Correlation between Metamorphopsia andEpiretinal Membrane Optical Coherence
Tomography Findings
Akinari Watanabe, MD, Sachiko Arimoto, MD, Okihiro Nishi, MD
Purpose: To examine the retinal morphologic features of metamorphopsia caused by epiretinal membrane(ERM) and to determine whether spectral-domain optical coherence tomography (SD-OCT) correlated withmetamorphopsia.
Design: Retrospective case series.
Participants: This study included 19 eyes of 19 patients with ERM diagnosed by clinical ophthalmic findings
and SD-OCT.
Methods: The 19 eyes were classified into 3 groups based on Amsler chart results: no metamorphopsia (n ⫽4), local metamorphopsia (n ⫽ 8), and broad metamorphopsia (n ⫽ 7). The thickness of the 3 inner retinal layers:
inner nuclear layer (INL), outer plexiform layer (OPL), and outer nuclear layer (ONL), on 5 horizontal SD-OCT
cross-sections (1 line through the fovea, 2 regularly spaced lines superior to the fovea, and 2 regularly spacedlines inferior to the fovea) were measured using the electronic calipers of the SD-OCT system.
Main Outcome Measures: Correlation between INL, OPL, and ONL thickness with metamorphopsia andvisual acuity.
Results: Metamorphopsia was detected in the same position as edematous areas of the INL with a thickness⬎50 ␮m. The maximum INL thickness was relatively significantly different between the subjects with nometamorphopsia and those with local or broad metamorphopsia (vs local, P ⫽ 0.06; vs broad, P ⫽ 0.04). Visualacuity significantly correlated with both maximum INL thickness (A ⫽ ⫺0.681; P ⫽ 0.001) and maximum ONL
thickness (A ⫽ ⫺0.708; P⬍0.001) in metamorphopsia.
Conclusions: Metamorphopsia induced by ERM may be related to the edematous areas of the INL detectedwith SD-OCT. The classification of ERM based on INL thickness is a potentially useful indication for surgery.
Financial Disclosure(s): The authors have no proprietary or commercial interest in any of the materials discussed
in this article. Ophthalmology 2009;116:1788 –1793 © 2009 by the American Academy of Ophthalmology.

Idiopathic epiretinal membrane (ERM) is a disorder inwhich the vitreomacular interface induces a tangential tractional force on the retina, leading to deformation of theretinal architecture. Generally, ERM is asymptomatic;
therefore, most patients with the disease have normal ornearly normal vision with occasional metamorphopsia. The
onset of metamorphopsia can be slow and imperceptible,
such that an Amsler chart is the only means of detection.
Although several possible causes of the metamorphopsia
and reduced visual acuity have been considered, including
macular distortion, vascular leakage, shallow tractional retinal detachment, opacity owing to ERM itself, and disarrayof the photoreceptors in the sensory retina,1–3 to date there
is no direct evidence supporting any of these possibilities.
Metamorphopsia is usually detected as a subjective
symptom using an Amsler chart, and there are currently no
examinations that provide objective data. Detection ofmetamorphopsia using an Amsler chart can also be influenced by visual acuity disturbances such as severe cataract
or corneal opacity. Metamorphopsia is a symptom associated not only with ERM but with several other diseases aswell. For that reason, establishing an objective method for
detecting metamorphopsia is clinically important.

1788© 2009 by the American Academy of Ophthalmology
Published by Elsevier Inc.

In the present study, we evaluated the correlation between the degree of metamorphopsia using an Amsler chartand the thickness of the inner retinal layers based on
3-dimensional (3D) spectral-domain optical coherence tomography (SD-OCT) to determine whether correlates ofsubjective metamorphopsia in patients with ERM could beobjectively detected using SD-OCT. In addition, we attempted to construct an ERM classification scheme basedon morphometric and objective OCT findings.

