About us |  Subscription |  Top cited articles |  e-Alerts  | Feedback |  Login   
  Home | Ahead of print | Current Issue | Archives | Search | Instructions Celebrating 60 Years   Print this article Email this article   Small font sizeDefault font sizeIncrease font size
 
 Official publication of All India Ophthalmological Society   Users Online: 77
  Search
 
   Next article
   Previous article 
   Table of Contents
  
 
    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Article in PDF (236 KB)
    Citation Manager
    Access Statistics
    Reader Comments
    Email Alert *
    Add to My List *
* Registration required (free)  


    Abstract
    Materials and Me...
    Results
    Discussion
    References
    Article Figures
    Article Tables

 Article Access Statistics
    Viewed6815    
    Printed175    
    Emailed13    
    PDF Downloaded415    
    Comments [Add]    
    Cited by others 19    

Recommend this journal

 


 
ORIGINAL ARTICLE
Year : 2006  |  Volume : 54  |  Issue : 1  |  Page : 11-15
 

Retinal nerve fibre layer thickness measurements in normal Indian population by optical coherence tomography


Aravind-Zeiss Centre of Excellence for Glaucoma, Aravind Eye Hospital, Tirunelveli, Tamil Nadu, India

Correspondence Address:
R Ramakrishnan
Aravind-Zeiss Centre of Excellence for Glaucoma, Aravind Eye Hospital, Tirunelveli, Tamil Nadu - 627001
India
Login to access the Email id


DOI: 10.4103/0301-4738.21608

PMID: 16531664

Get Permissions

 

   Abstract 

Purpose: To obtain retinal nerve fibre layer thickness measurements by optical coherence tomography (OCT) in normal Indian population. Materials and Methods: Total of 118 randomly selected eyes of 118 normal Indian subjects of both sex and various age groups underwent retinal nerve fiber layer thickness analysis by Stratus OCT 3000 V 4.0.1. The results were evaluated and compared to determine the normal retinal nerve fiber layer thickness measurements and its variations with sex and age. Results: Mean + standard deviation retinal nerve fiber layer thickness for various quadrants of superior, inferior, nasal, temporal, and along the entire circumference around the optic nerve head were 138.2 + 21.74, 129.1 + 25.67, 85.71 + 21, 66.38 + 17.37, and 104.8 + 38.81 Ám, respectively. There was no significant difference in the measurements between males and females, and no significant correlation with respect to age. Conclusion: Our results provide the normal retinal nerve fiber layer thickness measurements and its variations with age and sex in Indian population.


Keywords: Diagnostic techniques in glaucoma, imaging in glaucoma, optical coherence tomography, retinal nerve fiber layer


How to cite this article:
Ramakrishnan R, Mittal S, Ambatkar S, Kader MA. Retinal nerve fibre layer thickness measurements in normal Indian population by optical coherence tomography. Indian J Ophthalmol 2006;54:11-5

How to cite this URL:
Ramakrishnan R, Mittal S, Ambatkar S, Kader MA. Retinal nerve fibre layer thickness measurements in normal Indian population by optical coherence tomography. Indian J Ophthalmol [serial online] 2006 [cited 2014 Jul 24];54:11-5. Available from: http://www.ijo.in/text.asp?2006/54/1/11/21608


Optical coherence tomography (OCT) is a new diagnostic computerized technique, which is used for generating in vivo images of retinal nerve fiber layer (RNFL) thickness which is reproducible, quantitative, and objective.[1] OCT works on the principle of low-coherence interferometry, which generates retinal tomographs with <10 Ám axial and approximately 20 Ám transverse resolution.[1] OCT thus produces high-resolution cross-section images of the posterior pole of the eye, and can be useful in glaucoma diagnosis for its ability to study the diffuse and localized thinning of RNFL.[2],[3],[4] Ethnic differences in RNFL thickness have been reported with nerve fiber analyzer.[5] Therefore, one can expect a difference in RNFL thickness on OCT for Indian population. As the OCT normal database is commercially not available for Indian eyes, we aimed to study the RNFL measurement profile by OCT for the normal Indian population. These measurements will provide a reference for the comparison and further evaluation of results of glaucoma and other patients with the help of OCT in Indian population.


