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BRIEF COMMUNICATION
Year : 2015  |  Volume : 3  |  Issue : 1  |  Page : 29-30

Comparison between the measurements of different parameters obtained from optic nerve head analysis by using Heidelberg retinal tomography (HRT3) and Optical coherence tomography (Stratus OCT)


Raghudeep Eye Hospital, Director Glaucoma Clinic, Ahmedabad, Gujarat, India

Date of Submission07-Jan-2014
Date of Acceptance15-Sep-2014
Date of Web Publication14-Jan-2015

Correspondence Address:
Mayuri Khamar
Nagar School of Optometry, Municipal Medical College, Director Glaucoma Clinic, Raghudeep Eye Hospital, Gurukul Road, Memnagar, Ahmedabad - 380 052, Gujarat
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2320-3897.149367

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  Abstract 

Purpose: A cross-sectional prospective nonrandomized study was undertaken to find out whether Heidelberg retinal tomography (HRT3) and Optical coherence tomography (Stratus OCT) could be used interchangeably for the measurement of different parameters of optic nerve head in clinical practice. Materials and Methods: Measurements of disc area, cup area, rim area and cup-disc area ratio were obtained with the HRT3 and Stratus OCT printouts in 18 patients aged 20 to 70 years. True agreements between methods in measuring disc area, cup area, rim area and cup-disc area ratio were assessed using Bland-Altman statistical analysis. Eighteen patients with a mean age of 27.05 ± 5.04 years were enrolled. Result: Differences between mean (bias) were -0.81 ± 0.58 mm2 for disc area, -0.31 ± 0.32 mm2 for cup area,-0.50 ± 0.64 mm2 for rim area, -0.04 ± 0.09 for cup-disc area ratio while using HRT3 and Stratus OCT, respectively. Conclusion: Large range of differences were observed in measurements of disc area, cup area, rim area and cup-disc area ratio with HRT3 and Stratus OCT.

Keywords: Heidelberg retinal tomography, Optical coherence tomography, optic disc area, optic disc cup area, optic disc rim area, optic cup-disc ratio


How to cite this article:
Khamar M, Danayak P, Majumder C. Comparison between the measurements of different parameters obtained from optic nerve head analysis by using Heidelberg retinal tomography (HRT3) and Optical coherence tomography (Stratus OCT). J Clin Ophthalmol Res 2015;3:29-30

How to cite this URL:
Khamar M, Danayak P, Majumder C. Comparison between the measurements of different parameters obtained from optic nerve head analysis by using Heidelberg retinal tomography (HRT3) and Optical coherence tomography (Stratus OCT). J Clin Ophthalmol Res [serial online] 2015 [cited 2022 Jan 26];3:29-30. Available from: https://www.jcor.in/text.asp?2015/3/1/29/149367

Early diagnosis of glaucoma is centered on evaluation of morphometric parameters of the optic nerve head (ONH) as changes in the optic disc often precede visual field loss. [1,2] Rim area is often the first area to show glaucomatous changes, and the measurement of rim area has already been established as a reliable tool for separating glaucomatous eyes from normal eyes. [3,4] A change in the appearance of the ONH topography is an important objective sign for diagnosing and managing glaucoma. Automated instruments have been developed to quantitatively assess optic disc topography.

The aim of this study was to find out whether we can use Heidelberg retinal tomography (HRT3) and Optical coherence tomography (Stratus OCT) interchangeably for the measurement of different ONH parameters namely cup area, disc area, rim area and cup-disc area ratio.


  Materials and Methods Top


A cross-sectional prospective nonrandomized study was undertaken at our hospital from November 2009 to October 2010. The study adhered to the tenets of the declaration of Helsinki. The study was approved by the Institutional Review Board. Written informed consent was obtained from all patients before start of the study. Glaucomatous and non-glaucomatous subjects within an age group of 20 to 70 years based on the availability in the outpatient department, with a best corrected distance visual acuity of 6/12 or >6/12 with Snellen's chart were included to achieve a good number of subjects for the research.

Patients that were excluded from the study were those with refractive error exceeding ± 5.0 diopter (D) Spherical and/or 3.0 D Cylinder, presence of media abnormality, atypical ONH such as tilted disc and patients with nystagmus and strabismus.

A detailed history of the patient including medical and family history was taken. All subjects underwent a complete ophthalmologic examination using a Snellen's Visual acuity chart, Torchlight, Streak Retinoscope, Slit lamp, Goldman Applanation Tonometer, Indirect Ophthalmoscope, +20 D lens, HRT3 and Stratus OCT machines.

