Fourier-domain Optical Coherence Tomography Research Articles

Angular scan optical coherence tomography imaging and metrology of spherical gradient refractive index preforms.

The fabrication of high-performance spherical gradient refractive index (S-GRIN) optics requires nondestructive metrology techniques to inspect the samples. We have developed an angular-scan, swept-source-based, Fourier-domain optical coherence tomography (OCT) system centered at 1318 nm with 5 mm imaging depth capable of 180° polar scan and 360° azimuthal scan to investigate polymeric S-GRIN preforms. We demonstrate a method that enables simultaneous mapping of the group optical thickness, physical thickness, the radially-averaged group refractive index, and the transmitted wavefront of the S-GRIN preforms. The angular scan OCT imaging and metrology enables direct visualization, molding uniformity characterization, and optical property evaluations of the preforms. The results on two generations of S-GRIN preforms are discussed that showcase the evolution of the manufacturing process in response to the OCT metrology feedback.

Common Path Side Viewing Monolithic Ball Lens Probe for Optical Coherence Tomography

1 ; Common path probes are highly desirable for optical coherence tomography as they reduce system complexity and cost by eliminating the need of dispersion compensation and polarization controlling optics. In this work, we demonstrate a monolithic ball lens based, common path, side viewing probe that is suitable for Fourier domain optical coherence tomography. The probe design parameters were simulated in Zemax modeling software and the simulated performance parameters were compared with experimental results. We characterized the performance of the probe by measuring its collection efficiency, resolution, and sensitivity. Our results demonstrated that with a source input power of 25 mW, we could achieve sensitivity of 100.5 dB, which is within 7 dB of the maximum possible sensitivity that could be achieved using a separate reference arm. The axial resolution of the system was found to be 15.6 µm in air and the lateral resolution (full width half maximum) was approximately 49 µm. The probe optics were assembled in a 1 mm diameter hypotube with a 500 µm inner diameter. Images of finger skin acquired using this probe demonstrated clear visualization of the stratum corneum, epidermis, and papillary dermis, along with sweat ducts.

Comparison of laser in situ keratomileusis flaps created by 2 femtosecond lasers.

To compare flap morphology created by the WaveLight FS200 femtosecond laser and the VisuMax femtosecond laser, assessing the uniformity, accuracy, and predictability of flap creation. A total of 400 eyes had corneal flaps created with the WaveLight FS200 femtosecond laser (200 eyes) or the VisuMax femtosecond laser (200 eyes). The desired flap thickness was 110 μm. At 1 week postoperatively, all eyes were evaluated with RTVue Fourier-domain optical coherence tomography. Dimensions of the flaps were tested for their regularity, uniformity, accuracy, and predictability comparison. One week after surgery, the central flap thickness and the mean flap thickness of the FS200 group were 105.4 ± 3.4 μm and 105.7 ± 2.6 μm, respectively. They were both thinner than those of the VisuMax group, which were 110.8 ± 3.9 μm and 111.3 ± 2.3 μm, respectively. The mean deviation between the achieved and attempted flap thickness of the FS200 group (5.2 ± 1.9 μm) was greater than that of the VisuMax group (3.2 ± 1.8 μm). Flap thickness measurements at 36 points in both groups were close to the intended thickness. Morphology of the flaps in the 0-, 45-, 90-, and 135-degree lines created by the FS200 femtosecond laser and VisuMax femtosecond laser were uniform and regular. Flap dimensions created by the WaveLight FS200 femtosecond laser and VisuMax femtosecond laser were uniform and regular. Although the flap thickness created by the FS200 was less than that created by the VisuMax, measurements of both femtosecond lasers were close to the intended thickness.

Morphometry of the trabecular meshwork in vivo in a healthy population using fourier-domain optical coherence tomography.