   Materials and Methods Top


This study was conducted at the Aravind-Zeiss Center for Excellence in Glaucoma, Tirunelveli, from March 2003 to May 2003. The subjects were either healthy patients presenting for eye evaluation with complaints of refractive errors, or they were the staff members of hospital without a diagnosis of glaucoma. All subjects underwent anterior segment slit-lamp examination, Goldman applanation tonometry, gonioscopy, and stereoscopic fundus examination by a 78D lens to exclude any anterior or posterior segment pathology. Patients with a history of diabetes mellitus, cardiac disease, ocular trauma, intraocular surgery, laser therapy, family history of glaucoma, best-corrected visual acuity of less than 20/30, hypermetropia more than + 3D, myopia more than - 5D, or astigmatism more than 2D (checked on Topcon autorefractometer RM A7000) were excluded from the study.

Normal-appearing disc, cup, and neuroretinal rim on careful examination of optic nerve head with 78D aided stereoscopic slit-lamp indirect ophthalmoscopy, with cup-disc ratio of less than 0.7 or cup-disc ratio asymmetry of less than 0.2 being the selection criteria for further evaluation.

After making above exclusions, 134 normal subjects (21-76 years) consisting of 70 (52.3%) males and 64 (47.7%) females, stratified for both sexes into subgroups with frequency distribution of 10 years, the starting age being 20 years, were randomly selected. Informed consent was obtained from all subjects. Automated visual-field examination was done using 24-2 Swedish interactive thresholding algorithm standard visual-field examination (Humphery visual-field analyzer, model 750). An abnormal visual field was defined as the presence of any one of the following three criteria defined by Anderson:[6] (1) a glaucoma hemifield test outside normal limits, (2) P < 5% for corrected pattern standard deviation, (3) a cluster of at least three contiguous nonedge points with P < 5%, including at least one of these with P < 1% in the pattern-deviation plot. Nine subjects on the basis of abnormal visual fields and seven on the basis of unreliable fields were excluded from the study. Unreliable fields were those with fixation loss >20% and false-positive or false-negative ratio > 33%.[6]

Selected cases (118 subjects-61 males and 57 females, 21-74 years) underwent OCT (Stratus OCT 3000; Carl Zeiss Ophthalmic Systems-Humphrey Division, Dublin, CA, USA) evaluation for both eyes, following pupillary dilatation with 1% tropicamide and 5% phenylephrine.[4] Single experienced observer captured images with the patient fixating at the internal fixation target.[7] A rough setting of subject's refraction (spherical equivalent) was recorded into the machine. After acquiring the best possible fixation and clear retinal video image, RNFL of each eye was imaged using fast-RNFL-thickness 3.4 scanning protocol, which automatically records three circular scans of diameter 3.4 mm around the center of the optic disc for 256 points along the scanning circle.

Measurements were then assessed using RNFL thickness average analysis protocol. These scanning and analysis tools are part of the Stratus OCT 3000 Application Version V4.0.1 software provided in the OCT 3000. Quality of scanned image was assessed on the basis of signal-to-noise ratio (SNR) and accepted A-scan percentage values. As a guideline, an A-scan was considered good if the maximum of each A-scan in the image is at least 6 dB above the noise floor in 95% of axial scan length or has a SNR greater than 31 dB. Finally, the quality of scan image was subjectively assessed to notice the richness of red and yellow color, which if high, suggests a good scan.[8] The scans were repeated till we obtained good image quality based on the above criteria.

Mean RNFL thickness in micrometers along the whole circle circumference, four quadrants, twelve clock hours, and at 256 A-scan lengths were obtained. The sectors were defined in degrees, wherein 0║ was temporal horizontal point and the 360║ measurements along the circle were clockwise in right eye and anticlockwise in left eye. Superior quadrant was from 45░ to 135░, nasal from 135░ to 225░, inferior from 225░ to 315░, and temporal quadrant was from 315░ to 45░. Twelve 30░ sectors were also defined in clockwise order for right eye and in counterclockwise order for the left eye ([Figure - 1]: 1-superior-nasal, 2-nasal-superior, 3-nasal, 4-nasal-inferior, 5-inferior-nasal, 6-inferior, 7-inferior-temporal, 8-temporal-inferior, 9-temporal, 10-temporal-superior, 11-superior-temporal, and 12-superior). Maximum RNFL thickness in superior and inferior quadrants was also analyzed. Other parameters such as Smax/Imax, Smax/Tavg, Imax/Tavg, Smax/Navg, and max-min, provided with RNFL thickness average analysis protocol are dependent on the above parameters, and were thus not studied.

