Article

Lasers take aim at floaters

Patients don’t have to “just get used to them.”

Like others, I previously thought of floaters as just a nuisance and part of the normal aging process. I felt there was no need to address them and often counseled patients to live with them. However, in symptomatic patients, the visual symptoms associated with floaters are a growing concern and warrant more than merely observation.

A study by Wagle et al. addressed the impairment on functional quality associated with floaters in 311 outpatients.1 The utility values of floaters were equal to AMD and similar to glaucoma, mild angina, stroke and asymptomatic HIV. A 2016 study by Garcia et al. showed there was a 52.5% reduction in contrast sensitivity function following posterior vitreous detachment (PVD.)2 In a survey of 603 smartphone users, 76% (n=458) indicated that they notice floaters, with 199 (33%) of these individuals citing noticeable vision impairment as a result of their floaters.3

Along with their significant impact on vision and quality of life, a study by Webb et al. found that floaters are very common in the general population, irrespective of age, race, gender and eye color. Furthermore, myopes and hyperopes were respectively 3.5 and 4.4 times more likely to report moderate severe floaters.3

Historically, the only treatment offered for vitreous floaters was a pars plana vitrectomy (PPV). Unfortunately, not all patients are good candidates for a PPV, and for these patients the only option was to observe many of the common types of floaters, such as a Weiss ring or other solitary vitreous opacities. Unfortunately, these floaters can still negatively affect patient’s quality of life.

Now, with advances in laser technology, the definition of clinically significant vitreous opacity has changed: Symptomology does not have to be as severe as that for a vitrectomy. Smaller floaters that were often considered to be not clinically significant to warrant surgery, such as Weiss rings, amorphous clouds and strings, are now potential candidates for treatment. These patients who were historically ignored can be treated earlier in the disease process.

It is important to note that laser floater treatment (LFT) is not intended to replace or compete with vitrectomy. The ideal patient for LFT is very different from that of a vitrectomy patient.

Here, I will discuss how LFT has advanced and techniques have evolved, along with pearls for successful treatment and patient selection.

VISUALIZATION

Visualization is key to providing spatial context during LFT. Without the proper technology, it is very difficult to identify many of the symptomatic floaters and confirm a safe distance from the posterior capsule and the retina. Surgeons need to be able to determine where they are within the vitreous in relation to other ocular structures, such as retina and lens. Limited visualization is a reason why some of the earlier studies demonstrated variable efficacy and safety; often they were only treating floaters right behind the lens (Figure 1).

Figure 1. Standard YAG laser tower - on the left, the laser beam and the illumination beam con- verge when focused on the pos- terior capsule. On the right side, the laser beam and illumination beam cross when attempting to focus on a floater in the posterior vitreous, thus not allowing a view of the floater and the relationship between the floater and the retina.

With Ellex’s YAG laser illumination system (True Coaxial Illumination, or TCI), surgeons have full visualization of the entire vitreous from the lens to the retina. This is achieved by using a retractable, reflecting mirror designed to move out of the laser pathway during the treatment. The laser, the oculars and the illumination tower use the same optical pathway, allowing for coaxial illumination and thus simultaneous visualization of both the retina and the floater. This is important to prevent inadvertently disrupting the retina (Figure 2).

Figure 2. Reflex laser tower — the mirror moves out of the way of the laser beam allowing for coaxial illumination. Laser, aiming beam and illumination tower are on the same optical pathway, thus allowing for visualization of the floater in the posterior vitreous.

The TCI design also enables titration of the red reflex by moving the slit lamp obliquely, or off axis, since the laser can fire at any position of the slit lamp. For example, a floater in the middle of the vitreous that is seen using coaxial positioning with a full red reflex can occasionally have a lot of glare or too much light entering the eye (Figure 3). We can titrate the degree of anterior illumination by moving the slit lamp slightly oblique, around 10° to 15°. This allows us to limit the amount of anterior glare and maximize contrast of the floater, while also maintaining enough posterior illumination to know where we are in the middle or posterior vitreous.

Figure 3. Full coaxial illumination. Slit lamp in the center position. Nice red reflex demonstrating retina is not in focus, but floater is a little obscured by the glare of the red reflex.

By moving the laser slit lamp to an oblique or off-axis position, we allow ourselves better contrast of the anterior floater by titrating off some of the glare and minimize axial red reflex but still providing enough illumination to determine if the floater is located a safe distance from the retina (Figure 4).

