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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 21  |  Issue : 3  |  Page : 180-186

Foveal avascular zone area measurements in a normal Egyptian population using Heidelberg optical coherence tomography angiography and its various correlations


1 Refractive Research Unit, Research Institute of Ophthalmology, Giza, Egypt
2 Medical Retina Unit, Research Institute of Ophthalmology, Giza, Egypt

Date of Submission16-Oct-2019
Date of Decision01-Dec-2019
Date of Acceptance01-Jan-2020
Date of Web Publication23-Sep-2020

Correspondence Address:
MD Tamer A Refai
Refractive Unit, Research Institute of Ophthalmology, 168-Nile Street, Agouza, Giza 12211
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/DJO.DJO_53_19

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  Abstract 


Purpose The aim of this study was to measure the foveal avascular zone (FAZ) area at both superficial and deep retinal capillary plexus levels in normal emmetropic and highly myopic eyes, using the Heidelberg optical coherence tomography angiography (OCTA) and to find its correlation with central macular thickness and volume and best-corrected visual acuity.
Patients and methods This is a prospective cross-sectional observational study that involved 69 normal emmetropic and highly myopic eyes of Egyptian patients. FAZ area (both at the superficial and deep capillary plexus levels), central macular thickness, and volume were measured by the Heidelberg OCTA. Best-corrected visual acuity in Illiterate E lines was also reported.
Results In normal individuals, the mean value of the FAZ was 0.38±0.11 mm2 for the superficial FAZ and 0.29±0.10 mm2 for the deep FAZ, with higher statistically significant values for the superficial FAZ size (P<0.05, t test=13.64). Pearson correlation test revealed a statistically significant negative correlation (P<0.05) between central macular thickness and both the superficial FAZ size (r=−0.33) and deep FAZ size (r=−0.39) and a highly significant negative correlation (P<0.01) between central macular volume and both superficial FAZ size (r=−0.40) and deep FAZ size (r=−0.42). Best-corrected visual acuity showed an insignificant correlation (P>0.05) with both superficial and deep FAZ size. Neither high myopia nor sex influenced the results.
Conclusion Using the Heidelberg OCTA in normal Egyptian individuals, the superficial FAZ size ranged from 0.19 to 0.85 mm2, which was larger than the deep FAZ, which ranged from 0.09 to 0.73 mm2. FAZ size measurements were strongly correlated with central macular thickness and volume. Neither high myopia nor sex influenced the results.

Keywords: best-corrected visual acuity, emmetropic eyes, Heidelberg (optical coherence tomography angiography), high myopia, superficial and deep retinal foveal avascular zone size


How to cite this article:
Refai TA, Hassanin OA, Fouly MA. Foveal avascular zone area measurements in a normal Egyptian population using Heidelberg optical coherence tomography angiography and its various correlations. Delta J Ophthalmol 2020;21:180-6

How to cite this URL:
Refai TA, Hassanin OA, Fouly MA. Foveal avascular zone area measurements in a normal Egyptian population using Heidelberg optical coherence tomography angiography and its various correlations. Delta J Ophthalmol [serial online] 2020 [cited 2020 Oct 30];21:180-6. Available from: http://www.djo.eg.net/text.asp?2020/21/3/180/295884




  Introduction Top


The foveal avascular zone (FAZ) is the area in the central macula that is devoid of retinal capillaries [1],[2]. It is highly specialized for sharp vision [3],[4]. Alterations in the FAZ area may be related to visual function and therefore could aid in the diagnosis and prognosis of retinopathies [5],[6],[7],[8],[9]. The size of the FAZ, for a longtime, was classically measured with fluorescein angiography [10]. However, measurement of FAZ size by fluorescein angiography carried the disadvantages of being associated with imperfections [11]. It also requires the administration of intravenous dye in addition to its inability to image the deep retinal capillary plexus separately from the superficial retinal capillary plexus [12],[13].

Optical coherence tomography angiography (OCTA) was introduced as a useful tool for evaluation of retinal vasculature in a rapid, noninvasive manner. It can provide higher resolution images than conventional fluorescein angiography [13], with the ability to accurately and separately image the deep retinal capillary plexus [12].

The aim of this study was to provide a guide for normative data of the FAZ area at both the superficial and deep retinal capillary plexuses in normal emmetropic and highly myopic eyes by the OCTA and to find its correlation with central macular thickness and volume and best-corrected visual acuity.


  Patients and methods Top


This is a prospective cross-sectional observational study. All participants signed a written informed consent to participate in the study and for publication of data. The study involved 69 normal eyes of Egyptian individuals without history or signs of retinal vascular diseases that could alter the FAZ diameter like hypertension and diabetes and without any previous intraocular surgery and without media opacities interfering with the acquisition of good-quality images. Approval of the Regional Ethical Committee was also obtained.

