The use of YAG laser for the treatment of vitreous opacities was first reported in the 1980s. Since its initial inception, YLV has become more widely adopted as patients have become increasingly aware and interested in the procedure for management of their visual debilitations. Despite this, the procedure remains controversial due to a lack of high-quality evidence on treatment efficacy, and potential adverse events.
Several previous studies have shown variable rates of patient satisfaction and relatively low rates of complications following YLV. In the only published randomized clinical trial on YVL, Shah and Heier reported that 53% of patients described significant or complete resolution of symptoms in the YAG-treated group compared to 0% in the control sham laser group. Other studies have demonstrated variable rates of YLV success, including Delaney et al with 38% of eyes experiencing moderate symptom improvement, Souza et al publishing a 46.1% rate of floater symptom amelioration, and Luo et al with 75% of patients reporting “significant success”. As for complication rates, one study reported a 0.8% adverse event rate out of nearly 1,300 patients who were treated with YLV, including 7 cases of intraocular pressure spikes, 2 cases of lens damage, and 1 case of retinal hemorrhage.
Qualitative and quantitative measurement of vitreous opacities has been attempted by several groups in the past with varying degrees of success. Souza et al used a 5-level qualitative scale to grade color fundus photographs before and after YLV. The criteria used in their grading system was not published, and unfortunately such qualitative grading scales are typically subject to interpreter discretion and inter-grader variability. Sun et al obtained infrared fundus images using the Heidelberg Retina Angiograph 2 system to generate a high-quality composite of ten averaged images, and used ImageJ to evaluate the area of the floaters and their shadows cast. Overall, their study showed a significant decrease in median shadow area from 1.41 cm2 to 0.12 cm2 after YLV (p = 0.001), with 64% of eyes achieving significant and complete resolution of vitreous floaters. Shaimova et al measured the area of false nonperfusion on OCT angiography with RTVue xR Avanti to determine the size of the artifactual shadow cast by vitreous opacities. While these two methodologies can provide numerical values for vitreous opacity size and shadow area, which can be beneficial for research purposes, such measurements and calculations are cumbersome and time consuming to perform, and likely less practical in a clinical setting. Furthermore, these three studies all describe retinal/vitreous imaging analysis using still images, which does not recapitulate the real-world dynamics of mobile vitreous opacities.
Ultrasound characterization allows visualization of vitreous opacities in real-time by detecting the disparity in acoustic impedance between the dense floaters with high echogenicity and the vitreous body with low echogenicity. Clinical analysis of ultrasound B-scan imaging for vitreous opacities is primarily qualitative, although a few studies have evaluated the applications of quantitative ultrasonography. Garcia et al quantified vitreous echodensity by measuring acoustic scattering in B-scans in arbitrary unit (AU) measurements; with higher AUs indicating higher levels of energy scatter. While this method is useful for characterizing the overall vitreous density, it does not provide information on the localization of vitreous opacities, or their impact on retinal shadowing and patient symptomatology. Mamou et al analyzed quantitative ultrasound imaging by defining regions of interest within B-scans and algorithmically determining three parameters: energy, mean amplitude of acoustic values, and percentage of vitreous filled by echodensities. These parameters provide a more detailed assessment of vitreous structure and floater severity and allow for quantitative comparison between patients and across treatments.
En face SLO OCT imaging can provide information on the morphology of vitreous opacities and highlight structural details such as individual vitreous fibrils to facilitate comparisons between pre- and post-YLV treatment (Figure 2). Dynamic OCT captures the movement of the patient’s vitreous in real time, allowing for the localization of vitreous opacities and their shadows as the patient fixates on a target or is asked to perform eye movements. Both the depth (Figure 3) and gain (Figure 4) of the OCT B-scan can be manipulated to reveal vitreous opacities that may have been missed on the standard OCT B-scan. These imaging modalities are also helpful to screen and select for patient characteristics that are more amenable for successful YLV, including a single floater, clear vitreous, floater > 2 mm from the retina, floater > 5 mm from the crystalline lens, and no peripheral pathology. As previous studies have demonstrated an increased risk of retinal damage when laser pulses of 4-8 mJ were directed 2-4 mm from the retina, and when higher energy settings of 4-15 mJ resulted in complications such as crystalline lens damage, retinal hemorrhages, and retinal tears/detachment, it is especially important to evaluate the vitreous anatomy in order to identify which patients might be at higher risk of adverse events if treated with YLV, and when an appropriate endpoint would be to stop performing repeat YLV procedures for non-resolving floaters.
While SLO and dynamic OCT imaging provide valuable information for clinicians to evaluate vitreous opacities, they cannot provide an objective quantification of the anatomic characteristics of these opacities, nor the degree of visual debilitation that they cause for the patient. Furthermore, there is currently no universally accepted grading scale for assessing vitreous opacities, which limits the applicability of these imaging techniques for statistical analysis in research studies and quantitative treatment guidelines.