Correlational study of central corneal thickness measurements on Hong Kong Chinese using optical coherence tomography, Orbscan and ultrasound pachymetry

Central Corneal Thickness Measurement in Patients with Glaucoma and Glaucoma Suspects by Spectral-Domain and Swept-Source Optical Coherence Tomography Compared with the Standard Ultrasonic Method

Purpose

To evaluate the agreement of central corneal thickness (CCT) measurements between spectral-domain (SD) and swept-source (SS) optical coherence tomography (OCT) compared with the gold standard ultrasonic corneal pachymetry (US CP).

Methods

Adults with glaucoma and glaucoma suspects presenting with typical optic nerve head findings and high intraocular pressure with or without visual field damage were included. Patients underwent anterior segment (AS) SD-OCT (Spectralis, Heidelberg Engineering), AS SS-OCT (DRI-Triton, Topcon), and US CP. For both AS SD-OCT and AS SS-OCT, an 8.3 and a 3.0 mm single horizontal B-scan at the central cornea were performed and manually measured respectively. CCT was measured by three blinded different trained examiners. Intraclass correlation coefficient (ICC) and Bland-Altman plots were used for statistical analysis.

Results

Twenty-six eyes from 16 patients with glaucoma and glacuoma suspects were included. The mean (SD) age was 59.1 (10.5) years, and 87% were women. The mean (SD) CCT measurements were 548.04 (33.11) µm for AS SD-OCT, 538.88 (34.84) µm for AS SS-OCT, and 537.12 (29.20) µm for US CP. The overall agreement ICC was 0.915 (95% CI, 0.785-0.964; p<0.001). The best agreement was found between AS SS-OCT and US CP (ICC = 0.929; 95% CI, 0.849-0.967; p<0.001). When comparing AS-OCT methods with US CP, a difference of less than 10 µm was found in 53.8% of the eyes examined by SS-OCT, and in 50% of the eyes examined by SD-OCT.

Conclusion

OCT emerges as an effective modality for CCT measurements. This technology provides advantages such as patient comfort, B-scan trackability, and the possibility to conduct multiple glaucoma diagnostic modalities in a single device.

Normative Values for Corneal Tomography and Comparison of Both Eyes in Young Saudi Males with 20/20 Vision Using Pentacam-HR Scheimpflug Imaging

Purpose

Anterior segment evaluation using Scheimpflug imaging with the Pentacam scanner allows the acquisition of a plethora of information. It aids in screening and diagnosing corneal pathologies and determining suitability for keratorefractive procedures. This research has significant benefits in terms of establishing normative tomographic values, which is crucial in countries where Keratoconus (KC) is more prevalent, especially among young age group, along with aiding future research in the field of refractive surgery by providing relevant normative data.

Methods

A retrospective review of digital corneal tomography images for a group of medically and ophthalmologically free males aged between 18 and 21 years with 20/20 unaided distant visual acuity was performed.

Results

A total of 1272 subjects (2544 eyes) were included. Findings revealed a mean maximal corneal curvature (Kmax) of 42.91 ± 1.40D (range 36.90–47.80D). The mean flat keratometry (K1) was 41.87 ± 1.31D (range 36.00–46.40D). The mean steep keratometry (K2) was 42.66 ± 1.35D (range 36.70–47.60D). The mean corneal astigmatism (CA) was 0.79 ± 0.37D (range 0.00D-2.30D). The mean central corneal thickness (CCT) was 558.53 ± 33.84 μm (range 421–677 μm). The mean thinnest corneal location thickness (TCLT) was 551.64 ± 34.08 μm (range 417–669μm). The mean corneal diameter (CD) and anterior chamber depth (ACD) were 12.13 ± 0.39 mm (range 10.50–13.60 mm) and 3.12 ± 0.29 mm (range 2.08–4.08 mm), respectively. The median differences between both eyes of the same subject were as follows: kmax difference of 0.20D (IQR 0.1–0.4); K1, K2 and CA difference of 0.20D (IQR 0.1–0.3) for all 3 parameters; CCT and TCLT difference of 5.00 μm (IQR 3.0–9.0) and 6.00 μm (IQR 3.0–10.0), respectively; CD difference of 0.10 mm (IQR 0.0–0.1); and ACD difference of 0.04 (IQR 0.02–0.06).

Conclusion

We believe our data can aid in establishing normative tomographic values and acceptable differences between both eyes. Our data may also help detect subtle corneal pathology and be useful for researchers and innovators in the field of ophthalmology.

The relationship of central corneal thickness with the status of diabetic retinopathy

Background

To compare central corneal thickness (CCT) values measured by three different devices: slit-scanning topography (SST), ultrasonic pachymetry (UP), and optical coherence tomography (OCT) in diabetic eyes and compare the CCT values in patients with and without diabetic retinopathy.

Methods

Ninety-six patients with diabetes mellitus were included in this prospective study and divided into two groups according to the presence of diabetic retinopathy, as Group I with retinopathy and Group II without. The CCT of 96 eyes was measured by three different devices; SST (Orbscan II), UP and OCT. The results of CCT measurements with three different devices were compared. Also, the intergroup differences in CCT measurements were evaluated.

Results

The CCT was statistically insignificantly different between the two groups. Although the three methods of CCT measurements correlated well with each other, SST showed significantly (p < 0,0001) higher CCT results compared to both UP and OCT.

Conclusions

According to our results, neither the duration of DM nor the presence of diabetic retinopathy did have a significant effect on the CCT. The CCT values obtained with three devices were all in correlation. However, the results of SST were significantly higher compared to the other two. Our findings emphasize the value anterior segment OCT in CCT measurements, since it is a non-contact method and correlate very well with UP.

Central corneal thickness in a Jordanian population and its association with different types of Glaucoma: cross-sectional study

BACKGROUND

Central corneal thickness (CCT) has long been implicated to affect glaucoma predisposition. Several reports have identified that thinner CCT is a risk factor for open-angle glaucoma, and that CCT can be very variable between different ethnic groups. In this study, we aim to identify the relation between CCT and different glaucoma parameters in different types of glaucoma in an Arabian ethnicity.

