0.995 to 0.998)
Inferior-Nasal554.65 ± 34.652.988.250.50.998 (0.996 to 0.998)
Inferior550.28 ± 34.672.677.40.50.998 (0.997 to 0.999)
Inferior-Temporal546.09 ± 34.7738.310.50.998 (0.996 to 0.998)
5 – 7Temporal581.14 ± 34.914.4712.380.80.995 (0.992 to 0.996)
Superior-Temporal603.91 ± 35.895.2414.510.90.993 (0.99 to 0.995)
Superior619.28 ± 34.364.9413.680.80.993 (0.99 to 0.995)
Superior-Nasal613.45 ± 34.956.2217.2310.989 (0.985 to 0.993)
Nasal600.9 ± 35.545.4215.010.90.992 (0.989 to 0.995)
Inferior-Nasal594.7 ± 35.785.3414.790.90.993 (0.989 to 0.995)
Inferior589.09 ± 35.154.2511.770.70.995 (0.993 to 0.997)
Inferior-Temporal580.14 ± 34.685.9916.5910.99 (0.986 to 0.993)
7 – 9Temporal621.88 ± 37.856.6918.531.10.989 (0.985 to 0.993)
Superior-Temporal650.95 ± 38.9610.8430.031.70.973 (0.961 to 0.982)
Superior665.19 ± 35.5811.632.131.70.962 (0.946 to 0.974)
Superior-Nasal664.04 ± 37.1510.6829.581.60.971 (0.959 to 0.98)
Nasal651.29 ± 38.647.320.221.10.988 (0.983 to 0.992)
Inferior-Nasal643.42 ± 40.059.8927.41.50.979 (0.97 to 0.986)
Inferior632.57 ± 37.910.6629.531.70.972 (0.961 to 0.981)
Inferior-Temporal621.35 ± 36.7911.6732.331.90.964 (0.949 to 0.976)

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-TPRK patients (n = 68)

Diameter (mm)RegionMEAN ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center52.17 ± 4.491.353.742.60.968 (0.954 to 0.979)
2 – 5Temporal54.27 ± 4.611.454.022.70.965 (0.949 to 0.977)
Superior-Temporal52.51 ± 4.771.634.523.10.958 (0.939 to 0.972)
Superior50.96 ± 5.241.845.13.60.956 (0.935 to 0.971)
Superior-Nasal51.17 ± 5.121.84.993.50.956 (0.935 to 0.971)
Nasal52.38 ± 4.911.524.212.90.966 (0.951 to 0.978)
Inferior-Nasal53.42 ± 5.171.574.352.90.967 (0.953 to 0.978)
Inferior54.24 ± 5.041.684.653.10.961 (0.943 to 0.974)
Inferior-Temporal54.67 ± 4.781.694.683.10.955 (0.935 to 0.97)
5 – 7Temporal52.27 ± 4.931.724.763.30.956 (0.936 to 0.971)
Superior-Temporal49.38 ± 5.261.534.243.10.97 (0.957 to 0.98)
Superior46.73 ± 5.51.95.264.10.957 (0.938 to 0.972)
Superior-Nasal48.9 ± 5.331.724.763.50.963 (0.946 to 0.975)
Nasal51.03 ± 4.921.64.433.10.963 (0.946 to 0.975)
Inferior-Nasal50.63 ± 4.891.614.463.20.961 (0.944 to 0.974)
Inferior50.29 ± 4.92.276.294.50.918 (0.881 to 0.945)
Inferior-Temporal51.73 ± 4.491.84.993.50.94 (0.913 to 0.961)
7 – 9Temporal50.29 ± 4.352.015.5740.918 (0.88 to 0.946)
Superior-Temporal46.91 ± 4.61.574.353.30.958 (0.939 to 0.972)
Superior43.64 ± 5.152.77.486.20.888 (0.837 to 0.926)
Superior-Nasal47.27 ± 4.782.15.824.40.927 (0.893 to 0.951)
Nasal51.98 ± 4.551.915.293.70.934 (0.904 to 0.956)
Inferior-Nasal50.84 ± 4.532.065.714.10.922 (0.886 to 0.948)
Inferior49.08 ± 4.492.336.454.70.892 (0.843 to 0.928)
Inferior-Temporal50.09 ± 4.082.567.095.10.826 (0.747 to 0.884)

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-TPRK patients (n = 68)

