Laser vitreolysis

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Introduction

Laser Vitreolysis is a medical procedure involves the application of nanosecond pulses of low-energy laser light to evaporate and dissection the vitreous opacities.

Vitreous opacities, also known as floaters, are among the most common ocular conditions. In some patients, floaters symptoms can adversely affect quality of life, interfere with reading or driving and may persist for a long time.[1][2]

A study by Wagle and coworkers addressed the impairment on vision quality associated with floaters in 311 outpatients. This study demonstrates that floaters have as much influence on quality of life as other ocular and systemic diseases. The utility values of floaters were equal to age-related macular degeneration, and similar to glaucoma, mild angina, stroke and asymptomatic HIV.[1] A study by Webb and coworkers demonstrated that floaters are common in the general population, irrespective of age, race, gender and eye color. In a review of 603 smartphone users, 76% (n=458) indicated that they notice floaters, with 199 of these individuals citing noticeable vision impairment as a result of their floaters. Myopes and hyperopes were 3.5 and 4.4 times, respectively, more likely to report moderate or severe floaters. [3] A study by Garcia and coworkers showed that there was a 52.5% reduction in contrast sensitivity function following posterior vitreous detachment.[4]

Three management options exist for symptomatic floaters: patient education and observation, pars plana vitrectomy and YAG vitreolysis.The most common advice to patients by ophthalmologists are “try to ignore them” and “learn to live with them”. 23G vitrectomy can be successful but is an invasive procedure and most retinal specialists are reluctant to accept this procedure for floaters due to potential risks including retinal tears and detachments, proliferative vitreoretinopathy, choroidal bleeding, macular shrinkage, and cataract progression.[5] [6][7][8]

YAG laser treatments for posterior ocular segment have been performed with variable success since the 1980s. These conditions included vitreoretinal tractions due to proliferative diabetic retinopathy, sickle cell retinopathy, vitreous cyst and rhegmatogenous retinal detachment.[5] The first report of YAG laser vitreolysis for floaters was published in 1993. In that study, Tsai and collaborators used YAG laser to treat 15 patients with localized prepapillary or central vitreal opacities. All patients were satisfied with the treatment and stated that their floaters disappeared immediately after the operation. During the 12 month follow up period, no patient showed any significant visual deterioration or recurrence of subjective floaters .[9] Other older data sets suggested only modest efficacy and possible safety concerns that led many doctors to be skeptical about the procedure.[10] It is important to note these older studies were using laser technology not optimized for laser floater treatment. The latest developments and achievements in lasers, optics and lightning systems which using the same optical pathway, allowing for simultaneous visualization of both the retina and the floater for more accurate treatment.

Principle of action

The mechanism of action is called “plasma formation” and “optical breakdown” which are terms used in describing laser physics. Optical breakdown requires a very high frequency electrical field in the optical region of the electromagnetic spectrum that is confined to a very small area. The temperature at the center of the area of optical breakdown has been calculated to be several thousand degrees. The laser performs photoconversion of the solid floater into a gas with a combination of photochemical, thermal, thermoacoustical and electromagnetic optical field effects. It is important that the laser is firing in the range that obtains optical breakdown to change the form of matter from a solid to a liquid and to some extent to a gas. The gas bubbles that form float away and gradually dissolve. The dissolved gases can then pass across cell membranes and be carried away by the blood vessels. The smaller the focal area and the shorter the pulse width, the less energy is needed to create the plasma and associated shockwave. Due to the short duration of the pulse (4 ns), heat is dissipated before the next shot is fired. If the laser is fired into the vitreous below the optical breakdown level (normally about 2.2 mJ) the floaters will only be fragmented and the success rate will be quite low.[11]

Indications

Most specialists are guided by the following criteria for selecting patients for laser vitreolysis:

  • Patient has significant symptoms Floater symptoms such as difficulty in driving, reading, use of a computer, significant annoyance, or their concentration significantly affected. [11][12][13][14] Since the procedure is performed to improve the patient's quality of life, it is not indicated for asymptomatic opacities.
  • Patient has the floater longer than 2 months without significant improvement Any debris associated with acute posterior vitreous detachment may disappeare by the time of the treatment, which increase the probabilities of the patients remaining symptom-free after this period. In addition, posterior vitreous detachment becomes more complete which brings the floater forward for easier, safer treatment.[11][15]
  • The opacity at least 2 millimeters from the lens and retina The laser focus should be set manually with a certain distance to the lens and retina. In most studies, a safety distance of 2-5 mm from the crystalline lens and 2-4mm from the retina was determined.[11][14][16][17] In cases where the 2 mm threshold distance is not preserved, complications concerning the lens or retina can possibly occur.

