|Year : 2020 | Volume
| Issue : 1 | Page : 22-25
A comparative study of OCT findings in low and high myopia
Tarek M Abdalla1, Amr I Elawamry1, Ossama T Nada1, Mariam R Helal2
1 Department of Ophthalmology, Ain Shams University, Assiut, Egypt
2 Department of Ophthalmology, Assiut Police Hospital, Assiut, Egypt
|Date of Submission||16-May-2019|
|Date of Acceptance||21-Jun-2019|
|Date of Web Publication||15-May-2020|
MBBCh Mariam R Helal
Assiut Police Hospital, Assiut, 71515
Source of Support: None, Conflict of Interest: None
Aim This study aimed to compare macular findings between low and high myopia.
Patients and methods In all, 60 myopic eyes were included in this study. They were divided according to refraction into low myopia of less than or equal −6 SD and high myopia of more than −6 SD. All patients were subjected to automated refraction, correction of vision, A-scan by Isa intra Ocular length (IOL) master for axial length, and optical coherence tomography (OCT) scan for macular mapping.
Results The mean central macular thickness (CMT) of low myopic cases was 255.5±17.13, with all low myopic cases showing no complication by OCT while the mean CMT of high myopia was 262.10±67.51 with some complications. Regarding choroidal neovascularization (CNV), it was statistically significantly higher in the high myopic group when compared with the low myopic group, while macular hole showed no significance. Thinning of RPE and myopic contour showed high significant statistical difference to high myopic group.
Discussion The mean CMT of low myopic cases was slightly thinner than in high myopic cases but with no statistical significance. Myopic CNV is more common with high myopia and may be related to sex. Thinning of RPE and myopic contour are mainly found in high myopia.
Conclusions In our study, there was no significant correlation between CMT and axial length. Regarding CNV, it was statistically significantly higher in the high myopic group when compared with the low myopic group, while macular hole showed no significance. Thinning of RPE and myopic contour are mainly found in high myopia.
Keywords: axial length and OCT, myopia, pathological myopia, simple myopia
|How to cite this article:|
Abdalla TM, Elawamry AI, Nada OT, Helal MR. A comparative study of OCT findings in low and high myopia. J Egypt Ophthalmol Soc 2020;113:22-5
|How to cite this URL:|
Abdalla TM, Elawamry AI, Nada OT, Helal MR. A comparative study of OCT findings in low and high myopia. J Egypt Ophthalmol Soc [serial online] 2020 [cited 2020 Jun 5];113:22-5. Available from: http://www.jeos.eg.net/text.asp?2020/113/1/22/284338
| Introduction|| |
Myopia is a Greek word, meaning closing or contracting the eye . Myopia is a spherical refractive error where parallel light rays enter the eye making the point of conjugate focus displaced anteriorly in front of the retina, when the eye is not accommodating . Prevalence of myopia is in constant increase, it has affected around 22.9% of the whole world population. Myopia is classified into simple, low myopia, and pathological high myopia. Simple myopia is usually minimal (<−6.00 SD) starting during childhood or adolescence with slow progression through the adolescent growth period to be stable in the early twenties .
Pathologic myopia is high myopic refractive error affecting young children with continuous progression. Pathologic myopia is usually with (>−6.00 SD) or axial length (AL) more than 26.5 mm. Those with high axial myopia are more prone to develop progressive degeneration of the retina threatening their quality of vision .
SD-OCT is capable of taking many scans of average 30 000 scans per second decreasing the artifact that could be done by eye movement, giving better resolution and less opportunity to miss any pathological lesion unintentionally .
In our study, we aimed to compare macular optical coherence tomography (OCT) findings between low and high myopic cases among a group of Egyptian population.
| Patients and methods|| |
Our study comprised 60 myopic eyes attending the Al Nour Investigative Eye Center in Assiut. This study was approved by ethical committee of Ain Shams University. Ages of the participants ranged from 20 to 70 years. They were divided according to refraction into low myopia of less than −6 SD (30 patients, 15 women and six men) and high myopia of more than −6 SD (30 patients, 12 women and seven men). The patients had no current ocular disease. Patients were excluded if they had dense media opacity, had any ocular surgery in the same eye, taking any ophthalmic eye drops, ointments or injections, with systemic diseases such as diabetes mellitus or toxoplasmosis. In addition to full ophthalmological examination, all patients were subjected to AL measurement by Isa intra Ocular length (IOL) Master 500, SD-OCT Heidelberg Engineering (10 Forge Parkway, Franklin, MA, USA) to assess the macula. Macular evaluation by OCT will include vertical and horizontal line scans averaged to 100 frames measuring 30°, centered around the fovea and macular thickness maps 15×15 averaged to 10 frames, centered around the fovea. All patients signed an informed written consent before investigations including the type and technique of the procedure.