Diameter (mm)RegionMEAN ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center366.52 ± 38.872.577.120.70.999 (0.998 to 0.999)
2 – 5Temporal404.29 ± 35.085.9316.431.50.99 (0.986 to 0.994)
Superior-Temporal419.81 ± 35.56.3717.641.50.989 (0.984 to 0.993)
Superior432.45 ± 36.516.4117.761.50.99 (0.985 to 0.993)
Superior-Nasal427.0 ± 37.457.3720.411.70.987 (0.981 to 0.991)
Nasal419.1 ± 37.677.0919.641.70.988 (0.983 to 0.992)
Inferior-Nasal415.79 ± 35.56.4917.981.60.989 (0.984 to 0.993)
Inferior411.65 ± 34.095.8716.261.40.99 (0.985 to 0.993)
Inferior-Temporal404.64 ± 35.016.3317.531.60.989 (0.984 to 0.993)
5 – 7Temporal474.68 ± 33.727.921.881.70.981 (0.973 to 0.988)
Superior-Temporal501.59 ± 32.548.1622.61.60.978 (0.969 to 0.986)
Superior521.19 ± 32.187.6521.191.50.981 (0.972 to 0.987)
Superior-Nasal509.37 ± 34.0110.3128.5620.968 (0.953 to 0.979)
Nasal496.88 ± 34.519.4926.291.90.974 (0.962 to 0.983)
Inferior-Nasal495.53 ± 31.08.4123.31.70.974 (0.963 to 0.983)
Inferior491.93 ± 29.49.5926.561.90.962 (0.945 to 0.975)
Inferior-Temporal476.61 ± 32.358.1222.491.70.978 (0.968 to 0.986)
7 – 9Temporal539.85 ± 32.948.4823.491.60.977 (0.967 to 0.985)
Superior-Temporal570.81 ± 31.378.0722.351.40.977 (0.967 to 0.985)
Superior589.68 ± 31.991027.71.70.965 (0.95 to 0.977)
Superior-Nasal584.17 ± 34.9515.2842.332.60.928 (0.895 to 0.952)
Nasal568.77 ± 32.48.7124.131.50.975 (0.964 to 0.983)
Inferior-Nasal562.62 ± 30.959.8227.21.70.964 (0.948 to 0.976)
Inferior554.49 ± 38.5323.1964.244.20.842 (0.77 to 0.895)
Inferior-Temporal538.27 ± 32.5611.7732.62.20.953 (0.931 to 0.969)

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-TPRK patients (n = 68)

Diameter (mm)RegionMean ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center418.7 ± 38.312.98.030.70.998 (0.997 to 0.999)
2 – 5Temporal458.56 ± 34.116.0816.841.30.989 (0.984 to 0.993)
Superior-Temporal472.32 ± 35.196.4417.841.40.989 (0.984 to 0.993)
Superior483.41 ± 36.316.3517.591.30.99 (0.985 to 0.993)
Superior-Nasal478.17 ± 37.47.2820.171.50.987 (0.981 to 0.992)
Nasal471.49 ± 37.426.9919.361.50.988 (0.983 to 0.992)
Inferior-Nasal469.21 ± 35.046.4617.891.40.989 (0.983 to 0.992)
Inferior465.89 ± 33.285.8816.291.30.989 (0.985 to 0.993)
Inferior-Temporal459.31 ± 33.976.3217.511.40.988 (0.983 to 0.992)
5 – 7Temporal526.95 ± 32.868.0822.381.50.979 (0.97 to 0.986)
Superior-Temporal550.97 ± 32.857.9922.131.50.98 (0.97 to 0.987)
Superior567.92 ± 32.397.3620.391.30.982 (0.974 to 0.988)
Superior-Nasal558.26 ± 34.1710.0627.871.80.97 (0.956 to 0.98)
Nasal547.91 ± 34.659.1625.371.70.976 (0.965 to 0.984)
Inferior-Nasal546.16 ± 31.258.1522.581.50.976 (0.966 to 0.984)
Inferior542.23 ± 29.768.724.11.60.97 (0.957 to 0.98)
Inferior-Temporal528.34 ± 32.128.2322.81.60.977 (0.967 to 0.985)
7 – 9Temporal590.14 ± 32.758.7124.131.50.975 (0.964 to 0.984)
Superior-Temporal617.71 ± 31.68.1522.581.30.977 (0.967 to 0.985)
Superior633.32 ± 31.759.4526.181.50.969 (0.955 to 0.979)
Superior-Nasal631.45 ± 35.0615.1842.052.40.929 (0.897 to 0.953)
Nasal620.75 ± 32.818.7424.211.40.975 (0.964 to 0.984)
Inferior-Nasal613.46 ± 31.269.7727.061.60.965 (0.95 to 0.977)
Inferior603.56 ± 37.9222.2861.723.70.851 (0.784 to 0.902)
Inferior-Temporal588.35 ± 32.7311.8532.8220.953 (0.931 to 0.969)

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-SMILE patients (n = 61)