Contraindications

The following contraindications for the procedure have been identified:[5][11][15]

  • Floaters too numerous to treat
  • Floaters caused by recurrent inflammation
  • Floaters from fresh vitreous or pre-retinal hemorrhage
  • Floaters associated with untreated, symptomatic retinal tears or untreated retinal detachment
  • Floaters off the central visual axis to the point they are untreatable
  • A floater that is so large and it could not be eliminated with reasonable laser power, a reasonable number of shots, and less than 5 treatment sessions.
  • Corneal scars, irregularity, edema or excessive lenticular astigmatism preclude adequate visualization of the target aiming beam
  • Patients with a history of significant psychiatric problems that may recur or worsen if there is no improvement with treatment or if there were a complication.
  • Uncompensated glaucoma or high intraocular pressure

Preoperative Management

A comprehensive eye exam includes:

  • Special test questionnaires as Vitreous Floaters Functional Questionnaire (VFFQ) or the National Eye Institute Visual Functioning Questionnaire (VFQ) may be used to assess subjective feelings. A number of authors have shown the possibility of their effective use in patients with vitreous floaters.[18] [19]The patient can also draw opacities that interfere with him so that the surgeon can differentiate symptomatic and asymtomatic opacities.
    B-scan of Weiss ring located 7.41mm from the retina
  • Slit lamp biomicroscopy can be used to examine anterior segment, central and posterior vitreous structure. For a better visualization of the middle vitreous body special contact lenses can be used. Optimal visualization is key to performing laser floater treatment. Appreciating spatial context is crucial for safety and efficacy.
  • The approximate refraction (helpful because it gives a general idea of the axial length of the eye which may affect which surgical contact lens to choose).
  • Measurement of intraocular pressure.
  • B-scan ultrasound Ultrasound can be used to image opacities within the vitreous body. Quantitative ultrasonography of vitreous provides a measure of floater severity.[20] [21]It is also used as the main method for determining the location of the opacity in relation to the retina and lens.
  • Optical coherence tomography (OCT) This technology helpful for objective assessment of artifactual shadows of vitreous floaters.[14][22][23]
  • SLO image of Weiss ring
    Scanning Laser Ophthalmoscope (SLO) can be used to determine position, size and motility of the vitreous floaters with respect to the patient's visual axis. It is useful to perform image analysis of such SLO photos with the aim of quantifying the umbra and penumbra effects cast by vitreous opacities as a way of indexing floater size and density. Recent imaging studies have combined SD-OCT with scanning laser ophthalmoscopy to better evaluate the vitreo-macular interface in various disease states including vitreous floaters; [7][23][24]

Procedure

The following steps should be performed for successfully laser vitreolysis: [9][11][15][16][17][25]

  • Explain the purpose and nature of the procedure and obtain informed consent.
  • Apply mydriatic drops .
  • Apply topical anaesthesia.
  • Apply contact lens for vitreolysis The contact lens is the best instrument to reveal the relationship of the floater to the patient’s retina and lens. These lenses increase the cone angles anterior and posterior to the contact lens and compress the diameter of the focus, increasing its irradiance.
  • Set defocus to zero. The aiming beams of the laser are placed on the floater and the laser is fired. This vaporizes a small part of the floater frequently producing a gas bubble. The power setting is 3 to 10 millijoules with the larger setting used in the posterior vitreous and on the denser floaters. Most isolated floaters require less than 100 shots. It should be noted that the treatment efficiency and the required degree of laser exposure (the number of pulses and the total energy per session) depend on the initial type of opacity, structure, its size and density.
  • No post-operative topical medication prescribed.
  • Follow-up treatments may be undertaken on the next day after previous session, although it may take up to a month to truly assess if another session is necessary based on symptoms. Patient symptomatic improvement can vary depending on the type of clinically significant vitreous opacities. The reported number of required sessions ranged between one and six.

