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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 110  |  Issue : 3  |  Page : 94-99

Subfoveal choroidal thickness versus foveal thickness in patients with myopia


Department of Ophthalmology, Faculty of Medicine, Ain Shams University, Cairo, Egypt

Date of Submission10-Jun-2017
Date of Acceptance21-Jul-2017
Date of Web Publication6-Nov-2017

Correspondence Address:
Walid Mohamed El-Zawahry
Department of Ophthalmology, Faculty of Medicine, Ain Shams University, Abbassia Square, Cairo, 11371
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ejos.ejos_32_17

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  Abstract 

Purpose
The aim of this study was to explore the influence of myopia on the foveal thickness and its correlation with subfoveal choroidal thickness (SFCT), the axial length (AL), and spherical equivalent (SD) in patients with myopia.
Patients and methods
We included 120 patients with myopia, and their ages ranged from 25 to 35 years. Moreover, 30 age-matched and sex-matched healthy emmetropic individuals were included as a control group. All participants underwent a complete ophthalmologic examination which included best-corrected visual acuity test, slit-lamp examination, Goldman applanation tonometry, indirect ophthalmoscopy, Axial length (AL) measurement (PacScan 300A, Sonomedescalon Inc., New York, USA), and spectral domain optical coherence tomography (Retinascan RS-3000 Advance, NIDEK, Gamagori, Japan).
Results
Foveal thickness was statistically higher in patients with myopia than that of healthy emmetropic participants, whereas SFCT was statistically lower in the patients with myopia than that of emmetropic individuals. Foveal thickness showed positive correlation with SD and AL, but it showed negative correlation with visual acuity (VA) and SFCT. SFCT showed significant positive correlation with the VA, but it showed negative correlation with SD, AL, and foveal thickness. Multiregression analysis showed that the most important determinant of foveal thickness in this study was AL and SFCT (β=0.35 and −0.66, respectively, and P<0.001 and <0.001, respectively).
Conclusion
With the increase in myopia degree and AL, the average foveal thickness increased and SFCT decreased. SFCT and AL are the most important predictive factors of VA in myopic eyes.

Keywords: axial length, myopia, spherical equivalent-foveal thickness, subfoveal choroidal thickness


How to cite this article:
El-Zawahry WM. Subfoveal choroidal thickness versus foveal thickness in patients with myopia. J Egypt Ophthalmol Soc 2017;110:94-9

How to cite this URL:
El-Zawahry WM. Subfoveal choroidal thickness versus foveal thickness in patients with myopia. J Egypt Ophthalmol Soc [serial online] 2017 [cited 2017 Dec 18];110:94-9. Available from: http://www.jeos.eg.net/text.asp?2017/110/3/94/217699


  Introduction Top


Myopia is a risk factor for retinal detachments, glaucoma, and degenerative changes in the central retina, which can cause significant vision loss [1],[2].

Myopia prevalence is increasing, hence the economic and visual problems of these related diseases may also increase [3],[4]; therefore, it is important to understand why the myopic eyes are more susceptible to disease.

Refractive error and axial length (AL) also influence retinal thickness (RT) and choroidal thickness. Central (foveal) RT typically increases with increasing AL and myopia [4],[5]; however, the peripapillary retinal nerve fiber layer thickness distribution differs with increasing myopia (generally a thinning in the retinal nerve fiber layer) [6],[7]. Conversely, subfoveal choroidal thickness is correlated negatively with Axial length (AXL), that is, decreasing with increasing levels of myopia [8],[9],[10].

Previous researches have shown that the retina is thinner in individuals with myopia [11] and in the tree shrew with induced myopia [12]. This structural thinning was found to be related to reduced retinal function in humans [13]. Moreover, these changes are accompanied by a high incidence of macular abnormalities [2],[14].

So, monitoring the macular thickness in myopic eyes is important. Optical coherence tomography (OCT), which give high-resolution retinal images, measures RT with high repeatability [15] and permits more sensitive and consistent measures of the retina in the living eye, which should improve our understanding of the pathophysiology of myopia and its connection to the development of other ocular diseases [16].

To the best of our knowledge, the correlation between foveal thickness and subfoveal choroidal thickness (SFCT) was not assessed before in the case of myopia. Hence, our aim was to explore the influence of myopia on the foveal thickness and its correlation with SFCT, the AL, and refraction in individuals with myopia.


  Patients and methods Top


All procedures done in studies, including enrolment of human participants, were in accordance with the ethical standards of the Faculty of Medicine Ain Shams University research committee and with the 1964 Helsinki Declaration and its later amendments or similar ethical standards. Informed consent was obtained from all individual participants included in the study.

