Introduction

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Adults are increasingly afflicted with vision degrading myodesopsia (VDM) due to the aging of the population and the prevalence of myopia worldwide [1]. VDM may manifest as spots, cobwebs, shadows, and other assorted shapes as the eyes move [2, 3]. Although many studies show that YAG (yttrium–aluminum garnet) laser vitreolysis and vitrectomy for VDM are effective [4,5,6,7,8], the associated complications should be considered [9]. Observation is still the major process for VDM. While patients may become accustomed and neuroadapt to their floaters, especially the posterior vitreous detachment (PVD) type due to the Weiss ring migrating anteriorly and away from the visual axis gradually [10, 11]. However, the duration of symptoms and likelihood of spontaneous remission remain uncertain.

This study described the ratio and time of spontaneous remission of VDM patients with PVD type during long-term follow-up. Additionally, associated factors with significant spontaneous remission of VDM symptoms were explored.

Methods

Study population

This retrospective cohort study was conducted on patients with VDM of PVD type who refused any treatment process at He Eye Specialist Hospital. The study design adhered to the Declaration of Helsinki principles and was approved by He Eye Specialist Hospital’s Institutional Review Board. Written informed consent was waived due to the retrospective design. The patients whose initial visits occurred between January 2019 and December 2020 were collected. All patients were followed for at least 12 months after their floater symptoms first appeared. Exclusion criteria were (1) secondary vitreous floaters such as vitreous inflammation or hemorrhage and (2) patients undergoing other intraocular surgery that might disturb vitreous condition such as cataract or glaucoma surgeries during follow-up; however, pseudophakic eyes at the initial visits were included. If patients had floaters in both eyes, the eye with the more severe symptoms was chosen.

Ophthalmological examination

All patients underwent a slit-lamp examination, visual acuity, intraocular pressure, refractive status, vitreous and fundus examinations with a dilated pupil, and an ultrasound B scan. Some patients were examined with an ultrawide-field scanning laser ophthalmoscope (Optos® 200Tx, Optos®, Dunfermline, UK) to assist peripheral retinal screening at baseline. Optos images were not employed for floater evaluation in this study. Patients had a thorough fundus examination to look for Weiss ring or detached hyaloid. The Weiss ring should be visible under mydriasis at the optic nerve head and/or the posterior hyaloid was separated via B-scan ultrasound imaging [12]. All ultrasound B-scans were performed at baseline by one doctor (Q. L.).

Data collection

The baseline demographic data collected from each patient’s record included age, sex, and laterality of involved eye. The sketch of floaters was shown to patients based on the drawing in previous articles [13, 14] (Fig. 1). The patterns of floaters were classified as spotty, string-like, lamelliform, blocky, and cloudy. All patients individually choose the pattern that closely resembled their visual floater symptoms. The number (≤ 3 or > 3) of floaters reported by patients were also recorded. Primary outcome measures included a subjective improvement (from 0 to 100%) and a five-level qualitative scale described by Delaney et al. [15] at the final visit. The significant remission was defined as the remission of 50% or greater.

Fig. 1
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Schematic drawing showing the different types of floaters

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Statistical analysis

Continuous values were described using the mean and standard deviation (SD), while categorical variables were represented using percentages. The Kaplan–Meier survival curve was generated for survival analysis. Multiple binary logistic regression and univariate analysis were utilized to identify risk factors related to significant spontaneous remission. For this investigation, the alpha level was set at 0.05 and the power of the statistic was established at 95%. SPSS (SPSS Inc., USA), version 27.0, was used to conduct all statistical analyses.

Results

This study included 179 patients, three of whom underwent retinal laser photocoagulation due to peripheral retinal tears on their initial visit but did not receive any treatment for floaters. In total 548 patients were not treated for floaters, and 367 patients with follow-up periods of less than 12 months or patients lost during follow-up were excluded, along with 2 patients who underwent cataract surgery during follow-up period (Fig. 2). The mean age of all patients was 60.56 ± 0.47 years, with a distinct female predominance (74.86%), and a mean follow-up duration was 23.89 ± 6.63 months. Among the total patients included in this study, 46.39% (n = 83) of the patients had Optos images assessment at baseline. Of the patients, 40.78% had significantly spontaneous remission in their floater symptoms after 16.55 ± 10.63 months (Table 1; Fig. 3). Of these patients, 40.67% experienced remission of floater symptoms within the first year. The Kaplan–Meier survival curve is shown in Fig. 4.

Fig. 2
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Flow chart for the inclusion and exclusion of patients

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Table 1 The demographic data of patients
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Fig. 3
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Subjective efficiency of a 5-level qualitative scale

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Fig. 4
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Kaplan–Meier curve of the survival time to significant spontaneous remission of VMD since the onset of floater symptoms

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In the univariate analysis, age (OR = 1.036, 95% CI = 1.002–1.071, P = 0.040), myopia (OR = 0.235, 95% CI = 0.077–0.716, P = 0.011), number of floaters > 3 (OR = 0.374, 95% CI = 0.199–0.706, P = 0.002), and floaters with a string-like pattern (OR = 0.370, 95% CI = 0.166–0.824, P = 0.015) and cloudy pattern (OR = 0.087, 95% CI = 0.011–0.717, P = 0.023) correlated with significant spontaneous remission. In the multiple binary logistic regression analysis, myopia (OR = 0.280, 95% CI = 0.084–0.932, P = 0.038), the number of floaters > 3 (OR = 0.343, 95% CI = 0.172–0.683, P = 0.002), and floaters with string-like pattern (OR = 0.370, 95% CI = 0.166–0.824, P = 0.015) and blocky pattern (OR = 0.299, 95% CI = 0.090–0.993, P = 0.049) were negatively correlated with the significant spontaneous remission of VDM symptoms (Table 2). Significant spontaneous remission was observed in 53.4% and 52.0% of patients with spotty floaters and lamelliform floaters, respectively. Although only one patient with cloudy floaters had a significant spontaneous remission (Fig. 5).

