Study design and subjects
This study was designed as a retrospective, comparative case series conducted in a single hospital. The study adhered to the tenets of the Declaration of Helsinki and was approved by the institutional review board of Keimyung University Dongsan Hospital (IRB no. 2020-12-069). The patients signed informed consent for the use of their data. We retrospectively reviewed the electronic medical records of patients with a history of a failed primary IMH surgery who were treated with fluid-gas exchange between January 2013 and December 2019. The patients with at least 6 months of follow-up period after the procedure were enrolled in the study. The exclusion criteria were as follows: myopia > 6 dioptres, presence of rhegmatogenous retinal detachment, diabetic retinopathy, age-related macular degeneration, or a history of previous vitrectomy due to causes other than IMH.
All patients had a full-thickness IMH and underwent primary vitrectomy with internal limiting membrane peeling using the inverted flap technique. Cataract surgery was performed simultaneously when the cataract impaired posterior visualisation. The patients were instructed to remain in a face-down position for ≥ 7 days. The fluid-gas exchange procedure was performed on 19 eyes in which an unclosed MH was noted in the spectral-domain OCT (Spectralis OCT/SLO; Ophthalmic Technologies, Toronto, Ontario, Canada) or swept-source OCT (DRI OCT-1; Topcon, Tokyo, Japan) during the follow-up period. The procedure was based on a previous report by Jang et al.20, and the patients were instructed to stay in the face-down position for 7 days. The type and percentage of gas used in the primary surgery were determined by the surgeon’s preference. During the fluid-gas exchange, 16% of SF6 gas or 14% of C3F8 gas was used. All aforementioned surgical and other procedures were performed by a single clinician (Y.C.K.).
Based on the classification by Imai et al.6, the outcomes of the fluid-gas exchange procedure were classified as U-type closure, V-type closure, W-type closure, or unclosed. The patients were divided into the successful and unsuccessful groups according to the absence or presence of bare retinal pigment epithelium after the fluid-gas exchange procedure, respectively (Fig. 1). Demographic and clinical characteristics were compared between the two groups to assess the prognostic factors.
Clinical data collection
The demographic characteristics including age, sex, and laterality were assessed in all patients. Furthermore, the duration of decreased visual acuity, baseline IOP measured by a non-contact tonometer (Canon TX-20, Canon Inc, Kanagawa, Japan), spherical equivalent, lens status (phakic or pseudophakic), axial length, type of primary surgery (vitrectomy alone or combined cataract surgery) with the type of gas and the percentage used for tamponade during primary surgery, interval period between the primary surgery and fluid-gas exchange, and the type and percentage of gas used in the fluid-gas exchange were recorded. The baseline and final logMAR BCVA values were also assessed. OCT images of all patients were recorded at baseline, pre-procedure, and post-procedure until the last follow-up. CSRT, BD, MD, MH height, MHV height, left arm length, and right arm length were measured using the OCT software measuring tool at baseline and pre-procedure. In addition, the MHI based on the publication by Kusuhara et al.12, the THI and DHI by Ruiz-Moreno et al.13, the HFF by Ullrich et al.4, and the MHV by Ozturk et al.15 were calculated.
Statistical methods
Data were calculated as the mean ± standard deviation (SD) or n (%; e.g., number of eyes). Statistical analyses were performed using Statistical Package for the Social Sciences version 12.0 (IBM, Chicago, IL, USA). Between-group differences in age, symptom duration, total follow-up period, baseline and final BCVA, baseline IOP, baseline spherical equivalent, percentages of gas tamponade used in primary surgery and fluid-gas exchange, baseline axial length, and baseline and pre-procedure values of BD, MD, MH height, MHI, HFF, DHI, THI, and MHV were compared using the Mann-Whitney U test. Categorical variables, such as sex, affected eye, lens status, type of surgery, and type of gas used in the primary surgery and fluid-gas exchange were compared using the chi-square test or Fisher’s exact test. The comparison of baseline and post-procedure BCVA between the two groups was performed using the Wilcoxon signed-rank test. All the tests had two-tailored critical regions for a significance level of 0.05.