Diameter (mm)RegionMEAN ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center57.19 ± 4.081.353.742.40.961 (0.943 to 0.975)
2 – 5Temporal58.56 ± 4.111.43.882.40.959 (0.939 to 0.973)
Superior-Temporal56.49 ± 3.881.33.62.30.96 (0.941 to 0.974)
Superior54.9 ± 3.691.263.492.30.958 (0.938 to 0.973)
Superior-Nasal55.13 ± 3.731.43.882.50.949 (0.925 to 0.967)
Nasal56.33 ± 3.891.624.492.90.936 (0.906 to 0.959)
Inferior-Nasal58.16 ± 4.131.74.712.90.937 (0.907 to 0.959)
Inferior59.28 ± 4.231.544.272.60.952 (0.929 to 0.969)
Inferior-Temporal59.34 ± 4.221.594.42.70.949 (0.924 to 0.967)
5 – 7Temporal56.57 ± 3.971.744.823.10.928 (0.894 to 0.954)
Superior-Temporal54.68 ± 3.641.74.713.10.916 (0.875 to 0.945)
Superior52.91 ± 3.671.614.4630.927 (0.893 to 0.953)
Superior-Nasal54.85 ± 3.591.464.042.70.939 (0.91 to 0.961)
Nasal56.56 ± 3.751.534.242.70.938 (0.908 to 0.96)
Inferior-Nasal56.77 ± 4.111.684.6530.937 (0.907 to 0.96)
Inferior56.23 ± 4.41.754.853.10.942 (0.914 to 0.962)
Inferior-Temporal56.28 ± 4.571.925.323.40.934 (0.902 to 0.957)
7 – 9Temporal50.41 ± 4.042.085.764.10.894 (0.842 to 0.931)
Superior-Temporal47.84 ± 3.412.176.014.50.817 (0.729 to 0.882)
Superior45.79 ± 3.572.135.94.70.847 (0.773 to 0.901)
Superior-Nasal49.15 ± 3.822.045.654.20.886 (0.831 to 0.926)
Nasal53.52 ± 4.411.935.353.60.927 (0.893 to 0.953)
Inferior-Nasal52.67 ± 3.951.614.463.10.938 (0.908 to 0.96)
Inferior51.85 ± 3.721.835.073.50.905 (0.859 to 0.939)
Inferior-Temporal51.83 ± 3.721.674.633.20.923 (0.886 to 0.95)

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-SMILE patients (n = 61)

Diameter (mm)RegionMEAN ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center396.87 ± 29.1812.770.31.0 (0.999 to 1.0)
2 – 5Temporal436.14 ± 25.144.8813.521.10.987 (0.981 to 0.992)
Superior-Temporal447.62 ± 27.155.414.961.20.987 (0.98 to 0.991)
Superior456.43 ± 29.576.2417.281.40.985 (0.978 to 0.99)
Superior-Nasal450.6 ± 31.866.5618.171.50.986 (0.979 to 0.991)
Nasal445.36 ± 31.535.7715.981.30.989 (0.983 to 0.993)
Inferior-Nasal444.26 ± 28.654.9213.631.10.99 (0.985 to 0.994)
Inferior443.09 ± 26.425.4415.071.20.986 (0.979 to 0.991)
Inferior-Temporal438.04 ± 25.45.9616.511.40.981 (0.972 to 0.988)
5 – 7Temporal504.33 ± 27.377.9421.991.60.971 (0.956 to 0.981)
Superior-Temporal527.63 ± 28.988.3223.051.60.971 (0.957 to 0.981)
Superior542.88 ± 30.879.2425.591.70.969 (0.954 to 0.98)
Superior-Nasal529.87 ± 34.6511.1230.82.10.964 (0.946 to 0.976)
Nasal519.49 ± 34.39.0725.121.70.976 (0.964 to 0.984)
Inferior-Nasal520.07 ± 30.617.6521.191.50.979 (0.968 to 0.986)
Inferior519.0 ± 28.188.222.711.60.97 (0.956 to 0.981)
Inferior-Temporal506.91 ± 28.069.5926.561.90.958 (0.938 to 0.973)
7 – 9Temporal572.27 ± 30.07.721.331.30.977 (0.966 to 0.985)
Superior-Temporal603.31 ± 30.698.4723.461.40.974 (0.961 to 0.983)
Superior620.2 ± 31.9412.835.462.10.941 (0.912 to 0.962)
Superior-Nasal614.25 ± 34.8614.5840.392.40.935 (0.903 to 0.958)
Nasal596.6 ± 33.087.9922.131.30.98 (0.97 to 0.987)
Inferior-Nasal592.12 ± 31.628.0522.31.40.978 (0.967 to 0.986)
Inferior581.24 ± 29.611.9933.212.10.939 (0.91 to 0.961)
Inferior-Temporal569.06 ± 30.9612.3834.292.20.941 (0.913 to 0.962)

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-SMILE patients (n = 61)