METHODS

We classified our participants into four main groups: primary open-angle glaucoma (POAG), primary angle-closure glaucoma (PACG), pseudoexfoliative glaucoma (PXFG), and a control group. We obtained demographics, intraocular pressure (IOP), cup to disc ratio (CDR), visual field mean deviation (MD) and pattern standard deviation (PSD), CCT, and retinal nerve fiber layer (RNFL) thickness for each participant.

RESULTS

We included A total of 119 eyes with glaucoma, including POAG (54 eyes), PXFG (31 eyes) and PACG (34 eyes), we also included 57 control eyes. We found that PACG eyes have the thinnest CCT. Mean measurements of CCT for our groups were: 538.31 μm (SD = 36.30) in eyes with POAG, 544.45 μm (SD = 28.57) in eyes with PXFG, 506.91 μm (SD = 34.55) in eyes with PACG and 549.63 μm (SD = 42.9) in the control group. We found that CCT is significantly correlated with CDR (p = 0.012, r = - 0.231), MD (p < 0.001, r = 0.327),and RNFL thickness (p = .007, r = .283).

CONCLUSION

In Arabian ethnicity, PACG patients have the thinnest CCT compared to other types of glaucoma, namely POAG and PXFG. We demonstrated that glaucomatous eyes with thinner corneas will probably have more advanced glaucomatous optic neuropathy. Our results emphasize the importance of taking ethnicity into account upon glaucoma management.

Agreement and repeatability of central corneal thickness measurements by four different optical devices and an ultrasound pachymeter

PURPOSE

To compare the repeatability and agreement of central corneal thickness (CCT) measurements by spectral-domain optical coherence tomography (OCT), corneal topography (CT) with a combined Scheimpflug-Placido system, optical biometry (OB), specular microscopy (SM), and ultrasound pachymetry (UP).

METHODS

A single observer measured CCT twice in 150 eyes of 150 subjects with each of five devices: Nidek RS-3000 Advance OCT, CSO Sirius combined Scheimpflug-Placido disc system CT, Nidek AL-Scan partial coherence interferometry-based OB, Tomey EM-3000 SM, and Reichert iPac ultrasonic pachymeter. Pachymetry values corrected by the SM device software were also recorded. Levels of agreement between devices were evaluated by Bland-Altman plots with 95% limits of agreement, and repeatability for each device was analysed with intraclass correlation coefficients.

RESULTS

The mean CCTs measured by OCT, CT, OB, SM, corrected SM, and UP were 544.60 ± 29.56, 536.19 ± 32.14, 528.29 ± 29.45, 524.88 ± 32.38, 537.88 ± 32.38, and 545.29 ± 30.75 μm, respectively. Mean CCT differed significantly between the devices (p < 0.05) apart from between OCT and UP, and between CT and corrected SM. Mean paired differences between devices ranged between 0.68 and 20.41 μm. Repeatability with all devices was excellent (> 0.99). The range of limits of agreement was the least between OCT and UP.

CONCLUSIONS

Different CCT measurement techniques produce quite different results, so CCT evaluation and follow-up should be performed using the same device or devices with close compatibility.

Measurement of anterior segment parameters in Saudi adults with myopia

Purpose

To measure anterior segment parameters of the eye in myopic Saudi population using Pentacam.

Method

This is retrospective cross-sectional study. Subjects were divided into three groups: low, moderate and high myopia groups. Anterior segment parameters including: central corneal thickness (CCT), thinnest corneal thickness (TCT), apex corneal thickness (Apex CT), corneal volume (CV), anterior chamber depth (ACD), anterior chamber volume (ACV) and corneal astigmatism (CA) were measured by Pentacam.

Results

A total of 504 eyes of 252 Saudi subjects with myopia were included in this study. The mean age ± standard deviation (SD) of subjects was 28.73 ± 6.18 years. The mean CCT, TCT, Apex CT, CV, ACD, ACV and CA for all myopic subjects were 557.21 ± 29.36, 554.09 ± 29.28, 556.10 ± 37.06, 61.30 ± 3.23 μm, 3.31 ± 0.27 mm, 211.15 ± 34.22 mm³ and 0.89 ± 0.52 D, respectively. No significant differences (P > 0.05) were found between right and left eyes in all anterior segment parameters of all myopic eyes. However, a significant difference (P < 0.05) was found in ACD between low (3.27 ± 0.26 mm) and moderate (3.35 ± 0.30 mm) myopic groups. Within low myopia group, significant differences (P < 0.05) were found in ACD, ACV and CA between different genders. Anterior chamber depth and ACV values were lower in females while CA was lower in males. In addition, significant positive correlation was found between ACV and ACD in all myopic groups.

Conclusion

This study provided valuable measurements of the anterior segments parameters of the eye in myopic Saudi population. These parameters could be useful for ophthalmic practitioners in the clinic.

Central Corneal Thickness Measurements with Optical Coherence Tomography and Ultrasound Pachymetry in Healthy Subjects and in Patients after Photorefractive Keratectomy

Purpose

To compare central corneal thickness measurements made using two different methods, optical coherence tomography (OCT) and ultrasound pachymetry, applied both in normal eyes and in eyes on which photorefractive keratectomy (PRK) had been performed. A second objective was to assess the intrasession variability of OCT measurements.

Methods

In this prospective study, central corneal thickness was measured in 20 normal subjects (normal group) and in 20 PRK patients using the StratusOCT instrument model 3000 (Carl Zeiss Meditec), and also with an ultrasound pachymeter. Five OCT measurements were performed using the Fast Macular Thickness protocol. Corneal thickness data were obtained with the Scan Profile analysis protocol. The OCT measurement results were compared with the mean value of three ultrasound pachymetry measurements for the same eye.

