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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 110  |  Issue : 4  |  Page : 114-117

Measurement of central corneal thickness by different techniques


Department of Ophthalmology, Faculty of Medicine, Mansoura University, Mansoura, Egypt

Date of Submission08-Jun-2017
Date of Acceptance08-Oct-2017
Date of Web Publication8-Mar-2018

Correspondence Address:
Manal Ali Kasem
Department of Ophthalmology, Faculty of Medicine, Mansoura University, Gomhoria Street, Mansoura, 35511
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ejos.ejos_41_17

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  Abstract 

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


How to cite this article:
Azzam RI, Kasem MA, Khattab A, El-Fallal HM. Measurement of central corneal thickness by different techniques. J Egypt Ophthalmol Soc 2017;110:114-7

How to cite this URL:
Azzam RI, Kasem MA, Khattab A, El-Fallal HM. Measurement of central corneal thickness by different techniques. J Egypt Ophthalmol Soc [serial online] 2017 [cited 2018 Jul 18];110:114-7. Available from: http://www.jeos.eg.net/text.asp?2017/110/4/114/226940


  Introduction Top


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],[5],[6],[7],[8],[9],[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 Top


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 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 eye examinations, which included the following:
  1. Uncorrected and best-corrected visual acuity.
  2. Slit lamp biomicroscopy examination (Haag-Streit, 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.


  Results Top


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].
Table 1 Correlation among pentacam, specular microscopy, and ultrasound biomicroscopy

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The highest positive correlation of CCT readings was by pentacam and specular microscopy ([Figure 1]a), followed by the correlation between pentacam and UBM ([Figure 1]b) and between UBM and specular microscopy ([Figure 1]c).
Figure 1 (a) A scattered plot of central corneal thickness measurements by specular microscopy versus pentacam. (b) A scattered plot of central corneal thickness measurements by ultrasound biomicroscopy versus specular microscopy. (c) A scattered plot of central corneal thickness measurements by ultrasound biomicroscopy versus pentacam.

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  Discussion Top


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 eyes with healthy corneas, where a good agreement among the three methods was found. This study mentions the agreement of these three techniques with each other in a single research.

In this study, CCT measured by pentacam ranged from 465 to 630 µm, with a mean of 532.88±34.15 µm. Mean CCT measured by specular microscopy was 456–601 µm, with a mean of 531.92±33.64 µm, and when measured by UBM, it ranged from 463 to 602 µm, with a mean of 533.97±31.10 µm.

Comparison of pentacam with noncontact specular microscopy

The results of this study showed that the mean CCT measurements by pentacam were thicker than those measured by specular microscopy by 0.96 µm. Ucakhan and colleagues, found that CCT measurement by NCSM was thinner than that obtained by pentacam, and this agrees with this study [12],[13],[14],[15],[16].

Comparison of ultrasound biomicroscopy with pentacam

In this study, the mean CCT measurements by UBM was thicker than the mean measurements by pentacam by 1.09 µm. Kanellopoulos and Asimellis [17], found that the UBM had a mean CCT of 545.1±28.3 µm, which was more than that given by pentacam (538.0±30.7 µm), and this agrees with this study’s results.

This may be explained by corneal hydration following the application of local anesthesia.

Comparison of ultrasound biomicroscopy with noncontact specular microscopy

The mean CCT measurements by UBM were thicker than the mean measurements by specular microscopy by 2.05 µm. It can be explained by the topical anesthesia that was used before UBM, which may alter the corneal thickness, the location where the ultrasonic probe is applied.

On the contrary, Tam and Rootman [8] found that the mean CCT by specular microscopy was 572 µ which was significantly greater than that measured by UBM (555 µ). This is explained by the compression of the epithelium produced by ultrasound probe. This produces a slightly thinner CCT when measured with UBM.


