|Year : 2017 | Volume
| Issue : 1 | Page : 22-27
Choroidal thickness in healthy Egyptians and its correlation with age
Mona K Abdellatif
Department of Ophthalmology, Ain Shams University, Cairo, Egypt
|Date of Submission||31-Jul-2016|
|Date of Acceptance||06-Mar-2017|
|Date of Web Publication||17-May-2017|
Mona K Abdellatif
30 Emtedad Ramsis 2, 2nd Floor, APT 21, Cairo - 11471
Source of Support: None, Conflict of Interest: None
Purpose The aim of this study was to investigate choroidal thickness in healthy Egyptians and its correlation with age.
Patients and methods This cross-sectional study included 134 eyes of 89 healthy Egyptians who were divided into three age groups: group 1, 20–40 years old; group 2, 40–60 years old; and group 3, more than 60 years old. Spectral-domain optical coherence tomography using enhanced depth imaging was used to calculate choroidal thickness map in the macular area. Eyes with high myopia and hyperopia were excluded.
Results The mean (±SD) central choroidal thickness was 337.23±37.51, 285.29±31.23, and 270.24±22.37 µm in groups 1, 2, and 3 consecutively (P<0.001). The choroidal thickness was highest in the central 1 mm zone, followed by the superior quadrant, and the thinnest quadrant was the nasal one in the three groups. Regression analysis showed significant choroidal thickening in group 1 (B=4.941, P=0.001), nonsignificant thinning in group 2 (B=−0.301, P=0.739), and significant thinning in group 3 (B=−3.774, P=0.001).
Conclusion Choroidal thickness varies significantly with age. Significant choroidal thinning starts in the fifth decade of life, but is more statistically significant after the age of 60 years. This proves that choroidal thinning is not fixed in all age groups.
Keywords: age, choroidal thickness, enhanced depth imaging, optical coherence tomography
|How to cite this article:|
Abdellatif MK. Choroidal thickness in healthy Egyptians and its correlation with age. J Egypt Ophthalmol Soc 2017;110:22-7
| Introduction|| |
The choroid serves many essential functions for the eye. It acts as a heat sink for the retina , and delivers blood to 85% of the eyes, including the photoreceptors and the prelaminar portion of the optic nerve head .
The choroid is the source of many vision-threatening diseases, such as age-related macular degeneration , polypoidal choroidal vasculopathy , central serous chorioretinopathy , and high-myopia-related chorioretinal atrophies . In addition, the outer retina, including the photoreceptors, is nourished by the choroidal vasculature; extreme choroidal thinning and loss of the vascular tissues often lead to photoreceptor damage and visual dysfunction . Because choroidal abnormalities such as vascular hyperpermeability, vascular changes and loss, and thinning are critical to the onset and progression of such diseases, ophthalmologists and researchers are shifting their interest to the choroidal abnormalities .
Spectral-domain optical coherence tomography (SD-OCT) is a noninvasive technique to visualize cross-sectional images of vitreoretinal structures. Image averaging during eye tracking increases the signal-to-noise ratio and improves image quality. The point of maximum sensitivity on SD-OCT (known as the ‘zero delay line’) is in the vitreous; with increasing depth, the signal is reduced and details of the choroid are reduced . More recently, enhanced depth imaging on SD-OCT has increased the ability to visualize the choroid, capturing images with the choroid close to the zero delay line . However, with this modality, details of the posterior vitreous are reduced. On the conventional SD-OCT B-scan of the macula, the preretinal vitreal pocket was clear. However, the outer choroidal border was not detected. The enhanced depth imaging on SD-OCT scan increased the visibility of the choroid borders, but the preretinal vitreal pocket was not seen .
On the basis of histologic examination, choroidal thickness (CT) ranges from 170 to 220 µm . However, recent advances in technologies, such as partial coherence inferometry  and enhanced depth imaging  using a Heidelberg system, have shown an approximate subfoveal CT of 300 µm in healthy volunteers. CT is affected by age ,. In high myopes, the mean CT at the fovea is 100.5 µm; central CT is significantly associated with refractive error and posterior staphyloma height .
The aim of this study was to determine the baseline CT in healthy Egyptian volunteers and its correlation with age. To our knowledge, no similar study was conducted on the Egyptian population.
| Patients and methods|| |
We conducted a cross-sectional nonrandomized comparative case study consisting of 134 eyes in 89 healthy Egyptian volunteers. The study was approved by the Research Ethical Committee at Faculty of Medicine and all procedures conformed to the guidelines provided by the World Medical Association Declaration of Helsinki on ethical principles for medical research involving humans.
