To evaluate the differences in individual segmental retinal layer thickness in adult patients with high myopia.
This study compared the retinal layers of patients with high myopia (axial length of ≥26.0 mm) with those of normal controls using spectral-domain optical coherence tomography. The thicknesses of the retinal layers were compared using nine Early Treatment Diabetic Retinopathy Study subfields. Choroidal thickness was also measured in the subfoveal area.
We included 37 eyes with high myopia and 37 eyes of healthy subjects. The mean age was 42.95 and 47.73 years (
In high myopia without pathologic changes, there was a meaningful thinning of the retina and choroid, especially in most Early Treatment Diabetic Retinopathy Study subfield areas of the deep vascular complex, perifoveal area of the superficial vascular complex, and most areas of the outer nuclear layer in the outer retinal layer, which are associated with myopic axial elongation.
High myopia is defined as a refractive error with a spherical equivalent (SE) ≤−6.0 diopters (D). The prevalence of myopia has been reported to be as high as 80% in Asia and 22.9% in other regions of the world [
Although most refractive errors can be corrected with glasses or contact lenses, high myopia can cause irreversible retinal disorders such as chorioretinal atrophy, choroidal neovascularization, and macular retinoschisis due to the small fiber diameters and histological immaturity [
Optical coherence tomography (OCT) is a non-invasive diagnostic tool that is used to obtain a cross-sectional retinal image with fine resolution, which facilitates the assessment of the microstructural retinal layers [
In the present study, we evaluated the differences in retinal layer thickness in adult patients with high myopia without retinal or optic nerve diseases, by comparing their eyes with those of normal subjects.
This retrospective, cross-sectional study was approved by the institutional review board (2019-12-014) and adhered to the tenets of the Declaration of Helsinki. Patients who visited our retinal clinic and were examined between January 2016 and October 2019 were enrolled. The requirement for informed consent was waived due to the retrospective nature of the study. The high myopia group consisted of eyes with axial lengths (ALs) of ≥26.0 mm, and the control group consisted of eyes with SEs between +3.0 and −6.0 D and AL of <26.0 mm.
Each patient underwent a complete ophthalmic examination, which included best-corrected visual acuity (BCVA), intraocular pressure (IOP) using non-contact tonometry, refraction, AL using an IOL Master 500 (Carl Zeiss, Jena, Germany), and keratometry. We used a Snellen visual acuity chart to measure the BCVA, which was converted into logarithm of the minimum angle of resolution. The exclusion criteria were as follows: BCVA <20 / 25; IOP ≥21 mmHg; a medical history of any systemic disease such as diabetes or hypertension; any ophthalmic disease that could affect the retinal layer thickness such as glaucoma and retinal and neuro-ophthalmic diseases; structural change caused by high myopia, including staphyloma, lacquer cracks, myopic neovascularization, which could induce processing errors such as individual retinal layer segmentation; a history of intraocular surgery except cataract extraction.
