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ORIGINAL ARTICLE
Year : 2021  |  Volume : 9  |  Issue : 1  |  Page : 14-17

Effect of high myopia on macular thickness: An optical coherence tomography study in a tertiary care hospital, Karnataka, India


Department of Ophthalmology, S. Nijalingappa Medical College and Research Centre and HSK Hospital, Bagalkot, Karnataka, India

Date of Submission09-Jun-2020
Date of Decision19-Sep-2020
Date of Acceptance30-Oct-2020
Date of Web Publication10-Apr-2021

Correspondence Address:
Raksha Halmuthur Venkatesh
LIG-74, Opp. Water Tank, 1st Phase, KHB Colony, Gopala, Shivamogga - 577 205, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jcor.jcor_80_20

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  Abstract 


Aim: The aim is to study the correlation of high myopia with macular thickness by optical coherence tomography (OCT). Design: Case control study. Subjects and Methods: Sixty patients visiting outpatient department, Department of Ophthalmology of a tertiary care hospital, were enrolled in the study. The macular thickness of 30 high myopes and 30 emmetropes was measured using OCT. All high myopes had a spherical equivalent of ≥-6.0 Diopters (D) and intraocular pressure <21 mmHg. All the participants were chosen after excluding other ophthalmic diseases or any history of ocular or refractive surgery. Statistical Analysis: Variables are expressed as mean ± standard deviation. Data analysis was performed using SPSS version 20. Unpaired and Paired t-test were used. P ≤ 0.05 was considered statistically significant. Results: The para and perifoveal retinal thickness were significantly thin in high myopic eyes as compared to emmetropic eyes. The central foveal thickness was 298.93 ± 38.813 μm in high myopes and 224.63 ± 16.439 μm in emmetropes, which was statistically significant P < 0.001. Conclusion: The macular thickness was significantly decreased in myopic eyes compared to emmetropic eyes. However, the central foveal thickness was significantly high in high myopes. Therefore, the analysis of macular thickness in the evaluation of macular diseases or glaucoma should be considered based on refractive errors and the location of measurement.

Keywords: Macular thickness, myopia, optical coherence tomography


How to cite this article:
Choudhary A, Venkatesh RH, Jayashree M P, Surendrappa HD, Divya R, Darshini L M. Effect of high myopia on macular thickness: An optical coherence tomography study in a tertiary care hospital, Karnataka, India. J Clin Ophthalmol Res 2021;9:14-7

How to cite this URL:
Choudhary A, Venkatesh RH, Jayashree M P, Surendrappa HD, Divya R, Darshini L M. Effect of high myopia on macular thickness: An optical coherence tomography study in a tertiary care hospital, Karnataka, India. J Clin Ophthalmol Res [serial online] 2021 [cited 2021 Aug 3];9:14-7. Available from: https://www.jcor.in/text.asp?2021/9/1/14/313479



It has been shown in histopathological studies that there is increasing scleral and retinal thinning with myopia.[4],[5] In myopic eyes, the globe is enlarged with increase in axial length and the stretching beyond normal dimensions may result in thinning of the retina. With the availability of modern imaging technologies, in vivo measurements of retinal thickness have been made possible, and the relationship between myopia and retinal thickness has been examined.[6],[7],[8],[9],[10]

Since its introduction in 1991 by Huang et al.[11] the optical coherence tomography (OCT) has become one of the most widely used equipment for assessing the fovea and peripapillary nerve fiber layer in diseases such as macular edema, central serous retinopathy, clinically significant macular edema in diabetes, wet age-related macular degeneration, traumatic macular involvement, macular and nonmacular retinoschisis, retinal detachment, optic atrophy, and chronic glaucomas.

The present study aims to collect the normographic data of high myopes of ≥6 Diopter (D) with respect to the thickness of the macular region, so as to interpret and distinguish the physiological changes of high myopia from associated diseases in such individuals.


  Subjects and Methods Top


After obtaining clearance from the Institutional ethics committee, the present study was carried out as per the tenets of the Declaration of Helsinki. Patients were chosen randomly from the outpatient Department of Ophthalmology of a tertiary care hospital, Karnataka. A well-informed consent was obtained from all patients before examination.

Inclusion criteria were patients with myopia of ≥6D, Emmetropic patients. Exclusion criteria were any ocular diseases, refractive surgery, diabetes mellitus, hypertension, and any other systemic illness. Patients were divided into two groups: Group I-patients with high myopia (≥6 D) and Group II-emmetropic patients.

