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Original article
Measurement of central corneal thickness by different techniques Reem Hassan Ibrahim Azzam, Manal Ali Kasem, Abeer Khattab, Hossam Mohamed Ali El-Fallal Department of Ophthalmology, Faculty of Medicine, Mansoura University, Mansoura, Egypt Correspondence to Manal Ali Kasem, MD, Department of Ophthalmology, Faculty of Medicine, Mansoura University, Gomhoria Street, Mansoura, 35511, Egypt. e-mail:
[email protected] Received June 2017 Accepted October 2017 Journal of the Egyptian Ophthalmological Society 2017, 110:114–117
Purpose The aim of this study was to compare the central corneal thickness (CCT) measurements by three different techniques: pentacam, noncontact specular microscopy, and ultrasound biomicroscopy (UBM) devices. Patients and methods This prospective observational cross-sectional study was performed on patients seeking medical care at the outpatient clinic of Ophthalmology Center at Mansoura University. They were consecutively recruited and selected, and measurement of CCT by pentacam, UBM, and specular microscopy was done. Thereafter, the results were compared as an evaluation study of all techniques. Results This study included 200 eyes of 100 patients. The age of the included patients in the study ranged from 20 to 50 years. The mean age was 34.56±9.94 years. The CCT ranged from 465 to 630 μm, with a mean of 532.88±34.15 μm when measured by pentacam. When measured by specular microscopy, it ranged from 456 to 601 μm, with a mean 531.92±33.64 μm, and when measured by UBM, it ranged from 463 to 602 μm, with a mean 533.97±31.10 μm, with P value of 0.824 (nonsignificant). Conclusion CCT measurements obtained by UBM tend to be thicker than those obtained by pentacam and noncontact specular microscopy, but the measurements of all three are strongly positively correlated with each other. So, any of these devices can be easily substituted by the other for the measurement of CCT. Keywords: corneal thickness, pentacam, specular microscopy, UBM J Egypt Ophthalmol Soc 110:114–117 © 2018 Journal of the Egyptian Ophthalmological Society 2090-0686
Introduction Measurement of central corneal thickness (CCT) has a great value in different fields of ophthalmology and optometry, especially in diagnosis and treatment of corneal disorders [1,2]. CCT is also an important parameter in refractive surgery. It helps in predicting the long-term complications such as postsurgical keratectasia, which shows the importance of accurate corneal thickness measurement [3]. Different equipments are used now to measure CCT such as ultrasound pachymetry, contact and noncontact specular microscopy (NCSM), optical coherence tomography, pentacam, ultrasound biomicroscopy (UBM), partial coherence interferometry, and confocal microscopy [4–10]. The value of CCT measurements may differ among these instruments. This is based on a variety of techniques and devices, and each has its own advantages and disadvantages [11].
The aim of this study was to compare the CCT measurements by three different techniques: pentacam, NCSM, and UBM devices. Patients and methods This is an observational cross-sectional study, and it was performed on patients seeking medical care at the Outpatient Clinic of Ophthalmology Center at Mansoura University. They were consecutively recruited and selected, with the aim of measuring CCT by pentacam, UBM, and specular microscopy and then comparing the results as an evaluation study of all techniques. Patients included in this study aged from 20 to 50 years, were of both sexes, and had spherical This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License, which allows others to remix, tweak, and build upon the work noncommercially, as long as the author is credited and the new creations are licensed under the identical terms.
© 2018 Journal of the Egyptian Ophthalmological Society | Published by Wolters Kluwer - Medknow
DOI: 10.4103/ejos.ejos_41_17
[Downloaded free from http://www.jeos.eg.net on Thursday, March 8, 2018, IP: 186.176.248.152] Measurement of central corneal thickness Azzam et al.
equivalent ranged from +2 to −2 D with healthy cornea and intraocular pressure less than 21 mmHg. Patients excluded in this study had the following criteria: (1) Corneal diseases such as corneal dystrophies, degeneration, ectatic diseases, and keratitis. (2) Systemic diseases affecting eyes such as diabetes mellitus and Herpes Zoster. (3) Past history of ocular surgery such as refractive and cataract surgeries. (4) Contact lens wearers. In this study, 200 eyes of 100 patients of both sexes between 20 and 50 years were enrolled after obtaining complete informed consent from all of them in the period from January 2014 to December 2014 and approval of the Institutional Review Board of Mansoura Faculty of Medicine. The candidates underwent comprehensive examinations, which included the following:
eye
(1) Uncorrected and best-corrected visual acuity. (2) Slit lamp biomicroscopy examination (HaagStreit, Bern, Switzerland) for detection of any corneal abnormalities and ensuring clarity of anterior chamber. (3) Measurement of intraocular pressure was performed using the Goldmann applanation tonometer attached to Haag-Streit slit lamp. (4) Fundus examination using 90 D Volk noncontact lens. Measurements of CCT were done between 9 a.m. and 2 p.m. at least 2 h after waking up. Examination started first by pentacam (Tomey Corporation, Nagoya, Japan). After getting pentacam readings, CCT was assessed by NCSM (Tomey Corporation) followed by UBM (Humphrey, Fresno, California, USA). Statistical analysis
The data analyses were performed using SPSS program version 15.00 (SPSS Inc., Chicago, Illinois, USA). Qualitative data were presented as numbers and percentage. Quantitative data were described by mean±SD and range. The results of CCT measurements obtained using each device were compared by using a repeated measures analysis of variance test. Pearson’s correlation coefficient was used to illustrate strength of relation between two variables. P value less than 0.05 was considered significant statistically.
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Results The study included 200 eyes of 100 patients who underwent CCT measurement using pentacam, specular microscopy, and UBM. The age of the included patients in the study ranged from 20 to 50 years. The mean age was 34.56±9.94 years. Central corneal thickness measurements
The CCT ranged from 465 to 630 μm, with a mean 532.88±34.15 μm, when measured by pentacam. When measured by specular microscopy, it ranged from 456 to 601 μm, with a mean 531.92±33.64 μm, and when measured by UBM, it ranged from 463 to 602 μm, with a mean 533.97±31.10 μm, with P value of 0.824. Correlation between pentacam, specular microscopy, and UBM
There was a strong positive correlation between specular microscopy and pentacam (r=0.949, P>0.01; Pearson’s correlation coefficient). This correlation was more than that between pentacam and UBM (r=0.901 probability, P>0.01; Pearson’s correlation coefficient) and between UBM and specular microscopy (r=0.894 probability, P=0.01; Pearson’s correlation coefficient), as shown in Table 1. The highest positive correlation of CCT readings was by pentacam and specular microscopy (Fig. 1a), followed by the correlation between pentacam and UBM (Fig. 1b) and between UBM and specular microscopy (Fig. 1c). Discussion In this era of developing refractive surgeries, accurate estimation of CCT becomes mandatory, so several techniques are available now for estimation of CCT. Each of them has its own advantages and disadvantages. Several research studies have investigated the comparison of CCT measurement between different devices to determine whether any one of these devices can be more accurate than others [2]. In this study, CCT measurements by pentacam, specular microscopy, and UBM were estimated in Table 1 Correlation among pentacam, specular microscopy, and ultrasound biomicroscopy Pentacam
UBM
r
P
r
P
Specular microscopy
0.949
