In this prospective cohort study, 44 eyes of 44 consecutive 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 and 1,4 months after operation. MH was ensured by OCT. We defined the minimum diameter as the diameter of a MH.
Patients with glaucoma, myopia<–3.0 diopters (D), severe cataract, or other ocular diseases that could interfere with the measurements were excluded. The opacities of the patients’ lens should be under N3C2P1 grade assessed by Lens Opacities Classification System III (LOCSIII).
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 internal limiting membrane 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 2disc diameter around the MH. A fluid–gas exchange was carried out, and the vitreous was filled with air. All surgery was performed without any serious postoperative complications. Patients were asked to stay in a prone position for 5–7 days after surgery. One and four months after surgery, patients returned for a follow-up visit. Color fundus photography, optical coherence tomography (OCT) (confirming the closure of the MH) and microperimetry–3 were performed for each patient.
Microperimetry (MP) was selected for retinal function evaluating. MP is 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) is the newest generation of microperimetry. It has a wider range of stimulus intensity, from 0 to 34 dB, compared to the MP–1. The MP–3 measures perimetric threshold values, even for normal eyes. A maximum stimulus luminance of 10,000asb allows evaluation of low-sensitivity. The MP–3 device features faster tracking, increased automation and a broader dynamic range compared with the MP–1.9 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.10
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 31.4asb. This pattern gives a suitable evaluation of macular sensitivity and enables the 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, are divided and shown in Figure 2.
When calculating, the points located on X-axis or Y-axis will be excluded. For example, when comparing the retinal sensitivity between superior and inferior retina, the points located on X-axis (point B1,2,3 and D1,2,3, figure 2) will be excluded. On the same way, when comparing the retinal sensitivity between nasal and temporal retina, the points located on Y-axis (point A1,2,3 and C1,2,3, figure 2) will be excluded. When calculating, we only choose 28 points in the outer ring zone instead of all 45 points, which located in the normal retina instead of MHs area (Figure 3).
These 28 points located in the outer two rings, which only 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 2500um (about 1.6PD). During the operation, the ILM we peeled off was at least 2PD, which means the 8° area was completely contained in the ILM peeling area. If the distance from the margin of MH to the selected points was less than 0.5°, the points will also be 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.