Thirty high myopic eyes and thirty emmetropic eyes were included in the study. Macular thickness was measured by Fourier domain OCT (Optovue RTVue model RT100). The fast macular thickness scanning protocol was used. The calculation of macular thickness was based on the 6 mm retinal thickness map analysis printout. The map was composed of nine sectorial thickness measurements in three concentric circles with diameters of 1, 3, and 6 mm. The central 1 mm circular region represented the fovea. The area bounded by the outer (6 mm) and middle (3 mm) circles formed the outer ring (perifovea) and the area bounded by middle (3 mm) and inner circles (1 mm) formed the inner ring (parafovea). The perifovea and parafovea were further divided into four quadrantic zones: Temporal, superior, nasal, and inferior study [Figure 1] and [Figure 2].
Figure 1: Macula divided into different zones

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Figure 2: Optical coherence tomography recorded by fast protocol

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Analysis of the collected data was performed using IBM SPSS Version 20 (Armonk, NY: IBM Corp). Variables were expressed as mean ± standard deviation. The significance of difference of macular thickness between myopic and emmetropic was determined by using unpaired t-test, quadrantic comparison by paired t-test. P ≤ 0.05 was considered statistically significant.


  Results Top


Thirty eyes of high myopes and thirty eyes of emmetropes were enrolled in the present study. In both the groups, the age of the patients varied from 11 to 46 years. The refractive errors of myopes ranged from −6D to −12D. The zonal macular thickness measurements in each group are summarized in [Table 1] and [Table 2].
Table 1: Inner macular thickness (parafovea) in myopes and emmetropes

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Table 2: Outer macular thickness (perifovea) in myopes and emmetropes

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The central foveal thickness was 298.93 ± 38.813 μm in high myopes and 224.63 ± 16.439 μm in emmetropes, which was statistically significant P < 0.001.

In the parafoveal area (inner ring), retinal thickness was significantly thin in Group 1 (myopic eyes) as compared to Group 2 (emmetropic eyes). Each zone of the parafoveal area of myopic eyes was compared with a similar zone of emmetropic eyes. Statistical analysis revealed that thinning of superior, temporal, and inferior zones in the parafoveal area in high myopes was significant P = 0.002, P < 0.001, and P < 0.001, respectively [Table 1].

Group 1 revealed that the nasal quadrant was the thickest and the temporal quadrant was the thinnest in the parafoveal area. However, the intragroup comparison was statistically significant when the superior quadrant was compared with temporal and nasal, the inferior quadrant was compared with nasal and temporal quadrants, and the nasal quadrant was compared with temporal quadrant (P < 0.001 on paired t-test).

Similarly, in the perifoveal area (outer ring), retinal thickness was significantly thin in Group 1(myopic eyes) as compared to Group 2 (emmetropic eyes). Each zone of the perifoveal area of myopic eyes was compared with a similar zone of emmetropic eyes. Statistical analyses revealed significant thinning of all the zones in the perifoveal area in high myopes [Table 2].

Interzonal comparison in Group 1 (myopes) was statistically significant when the superior quadrant was compared with temporal and inferior quadrants (P < 0.001) and also when the nasal quadrant was compared with inferior and temporal quadrants (P < 0.001).


  Discussion Top


Contrary to histologic findings and clinical observations that retinal thinning or chorioretinal atrophy is more common in myopia,[5],[12],[13],[14] the correlation between average macular thickness and myopia has been found to be insignificant in previous in vivo imaging studies.[6],[7],[8],[9],[10] However with the advent of newer imaging modalities, like SD-OCT assessment of macular thickness has led to some positive correlations in our study.

In myopic eyes, the elongation of the globe leads to mechanical stretching and thinning of the retina. The extent of the elongation is related to the degree of retinal thinning. In an OCT macular thickness study, Wakitani et al.[7] proposed that the peripheral retina is thinner in myopic eyes rather than the central retina. Studies done by Lim et al.[6] and Liu et al.[15] also had similar results stating that thinning in myopia occurred more frequently in the peripheral part. This finding was attributed to the fact that the peripheral retina lacks large blood vessels and optic fibers, which makes them less resistant to traction and stretch, and the decrease in peripheral retinal thickness may compensate for the stretching over the entire retina to preserve the central retinal thickness.

On contrary, a study done by Lam et al.,[16] proposed that perifoveal macular thickness reduced in myopia but not the parafovea. Similarly, Zhao et al.[17] reported that para and perifoveal thickness were significantly thinner in high myopes. In a study done by Waris et al.,[18] there was significant macular thinning in both para and perifoveal region. In the present study, statistically significant thinning was seen in superior, temporal, and inferior zones in the parafoveal area and all the zones in the perifoveal area of high myopes.

