|Year : 2015 | Volume
| Issue : 2 | Page : 85-88
Retinal Nerve Fibre Layer Measurements in Normal Eyes in Zaria Using Optical Coherence Tomography
Fatima A Mahmud-Ajeigbe, Halima A AbdulRahman, AbdulKadir L Rafindadi, Emmanuel R Abah
Department of Ophthalmology, Ahmadu Bello University Teaching Hospital, Shika, Zaria, Nigeria
|Date of Submission||24-Dec-2014|
|Date of Acceptance||25-Mar-2015|
|Date of Web Publication||20-May-2015|
Dr. Fatima A Mahmud-Ajeigbe
Department of Ophthalmology, Ahmadu Bello University Teaching Hospital, Shika, Zaria
Purpose: To determine the retinal nerve fiber layer (RNFL) measurements in normal eyes in Zaria and to investigate the effect of age and axial length on RNFL thickness. Materials and Methods Forty eyes of 40 healthy subjects aged between 18 and 73 underwent peripapillary RNFL thickness measurement by a series of three circular scans with a 3.4 mm diameter (Stratus optical coherence tomography, RNFL thickness 3.4 acquisition protocol). The mean RNFL values were correlated with age and axial length. The statistical analysis used was Pearson's coefficient of correlation, linear regression, and paired t-test with the analyse-it® software for Excel. Results: The mean age of the subjects was 35 years, range18.0-73.0 years. Mean RNFL thickness global average was 107.055 μm standard deviation (SD 9.219 μm) with the RNFL in the superior quadrant being the thickest (mean: 139.0 mm SD 15.0 mm), there was no significant correlation with axial length in this study (P = 0.56) but there was a negative correlation between global RNFL average and age (r = 0.56 P = 0.0002). Conclusion: This study provides normative RNFL values for normal eyes in Zaria locality. It can be used as a reference for the normal measurements of RNFL in this environment. Age demonstrates a significant negative correlation with RNFL thickness.
Keywords: Age, optical coherence tomography, retinal nerve fibre layer
|How to cite this article:|
Mahmud-Ajeigbe FA, AbdulRahman HA, Rafindadi AL, Abah ER. Retinal Nerve Fibre Layer Measurements in Normal Eyes in Zaria Using Optical Coherence Tomography. Sub-Saharan Afr J Med 2015;2:85-8
|How to cite this URL:|
Mahmud-Ajeigbe FA, AbdulRahman HA, Rafindadi AL, Abah ER. Retinal Nerve Fibre Layer Measurements in Normal Eyes in Zaria Using Optical Coherence Tomography. Sub-Saharan Afr J Med [serial online] 2015 [cited 2019 Oct 20];2:85-8. Available from: http://www.ssajm.org/text.asp?2015/2/2/85/157430
| Introduction|| |
Optical coherence tomography (OCT) is an important adjunctive diagnostic tool in the management of diseases of the retina and optic nerve.
Optical coherence tomography is a non-invasive imaging technology used to obtain high resolution cross-sectional images of the retina. OCT is similar to ultrasound testing, except that imaging is performed by measuring light rather than sound. 
Optical coherence tomography uses low coherence interferometry to produce a two dimensional cross-sectional image of optical tissues by measuring the echo time delay and intensity of backscattered or back reflected light from microstructures inside tissues in a way that is analogous to ultrasonic pulse-echo imaging giving high resolution images of the structures. 
High resolution imaging of retinal structures is clinically relevant for the diagnosis of a variety of conditions such as Glaucoma, and various diseases of the macular.
Retinal nerve fiber layer (RNFL) assessment is important in the management of glaucoma. ,, This is because it has been found that RNFL loss precedes the development of visual field loss in Glaucoma patients.  Other imaging methods of assessing the RNFL such as scanning laser polarimetry and Heidelberg retinal tomography have been found to be objective with reproducible measurements as has the OCT. ,,,,,
It is therefore necessary to have normative values for different populations as RNFL thickness has been shown to differ with age and race. ,
However, there are as yet no published studies that have attempted to establish normative values for RNFL measurements in healthy Nigerian eyes.
This study was to determine the RNFL measurements in normal and healthy Nigerian eyes in Zaria and environs and to investigate the effect of age and axial length on RNFL thickness.
| Materials and Methods|| |
The study took place between January and April 2012 in a Hospital in Zaria, Kaduna State, Nigeria. Subjects were randomly selected from the Ophthalmology Out-patient Clinic of the hospital. A consecutive sampling was done of the subjects who were patients that presented to the clinic for minor ailments such as conjunctival inflammations or refractive errors, it also included the patients' relatives or attendants who had no evidence of ocular disease. The study was carried out according to the declaration of Helsinki and verbal informed consent was obtained from all subjects. Any Subjects above the age of 18 years were eligible for the study.
