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T-membranotomy technique can be used to displace vitreous floaters
The Nd:YAG laser creates a T-shaped incision in the detached posterior vitreous membrane to eliminate floaters.
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Floaters are a common visual complaint, particularly in mature eyes. Although they pose no threat to eye health, these small collagen bundles located in the vitreous can be a great nuisance. In most cases, floaters resolve within weeks or months. And when they do not resolve quickly, the affected individual usually grows accustomed to their presence and ceases to notice them over time.
Some individuals, however, have a particularly low tolerance to floater-related visual obscurations and simply cannot adjust to floater-filled vision. Individuals with highly vision-dependent occupations and postoperative cataract surgery patients, who experience a sudden increase in awareness of pre-existing floaters following the removal of their cataracts, are also less able or willing to tolerate the presence of floaters. Such individuals require an effective method of removing floaters — a need traditionally met by the removal of the vitreous humor via vitrectomy.
A much-needed alternative
Like most invasive surgical procedures, vitrectomy is not risk free. The complications associated with the procedure, such as retinal detachment, anterior vitreous detachment and macular edema, can threaten vision or worsen existing floaters. As such, clinicians today are more likely to advise a patient to persevere with floaters rather than undergo a vitrectomy.
For those unable to accept a wait-and-see approach, Nd:YAG laser vitreolysis, performed with a device such as the Ultra Q Nd:YAG laser (Ellex), may provide an effective outpatient method for achieving floater-free vision while bypassing many of the risks of vitrectomy. Indeed, two small-scale studies, one by Tsai et al in 1993 and the other by Toczolowski et al in 1998, have already demonstrated a complication-free and near 100% rate of floater removal with Nd:YAG laser vitreolysis.
The potential efficacy of Nd:YAG laser in floater removal came to my attention more than 10 years ago. Tsai and Toczolowski had success when using the laser to directly destroy existing floaters, but I recognized the moderately high time demands of this strategy, particularly in eyes with a large number of floaters. I also noted that using lasers to vaporize structures as small as floaters carried a marked risk of damaging surrounding ocular tissue. This, of course, is in addition to the other known risks of laser vitreolysis, such as increased IOP, retinal damage and detachment, and postoperative development of traumatic cataracts, which are notoriously difficult to remove without significant capsular damage.
To that end, I developed a procedure called the T-membranotomy. The procedure involves the use of a Nd:YAG laser to create a T-shaped incision in the detached posterior vitreous membrane. In doing so, all floaters within the vitreous can be eliminated through the membrane opening and evacuated in a nasal or temporal direction. In standard laser vitreolysis, floaters that are too small to be broken down by the laser and floaters situated too close to the retina for safe laser application (premacular bursa floaters) are usually not treated. This means that patients with such floaters may still experience floater-related visual disturbances even after spending time and money on a laser vitreolysis procedure. In contrast, the T-membranotomy technique creates a passageway through which floaters of all sizes can exit the optical axis, overcoming this limitation of standard laser vitreolysis and avoiding patient disappointment.
Studying the laser in a clinical setting
To investigate the clinical safety and efficacy of the Nd:YAG laser T-membranotomy technique, I performed a study in collaboration with my colleagues at my Dutch practice. We retrospectively assessed a total of 100 eyes with a 9-month or longer history of floaters related to posterior vitreous detachment. Thirty-five eyes were treated with pars plana vitrectomy, and 65 eyes were treated with T-membranotomy-based YAG laser vitreolysis. We observed a slightly lower rate of self-reported postoperative visual improvement among patients treated with YAG laser than in those treated with vitrectomy, at respective rates of 80% and 90%. Over a 10-year follow-up period, safety of the procedure was indicated by the absence of any complications among YAG-treated patients. The results strongly support the use of YAG laser vitreolysis for floater removal among patients with a history of floaters arising secondary to posterior vitreous detachment and persisting for at least 9 months.
Treating floaters with lasers
Nd:YAG lasers were initially designed for conventional anterior segment photodisruption procedures, such as posterior capsulotomy after cataract surgery and laser iridotomy to relieve pressure in the anterior chamber, in a noninvasive outpatient-based setting. These lasers can effectively cut through ocular tissue, including vitreous membranes, with little to no patient discomfort.
In the case of YAG laser vitreolysis, for the majority of patients only one Nd:YAG laser session is needed to produce floater-free vision; however, in some patients a second treatment may be required to remove residual floaters. Because this method does not involve the introduction of surgical instruments into the eye, as with vitrectomy, the risk of complications remains low, even when a second treatment is required.
Whether used to cut membranes or to break up individual floaters, the low-energy level of the Ultra Q microsurgical laser minimizes the risk of damage to surrounding ocular tissue. Specifically, its patented cavity design produces an ultra Gaussian beam that concentrates all of the energy in the center of a finely focused ray. This technology, coupled with a fast pulse-rise time, allows the laser to achieve the optical breakdown necessary to cut through tissue. And this is achieved using much lower energy levels and with higher precision, fewer shots and less cumulative energy than other laser systems. The Ultra Q typically achieves optical breakdown in air at 1.8 mJ, an energy level that is approximately half that of other Q-switched YAG lasers.
A recent innovation to the Ultra Q is Reflex Technology. Providing optimal illumination of the vitreous, this light delivery system allows the Ultra Q to achieve good coaxial vision by converging the operator’s vision, target illumination and treatment beam onto the same optical path. A retractable reflecting mirror, programmed to move out of the laser’s pathway during firing mode, ensures coaxial illumination at all times and enables full visualization of floaters. This technology, combined with a two-point aiming beam and a continuously adjustable anterior and posterior offset control for greater precision when treating close to the retina and/or the lens, ensures precise localization of the focal plane and effective treatment results.
In contrast, conventional YAG lasers provide a compromised view of the vitreous, making it difficult to visualize and focus on the targeted floaters and membranes. In addition, if the slit generator on these systems is used in a central position, the mirror that reflects the illumination beam has to be positioned in the path of the treatment beam, which results in clipping of the laser beam and reduces the amount of energy delivered. This, in turn, compromises the ability to reach the power density required for effective optical breakdown, limiting treatment efficacy, particularly deeper in the vitreous where more energy can sometimes be required.
Summary
Patients with persisting floaters often experience restless vision. Much like having an itch that cannot be scratched, the patient cannot settle until the problem is resolved. The nuisance of having floaters can be further exacerbated by a physician who denies a patient treatment because either he underestimates the impact of the floaters on the patient’s quality of life or he does not know a safe method of floater removal. The high efficacy associated with T-membranotomy-based YAG laser vitreolysis means that this no longer has to be the case. Patients can now achieve the symptom resolution they desire with minimal risk of causing additional ocular problems.