In the study by Samuel et al.,[19] it was concluded that the foveal thickness in high myopes was significantly greater than moderate and mild myopes. This result is similar to the study done by Xie et al.[20] Furthermore, in a study by Choi et al.,[21] the thickness of fovea increased with the level of myopia. A study done by Lam et al.[16] in the Chinese population, they found that the foveal thickness was significantly higher in high myopes than low to moderate myopes (P = 0.002). Similar outcomes were found by study done on the Asian population by Lim et al.[6] In the present study, the central foveal thickness was found to be high compared to emmetropes, which was statistically significant P < 0.000. This finding can be attributed to the retinomotor movements of the photoreceptors. In a form-deprivation myopia animal model, it was observed that the photoreceptor outer segments were elongated.[22] This increase in foveal thickness could also be an early sign of vitreoretinal traction in highly myopic eyes. This further necessitates a longitudinal follow-up study to address the issue.

Conclusion

Thus, this study described the variations in macular thickness in high myopes, which helps the clinicians to understand and thus interpret the various retinal thickness nomograms. The study highlights the fact that refractive error can be a significant factor in affecting the macular thickness, which should be considered while evaluating macular diseases such as diabetic macular edema, especially in myopes.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Lim MC, Hoh ST, Foster PJ, Lim TH, Chew SJ, Seah AK, et al. Use of optical coherence tomography to assess variations in macular retinal thickness in myopia. Invest Ophthalmol Vis Sci 2005;46:974-8.  Back to cited text no. 6
    
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8.
Zou H, Zhang X, Xu X, Yu S. Quantitative in vivo retinal thickness measurement in Chinese healthy subjects with the retinal thickness analyzer. Invest Ophthalmol Vis Sci 2006;47:341-7.  Back to cited text no. 8
    
9.
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Gobel W, Hartmann F, Haigis W. Determination of retinal thickness in relation to the age and axial length using optical coherence tomography. Ophthalmologe 2001;98:157-62.  Back to cited text no. 10
    
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Huang D, Swanson EA, Lin CP, Schuman JS, Stinson WG, Chang W, et al. Optical coherence tomography. Science 1991;254:1178-81.  Back to cited text no. 11
    
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Spencer WH. Ophthalmic Pathology: An Atlas and Textbook. 3rd ed. Philadelphia, PA: WB Saunders; 1985. p. 395-400.  Back to cited text no. 12
    
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Curtin BJ, Karlin DB. Axial length measurements and fundus changes of the myopic eye. Trans Am Ophthalmol Soc 1970;68:312-34.  Back to cited text no. 13
    
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Curtin BJ. The posterior staphyloma of pathologic myopia. Trans Am Ophthalmol Soc 1977;75:67-86.  Back to cited text no. 14
    
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Liu L, Zou J, Jia LL, Yang JG, Chen SR. Spectral and time-domain optical coherence tomography measurements of macular thickness in young myopic eyes. Diagn Pathol 2014;9:38.  Back to cited text no. 15
    
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Lam DS, Leung KS, Mohamed S, Chan WM, Palanivelu MS, Cheung CY, et al. Regional variations in the relationship between macular thickness measurements and myopia. Invest Ophthalmol Vis Sci 2007;48:376-82.  Back to cited text no. 16
    
17.
Zhao Z, Zhou X, Jiang C, Sun X. Effects of myopia on different areas and layers of the macula: A Fourier-domain optical coherence tomography study of a Chinese cohort. BMC Ophthalmol 2015;15:90.  Back to cited text no. 17
    
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Waris A, Malakar M, Askari SN, Ashraf H, Asagar A. Optical coherence tomography assisted macular thickness profile in high myopia. Studies 2015;9:NC01-3.  Back to cited text no. 18
    
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Samuel NE, Krishnagopal S. Foveal and macular thickness evaluation by spectral OCT SLO and its relation with axial length in various degree of myopia. J Clin Diagn Res 2015;9:NC01-4.  Back to cited text no. 19
    
20.
Xie R, Zhou XT, Lu F, Chen M, Xue A, Chen S, et al. Correlation between myopia and major biometric parameters of the eye: A retrospective clinical study. Optom Vis Sci 2009;86:503-8.  Back to cited text no. 20
    
21.
Choi SW, Lee SJ. Thickness changes in the fovea and peripapillary retinal nerve fiber layer depend on the degree of myopia. Korean J Ophthalmol 2006;20:215-9.  Back to cited text no. 21
    
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Liang H, Crewther DP, Crewther SG, Barila AM. A role for photoreceptor outer segments in the induction of deprivation myopia. Vision Res 1995;35:1217-25.  Back to cited text no. 22
    


    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2]



 

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