We measured the length, thickness, and area of the trabecular meshwork (TM) in vivo using Fourier domain optical coherence tomography (FD-OCT) in a Caucasian population of healthy subjects. A cross-sectional study was done of 1006 healthy subjects. Left eyes were randomly selected. Age, sex, IOP, and spherical refractive error were noted. The depth and volume of the anterior chamber and the central corneal thickness were measured with Pentacam, while IOL Master was used to measure the axial length. The length, thickness, and area of the TM were measured through FD-OCT RTVue. A study was done to determine the correlation between TM size, and other demographic and ocular parameters. Finally, the reproducibility of the measurements was assessed for a subgroup of 50 eyes from 50 patients. We were able to measure the TM in 91.1% of the total eyes studied. The mean TM length was 496.99 ± 92.77 μm (range, 275-800), TM thickness was 174.16 ± 28.14 μm (range, 100-276), and TM area was 0.069 ± 0.031 mm(2) (range, 0.023-0.133). No differences were found in terms of length and area for sex, although the TM was slightly thicker in men (P = 0.046). No correlation was observed between the TM measurements and any of the studied demographic or ocular parameters (R < 0.09, P < 0.001). Intra- and interobserver reproducibility of the measurements were good (intraclass correlation coefficient > 0.750, P < 0.001). The FD-OCT is an effective and reproducible examination technique to measure the length, thickness, and area of the TM in vivo.

Assessment of lower tear meniscus measurements obtained with Keratograph and agreement with Fourier-domain optical-coherence tomography

AimsTo compare intraobserver repeatability and interobserver and intersession reproducibility of lower tear meniscus height measurements (LTMH) obtained with the new Keratograph 5M and a Fourier-domain optical-coherence tomography (OCT; Spectralis OCT)...

Spectral fractionation detection of gold nanorod contrast agents using optical coherence tomography.

We demonstrate the proof of concept of a novel Fourier-domain optical coherence tomography contrast mechanism using gold nanorod contrast agents and a spectral fractionation processing technique. The methodology detects the spectral shift of the backscattered light from the nanorods by comparing the ratio between the short and long wavelength halves of the optical coherence tomography signal intensity. Spectral fractionation further divides the halves into sub-bands to improve spectral contrast and suppress speckle noise. Herein, we show that this technique can detect gold nanorods in intralipid tissue phantoms. Furthermore, cellular labeling by gold nanorods was demonstrated using retinal pigment epithelial cells in vitro.

In vivo evaluation of the cornea and conjunctiva of the normal laboratory beagle using time- and Fourier-domain optical coherence tomography and ultrasound pachymetry.

To obtain normative data for the canine cornea and conjunctiva using high-resolution time- and Fourier-domain optical coherence tomography (TD-OCT and FD-OCT) and ultrasound pachymetry (USP). One hundred sixty-eight eyes of 133 healthy young intact laboratory beagles. The cornea and conjunctiva of 16 eyes of 8 healthy young intact female beagles were imaged using FD-OCT. Corneal thickness was measured with FD-OCT and USP, while corneal epithelial thickness and conjunctival epithelial thickness were measured with FD-OCT. The central corneal thickness (CCT) was determined in 152 eyes of 125 healthy young adult intact female (35) and male (90) beagles using TD-OCT. Mixed effects linear regression was used for statistical analysis. The CCT was (mean±standard deviation) 497.54±29.76, 555.49±17.19, and 594.81±33.02μm as measured by FD-OCT, USP, and TD-OCT, respectively. The central, superior paraxial, superior perilimbal corneal epithelial thickness and superior bulbar conjunctival epithelial thickness were 52.38±7.27, 56.96±6.47, 69.06±8.84 and 42.98±6.17μm, respectively. When comparing techniques used for measuring CCT (USP vs. FD-OCT and FD-OCT vs. TD-OCT), USP and TD-OCT generated significantly greater values in comparison with FD-OCT (both P<0.001). For all dogs, CCT increased with increasing age and body weight (both P<0.001) and was higher in intact males vs. females using TD-OCT (P=0.034). High-resolution FD-OCT and TD-OCT provide detailed noninvasive evaluation of in vivo canine anterior segment structures. Normative values of the canine cornea and conjunctiva are reported.

Measurement of retinal blood flow in normal Chinese-American subjects by Doppler Fourier-domain optical coherence tomography.