Statistical analysis

Previous reports estimate the mean RNFL thickness[3],[9],[10],[11]ranging between 85.8 and 127 Ám and their standard deviation[9],[10],[11]ranging between 11 and 14.17 Ám on OCT analysis. Expecting to get RNFL thickness results with significant difference ( d ) of 10 Ám, power of 80% (Za=0.842) and significance level of 0.01 (Zβ=2.576) was used to determine the sample size. The sample size was determined using the formula n= 2 ( Za+Zβ) 2 S 2 /d 2 . Considering the standard deviation ( S ) of 14.17, the minimum sample size calculated was 84.

Data at 256 A-scan lengths were analyzed to provide the average, standard deviations, 95% confidence intervals, and normal distribution percentiles of RNFL thickness at 95%, 5%, and 1% of the sample population. Student's t -test for independent variables was used to compare the results for different sex. Pearson correlation coefficient and linear regression analysis was done to determine the effect of age on RNFL measurements. Measurements of average, quadrants, and clock hours of RNFL were compared for sex and age.


   Results Top


Of 134 enrolled subjects, 118 eyes of 118 subjects were studied with respect to their sex and age. There were 61 (51.7%) male and 57 (48.3%) female subjects with mean age of 45.2 + 13.56 years (range: 21-74 years). There were 33 (28.0%) myopic, 54 (45.8%) emmetropic, and 31 (26.3%) hypermetropic eyes with refraction ranging from -4.50 to + 2.75 Diopters of spherical equivalent. Mean peripapillary RNFL thickness on average was 105 + 38.79 Ám, with 95% confidence interval ranging from 97.8 to 111.8 Ám. RNFL thickness for superior, inferior, nasal, and temporal quadrants were 138.2 + 21.74 (95% CI: 134.3-142.1), 129.1 + 25.67 (95% CI: 124.5-133.7), 85.71 + 21 (95% CI: 81.9-89.5), and 66.38 + 17.37 (95% CI: 63.3-69.5) Ám, respectively. The mean RNFL thickness in four quadrants and for all clock hours is provided in [Table - 1]. The mean RNFL thickness was highest in the superior quadrant followed by inferior, nasal, and temporal quadrants [Table - 1]. The average A-scan data at 256 points formed a wave-like pattern with the superior and inferior quadrants forming the crest, and the temporal and nasal ones forming the trough, as seen in [Figure - 2]. There was no statistical difference regarding the sex [Table - 1] and no statistical correlation between the age and the average RNFL thickness [Table - 2]. Percentile levels at 95%, 5%, and 1% for the normal distribution are provided in [Table - 3] and displayed in [Figure - 2].


   Discussion Top


Several instruments and techniques are used for the analysis of the optic nerve head, with the idea of detecting glaucomatous damage in its early stages, even before the functional field loss is detectable.[12] OCT provides an assessment of the RNFL thickness by passing a near-infrared illumination (840 nm) beam into the eye and studying its reflectivity patterns by computer-assisted software. No reference plane is required to calculate RNFL thickness because OCT provides an absolute cross-sectional measurement of the retinal substructure, from which the RNFL thickness is calculated.[4] RNFL is seen as red-colored high-reflectivity zone adjacent to optically zero-reflective vitreous.[13],[14] RNFL thickness in previous studies have shown the high reproducibility[7] and reliability[13] of the new OCT machines and software, thus making it an important tool in glaucoma diagnosis and management. OCT has been recently introduced in India and the normative profile of various measurements is not established for the Indian population.