Diameter (mm)RegionMEAN ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center454.06 ± 28.931.443.990.30.999 (0.999 to 0.999)
2 – 5Temporal494.7 ± 25.385.0413.9610.987 (0.98 to 0.991)
Superior-Temporal504.11 ± 27.335.5215.291.10.986 (0.979 to 0.991)
Superior511.33 ± 29.836.3917.71.20.984 (0.977 to 0.99)
Superior-Nasal505.73 ± 32.566.8518.971.40.985 (0.978 to 0.99)
Nasal501.68 ± 32.135.9816.561.20.988 (0.983 to 0.992)
Inferior-Nasal502.41 ± 29.245.1414.2410.99 (0.985 to 0.993)
Inferior502.37 ± 26.785.4615.121.10.986 (0.979 to 0.991)
Inferior-Temporal497.38 ± 25.745.8716.261.20.982 (0.974 to 0.989)
5 – 7Temporal560.9 ± 27.767.2620.111.30.976 (0.965 to 0.985)
Superior-Temporal582.31 ± 28.867.7321.411.30.975 (0.963 to 0.984)
Superior595.79 ± 30.468.6824.041.50.972 (0.958 to 0.982)
Superior-Nasal584.73 ± 34.610.8430.031.90.965 (0.949 to 0.978)
Nasal576.05 ± 34.778.8924.631.50.977 (0.967 to 0.985)
Inferior-Nasal576.83 ± 31.277.1419.781.20.982 (0.974 to 0.988)
Inferior575.24 ± 28.797.6121.081.30.976 (0.964 to 0.984)
Inferior-Temporal563.19 ± 28.468.7824.321.60.967 (0.95 to 0.978)
7 – 9Temporal622.68 ± 30.517.4920.751.20.979 (0.969 to 0.987)
Superior-Temporal651.15 ± 31.088.1722.631.30.976 (0.965 to 0.985)
Superior665.99 ± 32.4312.8335.541.90.942 (0.915 to 0.963)
Superior-Nasal663.4 ± 35.214.0438.892.10.941 (0.913 to 0.962)
Nasal650.12 ± 34.848.1522.581.30.981 (0.972 to 0.988)
Inferior-Nasal644.79 ± 32.918.1322.521.30.979 (0.969 to 0.986)
Inferior633.09 ± 30.0512.3134.11.90.938 (0.908 to 0.96)
Inferior-Temporal620.89 ± 31.3812.3534.2120.943 (0.915 to 0.963)

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-FS-LASIK patients (n = 75)

Diameter (mm)RegionMEAN ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center58.36 ± 5.812.346.4840.94 (0.914 to 0.959)
2 – 5Temporal59.52 ± 5.493.569.8660.807 (0.724 to 0.87)
Superior-Temporal57.37 ± 4.953.018.345.20.838 (0.768 to 0.89)
Superior55.66 ± 4.452.567.094.60.86 (0.801 to 0.906)
Superior-Nasal55.59 ± 4.252.276.294.10.883 (0.833 to 0.921)
Nasal57.08 ± 4.372.145.933.70.905 (0.865 to 0.936)
Inferior-Nasal59.01 ± 4.722.376.5640.9 (0.857 to 0.932)
Inferior60.1 ± 5.242.677.44.40.897 (0.852 to 0.93)
Inferior-Temporal60.25 ± 5.793.389.365.60.854 (0.792 to 0.901)
5 – 7Temporal52.06 ± 4.463.048.425.80.778 (0.682 to 0.85)
Superior-Temporal50.65 ± 4.0838.315.90.721 (0.601 to 0.811)
Superior50.07 ± 3.942.77.485.40.773 (0.676 to 0.847)
Superior-Nasal51.78 ± 3.661.895.243.70.893 (0.848 to 0.928)
Nasal52.5 ± 3.61.423.932.70.943 (0.918 to 0.961)
Inferior-Nasal52.7 ± 3.661.724.763.30.914 (0.877 to 0.942)
Inferior52.76 ± 4.152.436.734.60.853 (0.79 to 0.901)
Inferior-Temporal52.74 ± 4.272.727.535.20.817 (0.738 to 0.876)
7 – 9Temporal49.16 ± 4.432.87.765.70.819 (0.741 to 0.878)
Superior-Temporal47.67 ± 4.022.898.016.10.737 (0.624 to 0.823)
Superior46.34 ± 4.212.948.146.30.761 (0.659 to 0.839)
Superior-Nasal49.36 ± 3.722.426.74.90.805 (0.722 to 0.868)
Nasal51.87 ± 3.281.644.543.20.9 (0.858 to 0.933)
Inferior-Nasal51.3 ± 3.471.64.433.10.918 (0.884 to 0.945)
Inferior51.13 ± 4.112.476.844.80.842 (0.775 to 0.893)
Inferior-Temporal50.55 ± 4.572.777.675.50.839 (0.771 to 0.891)

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-FS-LASIK patients (n = 75)