This cross-sectional study was conducted between November 2014 and March 2016. All participants were chosen from patients attending the ophthalmological outpatient’s clinics of Ain Shams University who came for ophthalmological examination from January 2016 till June 2016. It included 120 patients (120 eyes) with myopia, and their ages ranged from 25 and 35 years. Moreover, 30 (30 eyes) age-matched and sex-matched healthy emmetropic individuals were included as a control group.

Participants were divided into five groups according their spherical equivalent (SD): emmetropia less than or equal to ±0.5 D, mild myopia group, more than −0.5 to −3.00 D; moderate myopia group, more than −3.0 to −6.00 D; high myopia group, more than −6.0 to −10.00 D; and advanced myopia, more than −10.00 D.

We excluded any patient with pre-existing retinal diseases whether congenital or acquired specially DM, opaque media, glaucoma, previous eye trauma, previous retinal surgery, or previous optic nerve disease such as optic neuritis or ischemic optic neuropathy.

All patients underwent a complete ophthalmologic examination by the same ophthalmologist. Examinations included best-corrected visual acuity test, slit-lamp examination, Goldmann applanation tonometry, indirect ophthalmoscopy, AL measurement (PacScan 300A; Sonomedescalon Inc., New York, USA), and spectral domain optical coherence tomography (SD-OCT) (Retinascan RS-3000 Advance; NIDEK, Gamagori, Japan).

Axial length measurement

The AL was measured using A-scan ultrasonography (PacScan 300A; Sonomedescalon Inc.). Before measurement, the cornea was anesthetized with one drop of topical 0.4% benoxinate HCl. Overall, five readings were taken to get an average value. The standard deviation was below 0.1 mm for each individual.

Optical coherence tomography

An OCT scan was taken for every patient from 9 a.m. to 12 p.m. after mydriasis using mydriacyl 0.5% eye drops. We captured the SD-OCT scans using the macula line 12-mm horizontal scan. The scans consisted of 1024 A scans with high definition. Each image consisted of 120 averaged B scans, with a 4-μm resolution. The image intensity was properly adjusted to get the clearest image. The patient was properly positioned on the OCT device to get the best quality images. After capturing the macula line scan for measuring the foveal thickness (total retinal macular thickness was computed in microns for the central 1.0 mm area of the fovea), which is automatically calculated by the device, the OCT device was slowly approached from the patient’s eye till the image was inversed and we got the choroidal mode, then the image was captured when it was clear enough. SFCT was calculated as the perpendicular distance between the hyper-reflective outer border of the retinal pigment epithelium (RPE) and the sclerochoroidal interface, which was manually drawn using the embedded software (NAVIS-EX Image Filing software, RS3000-OCT, NIDEK, Gamagori, Japan) ([Figure 1]).
Figure 1 Foveal thickness in different studied groups.

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Statistical analysis

All data analyses were performed with the statistical package SPSS software version 15. Macular measurements among the four studied groups were evaluated by one-way analysis of variance, and then we conducted a post-hoc analysis [Tukey’s honestly significant difference (HSD)]. Associations between foveal thickness, SFCT, SD, and AL were expressed as Pearson’s correlation coefficient. Sex differences were done using χ2 analysis. Regression analyses were done to assess the different factors that can affect foveal thickness and SFCT. P values were considered statistically significant at less than 0.05.


  Results Top


We included 120 patients (120 eyes) with myopia, and their ages ranged from 25 to 35 years. Moreover, 30 age-matched and sex-matched healthy emmetropic individuals were included as a control group (30 eyes).

Subjects were divided into five groups according to the degree of their refractive error: emmetropia: less than or equal to ±0.5 D (male/female=15/15), mild myopia group, more than −0.5 to −3.00 D (male/female=16/14); moderate myopia group, more than −3.0 to −6.00 D (male/female=17/13); high myopia group, more than −6.0 to 10.0 D (male/female=14/16), and advanced myopia group greater than −10.0 D (male/female=13/17) (χ2=1.33 and P=0.86).

Sex was not significantly different in same group and between different ones.