- Any history or evidence of pathological conditions of the retina
- Any history or evidence of diabetes mellitus or any other systemic disease that could affect the eye
- Any history or evidence of glaucoma, or of first degree relative with glaucoma or intraocular pressure >21 mmHg
- Any history of intraocular surgery or laser therapy
- Best corrected visual acuity worse than 6/18 and refractive error of more than 5.00 DS.
All subjects had a complete ophthalmic examination which included:
- Visual acuity and refraction
- Slit lamp examination of anterior segments and +90 D exam of posterior segment
- Applanation tonometry
- A-scan ultrasonography
Optical Coherence Tomography
All included subjects were scanned with the Zeiss Optical Coherence Tomographer Stratus OCT® version 4.0.2 (Carl Zeiss Meditec Inc. Dublin, CA, USA). The peripapillary RNFL was scanned using the Fast RNFL Thickness (3.4) scanning protocol, and the best quality of scans was chosen as signified by a signal strength of 8 or greater. This was then analyzed using the RNFL Volume/tabular analysis protocol. Data analysis was done using the analyze-it program for excel software, and parameters used were Pearson's coefficient of correlation, linear regression, and paired t-test. A P-value < 0.05 was considered significant.
| Results|| |
Forty eyes of 40 subjects were examined. There was a female to male ratio of 3:1. The mean age of the subjects was 35.0 ± 13.3 years with the youngest subject being 18 years and the oldest 73 years [Figure 1]. The global RNFL thickness average for the subjects in this study was 107.06 ± 9.22 μm [Figure 2], the superior quadrant had an average measurement of 139.0 ± 15.0 μm, the inferior 135.8 ± 16.7 μm, the nasal 85.8 ± 17.7 μm, and the temporal quadrant an average of 67.7 ± 12.6 μm [Table 1].
The average RNFL thickness demonstrated a decrease in thickness with advancing age and there was a significant negative correlation with age r = −0.56, P = 0.0002 (Pearson's coefficient) [Figure 3]. The superior and inferior quadrants also had significant negative correlation with age (r = −0.38, P = 0.015 and r = −0.37, P = 0.019 respectively).
The difference between the superior and Inferior quadrants was not statistically significant. t = 1.18 P = 0.244 (paired t-test).
In our series the superior quadrant had the thickest RNFL followed by the Inferior, nasal and temporal quadrants [Table 1].
There was no significant correlation between the Global Mean RNFL thickness and axial length (P = 0.56).
| Discussion|| |
With the damage that occurs to the RNFL in Glaucoma, ,, the OCT becomes an invaluable adjunctive tool in the diagnosis and monitoring of patients with glaucoma. Studies have shown a correlation between OCT findings and functional abnormalities in Glaucoma patients. ,, These make it imperative for there to be normal values for different populations as it has also been suggested that there may be racial differences in RNFL thickness.  This study presents data for the Nigerian population living within Zaria and its environs.
The mean RNFL thickness in our study was 107.06 ± 9.22 μm which was similar to that reported by Hsu (107.4 ± 17.8 μm) in Taiwan  and Alamouti in Germany (109 ± 22 μm)  but varied with that reported from some others. ,,,, This is not surprising as RNFL has been shown to vary with race. , [Table 2] shows the mean RNFL values from previous studies. ,,,,,, In this study there was a significant negative correlation of mean RNFL thickness with age (r = −0.56, P = 0.0002). This was similar to previous studies. ,,,,,, The superior and Inferior quadrant RNFL thicknesses also had significant negative correlation with age which was also reported by Sony et al.  and Sung et al.  There was however no significant correlation with the nasal or temporal quadrants in our series though Kanamori et al.  and Sung et al.  reported negative correlations of the temporal and nasal quadrants respectively with age. Some investigators had reported no significant correlation of RNFL parameters with age. ,
The mean RNFL measurement was thickest in the superior quadrant (139 ± 15.0 μm) in this study followed by the inferior (135.8 ± 16.7 μm), nasal (85.8 ± 17.7 μm) then temporal (67.7 ± 12.6 μm) quadrants [Table 1]. There was also no statistically significant difference between the superior and inferior quadrant RNFL measurements. These suggest that the ISNT rule does not apply in this population. Kanamori et al. in Japan showed a similar pattern as ours where they found that the Superior quadrant thickness was higher than the inferior quadrant thickness,  while Sony et al. in India found the opposite and also found no significant difference between the superior and inferior quadrants RNFL thicknesses as we did in our study. 
These differences in quadrant RNFL thickness might also be explained by racial differences.
In this study we found no correlation between the RNFL thickness and axial length (P = 0.56) which was similar to what Pakravan et al. in Iran  found in their investigations but Budenz in the United States of America and Yoo in Korea , found a negative correlation of global average RNFL with axial length, with the RNFL getting thinner as the axial length increased.
| Conclusion|| |
This study provides normative data for normal eyes in Zaria and it's environs. These measurements may serve as reference values and guidelines in assessment of the RNFL.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]