The agreement between pair of methods in estimating the absolute value of disc area, cup area, rim area, cup-disc area ratios were analyzed as proposed by Bland and Altman. [5] Graphically, the difference between the measurements of each parameter by using HRT3 and Stratus OCT were plotted against their mean values. The bias for disc area, cup area, rim area and cup-disc area ratio was calculated individually and the graph was plotted against 95% CI (Confidence interval).


  Results Top


Eighteen Patients (8 Males, 10 Females), with a Mean (±SD) age of 27.05 ± 5.04 years were enrolled [Table 1] and [Table 2].
Table 1: Shows Mean of disc area, cup area, rim area and cup-disc area ratio with HRT3 and Stratus OCT


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Table 2: Shows difference between mean (bias), SD of bias and 95% confidence Interval (CI) of limit of agreement (LOA) for disc area, cup area, rim area and cup-disc area ratio


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  Discussion Top


Disc area, cup area, rim area and cup-disc ratio are important parameters when differentiating normal from glaucomatous disc. Confocal laser scanning ophthalmoscopy (CSLO) has shown good correlation between disc area and both rim area and cup-disc area ratio.

Neuroretinal rim area, as measured by the HRT3 is an effective, objective quantifiable indicator to determine whether a patient with glaucoma has stable or worsening disease. Stratus OCT is unique in its ability to detect the ONH margin in an automated fashion. When several methods are routinely used, clinicians must know whether they are interchangeable before they are used in diagnosis and follow-up or in research. Otherwise, investigators may reach different diagnostic conclusions regarding the same eyes only attributable to the use of different diagnostic techniques.

HRT and OCT have been developed to provide objective and reproducible analysis of optic disc morphometric parameters. [6,7] They have higher reproducibility and lower inter observer variability compared with the clinical assessment of the optic disc. In addition they allow easy documentation and archiving of disc status. For these reasons, they are increasingly being used by clinicians as diagnostic tools.

In this study the difference between mean (bias) for disc area was -0.81 ± 0.59 mm 2 , which is clinically

significant.

The HRT and OCT analyses in this study were performed according to the manufacturer's recommendations, supplying manifest refraction for both instruments and corneal curvature for HRT. It is possible that the difference in operating principles, manual determination of disc margin with HRT3 in comparison to the automatic detection of disc margin with Stratus OCT partially accounts for the observed differences in disc area, cup area and rim area.

In our study, a single measurement of ONH parameter was obtained by each modality by a single investigator. Our study did not correlate the axial length and refractive error of the patient with ONH parameters. One of the limitations of this study is less number of sample sizes due to the lack of research grant.


  Conclusion Top


In our study, it was found that a large mean bias and dispersal range existed between HRT3 and Stratus OCT in estimating disc area, cup area, and rim area but not in cup-disc area ratio, which precludes their interchangeable use in clinical practice or research. A larger sample size is needed to conclude about the interchangeable use of HRT and OCT in clinical practice.

 
  References Top

1.
Sommer A, Pollack I, Maumenee AE. Optic disc parameters and onset of glaucomatous field loss. I. Methods and progressive changes in disc morphology. Arch Ophthalmol 1979;97:1444-8.  Back to cited text no. 1
    
2.
Pederson JE, Anderson DR. The mode of progressive disc cupping in ocular hypertension and glaucoma. Arch Ophthalmol 1980;98:490-5.  Back to cited text no. 2
[PUBMED]    
3.
Jonas JB, Xu L. Optic disc haemorrhages in glaucoma. Am J Ophthalmol 1994;118:1.  Back to cited text no. 3
    
4.
Jonas JB, Budde WM, Panda-Jonas S. Ophthalmoscopic evaluation of the optic nerve head. Surv Ophthalmol 1999;43:293-320.  Back to cited text no. 4
    
5.
Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986;1:307-10.  Back to cited text no. 5
[PUBMED]    
6.
Rohrschneider K, Burk RO, Kruse FE, Völcker HE. Reproducibility of the optic nerve head topography with a new laser tomographic scanning device. Ophthalmology 1994;101:1044-9.  Back to cited text no. 6
    
7.
Panuescu LA, Schuman JS, Price LL, Stark PC, Beaton S, Ishikawa H, et al. Reproducibility of nerve fiber thickness, macular thickness, and optic nerve head measurements using Stratus OCT. Invest Ophthalmol Vis Sci 2004;45:1716-24.  Back to cited text no. 7
    



 
 
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