Eyes were divided into two groups: group A comprised emmetropic eyes, including eyes with no more than 1 D of refractive error, and group B comprised highly myopic eyes, with more than 6 D of myopia, with a range from −6.5 to −16.0 D. After full ophthalmic examination including slit-lamp examination both for anterior segment and posterior segment by fundus biomicroscopy and best-corrected visual acuity examination by Illiterate E chart, OCTA was done. The eyes were examined for FAZ size (both at the superficial and deep capillary plexus levels by using scanning mode 10°X5°, 256 sections, followed by manual outlining of good-quality processed photographs ([Figure 1]) rather than by subjective estimation. Central macular thickness was measured in μm (central 1 mm circle) as well as central macular volume in mm3 (central 1 mm circle) ([Figure 2]) by the Spectralis OCTA (Heidelberg Engineering, Heidelberg, Germany) using the full-spectrum amplitude–decorrelation algorithm with A-scan rate of 85 kHz.
Figure 1 FAZ size measurement by Heidelberg OCTA in some of our patients included in the study; upper pictures: Emmetropic eye, middle pictures: highly myopic eye, lower pictures: another highly myopic eye. OCTA, optical coherence tomography angiography.

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Figure 2 Central macular thickness and volume by Heidelberg OCTA in some of our patients included in the study. upper picture: Emmetropic eye, middle picture: highly myopic eye, lower picture: another highly myopic eye. OCTA, optical coherence tomography angiography.

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Studied items were subjected to statistical analysis using the statistical package for the social sciences software (SPSS Inc., Chicago, Illinois, USA), including mean, SD, minimum, and maximum as well as comparison by t test and correlation (Pearson) tests. P value more than 0.05 was considered statistically insignificant, whereas P value less than 0.05 was considered statistically significant, and P value less than 0.01 was considered highly significant.


  Results Top


A total of 69 eyes of 44 patients were included in the study, of which 42 eyes belonged to female patients and 27 eyes belonged to male patients. The age ranged from 16 to 83 years (mean=46.19±16.05 years). The superficial FAZ size ranged from 0.19 to 0.85 mm2 (mean=0.38±0.12 mm2). The deep FAZ size ranged from 0.09 to 0.73 mm2 (mean=0.29±0.10 mm2) ([Figure 3]). The central macular thickness ranged from 182 to 384 μm (mean=274.35±33.97 μm). The central macular volume ranged from 0.15 to 0.28 mm3 (mean=0.21±0.02 mm3). The best-corrected visual acuity ranged from 0.17 to 1.0 (mean=0.44±0.23) ([Table 1]).
Figure 3 showing mean superficial and deep FAZ size under study.

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Table 1 Mean values, SDs, and range of studied items

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The mean value of the FAZ was statistically significantly higher for the superficial FAZ than for the deep FAZ (t test=13.64, P<0.05, [Table 2]).
Table 2 Comparison between the size of the superficial and deep foveal avascular zone

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Pearson correlation test revealed a statistically significant negative correlation (P<0.05) between central macular thickness and each of the superficial FAZ size (r=−0.33) and deep FAZ size (r=−0.39). In addition, it revealed a highly significant negative correlation (P<0.01) between central macular volume and each of the superficial FAZ size (r=−0.40) and deep FAZ size (r=−0.42). However, an insignificant correlation (P>0.05) was found between best-corrected visual acuity and both of superficial FAZ size (r=0.02) and deep FAZ size (r=0.12) ([Table 3]).
Table 3 Pearson correlation between the foveal avascular zone size (mm2) and central macular thickness (μm), central macular volume (mm3) and best-corrected visual acuity

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Comparison of FAZ size measurements among emmetropic and highly myopic eyes revealed a higher mean value for superficial FAZ size in highly myopic eyes (0.39±0.11 mm2) than in emmetropic eyes (0.36±0.12 mm2); however, the difference was statistically insignificant (t test=−1.15, P=0.26). A comparable mean value for deep FAZ size was found in highly myopic eyes (0.29±0.10 mm2) and emmetropic eyes (0.29±0.11 mm2) (t test=0.04, P=0.97), denoting an insignificant difference ([Table 4] and [Figure 4]).
Table 4 Comparison between superficial foveal avascular zone size and deep foveal avascular zone size in emmetropic and highly myopic eyes

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Figure 4 showing mean superficial and deep FAZ size in emmetropic and highly myopic ayes under study.

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There were 27 eyes of male patients and 42 eyes of female patients. The superficial FAZ size was 0.35±0.10 mm2 in males and 0.39±0.12 mm2 in females, with a statistically insignificant difference (t test=−1.53, P=0.13). The deep FAZ size was 0.27±0.08 mm2in males and 0.30±0.11 mm2 in females, with also statistically insignificant difference (t test=−1.39, P=0.17).


  Discussion Top


OCTA is a useful tool that allows visualization of blood vessels in a noninvasive manner. Several OCTA devices had been used to image the retinal vasculature with different specifications and images. Among these devices is the XR Avanti AngioVue OCTA (Optovue Inc., Fremont, California, USA), which uses a split-spectrum amplitude–decorrelation angiography algorithm with A-scan rate of 70 kHz to extract the OCTA data on which several studies had been performed [14],[15] and the Zeiss AngioPlex (TM-Carl Zeiss Meditec Inc., Dublin, California, USA), which uses the optical microangiography algorithm with A-scan rate of 68 kHz to extract OCTA data, which was used to study normal healthy individuals [16],[17].