Results

The pachymetry–OCT correlation coefficients were 0.96 and 0.97 in the normal and PRK groups, respectively (p=0.14). Neither linear regression nor Bland-Altmann analysis revealed any significant systematic measurement error. Intrasession standard deviations in the normal and PRK groups were 4.9 μm and 3.8 μm, respectively.

Conclusions

Noncontact central corneal thickness measurements made using the StratusOCT instrument are accurate and reproducible, both in normal subjects and in post-PRK patients. The instrument system does not need any modifications to correctly detect and measure the center of the cornea.

Comparison of Central Corneal Thickness Measurements Using Ultrasonic Pachymetry, Anterior Segment OCT and Noncontact Specular Microscopy

PURPOSE

To evaluate and compare central corneal thickness (CCT) values measured with anterior segment optical coherence tomography (AS-OCT), noncontact specular microscopy (NCSM), and ultrasound pachymetry (USP).

MATERIALS AND METHODS

CCT was measured in 182 healthy eyes without ocular abnormalities other than refractive errors. Three consecutive measurements of CCT by the same examiner were obtained during the same session. The testing sequence of AS-OCT and NCSM was randomly selected. The USP always was performed after the noncontact examinations.

RESULTS

The average CCT measured by AS-OCT, NCSM, and USP were 535.8±35.5, 547.7±38.2, and 537.4±37.5 μm, respectively. The mean differences between modalities were 11.8±14.7 μm (P<0.01) between NCSM and AS-OCT, 10.3±17.7 μm (P<0.01) between NCSM and USP and 1.6±8.6 μm (P=0.02) between USP and AS-OCT.

CONCLUSIONS

AS-OCT, NCSM, and USP showed an overall strong agreement in measuring CCT. However, CCT measurements with AS-OCT showed a good correlation to those obtained by USP, NCSM tended to give statistically significant higher CCT readings than either alternative and showed the worse repeatability indices. On the basis of our results, CCT measurement obtained with different instruments cannot be considered directly interchangeable.

Comparison of Central Corneal Thickness using Anterior Segment Optical Coherence Tomography Versus Ultrasound Pachymetry

INTRODUCTION

Corneal thickness is an important and sensitive indicator of corneal health. It is useful in monitoring corneal diseases such as corneal oedema and keratoconus, and selecting patients for refractive surgery. Central Corneal Thickness (CCT) is a risk factor for Primary Open-Angle Glaucoma (POAG).

AIM

To compare CCT using ultrasound pachymetry and Anterior Segment Optical Coherence Tomography (AS-OCT), and also to find out the reproducibility of AS-OCT readings for both central and pericentral corneal areas.

MATERIALS AND METHODS

This prospective cross-sectional study was conducted on 120 patients above 40 years of age, and with clinically normal corneas, who underwent CCT measurements by both ultrasound and AS-OCT. Both the eyes were analysed. Two measurements by AS-OCT and 25 measurements by ultrasound pachymetry were taken. The readings were averaged and compared by paired t-test. Repeatability of the OCT pachymetry map sector averages, was assessed by pooled standard deviation, obtained from the two measurements taken from each eye.

RESULTS

The CCT in right eye by OCT and ultrasound was 516.28±29.76 µm and 532.42±29.71 µm, respectively. The CCT in left eye by OCT and ultrasound was 515.82±29.88 µm and 532.36±29.83 µm, respectively. The difference in CCT measurement by AS-OCT and ultrasound was statistically significant (p<0.001); mean ultrasound CCT being 16.14 µm and 16.54 µm greater than the mean AS-OCT, CCT in right eye and left eye respectively. For AS-OCT, intra-session repeatability was measured. Repeatability of the OCT mapping was 0.01 µm to 1.6 µm and 0.01 µm to 1.9 µm in the right eye and left eye respectively.

CONCLUSION

The CCT measurement by ultrasound pachymetry gives higher values compared to AS-OCT measurement. Hence, they cannot be interchangeably used in clinical practice. The AS-OCT provides highly repeatable pachymetry map measurements both centrally and pericentrally.

Impact of oral contraceptive pills on central corneal thickness in young women

OBJECTIVES

Hormonal changes during oral contraceptive pill (OCP) use may affect central corneal thickness (CCT) values. We aimed to evaluate the impact of OCP use on CCT values in healthy young women.

MATERIALS AND METHODS

Fifty women subjects who use OCP for contraception (Group 1) and forty control subjects (Group 2) who do not use OCP were included in this prospective study. None of the patients had any history of systemic or ocular diseases. The CCT values measured by ultrasonic pachymeter (Nidek US-4000 Echoscan, Japan) and the intraocular pressure (IOP) values were measured by noncontact tonometer (Reichert 7 CR Corneal Response Technology, USA) at the time of admission to our clinic. The demographic findings and body mass index (BMI) scores of participants were also recorded.

RESULTS

The mean ages were 32.8 ± 5.6 for OCP + patients (Group 1) and 31.3 ± 6.9 for OCP-patients (Group 2) (P = 0.28). The mean CCT values were significantly higher in Group 1 when compared to that of the Group 2 (540.9 ± 30.4 μm and 519.6 ± 35.6 μm, respectively) (P = 0.003). The mean IOP value was 14.3 ± 2.5 mmHg in Group 1 and 14.4 ± 2.7 mmHg in Group 2 (P = 0.96). The mean BMI scores were 24.4 ± 5.8 kg/m² in Group 1 and 24.6 ± 3.5 kg/m² in Group 2 (P = 0.83).

CONCLUSION

Our findings revealed that CCT values were significantly higher in patients with OCP use. Ophthalmologists should be aware of potential elevated CCT levels in these patients.

Corneal thickness, epithelial thickness and axial length differences in normal and high myopia

Background

Corneal biometric parameters can possibly be influenced by high myopia (HM). The influence of HM on corneal thickness (CT), epithelial thickness (ET) has not yet been clearly established. The aim of this study is to observe ET, CT and axial length (AL) differences between in normal and subjects with HMs and to investigate factors influencing the corneal biometric parameters and AL, such as age and gender.