Diameter (mm)RegionMEAN ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center389.22 ± 25.832.587.150.70.997 (0.995 to 0.998)
2 – 5Temporal433.02 ± 25.086.217.171.40.979 (0.97 to 0.986)
Superior-Temporal446.86 ± 26.146.6518.421.50.978 (0.968 to 0.985)
Superior456.66 ± 27.697.1819.891.60.977 (0.967 to 0.984)
Superior-Nasal449.21 ± 28.497.4520.641.70.976 (0.966 to 0.984)
Nasal439.5 ± 26.715.9616.511.40.983 (0.976 to 0.989)
Inferior-Nasal436.15 ± 25.175.6215.571.30.983 (0.976 to 0.988)
Inferior434.93 ± 24.745.9416.451.40.98 (0.972 to 0.987)
Inferior-Temporal431.36 ± 24.496.818.841.60.973 (0.962 to 0.982)
5 – 7Temporal507.58 ± 30.167.1619.831.40.981 (0.972 to 0.987)
Superior-Temporal532.82 ± 31.437.8121.631.50.979 (0.97 to 0.986)
Superior548.05 ± 31.358.0322.241.50.977 (0.968 to 0.985)
Superior-Nasal532.98 ± 32.459.5226.371.80.97 (0.957 to 0.98)
Nasal518.7 ± 29.97.7121.361.50.977 (0.967 to 0.984)
Inferior-Nasal516.17 ± 27.877.0719.581.40.978 (0.968 to 0.985)
Inferior514.39 ± 26.797.621.051.50.972 (0.96 to 0.981)
Inferior-Temporal504.52 ± 27.798.3923.241.70.968 (0.954 to 0.978)
7 – 9Temporal568.72 ± 31.237.4420.611.30.981 (0.972 to 0.987)
Superior-Temporal596.19 ± 31.918.423.271.40.976 (0.966 to 0.984)
Superior612.49 ± 33.1210.8129.941.80.962 (0.946 to 0.974)
Superior-Nasal603.23 ± 34.3911.7132.441.90.959 (0.941 to 0.972)
Nasal587.27 ± 30.476.9719.311.20.982 (0.974 to 0.988)
Inferior-Nasal580.41 ± 28.186.9919.361.20.979 (0.97 to 0.986)
Inferior569.72 ± 27.4211.4431.6920.935 (0.907 to 0.956)
Inferior-Temporal562.12 ± 29.911.5632.022.10.945 (0.922 to 0.963)

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in post-FS-LASIK patients (n = 75)

Diameter (mm)RegionMEAN ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center447.59 ± 25.151.273.520.30.999 (0.999 to 0.999)
2 – 5Temporal492.54 ± 25.674.8813.5210.988 (0.983 to 0.992)
Superior-Temporal504.23 ± 26.465.9516.481.20.983 (0.975 to 0.988)
Superior512.32 ± 27.786.6818.51.30.98 (0.972 to 0.987)
Superior-Nasal504.81 ± 28.317.0419.51.40.979 (0.97 to 0.986)
Nasal496.58 ± 26.075.4114.991.10.985 (0.979 to 0.99)
Inferior-Nasal495.15 ± 24.745.0914.110.986 (0.979 to 0.99)
Inferior495.04 ± 24.725.2214.461.10.985 (0.978 to 0.99)
Inferior-Temporal491.61 ± 25.215.5615.41.10.983 (0.976 to 0.989)
5 – 7Temporal559.64 ± 29.56.0616.791.10.986 (0.98 to 0.99)
Superior-Temporal583.47 ± 31.097.119.671.20.982 (0.974 to 0.988)
Superior598.12 ± 30.997.1219.721.20.982 (0.974 to 0.988)
Superior-Nasal584.76 ± 31.848.8924.631.50.973 (0.961 to 0.982)
Nasal571.21 ± 29.047.3320.31.30.978 (0.969 to 0.985)
Inferior-Nasal568.87 ± 27.266.4917.981.10.981 (0.972 to 0.987)
Inferior567.15 ± 26.616.6918.531.20.978 (0.969 to 0.985)
Inferior-Temporal557.26 ± 27.77.1719.861.30.977 (0.967 to 0.984)
7 – 9Temporal617.88 ± 31.416.8418.951.10.984 (0.977 to 0.989)
Superior-Temporal643.86 ± 32.328.122.441.30.978 (0.969 to 0.985)
Superior658.83 ± 33.1110.1428.091.50.967 (0.953 to 0.978)
Superior-Nasal652.6 ± 34.2211.2831.251.70.961 (0.945 to 0.974)
Nasal639.14 ± 30.887.1319.751.10.982 (0.974 to 0.988)
Inferior-Nasal631.71 ± 28.687.1219.721.10.979 (0.97 to 0.986)
Inferior620.85 ± 27.8811.3231.361.80.939 (0.913 to 0.959)
Inferior-Temporal612.66 ± 30.2110.9230.251.80.953 (0.932 to 0.968)

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in mild keratoconic patients (n = 20)

Diameter (mm)RegionMEAN ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center53.04 ± 3.381.413.912.70.937 (0.875 to 0.972)
2 – 5Temporal54.21 ± 3.481.624.4930.917 (0.837 to 0.964)
Superior-Temporal54.1 ± 2.911.363.772.50.917 (0.837 to 0.964)
Superior53.74 ± 3.191.734.793.20.881 (0.767 to 0.948)
Superior-Nasal54.07 ± 3.341.54.162.80.925 (0.852 to 0.967)
Nasal54.43 ± 3.621.494.132.70.938 (0.878 to 0.973)
Inferior-Nasal54.24 ± 3.361.464.042.70.93 (0.862 to 0.969)
Inferior53.23 ± 3.211.694.683.20.891 (0.786 to 0.952)
Inferior-Temporal52.61 ± 3.541.684.653.20.914 (0.831 to 0.962)
5 – 7Temporal54.45 ± 3.341.84.993.30.884 (0.773 to 0.949)
Superior-Temporal53.07 ± 2.971.734.793.30.86 (0.728 to 0.938)
Superior51.69 ± 3.812.436.734.70.82 (0.647 to 0.92)
Superior-Nasal53.3 ± 3.161.624.4930.898 (0.801 to 0.955)
Nasal54.98 ± 3.081.54.162.70.909 (0.82 to 0.96)
Inferior-Nasal55.65 ± 3.111.313.632.40.936 (0.873 to 0.972)
Inferior55.43 ± 2.931.554.292.80.889 (0.782 to 0.951)
Inferior-Temporal54.13 ± 3.541.654.5730.917 (0.838 to 0.964)
7 – 9Temporal53.44 ± 2.81.393.852.60.905 (0.814 to 0.958)
Superior-Temporal50.03 ± 2.811.724.763.40.84 (0.687 to 0.929)
Superior46.74 ± 4.642.887.986.20.831 (0.665 to 0.926)
Superior-Nasal49.93 ± 3.771.825.043.60.911 (0.824 to 0.961)
Nasal54.73 ± 2.821.644.5430.857 (0.718 to 0.937)
Inferior-Nasal54.51 ± 2.531.022.831.90.942 (0.886 to 0.974)
Inferior53.68 ± 2.541.13.0520.931 (0.864 to 0.97)
Inferior-Temporal53.6 ± 2.891.43.882.60.91 (0.822 to 0.96)

