In this prospective cohort study, 44 eyes of 44 patients with idiopathic MH were evaluated in Beijing Tongren Eye Center, Beijing Ophthalmology and Visual Science Key Lab; Beijing Tongren Hospital from November 2016 to April 2017. The Medical Ethics Committee of the Beijing Tongren Hospital approved the study protocol, and all participants gave their written informed consent. Color fundus photography, retinal optical coherence tomography (OCT) (Carl Zeiss, Dublin, CA, USA) and microperimetry-3 (NIDEK, Gamagori, Japan) were performed for each patient 1 week before, 1 and 4 months after operation. MH was ensured by OCT. We defined the diameter of a MH as the minimum diameter.
The inclusion criteria for patients included a diagnose of idiopathic MH conformed by OCT, a requirement of operation for treatment, and opacities of lens under NO3C2P1 grade assessed by Lens Opacities Classification System III (LOCSIII). Meanwhile, patients with glaucoma, myopia<-3.0 diopters (D), severe cataract, or other ocular diseases that could interfere with the measurements were excluded.
A standard 23-gauge 3-port pars plana vitrectomy was performed by the same experienced surgeon (W.L.). Phacoemulsification and IOL implantation were performed if necessary. A subtotal vitrectomy was performed followed by IML peeling without staining. The posterior hyaloid was elevated and trimmed in all patients. The ILM was peeled off with forceps in an area of about 2 disc diameter around the MH. A fluid–gas exchange was carried out, and the vitreous cavity was filled with air. All operations were performed without any serious postoperative complications. Patients were asked to stay in a prone position for 5-7 days after surgery. At 1 and 4 months after surgery, patients returned for a follow-up visit with examination of color fundus photography, optical coherence tomography (OCT) (confirming the closure of the MH) and microperimetry-3.
Retinal function of patient was evaluated by microperimetry (MP) which was a subjective, quantitative, non-invasive diagnostic exam aimed at assessing retinal functionality and to put it in strict correlation with retinal morphology. Microperimetry-3 (MP-3), as the newest generation of microperimetry, has a wider range of stimulus intensity from 0 to 34 dB. MP-3 can measure perimetric threshold values even for normal eyes. A maximum stimulus luminance of 10,000 asb allows evaluation of low-sensitivity. The MP-3 device features faster tracking, increased automation and a broader dynamic range compared with the MP-1. Another important feature of this microperimeter is that target light is projected onto the retina rather than a screen. The position of the retina is therefore tracked so that target presentations can be automatically aligned, and the exact same location is stimulated at each target presentation. In this manner, we would expect to observe highly reproducible measurements of retinal sensitivity.
The microperimetry examination was performed in a dark room. All patients underwent a dark adaptation for at least half an hour until the pupil size reached 4mm or larger. The infrared fundus image was registered, and the central fixation point was aligned to the center of MH in pre-operative examination. The follow-up pattern was used to make sure the pre- and post-operative examinations and comparisons were point to point perfectly matched. A customized pattern with 45 spots in central 8° visual field was used. The 45 test points in the MP-3 are shown in Figure 1.
The fixation target was a 1° diameter red circle, and the background luminance was set at 31.4 asb, giving suitable evaluation of macular sensitivity and enabling detection of small visual field defects in the macular area. Only reliable VFs were used in analyses, which were defined as fixation loss (FL) rate < 20% and a false-positive (FP) rate < 15%. We used a Goldman size III stimulus with duration of 200ms. Using the obtained retinal sensitivities, the mean sensitivity at the fovea, within two degrees, four degrees, six degrees and eight degrees were calculated. Four regions, superior nasal, inferior nasal, inferior temporal, superior temporal, were divided and shown in Figure 2.
When calculating, the points located on X-axis or Y-axis were excluded. We choose 28 points within the outer ring zone covering the normal retina, not including the 17 points for MHs area (Figure 3). These 28 points occupied 60% of the whole 45 points, but covered more than 75% area of the 8° retina. These points located from 4° to 8°. The diameter of 8° visual field was 2500 mm (about 1.6PD). During the operation, the ILM we peeled off covered an area of at least 2 PD, which meant the 8° area was completely contained in the ILM peeling area. The point with a distance of less than 0.5° from the margin of MH was also excluded (Figure 4).
We used follow-up pattern to ensure the selected dots located on the same position in every examination. All tests were conducted by one experienced microperimetry examiner. On the basis of the microperimetry findings, we evaluated mean retinal sensitivity (primary outcome) of all the selected points.
Statistical analysis was performed using a commercially available statistical software package (SPSS for Windows, version 25.0, IBM-SPSS, Chicago, IL, USA). BCVA measurements were converted to the logarithm of the minimum angle of resolution (LogMAR). The parameters are presented as mean ± standard deviations. Pre- and post-operative visual acuities and retinal sensitivity were compared using paired Student’s t test (in the normal distributed samples) or Mann-Whitney U test (in the non-normal distributed samples). A P-value < 0.05 was considered statistically significant.