Methods

A total of 97 normal subjects (97 eyes) and 48 HM subjects (48 eyes) were included. The ET and CT of the central 6-mm diameter (17 regions) and the AL data were captured. The 17 corneal and epithelial regions were the center (1 mm radius, area a), the inner ring (2.5 mm radius, area b), the outer ring (3 mm radius, area c) and the 8 radial scan lines in eight directions (Superior (1) , SN (2), Nasal (3), IN (4), Inferior (5), IT (6), Temporal (7), ST (8)) with an angle of 45° between each consecutive scan line (a, b 1–8, c 1–8).

Results

The ALs were increased about 4 mm in the HMs (P < 0.001). No differences in ET were observed; in contrast, significantly thicker CTs were observed in the HMs in 16 regions except the b5 subregion. In normal group, age was negatively correlated with AL but not CCT and CET and gender was correlated with CET. In HM group, age was not correlated with CCT , AL or CET and gender was correlated with AL and CCT but not CET.

Conclusions

CT was thicker in the HMs but not ET. Age and gender should be considered for AL, CT and ET in both normal and HM group.

Central corneal thickness in southern Egypt

The study aimed to determine mean central corneal thickness (CCT) in a southern Egyptian population according to gender and age using ultrasonic pachymetry and to compare these CCT measurements to different populations. A prospective, observational, consecutive case series of 4,368 non-glaucomatous subjects (emmetropes and myopes) aged 16-70 years was carried out from August 2010 to March 2013 at the outpatient ophthalmology clinic in Sohag University Hospital and the Laser Vision Center in Sohag City, Egypt. Refraction, keratometry, slit-lamp examination, and intraocular pressure (IOP) measurements were obtained for all subjects. CCT was measured by ultrasonic pachymetry. The average CCT was 530.06 ± 38.03 μm. Average CCT was 532.6 ± 33.3 μm in emmetropes, 531.5 ± 31.3 μm in myopes <6 diopters (D), 531.1 ± 31.4 μm in myopes >6 D and 533 ± 33 μm in hyperopes, with no statistically significant difference between the groups. There was a statistically significant difference in CCT between age groups and gender. There was a strong correlation between CCT and IOP among the non-glaucomatous population. CCT was found to be lower in Egyptians than in Caucasian, Hispanic, and Japanese populations but comparable to African and African American populations.

Increased central corneal thickness in patients with Turner syndrome

PURPOSE

To evaluate central corneal thickness (CCT) values in patients with Turner syndrome (TS) and compare these values with healthy subjects.

METHODS

A total of 31 subjects with TS and 67 age- and sex-matched healthy subjects made up the study and control group, respectively. The CCT values were measured by an ultrasound pachymeter in this cross-sectional prospective study. The ocular findings were recorded. We also evaluated to effect of karyotype analysis, recombinant growth hormone therapy (GHT), and mean duration of treatment on the CCT parameter in patients with TS.

RESULTS

The mean CCT values were 582.0 ± 40.8 µm (490-648) in the TS and 549.1 ± 34.6 µm (494-601) in the healthy group. The mean intraocular pressure (IOP) by Goldmann applanation tonometry was 16.3 ± 3.1 mm Hg (9-22) in the TS and 15.2 ± 2.5 mm Hg (10-21) in the healthy group. The mean CCT value was significantly higher in the TS group (p<0.05) but there was no statistically significant difference between the 2 groups for IOP (p>0.05). There was also no significant difference for CCT regarding the karyotype, GHT use, and mean duration of treatment in patients with TS (p>0.05).

CONCLUSIONS

Central corneal thickness values should be considered during measurement of IOP in individuals with TS as these values may be higher than in healthy subjects.

Central corneal thickness and axial length in an adult Nigerian population

Purpose

The aim of this study was to determine the relationship between central corneal thickness (CCT) and axial length (AL) in adult Nigerians.

Methods

A total of ninety-five (n  = 95) subjects aged between 20 and 69 years consisting of 56 males and 39 females were recruited for this study. The CCT was measured by ultrasound pachymetry using SW-1000P ultrasound pachymeter (Tianjin Suowei Electronics Technologies LTD, China) and the axial length by A-Scan ultrasonography using I-2100 A Scan Biometer (Cima Technology Inc., USA).

Results

The average CCT and AL were 547.0 ± 29.5 μm and 23.5 ± 0.70 mm, respectively. Age inversely correlated with CCT (r  = −0.32, p  = 0.02), but had no effect on AL (r  = 0.082, p  = 0.43). The association between CCT and AL showed an inverse trend but was not statistically significant (r  = −0.10, p  = 0.32). Neither CCT nor AL was affected by gender (p  = 0.11; p  = 0.63, respectively).

Conclusion

CCT decreases with age, but AL was not affected by age. The association between CCT and AL was not significant. Gender did not show any statistically significant effect on CCT and AL.

Comparison of central corneal thickness measured with anterior segment optical coherence tomography versus ultrasonic pachymetry

PURPOSE

To compare central corneal thickness measured with anterior segment optical coherence tomography (AS-OCT) and ultrasonic pachymetry (UP).

METHOD

A prospective, observational and cross-sectional study was performed. The central corneal thickness was measured in 112 eyes of 112 consecutive patients with AS-OCT and UP. All examinations were performed by the same examiner. The measurements obtained between the 2 instruments were compared to assess the level of agreement.

RESULTS

The average corneal thickness value obtained by AS-OCT was 531.47 ± 26.23 μm, while that measured by UP was 532.51 ± 26.04 μm. The intraclass correlation coefficient was 0.957 (P <.001). The Student's t-test did not show a statistically significant difference (1.04 ± 7.70 μm, P =.158). Finally, the Bland-Altman analysis showed a high level of agreement between 2 methods of measurement.

