Purpose
To evaluate the anatomic features of the photoreceptor inner/outer segment (IS/OS) junction before and after surgery by spectral-domain optical coherence tomography in patients undergoing idiopathic epiretinal membrane (ERM) surgery and to correlate these features with the functional outcomes.
Design
Prospective, cohort study.
Methods
We prospectively studied 45 eyes of 45 patients with idiopathic epiretinal membrane who had a preoperative visual acuity of 20/32 or less and were scheduled to undergo transconjunctival 25-gauge vitrectomy. The patients were divided into 2 groups based on the preoperative structural integrity of the IS/OS junction: the intact IS/OS junction group and the disrupted IS/OS junction group. Changes in the IS/OS junction and best-corrected visual acuity were compared between 2 groups before and at 3, 6, and 12 months after surgery.
Results
A total of 45 patients were recruited for this study. There were 34 eyes with an intact IS/OS junction (group 1) and 11 eyes with a disrupted or irregular IS/OS junction (group 2), as determined before surgery. Significantly better postoperative best-corrected visual acuity was seen in group 1 as compared with that in group 2 at 3, 6, and 12 months after the surgery ( P < .001). Significant improvement of visual acuity was also seen in group 1 when compared to group 2 ( P < .05). Of the 34 eyes in group 1, 17 (50%) showed disruption of the IS/OS junction at 3 months after surgery, although this disruption was only transient and resolved completely by 12 months after the surgery. However, none of the eyes from group 2 showed a normal appearance of the IS/OS junction at any time point during the study period of 1 year.
Conclusions
The IS/OS junction can recover in eyes with preoperative intact IS/OS junction as assessed over a follow-up period of 1 year after surgery. Preoperative integrity of the IS/OS junction may be an important prognostic factor for better visual recovery and better improvement of the postoperative best-corrected visual acuity after epiretinal membrane surgery.
Surgical correction of idiopathic epiretinal membrane (ERM), first reported by Machemer in 1978, is useful for improving vision. However, some cases show poor visual recovery even after complete removal of the ERM. Several factors, such as preoperative visual acuity, duration of the symptoms before surgery, and the presence or absence of cystoid macular edema, have been suggested as prognostic factors influencing the postoperative visual acuity. Recently, since the introduction of time-domain optical coherence tomography (OCT) as a useful tool for noninvasive diagnosis and monitoring of macular diseases, including ERM, investigators have suggested that the macular microstructure, such as the macular thickness and appearance of the photoreceptor layer, may be associated with the postoperative visual acuity. However, the relatively low resolution of the scanning image limits detailed delineation of the features of the photoreceptor layer. The introduction of spectral-domain OCT (SD OCT) has improved the speed and sensitivity of the examination, allowing scanning at a higher resolution. Furthermore, SD OCT also has the ability to provide high registration and enables analysis of volume rendering by allowing 3-dimensional imaging, thereby enhancing the visualization of the intraretinal architectural morphologic features.
Some studies using time-domain OCT have shown an association between the integrity of the photoreceptor inner segment/outer segment (IS/OS) junction and the visual acuity after ERM removal. However, no studies have reported an investigation of the postoperative changes of the IS/OS junction by SD OCT. Therefore, the purpose of this study was to evaluate the anatomic features of the IS/OS junction before surgery and after surgery by SD OCT in patients undergoing ERM surgery and to correlate these features with the functional outcomes.
Methods
A total of 45 consecutive eyes of 45 patients with idiopathic ERM who had a preoperative visual acuity of 20/32 or less and were followed up for 12 months or longer after surgical treatment at the Yokohama City University Medical Center between September 2007 and October 2009 participated to our study. Patients with eye diseases influencing the visual acuity, such as glaucoma, macular degeneration, diabetic retinopathy, or rhegmatogenous retinal detachment, were excluded.
Preoperative visual acuity and SD OCT images of the fovea were examined. Patients were divided into 2 groups according to the structural integrity of the IS/OS junction as assessed before surgery: the intact IS/OS junction group (group 1) and the disrupted IS/OS junction group (group 2).
A 25-gauge pars plana vitrectomy with internal limiting membrane peeling was performed by the same retina specialist (K.K.) in all the cases. Indocyanine green 0.06% was used for the staining before the removal of the internal limiting membrane in all the cases. The area of internal limiting membrane peeling was 2 to 3 optic disc diameters around the fovea. Cataract surgery was combined with the vitrectomy in the eyes with clinically significant cataract. Removal of the ERM was defined clinically by ophthalmoscopic and OCT examination.
The best-corrected visual acuity (BCVA) and SD OCT findings (Cirrus high-definition OCT; Carl Zeiss, Dublin, California, USA) were investigated 3, 6, and 12 months after the surgery. The BCVA was converted to the logarithm of the minimal angle of resolution (logMAR) units for the statistical analysis. The postoperative IS/OS junction features and visual acuity parameters, such as the BCVA at 12 months after the surgery (postoperative BCVA) and the differences between the preoperative and postoperative BCVA at 12 months after the surgery (improvement of the visual acuity), were compared between the 2 groups.