Figure 4. Slit lamp is 10° oblique (off axis). This titrates off some of the anterior illumination but keeps enough posterior illumination to see if the retina is in focus or not, which helps to maximize contrast with the floater and still provide spatial context (retina is far enough away).

An important clinical pearl: If the floater is in focus and the retina is also in focus, do not fire. Conversely, if the floater is in focus and retina is out of focus, you have enough spatial distance from the retina to fire (Figure 5).

Figure 5. The view achieved for a Weiss using the reflex tower providing true coaxial Illumination. With the slit lamp 15° oblique, we can maximize the view of the opacity and still provide spatial context of where the retina is located. Here, the floater is in focus but retina is not seen, indicating safe distance to fire.

Moreover, it is vital for the surgeon to understand how far behind the lens one can treat, which is of great concern when treating phakic patients. Using off axis slit lamp position allows the surgeon to identify the posterior capsule with more clarity than when the slit lamp is the center (on axis) position (Figures 6 and 7). The distance between the posterior capsule and the floater can be assessed similarly to how we assess the AC depth (slit lamp in an oblique position). We want to maintain at least 2-mm distance from the lens to avoid inadvertently hitting the lens.

Figure 6. A rope-like floater behind the lens. Due to full red glow of the coaxial beam (slit lamp in the center position), it is hard to tell where the posterior capsule is located. Not recommended to fire until the surgeon identifies the posterior capsule.

Figure 7. The laser slit lamp is in a slightly oblique (off axis) position, thus decreasing the glare and allowing for visualization of the posterior capsule and the floater. In this case, the floater is too close to the posterior capsule and one would not want to fire.

ENERGY DELIVERY

Previous studies that reported marginal results with YAG laser vitreolysis often set the energy level to 1 to 2 millijoules (mj), which is much less than the 4 to 8 mj typically required to vaporize floaters. Laser produces a small acoustic wave of energy that is circumferentially emitted surrounding the plasma creation, with some of the energy moving anteriorly toward the laser source. An “energy shield” develops, preventing further prorogation of energy posteriorly. The total energy “shock wave,” from the furthest anterior to posterior extent, is known as the convergence zone.

For YAG lasers, the increase in size of plasma (convergence zone) between 1 mJ and 10 mJ is less than 50% (non-linear relationship). So, when firing at 5 or 6 mJ (the average for most treatments), the convergence zone is less than 200 µm (Figure 8). We presented a study at ASCRS 2019 in which we held a B scan probe temporally while we performed LFT to observe the behavior of the vitreous surrounding the plasma creation.4 We found, even with energy at 7 mJ per shot fired, no movement of vitreous was evident, including at 1 mm from the plasma formation. Additionally, we saw no evidence of traction or pulling of the posterior hyaloid face.

Figure 8. The size of the convergence zone increases in a nonlinear fashion as the power on the laser is increased. At 1 mJ, the size of the convergence zone is 110 µm and increasing power to 10 mJ increases the size to 210 µm (less than 50% increase).

Plasma is the fourth state of matter, turning a solid into a gaseous state. So, despite perception, the floater is truly vaporized. However, vaporization occurs in a small area, which necessitates a larger number of shots to fully remove the opacity. Due to the 3-nanosecond pulse, heat is dissipated before the next shot is fired, which decreases risk of accumulation of energy (Figure 9).

Figure 9. Arrows in the picture above point to the narrow Gaussian curve of the energy delivery using the new reflex cavity. There is a sharper rise and fall of the energy, therefore limited wasting of energy.

New advanced YAG laser technology also feature a specially designed active cooling cavity. When firing several hundred shots in one sitting, standard laser cavities can overheat. The active cooling cavity of newer YAG lasers has been shown to decrease the risk of the cavity overheating. Further, this allows a stable delivery of energy (Figure 10).

Figure 10. Graph on the left side demonstrates a stable delivery of energy over hundreds of shots when using active cooling cavity, whereas on the right using a passive cooling cavity, the delivery of energy is not stable over hundreds of shots fired.

NEW DATA

The recently published paper by Shah and Heier was the first randomized placebo-controlled trials evaluating the safety and efficacy of laser floater treatment using advanced YAG technology specifically designed for laser-based floater treatment.5 This study involved 52 eyes, of which 36 patients were treated with the Reflex Technology platform (Ellex Medical). The study concluded that 54% of patients in the YAG laser group experienced symptomatic improvements compared to 9% of patients in the control group.