The collected data was revised and introduced to a PC using the statistical package for social sciences (IBM Corp. Released 2011, IBM SPSS Statistics for Windows, version 20.0.;IBM Corp., Armonk, New York). Data were presented by mean±SD, Student’s t test was used to assess the statistical significance between two study groups while using Pearson’s method for correlation analysis and c2 test for qualitative variables. P value: level of significance, P value more than 0.05: nonsignificant, P value less than 0.05: significant, P value less than 0.01: highly significant.
| Results|| |
The mean age among the low myopic case was 48±14.4, with women representing 71.4% of cases; the mean age among high myopic cases was 44.8±16.1, with women representing 63.2% of cases ([Table 1]).
|Table 1 Comparison between high and low myopic cases as regards personal data|
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There was a highly significant difference between high and low myopic cases as regards refraction, spherical equivalent, and AL with better findings among low myopic cases ([Table 2]).
|Table 2 Comparison between low and high myopic cases as regards refraction, spherical equivalent, and axial length|
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The mean refraction, spherical equivalent (SE), and AL of low myopic cases was −2.7±1.13, −3.03±1.28, and 24.04±0.91, respectively, while the mean refraction, SE, and AL of high myopic cases was −11.13±5.21, −12.52±3.59, 28.07±1.65, respectively ([Table 3],[Table 4],[Table 5],[Table 6],[Table 7]).
|Table 3 Comparison between low and high myopic cases as regards OCT findings|
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|Table 4 Correlation between refraction and central macular thickness among all cases|
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|Table 5 Correlation between axial length and central macular thickness among all cases|
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|Table 6 Correlation between high myopic cases with and without choroidal neovascularization as regards clinical parameters|
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|Table 7 Correlation between high myopic cases with and without macular hole as regards clinical parameters|
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The mean central macular thickness (CMT) of low myopic cases was 255.5±17.13, with all low myopic cases showing no complication by OCT, while the mean CMT of high myopia was 262.10±67.51. Regarding choroidal neovascularization (CNV), it was statistically significantly higher in the high myopic group when compared with the low myopic group, while macular hole showed no significance. Macular hole was not significant between two groups. Thinning of RPE and myopic contour showed high significant statistical difference with high myopic group.
| Discussion|| |
In agreement with Ohsugi , there was no significant findings including myopic macular complication in the low myopic group with respect to sex and, mean age, and the mean CMT was 255.5±17.13.
There was significant findings including macular complications in high myopia, where the mean CMT was 262.10±67.51; the mean CNV was positive in five (16.7%) patients, the mean macular hole in one (3.3%) patient, thinning of RPE in 10 (33.3%), and myopic contour in 30 (100%).
Evaluation of macular thickness is now considered a fundamental tool in the analysis and follow up of degeneration of macula in myopia. On the other hand, there is still no general agreement on the correlation of refractive errors with CMT where Huynh et al.  established that hyperopic patients have thicker CMT, while Wakitani et al.  established that myopic patients have thicker CMT and Lim et al.  established no significant correlation between CMT and refractive errors as in our study there was no correlation between them.
Myopia progresses with an increase in the refractive power and AL of the eye. Larsen  have initiated that when the AL of myopic patients increase, the sclera becomes mechanically stretched in the posterior pole.
There is a long debate about the correlation between CMT and AL. In our study, there was no correlation between them as in many other studies but Samuel and Krishnagopal  found in their study that AL is related to macular thickness in myopia where the foveae minimum of pathological myopia (178±26.4 μm) was more thick than low myopia. They found a positive correlation between AL and foveae minimum (P<0.05). Different outcomes can be due to differences in the number of patients in sample size through different studies as well as different protocols used with different OCT devices.
Myopic CNV is a very serious sight-threatening complication of myopia, especially pathological myopia (PM) where Avila et al.  studies had estimated the prevalence of PM in adults is 1–3%, while 5–11% of them developed myopic choroidal neovascularization (mCNV). The pathogenesis of mCNV is still a mystery. However, the presence of lacquer cracks and/or chorioretinal atrophy may be responsible for mCNV occurrence as stated by Ikuno et al. .
In our study, four out of five mCNV were women, perhaps due to the higher number of female participants in the study or myopia is more related to women as stated by Ohsugi et al.  and Gong et al. .
| Conclusion|| |
In our study, there was no significant correlation between CMT and AL or between CMT and refraction. Regarding CNV, it was statistically significantly higher in the high myopic group when compared with the low myopic group while macular hole showed no significance. Thinning of RPE and myopic contour are mainly found in high myopia.
As stated by Chan et al. , OCT became an essential investigative device to assess the fovea and macular thickness with a map and presence of any abnormalities in the normal architecture of the macula. Also, it is used to follow up the treatment schedule and compare it to the baseline or original image before treatment.
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Conflicts of interests
There are no conflicts of interests.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]