An experienced examiner obtained the measurements using SD-OCT (Spectralis; Heidelberg Engineering, Heidelberg, Germany). The foveal measurements obtained by the SD-OCT scan were performed using the built-in Spectralis mapping software, Heidelberg Eye Explorer ver. 6.9a. We used retinal thickness map analyses to display numeric averages of the measurements for each of the nine Early Treatment Diabetic Retinopathy Study (ETDRS) subfields (
The average thicknesses of the following nine zones were used in the analyses: SF, inner superior (IS), inner nasal (IN), inner inferior (II), inner temporal (IT), outer superior (OS), outer nasal (ON), outer inferior (OI), and outer temporal (OT). Automated retinal layer segmentation was conducted and the thickness of each layer of the nine zones was determined using automated Spectralis segmentation software. The thicknesses of the full retina, retinal nerve fiber layer (NFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), photoreceptor layer (PRL), and retinal pigment epithelium (RPE) were obtained (
The ocular parameters in the highly myopic and control groups were compared using an independent
A total of 74 eyes of 62 participants and 37 eyes in each group were enrolled. The mean ages of the highly myopic and control groups were 42.95 ± 12.3 and 47.73 ± 13.3 years, respectively, which were not significantly different (
The mean SF thicknesses of the NFLs of the high myopia and control groups were 11.24 ± 2.30 and 11.54 ± 2.97 μm, respectively (
The mean SF thicknesses of the GCLs (14.81 ± 4.96 and 14.89 ± 9.97 μm, respectively) and IPLs (18.46 ± 3.83 and 19.30 ± 6.32 μm, respectively) of the highly myopic and control groups were not statistically different. In addition, there were no significant differences among the mean thicknesses of the intermediate ring segments of the nine zones (IS, IN, II, and IT). However, the outer ring segments of the nine zones (OS, ON, OI, and OT) were thinner in the highly myopic group than in the control group (all
The mean SF thicknesses of the INLs (18.46 ± 5.49 and 19.46 ± 7.31 μm, respectively) and OPLs (29.49 ± 9.49 and 26.70 ± 8.76 μm, respectively) of the high myopia and control groups were not statistically different (
The mean SF thicknesses of the ONL were 81.70 ± 13.07 and 90.84 ± 11.87 μm in the highly myopic and control groups, respectively, which were significantly different (
In the PRL, the mean SF thicknesses (72.86 ± 3.35 and 72.37 ± 4.47 μm, respectively) were not statistically different. In addition, there were no statistical differences between the segments.
In the RPE, the mean SF thicknesses (16.62 ± 2.92 and 16.73 ± 1.92 μm, respectively) were not statistically different. There were no statistically significant differences among most of the mean thicknesses of the nine zones of the RPE, except for the IN segment, which were 14.86 ± 1.70 and 15.73 ± 1.82 μm in the highly myopic and control groups, respectively (
The mean choroidal thicknesses were 153.81 ± 64.80 and 239.54 ± 44.28 μm in the highly myopic and control groups, respectively, which were significantly different (
Highly myopic eyes can undergo several structural changes. Saka et al. [
Several previous studies have reported a relationship between the peripapillary retinal nerve fiber layer (pRNFL) and myopia. Leung et al. [
Previous studies have reported that the average thickness of all sectors of the ganglion cell (GC)-IPL is significantly lower in patients with high myopia and significantly correlated with SE and AL [
Thinning of the outer retinal layers occurs in pathological myopia [
Previous studies have reported a relationship between the disruption of photoreceptors and visual function in highly myopic patients. The disruption of the foveal ellipsoid zone and defects of the inner and outer segments, which involve the sublayer of photoreceptors, may be found in myopic eyes with poor vision [
Previous studies have reported choroidal thinning in high myopia [
In addition to its retrospective study design, our study had some limitations. First, our control group may not have completely represented normal eyes because their mean SE and AL were −2.35 ± 2.40 and 24.47 ± 0.95 D, respectively, which indicate mild to moderate myopia. However, the prevalence of myopia in eastern and southeastern Asian countries is increasing [
In the superficial capillary vascular complex of the macular area, there were no statistical differences between the NFL of eyes with high myopia and normal eyes. However, the perifoveal area of the GC-IPL was thinner in highly myopic patients. In the deep capillary vascular complex, most of the ETDRS subfields of the INL and OPL were thinner in eyes with high myopia than in normal eyes. In the outer retinal layer, most areas of the ONL were thinner in eyes with high myopia than in normal eyes. However, there were no statistical differences between the RPE and PRL thicknesses. Thinning of the choroid was also observed in highly myopic eyes. In conclusion, thinning of the choroid and retina, especially in most ETDRS subfields of the deep capillary vascular complex, were observed in high myopia without pathologic changes. Additionally, the perifoveal area of the superficial vascular complex and most ETDRS subfields of ONL in the outer retinal layer were also significantly thinner in highly myopic patients than in normal individuals; the thinning may be attributable to myopic elongation of the globe. We hypothesized that the deep capillary vascular complex and the perifoveal area of the superficial capillary vascular complex are more vulnerable to mechanical stretching, whereas the foveal area of the superficial capillary vascular complex and the PRL and PRE of the outer retinal layer were less affected in high myopia without pathologic changes. Overall, we identified structural changes in eyes with high myopia without pathologic features, which may facilitate a better understanding of myopization.