Analysis of variance test showed no significant differences between the four groups for age and best-corrected visual acuity, but there is significant difference between the five groups for visual acuity (VA), SD, and AL ([Table 1]).
Table 1 Clinical and demographic characteristics of the studied group’s participants

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Subfoveal choroidal thickness

Analysis of variance test showed that there is significant difference between the five groups regarding foveal thickness and SFCT ([Table 2],[Table 3],[Table 4] and [Figure 2]).
Table 2 Comparison between the five studied groups regarding central foveal thickness and subfoveal thickness (μm)

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Table 3 Correlation between foveal thickness with different factors including visual acuity, spherical equivalent, axial length, and subfoveal choroidal thickness in patients with myopia

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Table 4 Correlation between subfoveal choroidal thickness with different factors including best-corrected visual acuity, spherical equivalent, axial length, and foveal thickness in patients with myopia

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Figure 2 Correlation between foveal thickness and axial length in patients with myopia.

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Post-hoc (Tukey’s HSD) analysis showed that foveal thickness was significantly thinner in the control participants than myopic ones, and the thickness increased with increase of myopia ([Table 2]).

Post-hoc (Tukey’s HSD) analysis showed that SFCT was significantly higher in the control participants than myopic one, and the thickness decreased with increase of myopia ([Table 2]).

Foveal thickness showed significant positive correlation with the SD and AL, but it showed negative correlation with visual acuity (VA) and subfoveal choroidal thickness (SFCT) ([Figure 3] and [Figure 4]).
Figure 3 Correlation between foveal thickness and subfoveal choroidal thickness (SFCT) in patients with myopia.

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Figure 4 Correlation between visual acuity (VA) and subfoveal choroidal thickness (SFCT) in patients with myopia.

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SFCT showed significant positive correlation with the VA, but it showed negative correlation with SD, AL, and foveal thickness.

Multiregression analysis showed that the most important determinant of foveal thickness in this study was AL and SFCT (β=0.35 and−0.66, respectively, and P<0.001 and <0.001, respectively) ([Table 5]).
Table 5 Multiple regression analysis evaluating factors that influence central foveal thickness in patients with myopia

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Multiregression analysis showed that the most important determinant of SFCT in this study was SE and AL (β=−0.28 and −0.23, respectively, and P<0.001 and <0.001, respectively) ([Table 6]).
Table 6 Multiple regression analysis evaluating factors that influence subfoveal choroidal thickness

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  Discussion Top


In this cross-sectional study, we studied foveal thickness in comparison to SFCT. Overall, different degrees of myopia showed thicker foveal thickness with progressive thickening with progress of myopia. This is in agreement with Song et al. [17] who found that an increase in myopia degree/AL leads to an increase in average foveal thickness; Wu et al. [18] who found that the high myopia group had significantly greater mean RT in the foveola and fovea 1 mm area than the emmetropic group; and Lim et al. [5] who found that the inner macula was thinner and the fovea was thicker in patients with myopia. However, it was in contrary to Lam et al. [19] who investigated the relationship between myopia and macular thickness by Stratus OCT, and they found that there is no significant difference existed in the inner ring macular thickness among the different groups (high myopia, low to moderate myopia, and nonmyopic eyes).

Lim et al. [5] propose that this phenomenon may be because of the increased AL of the enlarged eyeball, resulting in stretching of the sclera. Moreover, retinal stretching would also occur with panretinal thinning. On the contrary, the stretching and flattening affinity of the internal limiting membrane and the centripetal force of the posterior vitreous lead to elevation of the foveola and fovea.

In addition, we found thinner SFCT than that of normal control eyes with decremental thinning with progress of different degrees of myopia. This in agreement with Wei et al. [20] who found that there is decrease in SFCT in the myopia of 15 µm for every increase in myopic refractive error of 1 D, or by 32 µm for every increase in AL of 1 mm. Ho et al. [21] also found that SFCT decreases with severity of myopia.

Foveal thickness showed significant positive correlation with the SD and AL, but it showed negative correlation with VA and SFCT.

SFCT showed significant positive correlation with the VA, but it showed negative correlation with SD, AL, and foveal thickness.

Multiregression analysis revealed that the most important determinant of foveal thickness in this study was AL and SFCT. Moreover, multiregression analysis showed that the most important determinant of SFCT in this study was SD and AL. We conducted multiple regression analyses for patients with myopia to show which factor in the study was the most important determinant of VA. We found that age was not attributable to VA. SD, AL, and SFCT were the most important determinant for VA (β=−0.49, 0.89, and 0.14‎, respectively) (P<0.001, <0.001, and 0.01, respectively).


  Conclusion Top


With the increase in myopia degree and AL, the average foveal thickness increased and SFCT decreased. SFCT and AL are the most important predictive factors of VA in myopic eyes.

We recommend being aware of the effect of refraction, AL, and SFCT when evaluating foveal thickness in patients with myopia with diabetic macular edema, glaucoma, or after-cataract maculopathy.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Figures

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

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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