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in mild keratoconic patients (n = 20)

Diameter (mm)RegionMEAN ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center461.9 ± 23.332.948.140.60.995 (0.99 to 0.998)
2 – 5Temporal477.73 ± 22.253.289.090.70.993 (0.986 to 0.997)
Superior-Temporal495.46 ± 24.155.3914.931.10.983 (0.968 to 0.993)
Superior508.79 ± 25.586.9219.171.40.975 (0.951 to 0.989)
Superior-Nasal505.35 ± 25.246.5918.251.30.977 (0.955 to 0.99)
Nasal493.18 ± 24.05.1314.2110.985 (0.97 to 0.993)
Inferior-Nasal481.48 ± 22.043.429.470.70.992 (0.985 to 0.997)
Inferior472.85 ± 20.643.7310.330.80.989 (0.979 to 0.995)
Inferior-Temporal468.97 ± 20.573.7210.30.80.989 (0.979 to 0.995)
5 – 7Temporal506.5 ± 22.754.8713.4910.985 (0.97 to 0.993)
Superior-Temporal536.88 ± 27.26.9419.221.30.978 (0.957 to 0.99)
Superior559.85 ± 29.269.2725.681.70.965 (0.932 to 0.985)
Superior-Nasal552.05 ± 28.499.0725.121.60.965 (0.931 to 0.985)
Nasal532.47 ± 26.697.0119.421.30.977 (0.954 to 0.99)
Inferior-Nasal518.75 ± 22.865.7816.011.10.978 (0.958 to 0.991)
Inferior508.61 ± 21.096.8518.971.30.963 (0.928 to 0.984)
Inferior-Temporal499.49 ± 22.169.0925.181.80.939 (0.88 to 0.973)
7 – 9Temporal542.45 ± 25.96.6218.341.20.978 (0.957 to 0.99)
Superior-Temporal580.31 ± 33.19.5626.481.60.972 (0.944 to 0.987)
Superior610.34 ± 39.2818.150.1430.92 (0.842 to 0.965)
Superior-Nasal601.58 ± 37.3414.1539.22.40.949 (0.899 to 0.977)
Nasal578.16 ± 31.979.1525.351.60.972 (0.945 to 0.988)
Inferior-Nasal566.38 ± 27.027.7721.521.40.972 (0.945 to 0.988)
Inferior554.67 ± 24.4810.0727.891.80.939 (0.88 to 0.973)
Inferior-Temporal542.9 ± 27.6815.4142.692.80.874 (0.752 to 0.944)

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in mild keratoconic patients (n = 20)

Diameter (mm)RegionMEAN ± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center514.95 ± 24.43.158.730.60.995 (0.989 to 0.998)
2 – 5Temporal531.95 ± 22.673.6810.190.70.991 (0.983 to 0.996)
Superior-Temporal549.56 ± 24.175.0714.040.90.985 (0.971 to 0.994)
Superior562.53 ± 25.286.3917.71.10.979 (0.958 to 0.991)
Superior-Nasal559.42 ± 24.86.317.451.10.978 (0.957 to 0.99)
Nasal547.6 ± 24.085.0814.070.90.985 (0.971 to 0.993)
Inferior-Nasal535.72 ± 22.763.8410.640.70.991 (0.982 to 0.996)
Inferior526.08 ± 20.864.5512.60.90.984 (0.969 to 0.993)
Inferior-Temporal521.57 ± 20.324.2711.830.80.985 (0.971 to 0.994)
5 – 7Temporal560.95 ± 22.115.3314.7610.981 (0.962 to 0.991)
Superior-Temporal589.94 ± 26.766.3517.591.10.981 (0.963 to 0.992)
Superior611.54 ± 29.18.2622.881.40.973 (0.946 to 0.988)
Superior-Nasal605.35 ± 27.968.4823.491.40.968 (0.938 to 0.986)
Nasal587.46 ± 26.477.0519.531.20.976 (0.953 to 0.989)
Inferior-Nasal574.4 ± 23.275.9816.5610.978 (0.956 to 0.99)
Inferior564.04 ± 20.987.4220.551.30.956 (0.914 to 0.981)
Inferior-Temporal553.62 ± 21.579.3325.841.70.931 (0.864 to 0.97)
7 – 9Temporal595.89 ± 25.356.86191.20.975 (0.951 to 0.989)
Superior-Temporal630.34 ± 32.628.9424.761.40.975 (0.95 to 0.989)
Superior657.08 ± 39.5316.9246.872.60.933 (0.867 to 0.97)
Superior-Nasal651.5 ± 36.7313.1336.3720.955 (0.911 to 0.98)
Nasal632.9 ± 32.259.0224.991.40.973 (0.947 to 0.988)
Inferior-Nasal620.89 ± 27.517.5320.861.20.975 (0.95 to 0.989)
Inferior608.35 ± 24.629.8427.261.60.943 (0.888 to 0.975)
Inferior-Temporal596.5 ± 27.6515.4142.692.60.874 (0.752 to 0.944)