To measure total retinal blood flow (TRBF) in normal, healthy Chinese Americans by using semi-automated analysis of Doppler Fourier-domain optical coherence tomography (FD-OCT) scans. Two hundred sixty-six normal, healthy Chinese-American participants (266 eyes) were enrolled from The Chinese American Eye Study. All participants underwent complete ophthalmic examination, including best-corrected visual acuity, indirect ophthalmoscopy, and Doppler FD-OCT imaging, using the circumpapillary double circular scan protocol. Total retinal blood flow and other vascular parameters (e.g., venous and arterial cross-sectional area and their velocities) were calculated by using Doppler OCT of Retinal Circulation software. Associations between TRBF and other clinical parameters were assessed by using bivariate correlations and linear regression. The mean age of study participants was 57.40 ± 5.60 (range, 50-82) years. The mean TRBF was 49.34 ± 10.08 (range, 27.17-78.08, 95% confidence interval: 25.98-69.10) μL/min. The mean venous area was 0.0548 (±0.0084) mm(2). Superior retinal hemispheric blood flow (25.50 ± 6.62 μL/min) was slightly greater than inferior retinal hemispheric blood flow (23.84 ± 7.19 μL/min, P = 0.008). The mean flow velocity was 15.16 ± 3.12 mm/s. There was a weak but significant negative correlation between TRBF and age (r = -0.15, P = 0.012). No significant correlation was found between TRBF and axial length (r = 0.11, P = 0.08). Retinal blood flow was not significantly correlated with any other clinical parameters, including body mass index, systolic blood pressure, diastolic blood pressure, and intraocular pressure. Normal Doppler OCT-derived total retinal blood values in a Chinese-American population showed considerable variability, some of which was explained by age. These observations should help design future studies evaluating TRBF in populations with eye disease.

Fourier domain optical coherence tomography with ultralong depth range

The depth ranges of typical implementations of Fourier domain optical coherence tomography (FDOCT), including spectral domain OCT (SDOCT) and swept source OCT (SSOCT), are limited to several millimeters. To extend the depth range of current OCT systems, two novel systems with ultralong depth range were developed in this study. One is the orthogonal dispersive SDOCT (OD-SDOCT), and the other is the recirculated swept source (R-SS) interferometer/OCT. No compromise between depth range and depth resolution is required in both systems. The developed OD-SDOCT system realized the longest depth range (over 100 mm) ever achieved by SDOCT, which is ready to be modified for depth-encoded parallel imaging on multiple sites. The developed R-SS interferometer achieved submicron precision within a depth range of 30 mm, holding potential in real-time contact-free on-axis metrology of complex optical systems.

Evaluation of ischemic diabetic maculopathy with Fourier-domain optical coherence tomography and microperimetry

ObjectiveTo evaluate the efficacy of high-speed Fourier-domain optical coherence tomography (FD-OCT) and fundus microperimetry (MP-1) in identifying the anatomic and functional features of ischemic diabetic maculopathy. DesignProspective noninterventional study. ParticipantsForty-two consecutive eyes (23 patients) with ischemic diabetic maculopathy and 40 normal eyes (25 control subjects) were included in this study. MethodsBest corrected visual acuity, ganglion cell complex (GCC) thickness measured with FD-OCT, and central light sensitivity recorded with MP-1 were evaluated. ResultsGCC thickness and light sensitivity were significantly reduced in all affected eyes versus control eyes. logMAR BVCA was significantly correlated with mean macular sensitivity (R=0.783, R2=0.611). ConclusionsGCC thickness and microperimetry integrated with fluorescein angiography could be a marker of retinal vascular abnormalities that is useful for the diagnosis of ischemic diabetic maculopathy.

Quantitative analysis of Microdistortions in Bowman's Layer using optical coherence tomography after SMILE among different myopic corrections.

To quantitatively analyze the characteristics of Bowman's layer microdistortions after femtosecond laser small incision lenticule extraction (SMILE) among different myopic corrections, and their correlations with stromal lenticule thickness. In this nonrandomized, prospective, controlled study, 63 eyes of 32 consecutive patients undergoing SMILE were divided into three groups according to the preoperative spherical equivalent (SE): greater than -6.00 D (20 eyes), -3.00 to -6.00 D (26 eyes), and -3.00 D or less (17 eyes). Measurement by slit-lamp microscope, uncorrected distance visual acuity (UDVA), manifest refraction, and Fourier-domain optical coherence tomography (FD-OCT) were conducted preoperatively and 1 day and 1 month postoperatively. Index M was calculated according to the OCT images to indicate the quantity of microdistortions in Bowman's layer. Microdistortions in Bowman's layer were observed in 65.0% (13 of 20 eyes) and 30.8% (8 of 26 eyes) in the greater than -6.00 D and -3.00 to -6.00 D groups, respectively, 1 day postoperatively, and in 60% (12 of 20 eyes) and 23.1% (6 of 26 eyes) 1 month later. No Bowman's layer microdistortion was detected in the -3.00 D or less group postoperatively. The quantitative index M of microdistortions was higher in the greater than -6.00 D group than in the -3.00 to -6.00 D group at 1 day and 1 month (P < .05). There was no statistically significant difference between the indexes M on 1 day compared to 1 month. Index M was correlated with the preoperative SE and lenticule thickness (P < .05). The incidence and range of microdistortions in Bowman's layer detected after SMILE are positively correlated with the myopic correction. High myopia tends to develop more microdistortions in Bowman's layer after SMILE.

