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Glaucoma SLT & MIGS: Moving Towards Proactive Patient Care

2T CPD in Australia | 0.5CD in New Zealand | 1 June 2018

By Dr. David Lubeck

With access to selective light therapy – as a highly effective first line option for glaucoma treatment – as well as minimally invasive glaucoma surgery for patients who would benefit from lower IOP but do not warrant the risk of traditional surgery, we have new options for the proactive treatment of glaucoma.

LEARNING OBJECTIVES

1. Understand the role of selective light therapy (SLT) in the glaucoma treatment algorithm, relative to minimally invasive glaucoma surgery (MIGS) procedures, medications and other surgical approaches
2. Determine patient selection criteria for SLT
3. Understand the role of MIGS in the glaucoma treatment algorithm, relative to medications, SLT and other surgical approaches
4. Determine patient selection criteria for ABiC (an interno canaloplasty) and the various MIGS options available.

It has long been understood that glaucoma is a multifactorial disease that affects various tissues in the visual pathway, including the trabecular meshwork (TM) in the anterior chamber (AC), the optic nerve head in the retina, and the lateral geniculate nucleus and the visual cortex in the central nervous system.1 The most important risk factor affecting disease progression is still thought to be an increase in intraocular pressure (IOP) – and thus reducing IOP remains the primary therapeutic strategy for treating open angle glaucoma and ocular hypertension.2


When assessing and planning treatment for a patient newly diagnosed with glaucoma, the key question is how much pressure lowering needs to be achieved to protect the optic nerve for the rest of the patient’s life – which is something that we can never know with certainty. Our goal is to create a timeline, reassess at regular intervals, adjust treatment as needed and the whole while, help the patient maintain the highest possible quality of life.


While medications have long been our first line of treatment for glaucoma, the side effects, variable compliance and cost often limit our success in preventing loss of vision. Frequently, glaucoma patients struggle managing and instilling topical medications. These same medications, even when properly used, can cause ocular surface and systemic problems.


Several studies have identified poor compliance as a major limitation of medication therapy. A study in the Journal of Glaucoma showed that nine out of 10 patients were not able to administer their eye drops properly.3 Poor compliance can lead to treatment failure: if the patient forgets to administer their eye drops, or uses them incorrectly, fluctuations or persistent elevation of IOP could lead to an earlier onset of vision loss.


When a patient thinks about having to use eye drops, at first they usually consider it to be a benign thing. They are unaware of the many possible side effects that can occur. Conjunctival hyperaemia, chemical irritation, burning, and allergic reaction are some of the unwelcome effects associated with the use of eye drops. Whether your patient is a young adult or a senior, having red or irritated eyes is an unwanted problem. Beyond ocular side effects, the more glaucoma drops that are prescribed, the greater the risk that systemic side effects will occur. One of the reasons that eye drops can cause systemic issues is that these drugs enter the bloodstream much more quickly than oral medications. Eye drops, after passing through the nasal lacrimal duct, enter into the nose and are quickly absorbed through the nasal mucosa, providing a direct path to the blood stream. A paper published in Cardiology in Review notes that the systemic absorption of many glaucoma medications can affect the sympathetic and parasympathetic nervous system of patients and cause cardiovascular toxicity.4 The fact of the matter is that eye drops for treating glaucoma, while effective in reducing IOP, are not without risks and side effects.


Previously, we had to rely on treatment paradigms only with extremes; medications on one end and invasive, bleb-dependent procedures including trabeculectomy and tube shunts on the other. Now, proven new minimally invasive treatment options for glaucoma such as Selective Light Therapy (SLT) and Minimally Invasive Glaucoma surgery (MIGS) are being successfully deployed around the world and in the process, helping shift the paradigm towards proactive glaucoma management, reducing or eliminating the need for medications.

SELECTIVE LIGHT THERAPY

Since its FDA approval in 2001, SLT, also known as Selective Laser Trabeculoplasty, has gained ground steadily as a primary treatment for open angle glaucoma. It can also be used to reduce the number of medications a patient is on. This, as an added benefit, helps address the issues of side effects and compliance associated with medications. SLT uses short pulses of relatively low energy, 532nm laser light to selectively target and irradiate the pigmented (melanin) cells in the trabecular meshwork to stimulate a process of cellular regeneration – releasing proteins and cytokines, improving circulation of fluid through the trabecular meshwork and inner wall of the Schlemm’s canal. As the normal function of the trabecular meshwork is restored, IOP is reduced. SLT works by a process known as selective photothermolysis, which refers to the absorption of energy by a chromophore in a period of time below its thermal relaxation time (TRT), or the amount of time it takes for the heat absorbed during a laser pulse to dissipate. Because the short, threenanosecond pulse duration of SLT is well below the one microsecond TRT of TM tissue, heat does not disseminate outside the affected cell and the TM architecture is preserved.