CONCLUSIONS

In the context of normal corneas, there was good agreement between the measurement of central corneal thickness with AS-OCT and UP, although there was a slight overestimation of the measurement using UP (1.04 μm).

Correlation of central corneal thickness measurements using Topcon TRK-1P, Zeiss Visante AS-OCT and DGH Pachmate 55 handheld ultrasonic pachymeter

BACKGROUND

Corneal pachymetry is an important aspect of modern eye care. This study aims to compare the measurement of central corneal thickness (CCT) using automated optical pachymetry, anterior segment optical coherence tomography (AS-OCT) and ultrasound.

METHODS

Fifty volunteers participated in this study. Central corneal thickness was measured using the Topcon TRK-1P (Topcon, Tokyo, Japan) automated optical pachymeter, the Visante AS-OCT (Carl Ziess Meditec, Dublin, CA, USA) and the Pachmate 55 handheld ultrasonic pachymeter (DGH, Exton, PA, USA). Pearson correlation coefficients were calculated to compare automated optical pachymetry and AS-OCT with ultrasound. Bland-Altman plots were generated and limits of agreement (LOA) calculated.

RESULTS

Fifty eyes were measured for comparison. The mean and standard deviation of the CCT measured by optical pachymetry was 523.7 ± 42.3 μm (range: 412 to 594), 536.0 ± 36.9 μm (range: 425 to 607) for AS-OCT and 553.4 ± 40.7 μm (range: 431 to 630) for ultrasound. Comparison of optical pachymetry and AS-OCT with ultrasound, generated Pearson correlation coefficients of 0.96 and 0.98, respectively. Measurements using optical pachymetry and AS-OCT were consistently lower than when measuring with ultrasound. Bland-Altman plots revealed mean differences of 29.7 μm between optical pachymetry and ultrasound (LOA -5.4 to -54.1) and of 17.4 μm (LOA +0.9 to -35.7) between AS-OCT and ultrasound.

CONCLUSION

Due to AS-OCT and automated optical pachymetry consistently measuring lower than ultrasound, it should be noted that these devices are not interchangeable in clinical practice.

Anterior Segment Optical Coherence Tomography and its Clinical Applications in Glaucoma

Anterior segment optical coherence tomography (ASOCT) is an imaging modality that provides both quantitative and qualitative information on the cornea, anterior chamber angle, iris and crystalline lens. ASOCT shows excellent repeatability and reproducibility for the measurement of corneal thickness, anterior chamber angle and anterior chamber depth. With realtime video recording, ASOCT can also effectively capture the dynamic changes of the iris and lens in response to light and eye accommodation. With this additional information, physiological and pathological changes of the anterior segment structures are now better understood. This article aims to provide an overview of the current applications of ASOCT in glaucoma.

HOW TO CITE THIS ARTICLE

Li H, Jhanji V, Dorairaj S, Liu A, Lam DSC, Leung CK. Anterior Segment Optical Coherence Tomography and its Clinical Applications in Glaucoma. J Current Glau Prac 2012;6(2):68-74.

The role of anterior segment optical coherence tomography in glaucoma

The anterior segment optical coherence tomography provides an objective method to assess the anterior segment of the eye, including the anatomy of the anterior chamber angle. This technology allows both qualitative and quantitative analyses of the angle and has shown potential in detecting and managing angle-closure glaucoma. In addition, it has a role in identifying pathology in some forms of secondary open-angle glaucoma and postsurgical management of glaucoma. Limitations of this technology include its cost and inability to visualize well structures posterior to the iris, such as the ciliary body. This paper focuses on potential benefits and limitations of anterior segment optical coherence tomography when compared with conventional gonioscopy and ultrasound biomicroscopy. Various clinical entities will be described to discuss its potential role in glaucoma practice.

Age, gender, corneal diameter, corneal curvature and central corneal thickness in Nigerians with normal intra ocular pressure

Purpose

To investigate the relationship between age, gender, corneal diameter, central corneal curvature, central corneal thickness (CCT) and intraocular pressure in Nigerians with normal intraocular pressure.

Methods

One hundred and thirty eyes from 130 subjects (mean age = 47.8 ± 16.8 years) including 77 males and 53 females were recruited. CCT was measured by ultrasound pachymetry, intraocular pressure was determined by non-contact tonometry, horizontal and vertical corneal diameters were measured with a ruler and central corneal curvature was measured by keratometry.

Results

The mean values obtained were as follows: CCT = 548.97 ± 34.28 μm, IOP = 15.61 ± 2.69 mmHg, average corneal curvature (AVK) = 42.98 ± 1.19 D, horizontal corneal diameter (HVID) = 11.39 ± 0.69 mm and vertical corneal diameter (VVID) = 10.51 ± 0.50 mm. There was a significant effect of age on CCT (r = −0.35, p < 0.001). A 10-year-increase in age was associated with a 7.0 μm decrease in CCT. Males had significantly wider HVID than females (p = 0.03). Subjects in older age groups have narrower HVID and VVID. Corneal curvature, corneal diameter and gender did not significantly affect CCT.

Conclusion

CCT of normotensive Nigerian adults decreases with increasing age. There was no correlation between CCT and IOP in normotensive subjects. CCT was not significantly influenced by gender, corneal curvature and corneal diameter.

Measuring Corneal Thickness with SOCT, the Scheimpflug System, and Ultrasound Pachymetry

Background and Objective. Evaluation of agreement, repeatability, and reproducibility of central and minimal corneal thickness (CCT and MCT) measurements obtained by SOCT, the Scheimpflug system, and ultrasound pachymetry. Materials and Methods. 28 eyes of healthy patients were enrolled. Pachymetry measurements were performed with SOCT, the Scheimpflug system, and ultrasound instrument. Each measurement was taken by 3 operators on 3 devices providing a total of 2100 measurements. Results. The mean CCT for SOCT, Scheimpflug system, and ultrasound instrument was 537.92, 545.94, and 555.74 μm, respectively, (P < .001). The respective mean coefficients of repeatability for CCT were 0.61, 0.82 and 0.80, whereas mean coefficients of interoperator reproducibility for CCT were 0.91, 1.11, and 1.25. Conclusions. CCT and MCT measurements show moderate agreement between instruments. The repeatability and interoperator reproducibility of the results obtained by SOCT are somewhat higher. The operator's impact on CCT and MCT measurements is insignificant in all devices.