Materials and Methods
Study Participants and Clinical Examination
The study was a nonrandomized, retrospective case series of 19eyes of 19 patients with idiopathic ERM diagnosed by clinicalfindings from ophthalmic examination and SD-OCT. Cases withsecondary membrane formation owing to diabetic retinopathy andeyes with previous retinal detachment surgery or pars plana vitrectomy were excluded. Eyes with reduced vision owing to othercauses, such as severe cataract, glaucoma confirmed by optic nerve
head glaucomatous changes, visual field defects, and age-related
macular degeneration, were excluded. We also excluded eyes forwhich accurate OCT images could not be obtained. The mean
ISSN 0161-6420/09/$–see front matterdoi:10.1016/j.ophtha.2009.04.046

Watanabe et al 䡠 Correlation between Metamorphopsia and OCT Findings
age ⫾ standard deviation (SD) of the 11 women and 8 men
diagnosed with ERM was 71.2⫾6.4 years (range, 55– 81). To
compare and understand normal retinal morphologic features,
healthy patients (5 men, 5 women) were also examined. The meanage ⫾ SD was 69.2⫾6.2 years (range, 56 –75).
All eyes were examined for the presence of metamorphopsia
using an Amsler chart. The eyes were classified into 3 groups: nometamorphopsia (defined as not detected by the Amsler chart),
local metamorphopsia (defined as metamorphopsia involving lessthan two thirds of the Amsler chart), or broad metamorphopsia(defined as metamorphopsia involving more than two thirds of theAmsler chart). In addition to comprehensive ophthalmic examination, including best-corrected visual acuity in decimal notation,
SD-OCT (3D OCT 1000 Topcon Corp, Tokyo, Japan) was performed to evaluate tomographic features and measure the innerretinal layers.

Optical Coherence Tomography Scanning
ProcedureThe 3D datasets were obtained using the raster scan protocol of
128 horizontal B-scan images, each composed of 512 axial scans.
This raster scan protocol covers an area of 6 mm (horizontal) ⫻ 6
mm (vertical) ⫻ 1.7 mm (axial) with a horizontal pixel spacing of
11 ␮m (6 mm/512) and a vertical pixel spacing of 47 ␮m (6mm/128). We obtained 3D datasets centered on the fovea for eachpatient. Volumetric rendering of the dataset was performed using
the image processing software provided by the SD-OCT for 3D
image reconstruction.

Thickness Measurements of the Inner Retinal
LayersTo measure the thickness of the inner retinal layers, 5 horizontal
B-scan cross-sections on 3D OCT were examined: 1 horizontal
B-scan cross-section through the fovea, 2 regularly spaced horizontal B-scan cross-sections superior to the fovea, and 2 regularly
spaced horizontal B-scan cross-sections inferior to the fovea (Fig 1).
The retinal layer borders were determined based on the refractive differences between the inner retinal layers using the macularsegmentation algorithm for OCT developed by Ishikawa et al4 andTan et al.5 The thickness of the inner nuclear layer (INL) and outer
nuclear layer (ONL), defined as the width of the lowest blackscattering and lowest black-reflection layers, and the thickness ofthe outer plexiform layer (OPL), defined as the width of the highlyreflective line between the INL and ONL, were measured vertically at as many points as possible on each of the 5 horizontal
B-scan cross-sections. In particular, the ONL thickness measurement was defined as the vertical length from the highly reflective
line corresponding to the junction between the photoreceptor innerand outer segment to the lower edge of the highly reflective line
corresponding to the OPL. The INL, OPL, and ONL thickness
measurements were carefully obtained at points where there were
obvious differences between the black reflective line and thehighly reflective line. The thickness measurements of the innerretinal layers were performed manually using the electronic calipers of the 3D-OCT 1000 system.

Statistical Analysis
Statistical analysis was performed using the Pearson correlation
factor, Student t test, and Welch’s t test. For all analyses, P⬍0.05
was considered significant. All statistical analyses were performed
using Statcel (2nd ed), an add-in module for Microsoft Excel(Statcel 2nd ed, OMS, Tokyo, Japan).

Results
Normal Cases
Mean thickness of the INL, OPL, and ONL, findings of the Amsler
chart and SD-OCT through the fovea are presented in Figure 2. The
Mean thicknesses of the INL, OPL, and ONL without the central
fovea were 31.1⫾5.1, 18.8⫾4.1, and 63.0⫾11.8 ␮m, respectively.
The mean thickness of the ONL at the central fovea was 113.0⫾10.9
␮m. Although the thickness of the ONL was highly variable, thethicknesses of the INL and OPL were almost fixed.