Repeatability outcomes for corneal epithelial thickness measurement using RTVue-XR spectral-domain optical coherence tomography in advanced keratoconus patients (n = 53)

Diameter (mm)RegionMEAN± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center49.01 ± 4.712.426.74.90.894 (0.839 to 0.934)
2 – 5Temporal50.53 ± 5.713.8910.787.70.777 (0.659 to 0.861)
Superior-Temporal54.05 ± 5.592.988.255.50.885 (0.825 to 0.928)
Superior54.63 ± 5.22.246.24.10.931 (0.895 to 0.957)
Superior-Nasal55.47 ± 5.032.216.1240.927 (0.89 to 0.955)
Nasal55.22 ± 4.871.925.323.50.943 (0.913 to 0.964)
Inferior-Nasal53.16 ± 5.242.226.154.20.933 (0.897 to 0.958)
Inferior50.19 ± 5.562.316.44.60.936 (0.902 to 0.96)
Inferior-Temporal48.13 ± 5.443.419.457.10.824 (0.732 to 0.891)
5 – 7Temporal55.03 ± 5.533.8310.6170.767 (0.644 to 0.855)
Superior-Temporal54.18 ± 5.953.6310.066.70.836 (0.75 to 0.898)
Superior51.29 ± 4.822.857.895.60.851 (0.773 to 0.907)
Superior-Nasal53.47 ± 4.552.115.843.90.918 (0.875 to 0.949)
Nasal55.76 ± 5.021.95.263.40.948 (0.921 to 0.967)
Inferior-Nasal56.62 ± 5.182.316.44.10.925 (0.886 to 0.953)
Inferior55.51 ± 5.751.975.463.50.958 (0.936 to 0.974)
Inferior-Temporal53.78 ± 6.063.058.455.70.899 (0.846 to 0.937)
7 – 9Temporal53.41 ± 4.593.098.565.80.785 (0.671 to 0.866)
Superior-Temporal49.86 ± 5.64.0111.1180.742 (0.605 to 0.839)
Superior46.44 ± 5.643.7210.380.798 (0.692 to 0.874)
Superior-Nasal49.75 ± 4.552.887.985.80.82 (0.727 to 0.888)
Nasal53.84 ± 4.21.684.653.10.941 (0.911 to 0.963)
Inferior-Nasal53.98 ± 4.732.15.823.90.926 (0.887 to 0.954)
Inferior53.59 ± 5.212.346.484.40.923 (0.883 to 0.952)
Inferior-Temporal53.56 ± 5.142.727.535.10.886 (0.826 to 0.929)

Repeatability outcomes for corneal stromal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in advanced keratoconus patients (n = 53)

Diameter (mm)RegionMEAN± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center422.05 ± 36.044.311.9110.995 (0.993 to 0.997)
2 – 5Temporal446.07 ± 36.028.7924.3520.98 (0.969 to 0.987)
Superior-Temporal468.77 ± 35.937.9622.051.70.983 (0.975 to 0.99)
Superior483.48 ± 35.016.4317.811.30.989 (0.983 to 0.993)
Superior-Nasal479.19 ± 32.746.0216.681.30.989 (0.983 to 0.993)
Nasal465.03 ± 31.055.9316.431.30.988 (0.981 to 0.992)
Inferior-Nasal451.45 ± 31.88719.391.60.984 (0.975 to 0.99)
Inferior440.95 ± 33.665.8816.291.30.99 (0.984 to 0.994)
Inferior-Temporal436.08 ± 35.416.4117.761.50.989 (0.983 to 0.993)
5 – 7Temporal485.25 ± 38.2211.9533.12.50.966 (0.947 to 0.979)
Superior-Temporal518.26 ± 37.7911.130.752.10.97 (0.954 to 0.981)
Superior542.78 ± 36.959.2825.711.70.978 (0.967 to 0.986)
Superior-Nasal534.53 ± 34.889.1925.461.70.976 (0.963 to 0.985)
Nasal512.59 ± 32.449.1225.261.80.973 (0.958 to 0.983)
Inferior-Nasal499.52 ± 33.8610.4128.842.10.967 (0.949 to 0.979)
Inferior489.37 ± 36.2111.0330.552.30.967 (0.95 to 0.98)
Inferior-Temporal480.26 ± 41.4114.1539.22.90.958 (0.936 to 0.974)
7 – 9Temporal529.0 ± 39.6713.938.52.60.956 (0.933 to 0.973)
Superior-Temporal544.64 ± 39.7314.08392.60.955 (0.931 to 0.972)
Superior567.74 ± 42.7619.8354.933.50.917 (0.874 to 0.948)
Superior-Nasal565.68 ± 40.1921.3359.083.80.886 (0.826 to 0.929)
Nasal549.51 ± 32.5213.2136.592.40.939 (0.907 to 0.962)
Inferior-Nasal551.89 ± 37.0114.8412.70.941 (0.91 to 0.963)
Inferior553.55 ± 45.6924.1566.94.40.887 (0.828 to 0.93)
Inferior-Temporal543.89 ± 55.0632.1589.065.90.854 (0.777 to 0.909)

