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ORIGINAL ARTICLE
Year : 2020  |  Volume : 33  |  Issue : 2  |  Page : 581-587

Hyperopic peripapillary retinal nerve fiber layer thickness and foveal thickness using optical coherence tomography


1 Department of Ophthalmology, Kafr Elshiekh Ophthalmology Hospital, Kafr Elshiekh, Egypt
2 Department of Ophthalmology, Faculty of Medicine, Menoufia University, Menoufia, Egypt

Date of Submission12-Sep-2019
Date of Decision28-Oct-2019
Date of Acceptance04-Nov-2019
Date of Web Publication27-Jun-2020

Correspondence Address:
Eman N El Gohary
Department of Ophthalmology, Kafr Elshiekh Ophthalmology Hospital, Kafr Elshiekh
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/mmj.mmj_285_19

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  Abstract 


Purpose
Studying the peripapillary retinal nerve fiber layer (RNFL) thickness and foveal thickness in hyperopia using optical coherence tomography.
Background
Significant hyperopia is defined to be any degree of hyperopia sufficient to cause symptoms requiring remediation. Peripapillary RNFL thickness was approved to be conversely correlated with axial length (AL) and the spherical equivalent in hyperopic populations. Optical coherence tomography is a modern noncontact and noninvasive imaging technique designed to produce high-resolution images and accurate measurements of the different retinal components.
Patients and methods
The presented study included ninety eyes: 45 of them were simple hyperopic eyes, and the other 45 eyes were emmetropic. The emmetropic eyes were age and sex matched to the case group. The participants were included in the study after obtaining informed consent and a detailed history. Ophthalmological examination including visual acuity assessment, cycloplegic refraction, best-corrected visual acuity, cover–uncover test and extraocular muscle movement examination, anterior segment examination, intraocular pressure measurement, fundus examination, AL measurement, and peripapillary RNFL thickness and foveal thickness measurements (all methods of assessment are mentioned in detail in the patients and methods section) was carried out.
Results
There was no statistically significant difference between the hyperopic and the emmetropic groups with regard to age and sex. There was a statistically significant increase in the thickness of the RNFL in the hyperopic group that was more than that of the emmetropic group, and there was a statistically significant increase in the thickness of the superior, inferior, and nasal quadrants in the hyperopic group more than that of the emmetropic group. There was no statistically significant difference in the temporal quadrant between both groups.
Conclusion
The AL is statistically significantly short, and the mean foveal thickness is statistically significantly high in the hyperopic eyes. The RNFL thickness is statistically significantly thick, and the superior, inferior, and nasal quadrants were thicker in the hyperopic eyes than in the emmetropic ones.

Keywords: fovea, foveal thickness, hyperopia, optical coherence tomography, retinal nerve fiber layer


How to cite this article:
El Gohary EN, El Sobky HM, Ibrahim AM. Hyperopic peripapillary retinal nerve fiber layer thickness and foveal thickness using optical coherence tomography. Menoufia Med J 2020;33:581-7

How to cite this URL:
El Gohary EN, El Sobky HM, Ibrahim AM. Hyperopic peripapillary retinal nerve fiber layer thickness and foveal thickness using optical coherence tomography. Menoufia Med J [serial online] 2020 [cited 2020 Oct 19];33:581-7. Available from: http://www.mmj.eg.net/text.asp?2020/33/2/581/287771




  Introduction Top


Hyperopia is defined as a refractive error in which parallel rays of light entering the eye reach a focal point behind the plane of retina while the accommodation is maintained in a state of relaxation[1].

Hyperopia is not a common refractive error in children and adults. Its effect varies greatly depending on the magnitude of hyperopia, the age of the individual, the state of accommodative and the convergence system, and the demand placed on the visual system[2].

The prevalence of refractive error among full-term infants has a normal bell-shaped distribution. Up to 9% of 6–9 month-old-infants have hyperopia, but this prevalence decreases to 3.6% in the 1-year-old population. Over the next 10–15 years of life, there is a further decrease in the prevalence of hyperopia and an increase in the frequency of myopia[3].

Significant hyperopia is defined as any degree of hyperopia sufficient to cause symptoms requiring remediation. The simplest functional classification system is based on the presence or absence of symptoms resulting from hyperopia. Hyperopia is classified into physiologic and pathologic hyperopia[4].

It has been reported that the mean peripapillary retinal nerve fiber layer (RNFL) thickness was conversely correlated with axial length (AL) and spherical equivalent (SE) in hyperopic populations[5].

This study was, therefore, carried out to study the measurement of peripapillary RNFL and foveal thickness in hyperopia using the spectral domain optical coherence tomography (OCT).


