Comparative Study of Central Corneal Thickness Using Fourier-Domain Optical Coherence Tomography Versus Ultrasound Pachymetry in Primary Open-Angle Glaucoma

A comparison of central corneal thickness measured using noncontact methods and ultrasonic pachymetry

Aim

The aim of this study is to compare central corneal thickness (CCT) measurements in healthy eyes using ultrasonic pachymetry (UP) with values obtained using anterior segment spectral domain optical coherence tomography (SD-OCT), the Scheimpflug camera system, and noncontact specular microscopy.

Material and Methods

One hundred and twenty-five eyes of 117 healthy individuals (56 women, 61 men) were included. All patients underwent consecutive CCT measurement with UP, the Scheimpflug camera, anterior segment SD-OCT, and specular microscopy. The four devices could be read. Measurements from the four devices were classified in pairs and compared using the paired t-test. Relations between the devices were analyzed using the Pearson test. An alpha error level of P < 0.05 was regarded as statistically significant.

Results

The mean age of the healthy individuals included in the study was 34.75 ± 14.55 years (20-76). Mean CCT values were 541.21 ± 29.24 μm with UP, 539.26 ± 29.27 μm with the Scheimpflug camera system, 532.21 ± 29.53 μm with SD-OCT, and 534.45 ± 29.20 μm with specular microscopy. The differences in measurements at the paired t-test were statistically significant (P < 0.001 for all). However, measurements using the four devices exhibited significant mutual correlation (P < 0.001 for all).

Conclusions

CCT can be measured using different devices. Noncontact methods have now begun replacing UP, regarded as the gold standard. Although CCT values obtained from different devices were correlated, the difference between these measurements was statistically significant. Therefore, the same device should be used for measurement in the diagnosis and follow-up of diseases such as corneal ectasia and glaucoma where corneal thickness is important.

[Accuracy of Optical Coherence Tomography versus Ultrasound in pachymetry]

PURPOSE

Measuring the central corneal thickness is an important step in the diagnosis and monitoring of glaucoma. Ultrasound pachymetry was the gold standard before the advent of OCT. The purpose of this study is to assess the reliability of OCT pachymetry compared to ultrasound pachymetry in black patients.

PATIENTS AND METHODS

Pachymetry was performed as part of a glaucoma work-up. Ultrasonic pachymetry was measured using the Alcon Ocuscan by the same operator and OCT pachymetry using the Topcon 2000 OCT. The Student's t-test was used to compare means with statistical significance of 5%. The Pearson's correlation coefficient (r²) was used to measure correlations.

RESULTS

One-hundred thirty-five right eyes and 135 left eyes, corresponding to 270 eyes of 135 patients, were examined. There was a female predominance (59 men/76 women), with a gender ratio of 0.78. The mean age was 42.3±17.3 [8-86] years. In the right eye, the mean OCT pachymetry was 522.4±36.8μ versus 528.2±37.9μ for ultrasonic pachymetry (P=1.00). In the left eye, the mean OCT pachymetry was 522.0±33.8μ versus 524.9±42.5μ for ultrasonic pachymetry (P=1.00). The overall mean OCT pachymetry was 522.2±35.2μ versus 526.5±40.2μ, with a non-significant difference (P=1.00). There was a strong correlation between ultrasonic pachymetry and OCT pachymetry (r²=0.83; P<0.05). On the other hand, there was a very low correlation between pachymetry and age (r²=0.09; P<0.05). Pachymetry decreased by 5μ per 10 years, corresponding to corneal thinning of 0.5μ per year.

CONCLUSION

OCT pachymetry can be a reliable alternative to ultrasound pachymetry and could be performed at the same time as the OCT for glaucoma assessment.

Corneal thickness measurement by secondary speckle tracking and image processing using machine-learning algorithms

Corneal thickness (CoT) is an important tool in the evaluation process for several disorders and in the assessment of intraocular pressure. We present a method enabling high-precision measurement of CoT based on secondary speckle tracking and processing of the information by machine-learning (ML) algorithms. The proposed configuration includes capturing by fast camera the laser beam speckle patterns backscattered from the corneal-scleral border, followed by ML processing of the image. The technique was tested on a series of phantoms having different thicknesses as well as in clinical trials on human eyes. The results show high accuracy in determination of eye CoT, and implementation is speedy in comparison with other known measurement methods.