Selected Cases with Epiretinal Membrane
The INL, OPL, and ONL thickness values and findings of theAmsler chart and SD-OCT through the fovea of 3 eyes of the 19
patients included in the study are presented in Figure 2 (case 1 withno metamorphopsia, case 2 with local metamorphopsia, and case 3
with broad metamorphopsia).
In case 1, ERM was observed over a broad retinal region, but
no metamorphopsia was detected. The INL, OPL, and ONL thickness ranged from 22 to 39, 11 to 29, and 31 to 116 ␮m, respectively. The INL and ONL tended to be slightly edematous.
In case 2, local metamorphopsia on the Amsler chart was
detected in the same position as edematous areas of the INL thatwere ⬎50 ␮m thick. The ONL and OPL in the same position ofmetamorphopsia tended to be edematous but had varying thicknesses. Edematous areas of the INL that were ⬎50 ␮m thick weremore clearly present in the same position of the metamorphopsia
than edematous areas of the ONL and OPL. The position ofmetamorphopsia on the Amsler chart correlated highly with theedematous areas of the INL.
In case 3, with broad metamorphopsia, the INL, OPL, and ONL
had diverse and severe edematous changes. The edematous area of
the INL that had a thickness of ⬎50 ␮m was in almost the same
position as the metamorphopsia.

Patient Characteristics
Patient characteristics are summarized in Table 1. The 19 eyes
were classified into 3 groups based on Amsler chart results: 4 eyeswith no metamorphopsia, 8 eyes with local metamorphopsia, and7 eyes with broad metamorphopsia.
The maximum thickness of the INL in eyes with no metamorphopsia tended to differ from that in eyes with local metamorphopsia (P ⫽ 0.06) and significantly differed from that in eyeswith broad metamorphopsia (P ⫽ 0.04). The OPL and ONL tended
to be edematous in the area of the metamorphopsia, but there wereno significant differences between eyes with no metamorphopsia
and those with local or broad metamorphopsia (vs local: OPL, P ⫽0.49; ONL, P ⫽ 0.77; vs broad: OPL, P ⫽ 0.12; ONL, P ⫽ 0.10).

Relationship between Visual Acuity and Inner
Nuclear Layer, Outer Plexiform Layer, and Outer
Nuclear Layer Thicknesses
There was a significant negative correlation between visual acuity
and the maximum thickness of the INL (A ⫽ ⫺0.681; P ⫽ 0.001)
and ONL (A ⫽ ⫺0.708; P⬍0.001) in the area of metamorphopsia(Fig 3). There was a slight negative correlation between visualacuity and ONL thickness at the central fovea (A ⫽ ⫺0.527; P ⫽0.043). Visual acuity and maximum OPL thickness did not correlate in the area of metamorphopsia (A ⫽ ⫺0.179; P ⫽ 0.463).

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Figure 1. Five horizontal B-scan cross-sections and thickness measurement of the inner retinal layer. Line C is a single horizontal B-scan cross-section
through the fovea. Lines A, B and D, E are 4 horizontal B-scan cross-sections, placed at regular intervals superior (A, B) and inferior (D, E) to that of
the horizontal line through the fovea. F, Measurements of the inner retinal layer on line C through the fovea performed using the electronic calipers.

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Watanabe et al 䡠 Correlation between Metamorphopsia and OCT Findings
Table 1. Patient Characteristics
Metamorphopsia Findings

None*

Local

Broad

No. of eyes
Mean age, y (range)
GenderMale
FemaleMean visual acuity (range)
P vs no metamorphopsia
Mean maximum INL thickness ⫾ SD (range) in the area correlating
to metamorphopsia
P vs no metamorphopsia
Mean maximum OPL thickness ⫾ SD (range) in the area
correlating to metamorphopsia
P vs no metamorphopsia
Mean maximum ONL thickness ⫾ SD (range) in the area
correlating to metamorphopsia
P vs no metamorphopsia
Mean maximum ONL thickness ⫾ SD (range) at the central fovea
P vs no metamorphopsia

469.0 (64–74)

8
69.8 (55–81)

7
74.6 (69–81)

2
2
1.03 (0.9–1.2)
43.8⫾4.4 (38–48)