The YAG laser group also showed greater improvement in the 10-point visual disturbance score than the control group. Improved symptoms were reported by 53% of patients in the YAG laser group and 0% in the sham arm. Although the YAG laser group showed improvements in general and peripheral vision, role difficulties and dependency, neither group showed changes in BCVA. That is important since we cannot use the Snellen chart to define if patients are clinically symptomatic.

Also, this study demonstrated no retinal adverse events in the treatment group, although a retinal defect was seen in the control group. This is a critical point, because the cause of retinal defects is often the result of vitreous traction. According to the AAO, the definition of YAG vitreolysis is the “severing of vitreous strands and opacities with a laser.” There is no evidence that the LFT causes traction on the retina. LFT and YAG capsulotomy are two different procedures working on different anatomical structures. With LFT, the treated collagen fibers do not have the same connection directly to the vitreous base as zonules attached to the posterior capsule, and, as such, the risk of retinal breaks is not the same. There have been no reports of increasing cataract formation after LFT if the lens was not directly hit at the time of the procedure.

In 2016, we presented an observational study at ASCRS which investigated patient satisfaction, complication rates and treatment specifics associated with laser floater.7 One hundred thirty patients were evaluated and satisfaction was assessed with a 1-10 self-rated scale, with higher values indicating greater patient satisfaction as well as a “Yes” or “No” indicating whether they were satisfied with improvement in daily functioning. Information on complications was recorded for all patients. Ninety-one percent of patients stated that they were satisfied with their improvement in daily visual functioning; average degree of improvement was 8.5 out of 10 (after multiple sessions in some patients).

Patients with a Weiss ring required 1.3 sessions to sufficiently vaporize the floater as compared to 3.2 sessions in patients with amorphous clouds. The number of laser shots to sufficiently vaporize floaters amorphous clouds was 568 shots (vs186 for Weiss rings). Power settings also varied depending on floater type with the average setting at 5.8mJ (range 2.9 - 9mJ). Best results and higher patient satisfaction scores were notably seen with solitary Weiss rings versus amorphous clouds. The adverse event profile included two phakic lenses that were hit, three IOP spikes, and one retinal hemorrhage. The two lenses were hit (both in the first 50 cases) before we appreciated the importance of using the laser slit lamp in the oblique position to view the posterior capsule and appreciate the distance of the floater from the lens. The retinal heme occurred due to the fact the retina was in focus at the same time as the floater. The retina was in focus at the same time as the floater and therefore the laser should not have been fired at that moment.

The three IOP spikes occurred in the post YAG cap patients where the amorphous clouds were right behind the lens. It correlated not with energy settings, but with number of shots. Now we decrease the number of shots to 300 or less if the floaters are close to the lens in a post YAG cap patient.

At ASCRS 2017, we also presented our data of LFT patinets with at least 1 to 4 years of follow-up. This retrospective study included 1272 procedures performed in 680 patients.8 Patients with both amorphous and solitary Weiss ring type of floaters were included. Ten adverse events were recorded (0.8%), comprising seven cases of IOP spikes, two cases of hitting the phakic lens (Figure 10) and one retinal hemorrhage (this included the adverse events fromt the 130 cases in the 2016 prospective paper). Patients with IOP spikes were placed on topical antihypertensive medications (average post-medication IOP, 19 mm Hg). The one of the phakic patients subsequently required cataract surgery and achieved a corrected visual acuity of 20/20, while the other patient is still being observed. The case of retinal hemorrhage resolved in 3 months with no long-term negative effects. There were no inflammatory issues faced, no AC or Vitreous cell or flare seen., nor was there exacerbation of diabetic retinopathy, progression of ERM or cystoid macular edema. Postoperative regimen for all cases included IOP checks immediately after the procedure, at 1 week, and 1 month. No anti-inflammatory drops or topical antihypertensive meds were given.

OBJECTIVE DATA

Qualitative analysis of the effects of LFT have been achieved with spectral domain OCT (SD-OCT) and scanning laser ophthalmoscopy by comparing shadows on the retina created by floaters before and after treatment. A recent study published in OSLI Retina in October 2018 on novel OCT applications, including shadow changes on a 5-line raster scan following vitreolysis, described cases in which patients had complained of a scotoma that would not go away.6 Multiple initial tests from other doctors did not reveal an etiology.

After further examination of the vitreous and evidence on SD-OCT of the shadow being cast by a large floater over the macula, YAG vitreolysis was performed. Following treatment, patients described resolution of the floater and the SD-OCT scans revealed resolution of the shadow that was cast on the retina (Figures 11 and 12).