In the present series, SD OCT was performed for each eye using 5-line raster scans. Scans with a signal strength of more than 8/10 were considered to be appropriate, and a representative image was selected. Two examiners (M.I. and S.Y.) who were blinded to information about the visual acuity of the patients interpreted the macular microstructure in the SD OCT images together. The photoreceptor layer was imaged as a hyperreflexive line showing the IS/OS junction above the retinal pigment epithelium. An intact IS/OS junction was defined as a continuous hyperreflexive line. However, diagnosis of a disrupted IS/OS was made based on loss or irregularity of the hyperreflexive line corresponding to the IS/OS junction.
The postoperative visual acuity parameters were compared between the 2 groups by the Mann–Whitney U test. The Wilcoxon signed-rank test was used to compare the preoperative and postoperative visual acuity in each group. All analyses were conducted using SPSS software (SPSS, Inc, Chicago, Illinois, USA). P < .05 was considered statistically significance.
Results
The baseline characteristics and clinical data of the patients are shown in Table 1 . All the 45 patients were included in this study. There were 34 patients in group 1 and 11 patients with disrupted or irregular IS/OS junctions in group 2. Of the 45 patients, 15 were men and 30 were women, with the patients ranging in age from 42 to 77 years (mean age ± standard deviation, 66.8 ± 8.2 years) in group 1 and from 52 to 74 years (mean age, 63.9 ± 6.2 years) in group 2. Both groups were comparable with regard to age, sex, preoperative logMAR visual acuity in the operated eye, and preoperative central foveal thickness. Preoperative cataract lens density also was assessed using the Lens Opacities Classification System III. The mean values measured using the Lens Opacities Classification System III were 1.56 ± 0.60 for nuclear color, 0.56 ± 0.86 for cortical opacity, and 0.10 ± 0.40 for posterior subcapsular opacity in group 1. The corresponding mean values in group 2 were 1.59 ± 0.66, 0.18 ± 0.60, and 0.00 ± 0.00. No significant differences were observed between the 2 groups.
| Group 1 | Group 2 | P Value a | |
|---|---|---|---|
| Operated eye | 34 | 11 | |
| No. of patients | 34 | 11 | |
| Male (%) | 12 (35) | 3 (27) | |
| Female (%) | 22 (65) | 8 (73) | |
| Age (yrs), mean ± SD (range) | 66.8 ± 8.2 (42 to 77) | 63.9 ± 6.2 (52 to 74) | .081 |
| Preoperative logMAR visual acuity in surgery eye, mean ± SD | 0.39 ± 0.16 | 0.52 ± 0.27 | .066 |
| Preoperative central foveal thickness, mean ± SD (μm) | 460 ± 90 | 447 ± 75 | .320 |
| NC Grade (LOCS III), mean ± SD | 1.56 ± 0.60 | 1.59 ± 0.66 | .441 |
| C Grade (LOCS III), mean ± SD | 0.56 ± 0.86 | 0.18 ± 0.60 | .093 |
| P Grade (LOCS III), mean ± SD | 0.12 ± 0.41 | 0.00 ± 0.00 | .314 |
The ERM was removed successfully in all the cases. Cataract surgery combined with a vitrectomy was performed in 42 eyes that had clinically significant cataracts. Vitrectomy alone was performed in 1 pseudophakic eye and in 2 eyes with clear lenses. These 2 phakic eyes were included in group 1. There were no complications in any of the cases, except for retinal breaks in 2 eyes, which were treated during surgery by laser photocoagulation.
The mean logMAR visual acuity at the baseline was 0.39 ± 0.16 in group 1 and 0.52 ± 0.27 in group 2. The mean logMAR BCVA at 3, 6, and 12 months after the surgery was 0.08 ± 0.11, 0.04 ± 0.11, and 0.01 ± 0.10, respectively, in group 1 and 0.39 ± 0.33, 0.35 ± 0.30, and 0.34 ± 0.28, respectively, in group 2. In both groups 1 and 2, the postoperative BCVA was significantly improved as compared with the preoperative visual acuity ( P < .001 in group 1; and P = .042, P = .012, and P = .012 in group 2 at 3, 6, and 12 months respectively). Although visual acuity at the baseline was not significantly different between groups 1 and 2, significant differences in the changes in logMAR BCVA values were seen at 3, 6, and 12 months after the surgery between the 2 groups ( P < .001; Figure 1 ).
The mean differences in the BCVA between the preoperative and postoperative values at 3, 6, and 12 months after surgery were 0.31 ± 0.19, 0.35 ± 0.19, and 0.39 ± 0.18, respectively, in group 1, and 0.13 ± 0.16, 0.18 ± 0.15, and 0.18 ± 0.16, respectively, in group 2. Thus, group 1 showed a greater degree of improvement of the visual acuity after the surgery ( P = .023, P = .011, and P = .002; Figure 2 ).
Of the 34 eyes from group 1, 17 (50%) showed transient disruption of the IS/OS junction at 3 months after surgery. However, at 6 months after the surgery, the proportion of eyes showing disruption of the IS/OS junction was decreased to 5 eyes (14.7%) in group 1, and by 1 year, the disruptions had resolved completely ( Figure 3 ). However, none of the eyes in group 2 showed a normal appearance of the IS/OS junction at any time during the study period of 1 year ( Table 2 ; Figure 4 ).