3
5
0.83 (0.4–1.0)
0.14
68.8⫾18.8 (50–109)

3
4
0.46 (0.1–1.0)
0.02
125.3⫾81.8 (47–289)

26.0⫾3.2 (22–29)

0.06
30.4⫾11.7 (14–50)

0.04
35.1⫾13.0 (25–59)

147.8⫾66.9 (95–245)

0.49
134.4⫾72.8 (52–225)

0.12
257.4⫾108.9 (104–389)

0.77
179.6⫾65.9 (78–248)
0.45

0.10
258.6⫾108.4 (87–389)
0.10

147.8⫾66.9 (95–245)

INL ⫽ inner nuclear layer; ONL ⫽ outer nuclear layer; OPL ⫽ outer plexiform layer; SD ⫽ standard deviation.
*In the case of metamorphopsia findings “none,” the INL, OPL, and ONL thicknesses in the area of metamorphopsia indicate the mean maximum
thickness value of INL, OPL, and ONL in the 5 horizontal B-scan cross-sections.

Discussion
In the present study, SD-OCT was useful for detecting
objective changes in the inner retinal layers. Metamorphopsia was detected in almost the same position as the edematous areas of the INL, especially areas that were ⬎50-␮m
thick. Maximum INL thickness differed significantly between eyes with no metamorphopsia and eyes with broad
metamorphopsia. The ONL and OPL also tended to beedematous in the area of metamorphopsia, but these changes
were not significantly related to the area of metamorphopsia. Therefore, INL thickness mapping based on SD-OCT
findings may be a useful and objective method for determining the position of metamorphopsia.
The simplest retinal circuit is a 3-neuron chain: cone tobipolar cell to ganglion cell.6 This is the so-called verticalpathway, and it is the shortest circuit between the retinal
image and one-to-one correspondence with the central nervous system.6 The INL contains horizontal, bipolar, amacrine, and Müller cell bodies; the OPL is the area in whichphotoreceptors communicate with the horizontal cells andbipolar cells. The ONL contains the photoreceptor cellbodies, both rods and cones.6
Metamorphopsia on the Amsler chart was detected in thesame position as the change in INL thickness, which might
be due to changes in the bipolar, horizontal, amacrine, andMüller cell bodies. We hypothesize that metamorphopsia
begins with changes in INL thickness, which interferes withthe one-to-one correspondence between the retinal image andthe central nervous system. There were also some edematouschanges in the OPL and ONL in the area of metamorphopsia,
which may result in insufficient synaptic junctions and low
photoreceptor sensitivity, leading to metamorphopsia.
There are some reports about the influence of central
retinal thickness on visual acuity in patients with ERM.
Suzuki et al7 reported that foveal thickness and visual acuityin patients with ERM were not related to macular pseudohole.
Liu et al8 reported that central retinal thickness and visualacuity were negatively correlated, and Michalewski et al9
reported a significant negative correlation between foveal
thickness and visual acuity. In the present study, visual acuity
and maximum ONL thickness in the area of metamorphopsia
or central fovea were significantly negatively correlated. There
was also a negative correlation between visual acuity andmaximum INL thickness in the area of metamorphopsia. Because the maximum INL thickness position was not at the
fovea, however, further study is required to understand thiscorrelation between visual acuity and INL thickness.
In most ophthalmology centers, macular surgery for
ERM removal is advocated if the best-corrected visualacuity falls below approximately 20/30 (0.6), but there are
no reports of objective indications for surgery, such as OCT
findings.10,11 In this study, eyes with a visual acuity of 20/30(0.6) showed thickness changes; that is, the INL had athickness of approximately 100 ␮m and the ONL had athickness of approximately 250 ␮m (Fig 3).

4™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™
Figure 2. Normal case and selected cases with epiretinal membrane. The thickness value of the healthy case indicates the mean thickness value of 10 cases. Cases
1 through 3 show selected cases with epiretinal membrane (case 1 with no metamorphopsia; case 2 with local metamorphopsia; case 3 with broad
metamorphopsia). A, Amsler chart findings. B, Spectral domain optical coherence tomography findings through the fovea. C, The thickness value of the inner
nuclear layer (INL). Red number indicates a greater than 50-␮m thickness. D, The outer plexiform layer (OPL) thickness value. E, The outer nuclear layer (ONL)
thickness value. Area enclosed by yellow line indicates the area correlating to metamorphopsia. OD, right eye; OS, left eye; VA ⫽ visual acuity.