No potential conflict of interest relevant to this article was reported.
Macular regions analyzed by spectral-domain optical coherence tomography scan in the retinal thickness map analysis. (A) The macular was divided into three subfields: the subfoveal (SF) region with the diameter of 1 mm, the parafoveal region ranging from 1 to 3 mm from the SF region and the perifoveal region from 3 to 6 mm from the SF region. (B) The boundaries of fundus structure were segmented by an automated algorithm, and the thickness profiles of the each retinal sublayers and choroid were determined. OS = outer superior; IS = inner superior; ON = outer nasal; IN = inner nasal; IT = inner temporal; OT = outer temporal; II = inner inferior; OI = outer inferior; NFL = retinal nerve fiber layer; GCL = ganglion cell layer; IPL = inner plexiform layer; INL = inner nuclear layer; OPL = outer plexiform layer; ONL = outer nuclear layer; PRL = photoreceptor layer; PR1 = photoreceptor layer1; PR2 = photoreceptor layer2; RPE = retinal pigment epithelium; ETDRS = Early Treatment Diabetic Retinopathy Study.
(A,B) Representative optical coherence tomography images of high myopic eyes in the retinal thickness map analysis of spectral-domain optical coherence tomography scan. The boundaries of fundus structure were segmented by an automated algorithm, and the thickness profiles of the each retinal sublayers and choroid were determined. NFL = retinal nerve fiber layer; GCL = ganglion cell layer; IPL = inner plexiform layer; INL = inner nuclear layer; OPL = outer plexiform layer; ONL = outer nuclear layer; PRL = photoreceptor layer; PR1 = photoreceptor layer1; PR2 = photoreceptor layer2; RPE = retinal pigment epithelium.
Optical coherence tomography B-scan images and 700% magnification images of representative (A) normal eye and (B) highly myopic eye. Seven hundred percent magnification was done in perifoveal area (white boxes). Axial length of normal eye and high myopic eye were 24.33 and 28.79 mm, respectively. In highly myopic eyes, individual retinal layers, especially ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), were thinner than in normal eyes. NFL = retinal nerve fiber layer; PRL = photoreceptor layer; RPE = retinal pigment epithelium.
Demographics
High myopia (n = 37) | Control group (n = 37) | ||
---|---|---|---|
Age (yr) | 42.95 ± 12.3 | 47.73 ± 13.3 | 0.114 |
Sex, male | 13 (35.0) | 15 (40.5) | 0.632 |
Laterality (right) | 23 (62.1) | 15 (40.5) | 0.063 |
Lens status (phakia) | 31 (83.7) | 32 (86.4) | 0.744 |
BCVA (logMAR) | 0.024 ± 0.03 | 0.016 ± 0.03 | 0.338 |
IOP (mmHg) | 13.59 ± 3.36 | 14.32 ± 3.59 | 0.370 |
Axial length (mm) | 27.28 ± 0.96 | 24.47 ± 0.95 | <0.001 |
Spherical equivalent (D) | −6.42 ± 3.96 | −2.35 ± 2.40 | <0.001 |
Values are presented as mean ± standard deviation or number (%).
BCVA = best-corrected visual acuity; logMAR = logarithm of the minimum angle of resolution; IOP = intraocular pressure; D = diopters.