  Patients and Methods Top


This case–control study was conducted on 90 eyes selected from the Ophthalmology Outpatient Clinic at Cairo University Hospital (Kasr El-Ainy) in the period spanning from October 2018 to April 2019 and divided into two groups: group 1 comprising 45 simple hyperopic eyes, and group 2 (controls) comprising 45 emmetropic eyes that were age and sex matched to the case group.

Patients with a history of any systemic disease, previous ocular surgery or any retinal pathology such as diabetic retinopathy, corneal opacity, cataract, nystagmus, or glaucoma were excluded from our study. Informed consent was obtained from the patients according to ethical principles after explaining the research study. Detailed medical history was taken from the patient. Detailed ophthalmological examination was performed for every patient including visual acuity assessment using Snellens chart, cycloplegic refraction (using cyclopentolate 1%) by the autorefractometer, best-corrected visual acuity using the decimal scale, slit-lamp examination of the anterior segment to exclude any ocular disorders such as corneal opacity or cataract, etc., cover–uncover test and extraocular muscle movement examination, intraocular pressure measurement by Goldmann applanation tonometry, and biomicroscopic fundus examination using + 90 D Volk lens. AL was measured using A-scan ultrasound biometry (contact type), and the peripapillary RNFL and central macular thickness (CMT) were measured using spectral domain OCT (Heidelberg, Germany) (using the fast macular thickness protocol and 6 mm lines, a radial spoke pattern was obtained in a continuous automated sequence, and internal fixation was used for all scans).

The CMT is defined as the CMT in a central 1 mm circle on the macular image[6].

The central circle of the RNFL scan, which is called 'global,' and the inferior, temporal, superior, and nasal quadrants (NQ)' thickness, were used to calculate the difference between the affected and the sound eyes.

The results were statistically analyzed by SPSS, version 20 (SPSS Inc., Chicago, Illinois, USA). Statistics were calculated in terms of percentage, mean, and SD, and the Student's t test, Mann–Whitney test, χ2 test, Spearman and Pearson's test, P value, and Wilcoxon test were used[7].


  Results Top


The presented study included 45 hyperopic eyes that comprised the cases and 45 emmetropic eyes that comprised the control group.

We carried out a comparison of age and sex between the studied groups. The mean age of hyperopic eyes was 30.36 years. Male patients represented 35.6% while female patients comprised 46.4% of the hyperopic group. In addition, 45 emmetropic eyes of controls who were matched by age and sex (P = 0.057, 0.177, respectively) to the cases were included in the study, as shown in [Table 1].
Table 1: Comparison between the two groups according to demographic data

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On comparison of the AL between the studied groups, the mean AL of the hyperopic group was found to be 21 mm, while the AL of the control group was 22.10 mm. There was a significant shortness in AL in the hyperopic group than in the emmetropic one (P < 0.001), as shown in [Table 2].
Table 2: Comparison between the two groups according to axial length

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In the comparison of mean foveal thickness (MFT) between the studied groups, the mean MFT of the hyperopic group was 253.1 μm, while that of the control group was 236.8 μm. There was a significant increase in the hyperopic MFT that was more than that in the emmetropic group (P < 0.001). In the comparison of central foveal thickness (CFT) between the two studied groups, the mean CFT of the hyperopic group was 191.3 μm, while that of the control group was 197.4 μm. There was no significant difference between both groups with regard to CFT (P < 0.001, t test), as shown in [Table 3].
Table 3: Comparison between the two groups according to mean foveal thickness and central foveal thickness

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On comparison of RNFL thickness between the studied groups, the mean RNFL thickness of the hyperopic group was 115.6 μm, while that of the control group was 95.50 μm. There was a significant increase in RNFL thickness in the hyperopic group that was more than that in the emmetropic group (P < 0.001). The mean superior quadrant (SQ) thickness of the hyperopic group was 139.5 μm, while that of the control group was 116.2 μm. There was a significant thicker SQ in the hyperopic group than that in the emmetropic group (P < 0.001). The mean inferior quadrant (IQ) thickness of the hyperopic group was 150.5 μm, while that of the control group was 116.7 μm. There was a significant thicker IQ in the hyperopic group than that in the emmetropic group (P < 0.001). The mean NQ thickness of the hyperopic group was 87.02 μm, while that of the control group was 74.67 μm. There was a significantly thicker NQ in the hyperopic group than in the emmetropic group (P < 0.001). The mean temporal quadrant (TQ) thickness of the hyperopic group was 83.91 μm, while that of the control group was 77.42 μm. There was no significant difference in the TQ thickness between both groups (P = 0.046), as shown in [Table 4].
Table 4: Comparison between the two groups according to retinal nerve fiber layer thickness