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According to these results, we classified ERM into 1 of
4 stages based on the INL thickness. Stage 0 represents
ERM without metamorphopsia and INL thickness ⱕ50 ␮m.
In stage 1, there is ERM with local metamorphopsia, amaximum INL thickness between 50 ␮m and 100 ␮m, andvisual acuity ⬎0.6. In stage 2, there is ERM with broad
metamorphopsia, an INL thickness ⬎100 ␮m, and visualacuity between 0.6 and 0.4. In stage 3, there is ERM withsevere and broad metamorphopsia, varying INL thickness,and visual acuity ⬍0.4 (Table 2).
In previous studies, ERM was classified based on aclinical scale or on OCT findings.12,13 Gass proposed classifying ERM severity on a clinical scale with grades 0
through 2.12 Wilkins et al13 and Mori et al12 classified ERM
into 2 groups based on OCT findings. With regard to theclassification of metamorphopsia on vertical and horizontal
center lines, Matsumoto et al14 divided ERM into 3 groups

Table 2. Epiretinal Membrane Classification

Stage

Degree ofMetamorphopsia

0

None

1
2
3

Local
Broad
Broad and severe

Maximum
Thickness of Inner
Nuclear Layer (␮m)⬍50
50–100⬎100
VariedVisualAcuityWithout
vision loss
⬎0.6
0.4–0.6⬍0.4

based on scanning laser ophthalmoscope images, fundus
photographs, and the metamorphopsia chart (M-chart). Ourclassification based on the degree of metamorphopsia, visual acuity, and OCT findings is a new classification that
may be useful in determining ERM cases with indistinct
metamorphopsia due to cataracts or corneal opacity. Oncethe maximum INL thickness is ⬎50 ␮m, patients may
become aware of metamorphopsia.
In our preliminary data, postoperative metamorphopsia
was detected in 10%, 33%, and 100% of eyes with a preoperative ERM classification of stages 1, 2, and 3, respectively.
The applicability of this new classification system for determining the indications for surgery and predicting postoperativevisual function must be further investigated.
To apply this ERM classification clinically, the positionof the maximum thickness of the INL must be determinedfrom B-scan cross-sections by dragging the mouse across a
3D data map, then measuring the INL thickness using theelectronic calipers of the 3D OCT 1000, and finally classifying the ERM stage according to INL thickness, visualacuity, and degree of metamorphopsia.
The limitations of the present study include a relatively small sample size, measurements based on only 5
horizontal B-scan cross sections, inclusion of erroneous
values based on measurements of layers with indistinct
signals, and manual measurement using electronic calipers. Future studies with a large sample size and improved OCT are needed.
In conclusion, metamorphopsia induced by ERM may becaused by edematous changes of the INL, especially INL
with a ⬎50-␮m thickness. Our new ERM classification
scheme may help clinicians to better understand the retinal
changes that underlie the subjective symptoms.

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Figure 3. Relationship between visual acuity and thickness of inner
nuclear layer (INL), outer plexiform layer (OPL), and outer nuclear layer(ONL). In the area correlating with metamorphopsia, 1, 2, and 3 show the
relationship between visual acuity and maximum thickness of the INL,
OPL, and ONL, respectively; 4 shows the relationship between visualacuity and thickness of the ONL at the central fovea.

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Footnotes and Financial Disclosures
Originally received: October 5, 2008.
Final revision: April 25, 2009.
Accepted: April 28, 2009.
Available online: July 30, 2009.

Financial Disclosure(s):The authors have no proprietary or commercial interest in any of thematerials discussed in this article.
Manuscript no. 2008-1189.

From the Nishi Eye Hospital.
Presented at: the 2008 Joint Meeting of the American Academy of Ophthalmology
and European Society of Ophthalmology, November 8-11, 2008, Atlanta, Georgia.

Correspondence:
Akinari Watanabe, MD, Nishi Eye Hospital, 4-14-26 Nakamichi, Higashinari, Osaka, Osaka 537-0025, Japan. E-mail: akinari@watanabeeye.net

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