Retinal layer thickness of superficial capillary vascular complex
High myopia | Control | ||
---|---|---|---|
NFL-SF | 11.24 ± 2.30 | 11.54 ± 2.97 | 0.632 |
NFL-IS | 26.22 ± 4.47 | 25.27 ± 5.40 | 0.364 |
NFL-IT | 18.27 ± 2.07 | 18.00 ± 1.87 | 0.558 |
NFL-II | 27.03 ± 4.82 | 24.35 ± 3.28 | 0.007 |
NFL-IN | 22.19 ± 3.19 | 21.68 ± 3.35 | 0.502 |
NFL-OS | 41.62 ± 5.53 | 39.32 ± 6.50 | 0.106 |
NFL-OT | 22.22 ± 1.85 | 19.57 ± 1.83 | 0.135 |
NFL-OI | 41.78 ± 0.86 | 40.08 ± 6.36 | 0.339 |
NFL-ON | 53.05 ± 7.93 | 50.14 ± 8.81 | 0.139 |
GCL-SF | 14.81 ± 4.96 | 14.89 ± 9.97 | 0.965 |
GCL-IS | 51.51 ± 5.56 | 52.24 ± 5.61 | 0.576 |
GCL-IT | 45.70 ± 7.26 | 47.24 ± 5.18 | 0.298 |
GCL-II | 50.62 ± 6.66 | 50.51 ± 5.90 | 0.941 |
GCL-IN | 50.32 ± 5.34 | 51.92 ± 5.05 | 0.191 |
GCL-OS | 34.11 ± 3.94 | 35.92 ± 3.02 | 0.030 |
GCL-OT | 34.64 ± 5.76 | 37.14 ± 3.80 | 0.032 |
GCL-OI | 31.59 ± 3.90 | 33.95 ± 5.22 | 0.032 |
GCL-ON | 37.16 ± 4.07 | 40.03 ± 2.81 | 0.001 |
IPL-SF | 18.46 ± 3.83 | 19.30 ± 6.32 | 0.493 |
IPL-IS | 39.81 ± 3.49 | 41.00 ± 3.35 | 0.140 |
IPL-IT | 39.84 ± 4.69 | 41.62 ± 3.59 | 0.071 |
IPL-II | 39.70 ± 3.96 | 40.43 ± 3.23 | 0.389 |
IPL-IN | 41.41 ± 2.92 | 42.78 ± 3.43 | 0.067 |
IPL-OS | 27.78 ± 3.13 | 29.27 ± 2.36 | 0.024 |
IPL-OT | 31.97 ± 3.32 | 33.32 ± 2.23 | 0.044 |
IPL-OI | 26.03 ± 2.85 | 27.89 ± 3.57 | 0.015 |
IPL-ON | 28.86 ± 2.43 | 30.89 ± 2.19 | <0.001 |
Values are presented as mean ± standard deviation.
NFL = retinal nerve fiber layer; SF = subfovea; IS = inner superior; IT = inner temporal; II = inner inferior; IN = inner nasal; OS = outer superior; OT = outer temporal; OI = outer inferior; ON = outer nasal; GCL = ganglion cell layer; IPL = inner plexiform layer.
Retinal layer thickness of deep capillary vascular complex
High myopia | Control | ||
---|---|---|---|
INL-SF | 18.46 ± 5.49 | 19.46 ± 7.31 | 0.508 |
INL-IS | 38.11 ± 4.20 | 41.78 ± 3.06 | <0.001 |
INL-IT | 36.00 ± 3.70 | 37.97 ± 3.06 | 0.015 |
INL-II | 38.84 ± 4.78 | 41.38 ± 4.95 | 0.028 |
INL-IN | 37.92 ± 4.05 | 42.16 ± 4.20 | <0.001 |
INL-OS | 30.78 ± 3.98 | 32.49 ± 2.29 | 0.027 |
INL-OT | 31.86 ± 2.98 | 33.46 ± 2.19 | 0.011 |
INL-OI | 29.92 ± 2.78 | 33.11 ± 4.83 | 0.001 |
INL-ON | 32.49 ± 3.32 | 34.76 ± 2.54 | 0.002 |
OPL-SF | 29.49 ± 9.49 | 26.70 ± 8.76 | 0.194 |
OPL-IS | 29.14 ± 5.35 | 33.73 ± 9.18 | 0.010 |
OPL-IT | 32.54 ± 6.45 | 31.51 ± 7.10 | 0.517 |
OPL-II | 43.73 ± 9.60 | 36.05 ± 10.2 | 0.001 |
OPL-IN | 36.46 ± 9.73 | 35.65 ± 10.9 | 0.737 |
OPL-OS | 24.16 ± 1.74 | 26.57 ± 2.45 | <0.001 |
OPL-OT | 24.14 ± 4.09 | 26.56 ± 2.90 | 0.002 |
OPL-OI | 26.70 ± 2.89 | 27.43 ± 2.76 | 0.271 |
OPL-ON | 27.59 ± 3.70 | 29.92 ± 4.21 | 0.014 |
Values are presented as mean ± standard deviation.