Any time we're trying to decide how to treat patients, we need to consider the ratio of risk to benefit, ultimately dictating which options we should pursue. In my opinion, the risk profile of SLT is excellent. Indeed, when you consider the risk of complications and side effects associated with SLT versus other glaucoma therapies, SLT has one of the highest benefit-to-risk ratios of all ophthalmic procedures. The most common adverse effects of SLT include; blurred vision for a few hours after the procedure, mild discomfort during laser delivery, redness for one to two days, and soreness with photosensitivity for a one to two days. Usually, these side effects are minor and transient, require no treatment, and do not have any long-term impact on vision.5

SLT has been proven to be an effective primary therapy option. A prospective, randomized study by L. Jay Katz  et al, Wills Eye Hospital, Philadelphia, compared SLT to a prostaglandin inhibitor as a primary therapy. Sixty-nine patients (127 eyes) were enrolled in the study and were treated and followed for up to one year. In the SLT group (N=29), the baseline IOP was 24.5mmHg, which was reduced to 18.2 mmHg at the final follow-up visit. In the medication group (N=25), the baseline IOP was 24.7mmHg, which was reduced to 17.7mmHg at the final visit. At the final follow up, 11 per cent of the SLT group had received additional SLT, compared to 27 per cent of the medication group requiring additional medication. The study concluded that there was no statistical difference between the SLT and medication groups. Indeed, SLT was considered to be safe and a highly effective primary treatment.6


Another factor that supports the use of SLT as a first line therapy is that it can be used as a diagnostic tool; i.e. to identify the patient’s pathology and predict future efficacy of treatments. If an SLT treatment successfully lowers IOP, it indicates that the primary obstruction to outflow is located in the trabecular meshwork. In contrast, a failed SLT treatment indicates that outflow resistance is located beyond the trabecular meshwork, either in the canal or distally. In summary, not only can SLT be used as a highly effective first line treatment, but it can also provide useful inference regarding the patient’s pathology and thereby assist with the selection of future treatment strategies.

On average, SLT delivers a 30 per cent reduction in IOP when used as a primary therapy.6 If the pressure lowering diminishes over time, or if the initial effect is inadequate, it can be repeated. If additional pressure lowering is required, medications can be added or other surgical interventions can be considered. Employing a treatment algorithm with SLT as a first line option will work well for many patients with open angle glaucoma.

Whether you’re an optometrist or ophthalmologist, considering treatment cost burden is an important part of assessing patient quality of life. SLT offers economic benefits to the patient and society as a whole. If medications are reduced or eliminated, not only does SLT improve compliance, it lowers direct and indirect costs to the patient, medical practice, and healthcare system. A study by Cantor, et al., published in Current Medical Research and Opinion found this to be true over the long term. The authors of this study calculated that the five-year cumulative cost of SLT was considerably less than the cost of medications and filtering surgery – US$4,838 for SLT versus $6,571 and $6,363 respectively for medications and surgery.7

MIGS – MINIMALLY INVASIVE GLAUCOMA SURGERY

MIGS is a class of glaucoma procedures defined as FDA approved, minimally invasive, performed ab-interno through a small incision (usually through the cornea) that spares the conjunctiva. The advent of MIGS has substantially changed the way that physicians approach the treatment of glaucoma, with surgery often considered simultaneously with medical or laser therapy.

Historically, glaucoma surgery was reserved for patients who were losing vision despite maximal medical therapy. Because of the high risks associated with trabeculectomy and tube shunt surgery, they were performed as a last resort. One of the hallmarks of MIGS is its excellent safety profile. MIGS therefore can be a valid treatment option in cases of glaucoma at any stage. For example, in the past, a patient with early glaucoma who had well controlled IOP on one or two medications would not have been a candidate for surgical glaucoma treatment. Today, this patient could undergo a MIGS procedure at the time of cataract surgery with the goal of reducing the need for ongoing glaucoma medications.

All of the MIGS procedures have safety profiles that are advantageous compared to traditional glaucoma surgeries, but their mechanisms of IOP reduction are different. To summarise, the various MIGS procedures work by increasing trabecular outflow, increasing uveoscleral outflow, increasing subconjunctival outflow, or decreasing aqueous production.