The thick and thin of the central corneal thickness in glaucoma

Central corneal thickness (CCT) is an important parameter in the assessment of any potential glaucoma patient. While it affects prognosis in ocular hypertension, its value in patients diagnosed with glaucoma is less certain. There are several biological factors and genetic components that may influence glaucoma progression, which have been associated with thinner CCT. The CCT itself can be affected by several factors including ethnicity, age, sex, glaucoma medications, genetics, and the subtype of glaucoma. Besides, there is variability in the measurement of CCT between difference types of devices. These factors need to be considered in the evaluation of glaucoma patients' CCT and its effect on interpretation of intraocular pressure levels and risk stratification.

No differences in central corneal thickness between open-angle and pseudoexfoliation glaucoma patients

Introduction

Measurements of intraocular pressure (IOP) with Goldmann applanation tonometry are affected by central corneal thickness (CCT), as thinner corneas underestimate and thicker corneas overestimate the true IOP value. The literature is controversial regarding CCT values in patients with primary open-angle glaucoma (POAG) and exfoliation glaucoma (XFG). The aim of this study was to evaluate CCT in patients with XFG and POAG.

Methods

CCT was evaluated with optical coherence tomography (OCT). All participants who were previously diagnosed with either POAG or XFG underwent ophthalmological examinations. Contact lens users and patients with corneal diseases were excluded.

Results

Totally, 145 patients were enrolled in this study. The mean CCT was 535±30.4 µm in patients with POAG and was 536±33.7 µm in patients with XFG. The result was not statistically significant (P=0.98). The mean age for all participants was 73.8±7.7 years. The study included totally 61 women and 84 men. The two groups were similar in their demographic data, and mean deviation was the only parameter that differed statistically when comparing POAG with XFG (P=0.02).

Conclusion

Our data indicate that patients with XFG do not have thinner corneas than those with POAG, and therefore, CCT can not explain why they progress differently.

Central corneal thickness in glaucoma

PURPOSE OF REVIEW

The purpose of this review is to summarize the role of central corneal thickness (CCT) in the clinical management of a glaucoma patient.

RECENT FINDINGS

The prognostic value of CCT is well recognized in patients with ocular hypertension. However, its predictive value in other glaucoma suspects and patients with established glaucoma is less certain. Tonometry artefacts can result from variations in CCT. However, an adequately validated correction algorithm for Goldmann applanation tonometry measurements does not exist. Newer methods of tonometry are potentially less influenced by CCT but are limited in their clinical use. There may also be biological and genetic associations between corneal thickness and glaucoma. Demographics, environmental factors, glaucoma treatment and the measurement device used have a significant influence on CCT, and should be considered when interpreting the effect of cornea thickness in patients with glaucoma. New measurements of the biomechanical properties of the cornea are likely to be better approximations of the globe biomechanics than CCT, but these require further evaluation.

SUMMARY

The clinical significance of CCT is well recognized in the context of glaucoma diagnosis and management, though the extent of its importance remains debatable. Corneal biomechanical properties may be more significantly associated with glaucoma than CCT.

A Comparison of Central Corneal Thicknesses Measured with Two Different Methods in Cases of Primary Open-Angle Glaucoma

Accurate and repeatable measurement of the central cornea thickness (CCT) is important in terms of follow-up of glaucoma patients. The aim of this study was to compare CCT measurements made with an ultrasonic pachymeter (USP) and with the Spectralis Anterior Segment Module optical coherence tomography (OCT) device. The study included 52 eyes of 26 primary open-angle glaucoma patients. CCT measurements were taken with the USP device and then with the OCT by imaging cornea slices. The mean CCT was measured as 555.71 ± 47.76 μm with USP and 569.46 ± 49.5 μm with OCT. Despite the differences between the measurements of the two methods, a very strong degree of consistency was seen between the CCT measurement with USP and OCT (ICC = 0.93, p < 0.001).

Accuracy of optical coherence tomography (OCT) in pachymetry for glaucoma patients

Background

Central corneal thickness (CCT) measurement has become an important test in the diagnosis and management of glaucoma. Currently, ultrasound corneal thickness measurement (pachymetry) is the most frequently used clinical technique and the gold standard to assess CCT. Newer instruments are currently available including the optical coherence tomography (OCT) instrument. The aim of the present study was therefore to evaluate the accuracy of the CCT measurements performed by three different observers, both with the OCT and ultrasound pachymetry (USP), in patients suffering from glaucoma.