Average nerve fiber thickness along the 3.4-mm-diameter circle around the optic nerve head was approximately 105 Ám. RNFL thickness was found to be more in superior followed by that of the inferior, nasal, and temporal quadrant, suggesting that ISNT rule does not apply to this subgroup of Indian population [Table - 1]. Overall measurements produced a double-hump pattern curve [Figure - 2], similar to the one previously reported with OCT and on histopathology.[15]

We noticed a significant difference in the average RNFL thickness between our group and other groups [Table - 4]. Mistlberger et al.[9] and Bowd et al.[3] reported a lower average nerve fiber layer thickness, whereas Soliman et al. ,[10] Mok et al.,[16] Carpineto et al. ,[13] and Guedes et al.[11] showed higher values compared with our study. This difference can be owing to different populations studied, difference in sample size, and changing OCT machine parameters. The comparison and summary of previous reports of RNFL thickness in normal individuals is provided in [Table - 4].

There was no significant difference seen between males and females for mean, quadrant, and clockwise RNFL thickness. There was a decrease in mean RNFL thickness with respect to age, but it was not statistically significant. Decline in RNFL thickness owing to loss of ganglion cells with age[17] has been stated in the previous OCT[16] and histopathological[14],[15] studies. Study with higher sample size may be required to highlight the above change in our population.

Similar to age-matched normative data with the OCT analysis protocol, we studied the 95%, 5%, and 1% levels of RNFL thickness for average, quadrants, and clock hours among our normal population sample [Table - 3]. These measurements help determining the thinnest, below 1% RNFL thickness, which is outside normal and is expected to be pathological. Measurements falling above 5% level are considered normal and represent 95% of population. Measurement falling between the 5% and 1% level comprise a borderline group and requires careful monitoring.

OCT normal database commercially available with Stratus OCT does not provide information on ethnic difference within its data groups and does not provide the information on numerical data. In our analysis of RNFL thickness in our subjects with normal optic disc and visual fields, we found that 11 (9.3%) eyes had clock hour thickness falling below 5% level on comparison with normative data provided with Stratus OCT having borderline. This indicates at the possibility of ethnic differences existing with Indian population being different form other groups. Although a larger sample size is required to find out the above difference, we recommend the percentile levels as provided in [Table - 3], which can assist in identifying cases distinguished as borderline on comparison with normative data by Stratus OCT machine.

In conclusion, we have obtained estimated normal RNFL measurements in Indian population using stratus OCT 3000. These measurements may serve as a reference during glaucoma screening with OCT in Indian population.