INL = inner nuclear layer; SF =subfovea; IS = inner superior; IT = inner temporal; II = inner inferior; IN = inner nasal; OS = outer superior; OT = outer temporal; OI = outer inferior; ON = outer nasal; OPL = outer plexiform layer.
Outer retinal layer thickness
High myopia | Control | ||
---|---|---|---|
ONL-SF | 81.70 ± 13.07 | 90.84 ± 11.87 | 0.002 |
ONL-IS | 68.22 ± 9.48 | 69.35 ± 12.19 | 0.656 |
ONL-IT | 65.92 ± 9.93 | 74.86 ± 9.86 | <0.001 |
ONL-II | 50.11 ± 12.29 | 64.86 ± 15.47 | <0.001 |
ONL-IN | 64.73 ± 13.47 | 71.22 ± 13.76 | 0.044 |
ONL-OS | 57.92 ± 6.67 | 60.08 ± 6.45 | 0.161 |
ONL-OT | 55.32 ± 4.91 | 59.14 ±6.43 | 0.005 |
ONL-OI | 46.32 ± 7.82 | 52.65 ± 8.14 | 0.001 |
ONL-ON | 52.49 ± 8.32 | 56.00 ± 7.89 | 0.067 |
PRL-SF | 72.86 ± 3.35 | 72.37 ± 4.47 | 0.599 |
PRL-IS | 66.94 ± 3.04 | 66.56 ± 2.03 | 0.532 |
PRL-IT | 67.70 ± 0.81 | 67.56 ± 1.48 | 0.810 |
PRL-II | 65.56 ± 2.41 | 66.62 ± 2.58 | 0.074 |
PRL-IN | 67.13 ± 2.32 | 67.62 ± 2.31 | 0.370 |
PRL-OS | 65.83 ± 2.29 | 66.08 ± 1.96 | 0.625 |
PRL-OT | 65.51 ± 2.55 | 66.24 ±2.12 | 0.186 |
PRL-OI | 63.86 ± 1.81 | 64.48 ± 2.19 | 0.188 |
PRL-ON | 65.29 ± 1.71 | 65.72 ± 1.86 | 0.303 |
RPE-SF | 16.62 ± 2.92 | 16.73 ± 1.92 | 0.852 |
RPE-IS | 14.92 ± 1.92 | 15.76 ± 2.11 | 0.079 |
RPE-IT | 14.19 ± 1.41 | 14.46 ± 1.48 | 0.425 |
RPE-II | 14.19 ± 1.88 | 14.84 ± 1.51 | 0.107 |
RPE-IN | 14.86 ± 1.70 | 15.73 ± 1.82 | 0.038 |
RPE-OS | 13.65 ± 1.31 | 14.08 ± 1.65 | 0.218 |
RPE-OT | 13.27 ± 1.42 | 13.24 ±1.36 | 0.934 |
RPE-OI | 13.11 ± 1.32 | 13.51 ± 1.21 | 0.175 |
RPE-ON | 13.59 ± 1.46 | 13.84 ± 1.16 | 0.432 |
Values are presented as mean ± standard deviation.
ONL = outer nuclear layer; SF = subfovea; IS = inner superior; IT = inner temporal; II = inner inferior; IN = inner nasal; OS = outer superior; OT = outer temporal; OI = outer inferior; ON = outer nasal; PPL = photoreceptor layer; RPE = retinal pigment epithelium.