Table 2 Univariate and multiple logistic regression analyses for the risk factors associated with significant spontaneous remission of floater symptoms
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Fig. 5
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Significant spontaneous remission of VMD in different patterns of floaters

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There were four (2.23%) patients who complained of the floater symptoms becoming worse during follow-up (Fig. 3), including two patients with cloudy floaters, one patient with string-like floaters, and one patient with lamelliform floaters. No patients had additional complications associated with floaters, such as retinal detachment, retinal holes, or vitreous hemorrhage during follow-up.

Discussion

In this study, 75 percent of the patients were female suggesting that VDM is more prevalent among women. Interestingly, we discovered that previous prospective studies enrolled more female patients with floater (59–76%) [4,5,6,7]. Chuo et al. [16] discovered that the female had twice the change in posterior vitreous detachment (PVD) as the male patients, and that there was a clear and continuous link between PVD and a history of menopause, regardless of age and myopia. They postulated that perimenopausal hormone changes would affect the vitreous collagen or vitreoretinal interface because hormonal changes could affect glycosaminoglycan synthesis and metabolism [17, 18].

Though the YAG laser has been used for treating symptomatic floaters for nearly three decades [19], there is still some debate about its efficacy and safety [3, 7, 20,21,22,23,24]. In some prospective studies, the subjective efficacy of YAG laser vitreolysis for SVO was between 53 and 77% [4,5,6]. It is interesting to note that Shah and Heier [25] found the efficacy of YAG vitreolysis at 6 months (53%), sustained at 2.3 years (50%) in an observational extension study, but three of 35 patients undergoing YAG laser vitreolysis without retinal tears at the 6-month visit had retinal tear at the final visit (2.3 years). The other associated factors with YAG laser vitreolysis such as focal cataract, elevation of IOP, retinal hemorrhage, or retinal detachment were also reported previously [26]. Pars plana vitrectomy is another primary treatment option for VDM [10, 27,28,29]. While vitrectomy has been documented in reducing the symptoms of floaters and is considered to be an effective option but may lead to additional side effects [30, 31]. In 17,615 eyes undergoing vitrectomy for vitreous opacities in the Intelligent Research in Sight Registry, 12.4% eyes returned to the operating room for cataract surgery, and 3.7% eyes returned to the operating room for a non-cataract procedure within 1 year [32].

When complete PVD occurs, the projections of vitreous opacities on the retina are usually dark because of the elevated hyaloid near the retina [33]. During follow-up, the vitreous floaters usually move anterior and peripheral, which makes the shadows of floaters disperse and light [33], so the patients may feel the floater symptoms spontaneously improved. There are a few studies that have assessed spontaneous remission of floater symptoms so far. In this study, we found that 40 percent of patients reported their floater symptoms gradually going into significant spontaneous remission during long-term follow-up and that remission would occur in about 40% of patients within the first year. Even though the ratio of spontaneous remission in PVD-type floaters appears to be high in this study, we were unable to compare it to interventions like YAG laser vitreolysis and PPV surgery. In an interesting finding, a survey of websites about how to treat vitreous floaters found that the most common advice was observation (55.8%), followed by laser treatment (27.6%), no specific advice (11.3%), and vitrectomy (5.8%) [34]. Previously, it was assumed that floaters were usually stable if their symptoms persisted for longer than 3–6 months, so patients with floater symptoms that lasted at least 3–6 months were often chosen in previous intervention studies [4,5,6]. Based on the results of this study, the intervention treatment should be given to people who have had VDM symptoms for at least 1 year.

In this study, myopia was found to be an unfavorable factor associated with spontaneous remission of floater symptoms. The possible reason could be that the types of floaters in these myopic eyes are not only due to PVD but may also be accompanied by some collagen aggregates. Studies have shown that myopia is linked to the clumping of collagen in the vitreous, and these floaters usually constant and persistent [35]. Patients with a few floaters (≤ 3) have approximately triple the chance of significant spontaneous remission compared to patients with more floaters (> 3). Interestingly, we also found that patients with spotty and lamelliform floaters were easier to undergo spontaneous remission, and more than half the patients underwent significant spontaneous remission. The possible explanation is that fewer and smaller floaters are more likely to be overlooked by patients and possibly undergo neuroadaptation. Although large floaters, such as cloudy floaters, are difficult to neglect, in this study, only one patient with cloudy floaters experienced a significant spontaneous remission.

A pooled data analysis recently revealed that the presence of isolated floaters had a great risk of developing retinal tears (16.5% of total eyes), but that risk decreased to 3.9% at follow-up (4–8 weeks) [36]. van Overdam et al. [37] hypothesized that retinal tear forms more quickly following the onset of symptoms. In the present investigation, three patients with peripheral retinal tears at baseline were treated with retinal laser photocoagulation, and no additional retinal tears or detachments were discovered throughout the long-term follow-up. Consequently, observation is probably the safest strategy.

There are several limitations to the current study, including its retrospective design and single-center study. The visual function questionnaire was not used to evaluate the change in visual quality either. We identified a few factors associated with spontaneous remission of floaters and formulated a number of hypotheses, but we lacked objective measurements of floaters to determine if they were real position shifting, population reduction, or neural adaptation. But to the best of our knowledge, this is the first study to report the spontaneous remission of VDM.

In conclusion, approximately 40 percent of VDM patients with the PVD type may feel their floater symptoms improve significantly during long-term observation. Observation is advisable in patients with symptomatic floaters after acute PVD. Fewer and smaller floaters are more likely to get spontaneous remission in non-myopia patients.