Comparison of central corneal thickness measurement using ultrasonic pachymetry, rotating Scheimpflug camera, and scanning-slit topography

PURPOSE

To evaluate and compare central corneal thickness measurements using rotating Scheimpflug camera, scanning-slit topography, and ultrasound pachymetry in virgin, healthy corneas.

DESIGN

Prospective, observational, cross-sectional study.

METHODS

Central corneal thickness in 157 healthy eyes of 157 patients without ocular abnormalities other than refractive errors was measured, in a sequential order, once with rotating Scheimpflug camera and scanning-slit topography and 3 times with ultrasound pachymetry as the last part of examination. All measurements were performed by a single experienced examiner. The results from scanning-slit topography are given with and without correction for "acoustic correction factor" of 0.92.

RESULTS

The average measurements of central corneal thickness by rotating Scheimpflug imaging, scanning-slit pachymetry, and ultrasound were 537.15 ± 32.98 μm, 542.06 ± 39.04 μm, and 544.07 ± 34.75 μm, respectively. The mean differences between modalities were 6.92 μm between rotating Scheimpflug and ultrasound (P < .0001), 2.01 μm between corrected scanning-slit and ultrasound (P = .204), and 4.91 μm between corrected scanning-slit and rotating Scheimpflug imaging (P = .001). According to Bland-Altman analysis, highest agreement was between ultrasonic and rotating Scheimpflug pachymetry.

CONCLUSIONS

In the assessment of normal corneas, rotating Scheimpflug topography measures central corneal thickness values with higher agreement to ultrasound pachymetry.

Visante OCT measurement of central corneal thickness following Descemet's stripping endothelial keratoplasty

A 63-year-old man with Fuchs' dystrophy and cataract underwent successful phacoemulsification, insertion of a posterior chamber intraocular lens, and Descemet's stripping endothelial keratoplasty (DSEK) of the right eye. At 1-month follow-up, measurement of central corneal thickness (CCT) obtained by ultrasound pachymetry was 549 μm. The ultrasound pachymetry measurement was thought to be an artifact, so anterior segment optical coherence tomography analysis of the right eye was performed. Both host and graft tissue were imaged in cross-section; optical coherence tomography measurement of CCT was 769 μm. Reliable measurements of CCT are clinically important following DSEK. This case demonstrates that anterior segment optical coherence tomography imaging and analysis software may provide a more appropriate measurement of CCT in patients who have undergone DSEK.

Comparison of central corneal thickness measurements with the Galilei dual Scheimpflug analyzer and ultrasound pachymetry

Purpose:

To compare corneal pachymetry assessment by the Galilei dual Scheimpflug analyzer with that done by ultrasound (US) pachymetry.

Materials and Methods:

Forty six patients (92 eyes) were subjected to corneal pachymetry assessment by Galilei dual Scheimpflug analyzer and US. All the readings were taken by a single operator. Intraoperator repeatability for the Galilei was assessed by taking 10 readings in one eye each of 10 patients. To study the interoperator reproducibility for the Galilei, two observers took a single reading in both the eyes of 25 patients.

Results:

The mean central corneal thickness (CCT) measured by US was 541.83 ± 30.56 μm standard deviation (SD) and that measured by Galilei was 541.27 ± 30.07 μm (SD). There was no statistically significant difference between both the methods (P < 0.001). The coefficient of repeatability was 0.43% while the coefficient of reproducibility was 0.377% for the Galilei.

Conclusion:

Objective, noncontact measurement of the CCT with the Galilei dual Scheimpflug analyzer was convenient, had excellent intraoperator repeatability and interoperator reproducibility, and findings were similar to those obtained with standard US pachymetry.

Human graft cornea and laser incisions imaging with micrometer scale resolution full-field optical coherence tomography

Micrometer scale resolution full-field optical coherence tomography (FF-OCT) is developed for imaging human graft corneas. Three-dimensional (3-D) images with ultrahigh resolution (respectively, 1 and 1.5 μm in the axial and transverse directions), comparable to traditional histological sections, are obtained allowing the visualization of the cells and the precise structure of the different layers that compose the tissue. The sensitivity of our device enables imaging the entire thickness of the cornea, even in edematous corneas more than 800 μm thick. Furthermore, we provide tomographic 3-D images of laser incisions inside the tissue at various depths without slicing the studied corneas. The effects of laser ablations can be observed, along various optical sections, directly in the bulk of the sample with high accuracy, providing information on the interface quality and also imaging tiny changes of the tissue structure. FF-OCT appears to be a powerful tool for subcellular imaging of the corneal structure and pathologies on the entire thickness of the tissue as well as interface quality and changes in the collagen structure due to laser incisions on ex vivo human cornea.

Optical coherence tomography anatomy of the corneal endothelial transplantation wound

PURPOSE

The goal of this study was to prospectively assess the deep lamellar endothelial keratoplasty (DLEK) wound anatomy and its evolution during the 12 months after surgery, using optical coherence tomography (OCT).

METHODS

The eyes of 8 patients (1 eye per patient) who consecutively underwent DLEK for Fuchs dystrophy or pseudophakic bullous keratopathy were prospectively studied before and 1, 3, 6, and 12 months after surgery. The Stratus OCT apparatus (Carl Zeiss Meditec, Dublin, CA) was used to acquire central and radial scans perpendicular to the wound at 3-, 6-, 9-, and 12-o'clock positions. The following parameters were analyzed: central total thickness, posterior donor-recipient edges gap, donor-recipient height mismatch, tissue compression, and graft detachment.