All participants underwent a full ophthalmic examination including autorefraction (Topcon RM8800, Topcon Corp., Tokyo, Japan), best-corrected visual acuity, intraocular pressure measurement with Goldmann applanation tonometer (GAT; Haag-Streit AG, Bern, Switzerland), slit lamp examination, and indirect ophthalmoscopy. Optical coherence tomography was performed using Nidek Rs 3000 Advance SD-OCT (Retinascan RS 3000 advance; Nidek Co. Ltd, Gamagori, Japan), with a scan speed of 53 000 A-scan/s. Patients who had undergone uneventful cataract surgery more than 1 year ago were included and their refractive error before surgery was recorded.
Exclusion criteria included any history or evidence of retinal or choroidal pathology, glaucoma, cataract, cataract surgery of less than 1-year duration, any retinal surgery, best-corrected visual acuity worse than 20/30, and refractive error greater than 6.00 or less than −6.0 D. A patient with refractive error −5 D was excluded due to marked choroidal thinning.
Spectral-domain optical coherence tomography
The choroid was imaged by positioning the Nidek Rs 3000 Advance SD-OCT closer to the eye to create an inverted image bringing the choroid to the zero delay line as described before. The image was obtained as white over black to increase the contrast between the choroid and the sclera; this makes the interface between the choroid and the sclera more evident. All images were obtained between 10 a.m. and 12 p.m.
Twelve radial lines were taken, which capture a 9 mm×9 mm wide area image centered on the macula; the border between the choroid and the sclera was drawn in the 12 lines manually. The CT was measured between the outer edge of the retinal pigment epithelium layer (already present in the software of the OCT machine) and the manual line, which represents the chorioscleral interface, and a CT map was drawn with an Early Treatment Diabetic Retinopathy Study chart, as shown in [Figure 1]. The CT map contains the central subfield (central CT), which is bounded by the innermost 1-mm-diameter circle. The inner subfields are bounded by the 3-mm-diameter circle divided into inferior, superior, nasal, and temporal. The outer subfields are bounded by the 6-mm-diameter circle divided into inferior, nasal, and temporal. The subfoveal CT was measured in the three groups vertically beneath the fovea.
|Figure 1 Choroidal thickness measurement of a 30-year-old participant. (a) optical coherence tomography with enhanced depth imaging; the blue line represents the chorioscleral interface and the yellow line represents the fovea. (b) Graph measuring the subfoveal choroidal thickness (346 µm). (c) The ETDRS map shows the choroidal thickness in the nine macular subfields. BM, Bruch’s membrane; ETDRS, Early Treatment Diabetic Retinopathy Study; RPE, retinal pigment epithelium|
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All data were collected and analyzed statistically using SPSS for Windows, version 16.0 (SPSS Inc., Chicago, Illinois, USA). Qualitative data were expressed as mean and SD. One-way analysis of variance was used to compare the mean values of CT between different age groups. Independent t-test was used to compare the mean values of CT between male and female patients in the same age group.
Pearson’s correlation coefficient (r) was performed to test the correlation between CT and age. Linear regression analysis was used to assess regression of CT with age. The significance of the data was determined using the probability (P). P value greater than 0.05 was considered nonsignificant, P value of at least 0.05 was considered significant, and P value of at least 0.01 was considered highly significant.
| Results|| |
A total of 134 eyes of 89 patients (45 male and 89 female) were included in this study; their demographic data are presented in [Table 1]. Patients’ ages ranged from 22.7 to 37.1 years with a mean age of 29.4 years in group 1, from 40.1 to 58.3 years with a mean age of 48.7 years in group 2, and from 60.3 to 70 years with a mean age of 64.6 years in group 3. No statistically significant difference was found between male and female patients in the three groups as regards age (P>0.05).
The mean central CT ([Table 2]) was highest in group 1 (337.23±37.51 µm) and lowest in group 3 (270.24±22.37 µm), as shown in [Figure 2]. The difference between groups 2 and 3 was statistically significant (P<0.05) and the difference between group 1 and the other two groups was highly significant (P<0.01). The CT map showed that the CT was highest in the central 1 mm zone, followed by the superior quadrant in the three groups (336.14±39.39, 280.04±34.42, and 267.36±29.28 µm in groups 1, 2, and 3, respectively). The thinnest quadrant was the nasal one (289.48±54.24, 253.24±47.02, and 237.67±44.52 µm in groups 1, 2, and 3, respectively) ([Figure 3]). There was no statistically significant difference between the central CT and the upper quadrant in the three age groups (P=0.12, 0.36, and 0.54 in groups 1, 2, and 3, respectively), but there was a statistically significant difference between the central CT and the remaining three quadrants (P<0.05). The central CT showed a statistically significant difference from the lower quadrant (P<0.05), nasal quadrant (P<0.01), and the temporal quadrant (P<0.01). CT was thinner in the outer 6 mm ring than in the inner 3 mm ring in the three groups in all quadrants.
|Table 2 Choroidal thickness in the nine Early Treatment Diabetic Retinopathy Study zones|
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|Figure 3 Central choroidal thickness (CT) and CT in the upper, lower, nasal, and temporal quadrants in the three age groups|
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We correlated the central CT with age and noticed a highly significant negative correlation (r=−0.617, P<0.001), with a highly significant correlation coefficient (r2=0.38). However, we did not observe significant differences when comparing central CT between male and female patients (P=0.836).