 
   References Top

1.Hee MR, Izatt JA, Swanson EA, Huang D, Schuman JS, Lin CP, et al . Optical coherence tomography of the human retina. Arch Ophthalmol 1995;113:325-32.  Back to cited text no. 1    
2.Zangwill LM, Williams J, Berry CC, Knauer S, Weinreb RN. A comparison of optical coherence tomography and retinal nerve fibre layer photography for the detection of nerve fibre layer damage in glaucoma. Ophthalmology 2000;107:1309-15.  Back to cited text no. 2  [PUBMED]  [FULLTEXT]
3.Bowd C, Weinreb RN, Williams JM, Zangwill LM. The retinal nerve fibre layer thickness in ocular hypertensive, normal, and glaucomatous eyes with optical coherence tomography. Arch Ophthalmol 2000;118:22-6.   Back to cited text no. 3    
4. Schuman JS. Optical coherence tomography for imaging and quantitation of nerve fibre layer thickness. In : Schuman JS, editor. Imaging in Glaucoma . USA: Slack Incorporate; 1997. pp. 95-103.   Back to cited text no. 4    
5.Poinosawmy D, Fontana L, Wu JX, Fitzke FW, Hitchings RA. Variation of nerve fibre layer thickness measurements with age and ethnicity by scanning laser polarimetry. Br J Ophthalmol 1997;81:350-4.  Back to cited text no. 5    
6.Anderson DR, Patella VM. Interpretation of single field. In: Anderson DR, Patella VM, editor. Automated Static Perimetry , 2nd ed.: St. Louis: Mosby; 1999. pp. 121-90.  Back to cited text no. 6    
7.Schuman JS, Pedut-Kloizman T, Hertzmark E, Hee MR, Wilkins JR, Coker JG, et al . Reproducibility of nerve fibre layer thickness measurements using optical coherence tomography. Ophthalmology 1996;103:1889-98.  Back to cited text no. 7    
8.Analysis protocols. User manual stratus OCT model 3000 . Dubin: Carl Ziess Meditec Inc; 2002. p. 3.  Back to cited text no. 8    
9.Mistlberger A, Liebmann J, Greenfield DS, Pons ME, Hoh ST, Ishikawa H, et al . Heidelberg retinal tomograph and optical coherence tomography in normal, ocular hypertensive and glaucomatous eyes. Ophthalmology 1999;106:2027-32.  Back to cited text no. 9    
10.Soliman MA, Thomas JT, Berg VD, Ismaeil AA, De Jong LA, De Smet MD. Retinal nerve fibre layer analysis: Relationship between optical coherence tomography and red-free photography. Am J Ophthalmol 2002;133:187-95.  Back to cited text no. 10    
11.Guedes V, Schuman JS, Hertzmark E, Wollstein, Correnti A, Mancini R, et al . Optical coherence tomography measurements of macular and nerve fibre layer thickness in normal and glaucomatous eyes. Ophthalmology 2003;110:177-89.  Back to cited text no. 11    
12.Schuman JS, editor. Imaging in Glaucoma . USA: Slack Incorporate; 1997. pp. 63-130.   Back to cited text no. 12    
13.Carpineto P, Ciancaglini M, Zuppardi E, Falconio G, Doronzo E, Mastropasqua L. Reliability of nerve fibre layer thickness measurements using optical coherence tomography in normal and glaucomatous eyes. Ophthalmology 2003;110:190-5.  Back to cited text no. 13  [PUBMED]  [FULLTEXT]
14.Toth CA, Narayan DG, Bopport SA, Hee MR, Fujimoto JG, Birngruber R, et al . A comparison of retinal morphology viewed by optical coherence tomography and light microscopy. Arch Ophthalmol 1997;115:1425-8.  Back to cited text no. 14    
15.Mikelberg FS, Drance SM, Yidegiligne HM, White VA, Schulzer M. Relation between optic nerve axon number and axon diameter to scleral canal area. Ophthalmology 1991;98:60-3.  Back to cited text no. 15    
16.Mok KH, Lee VW, So KF. Retinal nerve fibre layer measurement of the Hong Kong Chinese population by optical coherence tomography. J Glaucoma 2002;11:481-3.  Back to cited text no. 16  [PUBMED]  [FULLTEXT]
17.Jonas JB, Schmidt AM, Muller-Bergh JA, Schlotzer-Schrehardt UM, Naumann GO. Human optic nerve fibre count and optic disc size. Invest Ophthalmol Vis Sci 1992;33:2012-8.  Back to cited text no. 17  [PUBMED]  [FULLTEXT]


    Figures

[Figure - 1], [Figure - 2]

    Tables

[Table - 1], [Table - 2], [Table - 3], [Table - 4]