RESULTS

A posterior gap was observed in 4 of the 8 DLEK eyes. At 12 months, the mean gap contour, depth, and width were 242 +/- 67, 101 +/- 45, and 87 +/- 29 microm, respectively. A step was documented in all DLEK eyes (average step height 108 +/- 24 microm). A micrograft detachment was observed in one case and tissue compression in another. In all corneas, the mean central corneal thickness returned to normal range and almost normal anatomy with time after surgery.

CONCLUSIONS

OCT was found to be a very useful tool for DLEK corneal wound architecture analysis. It revealed microscopic wound irregularities and allowed their quantitative follow-up with time.

Intra-examiner repeatability and agreement of corneal pachymetry map measurement by time-domain and Fourier-domain optical coherence tomography

BACKGROUND

To assess the intra-examiner repeatability and agreement of corneal pachymetry maps measured by time-domain (Visante OCT) and Fourier-domain optical coherence tomography (RTVue OCT).

METHODS

This observational cross-sectional study enrolled 72 eyes from 72 volunteers. Only one eye of each patient was chosen randomly to receive repeated scanning with both devices by the same examiner, in order to test the intra-observer repeatability. The first scan by each device from all enrolled eyes was used to analyze the difference and agreement between the two devices. The agreement between the two devices was analyzed by the Bland-Altman method. Intra-observer repeatability of each OCT device was analyzed by intra-class correlation (ICC).

RESULTS

The mean corneal thickness of the central 2 mm zone was 524.3 ± 35.7 µm and 525.4 ± 35.3 µm by the Visante OCT and the RTVue OCT respectively (p = 0.089). The intra-observer repeatability of the RTVue OCT (ICC = 0.994) was superior to that of the Visante OCT (ICC = 0.989) in the central 2 mm zone. However, the intra-observer repeatability of the RTVue OCT in the pericentral 2 to 5 mm zone was not superior to that of the Visante OCT. Both OCT devices had similar repeatability in the pericentral 2 to 5 mm zone [ICC of the Visante OCT = 0.991; 95% confidence interval (CI) 0.986-0.995), ICC of the RTVue OCT = 0.991; 95% CI 0.985-0.994)).

CONCLUSIONS

The difference in CCT measurement by the Visante OCT and the RTVue OCT is probably too small to influence clinical decision making for refractive surgery and glaucoma management. The RTVue OCT demonstrated better intra-observer repeatability in the central 2 mm zone, which probably was related to its rapid image acquisition capability.

Comparison of fourier-domain and time-domain optical coherence tomography for assessment of corneal thickness and intersession repeatability

PURPOSE

To compare Fourier-domain optical coherence tomography (FD-OCT) with time-domain OCT (TD-OCT) for agreement in corneal pachymetry in the central (2-mm) zone and paracentral (2- to 5-mm) zone, minimum corneal thickness, and instrument intersession reliability in candidates with normal cornea.

DESIGN

Prospective comparative trial.

METHODS

The study was performed at a tertiary care ophthalmic hospital. One hundred normal candidates with no ocular pathology except mild refractive error were included. FD-OCT and TD-OCT were used for pachymetric analysis within 15 minutes of each other. Repeat testing on both machines was done on the next day. One eye from each patient was randomly selected for analysis of both comparison and reliability.

RESULTS

The mean thickness was significantly more for FD-OCT (difference being 5.8, 11.1, and 19.2 mum for central, paracentral, and minimal thickness). Highest correlation, best linear fit, and smallest range of 95% limits of agreement (LoA) was seen for central corneal thickness, followed by paracentral and minimum corneal thickness (R(2) values for the 3 best fit lines were 0.93, 0.86, and 0.58, respectively). In terms of intersession reliability, FD-OCT was better (coefficients of reliability <1.5% vs 4.5% of TD-OCT) with smaller 95% LoA range, suggesting its better performance.

CONCLUSIONS

The corneal thickness measurements between TD-OCT and FD-OCT were highly correlated but not similar. Conversion equations may be used for central and paracentral, but not for minimum, corneal thickness. Even though both the OCT instruments had good reliability, FD-OCT was better.

Comparison of Pentacam Scheimpflug Camera with Ultrasound Pachymetry and Noncontact Specular Microscopy in Measuring Central Corneal Thickness

PURPOSE

Although central corneal thickness (CCT) can be measured by several methods, interchangeability of different modalities has not been fully investigated. CCT is known to correlate with intraocular pressure (IOP). The aim of this study was to evaluate the agreement of Pentacam Scheimpflug system with noncontact specular microscopy (NCSM) and ultrasound (US) pachymetry in measuring CCT and the relation between IOP taken with Goldmann applanation tonometer (GAT) and the CCT measured with these three methods.

METHODS

The right eyes of 135 enrolled persons without antiglaucoma drug use (100 females and 35 males), who comprised 32 patients with primary open-angle glaucoma, 14 with ocular hypertension, 45 with primary angle-closure glaucoma, and 44 controls, were studied. Intermethod comparison of CCT was made by the 95% limits of agreement analysis according to Bland and Altman. Linear regression analysis was used to assess the relationship between IOP and CCT taken with each modality.

RESULTS

The mean CCT (+/-SD) taken with Scheimpflug, US, and NCSM was 559.49 +/- 38.44 microm, 553.01 +/- 39.33 microm, and 552.04 +/- 42.95 microm, respectively. The average values of CCT taken with the three instruments were not significantly different (one-factor ANOVA; p = 0.26), although the marginal mean difference between Scheimpflug and US or NCSM was statistically significant (paired t test; p = 0.0009 and 0.005, respectively). The 95% limits of agreement were 6.47 +/- 43.21 microm between Scheimpflug and US, 7.45 +/- 58.86 microm between Scheimpflug and NCSM, and 0.98 +/- 51.69 microm between US and NCSM. There was a positive association between IOP and CCT measured with US or NCSM, whereas there was no correlation between IOP and CCT measured with Scheimpflug.