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Spearman and Pearson's test was used to study correlations. In the hyperopic group, there was a negative correlation between the mean RNFL thickness and AL, MFT, and CFT (P = 0.010, 0.022, and 0.04, respectively) [Figure 1],[Figure 2]. Moreover, there was a negative correlation between the IQ of RNFL thickness and SE and AL (P = 0.026 and 0.002, respectively) [Figure 3]. Moreover, there was a negative correlation between the NQ of RNFL thickness and AL (P = 0.039) [Figure 4], and there was a negative correlation between the TQ RNFL thickness and MFT (P = 0.003) [Figure 5]. In the emmetropic group, there was a positive correlation between the mean RNFL thickness, SQ, IQ, NQ, and TQ and SE, AL, MFT, and CFT, as shown in [Table 5] and [Table 6].
Figure 1: Correlation between mean RNFL thickness and axial length (AL) in the hyperopia group. RNFL, retinal nerve fiber layer.

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Figure 2: Correlation between mean RNFL thickness and CFT in the hyperopic group. CFT, central foveal thickness; RNFL, retinal nerve fiber layer.

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Figure 3: Correlation between RNFL thickness, inferior quadrant (IQ) and spherical equivalent (SE) in the hyperopic group. RNFL, retinal nerve fiber layer.

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Figure 4: Correlation between RNFL, nasal quadrant (NQ) and axial length (AL) in the hyperopic group. RNFL, retinal nerve fiber layer.

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Figure 5: Correlation between RNFL thickness, temporal quadrant (TQ) and MFT in the hyperopic group. MFT, mean foveal thickness; RNFL, retinal nerve fiber layer.

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Table 5: Correlation between retinal nerve fiber layer thickness and axial length and spherical equivalent in each group (n=45)

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Table 6: Linear multivariate analysis for the parameters affecting retinal nerve fiber layer average in each group

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  Discussion Top


Hyperopia is defined as a refractive error in which parallel ray of light entering the eye reaches a focal point behind the plane of retina while the accommodation is maintained in a state of relaxation[8].

Hyperopia is not a common refractive error in children and adults. Its effect varies greatly depending on the magnitude of hyperopia, the age of the individual, the state of the accommodative and convergence system and the demand placed on the visual system[9].

It has been reported that the mean peripapillary RNFL thickness was conversely correlated with AL and SE in myopic and hyperopic populations[10].

The close association between hyperopia, amblyopia, and strabismus, especially in children, makes hyperopia a greater risk factor than myopia for a higher degree of permanent vision loss, and some performed studies showed that the MFT is significantly higher in eyes with hyperopic anisometropic amblyopia than in the fellow eyes and the normal participants' eyes, while other studies found no difference in retinal structure between the amblyopic and control groups[11].

The aim of our study was to measure the hyperopic peripapillary RNFL and foveal thickness using the spectral domain OCT.

In agreement with our results, Llorente et al.[12], by studying 24 myopic and 22 hyperopic eyes, found that AL was significantly shorter in hyperopic eyes.

Moreover, Strang et al.[13], suggested that hyperopia is predominantly axial in nature by data were collected on 57 patients with either emmetropic or hyperopic refractive error.

Concerning foveal thickness, in agreement with our results, Wu et al.[14] studied 72 children with hyperopic anisometropic amblyopia. The mean macular thickness was significantly thicker in the amblyopic eyes than in the contralateral sound eyes (181.4 ± 14.2 vs. 175.2 ± 13.3 μm, P < 0.01), but the CMT was not significantly different.

Furthermore, a prospective, cross-sectional study was carried out by Yalcin and Balci[15], which included 30 patients with hyperopic anisometropic amblyopia and another 30 adult patients as a control group. The MFT of the hyperopic eyes was 220 ± 38.25 μm and that of the fellow eyes was 202.87 ± 31.01 μm, while that of the emmetropic eyes was 198.91 ± 22.50 μm. They found a statistical difference between the studied groups (P = 0.025).

In contrast to our results, Yoon et al.[16] measured the macular and the peripapillary RNFL thicknesses using OCT in 31 patients with hyperopic anisometropic amblyopia. The mean macular retinal thickness was 252.5 and 249.7 μm in the amblyopic eyes and the normal eyes, respectively. There was no statistically significant difference found in the macular retinal thickness (P > 0.05), but they studied a small number of patients.

Concerning RNFL, our study showed that the mean RNFL thickness of the hyperopic group was 115.6 μm, while that of the control group was 95.50 μm. There was a significantly thicker RNFL in the hyperopic group than in the emmetropic group (P < 0.001).