Figure 11. Above: Arrow A indicates large opacity over the macula region. Shadow is seen being case over the macula on the 5 line raster scans. See arrow B.

Figure 12. Above: Arrow A: most of the opacity has been removed with the laser. Arrow B demonstrates the shadow now gone on the 5- line raster scan.

Ray tracing aberrometry, using the iTrace (Tracey Technologies), uses a laser beam parallel to the line of sight through the pupil to the retina. Aberrations caused by ocular structures result in a measurable shift in the perceived retinal location (point spread function). The maps produced show color-coded total and higher-order aberrations (HOA), including coma, spherical aberration and trefoil. It can measure internal quality of vision displayed to the user by the dysfunctional lens index (DLI), measuring quality of the optical system from behind the cornea to the retina. This can be used to compare wavefront and refractive information with a differential prior to and after surgery. The technology can also determine contrast sensitivity (MTF curve).

With respect to vitreolysis, with all things being equal (the cornea, the lens and the retina), this same index can be used to measure the impact of floaters before and after vitreolysis, effectively providing a dysfunctional “vitreous” index. If 10 is considered a perfectly clear media and 0 is considered opaque, many patients with floaters measure an index of between 3 and 6, which can be significantly improved with vitreolysis. We presented a paper on this topic at ASCRS 2017, which showed a significant improvement in HOA, MTF area under the curve and DLI score post LFT.7

PATIENT SELECTION AND EDUCATION

As with any procedure, patient selection is extremely important. For LFT, solitary opacities tend to have the best outcomes. It is important for surgeons to know when to say no. If the patient has a floater that is too close to the lens or too close to the retina, I recommend observation only. If the patient has a recent PVD symptom of a floater or flashes, I recommend observation and repeat a dilated examination within three to six months. We also give them time to neuroadapt.

Also, patients need to be aware there may need to be more than one session to achieve high satisfaction. In our 2016 ASCRS paper, we found it took three sessions to achieve high patient satisfaction in patients with amorphous clouds or string-like floaters.8 Some patients also may not have 100% resolution other symptoms. These are important concepts to address before performing LFT. It also important to ask patients to describe their symptoms, or even have them draw their floaters. This process can help you identify which opacity to treat in case of many floaters in the vitreous.

CONCLUSION

After performing more than 4,000 laser-based floater treatments during the past five years, I have come to appreciate the impact floaters can have on a patient’s daily functioning. A floater is “bad enough” when a patient states the floaters are interfering with daily life, regardless of the number of floaters or size.

With new laser technology, a better understanding of vitreous behavior and patient selection criteria as well as new protocols, we now have an alternative to observation or vitrectomy for our patients. OM

REFERENCES

  1. Wagle AM, Lim WY, Yap TP, et al. Utility values associated with vitreous floaters. Am J Ophthalmol. 2011;152:60-65.
  2. Garcia GA, Khoshnevis M, Yee KMP, Nguyen-Cuu J, Nguyen JH, Sebag J. Degradation of Contrast sensitivity function following posterior vitreous setachment. Am J Ophthalmol. 2016 Dec;172:7-12. Epub 2016 Sep 12. Accessed Jun. 5, 2019.
  3. Webb BF, Webb JR, Schroeder MC, North CS. Prevalence of vitreous floaters in a community sample of smartphone users. Int J Ophthalmol. 2013;6:402-405.
  4. Singh I. Real -time ultrasound evaluation of vitreous behavior during YAG Vvitreolysis for the treatment of symptomatic floaters. Presentation at: ASCRS/ASOA Annual Meeting; May 3-7, 2019; San Diego, CA.
  5. Shah CP, Heier JS. YAG laser vitreolysis vs sham YAG vitreolysis for symptomatic vitreous floaters: A randomized clinical trial. JAMA Ophthalmol 2017;135:9:918-923.
  6. Singh IP, Novel OCT application and optimized YAG laser enable visualization and treatment of mid- to posterior vitreous floaters. OSLI Retina. 2018;49:806-811.
  7. Singh IP. Pre- and postoperative objective assessment of quality of vision in patients undergoing YAG vitreolysis using wavefront berrometry. Presentation at: ASCRS/ASOA Annual Meeting; May 5-9, 2017; Los Angles, CA.
  8. Singh IP. Treating vitreous floaters: Patient satisfaction and complications of modern YAG vitreolysis. Presentation at: ASCRS/ASOA Annual Meeting; May 6-10, 2016; New Orleans, LA.

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