We retrospectively analyzed the medical records of patients who visited our retina clinic for vitreous floater within a month IOL from July 2017 to May 2020. All patients received thorough ophthalmological examination including best-corrected visual acuity (BCVA), manifest refraction, intraocular pressure (NT-530P, Nidek, Aichi, Japan), retinal examination after mydriasis, spectral domain optical coherence tomography (SD-OCT) (Version 5.3.2.0; Heidelberg Engineering, Heidelberg, Germany) and ultra-wide field scanning laser ophthalmoscopy (UWF) (Optomap®, Optos PLC, Dunfermline, Fife, Scotland, UK) were performed. We conducted SD-OCT line and raster scan in all eyes centered at the fovea. Automatic real-time (ART) mode was activated when horizontal and vertical line scans were conducted with 25 frames averaged. In the raster scan image, a 30 x 25 degree2 area was covered with 31 b-scans (consisting of 768 A-scans), which are 9.0 mm in length, and spaced at 240 μm apart. The peripapillary region was scanned using a circular scan 12° in diameter, centered on the optic disc. (Figure 1) Every retinal examination was performed on both eyes.
Study Subjects and Vitreous Floaters
Eligible subjects were adults older than 20 years old who experienced acute symptom (onset ≤ 1 month) of vitreous floaters for the first time of their life. In patients complaining vitreous floaters in both eyes, eyes with more recently developed floaters were selected. Exclusion criteria includes history of ocular surgery including cataract operation, history of ocular injections, any retinopathy including diabetic retinopathy or retinal venous occlusion, medial opacity including severe cataract or corneal opacity or eyes with obscure image which were not suitable for proper analyses. Eyes received refractive surgeries were excluded from the refraction analyses.
In this study, vitreous floaters were defined as symptoms of unprecedented amorphous ‘floating’ material. Other confusing symptoms such as fixed spots interrupts visual axis, transient wavy visual disturbance or metamorphopsia were excluded with through history taking. Concurrent subjective symptoms such as headaches, flashes, or ocular pain were asked also.
Analyses of Ophthalmologic Outcomes
Best-corrected visual acuity was measured with the manifest refraction test and was recorded in logMAR (logarithm of minimal angle of resolution). The spherical equivalent and cylindrical value were expressed in diopter (D). Central macular thickness (CMT) at the 1-mm center of the fovea was measured using a built-in software (Heidelberg Eye Explorer, version 1.10.2.0, Heidelberg Engineering, Heidelberg, Germany), which recorded the distance between the vitreoretinal surface and the border between the retinal pigment epithelium and the Burch’s membrane. Peripapillary RNFL (pRNFL) thickness was measured using the identical software.
Analysis of peripapillary vitreous opacity in UWF imaging
The presence of peripapillary vitreous opacity (pVO) was observed in UWF images taken on the eyes, after pupil dilation. The vitreous opacity found within 3 disc diameters from the center of the disc was included. (Figure 1) In cases where it was difficult to judge by pictures alone, the precise fundus examination with indirect ophthalmoscopy was considered together for the determination. The two investigators (GSS, MK) each independently analyzed the image, and for the inconsistencies, the senior investigator (JHS) made a final decision.
Anaylsis of PVD stage in SD-OCT imaging
The staging of PVD was performed base on the previously published paper 16 . In brief, stage 0 = no PVD; stage 1= PVD at mid-periphery and possible subtle PVD in the posterior retina; stage 2 = PVD, except for persistent adhesion to the papilla and fovea; stage 3= PVD, except for persistent adhesion to the papilla; and Stage 4= complete PVD. (Figure 1) The two investigators (GSS, MK) analyzed PVD respectively, and the opinions of senior investigator (JHS) were sought for discordant findings.
Statistical Analyses
Continuous values were expressed as “average ± standard deviation,” and categorical variables were described as proportions; differences between groups were determined using the chi-squared test or Fisher’s exact test. Comparison of ophthalmological values between eyes with/without vitreous floaters was performed using the paired t-test. Pearson’s correlation analyses were performed among various continuous values. Inter-class correlation (ICC) value was calculated to determine how consistent the two investigators’ interpretations on PVD at SD-OCT images were. All data were inserted into an Excel spreadsheet (Microsoft Corp.) and analyzed using SPSS software (version 23; IBM Corp, New York, NY). A P-value less than 0.05 was considered statistically significant.
Ethics approval and patient consent
This study was approved by the Institutional Review Board (IRB) of Hangil Eye Hospital (IRB number: IRB-20006) and complied with the Declaration of Helsinki in conducting the study. Given the retrospective design of this study and the use of anonymized data, requirements for informed consent were waived by the IRB.