  Conclusion Top


CCT measurements obtained by UBM tend to be thicker than those obtained by pentacam and NCSM, but measurements of all three are strongly positively correlated with each other. So, any of these devices can be easily substituted by the other for measurement of CCT.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Patwardhan AA, Khan M, Mollan SP, Haigh P. The importance of central corneal thickness measurements and decision making in general ophthalmology clinics: a masked observational study. BMC Ophthalmol 2008; 8:1.  Back to cited text no. 1
    
2.
Sng C, Ang M, Barton K. Central corneal thickness in glaucoma. Curr Opin Ophthalmol 2017; 28:120–126.  Back to cited text no. 2
    
3.
Malecaze F, Coullet J, Calvas P, Fournie P, Ame JL, Brodaty C. Corneal ectasia after PRK for low myopia. Ophthalmology 2003; 110:267–275.  Back to cited text no. 3
    
4.
Suzuki S, Oshika T, Oki K. Corneal thickness measuremesnts: scanning-slit corneal topography and noncontact specular microscopy versus ultrasonic pachymetry. J Cataract Refract Surg 2003; 29:1313–1318.  Back to cited text no. 4
    
5.
Bovelle R, Kaufman SC, Thompson HW, Hamano H. Corneal thickness measurements with the Topcon Sp-2000P specular microscope and an ultrasound pachymeter. Arch Ophthalmol 1999; 117:868–870.  Back to cited text no. 5
    
6.
Bechmann M, Thiel MJ, Neubauer AS. Central corneal thickness measurement with a retinal optical coherence tomography device versus standard ultrasonic pachymetry. Cornea 2001; 20:50–55.  Back to cited text no. 6
    
7.
Yekta A, Hashemi H, KhabazKhoob M, Dostdar A, Mehravaran S, Heravian J, Fotouhi A. Comparison of central corneal thickness measurements with Pentacam, Orbscan II, and Ultrasound Pachymeter. Iran J Ophthalmol 2009; 21:51–57.  Back to cited text no. 7
    
8.
Tam ES, Rootman DS. Comparison of central corneal thickness measurements by specular microscopy, ultrasound pachymetry, and ultrasound biomicroscopy. J Cataract Refract Surg 2003; 29:179–1184.  Back to cited text no. 8
    
9.
Sacu S, Findl O, Buehl W, Kiss B, Gleiss A, Drexler W. Optical biometry of the anterior eye segment: interexaminer and intraexaminer reliability of AC-Master. J Cataract Refract Surg 2005; 31:2334–2339.  Back to cited text no. 9
    
10.
Kaufman SC, Musch DC, Belin MW. Confocal microscopy: a report by the American Academy of Ophthalmology. Ophthalmology 2004; 111:396–406.  Back to cited text no. 10
    
11.
Lackner B, Schmidinger G, Pieh S, Funovics MA, Skorpik C. Repeatability and reproducibility of central corneal thickness measurement with Pentacam, Orbscan, and Ultrasound. Optom Vis Sci 2005; 82:892–899.  Back to cited text no. 11
    
12.
Ucakhan OO, Fujioka M, Amano S, Ciolino JB. Recent advances in ophthalmic anterior segment imaging. Br J Ophthalmol 2006; 91:551–557.  Back to cited text no. 12
    
13.
Fujioka M, Nakamura M, Tatsumi Y. Comparison of Pentacam Scheimpflug camera with ultrasound pachymetry and noncontact specular microscopy in measuring central corneal thickness. Curr Eye Res 2007; 32:89–94.  Back to cited text no. 13
    
14.
Al-Ageel S, Al-Muammar AM. Comparison of central corneal thickness measurements by Pentacam, specular microscopy, ultrasound pachymetry in normal and post-LASIK eyes. Saudi J Ophthalmol 2009; 23:181–187.  Back to cited text no. 14
    
15.
Tai LY, Khaw KW, Subrayan V. Central corneal thickness measurements with different imaging devices and ultrasound pachymetry. Cornea 2013; 32:766–771.  Back to cited text no. 15
    
16.
De Bernardo MD, Borrelli M, Mariniello M, Lanza M, Rosa N. Pentacam vs SP3000P specular microscopy in measuring corneal thickness. Cont Lens Anterior Eye 2015; 38:21–27.  Back to cited text no. 16
    
17.
Kanellopoulos AJ, Asimellis G. Forme fruste keratoconus imaging and validation via novel multi-spot reflection topography. Case Rep Ophthalmol 2013; 4:199–209.  Back to cited text no. 17
    


    Figures

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    Tables

  [Table 1]



 

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