Methods

Patients who had been previously diagnosed with glaucoma participated in this cross-sectional study. Glaucoma was defined as patients who had at least two repeatable Humphrey visual fields showing glaucoma damage using the software 24–2, and with the optic nerve showing typical glaucoma damage. The patients CCTs were measured with OCT and USP by three different examiners.

Results

Seventy eyes of 35 patients were included. The average age was 74 ± standard deviation (SD) 10.88, the average pachymetry value with OCT was 536 ± 29 μm, and the average pachymetry with USP was 532 ± 32 μm. The differences between OCT and USP were not significant (t-test, p = 0.32). The intraclass correlation coefficients were, for OCT, 0.99 [confidence interval (CI): 0.98–0.996], and for USP, 0.97 (CI: 0.95–0.98).

Conclusions

Agreement among the three observers using OCT or USP for pachymetry measurements was good. OCT might be used as an alternative method for pachymetry in glaucoma patients.

Comparison of Central Corneal Thickness Measurements Obtained by RTVue OCT, Lenstar, Sirius Topography, and Ultrasound Pachymetry in Healthy Subjects

PURPOSE

To compare central corneal thickness (CCT) measurement results obtained by RTVue OCT, Lenstar, Sirius topography, and ultrasound pachymetry (UP) (OcuScan RxP Ophthalmic Ultrasound System, Alcon Laboratories) in healthy subjects.

MATERIALS AND METHODS

256 eyes of 128 healthy subjects were included in the study. CCT measurements were obtained from the eyes for each subject using the UP, Lenstar, Sirius topography, and RTVue OCT instruments. Ultrasound pachymetry measurements were performed after the eyes were anesthetized with one drop of 0.5% proparacaine hydrochloride and were performed at the same day after 15 minutes after previous measurements.

RESULTS

Of 128 participants, 84 were male and 44 were female with a mean age of 33.15 ± 12.95 years (ranging from 18 to 75 years). The mean CCTs for UP, Lenstar, Sirius topography, and RTVue OCT were 535.60 ± 35.15 (440,00-668,00); 532.63 ± 34.44 (449,00-650,00); 526.05 ± 36.45 (314,00-640,00); 525.89 ± 33.21 (437,00-646,00) µm, respectively. The mean CCT measurements were statistically different among the three groups (p = 0.002). CCT measurements obtained using RTVue-OCT were significantly thinner than those obtained using UP (p = 0.009). Sirius CCT measurements were also thinner than UP (p = 0.011). Mean CCT measurements between UP and Lenstar were similar (p = 0.769). Measurements with Lenstar (r = 0.849), Sirius topography (r = 0.883), and RTVue OCT (0.949) were highly correlated with UP measurements.

CONCLUSION

RTVue OCT and Sirius topography significantly underestimated the CCT compared with UP. Although highly correlated, the measurement values with these devices are not directly interchangeable in clinical practice.

Visualization of synthetic mesh utilizing optical coherence tomography

INTRODUCTION AND HYPOTHESIS

Owing to the recent upsurge in adverse events reported after mesh-augmented pelvic organ prolapse (POP) repairs, our aim was to determine whether the location and depth of synthetic mesh can be measured postoperatively within the vaginal tissue microstructure using optical coherence tomography (OCT).

METHODS

Seventeen patients with prior mesh-augmented repairs were recruited for participation. Patients were included if they had undergone an abdominal sacral colpopexy (ASC) or vaginal repair with mesh. Exclusion criteria were a postoperative period of <6 months, or the finding of mesh exposure on examination. OCT was used to image the vaginal wall at various POP-Q sites. If mesh was visualized, its location and depth was calculated and recorded.

RESULTS

Ten patients underwent ASC and 7 patients had 8 transvaginal mesh repairs. Mesh was visualized in 16 of the 17 patients using OCT. In all ASC patients, mesh was imaged centrally at the posterior apex. In patients with transvaginal mesh in the anterior and/or posterior compartments, the mesh was visualized directly anterior and/or posterior to the apex respectively. Mean depth of the mesh in the ASC, anterior, and posterior groups was 60.9, 146.7, and 125.7 μm respectively. Mesh was visualized within the vaginal epithelial layer in all 16 patients despite the route of placement.

CONCLUSION

In this pilot study we found that OCT can be used to visualize polypropylene mesh within the vaginal wall following mesh-augmented prolapse repair. Regardless of abdominal versus vaginal placement, the mesh was identified within the vaginal epithelial layer.