Idiopathic ERM may cause visual impairment and metamorphopsia over time
12. Decreased visual acuity is one of the main presenting symptoms of idiopathic ERM, and the reduction in visual acuity cannot be correlated with the degree of metamorphopsia
13. The reason for the reduction in BCVA due to ERM may be related to the scattering, light-filtering and distortion effects of the membrane, axoplasmic flow inhibition, intraretinal edema and/or the membrane's traction effect causing the separation between RPE and photoreceptor outer segments
12. Traditionally, when deciding on surgery, the severity of symptoms and their impact on visual function are assessed
12,13. In many ERM studies, visual acuity was used as the sole measure of visual outcome
10-12. In a previous study, the improvement in BCVA after idiopathic ERM surgery was evaluated as functional success
11. In a study including 1131 patients, it was reported that preoperative median visual acuity was 0.25 and that there was a statistically significant increase in visual acuity level after primary ERM surgery
14. It was also stated that visual increase of approximately two Snellen lines was observed in 41.7% of the cases at postoperative period
14. Bouwens et al.
15 detected the visual improvement in 66% of the patients at the third month after idiopathic ERM surgery, while Dawson et al.
11 reported this rate as 69.6%. Our preoperative BCVA value was 0.24, and we determined statistically significant increase in visual acuity in the postoperative period. In our study, BCVA improved in 18 (81.8%) cases, decreased in 1 (4.5%) case and remained same in 3 (13.7%) cases after surgery. We also found an increase of more than two Snellen lines in BCVA in 8 (36.4%) patients at postoperative period. Our visual results appear to be consistent with the literature.
The prevalence of idiopathic ERM can alter from 2% to 34% depending on some factors such as ethnicity and age 12. It was reported that the incidence and prevalence of idiopathic ERM increased with age 2,16. In our study, the number of ERM patients aged >65 years was significantly higher than the number of ERM patients aged ≤65 years. However, we detected that mean BCVA changes after surgery in cases aged >65 years were similar to those in cases aged ≤65 years. The main purpose of the ERM surgery is to remove the membrane and release the retinal traction 4,17,18. ERM surgery was stated to reduce or eliminate the epiretinal, inner and outer retinal distortions, reconstruct the foveal region, and improve the macular architecture 19. Since it was thought that ILM could serve as a scaffold for the cellular proliferation, ERM/ILM double peel was recommended by some authors 4,20,21. In literature, it was reported that in many cases, peeling of the ILM occurred simultaneously with peeling of the ERM either en bloc peeling or spontaneously 12. In our study, the number of patients who underwent both ERM and ILM peeling was significantly higher than the number of patients applied only ERM peeling. Park et al. 22 and Bovey et al. 23 determined that combined peeling of ILM with ERM provided better visual results and lower recurrence rates than ERM removal alone. In contrast to these studies, Ahn et al. 24 showed that ERM peeling alone had better visual results at 1st month than the combined removal of ERM and ILM, but they found similar visual results at subsequent visits. The other studies reported that ILM peeling did not appear to improve the visual outcomes 12,17,20,21,25. Similarly, we detected that mean BCVA changes after surgery in cases applied both ERM and ILM peeling were similar to those in cases applied only ERM peeling.
Chromovitrectomy was defined as the usage of vital dyes for staining the transparent membranes, making them easier to visualize and remove during the vitreoretinal surgery 26. Thus, it can be easier to distinguish the ERM from retinal layers with the help of dyes 18. In our study, the number of patients in whom trypan blue was significantly higher than the number of patients with no dye. Dawson et al. 11 reported that the use of dye during idiopathic ERM surgery did not affect the visual improvement. Ozdek et al. 27 determined that the use of different stains in ERM surgery had no effect on visual outcome. Similarly, we found that visual acuity increases of the cases being used trypan blue were not difference from those of the cases with no dye.
Based on the surgeon's decision, intraocular gas tamponade such as air, SF6 or C3F8 was used to fill vitreous cavity at the end of the vitreoretinal surgery 28-30. In literature, the use of different gases was recommended to prevent early postoperative ocular hypotony by providing the maximum leakproofing in self-sealing sclerotomies and to reduce the retinal folds 28,29. In our study, in order to ensure rapid rehabilitation of the macular anatomy and to prevent ocular hypotony, intraocular gas tamponade (SF6, C3F8 or air) was used peroperatively in all cases. In our study, the numbers of patients given SF6, C3F8 or air were similar to each other. Leitritz et al. 28 and Leisser et al. 30 found that air tamponade usage in idiopathic ERM surgery did not make a significant difference in postoperative visual outcomes. Chabot et al. 29 detected that ERM peeling with air tamponade or SF6 tamponade had similar visual improvement after surgery. Ozdek et al. 27 showed that air or gas tamponade usage in ERM surgery did not affect the visual outcome. Similarly, we found that visual acuity increases in patients given SF6, C3F8 or air were not different from each other after surgery.
There were some limitations in our study. Data were collected retrospectively. It had relatively small case number and short follow-up period. Another limitation was the use of visual acuity as the sole measure of surgical success. Due to technical reasons and retrospective design, OCT data could not be accessed. Planning the future prospective studies with larger populations and longer follow-up periods, in which other parameters are used in addition to visual acuity, may provide more extensive data about the effects of the surgery for idiopathic ERM.
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