In previous studies, done by the XR Avanti AngioVue OCTA, Shahlaee et al. [18] studied 34 eyes of 17 healthy participants at the retina service of Wills Eye Hospital, UK. They found that the mean FAZ area was 0.27±0.101 mm2 at the superficial capillary network and 0.34±0.116 mm2 at the deep capillary network, and that measurements of FAZ area at the deep capillary network was subject to greater interobserver variability. In addition, Samara et al. [7] studied 70 eyes of healthy participants and they found that the size of the FAZ in the middle retina, that is, the deep capillary plexus was about 0.495±0.227 mm2, which was significantly larger than that of the inner retina, that is, the superficial capillary plexus, which was 0.266±0.097 mm2, and the FAZ size in both middle retina and inner retina was inversely correlated with central macular thickness and volume. Ghassemi et al. [14] studied 224 eyes of 112 volunteers with a mean age of 37.03 years (12–67 years). The mean superficial FAZ area was 0.27 mm2 and deep FAZ area was 0.35 mm2 (P<0.001), with no difference between both eyes. Females had a larger superficial FAZ (0.32±0.11 mm2 in females vs. 0.23±0.09 mm2 in males) and deep FAZ (0.40±0.14 mm2 in females vs. 0.31±0.10 mm2 in males) (P<0.001) than males. By multivariate linear regression analysis, in normal eyes, both superficial and deep FAZ areas varied with the sex and central foveal thickness. In addition, in a previous study done by Zeiss AngioPlex, Hussain and Hussain [16] studied eyes of 15 healthy young adults belonging to ethnic race from Middle East, India, and Philippines. The mean horizontal FAZ diameter of the superficial vascular plexus was 661.166 ±119.99 μm and the mean vertical FAZ diameter was 660.033±96.169 μm (P=0.9442). The mean horizontal FAZ diameter of the deep vascular plexus was 1011.2±154.526 μm, and the mean the vertical FAZ diameter of the deep vascular plexus was 818.033±102 μm. In the current study, done by Spectralis OCTA, we used the full-spectrum amplitude–decorrelation algorithm for extracting OCTA data. The mean value of the FAZ was 0.38±0.11 mm2 for the superficial FAZ, which was significantly higher than the deep FAZ (0.29±0.10 mm2). These results do not agree with previous studies using different OCTA machines. This might be related to a difference in autosegmentation of zones of the middle retina (i.e. the deep capillary plexus) and inner retina (i.e. the superficial capillary plexus) in the study with the Spectralis OCTA from other previously mentioned OCTA machines.

A statistically significant negative correlation was found, in the current study, between the central macular thickness and each of the superficial FAZ size and deep FAZ size. In addition, a highly significant negative correlation was found between central macular volume and each of the superficial FAZ size and deep FAZ size. These results agreed with previous studies done by Samara et al. [7] and Ghassemi et al. [14]. However, an insignificant correlation was found between best-corrected visual acuity and both of superficial FAZ size and deep FAZ size. Such correlation was not studied in the previously mentioned studies. No statistically significant differences were found in the FAZ size, in both superficial and deep capillary plexuses, between emmetropic and highly myopic eyes. However, slightly higher mean values were obtained, in the current study, for the superficial FAZ in highly myopic eyes (0.39±0.11 mm2) than in emmetropic eyes (0.36±0.12 mm2). Similarly, this comparison between emmetropic and highly myopic eyes was not studied in the previously mentioned studies. Sex showed no significant effect on the results, for both the superficial and deep FAZ. However, this does not agree with the study done by Ghassemi et al. [14], which was performed on a larger number of eyes using a different OCTA machine, that is, XR Avanti AngioVue OCTA.

In the present study, we tried to provide a guide for normative data for FAZ size variation in normal Egyptian individuals using the Heidelberg OCTA and its correlation with various factors. We recommend performing further studies on a wider scope to be able to produce normative data, hoping to be able to distinguish healthy from diseased eyes.


  Conclusion Top


Using the Heidelberg OCTA, in normal Egyptian individuals, the superficial FAZ size ranged from 0.19 to 0.85 mm2 (mean=0.38±0.12 mm2), whereas the deep FAZ ranged from 0.09 to 0.73 mm2 (mean=0.29±0.10 mm2), with higher values obtained for the superficial FAZ size. FAZ size measurements were strongly correlated with central macular thickness and volume. No statistically significant difference was found between emmetropic and highly myopic eyes for both the superficial and deep FAZ.

Acknowledgements

Acknowledgments are made for the Research Institute of Ophthalmology, Giza, Egypt, for funding that research.

The study was supported by the Research Institute of Ophthalmology.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
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