The trabecular meshwork is thought to be the main site of resistance to aqueous outflow. Consequently, many MIGS procedures target trabecular (conventional) outflow into Schlemm’s canal. Depending on their mechanism of action, however, some of these MIGS cannot overcome the problem of impaired distal outflow obstruction i.e. collector channels, deep venous plexus, and episcleral veins. Further, the maximal site of resistance, while thought to be most prevalent in the juxtacanalicular trabecular meshwork, has been shown to be variable in different individuals. This poses many challenges with stent based MIGS, in which the proper placement of the stent i.e. adjacent a patient collector channel, is paramount to treatment success. Recent additions to the MIGS treatment armamentarium go beyond the conventional outflow system in targeting the subconjunctival or suprachoroidal spaces. With suprachoroidal MIGS, the aim is to improve uveoscleral outflow by using the suprachoroidal space as a reservoir for aqueous flow in order to lower IOP. With subconjunctival MIGS, an artificial pathway is created for aqueous humor outflow to the subconjunctival space.

ABiC ab-interno canaloplasty, performed with the proprietary iTrack microcatheter (Ellex) is a comprehensive MIGS procedure that re-establishes the natural outflow channels, without damaging tissue, and without leaving behind a stent or shunt. A restorative MIGS procedure designed to re-establish the eye’s natural outflow drainage system, ABiC with iTrack accesses, catheterises, and viscodilates the trabecular meshwork, Schlemm’s canal, and also the distal outflow system, beginning with the collector channels. ABiC can be performed as a stand alone procedure or in conjunction with cataract extraction and has been shown to reduce IOP on average by 30 per cent and to reduce patients’ dependence on medications by up to 50 per cent.

ABiC is atraumatic and works by nondestructively re-establishing the natural outflow pathway. Other MIGS procedures are either destructive in their approach or bypass the natural outflow pathways. It has been suggested that ablating or removing tissue in the trabecular meshwork interferes with the physiology of blood aqueous barriers, which plays a crucial role in preventing the reflux of blood from the episcleral venous system into the anterior chamber. Interfering with this system may also lead to recurrent hyphemas, which have been noted with some of the MIGS procedures that involve ablation or removal of the trabecular meshwork.

The most unique aspect of ABiC with iTrack is its effects on the entire aqueous outflow system. To date, ABiC is the only MIGS procedure that successfully and comprehensively addresses all aspects of potential outflow resistance. This contrasts with other MIGS procedures, where only a segment of Schlemm’s canal is addressed, or where the trabecular meshwork is targeted in isolation. One of the challenges associated with the use of stent based MIGS is that the location of increased aqueous outflow resistance is often unclear: when targeting only a localised area of the outflow system only, there is a risk that the area of blockage will be missed or sub optimally treated.

ABiC with iTrack is also versatile. It is effective for the treatment of mild, moderate, and severe open angle glaucoma: primary, pigmentary, and pseudoexfoliative. Because of the versatility of ABiC, I frequently rely on it, especially when managing advanced or challenging cases of open angle glaucoma. ABiC with iTrack functions synergistically with SLT, whether SLT is performed before or after ABiC. Further, it can be combined with other MIGS procedures to maximise outflow facility.

Recent studies have highlighted the many synergies of employing the various MIGS procedures concurrently. A study presented at the 2018 meeting of the American Society of Cataract and Refractive Surgeons (ASCRS) in Washington by Dr. Jack Parker and colleagues, showed that combining phacoemulsification, trabecular bypass stenting (iStent) and ABiC achieved a significant difference in IOP after six months, as compared to cataract surgery and iStent placement. Seventy one eyes underwent the combined phacoemulsification, iStent and ABiC (group one), while 93 eyes were treated using combined phacoemulsification and iStent only (group two). IOP reduction in group one was 24 per cent, compared to 15 per cent in group two.10

During the ABiC procedure, the surgeon will sit temporal to the patient to create a tri-planar clear corneal incision. A second incision, approximately 90 degrees, is made with a 27 gauge needle or a 15 degree blade and directed towards the nasal angle. The iTrack catheter is then placed through the side port incision. A small goniotomy is created by lightly scoring across the trabecular meshwork in a horizontal fashion, exposing the inner lumen of Schlemm’s canal. The iTrack is grasped near the illuminated tip and placed into Schlemm’s canal. Once intubated, the canal will be circumnavigated 360 degrees: the patented fiberoptic tip of the iTrack catheter ensures proper positioning throughout the procedure.