In agreement with our results, the study by Yoon et al.[16] found that the mean RNFL thickness was 115.2 and 109.6 μm in the amblyopic eyes and the normal eyes, respectively. There was a significant increase in RNFL thickness in the hyperopic anisometropic amblyopia eyes (P = 0.019).

In addition, Tas et al.[17] collected 62 patients in the low hyperopic group, 60 patients in the moderate hyperopic group, and 42 patients in the high hyperopic group, and the groups were similar concerning age and sex; the study showed that there were significant differences between low and high-hyperopia groups concerning the mean RNFL thickness and the RNFL thicknesses of the inferior and NQs (P = 0.045, 0.008, 0.03, respectively).

Furthermore, the results obtained by Wu et al.[14] revealed that the mean peripapillary RNFL thickness was 113.9 ± 7.2 and 109.2 ± 6.9 μm in the amblyopic eyes and the normal eyes, respectively, reaching a statistical significance (P = 0.02).

In contrast to our results, Yalcin and Balci[15] concluded that the mean RNFL thickness for the hyperopic eyes was 101 ± 10.77 μm and that for the fellow eyes was 104.4 ± 10.95 μm, and, for the hemitropic eyes, it was 105.08 ± 10.10 μm. They revealed no statistically significant difference between these groups (P = 0.285), and this study was carried out on amblyopic eyes.

Concerning the relation between age, sex, AL, RNFL, and foveal thickness, a negative correlation was found between RNFL mean and AL, MFT, and CFT in hyperopic eyes, while a positive correlation was found between RNFL mean, SE, AL, MFT, and CFT in emmetropic eyes. There a negative correlation found between age and RNFL thickness average and between sex and RNFL thickness average in both groups. There was a negative correlation found between age and CFT in hyperopic eyes, but a positive correlation between age and MFT and CFT in emmetropic eyes. There was a negative correlation between MFT, SE, and AL and also between CFT, SE, and AL in hyperopic eyes.

In agreement with our results, Eriksson and Alm[18] carried out a study on 67 healthy individuals who underwent three repeated scans in both eyes with the macular thickness map protocol in the Stratus OCT. That protocol divides the macular area into nine early treatment diabetic retinopathy study (ETDRS) fields. They found a statistically significant negative relationship between retinal thickness and RNFL thickness and the age for all ETDRS fields. Retinal thickness and RNFL thickness decreased by 0.26–0.46 and 0.09 μm, respectively, per year.

A cross-sectional analysis was carried out by Adhi et al.[19] on 220 patients who had a mean age of 45.3 years (16–80 years). Using the ETDRS map, foveal thickness for all patients was measured to be 229 ± 20.46 μm. Mean macular thickness for all patients was 262.8 ± 13.34 μm. Male sex was associated with greater foveal (P < 0.0001) and mean macular (P < 0.0001) thickness compared with the female sex. However, there was no association between mean macular thickness (r2 = 0.01; P > 0.05) and foveal thickness (r2 = 0.00004; P > 0.05) and the age.

In contrast to our results, Göbel et al.[20] recruited 159 patients aged 13–92 years (205 eyes) without macular pathology. There was no correlation between the retinal thickness and either the AL or age. The mean retinal thickness in the fovea was 142 ± 18 μm.

In addition, Garcia-Valenzuela et al.[21] concluded that the average thickness measurement using the OCT imaging technique in the per papillary retina, macula, and posterior temporal retina was not influenced by either the AL or the refractive status of the eye.

Furthermore, Budenz et al.[22] performed per papillary fast RNFL scans on 328 normal participants by OCT. The mean RNFL thickness for the entire population was 100.1. Thinner RNFL measurements were associated with greater AL (P < 0.001) and older age (P < 0.001). For every decade of increased age, mean RNFL thickness measured thinner by ~2.0 μm (95% confidence interval, 1.2–2.8). For every 1 mm increase in AL, mean RNFL thickness measured decreased by approximately 2.2 μm (95% confidence interval, 1.1–3.4). There was no relationship between RNFL thickness and sex.

Furthermore, Song et al.[23] studied 198 ophthalmologically normal participants (104 men, 94 women) between July 2008 and January 2009. The average macular thickness was significantly lower in the female patients (P = 0.027). As age increased, average macular thickness decreased significantly (P = 0.002). Refractive error had no significant influence in partial correlation analysis, but AL correlated negatively with overall average macular thickness (P = 0.044).


  Conclusion Top


The AL showed a significant shortness, the MFT showed a significant increase and the RNFL showed a significant increase in the thickness, and the thickness of the superior, inferior, and NQs in the hyperopic eyes was more than that in the emmetropic eyes.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

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



 

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