Complications

Cataract

Iatrogenic cataract after laser vitreolysis

A few small case series have described post laser vitreolysis cataract.[26][27][28][29][30]

The disruptive laser energy can subsequently lead to a defect of the posterior capsule, which could result in a cataract formation.

Absence of cataract formation, as a potential complication of laser vitreolysis, could be achieved by the safe distance to the crystalline lens and the low energy applied during laser treatment. It is important to mention that it cannot always be guaranteed to observe this safety distance, for example due to unexpected patient movements, movement of floater during treatment or difficulties with focusing the laser beam onto the vitreous opacities. Even if the safety distance was observed, a high laser energy can unintentionally affect the lens or retina.

Retinal injury

Laser injury–related transient posterior pole retinal hemorrhages were reported.[11] [26][31][32]In one of these cases, the patient remained asymptomatic, while in the other, a transient scotoma was seen that lasted a few weeks and corresponded to the area of subretinal hemorrhage with nearby retinal whitening.

Laser-related retinal hemorrhage

A few small case series have described post laser vitreolysis retinal detachment.[17]

There is a report of retinal detachment when patients underwent laser vitreolysis immediately after Nd:YAG capsulotomy. Retinal detachments are associated with posterior capsulotomies probably because with that procedure, vitreous can herniate through the created capsulotomy into the anterior chamber and thereby increase vitreous traction on the retina. [33]It is suggested that Nd:YAG capsulotomy maybe performed first and then Nd:YAG vitreolysis may be performed after a safe interval and a thorough retinal examination.

Elevation of intraocular pressure

The intraocular pressure elevation after YAG laser vitreolysis has been reported.[15][26][34] Some cases had transient or prolonged elevation of intraocular pressure, other resulted in secondary glaucoma and trabeculectomy was required. [11][26]Although the pathomechanism explaining elevation in intraocular pressure is unknown, the authors hypothesized that the treatment may have caused the obstruction of the trabecular meshwork by floater debris, by inflammatory cells or macrophages, or by shockwave damage to the trabecular endothelial cells.[11][34]

There is some recommendations to prevent this complication: don’t operate on anyone with elevated pressure, glaucoma; don’t use an excessive number of shots (more than 300 total per eye); try to use less shots on any floater that is close to the trabeculum; never widen a posterior capsulotomy at the same sitting as the floater treatment.[11]

Outcomes

The U. S. Food and Drug Administration when approving YAG lasers for this procedure, classified this as a non-significant risk procedure. The spectrum of complications submitted to the ASRS ReST Committee is consistent with previous reports and indicates that complications remain relevant to laser vitreolysis as currently performed.

Cases of retinal detachment and raise IOP cannot determine whether there is a causal association between these complications and laser vitreolysis. Prospective studies are warranted to better understand the efficacy of this procedure and the frequency of attendant complications. Until then, practitioners should be aware of the profile of potential complications to properly inform patients during the consent process.

The position of focus and optimal energy applied during laser treatment is an important factor, which if miscalculated could result in complications. Using the patient’s subjective claim of the resolution of floaters as an outcome measure, the success rates claimed by existing publications are highly variable.[10][11][16][35][36][37]

Shah and colleagues were the first to conduct a randomized placebo-controlled trial evaluating the safety and efficacy of laser floater treatment using advanced YAG technology specifically designed for laser-based floater treatment. 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.[16]

Summary

The currently available evidence offers some indications that YAG laser vitreolysis may be a viable option for the symptomatic relief of selected patients with bothersome complaints due to vitreous opacities. The advantages of Nd:YAG laser is that the eye remains closed and that vitreous components are vaporised. Clearly, the importance of careful case selection, good history taking, detailed counseling, written informed consent, well documented by imaging and careful postoperative follow-up cannot be overemphasized. [38]

Centrally suspended, single floaters might be best candidates for vitreolysis or displacement, but this remains to be demonstrated. In particular, cases with chronic Weiss rings or solitary opacities may be the best candidates that will likely benefit the most from this procedure. On the other hand, notwithstanding how annoying the symptoms can be, the safety profile of this treatment seems far from optimal considering that the presence of vitreous floaters is not a vision-threatening condition.

Obviously, appropriate trials will need to be conducted to determine indications and characterize the long-term safety and efficacy of the procedure.

References

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