During canal intubation, several mechanical changes are taking place. Specifically, the iTrack separates the herniations of the trabecular meshwork into the collector channels caused by increased IOP. It also breaks inner lumen adhesions and opens the stenotic segments of the canal. Once the iTrack has navigated 360 degrees of Schlemm’s canal, it is slowly withdrawn and microboluses of viscoelastic are injected with the Visco-injector, as instructed by the surgeon. This process of viscodilation separates the compressed tissue planes of the meshwork and forces the withdrawal of herniated inner wall tissue from the collector channels. It also dilates and flushes the newly opened collector channels. Once the canal and distal system have been viscodilated, the iTrack is removed and all residual viscoelastic is removed from the anterior chamber.

CONCLUSION

Optometrists are frequently on the front line of the ocular treatment journey. It is usually with routine testing that a patient’s glaucoma is first diagnosed – initiating life long treatment. With the advent of technologies such as SLT and MIGS, we now have more options than ever before to prevent optic nerve damage in glaucoma patients, while also striving to maintain a high quality of life. From this standpoint, SLT and ABiC along with other MIGS procedures are evolutionary. SLT offers a highly effective first line therapy option, free of the side effects and compliance issues associated with antiglaucoma medications, while MIGS play an important role in bridging the gap in the treatment of patients who would benefit from lower IOP but do not warrant the risk of traditional surgery. We should therefore change our thinking to incorporate these procedures much earlier in the treatment course.

 

      Dr. David Lubeck is the Assistant Clinical Professor of Ophthalmology, UIC Eye Center, Chicago, Illinois and Director Center for Advanced Anterior Segment Surgery – Arbor Centers for Eye Care, Homewood, Illinois. 
 

References
1. Gupta N, Greenberg G, de Tilly LN, Gray B, Polemidiotis M, et al. Atrophy of the lateral geniculate nucleus in human glaucoma detected by magnetic resonance imaging. Br J Ophthalmol 2009;93: 56–60.
2. Singh K, Shrivastava A. Intraocular pressure fluctuations: how much do they matter? Curr Opin Ophthalmol 2009;20:84–87.
3. Raghav Gupta, MD, Bharat Patil, MD, Bhavin M. Shah, MD, Shveta Jindal Bali, MD, Sanjay K. Mishra, MD, and Tanuj Dada, MD. Evaluating Eye Drop Instillation Technique in Glaucoma Patients. J Glaucoma 2012; 21:189–192.
4. Han JA, Frishman WH, Wu Sun S, Palmiero PM, Petrillo R.Cardiovascular and respiratory considerations with pharmacotherapy of glaucoma and ocular hypertension. Cardiol Rev. 2008;16:95-108.)
5. Barkana Y, Belkin M. Selective laser trabeculoplasty. Surv Ophthalmol 2007;52:634-54.
6. Katz Jl, Steinmann WC, Kabir A, Molineaux J, Wizov SS, Marcellino G; SLT/Med Study Group. Selective laser trabeculoplasty versus medical therapy as initial treatment of glaucoma: a prospective, randomized trial. J Glaucoma. 2012; 21:460-8.
7. Cantor LB, Katz LJ, Cheng JW, Chen E, Tong KB, Peabody JW. Economic evaluation of medication, laser trabeculoplasty and filtering surgeries in treating patients with glaucoma in the US. Curr Med Res Opin. 2008;24:2905-18.
8. Gong H, Francis A. Schlemm’s canal and collector channels as therapeutic targets. In: Samples JR, Ahmed I, eds. Innovations in Glaucoma Surgery. New York: Springer; 2014:3-25.
9. Cha EDK, Xu J, Gong H. Variations in active areas of aqueous humor outflow through the trabecular outflow pathway. Invest Ophthalmol Vis Sci. 2015;56(7):4850.
10. Parker J et al. Combined Phacoemulsification, Trabecular Bypass Stenting, and Canaloplasty Versus Combined Phacoemulsification and Trabecular Stenting Alone. ASCRS 2018, Washington.
  • Incision Site: ABiC is performed via a self-sealing corneal incision.
  • Gonioscopic view of nasal angle one month postoperative. Note the normal appearance of the drainage angle despite previous surgical manipulation.
  • MIGS in combination: Insertion of iTrack into Schlemm’s Canal following previous iStent insertion.
  • SLT targets the trabecular meshwork, stimulating a process of restoration, which improves fluid outflow, thereby helping to restore IOP.
  • ABiC restores the natural outflow pathway, including the collector channel ostia.
  • SLT is a simple outpatient procedure, typically performed in under 10 minutes in the ophthalmologist’s office.

' With the advent of technologies such as SLT and MIGS, we now have more options than ever before to prevent optic nerve damage in glaucoma patients, while also striving to maintain a high quality of life... '