High resolution Fourier domain optical coherence tomography in the 2 μm wavelength range using a broadband supercontinuum source.

A 220 nm bandwidth supercontinuum source in the two-micron wavelength range has been developed for use in a Fourier domain optical coherence tomography (FDOCT) system. This long wavelength source serves to enhance probing depth in highly scattering material with low water content. We present results confirming improved penetration depth in high opacity paint samples while achieving the high axial resolution needed to resolve individual paint layers. This is the first FDOCT developed in the 2 μm wavelength regime that allows fast, efficient capturing of 3D image cubes at a high axial resolution of 13 μm in air (or 9 μm in paint).

Effect of hyaluronic acid on tear film thickness as assessed with ultra-high resolution optical coherence tomography.

The aim of this study was to assess the effect of a single drop of hyaluronic acid on tear film thickness (TFT) in healthy subjects. Sixteen healthy subjects (eight male/eight female) aged between 20 and 36 years were included in this randomized, double-masked placebo-controlled study. One eye received a single dose of hyaluronic acid (Olixia pure(®) ; Croma Pharma, Korneuburg, Austria) eye drops, and the fellow eye received physiologic saline solution as placebo control. The study eye was chosen randomly. TFT as measured with a custom-built Fourier-domain optical coherence tomography (FD-OCT) system was the main outcome variable and measured before and every 10 min until 1 hr after topical administration. Baseline TFT was 4.8 ± 0.5 μm in the study eye and 5.0 ± 0.4 μm in the control eyes. Hyaluronic acid significantly increased TFT (p = 0.008 versus placebo) with a maximum effect 10 min after instillation (13.9 ± 11.9%). Post hoc analysis revealed that an increase in TFT was seen until 30 min after administration compared to placebo. Data in the placebo group show high reproducibility with an intraclass correlation coefficient of 0.93 and a coefficient of variation of 5.4 ± 3.3%. The data of this study indicate that hyaluronic acid increases TFT for as long as 30 min in healthy subjects. In addition, our data provide evidence that our custom-built OCT system is capable of measuring residence time of lubricants on the ocular surface.

Tear Meniscus Evaluation Using Optical Coherence Tomography in Dry Eye Patients

Purpose: To evaluate the tear meniscus in aqueous tear-deficient dry eye patients using Fourier-domain optical coherence tomography (FD-OCT) and to investigate the clinical usefulness of tear meniscus values. Methods: The present study included 79 aqueous tear-deficient dry eyes and 50 normal eyes. Tear meniscus height (TMH), tear meniscus depth (TMD), and tear meniscus area (TMA) were imaged using FD-OCT and measured with computer calipers. Schirmer’s test, tear break-up time, and corneal fluorescein staining were also performed and the correlations between the tests were analyzed. Additionally, the diagnostic power of tear meniscus values was compared using area under the receiver operating characteristic curve (AUROC). Results: Tear meniscus values were significantly decreased in the aqueous tear-deficient dry eye group (p < 0.05). TMH, TMD, and TMA were positively correlated with Schirmer’s test and tear break-up time (p < 0.05), and TMH and TMD were negatively correlated with corneal fluorescein staining in the aqueous tear-deficient dry eye group (p < 0.05). The AUROCs of TMH, TMD, and TMA were 0.978, 0.788, and 0.957, respectively. Conclusions: Tear meniscus values measured using FD-OCT were significantly lower in aqueous tear-deficient dry eyes and were correlated with Schirmer’s test, tear break-up time, and corneal fluorescein staining. Tear meniscus measurements obtained using FD-OCT can be useful clinical parameters for the diagnosis and treatment of aqueous tear-deficient dry eye. J Korean Ophthalmol Soc 2015;56(3):323-330

Tear Meniscus Evaluation Using Optical Coherence Tomography in Meibomein Gland Dysfunction Patients