CONCLUSIONS

Although CCT values measured with Scheimpflug, US, and NCSM are closely similar, clinicians should keep in mind that these methods are not simply interchangeable.

The Reliability of Central Corneal Thickness Measurements by Ultrasound and by Orbscan System in Schoolchildren

PURPOSE

To compare the central corneal thickness measurements obtained by ultrasound (US) pachymetry and the Orbscan II system in healthy schoolchildren.

METHODS

A total of 356 schoolchildren aged 7 to 12 years underwent central cornal thickness (CCT) measurement with Orbscan II and ultrasonic pachymetry. All eyes were examined first with the Orbscan II and then by US pachymetry. The mean of the difference, standard deviation (SD), and 95% limits of agreement, with and without applying the acoustic correction factor, were determined. The differences between the devices in measuring mean CCT were calculated with paired-sample t test. Pearson correlation test was used to determine the correlation between variables. p < 0.05 was considered to be statistically significant. Linear regression analysis was used to quantify the correlation between the two methods.

RESULTS

Orbscan II measurements were significantly higher than US pachymetry measurements without applying the manufacturer-recommended acoustic correction factor (0.92) correction (580.39 +/- 37 microm and 562.95 +/- 32 microm, respectively) (p < 0.0001). When this acoustic correction factor was applied, the Orbscan II measurements demonstrated significantly lower results when compared with those of US pachymetry (533.96 +/- 34 microm and 562.95 +/- 32 microm, respectively) (p < 0.0001). The linear regression analysis lines showed approximately 45-degree slope indicating a strong correlation between these methods (US pachymetry = 145.71 + 0.72 x Orbscan II value without acoustic correction factor (microm), r = 0.89, p < 0.0001). There was a high degree of variability in differences between the 2 devices in individual subjects. The range was between 25 to -55 microm without the acoustic correction factor and 67 to -5 microm with the acoustic correction factor.

CONCLUSIONS

Although US pachymetry and Orbscan II demonstrated a strong linear correlation, there was a high degree of variability in differences between the two devices in individual subjects who participated.

Increased central corneal thickness in children with cerebral palsy

PURPOSE

To evaluate central corneal thickness (CCT) values in children with cerebral palsy (CP).

METHODS

Sixty-seven children with CP and 58 healthy control children (125 children total) were enrolled into the study. The CCT value was measured by ultrasound pachymetry. The consecutive measurements were taken from the center of the cornea of each eye.

RESULTS

In the CP group, the mean CCT value was 568.46 +/- 31.94 microm in the right eye and 568.01 +/- 32.50 microm in the left eye. In the control group, the mean CCT value was 549.53 +/- 26.16 microm in the right eye and 549.62 +/- 27.58 microm in the left eye. The CCT value was significantly higher in the CP group than in the control group for both eyes (P < 0.001). There was no statistically significant difference between the right and left eyes of children with CP and intellectual disability (ID) and those with CP and no ID (P = 0.344 and 0.076, respectively).

CONCLUSIONS

Children with CP had an increased CCT compared with healthy control subjects. There was however no significant difference in CCT values between the children with and without ID in our CP group.

Anterior ocular biometry using 3-dimensional optical coherence tomography

PURPOSE

To evaluate anterior ocular biometry by comparing the measurements of central corneal thickness (CCT) and anterior chamber depth (ACD) with 3-dimensional corneal and anterior segment optical coherence tomography (CAS-OCT) and other methods.

DESIGN

Cross-sectional study.

PARTICIPANTS

Forty eyes of 40 normal subjects.

METHODS

The CCT was measured by 4 methods (CAS-OCT, Scheimpflug camera, scanning-slit topography, and ultrasonic pachymetry), and the ACD was measured by 3 methods (CAS-OCT, Scheimpflug camera, and scanning-slit topography). The anterior chamber volume (ACV) was calculated with CAS-OCT. Repeatability and reproducibility of CAS-OCT measurements were evaluated.

MAIN OUTCOME MEASUREMENTS

The CCT and ACD were measured and compared between devices. The ACV was calculated with CAS-OCT. Coefficient of variation and intraclass correlation coefficient (ICC) were calculated to evaluate repeatability and reproducibility of CAS-OCT measurements.

RESULTS

The mean CCT was 547.0+/-39.0, 590.0+/-39.8, 525.0+/-45.0, and 545.0+/-40.3 microm with CAS-OCT, Scheimpflug camera, scanning-slit topography, and ultrasonic pachymetry, respectively. Significant differences were observed among the 4 methods (P<0.0001; 1-way analysis of variance [ANOVA]). The CCT measured with Scheimpflug camera was significantly larger than those measured with the other methods (P<0.0001; Bonferroni multiple comparison), but there was no significant difference among the other 3 methods. The mean ACD was 3.01+/-0.47, 3.04+/-0.52, and 2.88+/-0.50 mm with CAS-OCT, Scheimpflug camera, and scanning-slit topography, respectively. There was no significant difference among the 3 methods (P = 0.678; 1-way ANOVA). A significant linear correlation in CCT and ACD were observed between CAS-OCT and other methods (all P<0.0001). The mean ACV calculated with CAS-OCT was 169.7+/-23.1 mm(3). The coefficient of repeatability and reproducibility of CCT and ACD measurements were <5% and ICCs were >0.98.

CONCLUSIONS

The CCT measurements were comparable among CAS-OCT, ultrasonic pachymetry, and scanning-slit topography, but Scheimpflug camera yielded a significantly higher CCT value. There was no significant difference in ACD measurements among CAS-OCT, Scheimpflug camera, and scanning-slit topography. The ACV was noninvasively measured by CAS-OCT.

FINANCIAL DISCLOSURE(S)

The authors have no proprietary or commercial interest in any materials discussed in this article.