Regression analysis showed variable rates of central choroidal thinning in different age groups ([Table 3]). We observed statistically significant thickening in the first group (β=4.94 µm, P=0.001), whereas the second group showed statistically nonsignificant thinning (β=−0.301 µm, P=0.739). The third group had statistically significant thinning (β=−3.77 µm, P=0.001).
|Table 3 Regression analysis of central choroidal thickness in the three age groups|
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| Discussion|| |
Disturbance of choroidal blood flow plays a key role in disease states such as glaucoma, diabetic retinopathy, and age-related macular degeneration. Resistance to flow is related to the diameter of a vessel; thus, CT may be proportional to the blood flow in the choroid and may be an important metric for choroidal health. Therefore, it is important to study CT with more precision to better understand this vital structure . This is the first study to examine the CT in an Egyptian population. We demonstrated a significant correlation between age and central CT with an inverse relationship between age and central CT. Furthermore, our data confirm a variable rate of regression in CT with advancing age.
We believe that measuring the CT in the central 1 mm zone would be more accurate compared with the subfoveal CT, which represents the intersection of the 12 radial lines, as the latter is largely affected by tiny eye movements.
On comparing the results of our study with the previous studies, the mean central CT in the first group with a mean age of 29.4 years of 337.2±37.5 µm and the mean subfoveal CT of 346.95±37 µm were close to the results of Rahman et al. , who conducted their study on variable ethnic groups with a mean age of 38 years and reported a mean thickness of 332±90 µm, and to the results of Branchini et al. , who reported a mean thickness of 347.5±94.37 µm for a mean age of 35.2 years. Similarly, the results of Li et al.  in Danish university students with mean age 24.9 years demonstrated a mean CT of 342±118 µm. However, our results were lower than the results of Ikuno et al.  on healthy Japanese, who reported a CT of 354±111 µm with an average age of 39.4 years, and higher than that reported by Kim et al.  on Korean population with a mean age of 40.18 years, which was 307.26±95.18 µm.
The mean central CT in group 2 with a mean age of 48.7 years (285.3±31.2 µm) and the mean subfoveal CT of 294.3±29 µm was close to the results of Margolis and Spaide , who observed a CT of 287±76 µm with a mean age of 50.4 years, and to the results of Jirarattanasopa et al. , who observed a CT of 279.4±75.49 µm on Thai population with a mean age of 46.4 years. Similarly, our findings were close to the results of Manjunath et al. , who reported a mean thickness of 272±81 µm and an average age of 51.1 years, but it was higher than the results of McCourt et al. , who reported a mean thickness of 246.59±93.17 µm on the higher average age group (55.5 years).These discrepancies could be attributed to ethnic differences, age of the included population, or the device used in the different studies.
In group 3, the mean age was 64.6 years (270.24±22.4 µm) and the mean subfoveal CT was 278.6±22 µm; it was higher than that reported by Wei et al.  in a population-based Beijing eye study, which was 253.8 µm on 3233 participants with similar mean age to our study. This large population included could play an important role in the difference between the two studies together with the ethnic difference between the Egyptian and Chinese populations.
The choroid was found to be thickest subfoveally and thinnest nasally; this pattern of CT is in agreement with that reported by Ikuno et al. . The inner superior choroidal subfield was the thickest subfield, whereas the outer nasal subfield was the thinnest one.
Regression of central CT in patients less than 60 years of age was 1.988 µm/year (P<0.001), whereas in patients older than 60 years it was −3.774 µm/year (P=0.001). This is similar to the results of Kim et al. . This variability in the rate of choroidal thinning indicates that it is not a fixed static process throughout the adult life and that the actual choroidal thinning starts in the fifth decade of age. This explains the different rates of choroidal thinning reported by the previous studies, as with McCourt et al. (3.09 µm/year) , Wei et al. (4 µm/year) , Margolis and Spaide (1.56/year) , and Jirarattanasopa et al. (2.67 µm/year) .
| Conclusion|| |
This study showed that CT in an Egyptian population was similar to that reported in studies conducted in other populations. CT was affected by age and we report progressive thinning of the choroid by the fifth decade of life. Thinnest choroidal quadrant was nasal, and this has to be considered in diseases affecting the choroid.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]