Purpose: This study compared tear meniscus parameters between normal control, aqueous tear deficient dry eye, and meibomein gland dysfunction groups using Fourier-domain optical coherence tomography (FD-OCT). Methods: This study included 33 normal eyes, 79 aqueous tear-deficient dry eyes (ATD), and 48 meibomein gland dysfunction dry eyes (MGD). Following routine examination including Schirmer test, tear break-up time, corneal staining, and tear meniscus parameters such as tear meniscus height (TMH), tear meniscus depth (TMD), and tear meniscus area (TMA) were obtained using FD-OCT. The differences among groups were assessed. Results: The averages of TMH, TMD, and TMA were 295.58 ± 58.36 μm, 166.67 ± 30.43 μm, and 0.0360 ± 0.01100 mm in normal eyes, respectively, 226.43 ± 42.18 μm, 147.44 ± 38.38 μm, and 0.0209 ± 0.01015 mm in ATD, respectively, 272.81 ± 64.21 μm, 159.37 ± 44.05 μm, and 0.0295 ± 0.01271 mm in MGD, respectively. Tear meniscus parameters were significantly lower in ATD. Tear meniscus parameters in MGD were higher than ATD and lower than normal eyes, but the TMA was the only statistically significant value. Conclusions: Although tear meniscus parameters in MGD were higher than ATD, they could not be distinguished from normal eyes. Tear meniscus evaluation using FD-OCT could be a useful measurement system in classification and treatment choice for dry eye patients. J Korean Ophthalmol Soc 2015;56(11):1684-1691

Optical coherence tomography assisted retinal nerve fibre layer thickness profile in high myopia.

To evaluate the association of high myopia with retinal nerve fibre layer (RNFL) thickness by Fourier domain optical coherence tomography (FD OCT). Fifty highly myopic eyes (25 patients) and forty emmetropic eyes (20 Normal subject) were randomly selected after excluding concomitant ophthalmic disorder and RNFL thickness measured using the Fourier domain optical coherence tomography (FD OCT). The overall mean RNFL thickness in the myopic groups and control were 87.89 μm and 111.64 μm respectively. The mean retinal nerve fibre thickness was significantly less in myopic eyes as compared to control group (p =0.0001). Retinal nerve fibre layer thickness shows topographic double hump pattern in both the groups (myopes and emmetropes). Retinal nerve fibre thickness was significantly less in myopic eyes as compared to emmetropic eyes. The retinal nerve fibre layer thinning in high myopes may be confused with open angle glaucoma, a disease also prevalent in high myopes. There is therefore a need to have retinal nerve fibre layer thickness normogram for high myopes of a given population group to avoid wrong interpretation.

Comparison of Fourier-Domain and Time-Domain Optical Coherence Tomography in the Measurement of Thinnest Corneal Thickness in Keratoconus.

Objective. To compare fourier-domain optical coherence tomography (FD-OCT) and time-domain OCT (TD-OCT) in the determination of thinnest corneal thickness (TCT). Methods. This study included 55 keratoconus patients and 50 healthy volunteers. The RTVue-OCT (FD-OCT) and Visante-OCT (TD-OCT) were used for the measurement of the TCT. Three consecutive scans were performed. The comparison and agreement between the two modalities were analyzed by paired t-test, the Pearson correlation, intraclass correlation coefficient (ICC), and Bland-Altman plots. intraobserver repeatability was analyzed by the intraobserver within-subject standard deviation (S (w)), coefficient of variation (CV(w)), and ICC. Results. The TCT value of normal corneas was higher by RTVue-OCT (530.4 ± 19.7 μm) than Visante-OCT (521.5 ± 18.3 μm) (p < 0.001). For keratoconus eyes, the TCT was 425.0 ± 58.2 μm and 424.4 ± 55.7 μm (difference being 0.6 ± 10.2 μm, p = 0.604). Strong correlation (r = 0.938∼0.985) (ICC = 0.915–0.984) was observed between the two OCTs, and each OCT exhibited excellent repeatability in determining the TCT in all subjects (ICC = 0.984–0.994). Conclusions. The values of TCT obtained from RTVue-OCT and Visante-OCT were highly correlated; however, the two values were different. Both OCT instruments exhibited good intraobserver reliability. The existence of systematic differences suggested that the two instruments cannot be used interchangeably.

Corneal Epithelial Remodeling after LASIK Measured by Fourier-Domain Optical Coherence Tomography.