This article has been cited by
1 Adjusted color probability codes for peripapillary retinal nerve fiber layer thickness in healthy Koreans
Samin Hong,Sang-Myung Kim,Kyoungsoo Park,Jun Lee,Chan Kim,Gong Seong
BMC Ophthalmology. 2014; 14(1): 38
[Pubmed]
2 Retinal Nerve Fiber Layer Imaging with Spectral-Domain Optical Coherence Tomography
Christopher K.S. Leung, Marco Yu, Robert N. Weinreb, Cong Ye, Shu Liu, Gilda Lai, Dennis S.C. Lam
Ophthalmology. 2012;
[VIEW]
3 Automated diagnosis of diabetic retinopathy and glaucoma using fundus and OCT images
Arulmozhivarman Pachiyappan,Undurti N Das,Tatavarti VSP Murthy,Rao Tatavarti
Lipids in Health and Disease. 2012; 11(1): 73
[Pubmed]
4 Predictors of normal optic nerve head, retinal nerve fiber layer, and macular parameters measured by spectral domain optical coherence tomography
Rao, H.L., Kumar, A.U., Babu, J.G., Kumar, A., Senthil, S., Garudadri, C.S.
Investigative Ophthalmology and Visual Science. 2011; 52(2): 1103-1110
[Pubmed]
5 Evaluation of the Nerve Fiber Layer and Macula in the Eyes of Healthy Children Using Spectral-Domain Optical Coherence Tomography
Adem Turk, Osman Melih Ceylan, Ceyhun Arici, Soner Keskin, Cuneyt Erdurman, Ali Hakan Durukan, Fatih Mehmet Mutlu, Halil Ibrahim Altinsoy
American Journal of Ophthalmology. 2011;
[VIEW]
6 Linking structure and function in glaucoma
R.S. Harwerth,J.L. Wheat,M.J. Fredette,D.R. Anderson
Progress in Retinal and Eye Research. 2010; 29(4): 249
[Pubmed]
7 Linking structure and function in glaucoma
Harwerth, R.S., Wheat, J.L., Fredette, M.J., Anderson, D.R.
Progress in Retinal and Eye Research. 2010; 29(4): 249-271
[Pubmed]
8 Evaluation of factors associated with variability in retinal nerve fiber layer thickness in myopic juveniles aged 7-18 years
Chen, W., Fu, P., Yang, Q., Tao, R., Liu, Y., Wu, Y.-C., Lu, Q.-P.
Chinese Journal of Ophthalmology. 2010; 46(11): 1011-1015
[Pubmed]
9 A test of a linear model of glaucomatous structure-function loss reveals sources of variability in retinal nerve fiber and visual field measurements
Hood, D.C., Anderson, S.C., Wall, M., Raza, A.S., Kardon, R.H.
Investigative Ophthalmology and Visual Science. 2009; 50(9): 4254-4266
[Pubmed]
10 Retinal nerve fiber layer thickness in normal, ocular hypertensive, and glaucomatous Indian eyes: An optical coherence tomography study
Gyatsho, J., Kaushik, S., Gupta, A., Pandav, S.S., Ram, J.
Journal of Glaucoma. 2008; 17(2): 122-127
[Pubmed]
11 Modeling the effects of aging on retinal ganglion cell density and nerve fiber layer thickness
Harwerth, R.S. and Wheat, J.L.
GraefeŠs Archive for Clinical and Experimental Ophthalmology. 2008; 246(2): 305-314
[Pubmed]
12 Retinal Nerve Fiber Layer Thickness Measured by Optical Coherence Tomography in Non-glaucomatous Taiwanese
Peng, P.H. and Lin, H.S.
Journal of the Formosan Medical Association. 2008; 107(8): 627-634
[Pubmed]
13 Age-Related Losses of Retinal Ganglion Cells and Axons
Harwerth, R.S. and Wheat, J.L. and Rangaswamy, N.V.
Investigative Ophthalmology \& Visual Science. 2008; 49(10): 4437-4443
[Pubmed]
14 Retinal and optic disc findings in adolescence: A population-based OCT study
Huynh, S.C., Xiu, Y.W., Burlutsky, G., Rochtchina, E., Stapleton, F., Mitchell, P.
Investigative Ophthalmology and Visual Science. 2008; 49(10): 4328-4335
[Pubmed]
15 Retinal Nerve Fiber Layer Thickness in Normal, Ocular Hypertensive, and Glaucomatous Indian Eyes
Jamyang Gyatsho,Sushmita Kaushik,Amod Gupta,Surinder Singh Pandav,Jagat Ram
Journal of Glaucoma. 2008; 17(2): 122
[Pubmed]
16 Retinal Nerve Fiber Layer Thickness Measured by Optical Coherence Tomography in Non-glaucomatous Taiwanese
Pai-Huei Peng,Huey-Shyan Lin
Journal of the Formosan Medical Association. 2008; 107(8): 627
[Pubmed]
17 Retinal nerve fiber layer measurements by optical coherence tomography in Indian eyes
Sony, P.
Indian Journal of Ophthalmology. 2007; 55(1): 79-80
[Pubmed]
18 AuthorsŠ reply
Ramakrishnan, R., Mittal, S., Ambatkar, S., Kader, M.A.
Indian Journal of Ophthalmology. 2007; 55(1): 80
[Pubmed]
19 Retinal nerve fiber layer measurements in myopia: An optical coherence tomography study
Leung, C.K.-S., Mohamed, S., Leung, K.S., Cheung, C.Y.-L., Chan, S.L.-W., Cheng, D.K.-Y., Lee, A.K.-C., (...), Lam, D.S.C.
Investigative Ophthalmology and Visual Science. 2006; 47(12): 5171-5176
[Pubmed]



 

Top
Print this article  Email this article
Previous article Next article

    

ę 2005 - Indian Journal of Ophthalmology
Published by Medknow

Online since 1st April '05