Repeatability outcomes for total corneal thickness measurement using RTVue-XR spectral-domain optical coherence tomography in advanced keratoconus patients (n = 53)

Diameter (mm)RegionMEAN± SDSwTRT (μm)CoV (%)ICC (95% CI)
2Center471.06 ± 37.034.8913.5510.994 (0.991 to 0.996)
2 – 5Temporal496.6 ± 37.039.7426.9820.976 (0.964 to 0.985)
Superior-Temporal522.83 ± 36.058.523.541.60.981 (0.971 to 0.988)
Superior538.11 ± 34.646.1316.981.10.989 (0.984 to 0.993)
Superior-Nasal534.66 ± 32.425.9416.451.10.989 (0.983 to 0.993)
Nasal520.25 ± 30.866.818.841.30.983 (0.975 to 0.99)
Inferior-Nasal504.61 ± 32.488.3223.051.60.977 (0.966 to 0.986)
Inferior491.14 ± 36.136.5718.21.30.989 (0.983 to 0.993)
Inferior-Temporal484.2 ± 37.316.5718.21.40.99 (0.984 to 0.993)
5 – 7Temporal540.29 ± 37.8611.5231.912.10.968 (0.95 to 0.98)
Superior-Temporal572.44 ± 36.8910.0827.921.80.974 (0.961 to 0.984)
Superior594.07 ± 36.759.1125.231.50.979 (0.968 to 0.987)
Superior-Nasal588.0 ± 34.988.7924.351.50.978 (0.967 to 0.986)
Nasal568.36 ± 32.659.2425.591.60.972 (0.957 to 0.983)
Inferior-Nasal556.13 ± 33.7310.4528.951.90.966 (0.949 to 0.979)
Inferior544.89 ± 36.3911.1830.972.10.967 (0.95 to 0.979)
Inferior-Temporal534.04 ± 42.1313.7638.122.60.962 (0.942 to 0.976)
7 – 9Temporal582.42 ± 39.581438.782.40.955 (0.931 to 0.972)
Superior-Temporal594.51 ± 38.2713.6637.842.30.954 (0.93 to 0.971)
Superior614.18 ± 42.3520.8857.843.40.904 (0.854 to 0.94)
Superior-Nasal615.43 ± 39.8621.2458.833.50.885 (0.825 to 0.928)
Nasal603.35 ± 32.7713.4137.152.20.938 (0.905 to 0.961)
Inferior-Nasal605.87 ± 36.8214.5440.282.40.943 (0.913 to 0.964)
Inferior607.14 ± 44.9823.765.653.90.888 (0.83 to 0.93)
Inferior-Temporal597.45 ± 55.0132.0688.815.40.855 (0.778 to 0.91)
Authors

From the School of Ophthalmology and Optometry (N-JL, DC, L-LC, S-HC, Q-MW) and Eye Hospital (L-LC, S-HC, Q-MW), Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmolgy and Vision Science, Wenzhou, Zhejiang, China (N-JL, L-LC, S-HC, Q-MW); and the Department of Ophthalmology, West China Hospital Sichuan University, Chengdu, Sichuan, China (LW).

The authors have no financial or proprietary interest in the materials presented herein.

Drs. Lu and Ding Chen contributed equally to this work and should be considered as equal first authors.

AUTHOR CONTRIBUTIONS

Study concept and design (N-JL, DC); data collection (N-JL, DC); analysis and interpretation of data (N-JL, DC, L-LC, LW, S-HC); writing the manuscript (N-JL, DC); critical revision of the manuscript (N-JL, DC, L-LC, LW, S-HC, Q-MW); supervision (LW, S-HC, Q-MW)

Correspondence: Shi-Hao Chen, MD, OD (e-mail: chenle@rocketmail.com) and Qin-Mei Wang, MD (e-mail: wqm6@mail.eye.ac.cn), Eye Hospital of Wenzhou Medical University, 270 West Xueyuan Road, Wenzhou, Zhejiang 325027, China.

Received: May 21, 2019
Accepted: August 06, 2019

10.3928/1081597X-20190806-03

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