Purpose. To quantify corneal epithelial thickness changes after myopic LASIK by OCT. Methods. Epithelial thickness before and after myopic LASIK were measured by a Fourier-domain OCT system. Average central (within 1 mm diameter) and paracentral epithelial thickness (5~6 mm diameter) before and after LASIK were compared. Correlation between central epithelial thickness change and laser spherical equivalent setting was evaluated. An epithelial smoothing constant was estimated based on a mathematical model published previously. Results. Nineteen eyes from 11 subjects were included in the study. Eyes had myopic LASIK ranging from −1.69 D to −6.75 D spherical equivalent. The average central epithelial thickness was 52.6 ± 4.1 μm before LASIK and 56.2 ± 4.3 μm 3 months after LASIK (p = 0.002). The average paracentral epithelial thickness was 51.6 ± 6.6 μm before LASIK and 54.8 ± 4.3 μm 3 months after LASIK (p = 0.007). The change in average central epithelial thickness was correlated with laser spherical equivalent (R 2 = 0.40, p = 0.028). The epithelial smoothing constant was estimated to be 0.46 mm. Conclusions. Corneal epithelial thickens centrally and paracentrally after myopic LASIK. The extent of epithelial remodeling correlated with the amount of LASIK correction and could be predicted by a mathematical model.

Fourier-domain optical coherence tomography for monitoring the lower tear meniscus in dry eye after acupuncture treatment.

Dry eye is highly prevalent and has a significant impact on quality of life. Acupuncture was found to be effective to treat dry eye. However, little was known about the effect of acupuncture on different subtypes of dry eye. The objective of this study was to investigate the applicability of tear meniscus assessment by Fourier-domain optical coherence tomography in the evaluation of acupuncture treatment response in dry eye patients and to explore the effect of acupuncture on different subtypes of dry eye compared with artificial tear treatment. A total of 108 dry eye patients were randomized into acupuncture or artificial tear group. Each group was divided into three subgroups including lipid tear deficiency (LTD), Sjögren syndrome dry eye (SSDE), and non-Sjögren syndrome dry eye (Non-SSDE) for data analysis. After 4-week treatment, the low tear meniscus parameters including tear meniscus height (TMH), tear meniscus depth (TMD), and tear meniscus area (TMA) in the acupuncture group increased significantly for the LTD and Non-SSDE subgroups compared with both the baseline and the control groups (all P values < 0.05), but not for the SSDE. Acupuncture provided a measurable improvement of the tear meniscus dimensions for the Non-SSDE and LTD patients, but not for the SSDE patients.

Analysis of Choroidal Thickness Measured Using RTVue and Associated Factors in Open-Angle Glaucoma

Purpose: To compare the macular choroidal thickness, ganglion cell complex thickness, peripapillary choroidal thickness and retinal nerve fiber layer thickness among normal, primary open angle glaucoma (POAG) and normal tension glaucoma (NTG) patients using RTVue (Fourier-domain optical coherence tomography; Optovue, Fremont, CA, USA). Methods: A retrospective analysis of 32 normal controls, 32 POAG and 52 NTG patients was performed. Choroidal thickness, ganglion cell complex thickness and retinal nerve fiber layer thickness were compared among normal controls, POAG and NTG subjects. Additionally, the factors influencing choroidal thickness (age, axial length, spherical equivalent, central corneal thickness, mean deviation, nocturnal dip, blood pressure variability) were analyzed. Results: A total of 32 normal controls, 32 POAG and 52 NTG patients were enrolled in this study. Macular and peripapillary choroidal thicknesses were significantly thinner in the NTG patients. In NTG subjects, the significant influencing factors associated with macular and peripapillary choroidal thicknesses were age, axial length, nocturnal dip (diastolic blood pressure), diastolic blood pressure variability and ganglion cell complex thickness. In POAG patients, significant influencing factors associated with macular and peripapillary choroidal thicknesses were age and axial length. Conclusions: Choroidal thickness was significantly thinner in NTG patients compared with normal controls and POAG patients. Factors influencing choroidal thickness in NTG patients were age, axial length, nocturnal dip (diastolic blood pressure), diastolic blood pressure variability and ganglion cell complex thickness. In POAG patients, significant factors influencing choroidal thickness were age and axial length. J Korean Ophthalmol Soc 2015;56(7):1065-1074